Search for displaced muonic lepton jets from light Higgs boson decay in proton-proton collisions at $\sqrt{s}=7$ TeV with the ATLAS detector

EUROPEAN ORGANISATION FOR NUCLEAR RESEARCH (CERN)

CERN-PH-EP-2012-241

Submitted to: Pysics Letters B

Search for displaced muonic lepton jets from light Higgs boson

decay in proton-proton collisions at

√

s

= 7 TeV with the ATLAS

detector

The ATLAS Collaboration

Abstract

A search is performed for collimated muon pairs displaced from the primary vertex produced in the

decay of long-lived neutral particles in proton-proton collisions at

√

s

= 7 TeV centre-of-mass energy,

with the ATLAS detector at the LHC. In a 1.9 fb

−1

_{event sample collected during 2011, the observed}

data are consistent with the Standard Model background expectations. Limits on the product of the

production cross section and the branching ratio of a Higgs boson decaying to hidden-sector neutral

long-lived particles are derived as a function of the particles’ mean lifetime.

Search for displaced muonic lepton jets from light Higgs boson decay in proton-proton

collisions at

√

s

= 7 TeV with the ATLAS detector

The ATLAS Collaboration

Abstract

A search is performed for collimated muon pairs displaced from the primary vertex produced in the decay of long-lived neutral particles in proton-proton collisions at √s= 7 TeV centre-of-mass energy, with the ATLAS detector at the LHC. In a 1.9 fb−1

event sample collected during 2011, the observed data are consistent with the Standard Model background expectations. Limits on the product of the production cross section and the branching ratio of a Higgs boson decaying to hidden-sector neutral long-lived particles are derived as a function of the particles’ mean lifetime.

1. Introduction

A search is presented for long-lived neutral particles decay-ing to final states containdecay-ing collimated muon pairs in proton-proton collisions at √s= 7 TeV centre-of-mass energy. The event sample, collected during 2011 at the LHC with the ATLAS detector, corresponds to an integrated luminosity of 1.9 fb−1. The model considered in this analysis consists of a Higgs boson decaying to a new hidden sector of particles which finally produce two sets of collimated muon pairs, but the search described is equally valid for other, distinct models such as heavier Higgs boson doublets, singlet scalars or a Z0 that decay to a hidden sector and eventually produce collimated muon pairs.

Recently, evidence for the production of a boson with a mass of about 126 GeV has been published by ATLAS [1] and CMS [2]. The observation is compatible with the expected production and decay of the Standard Model (SM) Higgs boson [3–5] at this mass. Testing the SM Higgs hypothesis is currently of utmost importance. To this end two effects may be considered: (i) addi-tional resonances which arise in an extended Higgs sector found in many extensions of the SM, or (ii) rare Higgs boson decays which may deviate from those predicted by the SM. In this Let-ter we search for a scalar that decays to a light hidden sector, focusing on the 100 GeV to 140 GeV mass range. In doing so, we cover both of the above aspects, deriving constraints on additional Higgs-like bosons, as well as placing bounds on the branching ratio of the discovered 126 GeV resonance into a hid-den sector of the kind described below.

The phenomenology of light hidden sectors has been studied extensively over the past few years [6–10]. Possible characteris-tic topological signatures of such extensions of the SM are “lep-ton jets”. A lep“lep-ton jet is a cluster of highly collimated particles: electrons, muons and possibly pions [7, 11–13]. These arise if light unstable particles with masses in the MeV to GeV range (for example dark photons, γd) reside in the hidden sector and

decay predominantly to SM particles. At the LHC, hidden-sector particles may be produced with large boosts, causing the visible decay products to form jet-like structures.

Hidden-sector particles such as γd may be long-lived, resulting in

de-cay lengths comparable to, or larger than, the detector dimen-sions. The production of lepton jets can occur through various channels. For instance, in supersymmetric models, the light-est visible superpartner may decay into the hidden sector. Al-ternatively, a scalar particle that couples to the visible sector may also couple to the hidden sector through Yukawa couplings or the scalar potential. This analysis is focused on the case where the Higgs boson decays to the hidden sector [14, 15]. The SM Higgs boson has a narrow width into SM final states if mH < 2mW. Consequently, any new (non-SM) coupling to

ad-ditional states, which reside in a hidden sector, may contribute significantly to the Higgs boson decay branching ratios. Even with new couplings, the total Higgs boson width is typically small, well below the order of one GeV. If a SM-like Higgs bo-son is confirmed, it will remain important to constrain possible rare decays, e.g. into lepton jets.

Neutral particles with large decay lengths and collimated final states represent, from an experimental point of view, a chal-lenge both for the trigger and for the reconstruction capabilities of the detector. Collimated particles in the final state can be hard to disentangle due to the finite granularity of the detectors; moreover, in the absence of inner tracking detector informa-tion and a primary vertex constraint, it is difficult to reconstruct charged-particle tracks from decay vertices far from the inter-action point (IP). The ATLAS detector [16] is equipped with a muon spectrometer (MS) with high-granularity tracking de-tectors that allow charged-particle tracks to be reconstructed in a standalone configuration using only the muon detector infor-mation (MS-only). This is a crucial feature for detecting muons not originating from the primary interaction vertex.

The search presented in this Letter focuses on neutral particles decaying to the simplest type of muon jets (MJs), containing only two muons; prompt MJ searches have been performed both at the Tevatron [17, 18] and at the LHC [19]. Other searches for displaced decays of a light Higgs boson to heavy fermion pairs have also been performed at the LHC [20].

sce-nario where the Higgs boson decays to a pair of neutral hidden fermions ( fd2) each of which decays to one long-lived γd and

one stable neutral hidden fermion ( fd1) that escapes the

detec-tor unnoticed, resulting in two lepton jets from the γd decays

in the final state (see Fig. 1). The mass of the γd (0.4 GeV) is

chosen to provide a sizeable branching ratio to muons [14].

H fd2 fd2 fd1 fd1 γd γd µ− µ− µ+ µ+

Figure 1: Schematic picture of the Higgs boson decay chain, H→2( fd2 →

fd1γd). The Higgs boson decays to two hidden fermions ( fd2). Each hidden

fermion decays to a γd and to a stable hidden fermion ( fd1), resulting in two

muon jets from the γddecays in the final state.

2. The ATLAS Detector

ATLAS is a multi-purpose detector [16] at the LHC, consist-ing of an inner trackconsist-ing system (ID) embedded in a supercon-ducting solenoid, which provides a 2 T magnetic field parallel to the beam direction, electromagnetic and hadronic calorime-ters and a muon spectrometer using three air-core toroidal mag-net systems1_{. The trigger system has three levels [21] called}

Level-1 (L1), Level-2 (L2) and Event Filter (EF). L1 is a hardware-based system using information from the calorime-ter and muon spectromecalorime-ter, and defines one or more Regions of Interest (ROIs), geometrical regions of the detector, identi-fied by (η, φ) coordinates, containing interesting physics ob-jects. L2 and the EF (globally called the High Level Trigger, HLT) are software-based systems and can access information from all sub-detectors. The ID, consisting of silicon pixel and micro-strip detectors and a straw-tube tracker, provides pre-cision tracking of charged particles for | η | ≤ 2.5. The elec-tromagnetic and hadronic calorimeter system covers | η | ≤ 4.9 and, at η= 0, has a total depth of 9.7 interaction lengths (22 ra-diation lengths in the electromagnetic part). The MS provides trigger information (| η | ≤ 2.4) and momentum measurements (| η | ≤ 2.7) for charged particles entering the spectrometer. It consists of one barrel and two endcap parts, each with 16 sec-tors in φ, equipped with precision tracking chambers and fast detectors for triggering. Monitored drift tubes are used for pre-cision tracking in the region | η | ≤ 2.0 and cathode strip cham-bers are used for 2.0 ≤ | η | ≤ 2.7. The MS detectors are ar-ranged in three stations of increasing distance from the IP: in-ner, middle and outer. The air core toroidal magnetic field

al-1_{ATLAS uses a right-handed coordinate system with its origin at the}

nom-inal interaction point (IP) in the centre of the detector and the z-axis coinciding with the beam pipe axis. The x-axis points from the IP to the centre of the LHC ring, and the y-axis points upward. Cylindrical coordinates (r,φ) are used in the transverse plane, φ being the azimuthal angle around the beam pipe. The pseudorapidity is defined in terms of the polar angle θ as η= −ln tan(θ/2).

lows an accurate charged particle reconstruction independent of the ID information. The three planes of trigger chambers (re-sistive plate chambers in the barrel and the thin gap chambers in the endcaps) are located in middle and outer (only in the bar-rel) stations. The L1 muon trigger requires hits in the middle stations to create a low tranverse momentum (pT) muon ROI or

hits in both the middle and outer stations for a high pT ROI.

The muon ROIs have a spatial extent of 0.2×0.2 (∆η × ∆φ) in the barrel and of 0.1×0.1 in the endcap. L1 ROI information seeds, at HLT level, the reconstruction of muon momenta using the precision chamber information. In this way sharp trigger thresholds up to 40 GeV can be obtained.

3. Signal and background simulation

The set of parameters used to generate the signal Monte Carlo samples is listed in Table 1. The Higgs boson is generated through the gluon-gluon fusion production mech-anism which is the dominant process for a low mass Higgs boson. The gluon-gluon fusion Higgs boson production cross section in pp collisions at √s = 7 TeV, estimated at the next-to-next-to-leading order (NNLO) [22], is σ_SM = 24.0 pb for mH = 100 GeV and σSM = 12.1 pb for mH = 140 GeV.

The PYTHIA generator [23] is used, linked together with MadGraph4.4.2 [24] and BRIDGE [25], for gluon-gluon fusion production of the Higgs boson and the subsequent decay to hidden-sector particles.

As discussed in the introduction, the signal is chosen to enable a study of rare, non-SM, Higgs boson decays in the (possibly extended) Higgs sector. To do so we choose two points which envelope a mass range covering the 126 GeV resonance. The lower mass point, mH = 100 GeV, is chosen to be

compat-ible with the decay-mode-independent search by OPAL at LEP [26]. The higher mass point, mH = 140 GeV, is chosen

well below the WW threshold, where a sizeable branching ratio into a hidden sector may be naturally achieved. The masses of fd2 and fd1 are chosen to be light relative to the Higgs boson

mass, and far from the kinematic threshold at mfd1+mγd = mfd2.

For the chosen dark photon mass (0.4 GeV), the γd decay

branching ratios are expected to be [14]: 45% e+e−_{, 45% µ}+_µ−_,

10% π+π−_{. Thus 20% of the Higgs H→ γ}

dγd+ X decays are

expected to have the required four-muon final state.

The mean lifetime τ of the γd(expressed throughout this Letter

as τ times the speed of light c) is a free parameter of the model. In the generated samples cτ is chosen so that a large fraction of the decays occur inside the sensitive ATLAS detector volume, i.e. up to 7 m in radius and 13 m along the z-axis, where the trigger chambers of the middle stations are located. The detection efficiency can then be estimated for a range of γd

mean lifetime through re-weighting of the generated samples.

Higgs mass mfd2 mfd1 γdmass cτ

[ GeV] [ GeV] [ GeV] [ GeV] [mm]

100 5.0 2.0 0.4 47

140 5.0 2.0 0.4 36

Table 1: Parameters used for the Monte Carlo simulation. The last column is the γdmean lifetime τ multiplied by the speed of light c, expressed in mm.

Potential backgrounds include all the processes which lead to real prompt muons in the final state such as the SM pro-cesses W+jets, Z+jets, t¯t, WW, WZ, and ZZ. However, the main contribution to the background is expected from processes giv-ing a high production rate of secondary muons which do not point to the primary vertex, such as decays in flight of K/π and heavy flavour decays in multi-jet processes, or muons due to cosmic rays. The prompt lepton background samples are gen-erated using PYTHIA (W+jets, and Z+jets) and MC@NLO [27] (t¯t, WW, WZ, and ZZ). The generated Monte Carlo events are processed through the full ATLAS simulation chain based on GEANT4 [28, 29]. Additional pp interactions in the same and nearby bunch crossings (pile-up) are included in the simula-tion. All Monte Carlo samples are re-weighted to reproduce the observed distribution of the number of interactions per bunch crossing in the data. For the multi-jet background evaluation a data-driven method is used. The cosmic-ray background is also evaluated from data.

4. The kinematics of the signal

The main kinematic characteristics of the signal sample are:

• The γdpair are emitted approximately back-to-back in φ,

with an angular spread of the distribution due to the emis-sion of the fd1.

• The average pTof the γd in the laboratory frame is about

20 GeV for mH = 100 GeV and 30 GeV for mH = 140

GeV; due to the small mass of the γd, large boost factors

in the decay length should be expected.

• Fig. 2 shows the distribution of∆R = p(∆η)2+ (∆φ)2

be-tween the two muons from the γd decay. The∆R is

com-puted at the decay vertex of the γd from the vector

mo-menta of the two muons. Due to the small mass of the γd

the∆R is almost always below 0.1.

Since the two fd1are, like the two γd, emitted back-to-back in

φ, the observed missing transverse momentum Emiss

T , computed

at the event-generator level, is small and cannot be used as a discriminating variable against the background.

µ µ R ∆ 0 0.05 0.1 / 0.004 _d γ fraction of 0 0.05 0.1 0.15 = 100GeV H m = 140GeV H m ATLAS Simulation

Figure 2: ∆R distribution between the two muons from the γddecay for the

signal Monte Carlo samples with mH= 100 GeV and mH= 140 GeV.

5. Data samples and trigger selection

The dataset used for this analysis was collected at a centre-of-mass energy of 7 TeV during the first part of 2011, where a low level of pile-up events in the same bunch-crossing was present (an average of ≈ 6 interactions per crossing). Only periods in which all ATLAS subdetectors were operational are used. The total integrated luminosity used is 1.94 ± 0.07 fb−1 _{[30, 31].}

All events are required to have at least one reconstructed ver-tex along the beam line with at least three associated tracks, each with pT ≥ 0.4 GeV. The primary interaction vertex is

de-fined to be the vertex whose constituent tracks have the largest Σp2

T. This analysis deals with displaced γd decays with final

states containing only muons. Signal events are therefore char-acterized by a four-muon final state with the four muons com-ing from two displaced decay vertices. Due to the relatively low pTof the muons and to the displaced decay vertex, a

low-pT multi-muon trigger with muons reconstructed only in the

MS is needed. In order to have an acceptably low trigger rate at a low pTthreshold, a multiplicity of at least three muons is

required. Candidate events are collected using an unprescaled HLT trigger with three reconstructed muons of pT ≥ 6 GeV,

seeded by a L1-accept with three different muon ROIs. These muons are reconstructed only in the MS, since muons originat-ing from a neutral particle decayoriginat-ing outside the pixel detector will not have a matching track in the ID tracking system. The trigger efficiency for the Monte Carlo signal samples, defined as the fraction of events passing the trigger requirement with respect to the events satisfying the analysis selection criteria (described in Section 6) is 0.32±0.01stat for mH = 100 GeV

and 0.31±0.01statfor mH= 140 GeV.

The main reason for the relatively low trigger efficiency is the small opening ∆R between the two muons of the γd decay

(∆R ≤ 0.1) shown in Fig. 2. These values of ∆R are often smaller than the L1 trigger granularity; in this case the L1 pro-duces only one ROI. The trigger only fires if at least one of the γdproduces two distinct L1 ROIs. The single γdROI efficiency,

ε_2ROI (ε_1ROI), defined as the fraction of γd passing the offline

selection that give two (one) trigger ROIs is 0.296 ± 0.004_stat (0.626 ± 0.004stat) for mH = 100 GeV and 0.269 ± 0.003stat

(0.653 ± 0.003stat) for mH= 140 GeV. Fig. 3 shows the ε2ROI

as a function of the dark photon η and of the∆R of the two muons from the γddecay. The increased trigger granularity in

the endcap and the efficiency decrease at small values of ∆R are clearly visible.

The systematic uncertainty on the trigger efficiency is estimated with a sample of J/ψ → µ+µ−_{from collision data and a}

cor-responding sample of Monte Carlo events, using the tag-and-probe (TP) method. A cut on∆R ≤ 0.1 between the two muons is used to reproduce the small track-to-track spatial separation in the MS of the signal. The tag is a (MS+ID) combined muon, defined as a MS-reconstructed muon that is associated with a trigger object and combined with a matching “good ID track”. Good ID tracks must have at least one hit in the pixel detec-tor, at least six hits in the silicon micro-strip detectors and at least six hits in the straw-tube tracker. The probe is a good ID track which, when combined with the tag track, gives an

invari-ant mass inside a 100 MeV window around the J/ψ mass. A muon ROI that matches the probe in η and φ, and is different from the ROI associated with the tag, is searched for. The num-ber of probes with a matched ROI divided by the numnum-ber of probes without a matched ROI gives the εTP_2ROI/εTP_1ROIratio. Val-ues of εTP_2ROI/εTP_1ROI = 0.42±0.05_statfor the J/ψ → µ+µ−_data

and εTP_2ROI/εTP_1ROI= 0.39±0.05_statfor the corresponding Monte Carlo sample are obtained. The relative statistical uncertainty on the difference between these two estimates is 17% and this is taken conservatively to be the systematic uncertainty on the trigger efficiency. d γ η -2 -1 0 1 2 2RoI ∈ 0.0 0.2 0.4 0.6 0.8 = 100 GeV H m = 140 GeV H m (a) Simulation ATLAS µ µ R ∆ 0 0.02 0.04 0.06 2RoI ∈ 0 0.1 0.2 0.3 0.4 0.5 = 100 GeV H m = 140 GeV H m (b) Simulation ATLAS

Figure 3: ε2ROIas a function (a) of the η of the γdand (b) of the∆R of the muon

pair for the Monte Carlo samples with Higgs boson masses of 100 GeV and 140 GeV. The errors are statistical only.

6. Muon Jets reconstruction and event selection

MJs from displaced γddecays are characterized by a pair of

muons in a narrow cone, produced away from the primary ver-tex of the event. Consequently tracks reconstructed in the MS with a good quality track fit [32] are used. MJs are identified us-ing a simple clusterus-ing algorithm that associates all the muons in cones of∆R = 0.2, starting with the muon with highest pT.

The size of the cone takes into account the multiple scattering of the muons in the calorimeters. All the muons found in the cone are associated with a MJ. After this procedure, if any muons are unassociated with a MJ the search is repeated for this remain-der, starting again with the highest pT muon. This continues

until all possible MJs are formed. The MJ direction and mo-mentum are obtained from the vector sum over all muons in the MJ. Only MJs with two reconstructed muons are accepted and only events with two MJs are kept for the subsequent analysis.

The possible contribution to the background of SM processes which lead to real prompt muon pairs in the final state is evalu-ated using simulevalu-ated samples. After the trigger and the require-ment of having two MJs in the event, their contributions have been found to be negligible. The only significant background sources are expected to be from processes giving a high produc-tion rate of secondary muons which do not point to the primary vertex, such as decays in flight of K/π and heavy flavour de-cays in multi-jet production, or cosmic-ray muons not pointing to the primary vertex.

In order to separate the signal from the background, a num-ber of discriminating variables have been studied. The multi-jet background can be significantly reduced by using calorimeter isolation requirements around the MJ direction. The calorimet-ric isolation variable Eisol_T is defined as the difference between the transverse calorimetric energy ET in a cone of∆R = 0.4

around the highest pTmuon of the MJ and the ETin a cone of

∆R = 0.2; a cut Eisol

T ≤ 5 GeV keeps almost all the signal. The

isolation modelling is validated for real isolated muons with a sample of muons coming from Z → µµ decays. To further im-prove the signal-to-background ratio, two additional discrimi-nating variables are used: ∆φ between the two MJs and ΣpID T

for the MJ, defined as the scalar sum of the transverse momen-tum of the tracks, measured in the ID, inside a cone∆R = 0.4 around the direction of the MJ. The muon tracks of the MJ in the ID, if any, are not removed from the isolation sum, so that prompt muons, which give a reconstructed track in both the ID and MS, will contribute to theΣpID_T . As a consequence a cut on ΣpID

T of a few GeV will remove prompt MJs or MJs with very

short decay length.

For the background coming from cosmic-ray muons (mainly pairs of almost parallel cosmic-ray muons crossing the detector) a cut on the impact parameters of the muon tracks with respect to the primary interaction vertex is used.

The final set of selection criteria used is the following:

• Topology cut: events are required to have exactly two MJs, N_MJ= 2.

• MJ isolation: require MJ isolation with Eisol_T ≤ 5 GeV for both MJs in the event.

• Require |∆φ| ≥ 2 between the two MJs.

• Require opposite charges for the two muons in a MJ (Q_MJ= 0).

• Require a cut on the transverse and longitudinal impact pa-rameters of the muons with respect to the primary vertex: |d0|< 200 mm and |z0|< 270 mm.

• RequireΣpID

T < 3 GeV for both MJs.

The distributions of the relevant variables at the different steps of the cut flow are shown in Fig. 4. The results are summarized in Table 2. No events survive the selection in the data sample whereas the expected signals from Monte Carlo simulation, as-suming 100% branching ratio for H→ γdγd+X and the

[GeV] isol T E 0 10 20 30 Entries / 1.25 GeV 0 100 200 300 data = 140 GeV H m ATLAS -1 Ldt = 1.9 fb

∫

= 7 TeV, s = 7 TeV,

∫

Ldt = 1.9 fb-1 s

(a)

[rad] φ ∆ 0 1 2 3 rad 30 π Entries / 0 10 20 30 40 data = 140 GeV H m ATLAS -1 Ldt = 1.9 fb

∫

= 7 TeV, s = 7 TeV,

∫

Ldt = 1.9 fb-1 s

(b)

[GeV] ID T p Σ 0 10 20 30 Entries / GeV 0 50 100 data = 140 GeV H m ATLAS -1 Ldt = 1.9 fb

∫

= 7 TeV, s = 7 TeV,

∫

Ldt = 1.9 fb-1 s

(c)

Figure 4: Control plots for the cut variables on Monte Carlo (mH = 140 GeV) and on data. (a) Distribution of the calorimetric isolation around the MJ direction

E_Tisolafter the requirement of two MJs in the event. (b) Distribution of∆φ between the two MJs after the requirement of the isolation cut. (c) Distribution of ΣpID_T of the MJ after the requirement of the impact parameters cut. The points show the data and the histogram is the signal Monte Carlo normalized to 1.9 fb−1_{. The}

uncertainties are statistical only.

of 100 GeV and 140 GeV respectively. The method used to es-timate the cosmic-ray and multi-jet background yields, quoted in Table 2, is discussed in Section 7.

The resulting single γdreconstruction efficiency for the mean

lifetimes given in Table 1 is shown in Fig. 5 as a function of η, the∆R separation of the two muons from the γddecay and the

decay length in the transverse plane, Lxy, of the γd. The e

ffi-ciency is defined as the number of γd passing the offline

selec-tion divided by the number of γdin the spectrometer acceptance

(| η | ≤ 2.4) with both muons having pT ≥ 6 GeV. The low

re-construction efficiency at very short Lxyis a consequence of the

ΣpID

T cut.

The systematic uncertainty on the reconstruction efficiency is evaluated using a tag-and-probe method by comparing the reconstruction efficiency εTP_rec for J/ψ → µ+µ− _{samples from}

collision data and J/ψ → µ+µ− _{Monte Carlo simulation. The}

tag-and-probe definitions and the cut on∆R ≤ 0.1 between the two muons are the same as in Section 5. To measure the re-construction efficiency the ID probe track is associated with a MS-only muon track, different from the one associated with the tag. The result is shown in Fig. 6.

The relative difference between the result obtained from the J/ψ → µ+_µ− _{data and the J/ψ → µ}+_µ− _{Monte Carlo}

sam-ple in the same range of∆R ≤ 0.1, as for the signal, is taken as the systematic uncertainty on the reconstruction efficiency and amounts to 13%.

7. Multi-jet and cosmic-ray background evaluation To estimate the multi-jet background contamination in the signal region we use a data-driven ABCD method slightly mod-ified to cope with the problem of the very low number of events in the control regions. The ABCD method assumes that two variables can be identified, which are relatively uncorrelated, and which can each be used to separate signal and background. It is assumed that the multi-jet background distribution can be factorized in the MJ Eisol

T – |∆φ| plane. The region A is

de-fined by Eisol

T ≤ 5 GeV and |∆φ| < 2; the region B, defined by

Eisol

T ≤ 5 GeV and |∆φ| ≥ 2, is the signal region. The regions

C and D are the anti-isolated regions (Eisol_T > 5 GeV) and they are defined by |∆φ| < 2 and |∆φ| ≥ 2, respectively.

Neglect-d γ η -2 -1 0 1 2 rec ∈ 0.0 0.2 0.4 0.6 = 100 GeV H m = 140 GeV H m (a) Simulation ATLAS µ µ R ∆ 0 0.02 0.04 0.06 rec ∈ 0 0.1 0.2 0.3 0.4 0.5 = 100 GeV H m = 140 GeV H m (b) Simulation ATLAS [m] xy L 0 2 4 6 rec ∈ 0.0 0.1 0.2 0.3 0.4 = 100 GeV H m = 140 GeV H m (c) Simulation ATLAS

Figure 5: γdreconstruction efficiency εrec as a function (a) of η, (b) of ∆R and

(c) of the transverse decay length of the γdfor mH= 100 GeV and mH= 140

GeV and for the mean lifetimes given in Table 1. The reconstruction efficiency is defined as the number of γdpassing the offline selection divided by the

num-ber of γdin the spectrometer acceptance (| η | ≤ 2.4) with both muons having

cut cosmic-rays multi-jet total background mH= 100 GeV mH= 140 GeV data

NMJ= 2 3.0 ± 2.1 N/A N/A 135±11+29−21 90±9+17−13 871

Eisol_T ≤ 5 GeV 3.0 ± 2.1 N/A N/A 132±11+28₋₂₁ 88±9+17₋₁₃ 219

|∆φ| ≥ 2 1.5 ± 1.5 153 ± 18 ± 9 155 ± 18 ± 9 123±11+26₋₁₉ 81±9+15₋₁₂ 104

QMJ= 0 1.5 ± 1.5 57 ±15±22 59 ± 15 ± 22 121±11+26−19 79±8+15−12 80

|d0|, |z0| 0+1.64₋₀ 111±39±63 111±39±63 105±10+22₋₁₆ 66±8+12₋₁₀ 70

ΣpID

T < 3 GeV 0+1.64−0 0.06±0.02+0.66−0.06 0.06+1.64+0.66−0.02−0.06 75±9+16−12 48±7+9−7 0

Table 2: Cut flow for the signal selection on signal Monte Carlo, the corresponding cosmic-ray background, the multi-jet background estimation from the ABCD method (described in Section 7) and the data; the yields are normalized to an integrated luminosity of 1.9 fb−1_{. The first uncertainties are statistical and the second}

systematic. Tag-Probe R ∆ 0.0 0.1 0.2 0.3 0.4 T P rec ∈ 0.0 0.5 1.0 data ψ J/ MC ψ J/ = 100 GeV H m = 140 GeV H m ATLAS -1 Ldt = 1.9 fb

∫

= 7 TeV, s

Figure 6: Tag-and-probe reconstruction efficiency εTP

recas a function of the∆R

between the two muons, evaluated on a sample of J/ψ → µ+µ−from collision data and a corresponding sample of Monte Carlo events. The εTPrecfor the signal

Monte Carlo, evaluated with a similar tag-and-probe method, is also shown. The uncertainties are statistical only.

ing the signal contamination in regions A, C and D (E_Tisol> 5 GeV or |∆φ| < 2) the number of multi-jet background events in the signal region can be evaluated as NB = ND× NA/NC.

Due to the very low number of events in the control regions the values of NA, NC and NDas a function of the cut on the final

discriminant variableΣpID

T are extracted by modelling theΣp ID T

distributions with bifurcated Gaussian templates, with param-eters fitted from the data in the corresponding regions, and by integrating the fitted function in the range 0 <ΣpID

T < 3 GeV.

The low statistics in the four regions at each step of the cut flow give rise to large fluctuations in the multi-jet background estimate. The extracted yields are NA = (7.1 ± 1.5stat) · 10−3,

NC = (1.81±1.0stat) · 10−2and ND= (1.51±0.07stat) · 10−1and

the estimated number of multi-jet background events in the sig-nal region is NB = 0.06 ± 0.02stat. Possible sources of

system-atic uncertainty related to the background estimation method are also evaluated. The functional form is changed and the pro-cedure to estimate the number of multi-jet background events in the signal region is repeated. The difference in NB is taken

as the systematic uncertainty in the modelling of the multi-jet background shape and it amounts to+0.66_−0.06. The effect of possible signal leakage in the background regions is also considered and is found to be negligible.

The background induced by muons from cosmic-ray showers is evaluated using events collected by the trigger active when there are no collisions (empty bunch crossings). The number

of triggered events is rescaled by the collision to empty bunch crossing ratio and for the active time (since the trigger in the empty bunch crossing was not active in all the runs). No events survived the requirements on the impact parameters with re-spect to the primary vertex (|d0|< 200 mm and |z0|< 270 mm),

resulting in a cosmic-ray contamination estimate of 0+1.64₋₀ . The final yields for the different background sources are summa-rized in Table 2.

8. Systematic uncertainties

The following effects are considered as possible sources of systematic uncertainty:

• Luminosity

The overall normalisation uncertainty of the integrated lu-minosity is 3.7% [30, 31].

• Muon momentum resolution

The systematic uncertainty on the muon momentum reso-lution for MS-only muons has been evaluated by smearing and shifting the momenta of the muons by scale factors derived from Z → µµ data-Monte Carlo comparison, and by observing the effect of this shift on the signal efficiency. The overall effect of the muon momentum resolution un-certainty is negligible.

• Trigger

The systematic uncertainty on the single γd trigger e

ffi-ciency, evaluated using a tag-and-probe method is 17% (see Section 5).

• Reconstruction efficiency

The systematic uncertainty on the reconstruction e ffi-ciency, evaluated using a tag-and-probe method for the single γdreconstruction efficiency, is 13% (see Section 6).

• Effect of pile-up

The systematic uncertainty on the signal efficiency related to the effect of pile-up is evaluated by comparing the num-ber of signal events after imposing all the selection criteria on the signal Monte Carlo sample increasing the average number of interactions per crossing from ≈ 6 to ≈ 16. This systematic uncertainty is negligible.

• Effect of ΣpID

T cut

Since theΣpID_T cut could affect the minimum cτ value that can be excluded, the effect of this cut on the signal Monte Carlo has been studied. A variation of 10% on theΣpID_T cut results in a relative variation of <1% on the signal, which can therefore be neglected.

• Background evaluation

The systematic uncertainties that can affect the back-ground estimation are related to the data-driven method used. The functional model used to fit the ΣpID

T

distri-bution is varied to evaluate the systematic uncertainty in the modelling of its shape, which also includes the effect of theΣpID

T cut on the background estimation. This

sys-tematic uncertainty amounts to+0.66_−0.06 events. The effect of signal leakage is also negligible.

9. Results and interpretation

The efficiency of the selection criteria described above is evaluated for the simulated signal samples (see Table 1) as a function of the mean lifetime of the γd. Using

pseudo-experiments with cτ ranging from 0 to 700 mm the number of γd that decay in each region of the detector is weighted by

the corresponding total efficiency for that region. In this way the number of expected signal events is predicted as a func-tion of the γdmean lifetime. These numbers, together with the

expected number of background events (multi-jet and cosmic rays) and taking into account the zero data events surviving the selection criteria in 1.9 fb−1_{, are used as input to obtain limits}

at the 95% confidence level (CL). The CLs method [33] is used to set 95% CL upper limits on the cross section times branching ratio (σ×BR ) for the process H→ γdγd+ X. Here the

branch-ing ratio of γd→ µ µ is set to 45% with the γd mass set to 0.4

GeV, as previously discussed. The σ×BR is given as a function of the γd mean lifetime, expressed as cτ for mH = 100 GeV

and mH= 140 GeV. These limits are shown on Fig. 7. Table 3

shows the ranges in which the γdcτ is excluded at the 95% CL

for H→ γdγd+ X branching ratios of 100% and 10%.

Higgs boson mass excluded cτ [mm] excluded cτ [mm]

[ GeV] BR(100%) BR(10%)

100 1 ≤ cτ ≤ 670 5 ≤ cτ ≤ 159

140 1 ≤ cτ ≤ 430 7 ≤ cτ ≤ 82

Table 3: Ranges in which γdcτ is excluded at 95% CL for mH= 100 GeV and

mH= 140 GeV, assuming 100% and 10% branching ratio of H→ γdγd+ X.

10. Conclusions

The ATLAS detector at the LHC was used to search for a light Higgs boson decaying into a pair of hidden fermions ( fd2),

each of which decays to a γd and to a stable hidden fermion

( fd1), resulting in two muon jets from the γd decay in the final

state. In a 1.9 fb−1sample of √s = 7 TeV proton-proton col-lisions no events consistent with this Higgs boson decay mode

[mm] τ Dark photon c 1 10 102 103 +X) [pb] _d γ _d γ → BR(H ×σ 9 5 % C L L im it o n 0 10 20 30 40 50 = 100 GeV H m (stat.+syst.) σ 2 ± expected (stat.+syst.) σ 1 ± expected ATLAS -1 Ldt = 1.9 fb

∫

=7 TeV, s observed limit expected limit SM σ +X) = d γ d γ → BR(H × σ

(a)

[mm] τ Dark photon c 1 10 102 103 +X) [pb]_d γd γ → BR(H ×σ 9 5 % C L L im it o n 0 5 10 15 20 25 = 140 GeV H m (stat.+syst.) σ 2 ± expected (stat.+syst.) σ 1 ± expected ATLAS -1 Ldt = 1.9 fb

∫

=7 TeV, s observed limit expected limit SM σ +X) = d γ d γ → BR(H × σ

(b)

Figure 7: The 95% upper limits on the σ×BR for the process H→ γdγd+ X as

a function of the dark photon cτ for the benchmark sample with (a) mH = 100

GeV and with (b) mH= 140 GeV. The expected limit is shown as the dashed

curve and the solid curve shows the observed limit. The horizontal lines corre-spond to the Higgs boson SM cross sections at the two mass values.

are observed. The observed data are consistent with the Stan-dard Model background expectations.

Limits are set on the σ×BR to H→ γd γd+ X as a function of

the long-lived particle mean lifetime for mH = 100 GeV and

140 GeV with the chosen γd mass that gives a decay branching

ratio of 45% for γd →µ µ. Assuming the SM production rate

for a 140 GeV Higgs boson, its branching ratio to two hidden-sector photons is found to be below 10%, at 95% CL, for hid-den photon cτ in the range 7 mm ≤ cτ ≤ 82 mm. Bounds on the σ×BR of a 126 GeV Higgs boson may be conservatively extracted using the corresponding 140 GeV exclusion curve.

11. Acknowledgements

We thank CERN for the very successful operation of the LHC, as well as the support staff from our institutions without whom ATLAS could not be operated efficiently.

We acknowledge the support of ANPCyT, Argentina; Yer-PhI, Armenia; ARC, Australia; BMWF and FWF, Austria; ANAS, Azerbaijan; SSTC, Belarus; CNPq and FAPESP, Brazil; NSERC, NRC and CFI, Canada; CERN; CONICYT, Chile; CAS, MOST and NSFC, China; COLCIENCIAS, Colombia; MSMT CR, MPO CR and VSC CR, Czech Republic; DNRF, DNSRC and Lundbeck Foundation, Denmark; EPLANET and ERC, European Union; IN2P3-CNRS, CEA-DSM/IRFU, France; GNSF, Georgia; BMBF, DFG, HGF, MPG and AvH Foundation, Germany; GSRT, Greece; ISF, MINERVA, GIF, DIP and Benoziyo Center, Israel; INFN, Italy; MEXT and JSPS, Japan; CNRST, Morocco; FOM and NWO, Nether-lands; BRF and RCN, Norway; MNiSW, Poland; GRICES and FCT, Portugal; MERYS (MECTS), Romania; MES of Rus-sia and ROSATOM, RusRus-sian Federation; JINR; MSTD, Ser-bia; MSSR, Slovakia; ARRS and MVZT, Slovenia; DST/NRF, South Africa; MICINN, Spain; SRC and Wallenberg Founda-tion, Sweden; SER, SNSF and Cantons of Bern and Geneva, Switzerland; NSC, Taiwan; TAEK, Turkey; STFC, the Royal Society and Leverhulme Trust, United Kingdom; DOE and NSF, United States of America.

The crucial computing support from all WLCG partners is acknowledged gratefully, in particular from CERN and the ATLAS Tier-1 facilities at TRIUMF (Canada), NDGF (Den-mark, Norway, Sweden), CC-IN2P3 (France), KIT/GridKA (Germany), INFN-CNAF (Italy), NL-T1 (Netherlands), PIC (Spain), ASGC (Taiwan), RAL (UK) and BNL (USA) and in the Tier-2 facilities worldwide.

References

[1] The ATLAS Collaboration, Observation of a New Particle in the Search for the Standard Model Higgs boson with the ATLAS detector at the LHC, Phys. Lett. B 716 (2012) 1-29 [arXiv:1207.7214].

[2] The CMS Collaboration, Observation of a new boson at a mass of 125 GeV with the CMS experiment at the LHC, Phys. Lett. B 716 (2012) 30-61 [arXiv:1207.7235].

[3] F. Englert and R. Brout, Broken Symmetry and the Mass of Gauge Vector Mesons, Phys. Rev. Lett. 13 (1964) 321.

[4] P.W. Higgs, Broken symmetries, massless particles and gauge fields, Phys. Lett. 12 (1964) 132.

[5] G.S. Guralnik, C.R. Hagen and T.W.B. Kibble, Global Conservation Laws and Massless Particles, Phys. Rev. Lett. 13 (1964) 585.

[6] M. J. Strassler and K. M. Zurek, Echoes of a Hidden Valley at Hadron Colliders, Phys. Lett. B 651 (2007) 374 [arXiv:0604261].

[7] N. Arkani-Hamed and N. Weiner, LHC Signals for a Superunified Theory of Dark Matter, JHEP 12 (2008) 104 [arXiv:0810.0714].

[8] T. Han, Z. Si, K. M. Zurek, and M. J. Strassler, Phenomenology of Hidden Valleys at Hadron Colliders, JHEP 07 (2008) 008.

[9] S. Gopalakrishna, S. Jung, and J. D. Wells, Higgs Boson Decays to Four Fermions Through an Abelian Hidden Sector, Phys. Rev. D 78 (2008) 055002 [arXiv:0801.3456].

[10] M. J. Strassler and K. M. Zurek, Discovering the Higgs Through Highly-Displaced Vertices, Phys. Lett. B 661 (2008) 263-267 [arXiv:0605193]. [11] M. Baumgart, C. Cheung, J. T. Ruderman, L. T. Wang, and I. Yavin,

Non-Abelian Dark Sectors and Their Collider Signatures, JHEP 04 (2009) 014 [arXiv:0901.0283].

[12] C. Cheung, J. T. Ruderman, L. T. Wang, and I. Yavin, Lepton Jets in (Supersymmetric) Electroweak Processes, JHEP 04 (2010) 116 [arXiv:0909.0290].

[13] Y. Bai and Z. Han, Measuring the Dark Force at the LHC, Phys. Rev. Lett. 103 (2009) 051801 [arXiv:0902.0006].

[14] A. Falkowski, J. T. Ruderman, T. Volansky, and J. Zupan, Hidden Higgs Decaying to Lepton Jets, JHEP 05 (2010) 077.

[15] A. Falkowski, J. T. Ruderman, T. Volansky, and J. Zupan, Discovering Higgs Decays to Lepton Jets at Hadron Colliders, Phys. Rev. Lett. 105 (2010) 241801 [arXiv:1007.3496].

[16] The ATLAS Collaboration, The ATLAS Experiment at the CERN Large Hadron Collider, JINST 3 (2008) S08003.

[17] V.M. Abazov et al. [D0 Collaboration], Search for Dark Photons from Supersymmetric Hidden Valleys, Phys. Rev. Lett. 103 (2009) 081802. [18] V.M. Abazov et al. [D0 Collaboration], Search for Events with Leptonic

Jets and Missing Transverse Energy in pp Collisions at√s= 1.96 TeV, Phys. Rev. Lett. 105 (2010) 211802.

[19] The CMS Collaboration, Search for Light Resonances Decaying into Pairs of Muons as a Signal of New Physics, JHEP 07 (2011) 098 [arXiv:1106.2375].

[20] The ATLAS Collaboration, Search for a light Higgs boson decaying to long-lived weakly-interacting particles in proton-proton collisions at √s= 7 TeV with the ATLAS detector, Phys. Rev. Lett. 108 (2012) 251801. [21] The ATLAS Collaboration, Performance of the ATLAS Trigger System in

2010, Eur. Phys. J. C 72 (2012) 1849 [arXiv:1110.1530].

[22] LHC Higgs Cross Section Working Group, S. Dittmaier, C. Mariotti, G. Passarino, and R. Tanaka (Eds.), Handbook of LHC Higgs Cross Sec-tions: 1. Inclusive Observables, CERN-2011-002 (CERN, Geneva, 2011) [arXiv:1101.0593].

[23] S. Mrenna, T. Sj¨ostrand and P. Z. Skands, PYTHIA 6.4 physics and man-ual, JHEP 05 (2006) 026 [arXiv:0603175].

[24] J. Alwall, M. Herquet, F. Maltoni, O. Mattelaer and T. Stelzer, Mad-Graph 5 : Going Beyond, JHEP 1106 (2011) 128 [arXiv:1106.0522]. [25] P. Meade and M. Reece, Bridge: Branching Ratio Inquiry/ Decay

Gener-ated Events[arXiv:0703031].

[26] G. Abbiendi et al. [OPAL Collaboration], Decay mode independent searches for new scalar bosons with the OPAL detector at LEP, Eur. Phys. J. C 27 (2003) 311 [arXiv:0206022].

[27] S. Frixione and B.R. Webber, Matching NLO QCD computations and par-ton shower simulations, JHEP 0206 (2002) 029 [arXiv:0204244]. [28] S. Agostinelli et al., GEANT4 - a simulation toolkit, Nucl. Instrum. Meth.

A 506 (2003) 250.

[29] The ATLAS Collaboration, The ATLAS Simulation Infrastructure, Eur. Phys. J. C 70 (2010) 823 [arXiv:1005.4568].

[30] The ATLAS Collaboration, Luminosity Determination in pp Collisions at_√ s= 7 TeV using the ATLAS Detector at the LHC, Eur. Phys. J. C 71 (2011) 1630 [arXiv:1101.2185].

[31] The ATLAS Collaboration, Luminosity Determination in pp Collisions at_√ s= 7 TeV using the ATLAS Detector in 2011, ATLAS-CONF-2011-116. http://cdsweb.cern.ch/record/1376384/files/ATLAS-CONF-2011-116.pdf [32] The ATLAS Collaboration, Expected Performance of the ATLAS

Experi-ment - Detector, Trigger and Physics, 2009 [arXiv:0901.0512].

[33] A. L. Read, Presentation of search results: The CL(s) technique, J. Phys. G 28 (2002) 2693-2704.

The ATLAS Collaboration

G. Aad47_{, T. Abajyan}20_{, B. Abbott}110_{, J. Abdallah}11_,

S. Abdel Khalek114_{, A.A. Abdelalim}48_{, O. Abdinov}10_,

R. Aben104_{, B. Abi}111_{, M. Abolins}87_{, O.S. AbouZeid}157_,

H. Abramowicz152_{, H. Abreu}135_{, E. Acerbi}88a,88b_,

B.S. Acharya163a,163b_{, L. Adamczyk}37_{, D.L. Adams}24_,

T.N. Addy55_{, J. Adelman}175_{, S. Adomeit}97_{, P. Adragna}74_,

T. Adye128_{, S. Aefsky}22_{, J.A. Aguilar-Saavedra}123b,a_,

M. Agustoni16_{, M. Aharrouche}80_{, S.P. Ahlen}21_{, F. Ahles}47_,

A. Ahmad147, M. Ahsan40, G. Aielli132a,132b, T. Akdogan18a, T.P.A. Åkesson78, G. Akimoto154, A.V. Akimov93,

M.S. Alam1, M.A. Alam75, J. Albert168, S. Albrand54, M. Aleksa29, I.N. Aleksandrov63, F. Alessandria88a, C. Alexa25a, G. Alexander152, G. Alexandre48, T. Alexopoulos9, M. Alhroob163a,163c, M. Aliev15, G. Alimonti88a_{, J. Alison}119_{, B.M.M. Allbrooke}17_,

P.P. Allport72_{, S.E. Allwood-Spiers}52_{, J. Almond}81_,

A. Aloisio101a,101b_{, R. Alon}171_{, A. Alonso}78_{, F. Alonso}69_,

B. Alvarez Gonzalez87_{, M.G. Alviggi}101a,101b_{, K. Amako}64_,

C. Amelung22_{, V.V. Ammosov}127,∗_{, S.P. Amor Dos Santos}123a_,

A. Amorim123a,b_{, N. Amram}152_{, C. Anastopoulos}29_,

L.S. Ancu16_{, N. Andari}114_{, T. Andeen}34_{, C.F. Anders}57b_,

G. Anders57a_{, K.J. Anderson}30_{, A. Andreazza}88a,88b_,

V. Andrei57a_{, M-L. Andrieux}54_{, X.S. Anduaga}69_{, P. Anger}43_,

A. Angerami34, F. Anghinolfi29, A. Anisenkov106, N. Anjos123a, A. Annovi46, A. Antonaki8, M. Antonelli46, A. Antonov95, J. Antos143b, F. Anulli131a, M. Aoki100, S. Aoun82, L. Aperio Bella4, R. Apolle117,c, G. Arabidze87, I. Aracena142, Y. Arai64, A.T.H. Arce44, S. Arfaoui147, J-F. Arguin14, E. Arik18a,∗, M. Arik18a, A.J. Armbruster86, O. Arnaez80_{, V. Arnal}79_{, C. Arnault}114_{, A. Artamonov}94_,

G. Artoni131a,131b_{, D. Arutinov}20_{, S. Asai}154_,

R. Asfandiyarov172_{, S. Ask}27_{, B. Åsman}145a,145b_{, L. Asquith}5_,

K. Assamagan24_{, A. Astbury}168_{, M. Atkinson}164_{, B. Aubert}4_,

E. Auge114_{, K. Augsten}126_{, M. Aurousseau}144a_{, G. Avolio}162_,

R. Avramidou9_{, D. Axen}167_{, G. Azuelos}92,d_{, Y. Azuma}154_,

M.A. Baak29_{, G. Baccaglioni}88a_{, C. Bacci}133a,133b_,

A.M. Bach14_{, H. Bachacou}135_{, K. Bachas}29_{, M. Backes}48_,

M. Backhaus20_{, E. Badescu}25a_{, P. Bagnaia}131a,131b_,

S. Bahinipati2, Y. Bai32a, D.C. Bailey157, T. Bain157, J.T. Baines128, O.K. Baker175, M.D. Baker24, S. Baker76, E. Banas38, P. Banerjee92, Sw. Banerjee172, D. Banfi29, A. Bangert149, V. Bansal168, H.S. Bansil17, L. Barak171, S.P. Baranov93, A. Barbaro Galtieri14, T. Barber47, E.L. Barberio85, D. Barberis49a,49b, M. Barbero20,

D.Y. Bardin63_{, T. Barillari}98_{, M. Barisonzi}174_{, T. Barklow}142_,

N. Barlow27_{, B.M. Barnett}128_{, R.M. Barnett}14_,

A. Baroncelli133a_{, G. Barone}48_{, A.J. Barr}117_{, F. Barreiro}79_,

J. Barreiro Guimar˜aes da Costa56_{, P. Barrillon}114_,

R. Bartoldus142_{, A.E. Barton}70_{, V. Bartsch}148_{, A. Basye}164_,

R.L. Bates52_{, L. Batkova}143a_{, J.R. Batley}27_{, A. Battaglia}16_,

M. Battistin29_{, F. Bauer}135_{, H.S. Bawa}142,e_{, S. Beale}97_,

T. Beau77_{, P.H. Beauchemin}160_{, R. Beccherle}49a_{, P. Bechtle}20_,

H.P. Beck16_{, A.K. Becker}174_{, S. Becker}97_{, M. Beckingham}137_,

K.H. Becks174, A.J. Beddall18c, A. Beddall18c, S. Bedikian175, V.A. Bednyakov63, C.P. Bee82, L.J. Beemster104, M. Begel24,

S. Behar Harpaz151, P.K. Behera61, M. Beimforde98, C. Belanger-Champagne84_{, P.J. Bell}48_{, W.H. Bell}48_,

G. Bella152_{, L. Bellagamba}19a_{, F. Bellina}29_{, M. Bellomo}29_,

A. Belloni56_{, O. Beloborodova}106, f_{, K. Belotskiy}95_,

O. Beltramello29_{, O. Benary}152_{, D. Benchekroun}134a_,

K. Bendtz145a,145b_{, N. Benekos}164_{, Y. Benhammou}152_,

E. Benhar Noccioli48_{, J.A. Benitez Garcia}158b_,

D.P. Benjamin44_{, M. Benoit}114_{, J.R. Bensinger}22_,

K. Benslama129_{, S. Bentvelsen}104_{, D. Berge}29_,

E. Bergeaas Kuutmann41_{, N. Berger}4_{, F. Berghaus}168_,

E. Berglund104, J. Beringer14, P. Bernat76, R. Bernhard47, C. Bernius24, T. Berry75, C. Bertella82, A. Bertin19a,19b, F. Bertolucci121a,121b, M.I. Besana88a,88b, G.J. Besjes103, N. Besson135, S. Bethke98, W. Bhimji45, R.M. Bianchi29, M. Bianco71a,71b, O. Biebel97, S.P. Bieniek76, K. Bierwagen53, J. Biesiada14, M. Biglietti133a, H. Bilokon46, M. Bindi19a,19b, S. Binet114_{, A. Bingul}18c_{, C. Bini}131a,131b_{, C. Biscarat}177_,

B. Bittner98_{, K.M. Black}21_{, R.E. Blair}5_{, J.-B. Blanchard}135_,

G. Blanchot29_{, T. Blazek}143a_{, C. Blocker}22_{, J. Blocki}38_,

A. Blondel48_{, W. Blum}80_{, U. Blumenschein}53_,

G.J. Bobbink104_{, V.B. Bobrovnikov}106_{, S.S. Bocchetta}78_,

A. Bocci44_{, C.R. Boddy}117_{, M. Boehler}47_{, J. Boek}174_,

N. Boelaert35_{, J.A. Bogaerts}29_{, A. Bogdanchikov}106_,

A. Bogouch89,∗_{, C. Bohm}145a_{, J. Bohm}124_{, V. Boisvert}75_,

T. Bold37_{, V. Boldea}25a_{, N.M. Bolnet}135_{, M. Bomben}77_,

M. Bona74, M. Boonekamp135, C.N. Booth138, S. Bordoni77, C. Borer16, A. Borisov127, G. Borissov70, I. Borjanovic12a, M. Borri81, S. Borroni86, V. Bortolotto133a,133b, K. Bos104, D. Boscherini19a, M. Bosman11, H. Boterenbrood104, J. Bouchami92, J. Boudreau122, E.V. Bouhova-Thacker70, D. Boumediene33, C. Bourdarios114, N. Bousson82,

A. Boveia30_{, J. Boyd}29_{, I.R. Boyko}63_{, I. Bozovic-Jelisavcic}12b_,

J. Bracinik17_{, P. Branchini}133a_{, G.W. Brandenburg}56_,

A. Brandt7_{, G. Brandt}117_{, O. Brandt}53_{, U. Bratzler}155_,

B. Brau83_{, J.E. Brau}113_{, H.M. Braun}174,∗_{, S.F. Brazzale}163a,163c_,

B. Brelier157_{, J. Bremer}29_{, K. Brendlinger}119_{, R. Brenner}165_,

S. Bressler171_{, D. Britton}52_{, F.M. Brochu}27_{, I. Brock}20_,

R. Brock87_{, F. Broggi}88a_{, C. Bromberg}87_{, J. Bronner}98_,

G. Brooijmans34_{, T. Brooks}75_{, W.K. Brooks}31b_{, G. Brown}81_,

H. Brown7_{, P.A. Bruckman de Renstrom}38_{, D. Bruncko}143b_,

R. Bruneliere47, S. Brunet59, A. Bruni19a, G. Bruni19a, M. Bruschi19a, T. Buanes13, Q. Buat54, F. Bucci48, J. Buchanan117, P. Buchholz140, R.M. Buckingham117, A.G. Buckley45, S.I. Buda25a, I.A. Budagov63, B. Budick107, V. B¨uscher80, L. Bugge116, O. Bulekov95, A.C. Bundock72, M. Bunse42, T. Buran116, H. Burckhart29, S. Burdin72, T. Burgess13_{, S. Burke}128_{, E. Busato}33_{, P. Bussey}52_,

C.P. Buszello165_{, B. Butler}142_{, J.M. Butler}21_{, C.M. Buttar}52_,

J.M. Butterworth76_{, W. Buttinger}27_{, S. Cabrera Urb´an}166_,

D. Caforio19a,19b_{, O. Cakir}3a_{, P. Calafiura}14_{, G. Calderini}77_,

P. Calfayan97_{, R. Calkins}105_{, L.P. Caloba}23a_{, R. Caloi}131a,131b_,

D. Calvet33_{, S. Calvet}33_{, R. Camacho Toro}33_,

P. Camarri132a,132b_{, D. Cameron}116_{, L.M. Caminada}14_,

R. Caminal Armadans11_{, S. Campana}29_{, M. Campanelli}76_,

V. Canale101a,101b_{, F. Canelli}30,g_{, A. Canepa}158a_{, J. Cantero}79_,

R. Cantrill75, L. Capasso101a,101b, M.D.M. Capeans Garrido29, I. Caprini25a, M. Caprini25a, D. Capriotti98, M. Capua36a,36b,

R. Caputo80, R. Cardarelli132a, T. Carli29, G. Carlino101a, L. Carminati88a,88b_{, B. Caron}84_{, S. Caron}103_{, E. Carquin}31b_,

G.D. Carrillo-Montoya172_{, A.A. Carter}74_{, J.R. Carter}27_,

J. Carvalho123a,h_{, D. Casadei}107_{, M.P. Casado}11_,

M. Cascella121a,121b_{, C. Caso}49a,49b,∗_,

A.M. Castaneda Hernandez172,i_{, E. Castaneda-Miranda}172_,

V. Castillo Gimenez166_{, N.F. Castro}123a_{, G. Cataldi}71a_,

P. Catastini56_{, A. Catinaccio}29_{, J.R. Catmore}29_{, A. Cattai}29_,

G. Cattani132a,132b_{, S. Caughron}87_{, V. Cavaliere}164_,

P. Cavalleri77_{, D. Cavalli}88a_{, M. Cavalli-Sforza}11_,

V. Cavasinni121a,121b, F. Ceradini133a,133b, A.S. Cerqueira23b, A. Cerri29, L. Cerrito74, F. Cerutti46, S.A. Cetin18b,

A. Chafaq134a, D. Chakraborty105, I. Chalupkova125, K. Chan2, P. Chang164, B. Chapleau84, J.D. Chapman27, J.W. Chapman86, E. Chareyre77, D.G. Charlton17, V. Chavda81,

C.A. Chavez Barajas29, S. Cheatham84, S. Chekanov5, S.V. Chekulaev158a_{, G.A. Chelkov}63_{, M.A. Chelstowska}103_,

C. Chen62_{, H. Chen}24_{, S. Chen}32c_{, X. Chen}172_{, Y. Chen}34_,

A. Cheplakov63_{, R. Cherkaoui El Moursli}134e_{, V. Chernyatin}24_,

E. Cheu6_{, S.L. Cheung}157_{, L. Chevalier}135_{, G. Chiefari}101a,101b_,

L. Chikovani50a,∗_{, J.T. Childers}29_{, A. Chilingarov}70_,

G. Chiodini71a_{, A.S. Chisholm}17_{, R.T. Chislett}76_{, A. Chitan}25a_,

M.V. Chizhov63_{, G. Choudalakis}30_{, S. Chouridou}136_,

I.A. Christidi76_{, A. Christov}47_{, D. Chromek-Burckhart}29_,

M.L. Chu150_{, J. Chudoba}124_{, G. Ciapetti}131a,131b_{, A.K. Ciftci}3a_,

R. Ciftci3a, D. Cinca33, V. Cindro73, C. Ciocca19a,19b, A. Ciocio14, M. Cirilli86, P. Cirkovic12b, Z.H. Citron171, M. Citterio88a, M. Ciubancan25a, A. Clark48, P.J. Clark45, R.N. Clarke14, W. Cleland122, J.C. Clemens82, B. Clement54, C. Clement145a,145b, Y. Coadou82, M. Cobal163a,163c,

A. Coccaro137, J. Cochran62, J.G. Cogan142, J. Coggeshall164, E. Cogneras177_{, J. Colas}4_{, S. Cole}105_{, A.P. Colijn}104_,

N.J. Collins17_{, C. Collins-Tooth}52_{, J. Collot}54_,

T. Colombo118a,118b_{, G. Colon}83_{, P. Conde Mui˜no}123a_,

E. Coniavitis117_{, M.C. Conidi}11_{, S.M. Consonni}88a,88b_,

V. Consorti47_{, S. Constantinescu}25a_{, C. Conta}118a,118b_,

G. Conti56_{, F. Conventi}101a, j_{, M. Cooke}14_{, B.D. Cooper}76_,

A.M. Cooper-Sarkar117_{, K. Copic}14_{, T. Cornelissen}174_,

M. Corradi19a_{, F. Corriveau}84,k_{, A. Cortes-Gonzalez}164_,

G. Cortiana98_{, G. Costa}88a_{, M.J. Costa}166_{, D. Costanzo}138_,

D. Cˆot´e29, L. Courneyea168, G. Cowan75, C. Cowden27, B.E. Cox81, K. Cranmer107, F. Crescioli121a,121b,

M. Cristinziani20, G. Crosetti36a,36b, S. Cr´ep´e-Renaudin54, C.-M. Cuciuc25a, C. Cuenca Almenar175,

T. Cuhadar Donszelmann138, M. Curatolo46, C.J. Curtis17, C. Cuthbert149, P. Cwetanski59, H. Czirr140, P. Czodrowski43, Z. Czyczula175_{, S. D’Auria}52_{, M. D’Onofrio}72_,

A. D’Orazio131a,131b_{, M.J. Da Cunha Sargedas De Sousa}123a_,

C. Da Via81_{, W. Dabrowski}37_{, A. Dafinca}117_{, T. Dai}86_,

C. Dallapiccola83_{, M. Dam}35_{, M. Dameri}49a,49b_,

D.S. Damiani136_{, H.O. Danielsson}29_{, V. Dao}48_{, G. Darbo}49a_,

G.L. Darlea25b_{, J.A. Dassoulas}41_{, W. Davey}20_{, T. Davidek}125_,

N. Davidson85_{, R. Davidson}70_{, E. Davies}117,c_{, M. Davies}92_,

O. Davignon77_{, A.R. Davison}76_{, Y. Davygora}57a_{, E. Dawe}141_,

I. Dawson138_{, R.K. Daya-Ishmukhametova}22_{, K. De}7_,

R. de Asmundis101a, S. De Castro19a,19b, S. De Cecco77, J. de Graat97, N. De Groot103, P. de Jong104, C. De La Taille114,

H. De la Torre79, F. De Lorenzi62, L. de Mora70, L. De Nooij104_{, D. De Pedis}131a_{, A. De Salvo}131a_,

U. De Sanctis163a,163c_{, A. De Santo}148_,

J.B. De Vivie De Regie114_{, G. De Zorzi}131a,131b_,

W.J. Dearnaley70_{, R. Debbe}24_{, C. Debenedetti}45_,

B. Dechenaux54_{, D.V. Dedovich}63_{, J. Degenhardt}119_,

C. Del Papa163a,163c_{, J. Del Peso}79_{, T. Del Prete}121a,121b_,

T. Delemontex54_{, M. Deliyergiyev}73_{, A. Dell’Acqua}29_,

L. Dell’Asta21_{, M. Della Pietra}101a, j_{, D. della Volpe}101a,101b_,

M. Delmastro4_{, P.A. Delsart}54_{, C. Deluca}104_{, S. Demers}175_,

M. Demichev63, B. Demirkoz11,l, J. Deng162, S.P. Denisov127, D. Derendarz38, J.E. Derkaoui134d, F. Derue77, P. Dervan72, K. Desch20, E. Devetak147, P.O. Deviveiros104, A. Dewhurst128, B. DeWilde147, S. Dhaliwal157, R. Dhullipudi24,m,

A. Di Ciaccio132a,132b, L. Di Ciaccio4, A. Di Girolamo29, B. Di Girolamo29, S. Di Luise133a,133b, A. Di Mattia172, B. Di Micco29_{, R. Di Nardo}46_{, A. Di Simone}132a,132b_,

R. Di Sipio19a,19b_{, M.A. Diaz}31a_{, E.B. Diehl}86_{, J. Dietrich}41_,

T.A. Dietzsch57a_{, S. Diglio}85_{, K. Dindar Yagci}39_,

J. Dingfelder20_{, F. Dinut}25a_{, C. Dionisi}131a,131b_{, P. Dita}25a_,

S. Dita25a_{, F. Dittus}29_{, F. Djama}82_{, T. Djobava}50b_,

M.A.B. do Vale23c_{, A. Do Valle Wemans}123a,n_{, T.K.O. Doan}4_,

M. Dobbs84_{, R. Dobinson}29,∗_{, D. Dobos}29_{, E. Dobson}29,o_,

J. Dodd34_{, C. Doglioni}48_{, T. Doherty}52_{, Y. Doi}64,∗_,

J. Dolejsi125_{, I. Dolenc}73_{, Z. Dolezal}125_{, B.A. Dolgoshein}95,∗_,

T. Dohmae154, M. Donadelli23d, J. Donini33, J. Dopke29, A. Doria101a, A. Dos Anjos172, A. Dotti121a,121b, M.T. Dova69, A.D. Doxiadis104, A.T. Doyle52, N. Dressnandt119, M. Dris9, J. Dubbert98, S. Dube14, E. Duchovni171, G. Duckeck97, D. Duda174, A. Dudarev29, F. Dudziak62, M. D¨uhrssen29, I.P. Duerdoth81, L. Duflot114, M-A. Dufour84, L. Duguid75, M. Dunford29_{, H. Duran Yildiz}3a_{, R. Duxfield}138_,

M. Dwuznik37_{, F. Dydak}29_{, M. D¨uren}51_{, W.L. Ebenstein}44_,

J. Ebke97_{, S. Eckweiler}80_{, K. Edmonds}80_{, W. Edson}1_,

C.A. Edwards75_{, N.C. Edwards}52_{, W. Ehrenfeld}41_{, T. Eifert}142_,

G. Eigen13_{, K. Einsweiler}14_{, E. Eisenhandler}74_{, T. Ekelof}165_,

M. El Kacimi134c_{, M. Ellert}165_{, S. Elles}4_{, F. Ellinghaus}80_,

K. Ellis74_{, N. Ellis}29_{, J. Elmsheuser}97_{, M. Elsing}29_,

D. Emeliyanov128_{, R. Engelmann}147_{, A. Engl}97_{, B. Epp}60_,

J. Erdmann53_{, A. Ereditato}16_{, D. Eriksson}145a_{, J. Ernst}1_,

M. Ernst24, J. Ernwein135, D. Errede164, S. Errede164, E. Ertel80, M. Escalier114, H. Esch42, C. Escobar122, X. Espinal Curull11, B. Esposito46, F. Etienne82,

A.I. Etienvre135, E. Etzion152, D. Evangelakou53, H. Evans59, L. Fabbri19a,19b, C. Fabre29, R.M. Fakhrutdinov127,

S. Falciano131a, Y. Fang172, M. Fanti88a,88b, A. Farbin7, A. Farilla133a_{, J. Farley}147_{, T. Farooque}157_{, S. Farrell}162_,

S.M. Farrington169_{, P. Farthouat}29_{, F. Fassi}166_{, P. Fassnacht}29_,

D. Fassouliotis8_{, B. Fatholahzadeh}157_{, A. Favareto}88a,88b_,

L. Fayard114_{, S. Fazio}36a,36b_{, R. Febbraro}33_{, P. Federic}143a_,

O.L. Fedin120_{, W. Fedorko}87_{, M. Fehling-Kaschek}47_,

L. Feligioni82_{, D. Fellmann}5_{, C. Feng}32d_{, E.J. Feng}5_,

A.B. Fenyuk127_{, J. Ferencei}143b_{, W. Fernando}5_{, S. Ferrag}52_,

J. Ferrando52_{, V. Ferrara}41_{, A. Ferrari}165_{, P. Ferrari}104_,

R. Ferrari118a_{, D.E. Ferreira de Lima}52_{, A. Ferrer}166_,

D. Ferrere48, C. Ferretti86, A. Ferretto Parodi49a,49b, M. Fiascaris30, F. Fiedler80, A. Filipˇciˇc73, F. Filthaut103,

M. Fincke-Keeler168, M.C.N. Fiolhais123a,h, L. Fiorini166, A. Firan39_{, G. Fischer}41_{, M.J. Fisher}108_{, M. Flechl}47_,

I. Fleck140_{, J. Fleckner}80_{, P. Fleischmann}173_,

S. Fleischmann174_{, T. Flick}174_{, A. Floderus}78_,

L.R. Flores Castillo172_{, M.J. Flowerdew}98_,

T. Fonseca Martin16_{, A. Formica}135_{, A. Forti}81_{, D. Fortin}158a_,

D. Fournier114_{, A.J. Fowler}44_{, H. Fox}70_{, P. Francavilla}11_,

M. Franchini19a,19b_{, S. Franchino}118a,118b_{, D. Francis}29_,

T. Frank171_{, S. Franz}29_{, M. Fraternali}118a,118b_{, S. Fratina}119_,

S.T. French27_{, C. Friedrich}41_{, F. Friedrich}43_{, R. Froeschl}29_,

D. Froidevaux29, J.A. Frost27, C. Fukunaga155, E. Fullana Torregrosa29, B.G. Fulsom142, J. Fuster166, C. Gabaldon29, O. Gabizon171, A. Gabrielli131a,131b,

T. Gadfort24, S. Gadomski48, G. Gagliardi49a,49b, P. Gagnon59, C. Galea97, B. Galhardo123a, E.J. Gallas117, V. Gallo16, B.J. Gallop128, P. Gallus124, K.K. Gan108, Y.S. Gao142,e, A. Gaponenko14_{, F. Garberson}175_{, M. Garcia-Sciveres}14_,

C. Garc´ıa166_{, J.E. Garc´ıa Navarro}166_{, R.W. Gardner}30_,

N. Garelli29_{, H. Garitaonandia}104_{, V. Garonne}29_{, C. Gatti}46_,

G. Gaudio118a_{, B. Gaur}140_{, L. Gauthier}135_{, P. Gauzzi}131a,131b_,

I.L. Gavrilenko93_{, C. Gay}167_{, G. Gaycken}20_{, E.N. Gazis}9_,

P. Ge32d_{, Z. Gecse}167_{, C.N.P. Gee}128_{, D.A.A. Geerts}104_,

Ch. Geich-Gimbel20_{, K. Gellerstedt}145a,145b_{, C. Gemme}49a_,

A. Gemmell52_{, M.H. Genest}54_{, S. Gentile}131a,131b_,

M. George53_{, S. George}75_{, P. Gerlach}174_{, A. Gershon}152_,

C. Geweniger57a, H. Ghazlane134b, N. Ghodbane33, B. Giacobbe19a, S. Giagu131a,131b, V. Giakoumopoulou8, V. Giangiobbe11, F. Gianotti29, B. Gibbard24, A. Gibson157, S.M. Gibson29, M. Gilchriese14, D. Gillberg28,

A.R. Gillman128, D.M. Gingrich2,d, J. Ginzburg152, N. Giokaris8, M.P. Giordani163c, R. Giordano101a,101b, F.M. Giorgi15_{, P. Giovannini}98_{, P.F. Giraud}135_{, D. Giugni}88a_,

M. Giunta92_{, P. Giusti}19a_{, B.K. Gjelsten}116_{, L.K. Gladilin}96_,

C. Glasman79_{, J. Glatzer}47_{, A. Glazov}41_{, K.W. Glitza}174_,

G.L. Glonti63_{, J.R. Goddard}74_{, J. Godfrey}141_{, J. Godlewski}29_,

M. Goebel41_{, T. G¨opfert}43_{, C. Goeringer}80_{, C. G¨ossling}42_,

S. Goldfarb86_{, T. Golling}175_{, A. Gomes}123a,b_,

L.S. Gomez Fajardo41_{, R. Gonc¸alo}75_,

J. Goncalves Pinto Firmino Da Costa41_{, L. Gonella}20_,

S. Gonzalez172_{, S. Gonz´alez de la Hoz}166_,

G. Gonzalez Parra11, M.L. Gonzalez Silva26,

S. Gonzalez-Sevilla48, J.J. Goodson147, L. Goossens29, P.A. Gorbounov94, H.A. Gordon24, I. Gorelov102, G. Gorfine174, B. Gorini29, E. Gorini71a,71b, A. Goriˇsek73, E. Gornicki38, B. Gosdzik41, A.T. Goshaw5, M. Gosselink104, M.I. Gostkin63, I. Gough Eschrich162, M. Gouighri134a, D. Goujdami134c_{, M.P. Goulette}48_{, A.G. Goussiou}137_{, C. Goy}4_,

S. Gozpinar22_{, I. Grabowska-Bold}37_{, P. Grafstr¨om}19a,19b_,

K-J. Grahn41_{, F. Grancagnolo}71a_{, S. Grancagnolo}15_,

V. Grassi147_{, V. Gratchev}120_{, N. Grau}34_{, H.M. Gray}29_,

J.A. Gray147_{, E. Graziani}133a_{, O.G. Grebenyuk}120_,

T. Greenshaw72_{, Z.D. Greenwood}24,m_{, K. Gregersen}35_,

I.M. Gregor41_{, P. Grenier}142_{, J. Griffiths}7_{, N. Grigalashvili}63_,

A.A. Grillo136_{, S. Grinstein}11_{, Ph. Gris}33_{, Y.V. Grishkevich}96_,

J.-F. Grivaz114_{, E. Gross}171_{, J. Grosse-Knetter}53_,

J. Groth-Jensen171, K. Grybel140, D. Guest175, C. Guicheney33, S. Guindon53, U. Gul52, H. Guler84,p, J. Gunther124, B. Guo157,

J. Guo34, P. Gutierrez110, N. Guttman152, O. Gutzwiller172, C. Guyot135_{, C. Gwenlan}117_{, C.B. Gwilliam}72_{, A. Haas}142_,

S. Haas29_{, C. Haber}14_{, H.K. Hadavand}39_{, D.R. Hadley}17_,

P. Haefner20_{, F. Hahn}29_{, S. Haider}29_{, Z. Hajduk}38_,

H. Hakobyan176_{, D. Hall}117_{, J. Haller}53_{, K. Hamacher}174_,

P. Hamal112_{, K. Hamano}85_{, M. Hamer}53_{, A. Hamilton}144b,q_,

S. Hamilton160_{, L. Han}32b_{, K. Hanagaki}115_{, K. Hanawa}159_,

M. Hance14_{, C. Handel}80_{, P. Hanke}57a_{, J.R. Hansen}35_,

J.B. Hansen35_{, J.D. Hansen}35_{, P.H. Hansen}35_{, P. Hansson}142_,

K. Hara159_{, G.A. Hare}136_{, T. Harenberg}174_{, S. Harkusha}89_,

D. Harper86, R.D. Harrington45, O.M. Harris137, J. Hartert47, F. Hartjes104, T. Haruyama64, A. Harvey55, S. Hasegawa100, Y. Hasegawa139, S. Hassani135, S. Haug16, M. Hauschild29, R. Hauser87, M. Havranek20, C.M. Hawkes17,

R.J. Hawkings29, A.D. Hawkins78, D. Hawkins162, T. Hayakawa65, T. Hayashi159, D. Hayden75, C.P. Hays117, H.S. Hayward72_{, S.J. Haywood}128_{, M. He}32d_{, S.J. Head}17_,

V. Hedberg78_{, L. Heelan}7_{, S. Heim}87_{, B. Heinemann}14_,

S. Heisterkamp35_{, L. Helary}21_{, C. Heller}97_{, M. Heller}29_,

S. Hellman145a,145b_{, D. Hellmich}20_{, C. Helsens}11_,

R.C.W. Henderson70_{, M. Henke}57a_{, A. Henrichs}53_,

A.M. Henriques Correia29_{, S. Henrot-Versille}114_{, C. Hensel}53_,

T. Henß174_{, C.M. Hernandez}7_{, Y. Hern´andez Jim´enez}166_,

R. Herrberg15_{, G. Herten}47_{, R. Hertenberger}97_{, L. Hervas}29_,

G.G. Hesketh76_{, N.P. Hessey}104_{, E. Hig´on-Rodriguez}166_,

J.C. Hill27, K.H. Hiller41, S. Hillert20, S.J. Hillier17, I. Hinchliffe14, E. Hines119, M. Hirose115, F. Hirsch42, D. Hirschbuehl174, J. Hobbs147, N. Hod152,

M.C. Hodgkinson138, P. Hodgson138, A. Hoecker29, M.R. Hoeferkamp102, J. Hoffman39, D. Hoffmann82,

M. Hohlfeld80, M. Holder140, S.O. Holmgren145a, T. Holy126, J.L. Holzbauer87_{, T.M. Hong}119_{, L. Hooft van Huysduynen}107_,

S. Horner47_{, J-Y. Hostachy}54_{, S. Hou}150_{, A. Hoummada}134a_,

J. Howard117_{, J. Howarth}81_{, I. Hristova}15_{, J. Hrivnac}114_,

T. Hryn’ova4_{, P.J. Hsu}80_{, S.-C. Hsu}14_{, D. Hu}34_{, Z. Hubacek}126_,

F. Hubaut82_{, F. Huegging}20_{, A. Huettmann}41_{, T.B. Huffman}117_,

E.W. Hughes34_{, G. Hughes}70_{, M. Huhtinen}29_{, M. Hurwitz}14_,

U. Husemann41_{, N. Huseynov}63,r_{, J. Huston}87_{, J. Huth}56_,

G. Iacobucci48_{, G. Iakovidis}9_{, M. Ibbotson}81_{, I. Ibragimov}140_,

L. Iconomidou-Fayard114_{, J. Idarraga}114_{, P. Iengo}101a_,

O. Igonkina104, Y. Ikegami64, M. Ikeno64, D. Iliadis153, N. Ilic157, T. Ince20, J. Inigo-Golfin29, P. Ioannou8, M. Iodice133a, K. Iordanidou8, V. Ippolito131a,131b,

A. Irles Quiles166, C. Isaksson165, M. Ishino66, M. Ishitsuka156, R. Ishmukhametov39, C. Issever117, S. Istin18a, A.V. Ivashin127, W. Iwanski38, H. Iwasaki64, J.M. Izen40, V. Izzo101a,

B. Jackson119_{, J.N. Jackson}72_{, P. Jackson}142_{, M.R. Jaekel}29_,

V. Jain59_{, K. Jakobs}47_{, S. Jakobsen}35_{, T. Jakoubek}124_,

J. Jakubek126_{, D.K. Jana}110_{, E. Jansen}76_{, H. Jansen}29_,

A. Jantsch98_{, M. Janus}47_{, G. Jarlskog}78_{, L. Jeanty}56_,

I. Jen-La Plante30_{, D. Jennens}85_{, P. Jenni}29_,

A.E. Loevschall-Jensen35_{, P. Jeˇz}35_{, S. J´ez´equel}4_{, M.K. Jha}19a_,

H. Ji172_{, W. Ji}80_{, J. Jia}147_{, Y. Jiang}32b_{, M. Jimenez Belenguer}41_,

S. Jin32a_{, O. Jinnouchi}156_{, M.D. Joergensen}35_{, D. Joffe}39_,

M. Johansen145a,145b_{, K.E. Johansson}145a_{, P. Johansson}138_,

S. Johnert41, K.A. Johns6, K. Jon-And145a,145b, G. Jones169, R.W.L. Jones70, T.J. Jones72, C. Joram29, P.M. Jorge123a,