High Mass Higgs boson Searches in ATLAS and CMS

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High Mass Higgs boson Searches in ATLAS and

CMS

Joana MACHADO MIGUENS∗ †, on behalf of the ATLAS and CMS Collaborations

Faculdade de Ciencias, Universidade de Lisboa and LIP, Lisboa, Portugal

E-mail:jmiguens@cern.ch

The recently discovered resonance at 125 GeV shows properties, so far, consistent with the Stan-dard Model Higgs boson. It is, nonetheless, important to directly search the full mass range avail-able at the Large Hadron Collider (LHC). Searches for a high-mass Higgs boson, with SM-like properties, can be performed without placing any bias on the nature of the new particle. Moreover, they can be used as a starting point for Beyond the Standard Model scenarios, that can be stud-ied by simply rescaling the Standard Model analyses. The latest results from ATLAS and CMS, using data from the LHC to search for SM-like Higgs bosons with masses substantially above the observed 125 GeV Higgs boson, are presented. These include ZZ and WW decay modes and explore the 200 GeV to 1 TeV mass range, where no significant excesses have been observed.

The European Physical Society Conference on High Energy Physics 18-24 July, 2013

Stockholm, Sweden ∗_Speaker.

†_{Work financed in part by FCT, Portugal, through the grant SFRH/BD/69173/2010, co-financed by GRICES and}

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1. Introduction

ATLAS [1] and CMS [2] are two general-purpose detectors at the Large Hadron Collider

(CERN), that have successfully collected more than 25 fb−1 _{of proton-proton collision data. The}

ATLAS and CMS Collaborations have recently announced the discovery of a new particle [3,4],

with a mass of approximately 125 GeV and properties [5,6], so far, consistent with the Standard

Model (SM) Higgs boson. The question remains, however, if this particle is fully responsible for electroweak (EW) symmetry breaking, or if additional beyond the SM (BSM) physics, predicting more than one Higgs boson, exists to play this role. It is, therefore, crucial to explore the full accessible mass range, up to 1 TeV, for which the H → WW and H → ZZ decay modes are favoured.

The simplest extension of the SM Higgs sector predicts a heavy real EW singlet [7]

mix-ing with the H(125) particle. In this model, both gauge and fermion couplmix-ings of the heavy

state (H(125)) are scaled with respect to the SM, by a common factor κ0 _{(κ), with the relation}

κ2+ κ02=1 imposed by unitarity. The heavy state can have “non-SM-like” decays, including the

decay to H(125), which are parametrized by BRnew, such that BR0= (1 − BRnew)BRSM. Current

measurements on the H(125) favour a heavy state with a narrow width [7], which is modelled

us-ing the Narrow Width Approximation (NWA). To model a heavy resonance with a larger, SM-like width, analyses currently use the Complex Pole Scheme (CPS), since the Breit-Wigner description

of the lineshape is not valid for mH>400 GeV∗.

This paper presents the most recent efforts by ATLAS and CMS in the search for high-mass Higgs bosons, exploring the following decay modes: H → WW → `νqq, H → WW → `ν`ν, H → ZZ → ````, H → ZZ → ``νν and H → ZZ → ``qq.

2. H → WW → `νqq

Analyses in the `νqq final state search for one high transverse momentum (pT), isolated lepton,

either an electron (e) or a muon (µ), large missing transverse energy (Emiss

T ) and jet(s) compatible

with a W decay to quarks. The full invariant mass of the system, used to extract the signal, can be

reconstructed by placing the constraint m`ν =mW. W +jets events are the dominant background.

ATLAS has performed a search in the H → WW → `νqq channel [8], using 4.7 fb−1_of√_{s =}

7 TeV data and exploring the 300−600 GeV mass range. The signal is extracted by fitting the m`νj j

spectrum in data, with a functional form tested in the mj jsidebands. No significant excesses of data

above the background model were observed and upper limits on σ/σSM(production cross-section

normalized to the SM expectation) were extracted. The best sensitivity is reached at mH=400 GeV,

where the 95% CL (confidence level) observed (expected) limits are 1.9 (1.6) times the SM for the categories with 0 and 1 additional jets, and 7.9 (6.5) times the SM for events with 2 additional jets.

CMS’s analysis in the `νqq final state [9] uses 19.3 fb−1 _of√_{s = 8 TeV data to exploit the}

600 − 1000 GeV mass range. Boosted W bosons (pT>200 GeV) are selected, in which the decay

quarks form a single “fat jet” (J), reconstructed with a ∆R = 0.8 Cambridge-Aachen algorithm. The jet mass is pruned, to suppress multijet and pile-up contributions to the jet, and N-subjettiness,

∗_{Before the CPS prescription was available, conservative uncertainties, of the form 1.5(m}

H/TeV)3, were assigned

to the production cross-section to cover for this lineshape effect, as well as for the signal-continuum background inter-ference effect, that increases with the increasing width of the particle.

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High Mass Higgs boson Searches in ATLAS and CMS Joana MACHADO MIGUENS

an observable measuring the number of subjets in the jet, is used to further discriminate the

hadron-ically decaying W boson from multijet background. Both normalization and m`νJshape of W +jets

background in the final signal region, shown in Figure1-middle, are extracted from fits to data

in the mJ sidebands, shown in Figure1-left. No significant excesses were observed and 95% CL

upper limits on σ/σSMwere set. Observed (expected) limits range from 1.1 (1.05) times the SM at

mH=600 GeV, to 4.2 (4.6) times the SM at 1 TeV. In the BSM heavy EW singlet scenario, 95% CL

exclusion limits on σ×BR of H → WW → `νqq (cross section times branching ratio) are set for

different κ0 _{hypothesis (C}0_{, used in figures from CMS, is equivalent to κ}0_{), assuming BR}

new=0.

They range from 60 fb to 400 fb and are shown in Figure1-right.

)

2

Pruned jet mass (GeV/c

40 50 60 70 80 90 100 110 120 130 ) 2 Events / ( 5 GeV/c 50 100 150 200 250 300 350 WW/WZ/ZZ tt

Single Top W+jets

data Uncertainty ν e → = 8 TeV, W s at -1 CMS Preliminary, 19.3 fb )2 (GeV/c jνlm 400 500 600 700 800 900 1000 PULL -4 -2 0 2 4 ) 2 (GeV/c j ν l m 400 500 600 700 800 900 1000 ) 2 Events / ( 50 GeV/c 50 100 150 200 250 300 350 400 W+jets WW/WZ/ZZ t t Single Top 5, 600GeV × ggH qqH×5, 600GeV data Uncertainty ν e → = 8 TeV, W s at -1 CMS Preliminary, 19.3 fb ) 2

Higgs boson mass (GeV/c 600 650 700 750 800 850 900 950 1000 (pb) WW BR × 95% σ 0 0.1 0.2 0.3 0.4 0.5 0.6 = 0.3 2 exp., C' _{obs., C'} 2 = 0.3 _{th., C'} 2_{= 0.3} = 0.6 2 exp., C' _{obs., C'} 2 = 0.6 _{th., C'} 2_{= 0.6} = 0.8 2 exp., C' _{obs., C'} 2 = 0.8 _{th., C'} 2_{= 0.8} = 1.0 2 exp., C' _{obs., C'} 2 = 1.0 _{th., C'} 2_{= 1.0} µ =8TeV, e+ s at -1 CMS Preliminary, 19.3 fb = 0 new BR

Figure 1: Left: Data and MC distribution for the mJsidebands and signal region. Middle: m`νJdistribution in the signal region for electron events. Right: BSM exclusion limits as a function of mass for various values of κ02_{, with BR}

new=0. Figures from Ref. [9].

3. H → WW → `ν`ν

The H → WW → `ν`ν analysis is challenging, as the presence of two neutrinos in the final state does not allow for a full mass reconstruction. The basic signature of this channel consists of

two high pT, isolated, opposite charge leptons, either electrons or muons, and large ETmiss.

Contin-uum WW production is the largest source of background.

ATLAS has analyzed the `ν`ν channel [10] in the 260 − 1000 GeV range, using 20.7 fb−1_of

8 TeV data. Events with 0, 1 and 2 jets are used and SM-like and NWA hypothesis are

investi-gated. High invariant mass of the dilepton system (m``>50 GeV) and and small pseudo-rapidity

separation between the leptons (∆η < 1.0) are required to suppress the H(125) resonance (consid-ered background) and WW background. Top and WW processes are normalized using data control

regions. The transverse mass, mT=

q

(E``

T +ETmiss)2− |−→pT``+ −→pmissT |2, shown in Figure2-left, is

fitted to extract the signal. Data agrees with the background expectation and 95% CL limits are set on σ×BR of H → WW → `ν`ν, separately for gluon fusion (ggF) and vector boson fusion (VBF)

production. Figure2-middle shows these limits, as a function of mH, for ggF and NWA. Figure2

-right shows the analysis excludes a SM-like Higgs in the range 260 − 642 GeV. At mH=600 GeV,

upper limits on ggF (VBF) are 34 (16) fb for a SM-like width, and 32 (12) fb for NWA.

CMS has looked for a SM-like Higgs boson in the H → WW → `ν`ν channel [11], using the

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Not reviewed, for internal cir culation only [GeV] T m 50 100 150 200 250 300 350 400 450 500 Events /10 GeV 0 20 40 60 80 100 Data stat) SM (sys W+jets Z+jets tt Single Top ⌥ WZ/ZZ/W WW H [125 GeV] H [300 GeV] 10) ⇥ H [600 GeV] ( 10) ⇥ H [900 GeV] ( + 0 jets ⇤ µ ⇤ e ⇧ WW ⇧ H ATLAS Preliminary -1 Ldt = 20.7 fb ⌃ = 8 TeV s (a) [GeV] T m 50 100 150 200 250 300 350 400 450 500 Events /10 GeV 0 10 20 30 40 50 60 70 80 _Data stat) ⇥ SM (sys W+jets Z+jets tt Single Top ⌥ WZ/ZZ/W WW H [125 GeV] H [300 GeV] 10) ⇤ H [600 GeV] ( 10) ⇤ H [900 GeV] ( + 1 jets ⌅ µ ⌅ e ⌃ WW ⌃ H ATLAS Preliminary -1 Ldt = 20.7 fb = 8 TeV s (b) [GeV] T m 50 100 150 200 250 300 350 400 450 500 Events /20 GeV 0 2 4 6 8 10 12 14 + 2 jets µ e ⇤ WW ⇤ H Data stat) ⇧ SM (sys W+jets Z+jets tt Single Top ⌥ WZ/ZZ/W WW H [125 GeV] H [300 GeV] 10) ⌃ H [600 GeV] ( 10) ⌃ H [900 GeV] ( ATLAS Preliminary -1 Ldt = 20.7 fb ⌅ = 8 TeV s (c)

Figure 2: Transverse mass distributions for events in (a) the Njet=0, (b) the Njet=1, and (c) the Njet 2

final states. The distributions are shown after all selections in the relevant final state. The shaded area represents the uncertainty on the signal and background yields from statistical, experimental and

theoretical sources. Signal expectations for mH=300 GeV, 600 GeV and 900 GeV are shown, with

ggF and VBF contributions added. The mH=600 GeV and 900 GeV signals have been scaled by a

factor of 10 to enhance visibility. In all distributions the last bin includes the events in overflow.

5.3 W+ jets

The W+ jets background is estimated using a data CR in which one of the two leptons satisfies all the identification and isolation criteria, and the other lepton fails these criteria but satisfies a set of looser requirements. All other analysis selections are applied. The contribution to the signal region is obtained by scaling the number of events in the CR by extrapolation factors obtained from a dijet sample.

6 Systematic uncertainties

Systematic uncertainties arise from both experimental and theoretical sources. Some of these un-certainties are correlated between the signal and background predictions, so that the impact of each

8 Not reviewed, for internal cir culation [GeV] H m 300 400 500 600 700 800 900 1000 95% CL Limit on -3 10 -2 10 -1 10 (a) [GeV] H m 300 400 500 600 700 800 900 1000 95% CL Limit on -3 10 -2 10 -1 10 (b)

Figure 5: 95% CL upper limits on the Higgs boson production cross section times branching ratio for H!WW!`⌫`⌫ (with ` = e, µ, ⌧ including all ⌧ decay modes) for a Higgs boson with a SM-like lineshape. The limits are shown for (a) ggF production and (b) VBF production. The green and yellow bands show the ±1 and ±2 uncertainties on the expected limit. The expected cross section times branching ratio for the production of a SM Higgs boson is shown as a blue line.

[GeV] H m 300 400 500 600 700 800 900 1000 BR [pb] × σ 95% CL Limit on -3 10 -2 10 -1 10 1 10 Obs. ggF Exp. ggF σ 1 ± σ 2 ± BR × Th σ -1 Ldt = 20.7 fb ∫ = 8 TeV s ATLAS Preliminary , NWA ν µ ν e → WW → H (a) [GeV] H m 300 400 500 600 700 800 900 1000 BR [pb] × σ 95% CL Limit on -3 10 -2 10 -1 10 1 10 Obs. VBF Exp. VBF σ 1 ± σ 2 ± BR × Th σ -1 Ldt = 20.7 fb ∫ = 8 TeV s ATLAS Preliminary , NWA ν µ ν e → WW → H (b)

Figure 6: 95% CL upper limits on the Higgs boson production cross section times branching ratio for H!WW!`⌫`⌫ (with ` = e, µ, ⌧ including all ⌧ decay modes) for a Higgs boson with a narrow lineshape (NWA). The limits are shown for (a) ggF production and (b) VBF production. The green and yellow bands show the ±1 and ±2 uncertainties on the expected limit. The expected cross section times branching ratio for the production of a SM Higgs boson is shown as a blue line.

14 Not reviewed, for internal cir culation only [GeV] H m 300 400 500 600 700 800 900 1000 BR [pb] × σ 95% CL Limit on -3 10 -2 10 -1 10 1 10 Obs. ggF+VBF Exp. ggF+VBF σ 1 ± σ 2 ± BR × Th σ -1 Ldt = 20.7 fb ∫ = 8 TeV s ATLAS Preliminary , SM width ν µ ν e → WW → H (a) [GeV] H m 300 400 500 600 700 800 900 1000 BR [pb] × σ 95% CL Limit on -3 10 -2 10 -1 10 1 10 Obs. ggF+VBF Exp. ggF+VBF σ 1 ± σ 2 ± BR × Th σ -1 Ldt = 20.7 fb ∫ = 8 TeV s ATLAS Preliminary , NWA ν µ ν e → WW → H (b)

Figure 7: 95% CL upper limits on the Higgs boson production cross section times branching ratio for H!WW!`⌫`⌫ (with ` = e, µ, ⌧ including all ⌧ decay modes) for a Higgs boson with (a) a SM-like lineshape and (b) a narrow lineshape (NWA). The ggF and VBF production modes are both treated as signal contributions. The green and yellow bands show the ±1 and ±2 uncertainties on the expected limit. The expected cross section times branching ratio for the production of a SM Higgs boson is shown as a blue line.

Table 6: Observed 95% CL upper limits on · B (H!WW!`⌫`⌫ with ` = e, µ, ⌧ including all ⌧ decay modes) corresponding to mass hypotheses of 300 GeV, 600 GeV and 1 TeV for a Higgs boson with a SM-like and a scalar with a narrow (NWA) lineshapes.

· B (fb)

Lineshape Production mode mH=300 GeV mH=600 GeV mH=1 TeV

SM-like ggF 250 34 19

VBF 40 16 10

NWA ggF 230 32 29

VBF 39 12 10

15 Figure 2: Left: Transverse mass distribution for events with no accompanying jets in the final signal region. Middle (Right): 95% CL upper limits on σ×BR for H → WW → `ν`ν, for ggF (ggF + VBF) production of a Higgs with narrow (SM-like) width; the blue line represents the SM expectation. Figures from Ref. [10].

consisting of a two-dimensional (2D) fit of the data in mT=

q

2p``

TETmiss(1 − cos∆φ(ETmiss, ``))and

m``, is used to constrain the backgrounds and extract the signal in eµ final states. A 2D histogram

of m`` versus mT is shown in Figure3-left, for data minus expected background. For events with

same flavour leptons in the final state, a cut-based approach is used. Upper limits on σ/σSM are

placed and a Higgs boson with a mass in the range 128 − 600 GeV is excluded at 95% CL (for an

expectation of 115 − 575 GeV). As shown in Figure3-right, no significant excesses are observed

over the expectation, once the H(125) resonance is included as background process.

13.2 ± 2.9 17.0 ± 1.9 16.4 ± 11.1 13.7 ± 24.3 14.0 ± 25.9 11.5 ± -6.1 10.7 ± -1.7 15.9 ± 17.8 15.5 ± 25.4 17.1 ± -4.0 14.0 ± 11.4 17.7 ± 16.6 13.1 ± -9.3 22.7 ± -3.0 15.6 ± -8.4 14.3 ± 6.3 13.6 ± 7.4 15.5 ± 10.6 10.9 ± 12.3 14.5 ± 8.4 19.5 ± 12.6 13.3 ± -5.4 14.5 ± 7.1 15.4 ± 7.5 14.9 ± 18.4 20.2 ± -11.4 27.0 ± -4.6 16.6 ± -8.4 16.0 ± -0.2 17.7 ± 1.1 (GeV) T M 60 70 80 90 100 110 120 (GeV)ll M 20 30 40 50 60 70 80 90 100 -10 -5 0 5 10 15 20 25 Data - Background (8TeV) -1 CMS preliminary L = 19.5 fb

Higgs mass [GeV]

SM σ/ σ 95 % C L lim it on -1 10 1 10 2 10 110 200 300 400 500 600 CMS preliminary (shape-based) ν 2l2 → WW → H (8 TeV) -1 (7 TeV) + 19.5 fb -1 L = 4.9 fb observed median expected σ 1 ± expected σ 2 ± expected Figure 3: Left: 2D mT−m`` distribution for data minus background in events with no jets. Right: 95% CL upper limits on

σ /σSM, where a Higgs

boson with mH=125 GeV

has been added to the

background processes.

Figures from Ref. [11].

4. H → ZZ → ````

Even though the branching fraction is low, the H → ZZ → ```` channel profits from very high signal-to-background ratio and a very clean signature, consisting of two pairs of same flavour,

op-posite charge, isolated, high-pTleptons. Moreover, the full m4`invariant mass can be reconstructed

with excellent resolution. Continuum ZZ production is the dominant background in the analyses.

The ATLAS analysis in the 4-lepton channel [12] considers final states with electrons and/or

muons and splits events according to flavour. Further categorization, targeting different production

modes, is used: the VBF-like category includes events with two high-pTjets with a large rapidity

gap; the associated production (VH) category requires an additional lepton; and the ggF-like

cate-gory includes the remaining events. The m4`distribution is used as a signal discriminant and shows

no significant excesses. 95% CL limits on σ×BR for H → ZZ → 4` are estimated separately for

ggF, shown in Figure4-left, and combined VBF/VH production modes, assuming a SM-like Higgs.

CMS has analyzed the H → ZZ → ```` channel [13], considering not only electron and muon

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sensitivity at high mass. For this category, the reconstructed visible mass m2`2τ, shown in Figure4

-middle, is used to discriminate signal from background. For the categories with only electrons or muons, different signal discriminants are used, depending on the number of accompanying jets.

m4`, kD, a likelihood ratio kinematic discriminant built from a matrix element likelihood approach

using decay and production angles, and pT/m4` (for mH <160 GeV) are used for events with

fewer than two jets. m4`, kD and VD, a linear discriminant using VBF-sensitive variables, are

used for events with two or more jets. The observed distributions agree well with the background

expectation. Upper limits on σ/σSM are calculated using all channels, as shown in Figure4-right.

The analysis excludes a SM-like Higgs boson at 95% CL in the range 130 − 827 GeV, for an expectation of 113.5 − 778 GeV. [GeV] H m 200 400 600 800 1000 BR [fb]× σ 9 5 % C L l im it o n -1 10 1 10 2 10 3 10 Preliminary ATLAS 4l → ZZ → H -1 Ldt =20.7 fb ∫ =8 TeV s Obs ggF Exp ggF σ 1 ± σ 2 ± BR × SM σ (GeV) τ 2l2 m 100 200 300 400 500 600 700 800 900 1000 Events / 25 GeV 0 2 4 6 8 10 12 14 16

CMS preliminary _s_{= 7 TeV, L = 5.1 fb}-1_s_{= 8 TeV, L = 19.3 fb}-1

Data Z+X ZZ =350 GeV H m [GeV] H m 100 200 300 400 1000 SM σ / σ 9 5 % C L l im it o n -1 10 1 10 CMS Preliminary -1 = 7 TeV, L = 5.1 fb s -1 = 8 TeV, L = 19.6 fb s τ 4L + 2l2 → ZZ → H Observed Expected σ 1 ± Expected σ 2 ± Expected

Figure 4: Left: 95% CL upper limit on σ×BR of H → ZZ → ```` for a ggF produced SM-like signal as a function of mH; Figure from Ref. [12]. Middle: Distribution of the four-lepton reconstructed mass for

channels with one τ decay. Right: Observed and expected 95% CL limits on σ/σSM. Figures from Ref. [13].

5. H → ZZ → ``νν

The branching fraction for the H → ZZ → ``νν channel is high, but no full mass reconstruction

is possible. Analyses require two high-pT, isolated leptons, either electrons or muons, compatible

with a Z boson decay, and very large Emiss

T . Inclusive Z, ZZ, top and other diboson processes

contribute as backgrounds.

ATLAS has searched the 200 − 600 GeV mass range in this channel [14] using 4.7 fb−1 _of

7 TeV data. The transverse mass, m2

T= _q m2 Z+ |−→p``T|2+ q m2 Z+ |−→pmissT |2 2 −−→ p`` T + −→pmissT 2,

distribution was used to extract the signal. Since no significant excess was observed, upper limits

on σ/σSM were set. A SM-like Higgs boson is excluded at 95% CL in the 319 − 558 GeV mass

range (for an expectation of 280 − 497 GeV).

CMS has performed a search in the ``νν final state [15], using the full 7 + 8 TeV datasets and

analyzing the 200 − 1000 GeV mass range. Events are categorized according to lepton flavour and sensitivity to ggF or VBF production mode. Z+jets background events are modelled using γ+jet events in data. Non-resononant background processes are normalized from events with different

flavour leptons in the m``sidebands of the Z. Optimized ETmissand mT(similar definition to ATLAS,

with mZreplaced by m``) selections are applied depending on the category. The signal is extracted

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No excess of events above the expectation was observed and upper limits on σ/σSM were set,

excluding a SM-like Higgs boson at 95% CL in the 248 − 930 GeV mass range (for an expectation

of 254 − 898 GeV), as shown in Fig5-left. Results were also interpreted in the BSM heavy EW

singlet scenario. Fig5-middle shows limits on σ×BR for H → ZZ → ``νν as a function of mH,

considering ggF production, BRnew=0 and different hypothesis on κ0. The observed lines fall

below the theory lines for large κ0 _{hypothesis, excluding the heavy EW singlet in a large mass}

range. Similar upper limits, with different hypotheses on both κ0_{and BR}

new, are shown in Figure5

-right, for mH=400 GeV. The hatched area indicates the excluded phase-space, with a narrow-width

boson being favoured.

Higgs boson mass [GeV]

200 400 600 800 1000 th σ / 95% σ = µ -1 10 1 10 -1 L= 19.6fb ∫ =8 TeV s , -1 L= 5.0fb ∫ =7 TeV s CMS preliminary, theory median expected σ 1 ± expected σ 2 ± expected observed

Higgs boson mass [GeV]

200 400 600 800 1000 ) [fb] ν 2l2 → ZZ → BR(H × H → gg σ 1 10 2 10 Theory SM C'=1.0 C'=0.8 C'=0.6 C'=0.4 C'=0.2 -1 L=19.6 fb ∫ =8 TeV, s CMS preliminary, Observed @ 95% CL SM C'=1 C'=0.8 C'=0.6 C'=0.4 C'=0.2 SM Γ / Γ 0.4 0.6 0.8 1 new BR 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 -1 L= 19.6fb ∫ =8 TeV s , -1 L= 5.0fb ∫ =7 TeV s CMS preliminary, -1 10 1 10 C'=0.8 C'=0.6 C'=0.4 C'=0.2 TH σ / 95% CL σ Observed

Figure 5: Left: Expected and observed 95% CL limits on σ/σSMas a function of mH. Middle: Observed 95% CL upper limits on σ×BR for ggF H → ZZ → ``νν, as function of mH, for different κ0hypothesis and under the assumption BRnew=0. Right: Observed upper limits at 95% CL on σ, normalized to the theory cross-section assuming SM contributions from ggF and VBF, for mH=400 GeV, as function of both κ0and the width of the EW singlet relative to the SM, which follows the relation Γ0

/ΓSM= κ02/(1 − BRnew); the hatched area represents the excluded region. Figures from Ref. [15].

6. H → ZZ → ``qq

Analyses in the H → ZZ → ``qq channel require two high-pT, isolated leptons, either electrons

or muons, compatible with a Z-boson decay, and two jets, also compatible with Z decays. Jets are more often b-jets for signal than for Z+jets, which constitutes the largest background, a feature

that is exploited to discriminate signal and background. The full m``j j mass can be reconstructed

and is used to extract the signal.

ATLAS has analyzed the `` j j final state [16], in the 200−600 GeV mass range, using 4.7 fb−1

of 7 TeV data. The normalization and flavour composition of the Z+jets background are derived

directly from data using the mj jsidebands and the b-tagging discriminant, whereas the shapes are

extracted from simulation with small corrections from data. No significant excesses were observed

and 95% CL upper limits on σ/σSMwere set. The analysis excludes a SM-like Higgs boson in the

300 − 322 GeV and 353 − 410 GeV mass ranges, for an expectation of 351 − 404 GeV.

The analysis performed by CMS in the H → ZZ → ``qq channel [17] uses the full 7 + 8 TeV

datasets to search the 230 − 600 GeV mass range. An angular likelihood discriminant is built from production and decay angles, and used to separate signal from background. Events are categorized

according to b-tagging and a Emiss

T -based selection is used to suppress t¯t background. The Z+jets

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data corrections. Figure6-left shows the invariant mass, m``j j, distribution, which is fitted to extract

the signal. No significant excesses of data over the expected background are observed and upper

limits on σ/σSMare set, as shown on Figure6-right, as a function of mH. This analysis excludes a

SM-like Higgs boson in the 275 − 600 GeV range at 95% CL.

] 2 [GeV/c H m 300 400 500 600 SM σ / σ L im it 9 5 % C L o n 0 1 2 3 4 5 Expected 68% CL ± Expected 95% CL ± Expected Observed = 7,8 TeV s -1 CMS Preliminary 2012 5.3,19.6 fb

Figure 6: Left: m``j j distri-bution after final selection for events with 2 electrons and 2 b-tagged jets. Right: Ob-served and expected 95% CL upper limit on σ/σSM. Fig-ures from Ref. [17].

7. Summary and conclusions

Natural extensions of the SM Higgs sector predict heavy SM-like resonances, and are possible scenarios under the current measurements of the newly discovered boson with 125 GeV mass. H → WW and H → ZZ are the preferred decays to explore the high mass regime, and both ATLAS and CMS have performed searches in these channels. No significant excesses have been observed and large high-mass ranges have been excluded by both experiments, assuming SM-like scenarios, as well as under the BSM heavy EW singlet model, that currently favours a narrow-width resonance. References

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