Measurements of the properties of the recently discovered Higgs-like boson are presented using data samples recorded by the CMS experiment corresponding to integrated luminosities of up to 5.1 fb−1 at 7TeV and up to 12.2 fb−1

at 8TeV in proton proton collisions at the LHC. The results combine decay modes in pairs of photons, Z bosons, W bosons, tau leptons and b quarks. The mass of the boson is determined to be 125.8 ± 0.4 (stat.) ± 0.4 (syst.)GeV, and the signal strength at the measured mass is μ = 0.88 ± 0.21, normalized to the standard model expectation. Combined results on couplings, spin and parity reveal a broad agreement with the expectations of a standard model Higgs boson

Azzurri, P.

English

Measurements of the properties of the 
recently discovered Higgs-like boson are presented 
using data samples recorded by the CMS experiment corresponding to 
integrated luminosities of up to 5.1~fb$^{-1}$ at 7~TeV 
and up to 12.2~fb$^{-1}$ at 8~TeV in proton proton collisions at the LHC.
The results combine decay modes 
 in pairs of photons, Z bosons, W bosons, tau leptons and b quarks.
The mass of the boson is determined to be 125.8$\pm$0.4~(stat.)
$\pm$0.4 (syst.)~GeV, and the signal strength at the measured mass 
is $\mu = 0.88\pm 0.21$, normalized to the standard model expectation. 
Combined results on couplings, spin and parity reveal a broad 
agreement with the expectations of a standard model Higgs boson

Azzurri, Paolo

CERN Document Server

Measurements of the properties of the Higgs-like boson with the CMS experiment at the LHC

Scientific Open-access Literature Archive and Repository

DOI 10.1393/ncc/i2014-11654-1Colloquia: LaThuile13IL NUOVO CIMENTO Vol. 36 C, N. 6 Novembre-Dicembre 2013Measurements of the properties of the Higgs-like bosonwith the CMS experiment at the LHCP. Azzurri on behalf of the CMS CollaborationINFN, Sezione di Pisa - Largo B. Pontecorvo 3, 56127 Pisa, Italyricevuto il 20 Giugno 2013; approvato il 1 Luglio 2013Summary. — Measurements of the properties of the recently discovered Higgs-likeboson are presented using data samples recorded by the CMS experiment corre-sponding to integrated luminosities of up to 5.1 fb−1 at 7TeV and up to 12.2 fb−1at 8TeV in proton proton collisions at the LHC. The results combine decay modesin pairs of photons, Z bosons, W bosons, tau leptons and b quarks. The mass ofthe boson is determined to be 125.8 ± 0.4 (stat.) ± 0.4 (syst.)GeV, and the sig-nal strength at the measured mass is μ = 0.88 ± 0.21, normalized to the standardmodel expectation. Combined results on couplings, spin and parity reveal a broadagreement with the expectations of a standard model Higgs boson.PACS 14.80.Bn – Standard-model Higgs bosons.PACS 13.85.-t – Hadron-induced high- and super-high-energy interactions (energy> 10GeV).PACS 29.40.-n – Radiation detectors.PACS 29.85.Fj – Data analysis.1. – IntroductionIn the standard model (SM) the Brout-Englert-Higgs mechanism explains the elec-troweak symmetry breaking and allows the W and Z gauge bosons to acquire mass. Themechanism predicts the existence of a Higgs scalar boson (H), and its observation wasone of the main goals of the LHC physics program.Results on the properties of the recently observed boson by ATLAS [1] and CMS [2],and its compatibility with the SM Higgs boson are given here, based on proton-protoncollisions data samples collected by the CMS experiment [3] corresponding to integratedluminosities of up to 5.1 fb−1 at 7TeV and up to 12.2 fb−1 at 8TeV. Information hasbeen combined from four production channels and five decay modes [4-6]. The ana-lyzed production channels, in decreasing magnitude, are i) gluon fusion (ggH) gg → H,ii) vector boson fusion (VBF) WW,ZZ → qqH, iii) associated vector production (VH)W,Z → HW,Z and iv) associated top quarks production (ttH) gg → Htt. The searcheddecay modes are i) H → ZZ → 4, ii) H → γγ, iii) H → WW → νν, iv) H → ττ andv) H → bb.c© CERN on behalf of the CMS Collaboration under the Creative Commons Attribution License 3.0 356MEASUREMENTS OF THE PROPERTIES OF THE HIGGS-LIKE BOSON ETC. 357In the SM all the properties of the Higgs boson are fixed by the values of its mass(mH). The mass of the new boson is measured using the 4 and γγ final states, where theexperimental mass resolution for mH  125GeV is roughly 1–3%. Using the measuredsignal strengths in the various production and decay channels, the couplings of the newboson can be extracted. Finally the spin and parity of the new boson are analyzed,making use of the decay distributions in the ZZ→ 4 channel.In the following a brief overview of the search channels is given.– The ZZ → 4 analysis [7] searches a signal four-lepton invariant mass peak overa smaller and continuous background, mostly from fully leptonic non-resonant ZZdiboson decays. Selected events are categorized according to the multiplicity ofadditional jets, to discriminate ggH production from VBF and VH production.– The γγ analysis [8, 2] also looks for a signal mass peak, over a smoothly fallingbackground originating from QCD processes with diphotons or misidentified pho-tons. Selected events are classified according to the eventual presence of additionaljets or leptons into three categories: ggH (untagged), VBF or VH categories.– The WW → νν analysis [9] searches for events with opposite charge isolatedleptons and missing transverse energy. Selected events are categorized according tothe lepton flavors and to the presence of additional jets (for the VBF categories).An excess of signal events is searched over the main WW and top-quark backgroundproductions.– The ττ searches [10] categorizes ditau events based on the decay channel of each tau,and on the presence of additional jets for the VBF categories. Main backgroundsarise from Z → ττ , W plus jets and QCD multijet processes, and are estimatedwith data control samples. Dedicated searches of VH signal productions with taudecays have been performed in events with three or four final state leptons [11].– The bb decay search in the associated VH channel [12] selects events with weakbosons decaying to leptons (Z → ee, μμ, νν and W → eν, μν), and two b-jets fromthe Higgs boson decay. The main backgrounds arise from W/Z plus jets processesand top productions, and are estimated from data control samples. The Higgsboson bb decays associated to top-quark pairs have also been searched [13], withsemileptonic or fully leptonic top-quark pair decays. In this analysis backgroundsoriginate from top-pairs with additional QCD jets, and are estimated from theo-retical predictions.2. – Signal significance and massThe presence of Higgs signals is quantified with a test statistics based on the profilelikelihood ratio q [4], depending on a signal strength modifier μ to allow for deviationsfrom the SM Higgs predictions. The asymptotic approximation [14] is used to derive theresults and nuisance parameters are used to evaluate systematic uncertainties, treatedwith a frequentist approach.Signal model parameters, as μ, are measured with likelihood ratio profile. The 68%and 95% confidence level (CL) limits on a given parameter are determined with q = 1and q = 3.84, respectively. The two dimensional (2D) 68% and 95% contours for pairsof parameters are fixed by the q = 2.3 and q = 6 likelihood ratio values.358 P. AZZURRI on behalf of the CMS COLLABORATION (GeV)Xm122 124 126 128 ln LΔ- 2 012345678910Combinedγγ →H  ZZ→H CMS Preliminary -1 12.2 fb≤ = 8 TeV, L s  -1 5.1 fb≤ = 7 TeV, L s ZZ→ + H γγ →H  (GeV)Xm123 124 125 126 127 128 129SMσ/σ0.00.51.01.52.02.53.03.5 Combinedγγ →H  ZZ→H CMS Preliminary -1 12.2 fb≤ = 8 TeV, L s  -1 5.1 fb≤ = 7 TeV, L s ZZ→ + H γγ →H Fig. 1. – (Left) The signal likelihood ratio profile as a function of the boson mass q(mX) for theγγ and 4 channels separately and combined. (Right) The boson signal strength μ = σ/σSMversus the boson mass mX 68% and 95% CL contours.The local probability (p-value) is the probability to obtain a q value at least as largeas the one observed in data under the background-only hypothesis. The local significanceof the signal, in σ units, is related to the local p-value through the one-sided Gaussiantail integral convention.The mass of the observed boson mX is measured with the γγ and ZZ → 4 channels.Figure 1 shows the observed q profile as a function of mX. The horizontal lines at 1and 3.8 determine the observed mass 68% and 95% CL intervals, including all systematicuncertainties. The combined mass measurement, with separate statistical and systematicuncertainties is mX = 125.8± 0.4 (stat.) ± 0.4 (syst.) GeV.For a SM Higgs boson with mass 125.8GeV the observed (median expected) sig-nal significances with the analyzed data samples are: i) 4.4(5.0)σ for the 4 channel,ii) 3.0(4.3)σ for the WW channel, iii) 4.0(2.8)σ for the γγ channel, iv) 1.8(2.2)σ for theττ channel, v) 1.8(2.1)σ for the bb channel, all evaluated with fixed SM signal strength(μ = 1). The overall combined observed significance reaches 6.9σ.3. – Higgs boson signal strengthUsing a common signal strength modifier for all combined analysis channels yields anobserved value for mH = 125.8GeV of μ = σ/σSM = 0.88 ± 0.21, compatible with theexpected SM value μ = 1.The Higgs boson signal strength for mH = 125.8GeV, in different searched channelsand decay modes are shown in fig. 2. None of the fitted signal strengths deviates sig-nificantly from μ = 1 and the overall compatibility with the SM expectations with thecurrent sensitivity is good.To test the strengths of the Higgs boson couplings hypothesis to vector bosons and topquarks, a rough separation between the vector boson fusion and associated vector pro-ductions (VBF+VH) versus the gluon fusion and associated top productions (ggH+ttH),has been tested. Figure 3 shows the 68% CL contours of the measured signal strengthin the ggH+ttH and VBF+VH production modes, for each of the five decay modes.MEASUREMENTS OF THE PROPERTIES OF THE HIGGS-LIKE BOSON ETC. 359SMσ/σBest fit 0 0.5 1 1.5 2 2.5 ZZ→H  WW→H γγ →H ττ →H  bb→H -1 12.2 fb≤ = 8 TeV, L s  -1 5.1 fb≤ = 7 TeV, L sCMS Preliminary  = 125.8 GeVH mSMσ/σBest fit -2 0 2 4 ZZ→H  WW (VH tag)→H  WW (VBF tag)→H  WW (0/1 jet)→H  (VBF tag)γγ →H  (untagged)γγ →H  (VH tag)ττ →H  (VBF tag)ττ →H  (0/1 jet)ττ →H  bb (ttH tag)→H  bb (VH tag)→H -1 12.2 fb≤ = 8 TeV, L s  -1 5.1 fb≤ = 7 TeV, L sCMS Preliminary  = 125.8 GeVH mFig. 2. – Measured Higgs boson signal strengths at mH = 125.8GeV, by decay mode (left), andwith additional tags targeting particular production mechanisms (right).4. – Compatibility with standard model Higgs couplingsAll production and decay combinations are assumed to be related to the Higgs bosoncross-section and decay fraction according to the formulaσ × BR(x → H → ff) = σx · ΓffΓH ,where x is the production mode (ggH, VBF, VH, ttH) and ff is the final state (f =Z,W, τ , γ,b).ggH+ttHμ-1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5qqH+VHμ02468ττ →H  WW→H  ZZ→H  bb→H γγ →H CMS Preliminary -1 12.2 fb≤ = 8 TeV, L s  -1 5.1 fb≤ = 7 TeV, L sFig. 3. – Signal strength for ggH+ttH versus VBF+VH production: the curves show 68% CLregions for each decay mode (left).360 P. AZZURRI on behalf of the CMS COLLABORATIONWZλ0 0.5 1 1.5 2 ln LΔ- 2 0.00.51.01.52.02.53.03.54.04.55.0ObservedExp. for SM HCMS Preliminary -1 12.2 fb≤ = 8 TeV, L s  -1 5.1 fb≤ = 7 TeV, L s (scaling of vector boson couplings)Vκ0 0.5 1 1.5 (scaling of fermion couplings)Fκ -2-101295% C.L.τ τ →H b b→H  ZZ→H  WW→H γ γ →H CMS Preliminary -1 12.2 fb≤ = 8 TeV, L s  -1 5.1 fb≤ = 7 TeV, L sSM Higgs Fermiophobic Bkg. onlyFig. 4. – Custodial symmetry test: the likelikood ratio q scan of the coupling modifier ratioλWZ (left). Vector boson and fermion couplings: 68% CL regions for the κV and κf couplingmodifiers for each decay channel. The cross indicates the global best-fit values.The gluon fusion production and diphoton decay are generated by loop diagrams, andparticularly sensitive to physics beyond the standard model (BSM). Effects of new BSMparticles would also modify the total decay width ΓH. To test the SM Higgs couplingshypothesis in the data, modified couplings strengths κi are introduced in the likelihood,and any deviation of κi from unity indicates a deviation from the SM Higgs couplings.4.1. Custodial symmetry . – As a test of the relation between the W and Z boson massesand their couplings to the Higgs boson, that are protected against radiative correctionsby the “custodial symmetry” property, the value of the ratio λWZ = κW/κZ is accessed.The likelihood scan q(λWZ) is shown in fig. 4, combining all input channels and leavingfree the κZ and κf coupling modifiers: the 95% CL interval for λWZ obtained from thedata is [0.67, 1.55].4.2. Couplings to vector bosons and fermions. – An important test of the expectedSM couplings is to fit for coupling deviations to vector bosons κV (common to W andZ), and to fermions κf . Figure 4 shows the interplay of the different decay channels inconstraining the (κV, κf) plane, with the 68% CL regions deriving from each decay modeand combined. The obtained 1D 95% CL intervals for κV and κf are [0.78, 1.19] and[0.40, 1.12], respectively.4.3. New physics effects. – New BSM physics could modify the production and decayrates of the Higgs boson. Loop diagrams, as in gluon fusion productions and diphotondecays, would be particularly sensitive to new effects, and deviations from the SM expec-tations are quantified with the κg and κγ scale factors. The data results in terms of 68%,95% and 99.7% CL regions in the (κγ , κg) plane are shown in fig. 5. The individual 95%CL regions are [0.98, 1.92] for κγ and [0.55, 1.07] for κg. Figure 5 also shows the likelihoodprofile of an additional BSM decay width, parameterized as BRBSM = ΓBSM/ΓH, withκg and κγ free, yielding the 95% upper limit BRBSM < 0.62.MEASUREMENTS OF THE PROPERTIES OF THE HIGGS-LIKE BOSON ETC. 361γκ0 1 2 3gκ0.00.20.40.60.81.01.21.41.61.82.0 CMS Preliminary-1 12.2 fb≤ = 8 TeV, L s  -1 5.1 fb≤ = 7 TeV, L sBSMBR0 0.2 0.4 0.6 0.8 1 ln LΔ- 2 0.00.51.01.52.02.53.03.54.04.55.0ObservedExp. for SM HCMS Preliminary -1 12.2 fb≤ = 8 TeV, L s  -1 5.1 fb≤ = 7 TeV, L sFig. 5. – The 68%, 95% and 99.7% CL regions in the (κg ,κγ ) plane (right): the cross indicatesthe best-fit values, and the diamond the SM point. The likelihood ratio q scan of a new physicsbranching ratio BRBSM (left), as observed in the data and expected for BRBSM = 0.4.4. Fermion couplings asymmetries. – Differences among the fermion couplings, aspossible in models with two or more Higgs doublets, are tested in terms of the λdu =κd/κu and λq = κ/κq coupling modifier ratios, allowing respectively differences inthe couplings to down and up fermions, and differences in the couplings to leptons andquarks. The observed 95% CL intervals are [0.45, 1.66] for λdu and [0.00, 2.11] for λq .Figure 6 shows two-dimensional scans of the likelihood ratio in the (λdu, κu) plane, andin the (λq , κq) plane, with the CL regions measured from the data.duλ0 1 2 3uκ0.00.20.40.60.81.01.21.4CMS Preliminary -1 12.2 fb≤ = 8 TeV, L s  -1 5.1 fb≤ = 7 TeV, L slqλ0 1 2 3qκ0.00.20.40.60.81.01.21.4CMS Preliminary -1 12.2 fb≤ = 8 TeV, L s  -1 5.1 fb≤ = 7 TeV, L sFig. 6. – The 68%, 95% and 99.7% CL regions in the (λdu, κu) plane (right): the cross indicatesthe best-fit values, and the diamond the SM point. The 68%, 95% and 99.7% CL regions in the(λq , κq) plane (right): the cross indicates the best-fit values, and the diamond the SM point.362 P. AZZURRI on behalf of the CMS COLLABORATIONpseudo-MELA0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1Events0123456data=126 GeVH, m+0=126 GeVH, m-0*γZZ/ZZ+XCMS preliminary -1 = 8 TeV, L = 12.2 fbs  -1 = 7 TeV, L = 5.1 fbs)0+/L0- ln(L× -2 -30 -20 -10 0 10 20 30Generated experiments050010001500200025003000  SM, 0+  0-  CMS dataCMS Preliminary -1 = 8 TeV, L = 12.2 fbs -1 = 7 TeV, L = 5.1 fbs Fig. 7. – Distribution of an optimal kinematic discriminant for 4 events to separate the JP = 0+and 0− signal hypothesis (left): data points with error bars, and expectations for backgroundand the two signal hypothesis, are shown. Signal plus background distributions of a test statisticcomparing the SM JP = 0+ and 0− signal hypothesis for 4 decays (right): the arrow indicatesthe value of the test statistic observed in data.4.5. Six coupling parameters model . – Looser tests of a model with six independentcouplings κV, κb, κτ , κt, κg and κγ have been performed, fitting one parameter at atime. The individual couplings modifiers 95% CL intervals obtained from teh data are:i) [0.58, 1.41] for κV, ii) [0.00, 1.80] for κτ , iii) [0.43, 1.92] for κg and iv) [0.81, 2.27] forκγ . No 95% CL constrain was obtained for κb and κt.5. – Analysis of the spin and parityInvestigations of the new discovered boson spin-parity quantum numbers have beenperformed with 4 events [7], making use of the full event kinematical decay informa-tion (angles and momenta of reconstructed leptons). The SM JP = 0+ hypothesis hasbeen tested against several other JP scenarios, and scenarios alternative to the SM aredisfavored, with (alternative) signal CL probabilities (CLs) of 2.4% or smaller.Figure 7, left, shows the distribution of an optimal discriminator for the comparisonof the SM JP = 0+ hypothesis with a JP = 0− signal hypothesis. The data pointsshow a clear preference for the JP = 0+ hypothesis, while the JP = 0− hypothesis isexcluded at a level over four standard deviations, and with a CLs value smaller than0.1%. Figure 7, right, shows the post-fit distributions of a test statistic comparingthe SM JP = 0+ hypothesis with the pseudoscalar signal hypothesis, where the datameasurement (indicated by an arrow) disfavors the 0− hypothesis with a CLs value of2.4%.6. – ConclusionsThe properties of the recently discovered boson, and its consistency with the SMHiggs boson have been investigated with the CMS experiment in four production modesand five decay channels, using data samples of up to 5.1 fb−1 at 7TeV and up to 12.2 fb−1MEASUREMENTS OF THE PROPERTIES OF THE HIGGS-LIKE BOSON ETC. 363at 8TeV in proton proton collisions at the LHC. The mass of the new boson is 125.8 ±0.4 (stat.)±0.4 (syst.) GeV. The combined signal strength is 0.88±0.21 in units of the SMHiggs boson cross section at the measured mass. The measured couplings are consistentwith the SM Higgs expectations, within the 20-50% uncertainties. The analysis of theobserved decay kinematics strongly disfavors the pure JP = 0− quantum numbers forthe signal hypothesis.REFERENCES[1] ATLAS Collaboration, Phys. Lett. B, 716 (2012) 1.[2] CMS Collaboration, Phys. Lett. B, 716 (2012) 30.[3] CMS Collaboration, JINST, 03 (2008) S08004.[4] CMS Collaboration, Phys. Lett. B, 26 (2012) .[5] CMS Collaboration, Combination of Standard Model Higgs boson searches andmeasurements of the properties of the new boson with a mass near 125GeV, CMS PhysicsAnalysis Summary, CMS-PAS-HIG-12-045 (2012).[6] LHC Higgs Cross Section Working Group, LHC HXSWG interim recommendationsto explore the coupling structure of a Higgs-like particle, arXiv:1209.0040 (2012).[7] CMS Collaboration, Discovery of a new boson in the search for the standard modelHiggs bosons in the H → ZZ → 4 channel in pp collisions at √s = 7 and 8TeV, CMSPhysics Analysis Summary, CMS-PAS-HIG-12-041 (2012).[8] CMS Collaboration, Search for a standard model Higgs boson decaying into two photonsin pp collisions, CMS Physics Analysis Summary, CMS-PAS-HIG-12-015 (2012).[9] CMS Collaboration, Evidence for a particle decaying into W+W− in the fully leptonicfinal state in a standard model Higgs bosons search in pp collisions at√s = 8TeV, CMSPhysics Analysis Summary, CMS-PAS-HIG-12-042 (2012).[10] CMS Collaboration, Search for standard model Higgs bosons decaying to tau pairs, CMSPhysics Analysis Summary, CMS-PAS-HIG-12-043 (2012).[11] CMS Collaboration, Search for a Standard Model Higgs bosons decaying to tau pairsproduced in association with a W or a Z boson, CMS Physics Analysis Summary, CMS-PAS-HIG-12-051 (2012).[12] CMS Collaboration, Search for standard model Higgs bosons produced in associationwith W or Z bosons, and decaying to bottom quarks, CMS Physics Analysis Summary,CMS-PAS-HIG-12-044 (2012).[13] CMS Collaboration, JHEP, 05 (2013) 145.[14] Cowan G. et al., Eur. 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Measurements of the properties of the Higgs-like boson with the CMS experiment at the LHC

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