We review the Higgs physics prospects of the ATLAS and CMS experiments at the LH

Tartarelli, F

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Higgs at the LHCF. Tartarelli (INFN – Milano)Aspen 2008 Winter Conference "Revealing the Nature of Electroweak Symmetry Breaking"13 19 J 2008 A C l d USA-  anuary  - spen, o ora o, Th ATLAS d CMS i t tti d f th t t f th LHCe  an   exper men s are ge ng rea y or e s ar  o  e  later this year. According to the current schedule:Beam commissioning starts May 08First 14 TeV collisions expected for July 08Current schedule foresees to reach L=2x1032 cm-2 s-1 by the end of the year with an integrated luminosity less than ~100 pb-1.About 4 pile-up (minimum bias) events expected at 1032 cm-2s-1 (because of larger bunch spacing and no. part./bunch)      Then the luminosity should reach 2x1033, the so-called “low luminosity”Pile-up of ~4 events per bunch crossing (at nominal 25 ns bunch spacing)            Finally (probably >2010) the luminosity should reach the design luminosity of 1034 cm 2 s 1 ”high luminosity”- - ,  Pile-up of ~20 events per bunch crossing 2Sub-detector                        N. of channelsPixels                                       80x106Silicon strip detector (SCT)               6x106T iti R di ti T k (TRT) 3 5 105rans on a a on rac er      . xElectromagnetic calorimeter              1.7x105Fe/scintillator (Tilecal) calorimeter      9800Hadronic end-cap LAr calorimeter       5600 Forward LAr calorimeter 3500 3Barrel Muon Spectrometer               7x105 End-cap Muon Spectrometer (TGC)       3.2x105Forward detectors 1.2x104total       ~ 87.6 x 106ATLAS statusThe installation of the ATLAS detector (and all related services) is nearly completed:Only part of the forward muons and forward shielding still to be installedStill a lot of work to be done during next months to be ready for collisionsHardware commissioning of all electronics components, controls and safety systems on going   Magnet system: Barrel solenoid + barrel toroid + 2 end-cap toroids: all installed, cold tested one by one  .In spring 2008 there will be a full magnet test (when ATLAS is closed andfully integrated) and then continuous operation.B l l id d d i f ll ’06 Fi ld i t t b d fi darre  so eno  mappe  ur ng a  . e  n muon sys em o e e neduring full magnet test 4 20.1 m diameter x 25.3 m length12000 3 l ~  m vo ume 118 t superconductor 370 t cold mass 830 t total weight56 k d t5  m supercon uc or 20.5 kA at 4.6 T 1.05 GJ stored EnergyMuon system: h bMost muon c am ers are installed and are being tested and read out through the final data flow/trigger chain. Total : ~12’000 m2 ~ 1 1 M channels   ,  .   6Calorimeters: d b l ( l l )Ha ronic arre  ti e ca orimeter  was the first detector to be integrated.Three (barrel + 2 endcaps)cryostats installed and filled withLAr. Detectors operated for longtime last year.7Inner detector: ll bd ( lA  ID su etectors pixe s, SCT,TRT) have been installed.Cooling to be ready soon: thenit will be possible to operate thedetector. Successful installation and testing of the 3 pieces of the       beam pipe inside the detector.Pixels:1744 modules, 50x400 μm2Strips:4088 modules, 80 μm micro-strips8Still a lot of work to do: service connections to be finalized, components to be commissioned, some back-end electronics to be installed,…No show-stoppers: full ATLAS will be ready on time for first collisionsDetector commissioning started already in 2006 with cosmics:Installation work during day and running with cosmics during week-ends and dedicated “Milestone” weeks (every 6-8 weeks)      One detector after the other integrated in central DAQ, trigger and DCS:First barrel calo then barrel muons end-caps TRT Next month pixels  ,   , , .   and Si-strips will complete the integration.Several useful studies on going are increasing our knowledge of the   -        detector:Timing studiesAli t f h b ( d f i l / t i )gnmen  o  muon c am ers an  o  p xe s s r psStudy of calorimeter response9What do we need to discover the Higgs boson?Good understanding of the detector and trigger. Several (all!) ingredients are needed to cover all the foreseen channels: electrons and photons, muons, b-tagging, jets, ETmiss, τ’sProve that we can do SM physics (top, W, Z)Control of the backgroundsHigh production cross sections for SM processes: bb, W, Z, tt,...pp inelastic: ≈70 mbb inclusive (pT>6 GeV): ≈6 μbtt: ≈800 pb[cfr: H(125 GeV): ≈40 pb] These processes are interesting per se and will be used for early physics studies and for various calibration     issues.However they represent a large     background to several new physicssearches including Higgs and SUSY:e.g., tt and W/Z+jets are background to several discovery channels112003 2006K factors includedBoth LHC experiments have been designed to discover a SM Higgs on all the t d G l hi bl ft f f i t l Lexpec e  mass range. oa  ac eva e a er a ew years o  runn ng a  ow . More than one channel available over most of the mass range.Recently, most of the studies have been focused on the discovery of a light Higgs (MH<200 GeV) during the initial lower luminosity period (L=1033 cm-2 s-1).This is not the easiest region at LHC: for higher masses,  the H→ZZ→4l represents the golden channel (at least up to 500-600 GeV)Which channels?“Compromise” between various factors: production mechanism, decay mode, A. Djouaditrigger, background levels. In general final states with leptons or photons in the final state are easier to handle at the LHC.Inclusive analyses:Do not use any feature of the production mechanism        .One makes less assumptions than in other search strategies.  However to d th b k d d t h l fi l t t ith l tre uce e ac groun s nee  o ave a c ean na  s a e w  ep ons or photons.The gluon-gluon fusion channel has the highest rate.The gluon-gluon fusion process is dominated by top and bottom quark loops. The large size of the top Yukawa coupling and of the gluon densityfunctions explains the high production rate for this process.           In this talk:  H→γγ, H→ZZ(*), H→WW(*)14H→γγFeatures: Low mass range: <140 GeV; small BR (~2x10-3) but can see signal over a smooth background; estimate background from data (side bands)   Trigger: High PT di-photon trigger, single photon triggerIrreducible: 2γ productionReducible: γ+jet , di-jet   Backgrounds:Analysis: Need good mass resolution (intrinsic light H width is negligible) ofabout 1%: 1. EM energy resolution2. Primary vertex determination: contributes to mass resolution. Can use stand alone calorimeter photon direction  -     reconstruction (ATLAS) or tracks in the event (ATLAS, CMS), including tracks from conversions.15H→γγN d d h t ID t d j t d j t j t b k d ll b lee  goo  p o on  o re uce γ+ e  an  e + e  ac groun s we  e owthe irreducible one: R~103 for εγ≈80%. The background of isolated high PTπ0 is particularly dangerous. Make use of:1. Photon isolation (with tracker and calorimeter)2. Study of shower shapes in calorimeterPhoton conversion recovery: about 50% γ convert before the calorimeterin the tracker material (on average 1 X0). Need to be reconstructedusing tracking informationSimplest analysis: count events i i d Thi i  Signal:ATLASn mass w n ows. s g ves a S≈6 for 30 fb-1 at MH=130 GeVLevel of background will be known from data. A 10-15% sys error from the fit to the background has been estimated.16H→γγThe significance can be increased (~30-40%) including additional handles:ATLAS: Builds a likelihood including also1. γγ PT (background has softer spectrum and less pronounced         rise at low PT)2. cosθ*, the photon decay angle in the H rest frame with respect to the H flight direction in the lab rest frame (the background distribution is somewhat enhanced for collinear photons)    CMS: Uses 6 variables: isolation of each photon E /M |η η | P       , Ti γγ, 1− 2 , Lγγ(ETi and ηi are the transverse energy and pseudorapidity of i-th γ)CMS17H→ZZ*→4lFeatures: Clean channel: can see peak over background; low statistic for MH<130 GeV and MH~170 GeV. Can use 4e, 4μ, 2e2μ.Trigger: High PT single and dilepton triggersIrreducible: qq,gg→ZZ*/γ*→4lReducible:  Zbb→4l, tt→4l Backgrounds:Analysis: Need reconstruction of relatively low PT electrons and muons Need good electron and muon energy resolution (1-2%); recoverbrems effects for electrons   Reducible background is handled via lepton isolation (tracking andcalorimeter) and impact parameter cutsB k d l l b ti t d f id b dac groun  eve  can e es ma e  rom s e an s18CMS studyUncertainty includes: Stat error on the estimation of the background from side     bands (from 2 % to 13% for MH<200 GeV/c)Theory uncertainty on the bkg shape (0.5% to 4.5%) MH=140 GeV MH=200 GeV 19H→WW*→2l2νf (Features: Particularly interesting or 2MW<MH<2MZ but its sensitivity extends also to lower masses) where all other decay modes are suppressed. Signature is 2μ, 2e, eμ + ETmiss.However no mass peak and high background that needs to be wellunderstood.Trigger: High P dilepton and single lepton triggersBackgrounds: T     Continuum WW, WZ, ZZ (including gg→WW)     tt production and single top production tWb also: Z, bb, W+jetsAnalysis: Select events with exactly two isolated (tracking and calorimeter) opposite sign primary leptons and ETmiss.Apply a jet veto in the event.Cut also on small dilepton mass and opening angle.20CMS studyEstimated background uncertainties: tt ±16%WW             ±17% (from control samples)Wt                ± 22%gg → WW    ± 30% (from theory)21Vector Boson FusionF tea ures: Originally studied for the medium-high mass range (MH>300 GeV), this process has been       found useful also in the low mass range. Lower rate than gluon-gluon fusion but clear signature.Signature: Two distinct signatures:1 T f d “t ” j t (l ti ith hi h ) ith l M. wo orwar  ag  e s arge η separa on w  g -pT  w  arge jj2. No jet activity in the central region (between the two  tag jets): jet vetoTypical cuts require:• Tag jets are assumed to be the highest ET jets in opposite hemispheres, with ET>~40 GeV, Δηjj>~4, Mjj>500-1000 GeV.• Higgs decay products between tag jets in η• No additional jet activity in the event22Vector Boson FusionExperimental issues: Good efficiency for the reconstruction of forward jet is required. There are also uncertainties on the      robustness of the jet veto with respect to radiation in the underlying event and to the presence of pile up   - . So far VBF channels have been studied t l l i it lATLASChannels:a  ow um nos y on y. qqH → qqγγqqH → qqWW(*) where can use WW(*) → lν lν and  lν jj   H h l l l h d d h d h dqq  → qqττ w ere can use ττ → νν νν, νν a ν an a  a23qqH→qqττ→qq lνν had νFeatures: Interesting channel for M <150 GeV: increases sensistivity to low    H       mass HTrigger: High P single lepton triggersBackgrounds: T   EW/QCD 2τ+2/3 jets tt production W+jetsAnalysis: Besides the VBF cuts, one has to apply cuts to select the primary isolated electron, together with a MT(l-ETmiss) cut to reduce the W background.τ jet identification important: use tracking and calorimeter information.The H mass can be reconstructed using the collinear approximation: the τ mass is neglected and it is assumed that         the ν direction coincides with the visible decay products of the τ’s 24qqH→qqττ→qq lνν had νExperimental  issues: Need good ETmiss resolutionNeed identification of hadronic τ’sIn the end H mass resolution ≈9%      .Dominant background:Z+jets with Z→ττ  (dangerous for low Higgs masses)C t l l f th b k don ro  samp es or e ac groun :Z+jets with Z→ee, Z→μμ1CMSFor 30 fb- , at MH=135 GeV, expect about 8 signal events with a significance of about 4 (CMS)25Associated productionsOther search channels  pp → WH, ZH, ttH  with  W → lν, Z → ll or Z → ννLow rates.Leptons from W, Z and t→Wb→lνb can provide trigger and discrimination from background. Provide useful channels with higher integrated luminosity (~100 fb-1).A few examples:26Other search channelspp → WH, ZH, ttH with H→γγ      It has been shown that the combination of these channels with the ones alreadydiscussed can increase the discovery potential. When fitting for the signalth ibilit i t di id th t l i i t i H+0jano er poss y s o v e e even  samp e n var ous ca egor es: ,H+1j, H+2jWH → WWW(*)Three lepton final state.ttH → ttbb (with one t decaying semileptonically)Complex final states: 4 b’s + 2 (or more) light jets. b-tagging is crucial. High ZH ll i i ibl H d d tcombinatorics. High ttbb and ttjj backgrounds. Significance ~3σ for 30 fb-1 (CMS;ATLAS results in progress) →  + nv s e  ecay pro uc sHiggs bosons decaying to stable neutral weakly interacting particles (neutralinos, gravitinos,...) in some SM extensions. Trigger on Z leptons and          require large ETmiss in the event 27For mH>140 GeV an accumulated statistics of order ~1 fb−1 might be      sufficientFor low mass higgs (< 140 GeV)      the situation is more complex: around 5 fb-1 are needed and l h l d t bsevera  c anne s nee  o e combinedIn both cases it is assumed that the detectors and the data are well understood.(old ATLAS ttH result has been assumed)28Measurement of Higgs propertiesMass measurement Best channels for this measurement areH and at higher masses H 4l→γγ     → . CMS estimates a precision <0.3 % up to 1350 GeV (stat error only) with 30 fb-ATLAS estimated about 0.1 % up to 400 GeV with 300 fb-1 including sys errors.The precision will be limited by the uncertainty on the lepton and photon energy scale, which is expected to be atthe level of 0 1%   .  29Width measurement For small H masses, the intrinsic H with is negligible with respect to the experimental l ti Di t t ithreso u on. rec  measuremen  w  reasonable accuracy can be performed only above ~200 GeV (better than 10% for MH>300 GeV with 300 fb-1)S i d CPp n an   In the SM, H has JPC=0++If H→γγ or gg→H are established, J=1 can be excluded. This and other JPCcombinations can be also excluded studying angular correlations in H→4l decays.30θ → polar angle l- wrt Z momentumϕ → angle between decay planesATLASWith 100 fb-1 can provide discriminationfrom J=1 and J=0/CP=-1 hypothesis for masses greater than ~200 GeV     Structure of HVV (V=W,Z) coupling  The presence of an additional CP even or CP odd term in the HVV couplingcan be excluded using a similar method for MH>200 GeV.For smaller masses the study of the Δφjj separation between tag jets in VBFevents can be used. The VBF H→ττ process has been studied down to 120 G V d th VBF H WW d 160 G Ve an  e  →  process aroun   e . 31Measurement of  couplings  Likelihood fit to expected number of events in all observable channels. Includesys errors from detector effects, luminosity, background normalization, cross sections.Concentrating on low Higgs masses (<200 GeV), several measurements are possible, depending on how many assumptions are done:1. Assuming Higgs have spin 0, σ·BR can be measured2. Assuming there is only one H boson, can fit ratio of widths Γi/ΓW, in this case normalized to the Γ of H→WW     3. Assuming there are no new particles in loop and no strong couplings tolight fermions, can obtain ratio of (5) couplings 4 A i th t Γ Γ SM “ ” b l t li. ssum ng a  V< V , can measure  a so u e coup ngs3233SUSY HiggsBecause of the large parameter space, searches are performed for specific choice of parameters: benchmark scenarios.In the MSSM (but there are also NMSSM preliminary studies):• Mhmax: maximum allowed mass for h. Replaces the “maximal mixing” scenario used in the past.• No-mixing: as above but no mixing in stop sector. Smaller Mh• Gluophobic H: large mixing suppresses gluon fusion production gg→h and          h→γγ, h→4l• Small α : small mixing angle of the neutral CP-even Higgs boson can eff            suppress h →bb, ττ• CPX: CP eigenstates h A H mix to mass eigenstates H H H Maximal   , ,      1, 2, 3.  mixing.34ChannelsSeveral channels have been studied in different mass ranges. In addition to channels similar to the SM ones (SM-like h at large MA, H at “low“ MA) rescaled for the corresponding MSSM cross sections and BRs, examples of relevant channels are:A/HDegenerate in mass in most of the parameter space. gg→bbH A with A/H→ττ or A/H→μμ,    Usually at least one of the b is tagged to reduce the backgroundThe ττ decay has a higher BR, 10% (bb, 90% has trigger problems) andexploits all possible ττ decays: lep-lep, lep-had, had-hadThe μμ decay has a much lower BR, but clean signature (thanks to the high muon resolution of the experiments) and full mass reconstruction.However it is not possible to separate A/H (and h)35         .ATLAS, 300 fb-1, MA=110 GeVProduction modes: t→H+b, gg→tbH+, gb→tH+H±Decays: most promising H+→τν which leads to τ+3 jets+EtmissFully hadronic final state: uses a τ trigger      .Backgrounds are: tt, Wt, W+3 jets36Handles: τ-ID, top mass reconstruction, lepton veto, b-tag, τ helicityATLAS, 30 fb-1, 5σ discovery potential in 4 benchmark scenariosAt least one Higgs boson is expected to be found in the allowed parameter space.However, in some regions of the parameter space only one Higgs boson (SM like)    , h, can be observed.At higher luminosity (300 fb-1)     the h boson can be seen in more than one channel in t f th tmos  o  e parame er space. 37ATLAS preliminaryATLAS, 300 fb-1, 5σdiscovery potential in  CPX scenario.Almost all of the    parameterspace is covered by the observation of at    least one Higgs boson (mainly the lightest H )1Small region of phase t dspace no  covere : corresponds to MH1<50 GeV.38Conclusions  I have presented a partial review of Higgs studies in ATLAS and CMS:Several results have been taken from the CMS Physics Performance          Technical Design Report  (CERN/LHCC 2006-021)Th ATLAS Ph i TDR hi h d t b k t ’99 (CERN/LHCC 99e  ys cs  w c  a es ac  o   -14/15) is being updated with a series of notes that will be published soon.Several SM H channels have been studied with detailed detector simulation and latest theoretical developments:There is already good sensitivity with ~10 fb-1, although more detailedstudies (including measurement of H properties) will require more data         Data will tell if the detector behave as expected and if we can control the background levels 39More than one channel along the expected mass range give robustness to the resultsMSSM well coveredThe two detectors are also powerful enough to face unexpected scenarios. First LHC collisions are expected later this yearBig activities on-going in commissioning the detectors, the offline computing, preparing alignment and calibration strategies,…We face a long period of development and understanding of the twodetectors Work has already started using cosmics data and will continue with first collisions.40Backup Material41(%)(%)(%)%%( ( (GEANT simulationO O1STACOSTACO 0pT(GeV)pT (GeV)42Real Dataσ/E = 9.4%/√E ⊕ 0.1% ⊕ 0.3/EMCBeam Energy (GeV)Resolution0.0050.010.0150.020.0250.030.0350.040.0450.050 20 40 60 80 100 120 140 160 180σ/ E9 4% /√E⊕R e solution.  .R esolutionResolutionExpected performance day-0 Physics samples for improvement (examples)ECAL  uniformity             1-2% (~0.5% locally)      Isolated electrons, Z→ eee/γ E-scale ~ 2 % Z → ee                                               HCAL  uniformity             ~ 3 %                       Single pions, QCD jetsJet    E-scale                   < 10%                        γ/Z + 1j, W → jj  in  tt events434445ε=30%464748

Higgs at the LHC

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