Physics at the LHC Monday The standard model

Physics at the LHC • Monday: • The standard model and QCD@LHC • LHC and the Detectors • Tuesday: • The Higgs Boson (theory) • The Top Quark (Arnaud Lucotte, LPSC) • Wednesday • The Higgs Boson (exp) • Higgs+SUSY (theory) • Thursday • 11: 00 LHCb (Frederic Machefert, LAL) • 15: 00 Higgs+SUSY (exp) • Friday • Xtra Dimensions (Gregory Moreau, LPT) • Exotics (Fabienne Ledroit, LPSC)

LEP and Electroweak Constraints MH=80+36 -26 Ge. V MH<153 Ge. V@95 C. L. LEP: Direct search in all possible channels MH>114. 4 Ge. V (expected: 115. 3 Ge. V)

Te. Vatron Ldt (fb LEP -1) 8 fb-1 With realistic improvements, expect 95%CL = SM with 3 fb 1 @ 115 Ge. V 5 fb 1 @ 160 Ge. V 8 fb 1 from 115 to 185 Ge. V

The Standard Model Higgs Boson Djouadi HDecay: Spira et al H bb H WW(*) H ZZ(*) LHC benchmarks: • H γγ • H 4 l (eeee, eeμμ, μμμμ) • H WW Leptonen • tt. H( bb) • vector boson fusion (VBF) ~ 120 Ge. V ~ 160 Ge. V Pour man’s definition of discovery: S/sqrt(B)>5 H ττ H γγ

Particle Identification/jet rejection Dijet cross section ~1 mb Z ee 1. 5 10 -6 mb W eν 1. 5 10 -5 mb Need a rejection factor of 105 (5. 104) for electrons (photons) Use the shower shape in the calorimeter Shower width TRT Cuts: electrons (photons) an efficiency of about 75 -80% with a rejection factor of 105 (7000) Multivariate techniques are being studied for possible improvements (likelihood, neural net) Use the combination of the calo+tracker

e/π separation using the TRT Typical TR photon energy deposits in the TRT are 8 -10 ke. V, while minimum-ionising particles, such as pions, deposit about 2 ke. V: count high threshold hits TR threshold – electron/pion separation MIP threshold – precise tracking/drift time determination Results from TB 2002 @20 Ge. V 5. 5 ke. V 0. 2 ke. V CTB 2004 @low energy 2 -9 Ge. V Bd 0�J/ψ Ks 0 90% electron efficiency 10 -2 pion rejection 90% electron efficiency 2 10 -2 pion rejection

γ/π0 separation • need a separation factor of at least 3 • use finely segmented first CALO compartment and search for secondary minima, shower width etc physics/0505127 --- Data --- MC p 0 → = 90 % E 2 nd max - Emin R (data) = 3. 18 ± 0. 12 (stat) R (MC) = 3. 29 ± 0. 10 (stat) Results obtained with Full simulation G 3/DC 1 or G 4/DC 2 are in agreement

The Standard Model Higgs Boson HDecay: Spira et al H WW(*) H ZZ(*) NNLO: 10 -20% g g H t NLO: 10 -20% t H H γγ t γ H bb: hopeless because of large Jet cross section Try for photons: • small branching ratio (10 -3) • mass peak “thin” dominated by ECAL resolution tt. H: • top-pairs plus bb

Higgs Boson γγ Inclusive analysis: 2 photons PT 1>40 Ge. V PT 2>25 Ge. V CMS Background: • irreducible: 0. 125 pb/Ge. V • reducible: 0. 03 pb/Ge. V • OK • good Energy resolution • good uniformity Material in front of Calorimeter: photon-conversions, energy loss ATLAS CMS

Higgs Boson γγ Important: • understand irreducible background! CDF: • prompt photon study • compare to NLO Di. Phox: reasonable agreement Cut based Analysis: • number of events in a window Optimized Analysis: • add PT and Angular distribution Or • add isolation and kinematic info OK for 30 fb-1 (non-optimized)

tt. H b. Wbb c, g, uds CMS at 50% efficiency: Combined Secondary Vertex Impact Parameter Secondary Vertex Soft-leptons Typically 50% identification efficiency with 10 -2 to 10 -3 mis-ID probability

Soft electrons H bb Two possibilities for seeded electron pions reconstruction • calo • tracker Reconstruction of electrons close to jets difficult, and interesting (btagging) especially for soft electrons. Dedicated algorithm: • builds clusters around extrapolated impact point of the tracks • calculates properties of the clusters e id efficiency = 80% • PDF and neural net for ID Pion rejection in: • useful per se as well as for b. J/Psi : 1050± 50 tagging WH(bb) : 245± 17 tt. H : 166 ± 6 J/Psi WH tt. H

tt. H ttbb Analysis: • tt. H Wb. Wb bb lνb jjb bb • Reconstruct all 6 jets • tag 4 b jets • reconstruct 2 top quarks • reco Higgs mass Backgrounds: • ttjj (jet mis-ID) • ttbb (irreducible) • background shape? ATLAS H ttjj background CMS: signal CMS: background

The Standard Model Higgs Boson HDecay: Spira et al H WW(*) H ZZ(*) H γγ At 200 Ge. V: ZZ Fully Leptonic channel Advantage: • large branching ratio (Higgs) • clean signal • electrons or muons • mass peak resconstructible Disadvantage: • hadronic Z decays not useable • BR(Z ll)*BR(W ll) ~ 0. 0036 Backgrounds: • ZZ (standard model) irreducible • Zbb (leptonic decays) reducible: isolation • tt (double leptonic plus 2 b decays) reducible: isolation qqbar ZZ known at NLO gg ZZ +20% rejection 100 (less than ZZ)

Higgs Boson ZZ CMS m. H=200 Ge. V e e CMS m. H=140 Ge. V Mass peak Great channel even for very few fb-1 Important: energy/momentum calibration leptons

The Standard Model Higgs Boson HDecay: Spira et al H WW(*) H ZZ(*) Around 160 Ge. V (2*m. W): WW Fully Leptonic channel Advantage: • large branching ratio (Higgs) • clean signal • electrons or muons Disadvantage: • no mass peak for additional discrimination • pure counting experiment • hadronic W decays not useable • BR(W lν)*BR(W lν) ~ 0. 04 H γγ Spin 0 decay: H W- W+ e- e+ Use of spin correlation to distinguish against WW standard model background

Higgs WW Selection (CMS note 2006 -047) 2 leptons <2, 30<ptmax<55 Ge. V, ptmin>25 Ge. V Etmiss>50 No jet Et(raw)>15 Ge. V <45°, 12<Mll<40 Systematic uncertainty on total bg ~13% Control samples for tt and qq WW (mll>60 Ge. V) MC for single top and gg WW Direct Production 10 fb-1 5σ 150 -180 Ge. V

Higgs in VBF NLO: ~5% q q q Forward Jets: W/Z H q Gauge boson fusion: qq. H qqττ, qq. WW Tagging the forward jet: • PT>40 Ge. V and PT>20 Ge. V • Δη>3. 8 • Jet veto central jet PT>20 Ge. V Further cuts: • PT(leptons)>10, 15 Ge. V Backgrounds: • WW+jets • tt • Wt (Arnaud) • γ*/Z+jets WW*: at rest in Higgs rest mass frame, mll=mνν ATLAS 10 fb-1 5σ 130 -190 Ge. V

• • Higgs in VBF to ττ Typical selection: – 2 tagging jets – Higgs decay products in central region between tagging jets – Jet veto (depends on pileup low lumi only) – Lepton-lepton or lepton-hadron final state for tau decays – Use missing transverse momentum + collinear approximation of tau decays to reconstruct invariant mass of tau pair – Resolution limited by missing pt resolution: ~10 Ge. V-13 Ge. V Main background: – Z + 2 jets – Dangerous for low MH l+ jet l+

Background Control for VBF pb Z + jet signal with 30 fb-1: • one jet + jet veto • ~1000 signal events with S/B ~6 • check mass reconstruction Z+ jet rates (ee, ): • control sample for Z+jets background, signal free: BR( lνν)^2 EW QCD Use Zjj to check: apply VBF cuts, reduces QCD, study of minijet emission Colorflow different in EW and QCD W/Z+n. J+X NLO: p. Tl > 15 Ge. V | l| < 2. 4 p. Tj > 20 Ge. V | j| < 4. 5 DRlj > 0. 4 DRll > 0. 2

Higgs: all channels 5σ 10 fb-1 per experiment: • ZZ, WW most significant channels (high mass) • difficult: mass at the LEP limit • combination 3 channels: m. H ~ 115 Ge. V S/ B~4 γγ: S=130, B=4300 2 tt. H( bb) : S=15, B=45, 2. 2 qqττ: S=10, B=10, 2. 7

Background systematics and bkg normalization from data Channel Main background S/B Bkg. sys for 5 s Proposed technique/comments H-> Irreduc. Reducible q 3 -5% 0. 8% Side-bands (bkg shape not known a priori) tt. H H->bb ttbb 30% 6% Mass side-bands Anti b-tagged ttjj ev. H->ZZ*-> 4 lep ZZ->4 l Reducible tt, Zbb 300 -600% 60% Mass side-bands Stat Err <30% 30 fb-1 H->WW*->ll WW*, t. W 30 -150% 6 -30% No mass peak Bkg control region and extrapolation VBF channels In general Rejection QCD/EW Study forward jet tag and central jet veto Use EW ZZ and WW QCD Z/W + jets VBF H->WW tt, WW, Wt 50 -200% 10% Study Z, W, WW and tt plus jets VBF H-> Zjj, tt 50 -200% 10 -40% Mass side-bands Beware of resolution tails

Measurement of Higgs boson properties Width: Mass: In the end: precision 0. 1% degradation of resolution beyond 500 Ge. V: Width of Higgs boson and statistics Width experimentally accessible only for m. H>200 Ge. V

Measurement of Higgs boson properties: Couplings Concentrate on “low” MH First step: Assume spin 0 Measure . BR in different channels Uncertainties: Selection efficiencies Background subtraction (Luminosity for absolute cross-sections) Second step: Assume only H Ratio of BR normalize to WW channels gives ratio of Partial Widths Atlas note phys-2003 -030

Measurement of Higgs boson properties: Couplings From the branching ratio-ratios to the couplings: • calculate α and β defined below Coupling ratios: Theoretical uncertainty: Coupling ratios from a fit of discovery channels: typically 20% à 50% Assumptions: • couplings to light fermions small • no new particles in loop

Measurement of Higgs boson properties: Spin and CP • Observation of gg H or H excludes spin 1 (Yang theorem) • MH>200 Ge. V, study spin/CP from H ZZ 4 l Measure α, β, R! Distribution of polar angle as function of Legendre Polynomials (P):

Measurement of Higgs boson properties: Spin and CP • Plane Angle: can exclude Spin-0, CP=-1 • Polarisation: above 250 Ge. V no problem

Measurement of Higgs trilinear coupling? From Higgs potential: trilinear coupling Look at Higgs pair production Small x-sec, ~ 20 fb (before BR!) HH WWWW same sign leptons (ll+4 j) Sigma(gg->HH)/SM m. H=170 Ge. V / SM Parton level study Baur, Plehn, Rainwater hep-ph/0211224 Still to be confirmed by more detailed exp. Studies including bkg systematics

Summary • Search for Higgs boson difficult • good understanding of detector required • electron and photon identification essential • b tagging for tt. H • forward jet tagging • most promising channels are at high mass • 10 fb-1 difficult for low mass region