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Standard Model at LHC

Standard Model at LHC. Eric COGNERAS, LPC Clermont-Ferrand On behalf of the ATLAS and CMS collaborations. HEP-MAD 07, Antananarivo , Madagascar 2007, september 14. Motivation. SM successfully tested at current energy LHC  prospect physics at higher energy :

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Standard Model at LHC

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  1. Standard Model at LHC Eric COGNERAS, LPC Clermont-Ferrand On behalf of the ATLAS and CMS collaborations HEP-MAD 07, Antananarivo, Madagascar 2007, september 14

  2. Motivation • SM successfully tested at current energy • LHC  prospect physics at higher energy : • Able to searchdirectly beyond SM • But also precise measurements of SM parameters • Goal for SM physics: • Deeper understand the SM with : • Precision EW measurements (MW, sin2qW ,…) • Top physics (mass,cross section,… measurement) • Indirect estimate the Higgs mass • Using MW, mTop, sin2qW precise measurement • Search for deviation from SM g t u c W d s b Z e µ t g ne nµ nt Eric COGNERAS - Standard Model @ LHC

  3. Experimental Framework The LHC • CERN (Geneva) • pp collision @ √s = 14 TeV (10 × Tevatron) • Luminosity : • Low luminosity phase L1033 cm-2s-1 (2008-2009?) [10 fb-1/year : 10× TV] • High luminosity phase L1034 cm-2s-1 (2010?-X) [100 fb-1/year : 100×TV] EW precisionmeasurement ATLAS and CMS  generalpurposephysics LHCb  b physics ALICE  heavy ion physics Experiments Eric COGNERAS - Standard Model @ LHC

  4. Experimental Framework • Tracking (||<2.5, B=2T) : • Si pixels and strips • Transition Radiation Detector (e/ separation) • Calorimetry (||<5) : • EM : Pb/LArwithAccordeonshape • HAD : Fe/scintillator (central), Cu-W/Lar (forward) • MuonSpectrometer (||<2.7) : • air-coretoroidswith muon chambers • Tracking (||<2.5, B=4T) : • Si pixel and strips • Calorimetry (||<5) : • EM : PbWO4crystals • HAD : brass/scintillator (central,end-cap), Fe/Quartz (forward) • MuonSpectrometer (||<2.5) : • return yoke of solenoidinstrumentedwith muon chambers Eric COGNERAS - Standard Model @ LHC

  5. p-p collisions Cross section and Event rate 1 or 2 orders of magnitude larger than Tevatron • LHC is a W, Z, top factory : • small statistical errors in precision measurements • large samples for studies of systematic effects (calibration and syst. controls) x2 x1 Hadron collider problem : PDF to be better known Eric COGNERAS - Standard Model @ LHC

  6. SM physics @ LHC • W/ Z physics (precision EW measurement) • Parameters related to indirect MH measurement : • W mass and width • sin²W • Constraints on the PDF • W/Z inclusive cross section as well as W/Z+jets • W rapidity • Measurement of gauge boson pair production • Triple Gauge Boson Coupling • Top physics • Parameters related to indirect MH measurement : • Top mass/cross section • Deeper understanding of Top quark : • Top spin correlation, probe of the Wtb vertex, single Top cross section, Top charge • QCD (→ see Albert talk on tuesday) • Higgs boson direct search • B physics • … SM physics at LHC covers a large number of topics  just focus on few items in this talk Eric COGNERAS - Standard Model @ LHC

  7. Precision EW Measurement • Eventselection: • 1 isolated lepton (e,µ) pT> 25 GeV in ||<2.4 • missing ET > 25 GeV • No jet withpT> 30 GeV • Recoil |u|< 20 GeV MWmeasurement • LHC expects : MW < 15 MeV • W channel : same as the Tevatron  using W→l decay But LHC statistics is higher (60M recons. W→l @ low Lumi [10× TV]) • Several methods available: • R=MTW / MTZ spectrum  Small syst, sample /10 • pTl spectrum  pile-up, theo. know. of PTW • MTW  high stat,pile-up q q’ Eric COGNERAS - Standard Model @ LHC

  8. Precision EW Measurement MW measurement • Use the knowledge on the Z boson to constrain the W mass • pTl spectrum shape is sensitive to MW • pT not necessary • Use Transverse mass to • cope with unmeasured pL • pT from pTl & recoil W mass: fit exp. shape to MC sample with different Values of MW Eric COGNERAS - Standard Model @ LHC

  9. Precision EW Measurement MW measurement : systematics • LHC goals : Wl : one lepton species, lowL, per experiment, after 1 year stat. error : negligible • syst. error : • MC modelling of phys. • detector responses physics detector • Combining channels and ATLAS/CMS exp., should reach MW  15 MeV Eric COGNERAS - Standard Model @ LHC

  10. Precision EW Measurement Determination of sin²W • Parity violation in neutralcurrent Asymmetry in the angular distribution of leptons from Z decay • (-dependence of cross-section) Use AFB in p-p→Z/*→l+l- Test of the Standard Model (universality) • At the Z pole, AFBcomesfrom the interference of vector and axial component of the coupling • Where a, b calculated to NLO QED and QCD • Assumption for p-p colliders : the quark direction is the same as the boost of the Z • Correct for large di-lepton rapidities • Only EM calorimeters provide the required large η-coverage (Z→e+e-) All events Events with quark direction correctly estimated Eric COGNERAS - Standard Model @ LHC

  11. Precision EW Measurement Determination of sin²W • Results Sensitivityincreaseswithforwardelectrons • Eventselection: • pTe> 20 GeV • 85.2 < Mee< 97.2 GeV Only Forward Electrons All Events L = 100 fb-1 • Current error on world average 1.6x10-4 • need small systematic error : • PDF uncertainty, • precise knowledge of lepton acceptance and efficiency • effects of higher order QCD Eric COGNERAS - Standard Model @ LHC

  12. Precision EW Measurement Triple gauge boson coupling • Probe the non abelian structure of SM • 14 possible WW and WWZ coupling • Use 5 independent, CP conserving, EM gauge invariance preserving couplings : g1Z, , Z, , Z • At SM tree level, g1Z==Z=1 and =Z =0 •  and Z grow with s  big advantage for LHC •  =-1, g1Z=g1Z -1, Z =Z -1 grow with s • LO Feynman diagram : • V1, V2, V3 = Z, W,  → WW, ZW, W • Diboson final states have predictablesproduction and manifest the gauge boson coupling • In SM, onlychargedcoupling WW  and WWZ are allowed q q’ s-channel • TGC manifest in : • Cross section enhancement • High pT(V=W, Z, ) • Production angle Eric COGNERAS - Standard Model @ LHC

  13. Precision EW Measurement Triple gauge boson coupling Exemple of WZ production • Useonly leptonic final state • Eventselection: • Exactly 3 leptonswithpT>25 GeV • At leastone pair of leptonswithsameflavour and opposite charge and |mll-MZ|<10 GeV • … SM g1Z= 0.05 Eric COGNERAS - Standard Model @ LHC

  14. QCD-orientedMeasurement Measurement of W/Z cross sections • Results(L=1 fb-1 [~600k Z→, ~6M W→]) Estimation of the cross section Z Eventselection: Z : 2 isolated µ, pTµ > 20 GeV, ||<2, 84<Mµµ<99 GeV,... W : 1 isolated µ, pTµ > 25 GeV, ||<2, 40<MT(µ,ETMiss)<200GeV,... CERN/LHCC 2006-021 CMS TDR 8.2 s(Zmm + X) = 1160 ± 1.5 (stat) ± 27 (syst)  116 (lumi) pb s(Wmn + X) = 14700 ± 6 (stat) ± 485 (syst)  1470 (lumi) pb Alreadydominated by systematics W Systematics come mainly from theory • (acceptance+PDF uncertainty). At a later stage these processes can be used as luminosity monitor (Error on luminosity: ~5%) Eric COGNERAS - Standard Model @ LHC

  15. QCD-orientedMeasurement e-rapidity e+ rapidity CTEQ61 CTEQ61 MRST02 MRST02 ZEUS02 ZEUS02 ds(We)/dy Generated Generated y ds(We)/dy Reconstructed Reconstructed y Constraints on PDF using W rapidity distributions • At LHC, experimental uncertainty is dominated by systematics (large event production) • Thetheoritical uncertainties are dominated by PDFs • Exp. uncertainty sufficiently small to distinguish between different PDF sets • PDF error sensitive to W→e rapidity distribution • e rapidity spectrum shape sensitive to gluon shape parameter (valence quark density) • Probe low-x gluon PDF at Q²=MW2 • PDF uncertainties only slightly degraded after detector simulation and selection cuts Eric COGNERAS - Standard Model @ LHC

  16. Top Quark Physics W helicity Top Mass + l+ Top Width Anomalous Couplings Production cross-section (90%) (10%) Top Spin W+ CP violation Top Charge Resonance production n Y t b Wt-channel Production kinematics s ~ 10 pb s ~ 250 pb s ~70pb t-channel W* (s-channel) Top Spin Polarization _ t Rare/non SM Decays X Branching Ratios |Vtb| • Direct discovery in 1995 (Fermilab) • Completes the 3 family structure of the SM • Very high mass  175 GeV thad = LQCD-1 >> tdecay  No Top Hadron : Opportunity to measureparameters of a free quark • Production at LHC: • tt production • single top production s ~ 833100pb @ 14TeV (NLO) 8M evts/y @ Low Lum Eric COGNERAS - Standard Model @ LHC

  17. tt Physics W (had) ≥4 jets (DR=0.4) pT>40 GeV t (had) pT>20 (25) GeV 2 b-jets t (lep) pT>20 GeV • Decay: Determined by decay of Ws Golden Channel • Fullyhadronicchannel (44 %) • Di-leptonicchannel (5 %) • Semi-leptonicchannel (30 % no t) • Selection : • Only e/µ events • Trigger • large eventyield • smallbackbround Eric COGNERAS - Standard Model @ LHC

  18. tt Physics Top quark mass measurement (Invariant mass spectrum of reconstructed Had. Top : most straightforward technique) Without b-tagging(early data) With b-tagging Event topology: 3 jets with highest ∑ pT L=100 pb-1 (1 day @ 1033 cm-2s-1) Selection efficiency : e=5.3 % L=O(100) pb-1 (few days @ 1033 cm-2s-1) S/B=O(100) Very small SM Bck Events Number of Events Full simulation Top signal (ATL-PHYS-PUB-2005-024) Signal (MC@NLO) W+n jets (Alpgen) + combinatorial W+jets background Selection efficiency : e=1-2% In thisway, m(top) ~1.3 GeV WhenKinematical Fit (using the leptonicside) isused, m(top) ~1 GeV Top mass (GeV) Mjjj (GeV) Eric COGNERAS - Standard Model @ LHC

  19. tt Physics • Semi-leptonic channel (ttbbqqmnl): L=10fb-1 Dstt/stt= 9.7%(syst)±0.4%(stat)±3%(lum) • Di-leptonic channel (ttbb lnllnl): L=10fb-1 Dstt/stt= 11%(syst)±0.9%(stat)±3%(lum) ereco = 5% (S/B=5.5) With Tau leptons (ttbb tnt lnl, t hadrons): Dstt/stt= 16%(syst)±1.3%(stat)±3%(lum) • Fully Hadronic channel: L=1fb-1 [ ereco=2%, S/B~1, et-tag=30% ] Dstt/stt= 20%(syst)±3%(stat)±5%(lum) ereco=2%, S/B<1/9 (QCD) CERN/LHCC 2006-021 CMS TDR 8.2 tt cross section ereco= 6.3% Eric COGNERAS - Standard Model @ LHC

  20. tt Physics (Eur.Phys.J.C44S2 2005 13-33) L=10fb-1 SM Error (±stat ±syst) (1/G)dG/dcos(ql*) (Mt=175 GeV) Semilep. + Dileptonic F0 0.703  0.004  0.015 FL 0.297  0.003  0.024 FR 0.000 (mb=0)  0.003  0.012 • Syst ( Eb-jet,mtop,FSR ) • dF0/F0 ~ 2% ; dFR ~ 0.01 cos(ql*) Top polarization Test the tbW decay vertex Measure Wpolarization (F0, FL, FR) through lepton angular distribution in W cm system: Eric COGNERAS - Standard Model @ LHC

  21. single Top Physics 1 lepton, pT>25GeV/c High Missing ET 2 jets (at least 1 b-jet) Common feature: Stat: 7000 events (S/B=3) t-channel: (Nj=2,Nb=1) Wt-channel: Stat: e~1%(S/B=15%) (Nj=3,Nb=1) s-channel: Stat:1200events for tb (S/B=10%) (Nj=2,Nb=2) • t-channel: Ds/s= 8%(syst)±2.7%(stat)±5%(lum) • Wt-channel: Ds/s= 23.9%(syst)±8.8%(stat)±9.9%(MC) • s-channel: Ds/s= 31%(syst)±18%(stat)±5%(lum) Production cross section (ATL-PHYS-PUB-2007-005) L=30fb-1 Separate Channels by (Nj,Nb) in final state: • Ds/s= 12%(syst)±1%(stat)±5%(lum) • Ds/s= 14%(syst)±1.5%(stat)±5%(lum) • Ds/s= 16%(syst)±12%(stat)±5%(lum) L=10fb-1 (CERN/LHCC 2006-021, CMS TDR 8.2) Eric COGNERAS - Standard Model @ LHC

  22. Conclusion • Precisionmeasurements are possible with hadron collider, as demonstrated by the Tevatron • LHC will prospect higherenergyphysics • Detector to beunderstoodwithearly data • Higherluminosity • Better S/B ratio • LHC goals are ambitious • MW < 15 MeV • mtop < 1 GeV • sin2qW ~ 10-4 But reachable … as soon as the detectors performances and the systematicswillbeunderstood Eric COGNERAS - Standard Model @ LHC

  23. Back-upSlides

  24. Precision EW Measurement MW measurement • Simple and powerful in principle : consider pTl spectrum correlation between Z and W decay CMS NOTE 2006/061 • stat. error negligible (~2 MeV) • BUT need to predict the spectrum precisely ! Eric COGNERAS - Standard Model @ LHC

  25. tt Physics Kinematical Fit (use leptonic side) • Minimization of a ² function with constraints on W and Top masses • Reduces FSR systematics • Cleaner event sample (using a cut on ²) • measure mtop as a function of ² Eric COGNERAS - Standard Model @ LHC

  26. tt Physics Although t and t are produced unpolarized their spins are correlated A= q s(tLtL) + s(tRtR) - s(tLtR) - s(tRtL) s(tLtL) + s(tRtR) + s(tLtR) + s(tRtL) flq 1 dN 1 ( 1 – ADaXaX´cosf ) = N dcosf2 l+,n t t Top spin correlation Testing the tt Production cross-section SM: Other angular distributions: aX=spin analysing power of X SM: Eric COGNERAS - Standard Model @ LHC

  27. tt Physics t q ql,n l,n qq SM Mtt<550 GeV Error (±stat ±syst) (Eur.Phys.J.C44S2 2005 13-33) • Semileptonic + Dileptonic • Syst (Eb-jet,mtop,FSR) • ~4% precision A 0.42 0.014 0.023 Ãxx´ AD -0.29 0.008 0.010 t A N(cosf > 0) - N(cosf < 0) 1 = - ADaXax´ N(cosf > 0) + N(cosf < 0) 2 Top spin correlation L=10fb-1 A) Spin correlations and angular distributions: (CERN/LHCC 2006-021, CMS TDR 8.2) B) Spin Asymmetries can also be used (X-check) (for L=10fb-1precision A,AD below 10% ) (hep-ex/0605190, subm. to Eur.Phys.J.C) Eric COGNERAS - Standard Model @ LHC

  28. tt Physics A- AFB A+ AFB [t=0] A± [t= (22/3-1)] ± cos(ql*) Probe the Wtb vertex B) Anomalous Couplings in the tbW decay (PRD67 (2003) 014009, mb≠0) Angular Asymmetries: AFB, A+ and A- SM(LO): Eric COGNERAS - Standard Model @ LHC

  29. tt Physics SM(LO): rL=0.423 rR=0.0005 (mb≠0) 1s Results: Probe the Wtb vertex B) Anomalous Couplings in the tbW decay Eric COGNERAS - Standard Model @ LHC

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