1 / 29

Standard Model at LHC

This presentation discusses the motivation for studying the Standard Model (SM) at the Large Hadron Collider (LHC) and the experimental framework for conducting these studies. It also highlights the importance of precision electroweak (EW) measurements in understanding the SM and searching for deviations from it. The focus is on the measurement of the W boson mass and the determination of sin^2(theta_W). The potential systematic errors and methods for reducing them are also discussed.

artiem
Download Presentation

Standard Model at LHC

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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

More Related