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Expectations from LHC for Top Physics

Expectations from LHC for Top Physics. Top Mass Couplings and decays Top spin polarization Single top production. Top quark mass is a fundamental parameter of the EW theory By far has the largest mass of all known fundamental particles In SM: top- and W-mass constrain Higgs mass

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Expectations from LHC for Top Physics

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  1. Expectations from LHC for Top Physics Top Mass Couplings and decays Top spin polarization Single top production

  2. Top quark mass is a fundamental parameter of the EW theory By far has the largest mass of all known fundamental particles In SM: top- and W-mass constrain Higgs mass Sensitivity through radiative corrections Scrutinize SM by precise determination top mass Top quark exists and will be produced abundantly !  window for new physics Many heavy particles decay in tt Handle on new physics by detailed properties of top And in addition… Experiment: Top quark useful to calibrate the detector (LHC) Beyond Top: Top quarks will be a major source of background for almost every search for physics beyond the SM (LHC) Motivations for Top Physics studies Marina Cobal - HCP2004

  3. pp (mainly) at s = 14 TeV Startup in April 2007 Initial/low lumi L1033 cm-2 s-1  2 minimum bias/x-ing  “Tevatron-like” environment 10 fb-1 /year Design/high lumi L=1034 cm-2 s-1 after ~ 3 years ~ 20 minimum bias/x-ing  fast ( 50 ns) radhard detect 100 fb-1 /year LHC and experiments TOTEM 27 km ring 1232 dipoles B=8.3 T ATLAS and CMS : pp, general purpose ALICE : heavy ions, p-ions LHCb : pp, B-physics Marina Cobal - HCP2004

  4. LC machine • Maybe some years after the LHC startup • ECM of operation 200-500 GeV, possible upgrade to 1 TeV • 80% Polarization of e- beam • Luminosity: 300 fb-1/year Marina Cobal - HCP2004

  5. Cross section determined to NLO precision Total NLO(tt) = 834 ± 100 pb Largest uncertainty from scale variation Compare to other production processes: Top production cross section approximately 100x Tevatron Opposite @ FNAL Top production at LHC ~90% gg~10% qq Low lumi LHC is a top factory! Marina Cobal - HCP2004

  6. ..and at LC? • The ttbar cross section is ~103 smaller than at LHC, but higher L • s ~0,85 pb at max, around 390 GeV, and falls down with energy as 1/s ~200000 tt/year at TESLA parameters Marina Cobal - HCP2004

  7. In the SM the top decays to W+b All decay channels investigated Using ‘fast parameterized’ detector response Checks with detailed simulations Di-leptons (e/) BR≈4.9%  0.4x106 ev/y No top reconstructed Clean sample Single Lepton (e/) BR=29.6%  2.5x106 ev/y One top reconstructed Clean sample Fully Hadronic BR≈45%  3.5x106 ev/y Two tops reconstructed Huge QCD background Large combinatorial bckgnd Top decay Marina Cobal - HCP2004

  8. Top mass: Where we are Marina Cobal - HCP2004

  9. Near future of Mtop Tevatron only (di-lepton events or lepton+jet ) from W decays Status of inputs (preliminary): mt=(178.0  2.7 (stat)  3.3 (syst)) GeV/c2 (latest Tevatron updated combination – RunI data) mt=(175  17 (stat)  8 (syst)) GeV/c2 (CDF di-leptons – RunII data) mt=(178+13-9(stat)  7 (syst)) GeV/c2 (CDF lepton+jets – RunII data) Matter of statistics (also for the main systematics) and optimized use of the available information. Each experiment expects 500 b-tagged tt l+jets events/fb  DMtop ~ 2-3 GeV/c2 for the Tevatron combined (2-4/fb) • mt  2.5 GeV ; mW  30 MeV  mH/mH  35% In 2009 (if upgrade is respected) from Tevatron: DMtop = 1.5 GeV !! Marina Cobal - HCP2004

  10. Problem for the top: what is the mass of a colored object? The top pole mass is not IR safe (affected by large long-distance contributions), cannot be determined to better than O(LQCD) Measurement of mt: At Tevatron/LHC: kinematic reconstruction, fit to invariant mass dist. at the LHC: accuracy  1-2 GeV (limited by FSR) At the LC, mainly from threshold behavior Measurement comparison data – Monte Carlo: involves transition from actually measured quantity to suitably defined (short-distance) top mass ‘Threshold mass’ at the LC: accuracy  20 MeV [M. Martinez, R. Miquel ’03] Transition to MS mass: dm  100 MeV [A. Hoang et al. ’00] What is the Top Mass? Marina Cobal - HCP2004

  11. Br(ttbbjjl)=30%for electron + muon Golden channel Clean trigger from isolated lepton The reconstruction starts with the W mass: different ways to pair the right jets to form the W jet energies calibrated using mW Important to tag the b-jets: enormously reduces background (physics and combinatorial) clean up the reconstruction Lepton side Hadron side LHC: MTop from lepton+jet Typical selection efficiency: ~5-10%: • Isolated lepton PT>20 GeV • ETmiss>20 GeV • 4 jets with ET>40 GeV • >1 b-jet (b40%, uds10-3, c10-2) Background: <2% W/Z+jets, WW/ZZ/WZ Marina Cobal - HCP2004

  12. Hadronic side W from jet pair with closest invariant mass to MW Require |MW-Mjj|<20 GeV Assign a b-jet to the W to reconstruct Mtop Kinematic fit Using remaining l+b-jet, the leptonic part is reconstructed |mlb -<mjjb>| < 35 GeV Kinematic fit to the tt hypothesis, using MW constraints j2 j1 b-jet t LHC: Lepton + jet, reconstruct top • Selection efficiency 5-10% Marina Cobal - HCP2004

  13. Method works: Linear with input Mtop Largely independent on Top PT Biggest uncertainties: Jet energy calibration FSR: ‘out of cone’ give large variations in mass B-fragmentation Verified with detailed detector simulation and realistic calibration LHC: MTop systematics Challenge: determine the mass of the top around 1 GeV accuracy in one year of LHC Marina Cobal - HCP2004

  14. Mtop LHC: Alternative mass determination • Select high PT back-to-back top events: • Hemisphere separation (bckgnd reduction, much less combinatorial) • Higher probability for jet overlapping • Use the events where both W’s decay leptonically (Br~5%) • Much cleaner environment • Less information available from two ’s • Use events where both W’s decay hadronically (Br~45%) • Difficult ‘jet’ environment • Select PT>200 GeV Various methods all have different systematics Marina Cobal - HCP2004

  15. Use exclusive b-decays with high mass products (J/) Higher correlation with Mtop Clean reconstruction (background free) BR(ttqqb+J/)  5 10-5  ~ 30%  103 ev./100 fb-1(need high lumi) Top mass from J/ MlJ/ Different systematics (almost no sensitivity to FSR) Uncertainty on the b-quark fragmentation function becomes the dominant error M(J/+l) M(J/+l) Pttop Marina Cobal - HCP2004

  16. Mtop at LC • Scan of the threshold for e+e-ttbar • Very precise measurements (< 20 MeV) • To perform this analysis with small systematic errors need to study: beam spread beamstrahlung initial state radiation • Simultaneous measurements of 3 physical observables: • stt • Pt of top • Forward-Backward asimmetry of top AtFB • Multiparameter fit up to 4 parameters • Mt (1S) • as(MZ) • Gt • gtH • Theoretical uncertainties to relate the 1S to the MS mass is ~ 100 MeV s(pb) Marina Cobal - HCP2004

  17. Georg Weiglin, LCWS04 Paris Marina Cobal - HCP2004

  18. Many theoretical models include the existence of resonances decaying to top-topbar SM Higgs(but BR smaller with respect to the WW and ZZ decays) MSSM Higgs(H/A, if mH,mA>2mt, BR(H/A→tt)≈1 for tanβ≈1) Technicolor Models, strong ElectroWeak Symmetry Breaking, Topcolor, “colorons” production, […] xBR required for a discovery σxBR [fb] 30 fb-1 830 fb 300 fb-1 mtt [GeV/c2] 1 TeV LHC: Search for resonances • Study of a resonance Χ once known σΧ, ΓΧ and BR(Χ→tt) at LHC • Reconstruction efficiency for semileptonic channel: • 20% mtt=400 GeV • 15% mtt=2 TeV 1.6 TeV resonance Mtt Marina Cobal - HCP2004

  19. Couplings and decays • Does the top quark behaves as expected in the SM? • Yukawa coupling to Higgs from ttbarH events • Electric charge • Top spin polarization • CP violation • At the LHC Yukawa coupling can be measured to < 20% from t-tbar H production • @ the LC, the precision of the measurement of the top Yukawa coupling will be better than ~ 10 % if mH ≤ 190 GeV/c2 • For a light Higgs (mH~120 GeV/c2): Precision ~ 5-6 % Marina Cobal - HCP2004

  20. LHC: Couplings and decays • According to the SM: • Br(t Wb)  99.9%, Br(t  Ws)  0.1%, Br(t  Wd)  0.01% (difficult to measure) • Can probe t W[non-b] by measuring ratio of double b-tag to single b-tag • Statistics more than sufficient to be sensitive to SM expectation for Br(t  W + s/d) • need excellent understanding of b-tagging efficiency/purity Marina Cobal - HCP2004

  21. Search for anomalous Wtb couplings • The Wtb vertex can be probed and measured using either top pair production or single top production • Total tt rate depends weakly from Wtb vertex structure • C and P asymmetries, top polarization, spin correlations can provide interesting info • The single top production rate is instead directly proportional to the square of the Wtb coupling • LHC could rivale the reach of a high L (500 fb-1) 500 GeV LC Marina Cobal - HCP2004

  22. LHC: FCNC Rare decays • In the SM the FCNC decays are highly suppressed (Br<10-13-10-10) • Any observation would be sign of new physics • FCNC can be detected through top decay or single top production • Sensitivity according to CMS studies (of top decays) : • t  Zq(CDF Br<0.137, ALEPH Br<17%, OPAL Br<13.7%) • Reconstruct t  Zq  (l+l-)j • Sensitivity to Br(t  Zq) = 1,6 X 10-4 (100 fb-1) • t  q(CDF Br<0.032) • Sensitivity to Br(t  q) = 2,5 X 10-5 (100 fb-1) • t  gq • Difficult identification because of the huge QCD bakground • One looks for “like-sign” top production (ie. tt) • Sensitivity to Br(t  gq) = 1,6 X 10-3 (100 fb-1) Marina Cobal - HCP2004

  23. FCNC • In general, the LHC will improve by a factor of at least 10 the Tevatron sensitivity to top-quark FCNC couplings • LC has smaller statistics but also smaller background • For anomalous interactions with a gluon the LHC has an evident advantage Marina Cobal - HCP2004

  24. LHC: tWbZ rare decay • Studied at LHC: Interesting: BR depends strongly on Mtop • Since Mtop~MW+Mb+MZ • With present error mt  5 GeV, BR varies over a factor  3 • B-jet too soft to be efficiently identified   “semi-inclusive” study for a WZ near threshold, with Z  l+l-and W ->jj • Requiring 3 leptons reduces the Z+jets background • Sensitivity to Br(t  WbZ)  10-3 for 1 year at low lumi. • Even at high L can’t reach SM predictions ( 10-7 -10-6) G. Mahlon hep-ph/9810485 G(tWbZ)/G(tWb) M(top) (GeV) Marina Cobal - HCP2004

  25. Radiative top production Radiative top decay LHC: Top Charge determination • Can we establish Qtop=2/3? • Currently cannot exclude exotic possibility Qtop=-4/3 • Assign the ‘wrong’ W to the b-quark in top decays • tW-b with Qtop=-4/3 instead of tW+b with Qtop=2/3 ? • Technique: • Hard  radiation from top quarks • Radiative top production, pptt cross section proportional to Q2top • Radiative top decay, tWb • On-mass approach for decaying top: two processes treated independently • Matrix elements havebeen calculated and fed intoPythia MC Marina Cobal - HCP2004

  26. LHC: Top Charge determination • Yield of radiative photons allows to distinguish top charge • Determine charge of b-jet andcombine with lepton • Use di-lepton sample • Investigate ‘wrong’ combination b-jet charge and lepton charge • Effective separation b and b-bar possible in first year LHC • Study systematics in progress 10 fb-1 One year low lumi events pT() Marina Cobal - HCP2004

  27. e+/+ + top LHC: Top spin correlations • In SM with Mtop175 GeV, (t)  1.4 GeV » QCD • Top decays before hadronization, and so can study the decay of ‘bare quark’ • Substantial ttbar spin correlations predicted in pair production • Can study polarization effects through helicity analysis of daughters • Study with di-lepton events • Correlation between helicity angles + and -for e+/+ and e-/- <CosΘ+ · CosΘ-> <CosΘ+ · CosΘ-> No helicity correlation With helicity correlation Marina Cobal - HCP2004

  28. Able to observe spin correlations in parameter C 30 fb-1 of data: ± 0,035 statistical error ± 0,028 systematic error 10 statistical significance for a non-zero value with 10 fb-1 Top spin correlations 30 fb-1 <CosΘ+ · CosΘ-> • For the LC case one can find a top spin quantization axis in which there • will be very strong spin correlations . Detailed studies, both at the ttbar • threshold and in the continuum region remain to be done. Marina Cobal - HCP2004

  29. Direct determination of the tWb vertex (=Vtb) Discriminants: - Jet multiplicity (higher for Wt) More than one b-jet (increase W* signal over W- gluon fusion) 2-jets mass distribution (mjj ~ mW for the Wt signal only) Three production mechanisms at LHC: Main Background [xBR(W→ℓ), ℓ=e,μ]: tt σ=833 pb [ 246 pb] Wbbσ=300 pb [ 66.7 pb] Wjjσ=18·103 pb [4·103 pb] LHC: Single top production 1) Determination of Vtb 2) Independent mass measurement 3) Opportunity to measure top spin pol. 4) May probe FCNC +16.6 Wg fusion: 245±27 pb S.Willenbrock et al., Phys.Rev.D56, 5919 Wt: 62.2 pb A.Belyaev, E.Boos, Phys.Rev.D63, 034012 W* 10.2±0.7 pb M.Smith et al., Phys.Rev.D54, 6696 -3. 7 Wg [54.2 pb] Wt [17.8 pb] W* [2.2 pb] Marina Cobal - HCP2004

  30. LHC: Single top results • Detector performance critical to observe signal • Fake lepton rate • b and fake rate id  • Reconstruction and vetoing of low energy jets • Identification of forward jets • Each of the processes have different systematic errors for Vtb and are sensitive to different new physics • heavy W’  increase in the s-channel W* • FCNC gu  t  increase in the W-gluon fusion channel • Signal unambiguous, after 30 fb-1: • Complementary methods to extract Vtb • With 30 fb-1 of data, Vtb can be determined to %-level or better(experimentally) Marina Cobal - HCP2004

  31. e+ e-  e+bt, ebt Single top at LC • Cross section calculated to LO at e+e-, gg and ge collision modes, including various beam polarizations • Recently calculated NLO corrections in the ge case, well under control • Production in ge collisions is of special interest • Rate is smaller than the top pair rate in e+e- only by a factor of 1/8 at 500-800 GeV energies. • It becomes the dominant LC process for top production at a multi-TeV LC • Direct Vtb measurement: • Same precision as LHC in the e+e- option. • Can arrive to 1% for a polarized ge collider. • Improved accuracy in |Vtb| could be input for LHC • Measure b-quark distribution function in proton (or be used as consistency check for new interactions) Marina Cobal - HCP2004

  32. Few final thoughts… • e+-e- collisions at 0.5-1 TeV • Kinematics: • can use momentum conservation • Better defined initial state • Background smaller than LHC • Not sure yet IF, WHEN, WHERE it will be built • LHC pp collision at 14 TeV • Kinematics: • can use PT conservation • Composite nature of protons  Underlying events, not fixed • Strongly interacting particle •  Large QCD background • Under construction Marina Cobal - HCP2004

  33. Interplay between LHC and LC • Not much interaction between the LHC and LC communities up to short time ago • In 2002 a LHC/LC study group was formed first in Europe and then soon it took a worldwide character • Working Group contains 116 members from among Theorists, CMS, ATLAS, Members of all the LC study Groups + Tevatron contact persons. • Document in preparation: www.ippp.dur.ac.uk/~georg/lhclc Electroweak and QCD precision physics E. Boos, A deRoeck, S. Heinemeyer, W.J. Stirling. Marina Cobal - HCP2004

  34. ATLAS cavern CMS yoke LHC is a reality now: Huge construction activities going on!! Marina Cobal - HCP2004

  35. What is left before the LHC starts? • Cover topics still open: cross section, couplings, exotic, resonances, • Define a strategy for validation of the MC input models (e.g: UE modeling and subtraction, jet fragmentation properties, jet energy profiles, b-fragmentation functions..) see M. Mangano talk at IFAE 2004 • Explore the effects of changing detector parameters in evaluating the top mass. • Perform commissioning studies with top events • Contribute to simulation validation • … Marina Cobal - HCP2004

  36. Determination MTop in initial phase Use ‘Golden plated’ lepton+jet Selection: Isolated lepton with PT>20 GeV Exactly 4 jets (R=0.4) with PT>40 GeV Reconstruction: Select 3 jets with maximal resulting PT Signal can be improved by kinematic constrained fit Assuming MW1=MW2 and MT1=MT2 LHC: Commissioning the detectors • Calibrating detector in comissioning phase • Assume pessimistic scenario: • -) No b-tagging • -) No jet calibration • -) But: Good lepton identification No background included Marina Cobal - HCP2004

  37. Signal plus background at initial phase of LHC Most important background for top: W+4 jets Leptonic decay of W, with 4 extra ‘light’ jets Alpgen, Monte Carlohas ‘hard’ matrix element for 4 extra jets(not available in Pythia/Herwig) LHC: Commissioning the detectors ALPGEN: W+4 extra light jets Jet: PT>10, ||<2.5, R>0.4 No lepton cuts Effective : ~2400 pb L = 150 pb-1 (2/3 days low lumi) With extreme simple selection and reconstruction the top-peak should be visible at LHC measure top mass (to 5-7 GeV) give feedback on detector performance Marina Cobal - HCP2004

  38. Conclusions • Precise determination of Mtop is crucial for EW physics: • Precision tests, constraints on Higgs sector, sensitivity to new physics • Challenge to get Mtop ~ 1 GeV with LHC, and ~ 100 MeV with LC • Confirmation that top-quark is SM particle and search for deviation from SM • Measure Vtb, charge, CP, spin, decays • Many precision measurements from LC • Use top quark for the LHC detectors commissioning • Interplay between LC and LHC could be as useful as it was for LEP+SLC+Tevatron Marina Cobal - HCP2004

  39. BACKUP SLIDES

  40. LEP+SLD: VCKM (4) UA2+Tevatron: s(1) NuTeV: predictions GF (1) SM APV: mfermions (9) (down to 0.1% level) mbosons (2) eeqq l.e.: What we know.. mH No observable directly related to mH. However the dependence can appear through radiative corrections. tree level quantities changed , r = f [ln(mH/mW), mt2] The uncertainties on mt, mW are the dominating ones in the electroweak fit By making precision measurements (already interesting per se): • one can get information on the missing parameter mH • one can test the validity of the Standard Model Marina Cobal - HCP2004

  41. LC Timeline • . Graphically summarized by Jae Yu Marina Cobal - HCP2004

  42. LC Machines • BASELINE MACHINE • ECM of operation 200-500 GeV • Luminosity and reliability for 500 fb-1 in 4 years • Energy scan capability with <10% downtime • Beam energy precision and stability below about 0.1% • Electron polarization of > 80% • Two IRs with detectors • ECM down to 90Gev for calibration • UPGRADES • ECM about 1 TeV • Allow for ~1 ab-1 in about 3-4 years http://www.fnal.gov/directorate/ icfa/LC_parameters.pdf Marina Cobal - HCP2004

  43. Rare SM top decays • Direct measurement of Vts, Vtdvia decays tsW, tdW • Decay tbWZ is near threshold (mt~MW+ MZ+mb)  BRcut(t bWZ)  610-7 (cut on m(ee) is 0.8 MW) • Decay tcWW suppressed by GIM factorBR(t cWW) ~ 110-13 • If Higgs boson is light: tbWH • FCNC decays: tcg, tc, tcZ(BR: 510-11 , 510-13 , 1.310-13 ) • Semi-exclusive t-decays tbM (final state 1 hadron recoiling against a jet: BR(t b)  410-8, BR(t bDs)  210-7) Marina Cobal - HCP2004

  44. Signal Signal ttH ttH tt tt topHq • Various approaches studied • Previously: ttbarHq Wb(b-bbar)j(lb) for m(H) = 115 GeV • Sensitivity to Br(t  Hq) = 4.5 X 10-3(100 fb-1) • New results for: • t tbarHq WbWW*q Wb(l lj) (lb) • ≥ 3 isolated lepton with pT(lep) > 30 GeV • pTmiss > 45 GeV • ≥ 2 jets with pT(j) > 30 GeV, incl. ≥ 1 jet con b-tag • Kinematical cuts making use of angular correlations • Sensitive to Br(t  Hq) = 2.4 X 10-3 for m(H) = 160 GeV (100 fb-1) Marina Cobal - HCP2004

  45. Non-SM Decays of Top • 4thfermion family Constraints on Vtqrelaxed: • Supersymmetry (MSSM) • Observed bosons and fermions would have superpartners  2-body decays into squarks and gauginos (t  H+ b ) • Big impact on 1 loop FCNC • two Higgs doublets • H LEP limit 77.4 GeV (LEP WG 2000) • Decay t  H+ b can compete with t  W+ b • 5 states (h0,H0,A0,H+,H-) survive after giving W & Z masses • H couples to heaviest fermions  detection through breakdown of e / m / t universality in tt production Marina Cobal - HCP2004

  46. Continuous jet algorithm Reduce dependence on MC Reduce jet scale uncertainty Repeat analysis for many cone sizes R Sum all determined top mass:robust estimator top-mass Determining Mtop from (tt)? huge statistics, totally different systematics But: Theory uncertainty on the pdfs kills the idea 10% th. uncertainty  mt  4 GeV Constraining the pdf would be very precious… (up to a few % might not be a dream !!!) Alternative methods • Luminosity uncertainty then plays the game (5%?) Luminosity uncertainty then plays the game (5%?) Marina Cobal - HCP2004

  47. Use the events where both W’s decay leptonically (Br~5%) Much cleaner environment Less information available due to two neutrino’s Sophisticated procedure for fitting the whole event, i.e. all kinematical info taken into account (cf D0/CDF) Compute mean probability as function of top mass hypothesis Maximal probability corresponds to top mass Top mass from di-leptons 80000 events (tt) = 20 % S/B = 10 • Selection: • 2 isolated opposite sign leptons • Pt>35 and Pt>25 GeV • 2 b-tagged jets • ETmiss>40 GeV Mean probability Marina Cobal - HCP2004 mass

  48. Use events where both W’s decay hadronically (Br~45%) Difficult ‘jet’ environment (QCD, Pt>100) ~ 1.73 mb (signal) ~ 370 pb Perform kinematic fit on whole event b-jet to W assignment for combination that minimize top mass difference Increase S/B: Require pT(tops)>200 GeV Top mass from hadronic decay • Selection • 6 jets (R=0.4), Pt>40 GeV • 2 b-tagged jets • Note: Event shape variables like HT, A, S, C, etc not effective at LHC (contrast to Tevatron) 3300 events selected: (tt) = 0.63 % (QCD)= 2·10-5 % S/B = 18 Marina Cobal - HCP2004

  49. j2 j1 b-jet Mtop t High Pt sample • The high pT selected sample deserves independent analysis: • Hemisphere separation (bckgnd reduction, much less combinatorial) • Higher probability for jet overlapping • Use all clusters in a large cone R=[0.8-1.2] around the reconstructed top- direction • Less prone to QCD, FSR, calibration • UE can be subtracted Mtop Statistics seems OK and syst. under control R Marina Cobal - HCP2004

  50. Calibration demands: Ultimately jet energy scale calibrated within 1% Uncertainty on b-jet scale dominates Mtop: light jet scale constrained by mW At startup jet-energy scale known to lesser precision ±10% MTop MTop Scale light-jet energy Scale b-jet energy Jet scale calibration Uncertainty on light jet scale:Hadronic 1%  Mt < 0.7 GeV 10%  Mt = 3 GeV Uncertainty On b-jet scale:Hadronic 1%  Mt = 0.7 GeV 5%  Mt = 3.5 GeV 10%  Mt = 7.0 GeV Marina Cobal - HCP2004

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