1. Fabrice Hubaut (CPPM) Top physics at LHC with tt events 1 Fabrice Hubaut (hubaut@in2p3.fr) CPPM/IN2P3–Univ. de la Méditerranée (Marseille, FRANCE) On Behalf of the ATLAS and CMS Collaborations Rencontres de Moriond 2006, QCD session, March 18-25

2. Fabrice Hubaut (CPPM) Top physics at LHC with tt events 2 5 orders of magnitude Motivations for top quark physics  Special role in the EW sector and in QCD  Heaviest elementary particle known  Yukawa coupling close to 1.0  Top and W masses constrain the Higgs mass  Short lifetime (<t QCD ): unique window on bare quarks  A tool for precise SM studies  Special role in various SM extensions through EWSB  New physics might be preferentially coupled to top  Non-standard couplings between top and gauge bosons  New particles can produce / decay to tops  A sensitive probe to new physics  Special interest even if it is just a «normal» quark  A major source of background for many searches  A tool to understand/calibrate the detector, all sub-detectors involved

3. Fabrice Hubaut (CPPM) Top physics at LHC with tt events 3 Top properties scorecard We still know little about the top quark, limited by Tevatron statistics Mass precision <2% Electric charge ⅔ -4/3 excluded @ 94% C.L. (preliminary) Spin ½not really tested – spin correlations Isospin ½not really tested BR to b quark ~ 100%at 20% level in 3 generations case V – A decayat 20% level FCNCprobed at the 10% level Top width?? First observe single top ! Yukawa coupling??  This leaves plenty of room for new physics in top production and decay  Tevatron run II starts to incisely probe the top quark sector  The LHC will open a new opportunity for precision measurements

4. Fabrice Hubaut (CPPM) Top physics at LHC with tt events 4 tt final states (LHC,10 fb -1 ) Top production and decay at LHC Full hadronic (3.7 M) : 6 jets Semileptonic (2.5 M) : l + + 4jets Dileptonic (0.4 M) : 2l + 2 + 2jets Strong Interaction tt Weak Interaction single top* BR (t  Wb) ~ 100 % in SM and no top hadronisation Tevatron σ ~7 pb 85% qq, 15% gg LHC σ ~850 pb 10% qq, 90% gg Tevatron σ ~3 pb 65%Wg, 30%Wt LHC σ ~300 pb 75%Wg, 20%Wt W-g (0.5 M) : l + + 2jets Wt (0.2 M) : l + + 3jets W* (0.02 M) : l + + 2jets Single top final states (LHC, 10 fb -1 ) W-g fusion W* W t * not observed yet ! W  e  W  e  qq See talk by M. Najafabadi Golden channel (early physics, precision meas.)

5. Fabrice Hubaut (CPPM) Top physics at LHC with tt events 5 Early studies (<1 fb -1 ) M jjj (GeV) L=100 pb -1 (1 day @ 10 33 cm -2 s -1 ) Signal (MC@NLO) W+n jets (Alpgen) + combinatorial  Observation of clean top sample should be very fast  Initial measurement of cross-section and mass  Feedback on detector performance (JES, b-tagging, …) and on MC description  Remarkable topology: t and t central and back-to-back in the transverse plane  Easy to trigger and select Isolated lepton p T > 20 GeV  trigger p T miss > 20 GeV 4 jets p T > 40 GeV 3 jets with highest ∑ p T NO b-TAG !! Full simulation

6. Fabrice Hubaut (CPPM) Top physics at LHC with tt events 6  When performance improve, such as b-tagging (  b  60%, r uds  100, r c  10)  non tt background (W+jets, bb,...) negligible  sel ~ 3%, 80k evts/10 fb -1 S/B~12 (tt   +X) Selection Precision studies (1-10 fb -1 ) 1 isolated lepton p T >20 GeV p T miss >20 GeV ≥4 jets (cone  R=0.4) p T >40 GeV 2 b-tagged jets  High statistics with a few fb -1, measurements limited by systematics  Dileptonic channel also interesting  6 equations (Σp T =0, M lv = M W, M lvb = M t ) with 6 unknowns (p ) Full reconstruction Use W  jj to calibrate light jet energy b with max. p T (jjb) for hadronic top p T miss for p T and M W constraint for p Z Other b for leptonic top:  ~12 GeV Purity of reconstructed tt ~ 70% with  rec ~ 30% combinatorial  ~11 GeV L=10 fb -1  Apply this selection-recons. for Χ-section, mass, polarization studies, …

7. Fabrice Hubaut (CPPM) Top physics at LHC with tt events 7 Top mass (1)  Measurement method (semileptonic)  Kinematic fit event by event using t and t sides M jj = M lv = M W and M jjb = M lvb = M t fit  (M t fit,  2 ) by slices of  2  top mass estimator: m t =M t fit (  2 =0)  This selects well reconstructed b-jets (low effect due to final state radiation or leptonic b-decay)  Results (semileptonic)  m t linear with generated top mass  Statistical error with 10 fb -1 : ~ 0.1 GeV hep-ex/0403021

8. Fabrice Hubaut (CPPM) Top physics at LHC with tt events 8 Top mass (2) Source Error 10 fb -1 b-jet scale (±1%)0.7 Final State Radiation0.5 Light jet scale (±1%)0.2 b-quark fragmentation0.1 Initial State Radiation0.1 Combinatorial bkg0.1 TOTAL: Stat  Syst 0.9  Other methods (invariant 3 jet jjb mass, large p T events,...) give higher systematics but will allow reliable cross-checks  A ~1 GeV accuracy on M t seems achievable with 10 fb -1 at ATLAS/CMS  Systematic errors on m t (GeV) in semileptonic channel  Systematics from b-jet scale (full simulation): 0.9 0.95 1. 1.05 1.1 b-jet miscalibration factor 184 180 176 172 168 Rec. Top mass (GeV) slope=0.7 GeV / % hep-ex/0403021

9. Fabrice Hubaut (CPPM) Top physics at LHC with tt events 9 Top mass (3)  Dileptonic (10 fb -1 )  Need to reconstruct full tt event to assess the 2 momenta  6 equations (Σp T =0, M lv = M W, M lvb = M t )  Assume m t and compute solution probability event by event using MC kinematic distributions  Choose m t with highest mean probability on all events  Systematic uncertainty: ~2 GeV (PDF + b-frag.)  Final states with J/  (100 fb -1 ) Input top mass=175 GeV mean probability Mass hypthesis (GeV)  Correlation between M lJ/  and m t  Low statistics: ~1000 evts/100 fb -1  No systematics on b-jet scale !  Systematic uncertainty: ~1 GeV (b-frag.) Charge identification hep-ex/0403021 hep-ph/9912320 M lJ/ 

10. Fabrice Hubaut (CPPM) Top physics at LHC with tt events 10  Angle between: lepton in W rest frame and W in top rest frame Standard Model (M top =175 GeV) 0.7030.2970.000 W polarization in top decay (1)  Test the top decay (in fully reconstructed tt) with W polarization... Longitudinal W + (F 0 ) Left-handed W + (F L ) Right-handed W + (F R ) NLO0.6950.3040.001 ...measured through angular distribution of charged lepton in W rest frame Sensitive to EWSBTest of V-A structure 1/21 cos  1/N dN/dcos  W+W+ b l+l+ t spin

11. Fabrice Hubaut (CPPM) Top physics at LHC with tt events 11 W polarization in top decay (2) SM Error (±stat ±syst) F0F0 0.703  0.004  0.015 FLFL 0.297  0.003  0.024 FRFR 0.000  0.003  0.012  Systematics dominated by b-jet scale, top mass and final state radiation (FSR)  With 10 fb -1, can measure F 0 with a ~2% accuracy and F R with a precision ~1%  Tevatron expectations (2 fb -1 ): δF 0 stat /F 0 ~12% and δF R stat /F R ~3% Combined results of semilep+dilep 2 parameter fit with F 0 +F L +F R =1 cos  1/N dN/dcos  (M t =175 GeV) hep-ex/0508061 10 fb -1 Semilep.

12. Fabrice Hubaut (CPPM) Top physics at LHC with tt events 12 W polarization in top decay (3) )  From W polarization, deduce sensitivity to tWb anomalous couplings  model independent approach, i.e. effective Lagrangian and 4 couplings (in SM LO ±1   2  limit (stat  syst) on = 0.04  3 times better than indirect limits (B-factories, LEP)  Less sensitive to and already severely constrained by B-factories F0F0 Anomalous coupling

13. Fabrice Hubaut (CPPM) Top physics at LHC with tt events 13 tt spin correlation  Test the top production … t and t are not polarized in tt pairs, but their spins are correlated  … by measuring angular distribution of daughter particles in top rest frame A D =-0.29 M tt <550 GeV =-0.24 top spin ≠ 1/2, anomalous couplings, t  H + b A=0.42 =0.33 Mass of tt system, M tt (GeV)  (a.u.) Tevatron LHC PL B374 (1996)169 SM Error (±stat ±syst) A0.42  0.014  0.023 ADAD -0.29  0.008  0.010 Semilep. + dilep. (10 fb -1 )  Syst. dominated by b-JES, top mass and FSR  ~4% precision on spin correlation parameters  Tevatron expectations (2 fb -1 ):  A stat /A~40% hep-ex/0508061

14. Fabrice Hubaut (CPPM) Top physics at LHC with tt events 14  In top production  Example of resonances decaying to tt, as predicted by various models  Generic analysis for a resonance X with σ Χ, Γ Χ and BR(Χ  tt)  In top decay  Example of t  H + b with subsequent H +   (2<tanβ<40)  Search for excess of  -events or deficit of dilepton events  H + discovery for M H+ <160 GeV with 30 fb -1 Direct search for new particles  xBR required for a discovery σxBR [fb] 1 TeV 830 fb 1.6 TeV resonance combinatorics + tt continuum m tt (GeV) 300 fb -1 30 fb -1 J.Phys.G28 (2002) 2443

15. Fabrice Hubaut (CPPM) Top physics at LHC with tt events 15 Flavor Changing Neutral Currents  Standard Model FCNC are highly suppressed (BR < 10 -13 -10 -10 )  Some models beyond SM can give HUGE enhancements (BR up to 10 -3 )  FCNC could be detected directly through top decay (tt, single top) or anomalous single top production  Any observation would be sign of new physics  ATLAS/CMS 5  sensitivity / 95% CL to FCNC branching ratio in tt events: Process 95% CL (today) LHC 95% CL (10 fb -1 ) LHC 5  (10 fb -1 ) t  Zq ~ 0.1 (LEP) 3·10 -4 5·10 -4 tqtq ~ 0.01 (HERA) 7·10 -5 1·10 -4 t  gq ~ 0.2 (TEV.) 1·10 -3 5·10 -3  improve current limits by ~10 2 -10 3 in 1 year: starts to probe models Reconstruct t  Zq  (l + l - )j Huge QCD background

16. Fabrice Hubaut (CPPM) Top physics at LHC with tt events 16 Conclusions  LHC will be a top factory: 10 7 events already with 10 fb -1  First steps towards precision measurements driven by systematics  Challenge to get top mass ~1 GeV  SM M H constrained to <30%  Test top production and decay e.g. by measuring W polarization ~1-2% and top spin correlation ~4%  anomalous tWb/gtt couplings, t  H + b, FCNC, …  New era of precision measurements in top sector in 3 years from now  Powerful probes in the search for new physics  Prior to precision measurements, a huge effort is needed (2007-2008)  Complete study using full simulations and NLO generators  Understand the detectors and control systematics  Early top signals will help !!

17. Fabrice Hubaut (CPPM) Top physics at LHC with tt events 17 Conclusions Rendez-vous in Moriond 2008 for first top events at LHC

18. Fabrice Hubaut (CPPM) Top physics at LHC with tt events 18 SPARES

19. Fabrice Hubaut (CPPM) Top physics at LHC with tt events 19 LHC statistics SM Process σ (nb)Evts / 10 fb -1 Minimum bias 10 8 ~ 10 15 bb 5 10 5 ~ 10 12 W → e  15~ 10 8 Z → e + e - 1.5~ 10 7 t 0.8~ 10 7 Dibosons 0.2~ 10 6 LHC: pp collisions at √s=14 TeV every 25 ns in 2007 2 phases: 10 33 cm -2 s -1 (initial, 2008-2009), 10 34 cm -2 s -1 (design, >2009)  High statistics at low luminosity  Hard cuts to select clean events  Few pile-up events  SM parameter measurements will be dominated by systematic errors  From Monte Carlo (MC): ISR/FSR, PDF,...  From detector and machine

20. Fabrice Hubaut (CPPM) Top physics at LHC with tt events 20 Utilizing tt events  Light jet energy scale (aim: 1%)  Extrapolation from testbeam data (1998-2004): 5-10%  Improve with in situ calibration (Z+jet, W  jj in tt events)  In situ calibration with tt events  A clean W  jj sample (up to 80%) can be extracted  Shift of W mass peak related to absolute energy scale  extract absolute jet energy scale  (E jet ) from data j1j1 j2j2 b-jet t W  2-3% reachable on absolute scale with 300 pb -1 only before after

21. Fabrice Hubaut (CPPM) Top physics at LHC with tt events 21 Utilizing tt events  b-tagging studies: simple demonstration  An enriched (>80%) sample of b-jets can be extracted  Cut on m(W had ) and m(top had ) masses  Look at b-jet probability for 4 th jet (must be b-jet if all assignments are correct) TOP CANDIDATE W CANDIDATE W+jets (background) ‘random jet’ no b enhancement expected ttbar (signal) ‘always b jet if all jet assignments are OK’ b enrichment expected b-jet probability B-JET CANDIDATE  check/calibrate b-tagging performance with data

22. Fabrice Hubaut (CPPM) Top physics at LHC with tt events 22 b-tagging Light jets b-jets 2D+1D 2D Jet weight b-tagging algorithms: a weight is given to each jet combining signed impact parameters (2D+1D) and secondary vertex reconstruction (mass, number of vertices, …)  b =60% R=230 3D+SVX

23. Fabrice Hubaut (CPPM) Top physics at LHC with tt events 23  Clean channel, easy to trigger on  2 neutrinos in final state  full reconstruction however possible  sel ~ 6%, 20k evts/10 fb -1 S/B~6 (tt   +X) Selection Dileptonic channel 2 isolated leptons with opposite charge, p T >20 GeV p T miss >40 GeV 2 b-tagged jets p T >20 GeV  High statistics with a few fb -1, measurements limited by systematics  Complementary to semileptonic channel Full reconstruction Assume top mass is known 6 equations (Σp T =0, M lv = M W, M lvb = M t ) with 6 unknowns (p ) If >= 1 solution (98%), solution’s probability based on MC kinematic distributions Purity of reconstructed tt ~ 65% with  rec ~ 80%

24. Fabrice Hubaut (CPPM) Top physics at LHC with tt events 24 F 0 =0.699 ± 0.005 F L =0.299 ± 0.003 F R =0.002 ± 0.003 F 0 =0.69 ± 0.03 F L =0.30 ± 0.02 F R =0.01 ± 0.02 F 0 =0.70 ± 0.03 F L =0.29 ± 0.02 F R =0.01 ± 0.02 W polarization: full simulation Good agreement Full sim / Fast sim on W and top kinematics  compute a unique function (from Fast sim.) to correct for cuts and rec. effects  apply it on Fast and Full sim. samples  Very good agreement Full sim / Fast sim 1/N dN/dcos  TopReX – Fast sim.TopReX – Full sim.MC@NLO – Full sim. 10 fb -1 0.7 fb -1 0.5 fb -1 cos  Preliminary

25. Fabrice Hubaut (CPPM) Top physics at LHC with tt events 25 tt spin correlation  Measurement of tt spin correlation (NP B690 (2004) 81) angle btwn spin analyzers direction in the t(t) rest frame angle between daughter and top spin axis s Wbl +,d,sv,u,clej *  (NLO) 0.40-0.401.-0.310.47 In top rest frame, polarisation (S) is measured with angular distributions of daughter: Degree to which its direction is correlated with top spin (spin analyzing power) * lej = least energetic jet in top rest frame

26. Fabrice Hubaut (CPPM) Top physics at LHC with tt events 26 Top charge  Q top =-4/3 (t  W - b instead of t  W + b) ?   Method 1: Measurement of radiative top production and/or decay   (pp  tt  ) is proportional to Q top 2  After selection+reconstruction (10 fb -1 )  (Q=-4/3) >  (Q=2/3)  Method 2: Measurement of daughter particle charge  Associate b-lepton pair from the same top  Compute the charge of b on a statistical basis:  Separate the 2 Q top hypothesis needs less data than Method 1 (~1 fb -1 )  Tevatron (Method 2) :  D0 (360 pb -1 ) excludes Q=-4/3 @ 94% CL (10/2005, not yet published) Q=2/3Q=-4/3 pp  tt  80250 Background 70

27. Fabrice Hubaut (CPPM) Top physics at LHC with tt events 27 Yukawa coupling  σ α g t 2 ·Br(H  bb, WW)  Need separate measurements of Higgs decay branching ratios  Statistical uncertainty on g t ~20% for M H <200 GeV with 30 fb -1 Systematics have to be carefully determined  g t = √2 M t / v ~ 1 : intriguing !!  Most difficult top quark property to measure!  Measurement from associated Higgs production ttH (  bb, WW)

28. Fabrice Hubaut (CPPM) Top physics at LHC with tt events 28 ATLAS/CMS ATLASCMS MAGNET (S) Air-core toroids + solenoid in inner cavity Calorimeters outside field 4 magnets Solenoid Calorimeters inside field 1 magnet TRACKER Si pixels+ strips TRD  particle identification B=2T  /p T ~ 5x10 -4 p T  0.01 Si pixels + strips No particle identification B=4T  /p T ~ 1.5x10 -4 p T  0.005 EM CALO Pb-liquid argon  /E ~ 10%/  E uniform longitudinal segmentation PbWO 4 crystals  /E ~ 2-5%/  E no longitudinal segm entation MUON Air   /p T < 10 % at 1 TeV standalone; larger acceptance Fe   /p T ~ 5% at 1 TeV combining with tracker HAD CALO Fe-scint. + Cu-liquid argon (10   /E ~ 50%/  E  0.03 Brass-scint. (> 5.8  +catcher   /E ~ 100%/  E  0.05

29. Fabrice Hubaut (CPPM) Top physics at LHC with tt events 29 LHC planning 2007 2008 2009 2010 2011 =3 10 30 =5 10 32 L=1 10 33 L=2 10 33 =5 10 33 L=1 10 34