1. Top Physics in ATLAS M. Cobal, University of Udine and INFN Trieste CSN1, April 2 2007

2. Talk outline Goals Show the planned strategy to reach early identification of a top signal Show organization and resources Outline Early identification of top events in ATLAS  Relevant backgrounds  Effects on ATLAS potential of conditions at detector startup No b-tagging Problems in EM  Top sample as calibration tool Towards a precise M top reconstruction ATLAS organization for top analysis Data flow and resources for analysis Italian situation Caveat: Results here are from (very) recent MC data production for the CSC notes. Analyses undergoing!

3. What do we know about the top quark? The top quark completes the three family structure of the SM It is massive Spin=1/2, Charge=+2/3, Isospin=+1/2 t  bW Large  =1.42GeV (m b,M W,a s,EW corr.) Short lifetime  had =  QCD -1 >>  decay “t-quarks are produced and decay as free particles” NO top hadrons  M/M <2% - 4/3 excluded @ 94%C.L.(D0) c  <52.5  m @95%C.L.(CDF) Not directly The TEVATRON is probing better than ever the top sector… The LHC will allow precision measurements of Top Quark Physics ~100%, FCNC: probed at the 10% level Not directly

4. 10% 90% Production: σ tt (LHC) ~ 830 ± 100 pb  1 tt/sec @ L=10 33 Top quark production at the LHC Cross section LHC = 100 x Tevatron Background LHC = 10 x Tevatron t t Final states: t  Wb ~ 1 W  qq ~ 2/3 W  l ν ~ 1/3 1) Fully-hadronic (4/9) 6 jets 2) Semi-leptonic(4/9): 1l + 1ν + 4 jets 3) Fully-leptonic (1/9): 2l + 2ν + 2 jets Golden channel (l=e,μ)  2.5 million events/year

5. 1. Essential for commissioning detector and tools: jet scale, b-tagging calibration 2. Fundamental for EW measurements  the top quark is interesting per se(m t ~190m p )  m t,  t, q t,  V tb ,  tt, BR t, tt, pdfs  m t can greatly help in the indirect constraint of the Standard Model (and new physics !) Production cross-section t mass W, t helicities Decay modes Light jet scale b-tagging 3. Fundamental for new physics search  both production and decay: X  tt, t  X, ttX  larger couplings with Higgs –new physics?-  top is background to many search channels Top at the LHC is important!

6. How many events at the beginning ? 10 pb -1  1 month at 10 30 and < 2 weeks at 10 31,  =50% 100 pb -1  few days at 10 32,  =50% Assumed selection efficiency: W  l, Z  ll : 20% tt  l +X :1.5% (no b-tag, inside mass bin) + lots of minimum-bias and jets (10 7 events in 2 weeks of data taking if 20% of trigger bandwidth allocated) 1 fb -1 Similar statistics to D0/CDF

7. Triggering.. Trigger efficiency: an issue at hadronic machines (huge QCD cross-section) Inclusive triggers allow to explore as much as possible the wide range of standard physics final states Trigger object P T /E T HLT thresholds (GeV) Rates (Hz) Muon6, 2040 Electron2520 Single Jet 2, 3, 4 Jets 160, 120, 65, 5010 First level Calo and muons Isolated lept., many jets and MET HLT Menus for 10 31 (and 10 33 ) Under study. CSC production just becomes available. Also b/  tagging possible with the inclusion of tracking devices in the 2nd level trigger Will become more complex with time and after inclusion of prescaled, calibration, monitor triggers. Illustrative triggers @ 10 31 for top

8. Which detector performance on day-one ? Based on detector construction quality, test-beam results, cosmics, simulation Ultimate statistical precision achievable after few weeks of operation. Then face systematics…. E.g. : tracker alignment : 100  m (1 month)  20  m (4 months)  5  m (1 year) ? Expected performance day 1 Physics samples to improve ECAL uniformity ~ 1% Minimum-bias, Z  ee e/  scale ~ 2 % Z  ee HCAL uniformity ~ 3 % Single pions, QCD jets Jet scale < 10% Z (  ll) +1j, W  jj in tt events Tracking alignment 20(100)-200  m in R  ? Generic tracks, isolated , Z  m

9. Backgrounds that you worry about W+4jets (largest bkg)  Problematic if 3 jets line up M top and W + remaining jet also line up to M top  Cannot be simulated reliably by Pythia or Herwig. Requires dedicated event generator AlpGen  Ultimately get rate from data Z+4 jets rate and MC (Z+4j)/(W+4J) ratio  Vast majority of events can be rejected exploiting jet kinematics. QCD multi-jet events  Problematic if one jets goes down beampipe (thus giving MET) and one jets mimics electron  Cross section large and not well known, but mostly killed by lepton ID and MET cuts.  Rely on good lepton ID and MET to suppress W  l e-,0e-,0

10. Non-W (QCD-multijet) background Not possible to realistically generate this background  Crucially depends on Atlas’ capabilities to minimize mis-identification and increase e/  separation This background has to be evaluated from data itself  E.g. method developed by CDF during run-1:  Rely now on e/  separation of 10 -5 Use missing ET vs lepton isolation to define 4 regions: A. Low lepton quality and small transverse M w +MET Mostly non-W events (i.e. QCD background) B. High lepton quality and small transverse M w +MET Observation reduction QCD background by lepton quality cuts C. Low lepton quality and high transverse M w +MET W enriched sample with a fraction of QCD background D. High lepton quality and high transverse M w +MET W enriched sample, fraction of QCD estimated by (B·C)/(A·D)

11. Background from QCD multi-jet Rough background estimate from QCD multi-jet events  Can generate a fake electron or a real non-prompt electron with P T >20 and MET>20 GeV Rate of fake/non-prompt electrons  Use large jets sample: look for events with ‘extra’ reconstructed ‘good’ electron and investigate its origins using MC truth information:  Rate of non-prompt electron found = 3x10 -5 Run through standard selection, omitting requirement on lepton and MET  Instead scale cross section with non-prompt rate just found (3x10 -5 ) multiplied by average jet multiplicity of QCD multijet events with P T >20 (2.77)  Background turns out to be quite low M(jjj)

12. Background events Top physics background Non-W (QCD) W+jets, Wbbar, Wccbar Wc WW,WZ,ZZ Z   Single top If b-tagging  Mistags or fake tags AlpGen W+ jets samples produced Ex: W+4 jets inclusive Effective  : 455 pb ~ 1.5 fb -1 W+4jet background available

13. Top physics ‘easy’ at the LHC: Top physics with b-tag information Selection: Lepton Missing E T 4 (high-P T )-jets (2 b-jets)  signal efficiency few %  very small SM background ‘Standard’ Top physics at LHC b-tag is important in selection Most measurements limited by systematic uncertainties ‘Early’ top physics at LHC Top signal identification without the use of b-tagging X-sec measurement (  /  ~ 20%, from fast sim, now repeated with full) Top signal (MC@NLO) W+jets background (ALPGEN) Top mass (GeV) Number of Events

14. Top physics without b-tag information  3 jets(R=0.4) P T > 40 GeV 4th jet P T > 20 GeV 1 lepton P T > 20 GeV MET P T > 20 GeV TOP CANDIDATE 1) Hadronic top: Three jets with highest vector-sum p T as the decay products of the top 2) W boson: Two jets in hadronic top with highest momentum in reconstructed jjj C.M. frame. W CANDIDATE Assign jets to W-boson and top-quark: In most pessimistic scenario b-tagging is absent at start Can we then observe the top with few robust selection cuts?

15. Commissioning top analysis Data sets:  Signal: MC@NLO  Background W+4 incl. jets: ALPGEN M top reconstructed  Events selected with closest M jj to nominal M w, within ± 10 GeV M(jjj) 100 pb -1 M(jj) 100 pb -1 is a few days of nominal low-luminosity LHC operation We can easily see top peak without b-tag requirement Udine W+4 jets top

16. Commissioning analysis Looking at 1.5 fb -1  Start with 689949 (no fully hadronic) ttbar Analysis efficiency: about 11%  Start with 683252 W+4 jet events Cross section:   = 834 ± 6 pb (0.8% stat. err.) After Commissioning cuts: 68286 W+jets 77391 ttbar signal S/B = 1,13 S/√B = 296 1.5 fb -1 Udine W+4 jets top

17. Commissioning: Jet MisCalibration PRELIMINARY!! Other systematics under study  due to JES miscalibration < 2.5%

18. Use simple kinematic cuts to improve the top sample purity M tot : Invariant mass of lept+ +jets system Cos  * : Angle between the i-th jet and beam direction in the rest frame of the total event (lept+ + jets) Commissioning: kinematics M tot Cos   * Cos   *Cos   * 1. After M tot cut: 45797 W+jets 63702 top S/B = 1,39 S/√B = 298 2. After Cos  * cut: 18584 W+jets 33431 top S/B = 1,80 S/√B = 245 W+4 jets top

19. Effects of detector problems on M top Example: Effects of dead EM calo HV regions on M top  Argon gap (width ~ 4 mm) is split in two half gaps by the electrode  HV by  η x  φ = 0.2 x 0.2 (or 0.1 x 0.2) sectors, separately in each half gap  There are ~ 33 / 1024 sectors where we may be unable to set the HV on one half gap  multiply energy by 2 to recover Irrealistic hypothesis: suppose that in ~ 33 / 1024 sectors we are unable to set ALL the HV particle

20. 10 5 tt events (~ 1.5 days @ L=10 33 ) Preselection of events: o At least one recontructed e or μ with P T >20 GeV and |η|<2.5 o MET>20 GeV o At least 4 jets with P T >40 GeV and |  <2.5, 2 b-tagged EM clusters Jets Results If the 33 weak HV sectors die (very pessimistic), effects on M top after a crude recalibration are: o Displacement of the peak of the mass distribution: -0.2 GeV M top (no dead regions ) – M top (dead regions)  

21. Light jet energy scale W  jj with full reconstruction: only 2 b-tagged jets, only 2 light jets & 150 GeV < m jjb < 200 GeV ~1.3fb -1 Determine  = E parton /E jet : smear quark 4-momentum taking into account energy and angular resolution, energy correlation. Generate set of template histograms with different energy scales. Fit each template histogram to M jj in the « data », find best  2.  = 1 « Data » Best fit With 1.3 fb -1 can calibrate as a function of E to better than 2%.

22. b-jet identification efficiency Calibrate b-tagging efficiency from data Dominant systematic uncertainty: ISR/FSR jets Study b-tag (performance) in complex events A clean sample of b-jets from top events 2 out of 4 jets in event are b-jets (a-priori) Use W boson mass to enhance purity B-jet identification efficiency: Important in cross-section determination and many new physics searches (like H, ttH)

23. b-jet efficiency: basic method Select using b-tag on hadronic side  Leptonic top b-jet ‘unbiased’ W jets: E T >40, 20 b-veto Hadronic side b-jet: E T >40 b-tag (weight>3) Leptonic side b-jet: E T >20 No tag requirement Select events where both tops have good reconstructed mass  Consider all assignments of jets to tops consistent with the b-tag and W mass requirements  Require hadronic side m jjb to be consistent with top mass  Consider all other jets as candidates for semileptonic top m l j  Mass peak should contain pure b- jets, with sidebands allowing an estimation of residual background Study the distribution of the b- tagging variable in these pure b-jets

24. Numerical results MC@NLO: Numbers of jets selected for 100 pb -1 data: For E T >40 GeV, combined relative error is 8% on  b for 100 pb -1 No background included yet Effects of systematics to be included b-jet E T N jet (jets in bin) N signal (b-jets from MC truth) Purity (Nsig/Njet) b-purity f b (%)  (  b )/  b stat (%) 20-40243560.23 109  8 23 40-803341440.43 99  4 15 80-1201821150.63 96  4 13 120-16081630.78 99  4 14 160+24180.76 102  8 27 PRELIMINARY!!

25. 1 lepton (e, µ) isolated, P T (lepton) > 20 GeV, |  | < 2.5 MET> 20 GeV Jet energy precalibration Jets selection  2 b-jets, P T > 40 GeV, |  | < 2.5   2 light-jets, P T > 40 GeV, |  | < 2.5 Errors dominated by systematics Possible to determine m t @ 1GeV (with L=10fb -1 )  =10.6GeV Top mass reconstruction with 10 fb -1 S/B ~ 100 for a generated top mass = 175 GeV/c 2 : M(top) = 176.1 ± 0.6 GeV/c 2  top  = 11.9 ± 0.7 GeV/c 2 Statistical error for 10 fb -1 : 0.05 GeV/c 2 W + 4 jets ATLAS, full sim.

26. Systematic effects for top physics Almost all SM measurements at LHC dominated by systematic errors. Can be divided into instrumental and from theory/modeling Dominant instrumental uncertainties for top physics: Luminosity: Reasonable goal is 3-5%  measure number of interactions/bunch crossing (HF) and  (pp) (TOTEM) Reconstruction related Jet energy scale need calibrated calorimetry (beam tests, MB, single particles, Z, W…) need jet energy calibration to a few % (with Z(  )+jet) need excellent energy flow (association tracker+calo+muon system) b-tagging efficiency+fake rate use tt for calibration: Lepton identification and energy scale use Z, other mesons. Less crucial than for the W mass measurement Theory related systematics are as important as instrumental ones !

27. Systematics Source of uncertainty Hadronic top  M top (GeV/c 2 ) Kinematic fit  M top (GeV/c 2 ) Light jet energy scale (1 %) 0.2 b-jet energy scale (1 %) 0.7 b-quark fragmentation 0.1 ISR0.1 FSR1.0.5 Combinatorial background 0.1 Total1.30.9 Statistical error0.050.1 PDFs MEs UE, MPI fragmentation PS

28. Top as background for SUSY Top has same signature of SUSY events (high P T jets, MET, possibly isolated leptons) but with softer spectra (gluino and scalar quarks heavier than top). Dominant backgnd for searches with isolated leptons. Top X-sec order of magnitudes larger than “typical” SUSY cross section (say, for 600 GeV squarks). SUSY PRELIMINARY!! 1 fb -1 e + e - or     MET (GeV) Need to know ttbar cross section + high energy tails of MET and jets distributions Data-driven methods use uncorrelated variables with SUSY in a corner of phase space, and estrapolate from control regions to signal region 2 leptons+MET search Milano

29. Other top-ics Top mass in different channels  Dilepton, All hadronic, J/psi SN-ATLAS-2004-040. – 1-10 fb -1 Top polarization SN-ATLAS-2005-052. – 10 fb -1 Single top production SN-ATLAS-2001-007, ATL-PHYS-PUB-2007-005 - 10 fb -1 Non-SM production (X  tt)  resonances in the tt system ATL-PHYS-PUB-2006-033 - 30 fb -1  Anomalous couplings SN-ATLAS-2004-046, ATL-PHYS-PUB-2006-031 Non-SM decay (t  Xb, Xq)  charged Higgs SN-ATLAS-2002-017, SN-ATLAS-2005-050 - 30 fb -1  FCNC t decays: SN-ATLAS-2007-059 (ttbar), ATL-PHYS-PUB-2006-029 (single t) 10 fb -1  R-Parity violating top decays SN-ATLAS-2007-059 Non-SM loop correction  precise measurement of the cross-section Associated production of Higgs  ttH ATL-PHYS-2001-022, ATL-PHYS-2003-024, ATL-PHYS-2004-031, 30 fb -1 ~100 Notes + 10 Scientific Notes

30. Top physics organization in ATLAS Top physics group (started and lead by M. Cobal, until 2003) About 60-70 people attending the meetings  France, Italy and Netherlands between the most active groups Several CSC notes in preparation, under the top flag:  CSC 6: cross section (M. Cobal editor)  CSC 7: top properties  CSC 8: single top  CSC 9: top mass Analysis model: look at Giacomo’s last CSN1 presentation

31. Top physics in Italy Italian involvement:  Ud: CSC 6 (top cross section)  Bo (recent interest, started to work with new data)  Ge (future involvement) B-jets energy calibration (calibration channels, triggers, online b- tagging…) Optimal application of b-tagging for event selection and background rejection (lvbbjj channel, Wbb and Wcc backgrounds…) Strong links with:  Light jets calibration (Pi)  SUSY: ttbar background (Mi)  Higgs: ttbar background (Rm1)  Muon reconstruction (Le, Na, Pv, Rm1)  EM reconstruction (Mi)  Muon performance (CS, LE, LNF, NA, PI, PV, RM1-2-3)

32. Data organization The final data analysis in ATLAS is based on AOD’s Computing Model: A complete AOD data set (200 TByte for a data-taking period of 10 7 s) will be available in the Italian cloud (a copy on Tier1, a copy on the ensemble of Tier2) In addition to AOD’s, groups performing analysis may want on the local Tier 2: local copies of a fraction of the ESD or Raw data for detailed and repeated detector studies For the MC samples is the same, but the AODs are produced in the Tier2s and then copied on the Tier1. Also in this case there will be a double copy in the italian cloud.

33. “Top” data for the CSC notes in Italy For the CSC notes production, only the AODs which have been effectively asked (“subscriptions”) are going to be transferred to the Tier2 Each Tier2 site has subscribed for a max of 25% of the whole AODs (10M evts, 4 TB). Subscriptions are centralized and are not submitted by single users or groups. Currently, the relevant samples for top analysis are in: MILANO (Tier2 s.j) T1_McAtNlo* pythia_W*, pythia_Z* AcerMCtt* AlpgenJimmyW* ROMA(Tier2) *ww* *zz* *WZ* *Zbbar* NAPOLI (Tier2) pythia_W* AlpgenJimmyW* ttbar, McAtNlo 600k 1420 pb-1 240 GB ttbar, AcerMC 200k 460 pb-1 80 GB W+jets, Alpgen 130k 100 pb-1 50 GB

34. Conclusions Early (commissioning) signal detectable without b-tagging Top quarks produced by the millions at the LHC:  Low background: measure top quark properties Top quarks are THE calibration signal for complex topologies:  Most complex SM candle at the LHC  Vital inputs for detector operation and SUSY background ■ Top quarks pair-like events … window to new physics:  FCNC, SUSY, MSSM Higgses, Resonances, … ■ Italy at the moment in leading position. No big problems found for data storage and distribution

35. Backup

36. Expected statistics @ LHC Data takingLuminosity (cm -2 s -1 ) Integrated luminosity (fb -1 ) Number of inclusive  t t events Very beginning (summer 2007) 10 32 10 days : 0.1≈ 80 000 Low luminosity (2008) 10 33 100 days : 10≈ 8 000 000 High luminosity (2010) 10 34 100 days : 100≈ 80 000 000

37.  all electromagnetic energy scale calorimeter cell signals are collected into projective towers, noise cancellation is applied at this level;  jet finding is run on towers, resulting in electromagnetic energy scale calorimeter tower jets;  cell signal weights based on cell energy density and location are applied to correct signals for e/h ≠ 1, dead material losses, leakage and B field effect (cone 0.7 is used to obtain weights);  additional correction factor dependent on E t and η corrects for jets in cracks and for different jet algorithms (cone0.4, K T 0.4, K T 0.6) → jets are calibrated to particle level – linearity<2% 30 GeV < p T <1.5 TeV – resolution at |  |<0.7  (E)/E=65%/√E 2%. Expected precision on JES @ LHC start 5%-10%.  additional corrections (parton jet scale) derived from W→jj, photon/Z+jet(s) could be applied → careful, potential biases due to collision physics environment! → various methods for calibration and JES validation are under study. calorimeter domain jet reconstruction domain physics analysis domain Tower Building ( ΔΔ × ΔΔ =0.1×0.1,non-discriminant) CaloCells (em scale) CaloTowers (em scale) Calorimeter Jets (em scale) Jet Finding (cone R=0.7,0.4;Fast KT) Jet Based Hadronic Calibration (“H1-style” cell weighting in jets etc.) Calorimeter Jets (fully calibrated had scale) Physics Jets (calibrated to particle level) Jet Energy Scale Corrections ( Dead Material,algorithm effects,etc.) Refined Physics Jet (calibrated to parton level) In-situ Calibration (underlying event,physics environment,etc.) ProtoJets (E>0,em scale) Tower Noise Suppression (cancel E<0towers by re-summation) Jet calibration

38. Jet resolution (ATLAS) b-tagging performances (ATLAS) A few words on jet performances  E /E = 60-80% /  E + 6-8 % (  E ≈ 9 GeV @ 100 GeV) Typical b-tagging efficiency = 60 %  Light jet rejection ~ 200

39. M top in the lepton + jets channel Principle Reconstruction of the hadronic W Invariant mass m jj for events with only 2 light jets: Choice of the light jet pair and rescaling:  2 based on M(W). Minimisation  choice of the light jet pair (j 1, j 2 ) and determination of the rescaling factors (  1,  2 ) reconstruction of the hadronic scaled W, kept as candidate if |M(W)–80.4|  2  W = 79.6 ± 0.4 GeV/c 2  jj = 8.8 ± 0.5 GeV/c 2 We select the hadronic W candidates in a mass window of ± 5  jj around ATLAS (full sim.)

40. Principle (cont.) Choice of the b-jet : b-jet giving the top of maximum P T Reconstruction of the resulting top mass for a generated top mass = 175 GeV/c 2 : M(top) = 176.1 ± 0.6 GeV/c 2  top  = 11.9 ± 0.7 GeV/c 2 Statistical error for 10 fb -1 : 0.05 GeV/c 2 Warning: expect a contamination due to tt  jjb jjb events Wrong b or W Wrong W ATLAS (MC@NLO and full sim.) M top in the lepton + jets channel

41. Performances Efficiency (%) (wrt semil. events) W purity (%)b purity (%)top purity (%) Full window2.70 ± 0.0556.0 ± 0.963.2 ± 0.940.5 ± 0.9 ± 3  (M top ) 1.82 ± 0.0469.1 ± 0.875.8 ± 0.858.6 ± 0.8 64000 events @ 10 fb -1 M top in the lepton + jets channel

42. Principle Very clean channel (background negligible) Indirect mass measurement (2 neutrinos) ■ Event selection : 2 leptons of opposite charge ( p T > 20 GeV/c, |h| < 2.5) MET > 40 GeV 2 b-jets (p T > 25 GeV/c, |h| < 2.5) Final state reconstruction: S et of 6 equations based on kinematic conservation laws, plus assumption of the top mass value More than one solution  compute weights based on kinematic MC distributions (cos  * t, E, E bar ) Keep the solution with highest weight M top in the di-leptons channel

43. Top mass measurement Compute this optimal weight for several input top masses  mean weight for all events, for a given m top M top estimator corresponds to the maximum mean weight  = 6.5 %  20 000 events @ 10 fb -1  M stat = 0.04 GeV/c 2 Systematic errors mean weight M top ATLAS, fast sim.

44. M top in the all hadronic channel Principle Advantage : full kinematic reconstruction of both sides Disadvantage: huge QCD multijet background S/B = 10 -8 ■ Event selection : ■ ≥ 6 jets with P T (j) > 40 GeV, |  | < 3 ■ ≥ 2 jets with b-tag, |  | < 2.5  S/B = 1/19 Final state reconstruction (kinematic fit): ■ 2 W reconstruction : choice of two light-jet pairs (  2, based on M W PDG constraint)  S/B = 1/3 Association of both W candidates to the right b-jet: (  2, based on m t constraint: m t1 = m t2 ) Top mass window (130-200 GeV/c 2 )  S/B = 6 Improvement : sample of events with P T (2 tops) > 200 GeV  S/B = 18

45. Performances  = 0.08 %  3300 events @ 10 fb -1  M stat = 0.18 GeV/c 2 Systematic errors: total systematic error of the order of 3 GeV/c 2 (FSR) QCD bkg ATLAS, fast sim. Source of uncertainty  m top (GeV/c 2 ) Light jet energy scale0.8 b-jet energy scale0.7 b-quark fragmentation0.3 ISR0.4 FSR2.8 TOTAL3 M top in the all hadronic channel

46. New physics: Resonances in M tt Structure in M tt - Interference from MSSM Higgses H,A  tt (can be up to 6-7% effect) Cross section (a.u.) M tt (GeV) Resonances in M tt Resonance at 1600 GeV # events Z’, Z H, G (1), SUSY, ? M tt (GeV) 400 GeV 500 GeV 600 GeV Gaemers, Hoogeveen (1984) ATLAS  s < 10 -23 s  no ttbar bound states within the SM Many models include the existence of resonances decaying to ttbar SM Higgs, MSSM Higgs, Technicolor Models, strong ElectroWeak Symmetry Breaking, Topcolor

47.  Study of a resonance Χ once known σ Χ, Γ Χ and BR(Χ→tt)  Assume detector resolution > Γ Χ  Excellent experimental resolution in mass, ranging from 3% to 6% ! Reconstruction efficiency for the semileptonic channel:  20% m tt =400 GeV  15% m tt =2 TeV  xBR required for a discovery 1 TeV  Shown sensitivity up to a few TeV Resonances in a tt system m tt (GeV) Rsonance at 1600 GeV Resolution m(tt) Study the detector sensitivity in an inclusive way: 5555 fast-sim

48. Single top @ LHC Electroweak top production Three different Processes (never observed yet) Powerfull Probe of V tb ( dV tb /V tb ~few% @ LHC ) t-channel Wt-channel W* (s-channel)  ~ 250 pb  ~70pb  ~ 10 pb V tb Probe New Physics Differently: ex. FCNC affects more t-channel ex. W´ affects more s-channel [ PRD63 (2001) 014018]

49. Cross Sections

50. Single top production Common selection 1 lepton, pT>25GeV/c High Missing E T  2 jets (at least 1 b-jet) (ATL-PHYS-PUB-2006-014) L=30 fb -1 Separate Channels by (N j,N b ) in final state: (  <1.5%) t-channel: Stat: 7000 events (S/B=3) Syst: dominated by E b-jet and Lum. Error Back: tt, Wbb and W+jets (N j =2,N b =1) Wt-channel: Stat: 4700 events,  ~1% (S/B=15%) (  /  ~ 4%) ( N j =3,N b =1) s-channel: Stat: 1200 events for tb (S/B=10%) Syst: E b-jet, Lum. Error, back X-section Back_t-channel, tt  7-8%) (N j =2,N b =2)

51.  (t L t L ) +  (t R t R ) -  (t L t R ) -  (t R t L )  (t L t L ) +  (t R t R ) +  (t L t R ) +  (t R t L ) A= l +, t  lq q t Other angular distributions: A D (LO) A D (NLO) -0.217 -0.237 SM: A(LO) A(NLO) 0.319 0.326 Although t and t are produced unpolarized their spins are correlated New Physics affects A a X =spin analysing power of X SM: 1 dN 1 N dcos  2 ( 1 – A D a X a X´ cos  ) = Top spin correlation (Eur.Phys.J.C44S2 2005 13-33) Semileptonic + Dileptonic Syst (E b-jet,m top,FSR) ~4% precision -0.29 0.42 SM M tt <550 GeV  0.008  0.010 ADAD  0.014  0.023 A Error (±stat ±syst)

52. A) Test the t  bW decay vertex Measure W polarization (F 0, F L, F R ) through lepton angular distribution in W cm system: Semilep. + Dileptonic Syst ( E b-jet,m top,FSR )  F 0 / F 0 ~ 2% ;  F R ~ 0.01 0.000 (m b =0) 0.297 0.703 SM  0.003  0.024FLFL  0.003  0.012FRFR  0.004  0.015F0F0 Error (±stat ±syst) (M t =175 GeV) ( Eur.Phys.J.C44S2 2005 13-33 ) L=10fb -1 Probing the Wtb vertex (1/  )d  /dcos (  l *)

53. B) Anomalous Couplings in the t  bW decay Angular Asymmetries: A FB, A + and A - A FB A+A+ A-A- cos(  l *) A FB [t=0] A ± [t= (2 2/3 -1)] ± SM(LO): (PRD67 (2003) 014009, m b ≠0) Probing the Wtb vertex

54. 1  Results : B) Anomalous Couplings in the t  bW decay SM(LO):  L =0.423  R =0.0005 (m b ≠0) L=10fb -1 Probing the Wtb vertex

55. Top quark FCNC decay GIM suppressed in the SM Higher BR in some SM extensions (2-Higgs doublet, SUSY, exotic fermions) 3 channels studied: BR in SM2HDMMSSMR SUSYQS t  qZ ~10 -14 ~10 -7 ~10 -6 ~10 -5 ~10 -4 tqtq ~10 -14 ~10 -6 ~10 -9 t  qg ~10 -12 ~10 -4 ~10 -5 ~10 -4 ~10 -7

56. Results BR 5  sensitivity Expected 95% CL limits on BR (no signal) Dominant systematics: M T and  tag < 20% t  qZtqtq t  qg L = 10 fb -1 5.1x10 -4 1.2x10 -4 4.6x10 -3 L = 100 fb -1 1.6x10 -4 3.8x10 -5 1.4x10 -3 t  qZtqtq t  qg L = 10 fb -1 3.4x10 -4 6.6x10 -5 1.4x10 -3 L = 100 fb -1 6.5x10 -5 1.8x10 -5 4.3x10 -4

57. Present and future limits Topological likelihood for three channels Resulting 95% CL limits t → qZ SM bck signal t → q  t → qg  With 10 fb -1 already 2 orders of magnitude better than LEP/HERA

58. H ±  tb Fast simulation 4 b-jets analysis No systematics (apart uncertainty on background cross sec) Runninng m b B-tagging  static L = 30 fb -1