Top Physics: from LHC to ILC Experimental excursus…

1. Top Physics: from LHC to ILCExperimental excursus… M. Cobal, University of Udine ILC in Firenze Firenze, 12-14 Sep 2007

2. Top production LHC ILC e+ (90%) g,Z + e- (10%) tt production cross section at LHC: ~833 pb At √s = 14 TeV tt production cross section at ILC: ~0.6 pb At √s = 500 GeV 2 tt events per second ! 8 millions tt events/year Assuming L =1034 cm-2s 120k tt events/year Assuming L =1034 cm-2s Production sensitive to tg and tZ coupling

3. Why do we need both LHC & ILC? • Two machines have different characters. • Advantage of linear collider: • e+ and e- are elementary particle(well-defined kinematics). • Less background than LHC experiments. • Beam polarization, energy scan. • Complementary performance to LHC in many cases • Will profit of the knowledge gained at LHC ILC LHC

4. BOTTOM jets b-tagging TOP t≈ 0.4 10-24s W n L trigger Top physics at the LHC & ILC DECAY Charged Higgs W helicity Anomalous couplings CKM matrix elements Calibration sample !! PROPERTIES Mass (matter vs. anti-matter) Charge Life-time and width Spin PRODUCTION Cross section Spin-correlations Resonances Xtt Fourth generation t’ New physics (SUSY) Flavour physics (FCNC) kinematic fit (mW) missing energy This data will extend the Tevatron precision reach and allow new possible topics.

5. Top strategy at LHC 1)Top properties and basic SM physics at s = 14 TeV: • Estimate of σtop : interesting even if error is large (first measurement ats = 14 TeV) • Start to tune Monte Carlo • Measure top mass  feedback on detector performance 2)Prepared to observe spectacular effects if present! • Resonances, Rare decays, FCNC • Measure differential cross sections (ds/dpT,ds/dMtt) sensitive to new physics (provides also an accurate test of SM predictions)

6. Top (ele) W+jets Day one at LHC: can we see the top? We will have a non perfect detector: apply a simple selection 100 pb-1 W =2 jets maximising pT W in jjj rest frame Mtop:167.0+-1.8 S/B: 5.8 e = 2.7% Hadronic top=3 jets maximising pT top 4 jets pT> 40 GeV Isolated lepton pT> 20 GeV ETmiss > 20 GeV • No b-tag • Systematics study undergoing • Expected Ds/s ~ 20%

7. A regime: semi-leptonic case More refined selection studied with the aim of applying it to x-section, mass, polarization studies.. Example: CMS NOTE 2006/064 • 1 isolated lepton pT>20 GeV • ≥4 jets ET>30 GeV |h|<2.4 • 2 b-tagged jets • Coverging kin. fit to mW stat total w/o lumi total w lumi esel~ 6.3% S/B~26.7 @5 fb-1Dstt(m)=0.6% (stat)± 9.2% (syst)±5.0%(lumi) Exploiting new topological variables from D0? • Sphericity S and Aplanarity A • Centrality C • HT = • Df(lep,n) • KTmin=min D(h,f) between 2 jets 1fb-1 Not very useful to separate from W+jets after selection

8. Summary of cross-section at LHC • The cross-section has also been extracted from in the di-leptonic and fully hadronic channels here examples from: CMS NOTES 2006-064/ 2006-077

9. Smearing of the partonic cross section Cross section at the ILC • A factor 1000 lower than at LHC • Location of x-sec rise  Mtop shape and normalization  Width and Yukawa coupling • Cross section lineshape can be computed precisely with perturbative methods • Need good knowledge of: • Machine-dependent beam energy spread • Effects of beamstrahlung • Effects of initial state radiation

10. What is Mtop?

11. 1 fb-1 100pb-1 Mtop at LHC: lepton + jets channel • Minimization of c2 • In situ rescaling • Reconstruct mW hadronic • Require 2 b-tagged jets • Efficiency : 3.31 ± 0.03 • S/B = 100 ± 11 • 8320 signal events @ 1 fb-1 Systematic uncertainties: Jet energy scale 1% on light jet  0.2 GeV/c2 on mtop 1% on b-jet  0.7GeV/c2 on mtop ISR/FSR , b-quark fragmentation: Samples under production/understanding <Mtop> = 175.9 ± 0.4 GeV/c2 stop = 10.9 ± 0.4 GeV/c2

12. Mtop at LHC: lepton + jets channel Selection of high pT top quarks pT(top) > 200 GeV/c: • t and t tend to be back-to-back  used as constraint to reduce bkg • 3 jets in 1 hemisphere tend to overlap: collect E in a cone around candidate top • less sensitive to jet calibration. Mass scale recalibration based on hadronic W,

13. PYTHIA 1fb-1 Mtop in Di-lepton and Hadronic channels Dilepton channel:clean but need to reconstruct 2 n’s. Reconstruction via 0C fit assuming mW and 2 equal masses for top mt1=mt2 (6 eq. ,6 unknowns) • The different n solutions are weighted using the SM prediction for the n and n E spectra • The solution with the highest weight is chosen  mtop S/B = 12 - Hadronic channel:full kinematic reconstruction of both sides but huge QCD multijet background: • 6-8 jets, ET>30 GeV • Centrality>0.68,aplanarity>0.024 • ETtot- ET of 2 leading j>148 GeV • 2 b-tagged jets • Best jet pairing obtained from likelihood based mainly on angular distrubution of jets CMS NOTE 2006-077

14. Checking surprises: ttbar mass One of most promising distributions for new physics in ttbar

15. Mtop at ILC • Strategy: perform a scan in √s around threshold region • Compare measurements of various observables to theoretical prediction as f(Mtop, Gtop, as) • 10 point scan, 30 fb-1/point • Assume (Δσtt/σtt)theo~3% • Consider: σtt, peak of PT(top), AFB • Experimental uncertainties: • ΔMtop(1S)=19 MeV • Δαs=0.0012 • ΔΓtop=32 MeV • Ultimate uncertainty on Mtop ≤ 100 due to theoretical uncertainty in mass definition 30 fb-1/point Dmtop=100 MeV

16. Mtop and Gtop measurement at ILC • Improve precision of the fundamental parameters. • Search for new physics in indirect ways. The threshold scan improves the top mass measurement and determines the top width. Top quark threshold scan Deviation of the top width in the Little Higgs model. GLC report C.F.Berger,M.Pelestein,F.Petriello

17. Single top @ LHC

18. Theoretical errors at the LHC (Z.Sullivan, Phys.Rev. D70 (2004) 114012) Less than at Tevatron, since the x-region for the gluon PDFs is better known. Should be similat to the t-channel and to gg→tt

19. 1 lepton, pT>25GeV/c High Missing ET 2 jets (at least 1 b-jet) Common feature: Single top production (ATL-COM-PHYS-2006-002) Separate Channels by (Nj,Nb) in final state: L=30fb-1 Stat: 7000 events (S/B=3) Syst: dominated by Eb-jet and Lum. Error Back: tt, Wbb and W+jets t-channel: (Nj=2,Nb=1) ( ds/s<1.5%) Wt-channel: Stat: 4700 events, e~1% (S/B=15%) ( ds/s ~ 4%) (Nj=3,Nb=1) Stat: 1200 events for tb (S/B=10%) Syst: Eb-jet, Lum. Error, back X-section Back_t-channel, tt s-channel: (Nj=2,Nb=2) (ATL-PHYS-PUB-2006-014) ( ds/s ~7-8%)

20. Single top at ILC

21. Yukawa coupling • Largest coupling of Higgs to fermions (gttH~0.7 vs gbbH~0.02): It may provide clues on the EWSB dynamics • Spectacular signature: 8 jets or one lepton and 6/8 jets. • LHC • Expected accuracy is ~12-15%, with mH=120-200 GeV and L=300 fb-1 • ILC • The low σttH (e.g. ~0,16 fb at √s=500 GeV for mH=120 GeV) and huge backgrounds require high luminosity. • Expected accuracy is ~33% for L = 1000 fb-1 (23% adding the had channel). • Correction to Born s and resummation effects can help to reach 10%

22. Top spin correlations t and t are produced unpolarized, but spins are correlated anomalous coupling (technicolor), tH+b, spin 0/2 heavy resonance H/KK gravitons  tt, would move A away from SM expectation s(tLtL) + s(tRtR) - s(tLtR) - s(tRtL) A= s(tLtL) + s(tRtR) + s(tLtR) + s(tRtL) Fit to double differential distribution CMS NOTE 2006/111 Semilep. (10 fb-1) Fitting to distribution of • lepton angle vs b-quark angle in the tt rest frame • lepton angle vs lower energy quark angle from the W-decay in the tt rest frame Eur.Phys.J.C44S2 2005 13-33 Semilep. + dilep. (10 fb-1) Fitting to distribution of • angles between top spin analyser in top rest frame versus angle of t spin analyser in antitop rest frame • Syst. dominated by b-JES, top mass and FSR A=0.41 0.014(stat) 0.023(syst) +0.055 Abt,lt=0.375 ±0.014(stat) (syst) Aqt,lt=0.346 ± 0.021(stat) (syst) -0.096 +0.026 -0.055 At the LC one can find a top spin quantization axis in which there will be very strong Spin correlations. Detailed studies remain to be done.

23. Anomalous couplings • One of main motivations to study top! • We may expect: • A modification of the SM couplings (gtt, gtt, Ztt and tWb vertexes) • The appearance of of new types of interactions (t→H+b, FCNC) • Any tVq coupling can be parametrized with 4 parameters, The coupling has a “vector-like” (gives the main contribution near threshold) and a “tensor-like” component (essential at high √s >> Mtop. • In principle LHC should measure better the vector and ILC the tensor component

24. Wtb coupling at LHC B) Anomalous Couplings in the tbW decay (PRD67 (2003) 014009, mb≠0) Angular Asymmetries: AFB, A+ and A- AFB [t=0] A± [t= (22/3-1)] ± SM(LO):

25. Wtb asymmetries/anomalous couplings asymmetries • a couplings

26. gWtb = 2gSM gtWb = gSM gWtb = gSM/2 Wtb coupling at ILC P. Batra, T. Tait PRD74(2006) 054021 • Above threshold measurements, may constrain anomalous non-SM structures. • From ttbar threshold region • only an indirect measurement • If there is a small non-standard decay mode of top, will alter G and distort the inferred coupling • At ~2Mtop on-shell tt dominates • At ~Mtop non top graphs dominate • Main backgnd from diagrams with an internediate Higgs • Nr of events f(Mtop, MH, G, and gtWb) • For ILC DMtop and DMH~100 MeV • Assume 100 fb-1 collected at √340 GeV • If DG =100 MeV DgtWb~2%

27. hep-ph/0412021 Probing EW couplings • Currently, only weak constraints (except for ttZ vector and axial-vector, but indirect, and for right handed tbW, from bsg rate) • If: V and top are on-shell, one has 4 form factors. • Sensitivities at 68.3% CL for the anomalous ttV (V=g,Z) couplings • With 30 fb-1 LHC will probe ttg with a precision of 10-35%

28. Flavour Changing Neutral Currents CMS NOTE 2006/093 u (c,t) 5σ sensitivity No FCNC at tree level in SM: u Z/γ Look for FCNC in top decays: SN-ATLAS-2007-059 tqg (2j+1l+1g+missing) tqg (3j+1l+missing) tqZ (2j+3l+missing) t @ 10 fb-1 2 orders of magnitude better than Tevatron/LEP/HERA

29. Results at LHC and ILC • BR 5s sensitivity • Dominant systematics: MT and etag < 20% • ILC will have lower statistics, but also lower background • Beam polarization very useful to improve limits from tqbar production (backgnd decrease) • For anomalous interaction with a gluon LHC is advantaged

30. Conclusions • One of most urgent problems in HEP: identify origin of masses and understand mechanism of EW symmetry breaking • Top quark might play a special role on this. At the LHC will be produced by millions  Almost no background: measure top quark properties • LHC will provide already incisive test of SM top physics and hints for New Physics beyond SM. • High precision measurements in the top sector will be needed to master the correct underlying theory • e+e- colliders have a number of features that make them particularly well suited for this task: well defined initial state, precise theoretical calculations, low backgrounds and excellent experimental accuracy.

31. 1 fb-1 100pb-1 Single top: t-channel • Cut analysis: low multiplicity jet events, one light j in forward, 1 b jet (other b-jet low pt) • S/B ~ 30% • Significance 18.6 @1fb-1 • Significance 5.8 @ 100pb-1. • Could be interesting for discovery at 100 pb-1 in case b-tag is not fully operational have to apply cuts on • mt(lept) & total energy of the events • angular correlations between jets, lepton and jets.

32. Single top: Wt-channel Also benefits from a high cross-section, • High tt back from which signal differs only by one b-tagged jet. • pT of the b-tag jet (above 50, 70 GeV) against W+jets • veto of a second b-tagged jet must be against tt • have to work on a specific b-tag veto tool based on a looser b-tag S/√B 3.9 s (stat!!) @ 100 pb-1 S/√B ~12 s with 1 fb-1

33. Single top: s-channel • Cross-section (~10 pb), tt+ W/Z+(b)jets backgrounds • Exactly 2 b-jets: against Z/W+(b)jets, • Only 2 jet events: against ttbar • Use angular correlations between b-jets and lepton, between b-j1 and b-j2 and global ET, M Improves with MVA, requires a knowledge of backgrounds: from data (using side distributions) S/√B 0.5 s (stat!!) @ 100 pb-1 S/√B ~5 s with 8-10 fb-1

34. Statistics and systematics on x-sec • Effects of varying the W+jets background level

35. FCNC kZtc=1 t-channel 4th generation,|Vts|=0.55, |Vtb|=0.835 (extreme values allowed w/o the CKM unitarity assumption) SM Top-flavor MZ’=1 TeV sen2f=0.05 Top-pion Mp±=450 GeV tR-cR mixing ~ 20% s-channel Single top and new physics T.Tait, C.-P.Yuan, Phys.Rev. D63 (2001) 0140018 Powerfull Probe of Vtb Probe New Physics differently: ex. FCNC affects more t-channel W´ affects more s-channel

36. Beyond the SM • non-SM production (Xtt)  resonances in the tt system  MSSM production  unique missing ET signatures from • non-SM decay (tXb, Xq)  charged Higgs  change in the top BR, can be investigated via direct evidence or via deviations of R(ℓℓ/ℓ)=BR(Wℓ) from 2/9 (H+,cs).  FCNC t decays: tZq tq tgq  highly suppressed in SM, less in MSSM, enhanced in some sector of SEWSB and in theories with new exotic fermions • non-SM loop correction  precise measurement of the cross-section  ttNLO-ttLO/ ttLO <10% (SUSY EW), <4% (SUSY QCD) typical values, might be much bigger for certain regions of the parameter space • associated production of Higgs  ttH

37. Z’, ZH, G(1),SUSY, ? 500 GeV 600 GeV 400 GeV New physics: Resonances in Mtt • t 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 • Resonances in Mtt • Structure in Mtt Gaemers, Hoogeveen (1984) Resonanceat 1600 GeV # events Cross section (a.u.) Mtt (GeV) - Interference from MSSM Higgses H,A tt (can be up to 6-7% effect) Mtt (GeV)

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

39. Resonances in a tt system • Usual usemi-leptonic events preselection • Use W and top mass constraint: • |mjj-mW|  20 GeV • b-jet associated with had top is the one maximising pTtop • |mbjj-mT|  40 GeV • neutrino pZ from mW constraint, solution giving best Mtop is retained 5fb-1 3xZ’ signal pT of top from resonance decay is larger than in direct production Add lower cut on top pT 370,390,500 GeV/c for mZ’ =1,1.5,2 GeV/c2 to increase purity (s/B~0.06-0.08)

41. Signal/background likelihood computed Likelihood analysis p.d.f. built using accept reject Discriminant variable LR=log10(LS/LB)  LR<-0.2 L=0.94 fb-1 Analysis results

42. With 50 pb-1 !

43. LHC:How many events at the beginning ? 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 (107 events in 2 weeks of data taking if 20% of trigger bandwidth allocated) 10 pb-1 1 month at 1030 and < 2 weeks at 1031,=50% 1 fb-1 Similar statistics to D0/CDF 100 pb-1 few days at 1032 , =50%

44. Loop Calculations: status of the art