Top physics at the LHC

1. Top physics at the LHC Paul de Jong Nikhef, Amsterdam on behalf of CMS and ATLAS

2. Top physics at the LHC = Top physics at the top factory

3. Outline: The LHC, CMS and ATLAS, first data and beyond The many hats of the top quark Early observation: rediscovering the top (again) Cross section measurements Calibration of CMS and ATLAS with top quarks Single top quark production Top properties: mass decay spin-spin correlations Anomalous top quark production, massive resonances All “results” presented are of course just simulations, based on CMS Physics TDR, and ATLAS CSC Note (under final review) 2

4. CMS: all heavy parts installed Silicon strip tracker installed Beam pipe bake-out end of June Then: pixels, at least one ECAL endcap Last two octants started cool-down LHC cold by mid-July Experiments close caverns mid-July First injection late July – early August First collisions two months later? Both experiments: adding final PS/electronics Interfacing to central DAQ and trigger Test, test, test Get initial “day-0” calibration ATLAS: installation complete Combined magnet test in progress Inner detector complete, commissioning cooling Beam pipe bake-out mid-July 3

5. In 2008, beam intensity and  will be limited. Also, some magnets quench earlier than expected: limit beam energy to 5 TeV. Pilot physics run October and November. 143156 bunches, luminosity few times 1031 cm-2 s-1 , 40 days, 10-50 pb-1 ? During winter shutdown commissioning to 7 TeV. Physics run May-November 2009 , 150 days, establish 75 ns operation (936 bunches), then 25 ns (2808 bunches), eventually to nominal  value, lumi 10321-2 x 1033 cm-2 s-1 , and 2-3 fb-1 ? 2010 and after: lumi expected to keep increasing steadily to ~2 x 1034 cm-2 s-1 and eventually ~80 fb-1 per year. After 2016 a major upgrade to LHC and experiments for a super-LHC. 4

6. Top at LHC 5 Top cross section: gluon-fusion-dominated (in contrast to Tevatron) Probes gluon pdf at x where it is relatively well known Test for advanced QCD methods beyond NLO. qqtt ~15% tt  bbjjjj: 45.5% bbljj: 43.5% (l = e,µ: 29%) bbll: 10.5% (l = e,µ: 4.7%) ~85% ggtt At L = 1033 cm-2 s-1 produce 1 tt per second, at L = 1034 we produce 108 tt per year! Better tt/W ratio than at Tevatron More phase space for radiation of extra jets

7. Three recent calculations of cross section: Moch and Uwer, arXiv:0804.1476: approx. NNLO Cacciari et al., arXiv:0804.2800: NLO + NLL resum, updated Kidonakis and Vogt, arXiv:0805.3844: NNLO-NNNLL+ Central values agree well, error estimates differ (different methodology) Using CTEQ6.5:  = 908 ± 83 (scales) ± 30 (pdf) pb (mt = 171 GeV, Cacciari et al.) MRSTW-06:  = 961 ± 90 (scales) ± 12 (pdf) pb Difference at LHC > estimated pdf error! More progress: spin correlations at NLO NLO corrections to tt+jet good advance towards NNLO At 10 TeV:  = 400 pb Will take longer to establish signal 6

8. The top quark has many hats Production: a test of QCD, resummation techniques Anomalous production and decay as direct probe of new physics Tool: Calibration of detector Properties (mass, couplings), an indirect probe of new physics Background to physics beyond SM 7

9. Early observation: tt  bbljj with l = e or µ Try to see an early signal, with no or limited b-tag CMS, early data, 10 pb-1 1 isolated µ, pT > 30 GeV at least 1 jet pT > 65 GeV Enough to rediscover top! (assuming QCD background under control) CMS ATLAS: e or µ, pT > 20 GeV, ≥ 4 jets (40,40,40,20 GeV) ETmiss > 20 GeV 3 jets with max sum pT are hadronic top ATLAS ATLAS, muons only ATLAS: / = 7% (stat) ± 15% (syst) ± 3% (pdf) ± 5% (lumi) likelihood method, 100 pb-1 3% (stat) ± 16% (syst) ± 3% (pdf) ± 5% (lumi) counting method 8

10. With working b-tagging, selection much cleaner, at the cost of some efficiency ATLAS ATLAS ATLAS, 1 or 2 b-tags CMS: uncertainty on tt for 1, 5 and 10 fb-1 in the muon channel CMS Issues: luminosity, b-tagging efficiency, pile-up, ISR/FSR 9

11. Dilepton channel: tt  bbll Small branching ratio, but clean CMS, 10 pb-1 isolated e or µ, pT > 30 GeV ETmiss > 20 or 30 GeV incompatible with Z mass stat error 9-13% Also looking at e and µ CMS CMS: / = 0.9% (stat) ± 11% (syst) ± 3% (lumi) in 10 fb-1 Systematics: pdf’s, b fragm., underlying events, b-tag, JES ATLAS ATLAS ATLAS: / = 4% (stat) +5-2 % (syst) ±2% (pdf) ± 5% (lumi) cut and count, 100 pb-1 4% (stat) ± 4% (syst) ± 2% (pdf) ± 5% (lumi) template method 5% (stat) +8-5 % (syst) ± 0.2% (pdf) ± 5% (lumi) likelihood method 10

12. Top as a Tool: Calibration with top events A clean sample of top events is a great tool to understand the detectors: b-quark-tagging: Count nr of events with n-tagged jets, 100 pb-1, ATLAS uncertainty 5% on b, 8-14% on tt ATLAS Selection of b-enriched jet sample, 200 pb-1 l+jets ATLAS 40-120 GeV jets, 6% (stat) ± 3% (syst) on b Selection of b-enriched jet sample, 1 fb-1, CMS 30-200 GeV jets, 6 (barrel)-10% (endcaps) on b Take care not to measure Vtb with a b-tag whose efficiency has been determined assuming Vtb ≈ 1… Jet energy scale Use MW to measure light JES, 50 pb-1, ATLAS 2% stat, 1% syst, jets > 40 GeV Use kinematic fit to measure light and b JES, 100 pb-1, CMS 0.9% stat, small syst, jets > 40 GeV CMS 11 Also: check lepton triggers, ETmiss reconstruction

13. Single top = electroweak top quark production t-channel: CMS ATLAS: cut-based analysis (basis), and multivariate (BDT) 1 fb-1 : / = 5.7% (stat) ± 22% (syst) 10 fb-1 : 2% (stat), 10% (syst) ATLAS ATLAS CMS: cut-based analysis 10 fb-1 : / = 2.7% (stat) ± 8% (syst) ± 8.7% (lumi) BDT > 0.6 1 fb-1 : Vtb / Vtb = ± 11% (stat+syst) ± 4% (theory) 12

14. tW channel (associated W production) Looks just like tt, but with one less b-jet ATLAS: cut-based analysis, and boosted decision trees CMS: cut-based analysis, with smart b-W pairing / = 8-9% (stat) ± 16-24% (syst) in 10 fb-1 s-channel: very difficult… very low cross section Could be mediated by new physics (H± ) ATLAS: Likelihood analysis CMS: cuts, with genetic algorithm In 10 fb-1 : / ≈ 35% (CMS) – 50% (ATLAS) ATLAS results summary: 13

15. Top properties: if the top is indeed the Q=2/3, spin=1/2, heavy partner of the b, then: Production: top essentially unpolarised, but spin-spin correlations Decay should be V-A, dominated by tbW Top charge: Q=2/3 vs Q=4/3 Decays into a b or into an anti-b? Measure with b-jet charge, or semileptonic tag 5 separation with 1 fb-1 (ATLAS) Systematics: ISR/FSR, MC model, pile-up Other suggestions: look at extra ’s in ttbar Top spin: top must be fermion cross section measurement will rule out s = 3/2 more info from spin-spin correlations 14

16. Top mass One of the most crucial parameters of the Standard Model Statistical error will soon be negligible Very careful treating of systematic errors needed Also theoretical interpretation not unambiguous: pole-mass? Golden channel: tt  bbljj good branching ratio W mass constraint from jj  can be reconstructed ATLAS: with b-tag, either geometric association of jets to W and top/anti-top, or association by minimizing 2 ; mass from peak fit, or full kinematic fit. To battle: (b) jet energy scale influence of extra jets 15

17. CMS: Semileptonic tt decay, via event-by-event likelihood (ideogram) in 10 fb-1 : mt = 0.2 GeV (stat) ± 1.1 GeV (syst) if b-JES known to 1.5% Also fully leptonic and fully hadronic decay channels Dilepton: mt = 4.5 GeV (<1 fb-1 ) 1.2 GeV in 10 fb-1 CMS All hadronic: mt = 4.2 GeV in 1 fb-1 CMS Alternative method: look for J/ from b-decay, plot mass with lepton from W CMS Error dominated by theory, not jet energy scales mt = 0.5 ± 1.5 GeV (20 fb-1 ) CMS 16

18. Top decay Top decay to b quarks: R = Br(tWb)/Br(tWq) = |Vtb |2 / (|Vtb |2 + |Vtd |2 + |Vts |2 ) Measure by counting b-tags in tt events, dominated by b-tag efficiency systematics Alternative non-SM decays may be possible: t bH+ , but also FCNC decays Top decay analysis: polarization of W’s is a good analyzer of V-A structure : angle between lepton in W frame, and W in top frame ATLAS: In 730 pb-1 : F0 = 0.70 ± 0.04 ± 0.02 FL = 0.29 ± 0.02 ± 0.03 FR = 0.01 ± 0.02 ± 0.02 Systematics: b-jet energy scale top mass hadronization scheme 17

19. Generally, the tbW vertex can be written as: anomalous couplings (F0 , FL , and FR depend on these couplings) (PR/L = (1 ± 5 )/2) ATLAS: measure FL /F0 , FR /F0 and angular (forward/backward) asymmetries Use TopFit to extract couplings: Dominating systematics: ISR/FSR, difference between MC generators, pile-up 18

20. Spin correlations: Top is produced unpolarized, but two spins are correlated. At threshold: ggtt produces 1 S0 state, qq  tt produces 3 S1 state Since t = 1.4 GeV > QCD top decays before hadronization: correlations preserved @LHC: if qq: A ~ -0.3 if gg: A ~ 0.3 Enhance A with Mtt cut : spin analysing power (~1 for lepton or d-type quark, ~0.5 for b or lowest energy jet) CMS, 10 fb-1 : A = 0.38 ± 0.03 (stat) +0.06-0.08 (syst) Systematics: ISR/FSR jet energy scale b-tag efficiency ATLAS, 200 pb-1 : a = 0.17 (stat) ± 0.15 (syst) 10 fb-1 : 0.02 (stat) ± 0.03 (syst) CMS CMS (before detector simulation) (before detector simulation) 19

21. Flavour-changing neutral current (FCNC) decays are suppressed in the SM but can appear in new physics (e.g. SUSY) Select tt  blqX (X=g,,Zll), l = e or µ ATLAS: likelihood analysis with kinematics Derive 95% CL limits for 1 fb-1 Systematics: ISR/FSR, pile-up, luminosity, backgrounds, MC generator CMS: X = , Z, cut-based analysis In 10 fb-1 : detect at 5 level: Br(tq) > 8.4 x 10-4 Br(tqZ) > 15 x 10-4 CMS, 5 discovery 20

22. Anomalous top quark production: a direct sign of new physics Anomalous single top quark rate from anomalous Vtb , or FCNC H± tb Gluino  stop top Resonances in tt invariant mass: general heavy Z’ bosons KK gravitons, gluons ZH in little Higgs models In many cases: production of high pT top quarks  decay products overlap: special reconstruction! generally efficiency decreases with top pT ATLAS: limits for a general resonance and for KK gluon 21

23. Summary At a top factory, statistics are not an issue for top properties measurements… (exception: rare decays) Systematics are an issue: Detector systematics: (b) jet energy scale b-tagging pile-up luminosity object identification and trigger Theoretical uncertainties: ISR/FSR and extra jets b-decay modeling differences between MC’s pdf’s fragmentation and hadronization 22

24. 5. Multiple Interactions

25. Summary At a top factory, statistics are not an issue for top properties measurements… (exception: rare decays) Systematics are an issue: Detector systematics: (b) jet energy scale b-tagging pile-up luminosity object identification and trigger Theoretical uncertainties: ISR/FSR and extra jets b-decay modeling differences between MC’s pdf’s fragmentation and hadronization Lots of hard, but eventually rewarding work for experimentalists! Lots of hard, but eventually rewarding work for theorists and experimentalists ! Provided these are under control, the LHC promises to test the nature of the top quark to excellent precision, and use the top quark as a tool, and as a probe of new physics. 22