Greg Heath University of Bristol Top physics results Greg Heath University of Bristol

UK HEP forum, Cosener's, 7th September 2011 Motivation Large cross-section About 20× Tevatron at 7 TeV Opportunity to study “bare” quark Decays before hadronisation Handles on New Physics Higgs mass uncertainties New phenomena coupling to top Top as background to discovery channels Exercise full detector and reconstruction in complex multi-parton events Leptons, jets, MET, b-tagging, tau-id UK HEP forum, Cosener's, 7th September 2011

Top production and decay Top pair production from initial gg pair dominates Top pair decay modes All hadronic (6 jets) – large BR, large QCD background Lepton+jets (4 jets) – smaller BR (per lepton), smaller background Dileptonic (2 jets) – smallest BR, cleanest Also consider single top production Theory predictions UK HEP forum, Cosener's, 7th September 2011

UK HEP forum, Cosener's, 7th September 2011 Top pair cross-section UK HEP forum, Cosener's, 7th September 2011

UK HEP forum, Cosener's, 7th September 2011 2011 dilepton analyses Robust cut and count analyses B-tagging improves efficiency Systematic errors dominate ATLAS CMS UK HEP forum, Cosener's, 7th September 2011

Lepton+jets analyses with b-tags b-tagging probability as input to likelihood fits to signal+background Combined fit to jet multiplicity bins CMS lepton+jets with b-tags ATLAS single lepton with b-tags m+jets e+jets m+jets e+jets UK HEP forum, Cosener's, 7th September 2011

Lepton+jets untagged (ATLAS) 2011 data (0.7 fb-1) Likelihood fit to event kinematics UK HEP forum, Cosener's, 7th September 2011

All-hadronic measurement (CMS) Kinematic fit to events with b-tagging Fit mass distribution to estimate t-tbar contribution UK HEP forum, Cosener's, 7th September 2011

Dilepton measurements with ts CMS – cut-based selection including b-tagging ATLAS – m+jets background minimised using BDT UK HEP forum, Cosener's, 7th September 2011

Cross-section summary Individual combinations (l+jets and dilepton) ATLAS CMS UK HEP forum, Cosener's, 7th September 2011

Other cross-section measurements Single top t-channel s-channel and tW Resonance searches Charge asymmetry UK HEP forum, Cosener's, 7th September 2011

UK HEP forum, Cosener's, 7th September 2011 Single top production Three EW diagrams contribute to production of single top quarks at hadron colliders t-channel production has the largest predicted cross-section Main backgrounds t-tbar and W+jets UK HEP forum, Cosener's, 7th September 2011

t-channel cross-section t-channel (dominant) Central b-tagged jet Forward light jet Leptonic decay of W Isolated lepton Large MT(ln) Variety of approaches Backgrounds are large 2 jets 3 jets Boosted decision tree (BDT) Cut-based UK HEP forum, Cosener's, 7th September 2011

t-channel cross-section ATLAS 2011 cut-based: CMS 2010 combined: (dominated by BDT) UK HEP forum, Cosener's, 7th September 2011

Wt and s-channel single top searches 95% CL 1.2s ATLAS signal exp 16±6 total exp 285±17 observed 296 UK HEP forum, Cosener's, 7th September 2011

Searches for t-tbar resonance ATLAS l+jets Reject extra jets from radiation ATLAS dilepton CMS l+jets Kinematic fit and b-tagging UK HEP forum, Cosener's, 7th September 2011

UK HEP forum, Cosener's, 7th September 2011 Charge asymmetry Small effect predicted in SM Top quark h distribution narrower than antiquark But dominant gg production is symmetric Measured quantity: Theory predicts small positive asymmetry Lepton+jets selection Fit to identify top and anti-top Unfold measured asymmetry CMS result: Theory: AC=0.013±0.001 Measured: AC=-0.016±0.030+0.010-0.019 ATLAS result: Theory: AC=0.006 Measured: AC=-0.024±0.016±0.023 UK HEP forum, Cosener's, 7th September 2011

UK HEP forum, Cosener's, 7th September 2011 Top properties UK HEP forum, Cosener's, 7th September 2011

mt in lepton+jets (ATLAS 2011) Template method Pick the “best” jet combination hypothesis per event Kinematic fit with mW constraint Simultaneous fit to mt and Jet Scale Factor UK HEP forum, Cosener's, 7th September 2011

mt in lepton+jets (CMS 2010) Ideogram method Kinematic fit and per-event likelihood vs mt Uses all jet combination hypotheses JES as systematic correction Additional CMS measurement in dilepton events: UK HEP forum, Cosener's, 7th September 2011

Measurement of pole mass ATLAS Direct measurements yield MC mass parameter mt Theoretical cross-section calculations depend on the pole mass Mass uncertainty 4× smaller than cross-section uncertainty Pole mass looks smaller than MC mass UK HEP forum, Cosener's, 7th September 2011

t-tbar mass difference Ideogram method modified Lepton+jets Use lepton to distinguish t and tbar Fit mass of hadronic top only 2011 data (1.09 fb−1) CMS UK HEP forum, Cosener's, 7th September 2011

UK HEP forum, Cosener's, 7th September 2011 Spin correlation ATLAS Parton level Data vs MC Top quark decays before hadronisation Spin correlations at production propagated to decay products Charged lepton from W decay carries full spin information Measure distribution of Df between leptons in dilepton events Fit to a mixture of SM and uncorrelated templates Results consistent with SM expectations SM fraction FSM=1.06±0.21 UK HEP forum, Cosener's, 7th September 2011

W helicity measurement ATLAS Test of V−A structure of top quark decay Angular distribution of lepton and b quark in W rest frame Fit to LH, RH and longitudinally polarised W Results consistent with SM expectations Longitudinal fraction F0=0.75±0.08 Improved limits on anomalous couplings UK HEP forum, Cosener's, 7th September 2011

UK HEP forum, Cosener's, 7th September 2011 Summary and outlook LHC is a top factory Initial measurements in l+jets and dilepton channels now systematics dominated Cross-section precision (7%) approaching that of theory prediction Single top production confirmed Top quark properties consistent with SM (so far) Top is an active field in searches for New Physics Many studies just beginning UK HEP forum, Cosener's, 7th September 2011

UK HEP forum, Cosener's, 7th September 2011 List of sources UK HEP forum, Cosener's, 7th September 2011

Top pair cross section measurements L+jets: ATLAS 2010 analysis: 3, 4, >4-jet subsamples (ATLAS-CONF-2011-035) CMS 2010 analysis similar (arXiv:1108.3773) B-tagging gives best results Untagged analysis on 2011 data (ATLAS-CONF-2011-121) Dilepton: ATLAS 2011 0.70 fb-1 (ATLAS-CONF-2011-100) Simple cut-based, no b-tagging CMS 2011 1.14 fb-1 (CMS PAS TOP-11-005) Combinations ATLAS combine the above two results (ATLAS-CONF-2011-108) CMS combine the two 2010 measurements (arXiv:1108.3773) All-hadronic and tau dilepton CMS all-hadronic measurement on 2011 data (CMS PAS TOP-11-007) ATLAS all-hadronic search on 2010 data (ATLAS-CONF-2011-066) ATLAS mu+tau measurement (ATLAS-CONF-2011-119) CMS mu+tau measurement (CMS PAS TOP-11-006) UK HEP forum, Cosener's, 7th September 2011

Production measurements; single top Spin correlation (ATLAS-CONF-2011-117) Charge asymmetry (ATLAS-CONF-2011-106) (CMS PAS TOP-11-014) Single top t-channel measurement (ATLAS-CONF-2011-101) t-channel measurement (arXiV:1106.3052) s-channel search (ATLAS-CONF-2011-118) Search for Wt (ATLAS-CONF-2011-104) UK HEP forum, Cosener's, 7th September 2011

Top mass and properties, exotica Template method (ATLAS-CONF-2011-120) Mass from cross-section (ATLAS-CONF-2011-054) Ideogram method (CMS PAS TOP-10-009) Mass in dileptons (included in arXiV:1105.5661) Mass difference (CMS PAS TOP-11-019) W polarisation (ATLAS-CONF-2011-122) Resonance search Dilepton channel (ATLAS-CONF-2011-123) Lepton+jets channel (ATLAS-CONF-2011-087) CMS search (CMS PAS TOP-10-007) Exotic searches Search for FCNC (ATLAS-CONF-2011-061) Search for anomalous MET (ATLAS-CONF-2011-036) UK HEP forum, Cosener's, 7th September 2011