Top Properties Measurements in ATLAS Mohsen Khakzad Carleton

Top Properties Measurements in ATLAS Mohsen Khakzad Carleton University (On behalf of the ATLAS Collaboration) Contents: Nov. 1, 2006 ➢ Introduction ➢ Top properties ➢ tt channels ➢ Single Top channels ➢ Conclusions Nov. 1, 2006 DPF 2006, Hawaii (Mohsen Khakzad) 1

Cross-sections at LHC Low lumi = 10 fb-1/y Process (pb) N/s N/year Total collected before start of LHC W l 3 104 30 108 104 LEP / 107 FNAL Z ee 1. 5 103 1. 5 107 LEP 1 107 104 Tevatron 106 1013 109 Belle/Ba. Bar tt 830 bb 5 108 ATLAS: ~95% gg ~15% ~5% qq (Opposite @ FNAL) ~85% LHC is a top factory Nov. 1, 2006 DPF 2006, Hawaii (Mohsen Khakzad) 2

LARGE HADRON COLLIDER at CERN Initial L (2007) ~1028 cm-2 s-1 Low L (2008) ~1032 cm-2 s-1 ~1 fb-1/year Design L (2009) • LHC provides: Ø PP Collisions at 14 Te. V CME Ø Constituent energies of 1 -2 Te. V Nov. 1, 2006 • Proton-Proton 1034 cm-2 s-1 100 fb-1/year collisions: Ø Maximum Luminosity of 10+34 cm-2 s-1 Ø Bunch spacing of 25 ns Ø 23 Events/Crossing DPF 2006, Hawaii (Mohsen Khakzad) 3

The Atlas Detector Three main sub-systems: 1) Inner Tracking System § Pixel Detector § Semiconductor Tracker § Transition Radiation Tracker 2) Calorimeter Barrel Carlorimeter § § 3) Ø Liquid Argon Electromagnetic Ø Hadronic (Tile-Calorimeter) 2 Liquid Argon End Caps Ø Electromagnetic (Pb) Ø Hadronic (Cu) Ø Forward Calorimeter (Cu, W) Muon Spectrometer § Large Air-core toroid (0. 5 T) § Monitored Drift Tubes and CSC § P Diameter Barrel toroid length Overall weight 25 m 26 m 46 m 7000 Tons Trigger: TGC and RPC Nov. 1, 2006 DPF 2006, Hawaii (Mohsen Khakzad) 4

Top physics: Motivations W helicity Top Mass n n Top quark pair production (tt) – cross-section – Search for resonances – spin correlations (10 fb-1) – Probing the Wtb vertex (30 fb-1) – Flavor changing neutral currents (FCNC) Electroweak Single top production – Single top cross-sections – Determination of Vtb (30 fb-1) – W and Top polarization (10 fb-1) l+ Top Width Production cross-section Resonance production Top Spin W+ Top Charge Anomalous Couplings CP violation n t Production kinematics Top Spin Polarization b _ Y t Rare/non SM Decays X Branching Ratios |Vtb| Top quark physics also important for Higgs Discovery! Nov. 1, 2006 DPF 2006, Hawaii (Mohsen Khakzad) 5

Top Spin and polarization studies (ref : ATL-PHYS-2000 -017) n Top lifetime is very short: Γt = 1. 42 Ge. V → t = 0. 44 x 10 -24 s – Top decays before losing spin information n Production and decay of the top can be extracted through the study of Polarization effects. n The Top quark polarization can be studied through the angular distribution of the decay products! daughter i spin θi Particle i : spin analyzing power of daughter particle i (-1 to 1) i Top quark decays before it can hadronize Nov. 1, 2006 DPF 2006, Hawaii (Mohsen Khakzad) 6

tt spin correlation (cont’d) n n tt are unpolarized but are correlated by spin Spin of quarks can be evaluated in the helicity basis 1 d. N N dcosf = 1 ( 1 – A a a cosf ) D X X´ 2 SM ; or top spin ≠ 1/2, anomalous coupling, t H+b Semilep. + dilep. (10 fb-1) mt = 175 Ge. V LHC SM A=0. 42 A=0. 33 ( 0. 014 0. 023) 0. 023 AD=-0. 29 ( 0. 008 0. 010) 0. 010 AD=-0. 24 Mtt<550 Ge. V Nov. 1, 2006 § Syst. dominated by b-JES, top mass and FSR § ~4% precision on spin correlation parameters DPF 2006, Hawaii (Mohsen Khakzad) 7

W polarization in top decay n Polarization of W in top decay is divided in: longitudinal, left-handed, right-handed Top decay : major source of longitudinal W’s – SM: Only longitudinal and left-handed W’s can be produced in the top rest frame. n Polarization depends only on Mt and MW (LO) 1/N d. N/dcos n F 0 + FL + FR F 0 FL n b t W+ cos l+ Longitudinal W+ (F 0) Standard Model (Mtop=175 Ge. V) NLO Sensitive to EWSB Nov. 1, 2006 0. 703 0. 695 l+ Left-handed W+ (FL) Right-handed W+ (FR) 0. 297 0. 304 0. 000 0. 001 Test of V-A structure DPF 2006, Hawaii (Mohsen Khakzad) 8

W polarization in top decay (cont’d) (ref: Eur. Phys. J. C 44 S 2 2005 13 -33) MC (Top. Rex) Semilep. Standard Model S+B, 10 fb -1 (mt = 175) F 0 FL F 0=0. 699 FL=0. 299 FR=0. 002 FR 0. 703 0. 004 0. 015 0. 297 0. 003 0. 024 0. 000 0. 003 0. 012 10 fb-1 precision (±stat ±syst) 0. 005 0. 023 0. 003 0. 028 0. 003 0. 013 • Syst ( Ebjet, mt, FSR ) • ATLAS can measure W polarization component F 0 with an accuracy ~3% and FR with a precision ~1. 3% in 1 LHC year (10 fb-1) Measurements largely dominated by systematics! Nov. 1, 2006 DPF 2006, Hawaii (Mohsen Khakzad) 9

Top Quark Yukawa Coupling n top quark Yukawa coupling yt can be measured from tt H production yt n large value of mt has led to proposals of alternate mechanisms [eg. topcolor suggests most of mt due to new strong dynamics] Ø would like to measure yt directly n for m. H < 130 Ge. V, H bb is dominant decay ( tt. H final state is WWbbbb) Ø look for events with one W l , the other W jj Nov. 1, 2006 DPF 2006, Hawaii (Mohsen Khakzad) 10

Top Quark Yukawa Coupling (cont’d) (ref: ATL-PHYS-98 -132) n Reconstruct H bb for mass distribution L=30 fb-1 H→bb L=100 fb-1 n For Higgs masses up to ~130 Ge. V, can reach statistical errors on yt < 10% with high luminosity – Systematics can be studied by comparing tt H production with tt Nov. 1, 2006 DPF 2006, Hawaii (Mohsen Khakzad) 11

n n n BR n Flavor Changing Neutral Currents (FCNC) In SM, FCNC top decays are highly suppressed (Br < 10 -13 - 10 -10) The top quark almost always decays to a b quark, B(t Wb)~1 B(t Ws)<0. 18%, B(t Wd)<0. 02% (other decays are really rare) Any observation of FCNC indication of New Physics! Process 95% CL (today) LHC 95% CL (10 fb-1) LHC 5 (10 fb-1) t Zq ~ 0. 1 (LEP) 3 x 10 -4 5 x 10 -4 t g q ~ 0. 01 (HERA) 7 x 10 -5 1 x 10 -4 t gq ~ 0. 2 (TEV. ) 1 x 10 -3 5 x 10 -3 n (ref: hep-ph/0409342 APPB 35(2004)2695) Reconstruct t Zq (l+l-)j Huge QCD background Discovery potential (5 ) according to ATLAS studies for 100 fb-1 t Hq Nov. 1, 2006 Br: 4. 5 X 10 -3 2. 4 X 10 -3 (m. H = 115 Ge. V, H bb) (m. H = 160 Ge. V, H WW*) DPF 2006, Hawaii (Mohsen Khakzad) 12

Single Top Cross section The production of single top quark via EW interaction has yet to be observed! Vtb Vtb t-channel W* (s-channel) ~ 250 pb ~70 pb ~ 10 pb Powerful Probe of Vtb ( d. Vtb/Vtb~few% @ LHC ) Theoretical uncertainties: • Quark-gluon luminosity inside b-quark (PDF) • Renormalization scale (m) • top mass (Dmt=4. 3 Ge. V (W*) changed by 3%) Nov. 1, 2006 DPF 2006, Hawaii (Mohsen Khakzad) 13

Single Top Cross section (cont’d) (ref: ATL-COM-PHYS-2006 -002) 1 lepton, p. T>25 Ge. V/c High Missing ET 2 jets (at least 1 b-jet) Common feature: L=30 fb-1 t-channel: Nov. 1, 2006 ( d / <1. 5%) S/B = 3 Wt-channel: ( d / ~ 4%) S/B = 1/7 s-channel: ( d / ~7 -8%) S/B = 0. 2 DPF 2006, Hawaii (Mohsen Khakzad) 14

Determination of Vtb n SM prediction : Vtb an element of CKM matrix ~ 1 n tt pairs : SM-dependent measurement (ref: SN-ATLAS-2000 -017 SN-ATLAS-2001 -007) – Confirm three-generation structure – Look for exotic top decays – Estimate of n Electroweak single top : direct measurement – σ |Vtb|² n Results for 30 fb-1 3 years at low luminosity : Channel Selected events S/B W* 900 Wg 49000 Nov. 1, 2006 Uncertainties on σ ΔVtb/Vtb statistics theory 0. 55 5. 6% 7. 5% 4. 7% 2. 3 0. 54% 11% 5. 5% DPF 2006, Hawaii (Mohsen Khakzad) 15

Conclusions q LHC has great potential for top physics q Earliest LHC physics results and sensitivity to new physics could come from top physics! è See talk by Frank Fiedler è Fully understand the full simulations and NLO generators, especially in the early data taking q First steps towards precision measurements driven by systematics § Challenge to get: § the errors on top mass ~1 Ge. V § SM MH constrained to <30% § Test top production and its decay by measuring: § W polarization ~1 -2% § top spin correlation ~4% § anomalous t. Wb/gtt couplings, t H+b, FCNC, … Nov. 1, 2006 DPF 2006, Hawaii (Mohsen Khakzad) 16

Conclusion cont’d Electroweak physics QCD top Higgs or new physics Top is still a unique window on particle physics! From John Womersley Nov. 1, 2006 DPF 2006, Hawaii (Mohsen Khakzad) 17