Top quark charge and problems around ATLAS and

Top quark charge and problems around ATLAS and CDF studies People involved: P. Bednář, J. Coss, M. Čiljak, S. Tokár, B. Žilka 14 Mar 2006 Top Quark Meeting, Munich, S. Tokar 1

Top Quark Charge Determination Motivation: CDF and D 0 analyses + precision EW data do not exclude: top quark seen in Fermilab is an exotic quark with Qtop=-4/3 ( D. Chang et al. , Phys. Rev. D 59, 091503). D 0: top charge is compatible with SM prediction (19 dilepton events) b(-1/3) t(2/3) W+(+1) SM 14 Mar 2006 b(-1/3) t’(-4/3) W (-1) Exotics Top Quark Meeting, Munich, S. Tokar 2

How to determine the top charge? q via radiative tt_bar events (sensitive to Qtop) ATLAS: Yes to measure X-section of Direct measurement of top-to-photon coupling CDF: No Qtop PHYS-2003 -35 q by measuring the charges of top decay products main drawback: b-jet charge ATLAS: Yes weighting b-jet tracks charges CDF: Yes semileptonic b-decay 14 Mar 2006 Top Quark Meeting, Munich, S. Tokar 3

Charge analysis of top quark decay n n SM (Qtop=2/3): exotics (Q = -4/3): W t l Qlepton 1 1 l b -1/3 b-jet n for top quark determination –determination of b-jet charge –lepton – b-jet association 14 Mar 2006 Critical moment Top Quark Meeting, Munich, S. Tokar 4

b-jet charge determination n weighting method Optimization for CDF: qi ith -particle charge, pi ith -particle momentum, j b-jet axis direction, k exponent coefficient Analysis first done for ATLAS (Atlfast, PHYS-2003 -35 ) n semileptonic B-meson decay 14 Mar 2006 Not treated yet Top Quark Meeting, Munich, S. Tokar 5

Event samples and Selection criteria n Samples for analysis: Experiment ATLAS ü dilepton events: ü lepton+jets events: All jet modes not suitable due to huge QCD bkgd ! Dilepton Lepton+jets 2 isolated leptons (e, ) p. T > 25 Ge. V, | |<2. 5 1 isolated leptons (e, ) p. T > 20 Ge. V, | |<2. 5 Missing ET > 40 Ge. V Missing ET > 20 Ge. V 2 jets , p. T > 25 Ge. V, | |<2. 5 1 or 2 b-tagged 2 b-jets, p. T > 25 Ge. V Tot. 4 jets, p. T >25 Ge. V, | |<2. 5 14 Mar 2006 Top Quark Meeting, Munich, S. Tokar 6

Lepton b-jet association q Invariant mass criterion l, bjet the same top lepton+jets case different tops dilepton case q Alternative: Event kinematic fit full reconstruction of event – a combination with minimal 2 defines correct l-bjet association 14 Mar 2006 mcr 160 Ge. V lepton-bjet invariant mass Mtop = 175 Ge. V assumed Top Quark Meeting, Munich, S. Tokar 7

Kinematic fit for lepton b-jet association n Kinematic fit (event by event) for l+jets sample: n Results: – – – CDF lepton and jets energy, jets direction ( , ), neutrino px, py, pz vary freely (in errors inter. ) 2 uses constraints Mjjb=mt, Ml b=mt , Mjj=MW mt – all possible combinations of 4 jets are fitted – mt and 2 for each of 24 combinations Kinematic fit for dilepton sample: less constraints than unknown variables additional hypothesis needed (see e. g. Lysak talk) n 14 Mar 2006 Top Quark Meeting, Munich, S. Tokar 8

MC truth b-tagging n MC truth used for b-tagging: cone R=0. 4 around b-quark direction for finding b-jet reconstructed by Athena Atlas Preliminary ! b-jet charge assoc. with b-quark and bbar-quark track charge weighting technique used to find b-jet charge d 0 > 100 , 3 track to b-jet 14 Mar 2006 Top Quark Meeting, Munich, S. Tokar 9

b-jet charge associated with l+ and l n Invariant mass criterion used for l-b association (Athena reconstruction, sample 310000 tt-bar events) -0. 037 0. 006 Qbjet(l+) 14 Mar 2006 0. 041 0. 006 Qbjet(l ) Top Quark Meeting, Munich, S. Tokar 10

b-jet charge vs # tracks n Common distribution f Qbjet(l+) and - Qbjet(l+) -0. 037 0. 005 1 trk -0. 036 0. 000 2 trk -0. 037 0. 005 3 trk 14 Mar 2006 -0. 032 0. 006 5 trk Top Quark Meeting, Munich, S. Tokar 11

b-jet charge vs track d 0 n Only tracks with d 0> threshold taken ( ( 1 trk needed) -0. 018 0. 003 d 0 10 -0. 034 0. 004 d 0 60 -0. 037 0. 004 d 0 100 14 Mar 2006 -0. 033 0. 005 d 0 150 Top Quark Meeting, Munich, S. Tokar 12

b-jet vs d 0, # of tracks 14 Mar 2006 Top Quark Meeting, Munich, S. Tokar 13

Top charge at CDF n use information from top finding procedure (Top. Mass. Fit. Summary, top candidates – 24 comb. ) – lowest 2 combination from tagged combinations – lowest 2 combination from all combinations n n n calculate charge via tracks inside b-jet cone (R=0. 4) using weighting method associate b-jet with lepton using fitter information check b-quark association of b-jets using MC truth (information from HEPG_bank ) 14 Mar 2006 Top Quark Meeting, Munich, S. Tokar 14

Charge of b-jet assoc. with SM top decay assumed: : + l /l Preliminary ! Q+ σ+ Q- σ- -0. 096 0. 041 0. 024 0. 046 1. 93 1 fb-1 -0. 064 0. 024 0. 056 0. 026 3. 40 3 fb-1 -0. 061 0. 019 0. 084 0. 021 5. 23 5 fb-1 15. 88 5 fb-1 MC -0. 146 14 Mar 2006 0. 014 0. 164 0. 014 Top Quark Meeting, Munich, S. Tokar sample 15

Lepton b-jet association: real vs MC MC b-tag B-jet charge l+ B-jet charge l CDF b-tag 14 Mar 2006 Top Quark Meeting, Munich, S. Tokar 16

b-jet tagging via MC truth (tagged events, cone ΔR = 0. 4) lepton charge (t-quark decay branch) L- (all) L- (lep) L- (had) L+ (all) L+ (lep) L+ (had) 14 Mar 2006 % of tagged b-jets with parton association 92 92 92 91 % of tagged b-jets with b-quark association bbar-quark association 30 28 31 62 62 62 Top Quark Meeting, Munich, S. Tokar 61 63 60 29 30 29 17

Background studies n n n Di-lepton mode: Drell-Yan - fakes from W+jets - di-boson production Lepton +jets mode: - mistags - W + heavy flavor - QCD fakes - di-bosons - Single top charge asymmetry (no) (Wc : yes, Wcc, Wbb ? ) (no) Not seen! (no) (Wc : yes, Wcc, Wbb ? ) (no) (yes) From CDF: signal/background approx. 2: 1 14 Mar 2006 Top Quark Meeting, Munich, S. Tokar 18

Other top quark issues n top mass in dilepton channel (big experience of Košice group for CDF – different kinematic fit approaches) top mass in all hadronic channel ( , Munich, Košice, Bratislava big experience in hadronic calorimetry) n tt-bar bound states (resonance in m(t, t-bar) due to coupling of top quark to a new heavy boson ) n q other top quark properties (spin, threshold phenomena, etc ) 14 Mar 2006 Top Quark Meeting, Munich, S. Tokar 19

Summary and outlook Ø ATLAS: Top charge determination is a good task for the first period of top quark physics (provide us with a lot of top peculiarities) Ø CDF has a good potential to determine the top charge via charges of top decay products Nearest plans: q to calculate background for ATLAS and CDF (W+jets, QCD, etc. ) q to take the real CDF data 14 Mar 2006 Top Quark Meeting, Munich, S. Tokar 20

P. S. manpower n n Bratislava team - 3 physicists 2 -3 Ph. D students 2 -3 undergraduate students Košice team - 3 physicists 1 -2 Ph. D students 2 -3 undergraduate students 14 Mar 2006 Top Quark Meeting, Munich, S. Tokar - - 21

Thank you ! 14 Mar 2006 Top Quark Meeting, Munich, S. Tokar 22

Extra slides 14 Mar 2006 Top Quark Meeting, Munich, S. Tokar 23

Charge of b-jet assoc. with l+/l Different lb-association, mtop not constrained 5 fb-1 Q+ σ+ Q- σ- -0. 0607 0. 0185 0. 0835 0. 0205 7. 39 -0. 0799 0. 0230 0. 1076 0. 0240 7. 98 M(lb)<Mcr min 2 tag. -0. 0762 0. 0192 0. 1012 0. 0199 9. 06 M(lb)<Mcr min 2 -0. 1464 0. 0135 0. 1637 0. 0141 22. 46 MC tag 14 Mar 2006 Top Quark Meeting, Munich, S. Tokar Assoc. Stand. tag 24

b-jet tagging using MC truth – (untagged events, cone ΔR = 0. 4) lepton charge (t-quark decay branch) L- (all) L- (lep) L- (had) L+ (all) L+ (lep) L+ (had) 14 Mar 2006 % of tagged b-jets with bparton association % of tagged b-jets with b quark association % of tagged b-jets with b~ quark association 58 55 60 61 20 11 27 43 50 36 37 43 32 17 10 25 Top Quark Meeting, Munich, S. Tokar 25