Top Quark Charge Determination in ATLAS and CDF

Top Quark Charge Determination in ATLAS and CDF S. Tokár, Comenius Univ. , Bratislava 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) b(-1/3) t(2/3) b(-1/3) W+(+1) SM 10/27/2020 t’(-4/3) W-(-1) Exotics S. Tokár, Tbilisi, Oct 2005 1

How to determine the top charge? q via radiative tt_bar events (sensitive to Qtop) to measure of X-section of Qtop Direct measurement of top-to-photon coupling q by measuring charges of top decay products main drawback: b-jet charge weighting b-jet tracks charges semileptonic b-decay … 10/27/2020 S. Tokár, Tbilisi, Oct 2005 2

Cross section measurements Cross section: hadron H structure function, ith parton cross section Top pair prod. : theory is at NNLO Problems: big logs Scales: R renormalization scale (determines coupling S) F factorization scale (determines parton structure) Usual choice: R = F (mtop/2, 2 mtop) At LO the scales - main source of uncertainty ! 10/27/2020 S. Tokár, Tbilisi, Oct 2005 3

Top charge via photon radiation in events Signal Processes (measurement of coupling top-photon) • Radiative production • Radiative top decay (matrix el. , PYTHIA) LO: S 2 Not in PYTHIA !!! Background processes (non sensitive to Qtop ) • Radiative W decay in (matrix el. , PYTHIA) • Other • Non processes leading to high p. T photon ( PYTHIA) radiative bkgd (W, Z+jets+ ) (matrix el. , PYTHIA) Ciljak et al. , PHYS-2003 -035 10/27/2020 S. Tokár, Tbilisi, Oct 2005 4

Why matrix elements? Pythia vs matrix elements p. T( ) > 10 Ge. V, | |<3. 5 PY =0. 66 pb ME = 2. 33 pb Using ISR, FSR for mt systematics is questionable ! Soft photon (gluon) approximation used in Pythia is insufficient 10/27/2020 S. Tokár, Tbilisi, Oct 2005 5

Radiative Top Production Radiative top production followed by top decay • Production phase: matrix elements implemented into PYTHIA + effective generation of phase space • In initial state : gg and/or • production cross section • Important: virtuality of radiating top is required • Decay of top : Top and W decay treated in narrow width approximation 10/27/2020 S. Tokár, Tbilisi, Oct 2005 6

Radiative top production diagrams + diagrams with d, s, c and b production by gluon fusion LHC: 87%, Tevatron: 15% 10/27/2020 production by quark annihilation LHC: 13%, Tevatron: 85% S. Tokár, Tbilisi, Oct 2005 7

Radiative top decay: (production), t Wb … • Decaying top quark is on-mass-shell • Photons from W and b do not feel the top charge • Destructive interference of the diagrams is expected: (-4/3) (2/3) 10/27/2020 S. Tokár, Tbilisi, Oct 2005 8

Selection criteria Selected sample: (radiative “lepton+jets” ev. ) general top quark cuts (C 1) njets 4, p. T > 20 Ge. V, < 2. 5 nbjets = 2, p. T > 20 Ge. V, < 2. 0 nlept = 1, p. T > 20 Ge. V, < 2. 5 nphot = 1, p. T > 30 Ge. V, < 2. 5 missing p. T > 20 Ge. V Radiative top production cuts 10/27/2020 W reconstruction criteria |m(jj)-MW| < 20 Ge. V m(jj)=min{|m(ji, jk)-MW|} m. T(l; ) < MW + 20 Ge. V m(b 1, 2 jj ) > 190 Ge. V & m. T(b 2, 1 l ; ) > 190 Ge. V S. Tokár, Tbilisi, Oct 2005 9

Effectiveness of selection criteria Criteria are optimized for radiative top pair production Radiative top pair production 10/27/2020 vs Radiative top decay S. Tokár, Tbilisi, Oct 2005 10

Radiative top production SM top radiative production Sample: 10 fb-1 (1 LHC L. L. year) Exotic q radiative production 30% uncertainty from scale CDF possibilities to measure photon-top coupling: None ! 10/27/2020 S. Tokár, Tbilisi, Oct 2005 11

Top charge via top decay products Suitable event samples: • Dilepton sample ( 400 k. Evnt/10 fb-1) • Lepton +jets sample (2500 k. Evnt/10 fb-1) • All jets mode not suitable huge QCD bkgd Cornerstone of the top charge determination: Ø association of l+ (W+) and/or l- (W-) with correct b-jets Ø to determine the charge of the associated b-jet Ø in SM the mean value of b-jet charge spectrum associated with l+ (l-) should be negative (positive) qi ith part. Charge ith part. momentum b-jet direction an exponent b-jet charge determination 10/27/2020 S. Tokár, Tbilisi, Oct 2005 12

Selection criteria Di-lepton Lepton + jets 2 isol. high p. T leptons (e, ) At least 2 jets, p. T > 25 Ge. V 1 or 2 b-tagged, | |< 2. 5 S/B 10 ( Yellow Rep. 2000 ) 1 isol. high p. T leptons (e, ) At least 2 b-jets, p. T > 40 Ge. V In total 4 jets p. T > 40 Ge. V, | |< 2. 5 S/B 65 (P. Grenier, phys-note) ATLAS experiment cuts 10/27/2020 S. Tokár, Tbilisi, Oct 2005 13

Association of lepton and b-jet l and bjet from the same top and bjet from different tops Di-lepton case Lepton+jets case 120 Ge. V < m(jjb) < 220 Ge. V mcr 160 Ge. V lepton-bjet invariant mass ATLAS: Particle generation PYTHIA detector resolutions and efficiencies ATLFAST 10/27/2020 S. Tokár, Tbilisi, Oct 2005 14

Reconstructed b-jet charge Sample: 0. 87 fb-1 160 k. Evn’s (lepton+jets), 22 k. Evn’s (dilepton) b-jet charge assoc. with l+ b-jet charge assoc. with l Independent fragmentation in PYTHIA ( Rcone = 0. 4 ) For 5 separation we need 60 inputs for each distribution 10/27/2020 S. Tokár, Tbilisi, Oct 2005 15

Top charge in CDF ü radiative events (sensitive to Qtop) ü measuring the charges of top decay products q weighting b-jet tracks charges Problems: association of W boson and b-jet (invariant mass criterion needs high statistics) Kinematic fit as a solution q semileptonic b-decay: b c, u +l charge of lepton defines charge of b-jet Problems: Low branching (2/9 of b-decay are taken) B 0 oscillation (change of lepton charge) 10/27/2020 S. Tokár, Tbilisi, Oct 2005 16

Lepton-bjet association Charge distributions for b-jets matched by hepg b and (sample 25 fb-1) <Q+> b-jet matched by hepg b <Q > b-jet matched by hepg Realistic matching: Each b-jet is associated with l + or l Association: based on Top mass fitter (b-tagged) combination with min. 2 b-jet charge distributions Q+ Q associated with l + and l constructed Factor to optimize SM: f. Q>1, Exotics: f. Q>1, 10/27/2020 bkgd: f. Q 1 S. Tokár, Tbilisi, Oct 2005 17

Charge of b-jet assoc. with l+/l ry! ina m i l e r p y r Ve SM top decay assumed: : Q+ σ+ Q- σ- -0. 0957 0. 0413 0. 0236 0. 0461 2. 73 1 fb-1 -0. 0641 0. 0237 0. 0559 0. 0263 4. 80 3 fb-1 -0. 0607 0. 0185 0. 0835 0. 0205 7. 39 5 fb-1 22. 46 5 fb-1 MC -0. 1464 10/27/2020 0. 0135 0. 1637 0. 0141 S. Tokár, Tbilisi, Oct 2005 sample 18

Wb pairing in L+J: top mass fit Different lepton - b-jet association criteria, Pythia MC sample (ttopel) ~ 25 fb-1 (8700 Top. Find + Top. Fit events) Q+ σ+ assoc. crit. Q- σ- -0. 0465 0. 0083 0. 0496 0. 0084 11. 57 2<9+tag -0. 0747 0. 0085 0. 0819 0. 0085 18. 33 2 <9+Mlb -0. 0674 0. 0102 0. 0713 0. 0101 13. 65 2 <9+Mlb+tag 2<9+tag: b-tagged comb. with min. 2(<9 )taken 2<9+Mlb: comb. with min. 2(<9 ) tagging ignored 2<9 +Mlb+tag: previous case but with tagged combination 10/27/2020 S. Tokár, Tbilisi, Oct 2005 ry Ve ! ry a n i im l e pr 19

Summary and outlook • Study of the top quark charge is of a great importance from view point of SM and possible new physics • ATLAS possibilities in the top charge: via radiative tt~ processes via charges of top decay products • CDF potential: top charge via charges of top decay products q. To finish basic studies on simulated CDF samples. q. To start analysis on real CDF data for “lepton +jets” mode. 10/27/2020 S. Tokár, Tbilisi, Oct 2005 20

Thank you ! 10/27/2020 S. Tokár, Tbilisi, Oct 2005 21