1. Top charge @ATLAS Full simulation study B. Zilka, S.Tokar Comenius University, Bratislava

2. 11/20/2016B.Žilka, S.Tokár, BA Top meeting2 Top Quark Charge Determination Motivation: CDF and D0 analyses + precision EW data do not exclude: quark seen in Fermilab is an exotic quark with Q top = - 4/3. (D. Chang et al., Phys. Rev. D59, 091503) D0: top charge is compatible with SM prediction (19 dilepton events) t(2/3) b(-1/3) SM W + (+1 ) W  (- 1) t’(-4/3) b(-1/3) Exotic s ATLAS wants more: the value of top charge

3. 11/20/2016B.Žilka, S.Tokár, BA Top meeting3 How to determine the top charge?  via radiative tt_bar events (sensitive to Qtop) to measure X-section of Direct measurement of top-to-photon coupling Q top PHYS-2003-35 by measuring the charges of top decay products  by measuring the charges of top decay products main drawback: b-jet charge  weighting b-jet tracks charges -> AtlFast  semileptonic b-decay (done at partonic level)  reconstructed B-hadrons (not treated yet)

4. 11/20/2016B.Žilka, S.Tokár, BA Top meeting4 Charge analysis of top quark decay  SM (Qtop=2/3):  exotics (Q = -4/3): b -1/3 Q lepto n 1111 t   W   l l b-jet Critical moment  for top quark determination –determination of b-jet charge –lepton – b-jet association

5. 11/20/2016B.Žilka, S.Tokár, BA Top meeting5 b-jet charge determination  weighting method q i  i th part. Charge w i  i th part. weight Not treated yet  single lepton in bjet cone (soft lepton trigger)  need to take into account B 0 oscillations ~ 1/10 bkgr.  Semileptonic B-meson decay

6. 11/20/2016B.Žilka, S.Tokár, BA Top meeting6 Weighting methods Charging algorithms differ in way we assign weight to bjet tracks... * Absolute pt: * Delta R relative to bjet axis: Longitudinal momentum relative to bjet axis:  i th particle charge  i th particle momentum  b-jet direction   an exponent Optimization for CDF :    Analysis first done for ATLAS (Atlfast, PHYS-2003-35 )

7. 11/20/2016B.Žilka, S.Tokár, BA Top meeting7 Event samples and Selection criteria  Samples for analysis: 226,000 ev. (0.5 pb -1 ), CSC 5200 data in AOD`s, dilepton & lep.+jets ttbar events w/o fully hadronic dilepton events: dilepton events: lepton+jets events: lepton+jets events: All jet modes not suitable due to huge QCD bkgd ! Tot. 4 jets, p T >25 GeV, |  | 25 GeV, |  |<2.5  2 b-tagged jets, p T > 20 GeV, |  | 20 GeV, |  |<2.5  2 jets, p T > 20 GeV, |  | 20 GeV, |  |<2.5 1 or 2 b-tagged Missing E T > 20 GeV Missing E T > 40 GeV 1 isolated leptons (e,  ) p T > 20 GeV, |  | 20 GeV, |  |<2.5 2 isolated leptons (e,  ) p T > 25 GeV, |  | 25 GeV, |  |<2.5Lepton+jetsDilepton ATLAS s/w 11.0.42

8. 11/20/2016B.Žilka, S.Tokár, BA Top meeting8 dilepton case (2 hi-pt leps.) lepton - b-jet association lepton+jets case l and b jet from different tops l and b jet from the same top Our cut: M cr =160 GeV lepton+jets case (1 hi-pt lep.) M top = 175 GeV Alternative:  Alternative: Event kinematic fit (event-by-event )  full reconstruction of event – a lepton +jets combination with minimal  2 defines correct l-b jet association.  Invariant mass criterion lepton-b jet inv. mass mcrmcr

9. 11/20/2016B.Žilka, S.Tokár, BA Top meeting9 statistics Lepton isolation: Analysis overall: Lepton+jets: Dilepton:

10. 11/20/2016B.Žilka, S.Tokár, BA Top meeting10 Track matching to b-jet criteria - Tracks pointing to bjet in  R < 0.4 cone are treated - Tracks with PileUp flag were rejected - Only tracks with pt higher than 1.5 GeV were taken - When more than 10 bjet tracks, only first 10 with highest pt were taken tracks with d0 < d0-threshold to secondary vertex taken tracks with d0 < d0-threshold to secondary vertex taken B-jets reconstructed by Athena were taken: Multiplicity of tracks inside bjet cone, taken from inv.mass b-matching sample

11. 11/20/2016B.Žilka, S.Tokár, BA Top meeting11 MC truth b-tagging  MC truth used for b-tagging: jet reconstructed by Athena found in cone  R=0.4 around b-quark direction charge of b-jet initiated by b-quark and by bbar-quark track charge weighting technique used to find b-jet charge d 0 wrt SVX < 80  m, 2 ≤ tracks to b-jet Q b =- 0.119±0.0012 Q bbar =0.122±0.0012 C b - charge callibration coef.

12. 11/20/2016B.Žilka, S.Tokár, BA Top meeting12 b-jet charge associated with l + and l   Invariant mass criterion used for l-b association (Athena reconstruction, sample 226,000 tt-bar events) -0.097  0.013 0.111  0.013 Q bjet (l + ) Q bjet (l  ) d0 wrt SVX <80um  tracks

13. 11/20/2016B.Žilka, S.Tokár, BA Top meeting13 b-jet charge vs minimal no. of tracks in bjet  Common distribution of Q bjet (l+) and - Q bjet (l-) -0.106  0.009-0.105  0.009 -0.093  0.008-0.071  0.01  1 trk  3 trk  2 trk  5 trk  all with d0 wrt SVX  80 um, Kappa=0.5

14. 11/20/2016B.Žilka, S.Tokár, BA Top meeting14 b-jet charge vs track d 0 wrt SVX   2 trk needed, Kappa=0.5 d 0  20  d 0  100  d 0  60  d 0  300  -0.126  0.013-0.113  0.01 -0.102  0.009-0.095  0.007  Common distribution of Q bjet (l+) and - Q bjet (l-)

15. 11/20/2016B.Žilka, S.Tokár, BA Top meeting15 b-jet vs d0, max d0 wrt SVX, no. of trks

16. 11/20/2016B.Žilka, S.Tokár, BA Top meeting16  Invariant mass criterion used for l-bjet association  top charge reco: Q top = C b.Q bjet (l+) + 1 Q topbar = C b.Q bjet (l-) - 1 Q topbar = C b.Q bjet (l-) - 1 top & topbar charge from lepton and b-jet charge Common distribution of Q top and - Q topbar Q top Q topbar Distribution of Q top and Q topbar Qtop=0.72±0.04 Qtopbar=-0.63±0.04 Qt=0.68±0.03 C b (  5.5) – from MC match

17. 11/20/2016B.Žilka, S.Tokár, BA Top meeting17 Background study  Di-lepton mode: charge asymmetry - Drell-Yan (no) - fakes from W+jets (Wc: yes, Wcc,Wbb ?) - di-boson production (no) ATLAS: proper sel. criteria can provide S/B > 10  Lepton +jets mode: - mistags (W+uds-jets) (no) - W + heavy flavor (Wc :yes, Wcc,Wbb ?) - QCD fakes (no) - di-bosons (no) - Single top (yes)

18. 11/20/2016B.Žilka, S.Tokár, BA Top meeting18 226k Events sample ( 0.5 pb -1 )  Very preliminary analysis of ~226k Events sample ( 0.5 pb -1 ) (CSC 5200 data, ttbar lepton+jets and dilepton samples) has been carried out charge weighting  bjet charge determined by charge weighting of bjet tracks  l-bjet invariant mass criterion enables to distinguish between bjet charges associated with l + and l - ATLAS has a big potential  (No doubt) experiment ATLAS has a big potential for finding top quark charge Summary  Continue  Continue top charge via weighting (upgrade reco: “b-tracks” by b-matching algorithm) b-jet charge calibration needed  In final procedure independent b-jet charge calibration needed background  Study of background processes  Otherapproaches  Other b-charge approaches photo-top quark coupling  Determination of photo-top quark coupling (radiative tt production, renew the results in PHYS-2003-35) Our Plans

19. 11/20/2016B.Žilka, S.Tokár, BA Top meeting19 Thank You!