contents

1. Analysis of Jet Charged Particle Momentum Distributions for Quark-Gluon Separation in ppbar Collision at sqrt(s)=1.8TeV

2. contents • Introduction • Experimental Data Sets • MC Data Sets • Charged Particles Associated with Jets • Charged Multiplicity in a Jet • Moment Analysis of Fragmentation • Gluon Fraction in Jet Samples • Conclusions

3. Abstruct • Jet analysis at CDF • with charged particle distributions in Jet • proton−anti-proton 1.8TeV • comparison with QCD inspired MC(PYTHIA,HERWIG) • gluon fraction • charged particle multiplicity • likelihood function <- PYTHIA,HERWIG • consistent with QCD predictions • Dijet : gluon-rich • gamma-Jet : quark-rich

4. Introduction • difference btw quark/gluon jet -> parton fragmentation • quark/gluon tagging method @e+e- annihilation • quark(gluon) enriched samples / the ratio of gluon • quark jet : harder fragmentation • gluon jet : softer fragmentation • models for hadronization • PYTHIA : string model • HARWIG : cluster model • data sets(q/g fraction is different) • dijet (gluon jet dominate @CDF energy) • γ-jet (compton effect dominate @CDF energy) • π0->2γBKGでgluon richな方向に • quark/gluon tagging • 3-jets • lowest energy->gluon • opening angle • largest->quark , others with lepton->quark

5. Experimental Data Sets • CDF detector • vertex time projection chamber • central tracking chamber(CTC) • central EMcal (CEM) • central Hcal • endwallHcal • central strip chambers(CES)

6. Experimental Data Sets “γ/π0”-jet “γ”-jet “π0”-jet • Dijet • ET threshold = 20/40 GeV • leading jet have ET up to 30/50 GeV • jet is found with fixed-cone(R=0.7) algorithm • momentum of jet : sum of momentum vectors • Minv : clustering algorithm • energy centroid : 0.1<|η|<0.7 • BtoB : dφ<25 ° • |Zv|<60cm • gamma-jet • isolated EM cluster ((E(R=0.7)-EEM)/EEM<0.15) • BtoB : dφ<25 ° • energy balance (Eγ/Ejet: 0.6~1.67) • photon id • hadron-to-EM cluster energy (Eh/EEM<0.005) • no tracks point @ cluster tower “γ”+jet event include 65% γ+jet “π0”+jet event include 35% γ+jet γfraction : Fγ neutral meson : wider EM-Shower chi2が小さいところではphotonの確率が大きい

7. MC Data Sets (“reference” sets) • PYTHIA/HARWIG √s=1.8TeV • Dijet and γ-jet • qq/gg(noqg) process • detector simulation program • reconstruction • ET<14~90 GeV • γ-jet • π0-jet : z=(Eπ+Pzπ)/(Ep+Pzp)>0.7 (large momentum fraction) • originate from dijet process • apply the same cut

8. Charged Particles Associated with Jets • track selection • track with pT<0.4GeV is curled • impact parameter < 0.5cm(collision-vertex - track axis) • z-position<60cm • track inside cone • ηT >1.2 : 1.1 rad from jet axis • |PL|>0.3GeV • jet-rest frame treating • assume pion masses • BKG subtraction(forward135°以内のmomentumを足し合わせる) • BKGの60%をsubtractでき, jetの90%が生きのこる PrimaryVertex i.p. Secondary Vertex

9. Charged Multiplicity in a Jet • parton species <- multiplicity in jet • Q2->∞ : CDF Dijet はgluon jet like

10. Charged Multiplicity in a Jet CDF “γ”+jetはquark jet like

11. Moment Analysis of Fragmentation • mechanical/electric moments • power degree (m=±2) • charged multiplicity • EM fraction • softさ/hardさを10のvariablesで調べる

12. Moment Analysis of Fragmentation gluon jets: broader? momentの意味？

13. Moment Analysis of Fragmentation quark jets: harder? momentの意味？

14. Moment Analysis of Fragmentation • CDF data • negative(positive) power moment • -> closer to gluon(quark) jets • ->emphasize soft(hard) component

15. gluon fraction in jet samples(1)gluon fractions evaluated from sub-process cross section • theoretical gluon fraction by PYTHIA • γ+jet • quark jet > gluon jet • photon brems. ->uncertain • Dijet • gluon jet > quark jet • π0+jet • less than that for Dijet by 5~10% • “γ”+jet, “π0”+jet sample • cut of real photon+jetdata(Fγ=0%) • “π0”+jet(Fγ=35%) • “γ”+jet(Fγ=65%)

16. gluon fraction in jet samples(2)gluon fractions by moment/likelihood method • log-likelihood • P(q,g) : normalized distribution function • separation power • Δ : difference of mean likelihood • σ : combined standard deviation • global likelihood • equal-weighted sum

17. gluon fraction in jet samples(2)gluon fractions by moment/likelihood method • separation power(30-40GeV) • 0.85(PYTHIA) • 0.70(HERWIG) • likelihood distribution • reference sample(Fg=0,25,50,75,100%) • consistency btw input & output gluon fraction

18. gluon fraction in jet samples(4)results and comparison with values obtained from sub-process cross section • correction • acceptance • efficiency • Dijet • Fg=70~100% • “γ”+jet • 40~60% • “π0”+jet • “γ”+jet +10~30% • “γ”+jet, “π0”+jetもFgが大きいが、その差はconsistent with expectation

19. gluon fraction in jet samples(5)evaluation of the gluon fraction from the multiplicity • 10 variables • not as much as affected the track efficiency change • charged multiplicity • affect the track multiplicity change

20. gluon fraction in jet samples(6)evaluation of the gluon fraction from asymmetric combination of variables • discrepancy (positive & negative) • Soft charged particles -> negative • hard charged particles-> positive • discrepancy (transverse & longitudinal) • angular spread

21. conclusion • jet fragmentation properties of Dijet & photon-jet • charged multiplicity difference btw photon-jet & dijet • consistent with QCD • moment analysis • 10 variables • gluon jet : softer and broader • larger color charge • CDF dijet : gluon-like • consistent with QCD • Q/G separation • log-likelihood • dijet : gluon-rich • photon-jet : quark-rich • gluon fraction • dijet : slight decreace • “π0”+jet : smaller gluon fraction than that of dijet • “γ”+jet : smaller gluon fraction than that of “π0”+jet • agree with QCD prediction • using only multiplicity • large uncertainties • combination