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

CONTENTS

1. Introduction2. Experimental Data Sets3. MC Data Sets4. Charged Particles Associated with Jets5. Charged Multiplicity in a Jet6. Moment Analysis of Fragmentation7. Gluon Fraction in Jet Samples8. Conclusions

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

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

EXPERIMENTAL DATA SETS CDF detector

vertex time projection chamber central tracking chamber(CTC) central EMcal (CEM) central Hcal endwall Hcal central strip chambers(CES)

EXPERIMENTAL DATA SETS 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

“γ”+jet event include 65% γ+jet“π0”+jet event include 35% γ+jet γfraction : Fγ

neutral meson : wider EM-Showerchi2が小さいところでは photonの確率が大きい

“π0”-jet

“γ/π0”-jet

MC DATA SETS (“REFERENCE” SETS) PYTHIA/HARWIG √s=1.8TeV Dijet and γ-jet

qq/gg(no qg) 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

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i.p. Primary

Vertex

Secondary Vertex

CHARGED MULTIPLICITY IN A JET parton species <- multiplicity in jet Q2->∞ :

CDF Dijet は gluon jet like

CHARGED MULTIPLICITY IN A JET

CDF “γ”+jetは quark jet like

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

MOMENT ANALYSIS OF FRAGMENTATION

gluon jets: broader?

momentの意味？

MOMENT ANALYSIS OF FRAGMENTATION

quark jets: harder?

momentの意味？

CDF data negative(positive) power moment -> closer to gluon(quark) jets ->emphasize soft(hard) component

MOMENT ANALYSIS OF FRAGMENTATION

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+jet data(Fγ=0%)

“π0”+jet(Fγ=35%)

“γ”+jet(Fγ=65%)

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

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

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

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

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

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