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

CONTENTS 1. Introduction 2. Experimental Data Sets 3. MC Data Sets 4. Charged Particles Associated with Jets 5. Charged Multiplicity in a Jet 6. Moment Analysis of Fragmentation 7. Gluon Fraction in Jet Samples 8. Conclusions

A BSTRUCT 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

I NTRODUCTION difference btw quark/gluon jet -> parton fragmentation quark/gluon tagging + 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 energy) γ-jet (compton effect 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

E XPERIMENTAL D ATA S ETS CDF detector vertex time projection chamber central tracking chamber(CTC) central EMcal (CEM) central Hcal endwall Hcal central strip chambers(CES)

E XPERIMENTAL D ATA S ETS Dijet E T threshold = 20/40 GeV leading jet have E T up to 30/50 GeV jet is found with fixed-cone(R=0.7) algorithm momentum of jet : sum of momentum vectors M inv : clustering algorithm energy centroid : 0.1<|η|<0.7 BtoB : dφ<25 ° |Z v |<60cm gamma-jet isolated EM cluster ((E (R=0.7) -E EM )/E EM <0.15) BtoB : dφ<25 ° energy balance (E γ /E jet : 0.6~1.67) photon id hadron-to-EM cluster energy (E h /E EM <0.005) no tracks cluster tower “γ”-jet “γ”+jet event include 65% γ+jet “π 0 ”+jet event include 35% γ+jet γfraction : F γ neutral meson : wider EM-Shower chi2 が小さいところでは photon の確率が大きい “π 0 ”-jet “γ/π 0 ”-jet

MC D ATA S ETS (“ REFERENCE ” SETS ) PYTHIA/HARWIG √s=1.8TeV Dijet and γ-jet qq/gg(no qg) process detector simulation program reconstruction E T <14~90 GeV γ-jet π 0 -jet : z=(E π +P zπ )/(E p +P zp )>0.7 (large momentum fraction) originate from dijet process apply the same cut

C HARGED P ARTICLES A SSOCIATED WITH J ETS track selection track with p T <0.4GeV is curled impact parameter < 0.5cm(collision-vertex - track axis) z-position<60cm track inside cone η T >1.2 : 1.1 rad from jet axis |P L |>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

C HARGED M ULTIPLICITY IN A J ET parton species <- multiplicity in jet Q 2 ->∞ : CDF Dijet は gluon jet like

C HARGED M ULTIPLICITY IN A J ET CDF “γ”+jet は quark jet like

M OMENT A NALYSIS OF F RAGMENTATION mechanical/electric moments power degree (m=±2) charged multiplicity EM fraction soft さ /hard さを 10 の variables で調べる

M OMENT A NALYSIS OF F RAGMENTATION gluon jets: broader? moment の意味？ gluon jets: broader? moment の意味？

M OMENT A NALYSIS OF F RAGMENTATION quark jets: harder? moment の意味？ quark jets: harder? moment の意味？

CDF data negative(positive) power moment -> closer to gluon(quark) jets ->emphasize soft(hard) component M OMENT A NALYSIS OF F RAGMENTATION

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 π 0 +jet less than that for Dijet by 5~10% “γ”+jet, “π 0 ”+jet sample cut of real photon+jet data(F γ =0%) “π 0 ”+jet(F γ =35%) “γ”+jet(F γ =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(F g =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 F g =70~100% “γ”+jet 40~60% “π 0 ”+jet “γ”+jet +10~30% “γ”+jet, “π 0 ”+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 “π 0 ”+jet : smaller gluon fraction than that of dijet “γ”+jet : smaller gluon fraction than that of “π 0 ”+jet agree with QCD prediction using only multiplicity large uncertainties combination