analysis of jet charged particle momentum distributions for quark-gluon separation in ppbar...
TRANSCRIPT
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