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Strange Particle Ratios on the Near- & Away-Side of
Jets at RHIC
Jiaxu Zuo BNL/SINAP
with Paul Sorensen BNL
For STAR Collaboration
23rd Winter Workshop 23rd Winter Workshop on Nuclear Dynamicson Nuclear Dynamics
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Outline
• Motivation
• Analysis Method
• Results & Discussions
• Summary
•STAR Au+Au 200GeV run4 Data
•13M Events
Related STAR analysis presented at WWND07:
•Near-side correlations of strange baryons and mesons (Jana Bielcikova)
•Mulit-strange triggers correlations (Betty Abelev)
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Di-hadron correlations
For high pT: away-side correlation is gone!back-to-back jets are quenched
At lower pT: away-side correlations returnbut they are highly modified with a double
bump!?We will try to understand what causes this behavior
pT,trig>4 GeV/c pT,ass>2 GeV/c
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pT,trig>2.5 GeV/c pT,ass>1.0 GeV/c
STAR preliminary
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Di-hadron correlations
what’s the baryon/meson ratio in the near- and away-side peak?
what are the anti-baryon-to-baryon ratios?
we will measure the ratios to try to understand the source of the correlations
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pT,trig>2.5 GeV/c pT,ass>1.0 GeV/c
STAR preliminary
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Intermediate pT particle ratios
large enhancement of baryon/meson ratio in central Au+Au relative to p+preaches maximum at pT~3 GeV/c
Perhaps related to faster increase with centrality of baryon production from recombination
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Intermediate pT particle
recombination pictures of intermediate pT particle production:supported by meson and baryon grouping of RCP and v2
can recombination explain particle ratios in the jet cones?
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Intermediate pT particle ratios
We can also learn about gluons vs quarks from B/B ratios
for example: anti-baryons dominated by gluon jetsbaryons mixture of quark and gluon
STAR preliminary
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Trigger-associate correlations
identified correlations at high-pT
can provide additional information on:• jet quenching • baryon/meson enhancement at
STAR• particle production
mechanisms
Λ from q-jet and g-jet, Λmore from g-jet
We’ll study identified associate particles using
•Trigger: High pT charged hadron pT>3.0 GeV/c
•Associate: KS, , or (i.e. V0 decay) with pT>1.0 GeV/c
parton
trigger hadron
Λ, Λ, K0S
Λ, Λ, K0S
parton
near-side associated
away-side associated
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Analysis method
Step 1: for each trigger-V0 pair fill a 3-D histogram with , , and minv
Step 2: I project over a given rangein this talk I show results for -1<<1: this combine jets & some ridge
Step 3: plot minv vs
fit the minv distribution to get the yield dN/d for KS, , or
minv
minv
Step 4: repeat 1 to 3 with mixed eventsStep 5: scale the mixed event background with measured v2
subtract off the background assuming zero-yield at the minimumor zero-yield at one (ZYAM or ZYA1)
Jana Bielcikova's talk
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Ks & Lambda Mass
• Fit Ks and Lambda Invariant Mass distribution in different bins
10-40%
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Same Event & v2 BackgroundS
TA
R p
relim
inar
y
for these plots, efficiency correction not applied
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Hadron_Ks & + Correlation
• distribution of Hadron_Ks & + Correlation 10-40%
• Near-Side: Ks seems higher than
Lambda+Anti-Lambda,point by point.
• Away-Side: It seems that Ks is lower
than Lambda+Anti-Lambda.
Particle Ratios Near-Side Away-Side
(+)/Ks0.765(0.120(Sta
t.)0.175(Sys.))
1.71(0.321(Stat.), 0.589(Sys.))
Near-Side Away-Side
3<pT,trig<6 GeV/c 1<pT,ass<4 GeV/c
efficiency corrections
now applied
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Baryon to Meson Ratio with Jets
• pbar to Ratio : Away-Side > Near-Side (PHENIX)
• Lambda to Ks Ratio : Away-Side > Near-Side
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• (B/M)Away /(B/M)Near Double Ratio at PHENIX & STAR
• Both STAR and PHENIX data are consistent with a larger B/M ratio on the away-side -> more matter seems to yield more baryons
(B/M)Away /(B/M)Near Double Ratio
1<pT,assoc<4, 3<pT,trig<6
PHENIX: Meson Trigger
PHENIX QM05 Nucl-ex/0510040
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The shape of the ratio
away
near
Medium
mach cone
Mediumaway
near
deflected jets
can we learn something about the shape on the away-side?• mach cone particles must be slower than the speed of sound• for our pT range they would have to be heavy
for mach-cone emission the bumps should have mostly heavy particles (+)/KS would get large in the bump region
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B/M Ratio in Distribution • A slope at Away-Side? Slow particle Slow particle Mach Cone Mach Cone
Ks Fast particle Ks Fast particle Mach Cone?? Mach Cone??• B/M ratio: Away-Side seems to increase in the "cone" region - B/M ratio: Away-Side seems to increase in the "cone" region -
as it should for mach cone emissionas it should for mach cone emission• Error bars are still too large to concludeError bars are still too large to conclude
???
away
nearM
edium
mach cone
Δ= Trigger
Δ = /2
Medium
Ass
ocia
te
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Hadron_ & Correlation
• distribution of Hadron_& Correlation 10-40%
• Near-Side:Anti-Lambda and Lambda seems consistent.
• Away-Side: Seems a little difference
between Anti-Lambda and Lambda from correlation function
Particle Ratios Near-Side Away-Side
/0.916(0.200(Stat.),
0.200(Sys.))0.894(0.173(Stat.),
0.368(Sys.))
Near-Side Away-Side
3<pT,trig<6 GeV/c 1<pT,ass<4 GeV/c
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• The Ratio at Near-Side & Away-Side is consistent with non-trigger Anti-B/B ratio.
STAR preliminary
Anti-B/B Ratio in Distribution
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Anti-B/B Ratio in Distribution
• Anti-B/B Ratio : • The same slope at Away-Side?? If it is, Why is it a slope??Why is it a slope??
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Summary• Measured the Conditional Yields of identified associate
particles on the near- and away-side of jets• Extracted particle ratios on the near and away-side• Systematic errors from v2 and background normalization
are large– errors can be reduced with more data (to reduce error on the level
of the background) – and better understanding of v2 (to reduce uncertainty on the shape
of the background)• Both STAR and PHENIX results consistent with larger B/M
ratio on the away-side than near-side• Shape of away-side has been studied
– some indication of a slope for B/M and / on the away-side (mach-cone? gluon vs. quark?)
– slope of B/M and / on the away-side seems to be independent of v2 and background subtraction method
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Backup
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V0 reconstructionV0s from UCLA/LBL picoDsts
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Near-Side
Away-Side
preliminary results
B/M Ratio in Distribution
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Near-Side Away-Side
STAR preliminary
Anti-B/B Ratio in Distribution
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Δη correlations - the ridge
Au+Au 20-30%
a
b
c c
b
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Ks, & Hadron v2 • V0 LYZ v2: 10-40%, pt [1,4]
Ks: <v2>=0.104353 (0.000916851)
<v2>=0.105984 (0.00108642)
• Hadron v2{4}: 10-40%, pt [3.2,6.5] <v2{4}>=0.151251 (0.00175313)
• Background: V0 & Hadron v2
• Background function: B()=b0(1+2<v2
A*v2B>cos(2))
AuAu@200GeV
0.0140.987Λ2/vΛ
2v
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