STARSTAR

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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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STAR preliminary

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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