Betty AbelevUI Chicago

Testing the Recombination Model at RHIC using multi-

strange baryon correlations

for the STAR Collaboration

23rd Winter Workshop on Nuclear Dynamics, Big Sky, MT

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Understanding the medium Measure

probes after Thermal freeze-out

Look for probes that traverse the entire medium – Initial

state hard scattering jets

p, K, ,

initial hard scattering

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Medium Probes: Strangeness Partonic system vs.

hadron gas

Canonical ensemble vs. grand-canonical– Exact q.n. conservation– Overall q.n.

conservation & chemical potentials

q q s s

g g s s

N K

K N

Ethres 530 MeV

Ethres 1420 MeV

Ethres = 2ms ≈ 200 MeV

R. Stock on strangeness enhancement:

“Fading away of small volume canonical constraints”

hep-ph/0312039

Hamieh et al.: Phys. Lett. B486 (2000) 61

En

hance

ment

of

stra

nge b

ary

ons

(sss)

(dss)

(uds)

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Strangeness at intermediate pT Strange particle RCP

(Central/peripheral)– Mesons suppressed more than baryons at

intermediate pT

Mesons suppressed more than baryons– Baryon/meson ratio increases with centrality

/K

0 S

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1 2 3 4 5 [GeV/c]

10-1

10-2

10-3

10-4

dN/p

Tdp

Tdy

Coalescence/Recombination of partons

Exponential (thermal) parton spectrum qualitatively explains baryon excess at mid pT

mesons baryons

TT TTT

SS SSS

TS TSS

STT

Recombination:– Shower (S)– Thermal (T)

S & T can mix– Particle spectra

are a sum of various components

3 GeV/c hadron can be

1. Produced via fragmentation

2. If meson: coalescence of 2 1.5 GeV/c partons

3. If baryon: 3 1 GeV/c partons (more abundant!)

R.Hwa et al, Phys.Rev.C70 (024904) 2004.

ReCo cartoon

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Prediction from Rec. Model by Hwa et al

R.C Hwa & C.B. Yang nucl-th/0602024

Shower s-quarks are suppressed w.r.t u & d quarks -- Ω: sss at intermediate pT comes mostly from TTT ! Differ significantly from Λ, which includes non-strange quarks

(STAR)•(STAR)

Use Azimuthal correlations

measure fragmentation (shower-quark contribution) ifif Ω: sss at intermediate pT come mostly from TTT

no Ω correlation partners!

Use Azimuthal correlations

measure fragmentation (shower-quark contribution) ifif Ω: sss at intermediate pT come mostly from TTT

no Ω correlation partners!

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x

y

Statistical Jet Measurement Particles from same jet closely aligned in

Use characteristic jet cone shape for a statistical jet study

High pHigh pTT

tracktrack

1. Find a trigger particle (pT>2 GeV/c)

2. Find an associated particle (pTtrg>pT

as>1.5 GeV/c) in the same event

3. Compute at primary vertex for each 4. Compute at primary vertex

q

q

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Azimuthal Correlation Function Results in a double-peaked

correlation function – Normalize by Ntriggers

p+p and d+Au: 2 Gaussians + flat background

Au+Au: 2 Gaussians +flat background+

flow

B )2σ

π)(Δ(- expA )

2σ

Δexp(-A )C(Δ

2π

2

π20

2

0 )]2cos(21[ 22 astrigvv

If no SSS contribution to spectrum

same-side -h would be flat in most central Au+Au

same-side away-side

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Mesons and Baryons seem to have different v2 at same pT.

If flow is collective– Should scale with

n, number of valence quarks (partons)

Scaling works!

How to get V2 for multi-strange?

Can use v2 for and

J. Adams et al (STAR), Phys. Rev. Lett. 95 (2005) 122301

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Au+Au azimuthal correlations results

A clear same-side -h peak is observed for 2.5-4.5 GeV/c baryon triggers!

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Au+Au azimuthal correlation results

The magnitude of the same-side peak is independent of s-quark content!

Uncertainty due to v2 determination methods

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Comparison to singly-strange (Λ & K0

S)

For same-side meson and baryon yields are similar No dependence on strangeness content Yields increase as a function of pT

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A reference: Correlations in d+Au

-h correlation is observed in d+Au. Same-side yield: 0.015±0.026

Away-side yield: 0.04±0.016

pTtrig>2.0 GeV/c

1.5 GeV/c <pTas<pT

trig

|h|<0.75

What kind of same-side signal to expect with no medium? (not enough statistics in p+p, not enough statistics to measure Ω. Look at Ξ-h in d+Au)

STAR Preliminary

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2-dimensional correlations: Extend analysis in 2

dimensions Same procedure as

for , only use coordinates of trigger and associated

Elongation in under the jet peak: “the ridge”

beam direction

ridge

ridge

jet

jet+ridge

p Ttr

igge

r =3

-6 G

eV

/c,

1.5

Ge

V/c

<p

Tas

soci

ated

< p

Ttr

igge

r

STAR, PRC73, 064907 (2006)\

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Jet and ridge as a function of centrality

Jet onlyJet + Ridge

Measuring jet only: divide the space in jet+ridge (1) and ridge-only (2) regions

Subtract (2) from (1) to obtain jet-only measurement

0

0

(2)(2)

(2)(2)

(1)(1)

jet-only contribution consistent across Nch

– At this pT trig & pT assoc.: 5 x increase of jet+ridge from d+Au to Au+Au increase is all in the ridge.

Compare d+Au result with result in Au+Au:– The pT-integrated (2-6 GeV/c) yield in Au+Au (0.20±0.05)

is 10 x the yield in d+Au (0.015±0.026)! – The ridge?

Jana Bielcikova’s talk, this w

orkshop

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-h in the dip

The signal is indistinguishable from the ridge (perhaps visually only)

We observe a dip in the signal in the =0 region This dip (though to be a detector effect) is still under

investigation Expect a significant loss of signal due to the dip

2.5<pTtrig<4.5 GeV/c

1.5<pTas<pT

trig

STAR Preliminary

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2-D correlation results • The point-by-point subtraction of the two regions: result consistent with 0

We don’t yet have the statistics to subtract the ridge

• Subtracting the fits: the result is encouraging, but is qualitative – large errors.

STAR Preliminary

STAR Preliminary

STAR Preliminary

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Conclusions Multi-strange baryon azimuthal correlations were

observed in d+Au and Au+Au data baryon same-side azimuthal correlation yield in

central Au+Au is ten times that in d+Au data Omega baryon same-side peak was observed in

most central Au+Au, contrary to predictions The ridge was observed in - baryon

correlations in Au+Au, and the excess Au+Au yield is likely due to the ridge

The statistics are not yet sufficient to separate jet and ridge contributions for multi-strange

Outlook:– Omega spectrum measured to a higher pT to detect onset

of fragmentation– Study of the ridge: its composition and dependence on

kinematic and geometrical variables– Study of the away-side