Probing the Medium at RHIC by Identified Particles

Olga Barannikova, UIC

Probing the Medium at RHIC by Identified Particles

Olga Barannikova Quark Matter 2006, Shanghai 2

Particle distributions in transverse momentumWhat’s hot, what’s not

pT2 GeV/c 10 GeV/c 0 6 GeV/c

Hard / pQCDSoft / Hydro

Pre-RHIC:

Motivation

Olga Barannikova Quark Matter 2006, Shanghai

Particle distributions in transverse momentumWhat’s hot, what’s not

Statistical Models Fragmentation +Jet quenching

0 1 2 3 4 5 6 7 8 9 10pT (GeV/c)

Motivation

Soft / Hydro Hard / pQCD


Olga Barannikova Quark Matter 2006, Shanghai

/k

o s

Particle distributions in transverse momentumIntermediate transverse momentum:

Motivation


Properties of the medium and hadronization mechanisms via identified particle measurements


Intermediate pT

Striking features in experimental observations of identified hadrons:

Out

line

:

xzy

1

2

3

3

cos212

1

nn

TT

nvdydpp

Nd

pd

NdE

PDF NLO FF

Rcp ~ RAB

STAR, PRL95 (2005) 152301


Quark content determines v2

Simplistic hadronization model :v2q = v2h(pT/n)/n

200 GeV Au+Au

min. bias (0–80%)

NCQ Scaling for V2

Deviation from perfect scaling: Imperfections of

recombination approach? Wrong scaling variable? Different hadronization

mechanism?

P. Sorensen, QM2005

o PHENIXPHENIX


Recombination: beyond the Valence Quarks

Simplified approximation: ideal NCO due to recombination ofmassive valence quarks

Gluon degrees of freedom as hidden constituents provide for deviations:

v2/n is larger for meson than baryon!

B. Müller, R. Fries, S Bass, Phys. Lett. B618, 77-83 (2005)


All particles originate from a common flow field

Scaling is observed over extended range of KET

Kinetic Energy Scaling

Pressure gradients converting work into kinetic energy

K E m m mT T T ( ) 1

PHENIX, nucl-ex/0608033

What is the scaling variable?


pT vs. KET Scaling

STAR

How is this observation accommodated the recombination approach?

KET/n seems to work better than pT/n with the constituent quark scaling

J. Jia1 and C. Zhang, hep-ph/0608187


Scaling in Transport Models

Hadron-string transport models reproduce the NCQ scaling qualitatively (The absolute values remain problematic)

Is the NCO scaling a unique feature of the recombination/coalescence models?

Y. Lu et al., JoP. G 32 1121 (2006)


Rcp Scaling

STAR: Nucl. Phys. A 757 (2005) 102

Two groups (2<pT<6GeV/c):

, Ks, K, K*, φ mesons

p, Λ, Ξ, Ω baryons

0-10%/60-80% p

0-10%/60-80%

0-10%/60-92%

2 4 6 8 10

2 4 6 8 10

2 4 6 8 10


Rcp from Recombination

Rcp splitting between baryons and mesons comes naturally in the recombination approach

Hwa, Yang

Recombination + Fragmentation is needed to reproduce identified spectra and Rcp measurements at

higher pT.

Fries, Muller,Nonaka, Bass

R.J. Fries, et al., Phys. Rev. Lett. 90 202303 (2003).R. C. Hwa, et al., Phys. Rev. C 70, 024905 (2004).V. Greco, et al., Phys. Rev. C 68, 034904(2003).


Intermediate pT:“Hard” pions vs. “Soft” protons

Kp

Between Soft and Hard

Crossover:

1.8 GeV/c , 2.6 GeV/c K,

3.8 GeV/c p

T.Hirano, Y.Nara, Phys.Rev.C69,034908(2004)Hydro+Jet

I. Vitev and M. Gyulassy, Phys. Rev. C 65, 041902 (2002)S. J. Casalderrey and E. V. Shuryak, hep-ph/0305160

……..


STAR

/K

0 s

pT (GeV/c)

STAR

Baryon-meson Anomaly

Higher relative baryon yields(ISR: p/π ~ 0.2)

Enhancement observed across all measured species: p/, /K,

All RHIC energies and ions

M. Lamont

L. Ruan

PHENIX, Phys. Rev. C 69, 024904 (2004)STAR, Phys. Rev. Lett. 97 (2006) 152301

PHENIX

D. Morrison_ p

/π


Baryon Enhancement

Soft + Hard: “Recombination” or “Interplay”?

Soft + Quench I. Vitev, M. Gyulassy, Nucl. Phys. A715, 779 (2003)

Hydro + pQCD T. Peitzmann, Nucl. Phys. A727, 179(2003)

Fries, et al. Greco, et al.

Vitev, Gyulassy

Hwa, et al.

Peitzmannp/π

PHENIX STAR

STAR

Coalescence V. Greco, et al. Phys. Rev. Lett. 90, 202302 (2003)

Recombination R.J. Fries, et al., Phys. Rev. C 68, 044902 (2003)R.C. Hwa and C.B. Yang, Phys. Rev. C 67, 034902 (2003)

How to distinguish hadronization mechanisms?


The Jet Factor

S. Blyth, this Quark Matter

Problems for pQCD sector:Large baryon/meson ratioSignificant v2 (from jet quenching?)

Similar E-loss for q- and g-jets

In ReCo composition is different for different particle species

'SSSSTSTTw qq

Could it be “soft-hard” recombination?

Look in the jets!

Details of Soft/Hard cocktail are extremely significant!

17

1.0

< p

T<

1.3

GeV

/c

2-particle Correlations

Baryons and mesons both have jet-like partner particles

Tri

gger

: b

aryo

n/m

eson

Tri

gger

: b

aryo

n/m

eson

h-trigger:baryon production is enhanced, particularly on away side

Baryon vs. meson triggers:lower associated jet yield

Recombination models:

Modified correlation is expected (SSTS)

Quantitative predictions for , p,, K ratios and hadron correlations at high pT

Ass

ocia

te: b

aryo

n/m

eson

Ass

ocia

te: b

aryo

n/m

eson

1.0

< p

T<

1.3

GeV

/c

J. Bielcikova, HP 2006

W. Holzmann, WWND 2006


Correlations in Recombination

pTAssoc. (GeV/c)

Near-side Yields Ratio

R. Hwa, Z. Tan: nucl-th/0503060

─ ReCo

J. Bielcikova, this Quark Matter

Two outstanding issues:

2. Multi-strange hadron correlations

1. Long range η correlations are not accounted forBaryon enhancement in the ridge

Qualitative agreement with Recombination predictions


Summary

A great variety of new experimental results on identified hadrons

The small subset of those presented in this talk was focused on striking features of identified measurements:

Hadronization and/or jet-medium interactions result in baryon enhancement, baryon-meson splitting in the intermediate pT sector, complex systematic at high pT

Elliptic flow is experienced by all hadrons (including strange and multi-strange), hydro-like at low-pT, NCO scaling at intermediate pT

Di-hadron correlations show jet structures for all hadrons studied, with indications of jet-induced baryon enhancements

Mechanisms of jet-medium interactions and hadronization are the keys to the understanding of the matter created

PID measurements hold those keys!


Backup

Olga Barannikova 21

Jet-induced Baryon Enhancement

Rich structure in Au+Au data: Suppression of the Away-side yield Broadening/”ridge” on the Near-side

J. Putschke, HQ 2006

3<pT trig<4 GeV/c, pT assoc>2 GeV/c

“Ridge”

Au+Au central“Jet”

pT assoc > 2 GeV/c

Au+Au 0-10%

STAR

pT trig GeV/c

hp

Baryon enhancement in soft ridge

Baryon enhancement in g-jets:

H. Liu and Zh. Xu, nucl-ex/0610035

New physics?


Pbar/p ratio: model

X.N. Wang: PRC58(2321)1998.PID spectra, centrality dependence of pbar/p and pbar/ ratios, address the color charge dependence of energy lossTo further understand how the gluon jet/quark jet interact with the medium created in Au+Au. collisions.


Pbar/p ratio: data

1. -/+ are consistent with flat at unity in all pT, no significant centrality dependence.

2. pbar/p ratio: no significant centrality dependence, not consistent with the jet quenching prediction (X.N. Wang, PRC 58 (2321) 1998).

STAR Preliminary


– In the NLO calculation that best describes p+p data, significant difference in the gluon contribution between proton and pion spectra

– Yet, no significant difference in suppression: no difference between gluon and quark energy loss?

Energy Loss: q vs. g


Why elliptic flow?

Origin of Flow

Mass ordering at low pT:hydro with early thermalization

(Multi-)strange hadron v2 hints the partonic origin of collectivity

Quark content determines v2

Simplistic hadronization model :v2q = v2h(pT/n)/n

PRC (72), 014904 (2005)

Above pT ~2 GeV/c two groups of hadrons:

, K0s, K,

p, Λ, ,

Sensitive to early evolution


V2 at High pT

High –pt : Density & geometry-driven absorption anisotropy


PHENIX PID Correlations

W. HolzmannWWND 2006

Away side baryon/meson ratio ~2x larger than on near side Away side baryon/meson ratio ~2x larger than on near side Centrality dependent trend of baryon/meson ratio observedCentrality dependent trend of baryon/meson ratio observed Qualitatively similar to ratio of singles distribution from PHENIX.Qualitatively similar to ratio of singles distribution from PHENIX. Particle species dependent jet modificationParticle species dependent jet modification

Probing the Medium at RHIC by Identified Particles

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