Study of Bulk Matter Properties through Strange Hadrons with the STAR experimentMarcelo G. MunhozUniversidade de São Paulo - Brasil

for the Collaboration

Outline• Present new results from the STAR Collaboration towards the understanding of relativistic heavy ion collisions dynamics▫ What are the observable signatures for the identification and characterization of the QGP, mainly related to strange hadrons ?

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“… a (locally) thermally equilibrated state of matter in which quarks and gluons are deconfined from hadrons, so that color degrees of freedom become manifest over nuclear, rather than merely nucleonic, volumes”,

STAR Collaboration, Nucl. Phys. A757 (2005)

Outline

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QGP

Outline

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Hot and High Density

Medium ?

Partonic degrees of freedom ?

Local Thermalization ?

• Bulk Strangeness production• v2

• Baryon/meson ratio vs pT

• v2 of strange hadrons

• v2 and v4: Hints from ideal hydro comparison?

d+Au collisions: Tests on cold nuclear matter

HIC

The STAR experiment at RHIC

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STAR Experiment

• Large acceptance detector

• Excellent particle identification capability

• High resolution tracking device

• All these points make STAR unique for strange and heavy flavored hadrons measurements

Bulk Properties and Strangeness•Bulk strangeness production is favored in the QGP environment relative to a pure hadronic one▫ Gluon fusion▫ Faster equilibration▫ Lower energy threshold for strangeness production

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J. Rafelski, B. Müller, PRL 48 (1982), 1066

Bulk Properties and Strangeness

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J. Rafelski, B. Müller, PRL 48 (1982), 1066

• QGP ⇒ Strangeness enhancement in heavy ion collisions relative to p+p or p+A collisions

• Can the “Strangeness Enhancement” be explained by a suppression in p+p collisions due to phase space limitations?

K. Redlich, A. Tounsi, Eur. Phys. J. C 24, 589–594 (2002)

Systematic Studies of Strangeness Production• Energy and system size

systematic measurements

• Allows to investigate the mechanisms behind strangeness production in these collisions

• What is the influence of the system geometry?

• How does strangeness production change as a function of energy?

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Systematic Studies of Bulk Strangeness Production• Strange hadrons production are enhanced relative to p+p

• Relative enhancement seems to be slightly lower than in SPS: no clear energy dependence

• Strangeness content “hierarchy”

• Production volume not proportional to Npart

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STAR Collaboration, nucl-ex/0809.0823

Systematic Studies of Bulk Strangeness Production

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STAR Collaboration, nucl-ex/0809.0823

• Strange hadrons production at Cu+Cu √sNN = 200 GeV does not follow the same Npart dependence as in Au+Au collisions▫ Multiple collision effect? Core-corona?

• The meson production shows equivalent enhancement, although it is not subject to “canonical suppression” ⇒ strangeness enhancement STAR Collaboration

Phys. Lett. B673, p.183 - 191, 2009.

Systematic Studies of Strangeness Production as a function of pT• Baryons are more

abundantly produced than mesons at intermediate pT as observed in Au+Au collisions at √sNN = 200 GeV

▫ p/π, Λ/Ks0, Ω/Φ

• This behavior can be qualitatively reproduced by models that assume the coalescence of partons

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STAR Collaboration, J. Phys. G34, S933-936, 2007

R. J. Fries et al, Phys. Rev., C68:044902, 2003R. C. Hwa and C. B. Yang, Phys. Rev., C67:034902, 2003V. Greco et al, Phys. Rev. Lett., 90:202302,2003.

Systematic Studies of Strangeness Production as a function of pT

• Same behavior of Λ/Ks0 ratio observed for Au+Au and Cu+Cu at

√sNN = 62.4 GeV • What about Ω/Φ ratio for Au+Au and Cu+Cu at √sNN = 62.4 GeV?

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STAR Preliminary

Cu+Cu, √sNN = 62.4 GeV

STAR Preliminary

Au+Au, √sNN = 62.4 GeV

Systematic Studies of Strangeness Production as a function of pT

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STAR Preliminary

Cu+Cu, √sNN = 62.4 GeV

STAR Preliminary

Au+Au, √sNN = 62.4 GeV

• Is there coalescence of partons at lower energy? • Is this the only approach to describe such behavior?• See G. Vasconcelos talk

2 2

2 2

y xy x

12 cos 2 , tan ( )y

x

pv

p

Azimuthal Anisotropy: Elliptic Flow

Almond shape overlap region in coordinate space

Anisotropy in momentum space

Interactions/ Rescattering

•Very important tool to probe the early stages of the collision dynamics !

Elliptic Flow and Strangeness

• Investigate particle type dependence (Ks0, Λ, Ξ)

• Low hadronic interaction (Ω, ): probe partonic collectivity

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partonic hadronic

J/Ψ, D , Ω, Ξ, Λ, KS0 , K, p

Elliptic Flow of Strange Hadrons• Hydro approach reproduces mass ordering

• v2 of strange hadrons shows baryon-meson difference:▫ nq scaling: hadronization of partons

• Indications of a different behavior for higher pT

STAR preliminary

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Hydro: P. Huovinen and P. V. Ruuskanen, Annu. Rev. Nucl. Part. Sci. 56, 163 (2006)

Elliptic Flow of Ω and

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• Ω and : low hadronic interaction ⇒ partonic collectivity !

STAR preliminaryPHENIX: nucl-ex/0604011v1

STAR preliminary

Elliptic Flow of Strange Hadrons

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STAR preliminaryHydro limit

€

v2

ε ⎡ ⎣ ⎢

⎤ ⎦ ⎥= v2

ε ⎡ ⎣ ⎢

⎤ ⎦ ⎥hydro

11+K 0.7

€

K ≡ λR⇒ 1K

=σ ⋅cs ⋅1SdNdy

where:H.-J. Drescher, A. Dumitru, C. Gombeaud and J.-Y Ollitraut, Phys. Rev. C76, 024905 (2007).

• From this approach, even in central Au + Au collisions, fitting results indicate that the system is still away from ideal hydro limit

The fourth harmonic (v4) of Strange Hadrons• v4(pT) has been measured for , KS

0 and

• The nq scaling for v4 is observed at (mT - m)/nq < 1 GeV/c2, similar to that of v2

• v4/v22 : can probe the

ideal hydro approach

STAR preliminary

STAR preliminary

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STAR preliminary

N. Borghini and J.-Y. Ollitraut, Phys. Lett. B 642 227 (2006)

Cold Nuclear Matter•Why d+Au collisions are interesting?▫Important probe to distinguish initial effects from final state interactions in Au+Au collisions

•Strangeness production in d+Au collisions▫Add important information on the particle type dependence of these effects for wide range of pT

▫The meson has a special role, since it is a meson with mass comparable to proton (baryon) and it has lower hadronic interaction cross section

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Cold Nuclear Matter and Strangeness• KS

0 and Λ yields fit the trend for the most peripheral Au+Au and Cu+Cu collisions

• Ξ yields fit the trend for the most peripheral Cu+Cu collisions

• The strangeness hierarchy is preserved in d+Au

STAR Preliminarystatistical error only for d+Au data

Number of Participants Npart

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Cold Nuclear Matter and Strangeness• Most central d+Au data approaches peripheral Au+Au ratio values

• Similar explanation as in Au+Au?▫ Au+Au: Enhanced rescattering effects

STAR Preliminary

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Cold Nuclear Matter and Strangeness• K0

s agree with pions at low pT

• Λ agrees with proton at intermediate pT (2 – 4 GeV/c)

• Indications of particle type (baryon/meson) dependence of RdAu for pT from 2.0 to 4 GeV/c

• More data are necessary for Φ-meson measurement

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ppinelbindAu

TTppineldAu

TTTdAu

NT

dydppdTdydppNdpR

/

)2/()2/()( 2

2

Summary

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Hot and High Density

Medium ?

Partonic degrees of freedom ?

Local Thermalization ?

• Strangeness enhancement and v2

• Hadronization through quark coalescence• Partonic collectivity

• Under investigation• Future effort

d+Au collisions: final state effects in HIC

HIC

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