Study of Bulk Matter Properties through Strange Hadrons with the STAR experiment

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Study of Bulk Matter Properties through Strange
Hadrons with the STAR experiment

• Marcelo G. Munhoz
• Universidade de São Paulo - Brasil
• for the Collaboration

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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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Outline

• a (locally) thermally equilibrated state of
  matter in which quarks and gluons are decon?ned
  from hadrons, so that color degrees of freedom
  become manifest over nuclear, rather than merely
  nucleonic, volumes,
• STAR Collaboration, Nucl. Phys. A757 (2005)

QGP
4
Outline
Hot and High Density Medium ?

• Bulk Strangeness production
• v2

• Baryon/meson ratio vs pT
• v2 of strange hadrons

Partonic degrees of freedom ?
HIC

• v2 and v4 Hints from ideal hydro comparison?

Local Thermalization ?
dAu collisions Tests on cold nuclear matter
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The STAR experiment at RHIC

• Large acceptance detector
• Excellent particle identification capability
• High resolution tracking device
• All these points make STAR unique for strange and
  heavy flavored hadrons measurements

STAR Experiment
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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

J. Rafelski, B. Müller, PRL 48 (1982), 1066
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Bulk Properties and Strangeness

• QGP ? Strangeness enhancement in heavy ion
  collisions relative to pp or pA collisions
• Can the Strangeness Enhancement be explained by
  a suppression in pp collisions due to phase
  space limitations?

J. Rafelski, B. Müller, PRL 48 (1982), 1066
K. Redlich, A. Tounsi, Eur. Phys. J. C 24,
589594 (2002)
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Systematic Studies of Strangeness Production
Year System Energy
2000 AuAu 130
2001 AuAu 200
2002 pp 200
2003 dAu 200
2004 AuAu 62.4 200
2005 CuCu 62.4 200
2006 pp 62.4 200
2007 AuAu 200
2008 pp 200
2008 dAu 200

• 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
STAR Collaboration, nucl-ex/0809.0823

• Strange hadrons production are enhanced relative
  to pp
• 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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Systematic Studies of Bulk Strangeness Production
STAR Collaboration, nucl-ex/0809.0823

• Strange hadrons production at CuCu vsNN 200
  GeV does not follow the same Npart dependence as
  in AuAu collisions
• Multiple collision effect? Core-corona?
• The meson f production shows equivalent
  enhancement, although it is not subject to
  canonical suppression ? strangeness enhancement

STAR Collaboration Phys. Lett. B673, p.183 - 191,
2009.
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Systematic Studies of Strangeness Production as a
function of pT

• Baryons are more abundantly produced than mesons
  at intermediate pT as observed in AuAu
  collisions at vsNN 200 GeV
• p/p, ?/Ks0, O/F
• This behavior can be qualitatively reproduced by
  models that assume the coalescence of partons

R. J. Fries et al, Phys. Rev., C68044902,
2003 R. C. Hwa and C. B. Yang, Phys. Rev.,
C67034902, 2003 V. Greco et al, Phys. Rev.
Lett., 90202302,2003.
STAR Collaboration, J. Phys. G34, S933-936, 2007
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Systematic Studies of Strangeness Production as a
function of pT
CuCu, vsNN 62.4 GeV
AuAu, vsNN 62.4 GeV
STAR Preliminary
STAR Preliminary

• Same behavior of ?/Ks0 ratio observed for AuAu
  and CuCu at vsNN 62.4 GeV
• What about O/F ratio for AuAu and CuCu at vsNN
  62.4 GeV?

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Systematic Studies of Strangeness Production as a
function of pT
CuCu, vsNN 62.4 GeV
AuAu, vsNN 62.4 GeV
STAR Preliminary
STAR Preliminary

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

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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 !

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Elliptic Flow and Strangeness
?, O, ?, ?, KS0
J/?, D
?, K, p

• Investigate particle type dependence (Ks0, ?, ?)
• Low hadronic interaction (O, f) probe partonic
  collectivity

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Elliptic Flow of Strange Hadrons
Hydro P. Huovinen and P. V. Ruuskanen, Annu.
Rev. Nucl. Part. Sci. 56, 163 (2006)

• 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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Elliptic Flow of O and f
STAR preliminary
PHENIX nucl-ex/0604011v1

• O and f low hadronic interaction ? partonic
  collectivity !

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Elliptic Flow of Strange Hadrons

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

where
H.-J. Drescher, A. Dumitru, C. Gombeaud and J.-Y
Ollitraut, Phys. Rev. C76, 024905 (2007).
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The fourth harmonic (v4) of Strange Hadrons

• v4(pT) has been measured for ?, KS0 and ?
• The nq scaling for v4 is observed at
• (mT - m)/nq lt 1 GeV/c2,
• similar to that of v2
• v4/v22 can probe the ideal hydro approach

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

• Why dAu collisions are interesting?
• Important probe to distinguish initial effects
  from final state interactions in AuAu collisions
• Strangeness production in dAu 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
STAR Preliminary
statistical error only for dAu data

• KS0 and ? yields fit the trend for the most
  peripheral AuAu and CuCu collisions
• ? yields fit the trend for the most peripheral
  CuCu collisions
• The strangeness hierarchy is preserved in dAu

dN/dy / ltNpartgt relative to pp
Number of Participants Npart
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Cold Nuclear Matter and Strangeness

• Most central dAu data approaches peripheral
  AuAu ratio values
• Similar explanation as in AuAu?
• AuAu Enhanced rescattering effects

STAR Preliminary
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Cold Nuclear Matter and Strangeness

• K0s agree with pions at low pT
• ? 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 F-meson measurement

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Summary
Hot and High Density Medium ?

• Strangeness enhancement and v2

• Hadronization through quark coalescence
• Partonic collectivity

Partonic degrees of freedom ?
HIC

• Under investigation
• Future effort

Local Thermalization ?
dAu collisions final state effects in HIC
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Thank you !