Recent results on strangeness from the STAR experiment

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Recent results on strangeness from the STAR
experiment

• Matthew A. C. Lamont, Yale University
• for the STAR Collaboration

Outline Bulk Measurements
Outside the Bulk
Production vs Energy Strangeness
Enhancement Elliptic Flow
pp Collisions Identified Particle
Ratios di-Hadron Correlations
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STAR strangeness talks at SQM

• F-meson production and flow in HIC at RHIC - S
  Blyth
• Resonance studies with STAR - S Salur
• E-by-E fluctuations in the K/p ratio at RHIC - S
  Das
• Global polarization measurements in AuAu - I
  Selyuzhenkov
• Strange hadron v2 - M Oldenburg
• Studying the sapce-time structure of
  multi-strange baryons - P Chaloupka

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Strange particles - weve got em
gt 95 of all particle production occurs below 2
GeV/c in pT This region dominates the bulk
properties of the system
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Strange Particles vs Energy

• Smooth increase in strange baryon production from
  17 GeV to 200 GeV
• Expected behaviour for ratios with decreasing net
  baryon density observed
• K/p also smooth and shows 50 enhancement over
  pp collisions at RHIC energies

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Strangeness Enhancement at RHIC
Enhancement at 200 GeV similar to SPS
Temperature variations from 165 to 170 MeV
Assuming a constant Tchem
V AaV0 A Npart/2 V0 4/3.pR3
a 1 - scales with Volume
a 2/3 - scales with Surface Area
a 1/3 - scales with Length
Thanks to K. Redlich !!
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Blast wave fits to data
Strong centrality dependence on freeze out
parameters for light hadrons Multi-strange
hadrons freeze out earlier, with a lower
ltßTgt Indicative of smaller cross-section for
interactions of multiply strange hadrons with
lighter species. Is this a signature of partonic
collectivity?
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v2 of strange hadrons

• Mass ordering observed at lower pT
• v2 saturates for pT gt 3 GeV/c
• Clear baryon/meson difference at intermediate to
  high pT observed
• New, high statistics measurement shows deviation
  from ideal scaling ...

The same scaling behaviour is observed in 62 GeV
data
Talk M. Oldenburg, PosterYan Lu
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v2 of multi-strange hadrons
Hydro P. Huovinen, private communication
Talks M. Oldenburg S-L Blyth Poster Yan Lu

• Multi-strange hadrons flow just as well as other
  baryons and mesons
• Collective flow is developed early, during
  partonic stage
• Strange quarks flow like the light quarks ....

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Moving away from the bulk ...
Strangeness in pp collisions
Strangeness at intermediate and high-pT in AuAu
collisions
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Strangeness in pp

• Large statistics data-set allows for the detailed
  analysis of data

Using Pythia (LO) requires changing the K factor
to match the data
(See also talk by S Salur on S)
NLO calculations show good agreement with
non-strange hadrons
Agreement with strange hadrons is not as
apparent, better for AKK than for Vogelsang
EPOS has very good agreement with all particles,
even Xi
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gluon vs quark jets _at_ 200 GeV

• ?/? ratio show dominance of gluon jets when
  compared to Pythia, but is not conclusive.

• mT scaling first studied using ISR data
• no absolute scaling observed in pp, but applying
  pre-factors shows some universal behaviour for
  baryons and mesons

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mT scaling in Pythia

• Pythia shows shape differences on the whole
• Gluon jet events show the difference

• Quark jet events show no difference
• Evidence for gluon jet domination at RHIC?

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Baryons vs Mesons
nucl-ex/0601042
The ?/K0S ratio from Yr2 data exhibits a peak in
the intermediate pT region which is consistent
with ReCo models.
The ?/K0S ratio from Yr4 data extends this
measurement to higher pT and shows that all
centralities appear to converge again
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RCP 200 and 62 GeV

• RCP from Yr2 show clear difference between
  baryons and mesons at intermediate pT
• The F and K clearly follow the mesons and not
  the baryons, not a mass effect

• Data from Yr4 extend the measurement out to much
  higher pT
• The strange and non-strange baryons and mesons
  are consistent and appear to show a similar
  suppression for pT gt 5 GeV/c.

NA57
200 GeV
200 GeV
vsNN 17.2 GeV
0-5
40-55
62 GeV data also shows baryon-meson
splitting Ratios go higher than at 200 GeV -
Cronin?
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Rcp vs Energy
NA57 G. Bruno, A. Dainese nucl-ex/0511020
The top SPS and top RHIC energy data are
consistent
62 GeV AuAu data also follows the same trend
Is coalescence present in all systems?
Will soon be able to test with CuCu data at 200
and 62 GeV
STAR Preliminary
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Strange Correlations in AuAu

• ?F correlations per trigger particle
• 3 lt pTtrigger lt 3.5 GeV/c
• 1 lt pTassoc lt 2 GeV/c
• ? lt 1

?-h
Correlations corrected for TPC acceptance and
efficiency of associated particles
?-h
v2 is then subtracted to give final correlations
Near side
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Correlations near side yields
No trigger particle dependence in the near side
yield/trigger in either dAu or AuAu
dAu
AuAu
No definite trigger particle dependence vs
centrality but meson triggers appear to be
systematically below baryon triggers
Reason for increase may be due to longe range
correlations in ?
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ReCo model and Correlations
R. Hwa, Z. Tan nucl-th/0503060
0-10/40-80
?,?-h
h-h
K0S-h
3 lt pTtrigger lt 6
The ratio of near side yields in central to
peripheral collisions is around 3 at 1 GeV/c and
decreases with increasing pTassoc
This is in good qualitative agreement with ReCo
model predictions though there are some
differences to the model (trigger pT, centrality)
Long range d? correlations are visible in the
STAR data and not taken into account in the plot.
This is pT dependent and may reduce any slope.
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Recent ReCo Model Predictions
Premise
The production of F and O particles is almost
exclusively from thermal s quarks even out to 8
GeV/c
Observables
1)The ratio of O/F yields should rise linearly
with pT
2) Any O or F di-hadron correlations are swamped
by the background and not observed
Being actively studied, but no results are
available as yet
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Correlations in CuCu

• Strange particle correlations are observed at
  intermediate pTtrigger
• Measurement is statistically challenging, but
  factor 10x more stats on disk !!

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Summary and Conclusions
Bulk Measurements
Above the Bulk

• High statistics pp measurement
• Provides a challenge to different models to
  reproduce the data
• Comparisons to Pythia indicate dominance of gluon
  jets
• New high statistics ?/K0S and RCP measurements
• Baryons and mesons exhibit similar suppression
  for pT gt 6 GeV/c
• Double ratio independent of energy!!
• Identified di-hadron correlations at intermediate
  pT
• No trigger particle dependence in the
  intermediate pT region
• Consistent with ReCo model
• Measurements possible in CuCu
• O/F ratio not conclusive, but work is ongoing on
  this and O-h correlations

• Production smooth with energy
• Enhancement similar to SPS energies
• Data provide a strict constraint on Tchem
• v2 measured to high pT
• Baryon-meson splitting in the intermediate to
  high pT region
• Multi-strange particles flow just as well as
  other particles
• partonic collectivity?
• Baryon-meson scaling observed

Strangeness is proving to be a very interesting
and versatile probe at RHIC !!
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?? correlations - the ridge