1. Strangeness Production in Heavy-Ion Collisions at STAR
Anthony Timmins for the STAR Collaboration
Introduction..
Bulk strangeness production…
Mid-pT spectra…
Hard processes and strangeness…
Summary…

2. Introduction Strangeness production helps us explore many processes…
STAR Preliminary
Strangeness production helps us explore many processes…
low q2
Strangeness enhancement
Flow
Recombination
high q2
Jet quenching
Flavor changing
New STAR data in this talk
Cu+Cu 62 GeV
High-pT p+p 200 GeV
High-pT Au+Au 200 GeV
pT > 5.5
pT > 7 GeV kaons…

3. Bulk strangeness production As a QGP signature…
Strangeness enhancement key measurement at 200 GeV
Old idea (Phys. Rev. Lett. 48 (1982) 1066)
s+s production cross section increases in QGP
s+s in QGP reaches thermal expectations on small time scale…
s ~3 fm/c (QGP)
s ~ fm/c (hadron gas)
Can it be understood via phase space restrictions?
Canonical Formalism
Strangeness in p+p suppressed relative to A+A? (Phys. Lett. B486 (2000) 61)
Also mentioned in

4. Bulk strangeness production Enhancement at 200 GeV…
Multiple Collisions
Single Collisions
f=1/4
New d+Au 200 GeV data (not shown)
See Xianglei Zhu’s talk later in session
Cu+Cu and Au+Au and enhancements (E) approximately described by simple function:
Predicts…
Rise in E with <Npart>
Higher E for central Cu+Cu
Above 1 E for d+Au 200 GeV
STAR Preliminary
Fraction of participants that undergo multiple collisions
1) Theoretical Issue, how do we relate the old to the observed enhancement factors?
K0S B = 2.10
B = 2.45
 B = 5.05
 B = 13.1

5. Bulk strangeness production dN/dy at 62 GeV…
STAR Preliminary
New Cu+Cu 62 GeV data
No p+p 62 GeV reference data yet
Can still investigate dN/dy per <Npart>
 and K0Sper participant yields can be described by
C f(Npart) + D
Reproduces qualitative features of yields per <Npart>
Turning to multi-strange…
Linear dependance on fraction of participants with multiple collisions
Cu+Cu K0S and : Stat errors only
Au+Au K0S and : Stat+Sys errors
Cu+Cu  and : Stat errors only
Au+Au  and : Stat errors only

6. Bulk strangeness production What about the ?
Enhanced in heavy-ion collisions at 62 and 200 GeV…
 has closed strangeness
Canonical Formalism predicts no enhancement…
Sits between Kaon and Lambda values at 200 GeV...
Also can be described by:
1) Typo-calculate
Since it has closed strangeness, and the phase space restrictions just apply to particles with open strangeness
arXiv: v1
62 GeV B = 1.2
200 GeV B = 2.9

7. Bulk strangeness production What does this scaling mean?
Proposed by F. Becattini and J. Manninen to be indicative of core-corona effects (arXiv: v1)
Participants with one collision = corona
Participants with multiple collisions = core
Strangeness equilibrated in core
B  particle density
Strangeness p+p like in corona
Alternative core-core model EPOS approximately reproduces scaling
As does AMPT (string+rescattering)….

8. Mid-pT spectra Baryon/meson ratios at Au+Au 200 GeV…
Strange baryon/meson anomalies established at STAR
Quark coalescence?
Mid-pT baryon production preferable to meson production
Coalescence models reproduce qualitative features of ratios
p/
/K0S
/
Predict turnover…
Fail to get pT position right…
2) Need Change to SQM 2006 plot…..
Sarah Blyth, Quark Matter 2006

9. Mid-pT spectra Baryon/meson ratios at 62 GeV…
STAR Preliminary
3) New data and new theory comparisons….
New Cu+Cu 62 GeV data…
High strange baryon/meson ratios observed for both systems
Coalescence occuring at lower energy?

10. Mid-pT spectra Comparisons to EPOS…
STAR Preliminary
Energy =
62 GeV
200 GeV
Pos H 0.1
V 1.92
Size 4.51
EPOS Core
Flow induced, gives higher mass particles pT kick at mid-pT
EPOS Corona
Dominates production at high-pT
Are high baryon/meson ratios unique to coalescence?

11. Hard processes and strangeness RAA of identifed particles…
STAR preliminary
pT (GeV/c)
New high-pT p+p and Au+Au 200 GeV data…
p+p shown Yichun Xu’s talk in Ridge Phenomena and Jet Flavor Conversion
Parton flavor conversion prediction (Phys. Rev. C77 (2008) )
Hard scattered partons interact with medium, convert flavour
Boosts kaon RAArelative to pion RAA
Data consistent with conversion scenario…
Point out mass hieracy,

12. Hard processes and strangeness RAA vs. system size…
Measure integrated RAA for pT > 5.5 GeV/c
<pT> ~ 6.2 GeV/c
Ratio
Above one for all centralities
Strangeness enhancement at high-pT!
In particular, RAA (K) > RAA () for Au+Au where <Npart> ~ 20
Does parton flavor conversion happen in small systems?
Can we dismiss the Cronin effect?
Do we have to push higher in pT for parton conversion searches?
Try
New high-pT p+p and Au+Au 200 GeV data…

13. Summary Bulk strangeness production
Enhancement for many particles appears to depend on fraction of participants that undergo multiple collisions
Expected in core-corona scenario
Also reproduced by AMPT
Mid-pT spectra
Coalescence typically describes trends
Core-corona+flow can also explain strange high baryon/meson ratios
Hard processes and strangeness
Hint of jet conversions in central Au+Au
Kaon RAA higher than pion RAA
Also applies to small systems
Can jet conversions happen there also?
Could other effects contribute?

14. Hard processes and strangeness Flavor changing…
Prediction: hard scattered partons interact with medium, convert flavour
Boosts Kaon RAArelative to non-conversion scenario
Kaon RAA factor of two higher at RHIC
Excellent PID for K0S at STAR…
LHC predicts modest increase

15. Mid-pT spectra Quark coalescence in AMPT…
Use particle ratios and constituent quark scaling
Extract shape of strange and up/down quark spectra
Use shapes as input for AMPT’s quark distributions
Run in coalescence mode…
Good description of ,  and  spectra in central Au+Au 200 GeV collisions
Shows quark spectra shapes can be extracted accurately…
Cut this slide….
Phys. Rev. C 78 (2008)