1. A few observations on strangeness production at SPS and RHIC
Outline
Strangeness Enhancement – Measurement of entropy?
RAA - Soft physics in the hard regime?
RCP - Energy dependence
mT distributions – Quark vs gluon jets

2. Strangeness enhancement
The enhancements grow with the strangeness of the baryon and centrality.
The enhancements show no linear dependence on Npart.
The enhancements are close to those measured in √sNN =17.3 GeV collisions.
See phase space suppression in p-p
Solid – STAR
Open – NA57
STAR Preliminary
Not well modeled by theory

3. Sensitivity of calculation
K. Redlich – private communication
Correlation volume:
V= AaNN·V0
ANN = Npart/2
V0 = 4/3p·R03
R0 = 1.1 fm
proton radius/
strong interactions
T= MeV
a= 1
Solid – STAR
Open – NA57
STAR Preliminary
Particle ratios indicate
T= 165 MeV
STAR Preliminary
Can it explain energy independence?

4. Energy systematics - motivation from h-
PHOBOS: Phys. Rev. C70, (R) (2004)
There’s a correlation between dNch/dh and Npart/2
small dotted lines are:
dNch/dh = npp(1-x)Npart/2 + xNbin
npp= Yield in pp
= 2.29 ( 1.27)
x = 0.13
N.B.: SPS energy only 17 GeV
From npp can predict yield at any Npart

5. HBT and dNch/dh Scaling works across a large energy range
HBT radii ~linear as a function
Npart1/3
Even better in (dNch/dh)1/3
power 1/3 gives approx. linear scale
Scaling works across a large energy range
nucl-ex/ M.Lisa et al.

6. Strangeness and dNch/dh
Look at yields relative to pp
SPS and RHIC data follows same curves as a func. of dNch/dη
dNch/dη - strongly correlated to the entropy of the system!
Entropy alone seems to drive much of the soft physics

7. Nuclear modification factors - RAA
HIJING/BBar +
KT ~ 1 GeV
Strong Colour Field
qualitatively describes RAA.
SCF - long range coherent fields
SCF behaviour mimicked by doubling the effective string tension
SCF controlsqq and qqqq
production rates and gs
Topor Pop et al. hep-ph/
SCF only produced in nucleus-nucleus collisions RAA≠ RCP
Effects dominate out to high pT

8. Nuclear modification factors - RCP
√sNN=62 GeV
0-5%
40-60%
√sNN=200 GeV
0-5%
40-60%
NA57, PLB in print, nucl-ex/
√sNN=17.3 GeV
First time differences between L and L
B absorption?
Recombination or different “Cronin” for L and K at SPS?

9. Gluon vs quark jets in p-p
No absolute mT scaling – “data” scaled to match at mT~1 GeV/c
Quark jets events display mass splitting
Gluon jets events display baryon/meson splitting
Way to explore quark vs gluon dominance

10. mT distributions of real data
Again no complete scaling
p-p
Appears to be scaling at low mT
STAR Preliminary
p+p 200 GeV
Dominated by gluon jets
Au-Au
Radial flow prevents scaling
at low mT
Seems to scale at higher mT –
no meson/baryon difference
Meson/baryon difference in the p-p not Au-Au

11. Summary Have gathered data for a very detailed study.
Evidence that strangeness production driven by the entropy of the system created, not only by Npart.
Evidence of phase space suppression out to high pT.
RCP meson/baryon difference seen at SPS too.
Starting exporation of strangeness role in fragmentation.

12. How does volume affect production?
Canonical (small system i.e. p-p):
Quantum Numbers conserved exactly.
Computations take into account energy to create companion to ensure conservation of strangeness.
Relative yields given by ratios of phase space volumes
Pn/Pn’ = fn(E)/fn’(E)
Grand Canonical limit (large system i.e. central AA):
Quantum Numbers conserved on average via chemical potential Just account for creation of particle itself.
The rest of the system “picks up the slack”.
When reach grand canonical limit strangeness will
saturate.
Not new idea pointed out by Hagedorn in 1960’s
(and much discussed since)

13. Predictions at higher energies
Canonical suppression increases with increasing strangeness
Canonical suppression
increases with decreasing energy
σ(Npart) / Npart = ε σ(pp) ε > 1 Enhancement!

14. But then at √s= 8.8 GeV
NA57 (D. Elia QM2004)
C to GC predicts a factor larger X- enhancement at √sNN =8.8 GeV than at 17 GeV
Perhaps yields don’t have time to reach limit – hadronic system?