1. Why would I want to look at strange particle production?
“Truth is ALWAYS strange”
Lord Byron ( )

2. Strangeness enhancement
General arguments for enhancement:
1. Lower energy threshold
TQGP > TC ~ ms = 150 MeV
Note that strangeness is conserved in the strong interaction
2. Larger production cross-section
Strange particles with charged
decay modes
Enhancement is expected to be more pronounced for
multi-strange baryons and their anti-particles
Arguments still valid but now use strange particles for MUCH MORE.

3. A theoretical view of the collision2 3 1
Hadronic ratios.
pT spectra.
Resonance production.
Partonic collectivity.
High pT measurements. 4
Tc – Critical temperature for transition to QGP
Tch– Chemical freeze-out (Tch  Tc) : inelastic scattering stops
Tfo – Kinetic freeze-out (Tfo  Tch): elastic scattering stops

4. The search
proton
After
Before
Primary
vertex
pion

5. PID over large pT range X K0s f K* L W K STAR Preliminary

6. Collective motion in Au-Au
data
data / power law
p-p
not absolute
mT scaling...
but if you rescale
Au-Au
not in Au-Au

7. Blastwave parameterization
Kinetic Freeze-out
Blastwave parameterization X
STAR Preliminary
Tdec = 100 MeV
Kolb and Rapp, PRC 67 (2003)
Large flow, lots of re-interactions, thermalization likely
p,K,p: Tkin decreases with centrality , X: Tkin = const.
Hydro does not need different T for multi-strange
Freeze-out T different – Is blastwave realistic?
Are re-interactions till freeze-out realistic either?

8. Strange baryon production at SPS
AGeV
40 AGeV
80 AGeV
158 AGeV
preliminary
preliminary
preliminary
NA49 Pb-Pb Collisions – C.Meurer QM2004
 L,  X,  W
A clear evolution of shape of L is visible.
No big change of shape of X and W with energy.
Due to baryon transport from beam to mid-rapidity

9. Baryon transport to mid-rapidity
Clear systematic trend with collision energy
Very similar trend between heavy ion and p-p
E866 -
At RHIC top energies ~25 TeV is stopped for particle production
That’s ~75% of the beam energy – plenty around for making strangeness
62.4 GeV data fits into pattern

10. Energy (in)dependence of yields
Centrality regions: NA57: 0-5% (L,K), 0-12% (X, W)
STAR*: 0-5% (L), 0-6% (K), 0-10% (X, W)
T, µB and V can all vary with energy, but in such a way as to ensure Λ, Ξ- yields stays constant
Change in baryon transport reflected in anti-particles and K
*Refs: Physical Review Letters 89 (2002),
nucl-ex/ , nucl-ex/

11. What can Kaons tell us? RHIC Au-Au
Kaons carry large percentage of strangeness content.
K- = us
K+ = su
Ratio tells about baryon
transport even though not a baryon.
By varying rapidity range can study many different physics regions – Especially at RHIC

12. Statistical hadronic models
Assume thermally (constant Tch) and chemically (constant ni) equilibrated system at chemical freeze-out
System composed of non-interacting hadrons and resonances
Given Tch and  's (+ system size), ni can be calculated in a grand canonical ensemble
Obey conservation laws: Baryon Number, Strangeness, Isospin
Short-lived particles and resonance feed-down need to be taken into account
Minimization of difference between calculated ratios and experimental data
Tch, mB

13. Constraining the parameters

14. [Becattini et al.: hep-ph/0310049]
Works very well
Data – Fit (s) Ratio
STAR Preliminary
Au-Au 200 GeV
Fit to NA49 data
[Becattini et al.: hep-ph/ ]
Tch = 1605 MeV
gs = 0.07
mB = 24  5 MeV
ms = 1.4 1.4 MeV
Tch = 1582 MeV
gs = 0.03
mB = 247 8MeV

15. Seems he was correct – don’t get above Tch ~170 MeV
Tch systematics
Hagedorn (1965):
If the resonance mass spectrum grows exponentially
(and this seems to be the case):
There is a maximum possible temperature for a system of hadrons.
Blue – Exp. fit
Tc= 158 MeV
r(m) (GeV-1)
filled: AA
open: elementary
Green states of 1967
Red – 4627 states of 1996 m
[Satz: Nucl.Phys.
A715 (2003) 3c]
Seems he was correct – don’t get above Tch ~170 MeV

16. Limits of thermodynamics
This exercise in “hadro-chemistry”
Applies to final-state (ordinary) hadrons
Does not (necessarily) indicate
Deconfinement
Says nothing about how
or when the system got
there or its dynamical
properties
A smooth continuation of trends seen
at lower energies
in p-p, even e+e-

17. Wroblewski factor Produced strange quarks to light quark ratio
P. Braun-Munzinger, J. Cleymans, H.Oeschler, K. Redlich, NPA 697(2002) 902

18. Elementary collisions thermal?
Beccatini, Heinz, Z.Phys. C76 (1997) 269
Also Seems to work well ?!

19. Statistics  Thermodynamics
p+p
Ensemble of events constitutes a statistical ensemble
T and µ are simply Lagrange multipliers
“Phase Space Dominance”
A+A
One (1) system is already statistical !
We can talk about pressure
T and µ are more than Lagrange multipliers they have physical meaning

20. How do we know when its thermal?
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.
Canonical suppression increases with increasing strangeness
Canonical suppression
increases with decreasing energy
σ(Npart) / Npart = ε σ(pp) ε > 1 Enhancement!
Not new idea pointed out by Hagedorn in 1960’s

21. In agreement with T=60 MeV
SIS energies
Pion density
n(p) = exp(-Ep/T)
Strangeness is conserved!
Kaon density – need to balance strangeness
NN N Λ K+
n(K+) = exp(-EK+/T)*
(gKV ∫ … exp[-EK/T] +
gL V ∫ … exp[-(EΛ-µB)/T])
KaoS ( Au-Au 1 GeV) M. Mang et al.
C: N ~ V2 (V 0)
GC: N ~ V (V )
Assume V ~ Npart
Pions/Apart constant
grand-canonical!
Kaons/Apart rising
canonical!
In agreement with T=60 MeV
J. Cleymans, H. Oeschler, K. Redlich, PRC 59 (1999)

22. Top SPS energies NA57, √sNN = 17.3 GeV
We seem to understand what is happening

23. But then at √s= 8.8 GeV
NA57 (D. Elia QM2004)
C to GC predicts a factor larger Ξ- enhancement at √sNN =8.8 GeV than at 17 GeV
Perhaps yields don’t have time to reach limit – hadronic system?
Need to see thermal fit. (word is it is not too bad)

24. But does it over saturate or ONLY just reach saturation?
And then at 200 GeV...
Preliminary
But does it over saturate or ONLY just reach saturation?
Not even flat any more!

25. What happens to other particles?
p – show Npart scaling
p – show slight increase
phase space suppression
of baryons?
K0s – show increase
only small phase space
suppression of strange
mesons?
What about the f?
Contains s and s quark, so not strange
should show no volume dependence

26. Can we find a scaling?
The more strangeness you add to the baryon the less it scales with Npart
The larger strangeness content scales better with Nbin
Still not perfect
Scaling dependant on pT?
Npart

27. RAA of strangeness Phase space suppression of strangeness in p-p
STAR Preliminary
Phase space suppression of strangeness in p-p
plus other effects all pT dependent – need to disentangle

28. Summary The more we learn the less we know!
Seems that X and W freeze-out differently as a function of centrality – except at SPS...
Net baryon density depends on collision energy not system
Appear to have strangeness saturation at most central top RHIC but not before
What happens at SPS?
Seems our simple thermal pictures are only approximately correct.
The devil is in the details but we have the data to figure it all out.

29. Backup and stuff
That’s really the end