Why would I want to look at strange particle production?

1
Why would I want to look at strange particle
production?
Truth is ALWAYS strange Lord Byron (1788-1824)
2
Strangeness enhancement

• General arguments for enhancement
• 1. Lower energy threshold
• TQGP gt 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 collision
2
3

• Hadronic ratios.
• pT spectra.
• Resonance production.
• Partonic collectivity.
• High pT measurements.

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
Primary vertex
pion
5
PID over large pT range
X
STAR Preliminary
K0s
f
STAR Preliminary
STAR Preliminary
K
L
STAR Preliminary
W
K
Preliminary
6
Collective motion in Au-Au
data / power law
data
not absolute mT scaling...
but if you rescale
not in Au-Au
7
Kinetic Freeze-out
Blastwave parameterization
STAR Preliminary

• 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
158 AGeV
80 AGeV
40 AGeV
30 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 Thats 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 ?, ?- yields stays constant
• Change in baryon transport reflected in
  anti-particles and K

Refs Physical Review Letters 89 (2002), 092301
nucl-ex/0206008, nucl-ex/0307024
11
What can Kaons tell us?
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
Works very well
STAR Preliminary Au-Au 200 GeV
Fit to NA49 data Becattini et al.
hep-ph/0310049
mB 24 ? 5 MeV ms 1.4 ?1.4 MeV
Tch 160?5 MeV gs 0.99?0.07
Tch 158?2 MeV gs 0.84?0.03
mB 247? 8MeV
15
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 - 1411 states of 1967 Red 4627 states of
1996
m
Satz Nucl.Phys. A715 (2003) 3c
Seems he was correct dont 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 ee-

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
pp
Ensemble of events constitutes a statistical
ensemble T and µ are simply Lagrange multipliers
Phase Space Dominance
AA

• 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 decreasing energy

• Canonical suppression increases with increasing
  strangeness

s(Npart) / Npart e s(pp) e gt 1
Enhancement!
Not new idea pointed out by Hagedorn in 1960s
21
SIS energies
Pion density n(p) exp(-Ep/T) Strangeness is
conserved! Kaon density need to balance
strangeness NN N ? K n(K)
exp(-EK/T) (gKV ? exp-EK/T gL V ?
exp-(E?-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!
J. Cleymans, H. Oeschler, K. Redlich, PRC 59
(1999)
In agreement with T60 MeV
22
Top SPS energies
NA57, vsNN 17.3 GeV
We seem to understand what is happening
23
But then at vs 8.8 GeV
NA57 (D. Elia QM2004)

• C to GC predicts a factor 4 - 5 larger ?-
  enhancement at vsNN 8.8 GeV than at 17 GeV

Perhaps yields dont have time to reach limit
hadronic system? Need to see thermal
fit. (word is it is not too bad)
24
And then at 200 GeV...
Not even flat any more!
But does it over saturate or ONLY just reach
saturation?
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?
Contains ?s and s quark, so not strange should
show no volume dependence
What about the f?
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?

100 200 300 Npart
27
RAA of strangeness
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

• Thats really the end