Transcript ppt file - Yale University

Why would I want to look at strange
particle production?
“Truth is ALWAYS strange”
Lord Byron (1788-1824)
Helen Caines
Yale University
Hot Quarks - July 2004
Strangeness enhancement
• General arguments for enhancement:
1. Lower energy threshold
Strange particles with charged
decay modes
TQGP > TC ~ ms = 150 MeV
q q  s s
g g  s s
Ethres  2ms  300 MeV
 NK
Ethres  530 MeV
K     N
Ethres  1420 MeV
K   us , u s      (64%,3.7m)
K 0s  (ds  d s )     (69%,2.7cm)
  ( ss )  K  K  (49%, n/a)
  (uds )  p  (64%,7.9cm)
   (dss )    (100%,4.9cm)
   ( sss )  K  (68%,2.5cm)
 resonances
Note that strangeness is conserved in the
strong interaction
2. Larger production cross-section
 QGP ss    HG ss 
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.
Helen Caines
Hot Quarks – July 2004
2
A theoretical view of the collision
2
1
3
♦ Hadronic ratios.
♦ pT spectra.
♦ Resonance production.
4
♦ 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
Helen Caines
Hot Quarks – July 2004
3
The search
proton
After
Before
Primary
vertex
pion
Helen Caines
Hot Quarks – July 2004
4
PID over large pT range

STAR
Preliminary
K0s

STAR
Prelimin
ary
STAR Preliminary
K*
preliminary

STAR
Prelimin
ary

Preliminary
preliminary
Helen Caines
Hot Quarks – July 2004
K
5
Collective motion in Au-Au
data
data / power law
not absolute
mT scaling...
p-p
but if you rescale
not in Au-Au
Au-Au
Helen Caines
Hot Quarks – July 2004
6
Kinetic Freeze-out
STAR Preliminary
Blastwave parameterization
Tdec = 100 MeV
Kolb and Rapp,
PRC 67 (2003) 044903.

 Large flow, lots of re-interactions, thermalization likely
 ,K,p: Tkin decreases with centrality , : Tkin = const.
 Hydro does not need different T for multi-strange
 Freeze-out T different – Is blastwave realistic?
Helen Caines
Are re-interactions till freeze-out realistic either?
Hot Quarks – July 2004
7
Strange baryon production at SPS
30
AGeV
40 AGeV
80 AGeV
NA49 Pb-Pb Collisions – C.Meurer QM2004
158 AGeV
 , ,  
A clear evolution of shape of  is visible.
No big change of shape of  and  with energy.
Due to baryon transport from beam to mid-rapidity
Helen Caines
Hot Quarks – July 2004
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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 62.4
the beam
plenty
for making strangeness
GeVenergy
data –fits
intoaround
pattern
Helen Caines
Hot Quarks – July 2004
9
Energy (in)dependence of yields
Centrality regions:
NA57: 0-5% (,K), 0-12% (,)
STAR*: 0-5% (), 0-6% (K), 0-10% (,)
 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
*Refs: Physical Review Letters 89 (2002), 092301
reflected in anti-particles and K
nucl-ex/0206008, nucl-ex/0307024
Helen Caines
Hot Quarks – July 2004
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What can Kaons tell us?
Kaons carry large percentage
of strangeness content.
RHIC Au-Au
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
Helen Caines
Hot Quarks – July 2004
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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
ni 
g


p 2 dp
2 2 0 e( E ( p )  ) / T  1
i
i
, Ei 
p 2  mi2
 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
Helen Caines
Hot Quarks – July 2004
Tch, B
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Constraining the parameters
Helen Caines
Hot Quarks – July 2004
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Data – Fit (s)
Ratio
Works very well
Fit to NA49 data
STAR Preliminary
Au-Au 200 GeV
[Becattini et al.: hep-ph/0310049]
Tch = 1582 MeV
gs = 0.840.03
Helen Caines
B = 247 8MeV
Tch = 1605 MeV B = 24  5 MeV
gs = 0.990.07
Hot Quarks – July 2004
s = 1.4 1.4 MeV
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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.
r(m) (GeV-1)
Blue – Exp. fit
Tc= 158 MeV
Green - 1411 states of 1967
Red – 4627 states of 1996
m
filled: AA
open: elementary
[Satz: Nucl.Phys.
A715 (2003) 3c]
Seems he was correct – don’t get above Tch ~170 MeV
Helen Caines
Hot Quarks – July 2004
15
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+eHelen Caines
Hot Quarks – July 2004
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Wroblewski factor
Produced strange quarks to light quark ratio
P. Braun-Munzinger, J. Cleymans, H.Oeschler, K. Redlich, NPA 697(2002) 902
Helen Caines
Hot Quarks – July 2004
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Elementary collisions thermal?
•
Beccatini, Heinz, Z.Phys. C76 (1997) 269
Also Seems to work well ?!
Helen Caines
Hot Quarks – July 2004
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Statistics  Thermodynamics
p+p
Ensemble of events constitutes a statistical ensemble
T and µ are simply Lagrange multipliers
“Phase Space Dominance”
A+A
Helen Caines
One (1) system is already statistical !
• We can talk about pressure
• T and µ are more than Lagrange
multipliers they have physical meaning
Hot Quarks – July 2004
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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’ = n(E)/n’(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
♦ Canonical suppression
with increasing
strangeness
increases
with decreasing energy
σ(N
)
/
N
=
ε
σ(pp)
ε
>
1
Enhancement!
part
part
Not new idea pointed out by Hagedorn in 1960’s
Helen Caines
Hot Quarks – July 2004
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SIS energies
Pion density
C: N ~ V2 (V 0)
n() = exp(-E/T)
GC: N ~ V (V )
Strangeness is conserved!
KaoS ( Au-Au 1 GeV) M. Mang et al.
Assume V ~ Npart
Kaon density – need to
balance strangeness
Pions/Apart constant
NN N Λ K+
grand-canonical!
n(K+) = exp(-EK+/T)*
Kaons/Apart rising
(gKV ∫ … exp[-EK/T] +
canonical!
g V ∫ … exp[-(EΛ-µB)/T])
In agreement with T=60 MeV
Helen Caines
J. Cleymans, H. Oeschler, K. Redlich, PRC 59
(1999)
Hot Quarks – July 2004
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Top SPS energies
NA57, √sNN = 17.3 GeV
We seem to understand what is happening
Helen Caines
Hot Quarks – July 2004
22
But then at √s= 8.8 GeV
NA57 (D. Elia QM2004)
 C to GC predicts a factor 4 - 5 larger - 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)
Helen Caines
Hot Quarks – July 2004
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And then at 200 GeV...
Preliminary
Not evenorflat
any more!
But does it over saturate
ONLY
just reach saturation?
Helen Caines
Hot Quarks – July 2004
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What happens to other particles?
 – 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 ? Contains s and s quark, so not strange
should show no volume dependence
Helen Caines
Hot Quarks – July 2004
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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
100
200
300 Npart
 Still not perfect
 Scaling dependant on pT?
Helen Caines
Hot Quarks – July 2004
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RAA of strangeness
STAR Preliminary
Phase space suppression of strangeness in p-p
plus other effects all pT dependent – need to disentangle
Helen Caines
Hot Quarks – July 2004
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Summary
 The more we learn the less we know!
 Seems that  and  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.
Helen Caines
Hot Quarks – July 2004
28
Backup and stuff
• That’s really the end
Helen Caines
Hot Quarks – July 2004
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