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Helen CainesYale University
1st Meeting of the Group on Hadronic Physics , Fermi Lab. – Oct. 2004
Bulk matter properties in RHIC collisions
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GHPM – Oct. 2004 2
Outline
Tc – Critical temperature for transition to QGPTch– Chemical freeze-out (Tch Tc) : inelastic scattering stopsTfo – Kinetic freeze-out (Tfo Tch): elastic scattering stops
♦ Hadronic ratios.
♦ Resonance production.
♦ pT spectra.
31 2
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RHIC detectors designed for PID
So far the RHIC experiments have published identified So far the RHIC experiments have published identified particle spectra for:particle spectra for:
, , , K, K, K, K00ss, p, d, , p, d, , , ±
00, , , , , , , K, K*0*0(892), (892), *(1385), *(1385), *(1520)
DD00, D, D±, J/, J/’s’s (+ anti-particles)(+ anti-particles) …
V0 decay vertices
Ks + + -
p + -
p + +
- + -
+ + +
+ K -
Au+Au
40% to 80%
0.2 pT 0.9 GeV/c
0
f0
K0S
K*0
STAR Preliminary
dE/dx in TPC
Time of Flight (ToF)
Electron ID viap/E in EMC
Resonances in invariant mass spectra
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A theoretical view of the collision
1
Chemical freezeout (Tch Tc) : inelastic scattering stops
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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.
Changing rapidity slice changes chemistry
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Models to evaluate Tch and B
Compare particle ratios to experimental data
Qi : 1 for u and d, -1 for u and d
si : 1 for s, -1 for s
gi : spin-isospin freedom
mi : particle mass
Tch : Chemical freeze-out
temperatureq : light-quark chemical potential
s : strangeness chemical potential
s : strangeness saturation factor
Particle density of each particle:Statistical Thermal ModelF. Becattini; P. Braun-Munzinger, J. Stachel, D. MagestroJ.Rafelski PLB(1991)333; J.Sollfrank et al. PRC59(1999)1637
Assume: ♦ Ideal hadron resonance gas ♦ thermally and chemically equilibrated fireball at hadro-chemical freeze-out
Recipe:♦ GRAND CANONICAL ensemble to describe partition function density of particles of species i
♦ fixed by constraints: Volume V, ,
strangeness chemical potential S,
isospin♦ input: measured particle ratios♦ output: temperature T and baryo-chemical potential B
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Centrality and Energy Dependence
●, K,p●, K,p, ,
STAR preliminary Au+Au at √sNN=200GeV and 62 GeV
TTLQCDLQCD~160-170MeV~160-170MeVTTLQCDLQCD~160-170MeV~160-170MeV
●, K,p●, K,p, ,
Energy dependence but small NEnergy dependence but small Nch ch dependence… dependence…
Close to chem. equilibrium !
Close to net-baryon free
Tch flat with centrality
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Rapidity Dependence
Fit resultsMeanUpper/Lower error
• Tch, s
– Small sensitivity to y– Close to strangeness equilibration in
central collisions over y=0-3 (ybeam=6)
• q, s – Reflect baryon density with yBRAHMS Au+Au 200 GeV
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(In)dependence of mid-rapidity yields
T, µB, and V can all vary with energy, but in such a way as to ensure yields stay ~constant
Preliminary
Preliminary
Preliminary
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200 GeV Au+Au
Results of Fit
Strangeness Enhancement
Resonance Suppression
Au+Au only stable particle ratios well described
STAR Preliminary
200 GeV p+p
p+p particle ratios well described
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How does volume affect production?
When reach grand canonical limit strangeness will
saturate.
– 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”.
Not new idea pointed out by Hagedorn in 1960’s(and much discussed since)
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How can we observe this
♦ Canonical suppression increases with decreasing energy
♦ Canonical suppression increases with increasing strangeness
σ(Npart) / Npart = ε σ(pp) ε > 1 Enhancement!
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SPS at √s= 17.3 & 8.8 GeV
C to GC predicts a factor 4 - 5 larger - enhancement at √sNN =8.8 GeV than at 17.3 GeVYields don’t have time to reach limit – hadronic system?
Temperature assumed is incorrect?
NA57 (D. Elia QM2004)
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But does it over saturate or ONLY just reach saturation?
And then at RHIC (200 GeV)...
not flat any more!
,K,p
,K,p,
STAR Preliminary
Au-Au √s=200 GeV
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Rcp of strange particlesR
cpBaryons and mesons are different
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RAA of strange particles
Baryons with s quarks scale differently to non-strange.
h-
Phase space suppression in p+p vs jet suppression in Au+Au.
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Is there a scaling?
The more strangeness you add the less it scales with Npart.
Npart scaling
Normalized to unity for 0-5% data
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Is there a scaling?
The larger strangeness content scales better with Nbin.
Still not perfect.
Normalized to unity for 0-5% data
Nbin scaling
The more strangeness you add the less it scales with Npart.
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s quarks have different scaling? How about scaling according
to quark content?
u, d – scale with Npart
– already observed.
s – scale with Nbin
– appears better for strange
particles.K0
s – 1/2*Npart + 1/2*Nbin
p – Npart
– 2/3*Npart + 1/3*Nbin
– 1/3*Npart + 2/3*Nbin
– Nbin
– Nbin
Pretty good!
Does strangeness “see” a different
correlation volume?– Npart
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A theoretical view of the collision
Chemical freezeout (Tch ) ~ 170 MeVTime between Tch and Tfo
2
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Resonance survival probability
Chemical freeze-out
Kinetic freeze-out
measured
lost
K
K lost
K*
K*
K
K*
Kmeasured
♦ Initial yield established at chemical freeze-out
♦ Decays in fireball mean daughter tracks can rescatter destroying part of signal
♦ Rescattering also causes regeneration which partially compensates
♦ Two effects compete – Dominance depends on decay products and lifetime
time
Ratio to “stable” particle reveals information on behaviour and timescale
between chemical and kinetic freeze-out
K*
K
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Resonance ratiosThermal model [1]: T = 177 MeV
B = 29 MeV
UrQMD [2]
*rescatt. > regen.* rescatt. > regen.rescatt. < regen.* rescatt. < regen.
[1] P. Braun-Munzinger et.al., PLB 518(2001) 41 D.Magestro, private communication[2] Marcus Bleicher and Jörg Aichelin Phys. Lett. B530 (2002) 81-87. M. Bleicher, private communication
Need >4fm between Tch and Tfo
/
TT chfoStable
Resonance
Stable
Resonance te
Small centrality dependence: little difference in lifetime!
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A theoretical view of the collision
31
Chemical freezeout (Tch ) ~ 170 MeVTime between Tch and Tfo 4fmKinetic freeze-out (Tfo Tch): elastic scattering stops
2
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Shape of the mT spectrum depends on particle massTwo Parameters: Tfo and
Fit range : mT – mass < 1 GeV/c2
Hydro-dynamical model
Tfo ~110 MeV, < > = 0.8 c
tanh 1 r
R
s
E.Schnedermann et al, PRC48 (1993) 2462
dn
mT dmT r dr mT K1
mT coshT
0
R
I0pT sinh
T
r =s (r/R)n
PHENIX
Au-Au 200 GeV
Lattice QCD: Tc = 17010 MeV
Tch
STAR Preliminary
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♦ , K, p: Common thermal freeze-out at Tfo ~ 90 MeV
<> ~ 0.60 c
♦ : Shows different thermal freeze-out behavior:
Tfo ~ 170 MeV
<> ~ 0.45 c
Multi-strange Kinetic Freeze-out
Tdec = 100 MeV
Kolb and Rapp,PRC 67 (2003)
044903.
Hydro does not need different T for multi-strange Freeze-out T different – Is blastwave realistic?
Are re-interactions till freeze-out realistic either?
Blastwave parameterization
Higher temperatureLower transverse flowProbe earlier stage of collision?
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p+p is not trivial
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pT spectra vs multiplicity
1) Re-bin and Divide by min.bias2) Scale by:<NMB>/ <Nk>
high mult. spectra are more enhanced at high pT then K0
s
→ More contribution of Minijets ??
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Summary
Appear to have strangeness saturation at most central top
RHIC energies but not before (s = 1).
Do s quarks “see“ a different correlation volume to light quarks?There is a rescattering between Tch and Tfo.
There is strong radial flow in Au-Au system.
Seems that and freeze-out differently.62.4 GeV rather similiar to 200 GeV
Our simple thermal pictures are only approximately correct.
The devil is in the details but we have the data to figure it all out.
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Backup from here
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What happens to other particles?
– Npart scaling
p – slight increase
phase space suppression
of baryons?
K0s – only small phase space
suppression of strange
mesons?
Not flat with centrality
What about the Containss and s quark, so not strangeshould show no volume dependence
factor 2 increase relative to p-p
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from BaBar
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Scale: (Nud/Nq)*Npart + (Ns/Nq)*Nbin Scale: (Nud/Nq)*0.5*Npart + (Ns/Nq)*Nbin
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C: N ~ V2 (V 0)
GC: N ~ V (V )
Assume V ~ Npart
Pions/Apart constant
grand-canonical!
Kaons/Apart rising
canonical!
SIS energies
KaoS M. Mang et al.
J. Cleymans, H. Oeschler, K. Redlich, PRC 59 (1999)
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Seems OK at SPS too
Again not bad
except for peripheral bin
- errors large.
Normalized to unity for 0-5% data
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Thermal model reproduced dataD
ata
– F
it (s
)
R
atio
Do resonances destroy
the hypothesis?
Created a Large System in Local Chemical Equilibrium
Used in fit
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Constraining the parameters
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How about at SPS?Again :
The more strangeness the less the particle scales with Npart.
Nbin scaling not correct either.
u,d vs s quark scaling,
not bad except for most peripheral bin - errors large.Npart scaling
Normalized to unity for 0-5% dataNbin scaling
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RAA of strange particles
K±, K0s, and h- all scale similarlyp, , show hierarchy.
Phase space suppression in p-p fighting jet suppression in Au-Au.
h-
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Flow Effect on Spectra
PHENIX, STAR Preliminary200 GeV
Flow increases as centrality increases
p
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Baryon transport to mid-rapidity Clear systematic trend with collision energy
B - all from pair production B - pair production + transported from ybeamto y=0
B/B ratio =1
- Transparent collisionB/B ratio ~ 0
- Full stopping, little pair
production
♦ ~2/3 of baryons from pair production♦ First time pair production dominates♦ Still some baryons from beam
Preliminary
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p-p
Collective motion in Au-Audata / power law
Au-Au
not absolutemT scaling...
but if you rescale
not in Au-Au
data