Bulk matter properties in RHIC collisions

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Bulk matter properties in RHIC collisions
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Outline
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• Hadronic ratios.
• Resonance production.
• pT spectra.

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
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RHIC detectors designed for PID
So far the RHIC experiments have published
identified particle spectra for p?, p0, K?,
K0s, p, d, L, X , W r0, f, D, h, K0(892),
S(1385), L(1520) D0, D, J/Ys (
anti-particles)
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A theoretical view of the collision
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

• Statistical Thermal Model
• F. Becattini P. Braun-Munzinger, J. Stachel, D.
  Magestro
• J.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

Particle density of each particle
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
temperature mq light-quark chemical
potential ms strangeness chemical
potential gs strangeness saturation factor
Compare particle ratios to experimental data
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Centrality and Energy Dependence
STAR preliminary AuAu at vsNN200GeV
and 62 GeV
TLQCD160-170MeV
TLQCD160-170MeV
Energy dependence but small Nch dependence
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Rapidity Dependence

• Tch, gs
• Small sensitivity to y
• Close to strangeness equilibration in central
  collisions over y0-3 (ybeam6)
• mq, ms
• Reflect baryon density with y

Fit results Mean Upper/Lower error
BRAHMS AuAu 200 GeV
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(In)dependence of mid-rapidity yields
Preliminary
Preliminary

• T, µB, and V can all vary with energy, but in
  such a way as to ensure yields stay constant

Preliminary
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Results of Fit
200 GeV pp
Strangeness Enhancement
STAR Preliminary
pp particle ratios well described
AuAu only stable particle ratios well described
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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
1960s (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

s(Npart) / Npart e s(pp) e gt 1
Enhancement!
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SPS at vs 17.3 8.8 GeV
NA57 (D. Elia QM2004)

• C to GC predicts a factor 4 - 5 larger X-
  enhancement at vsNN 8.8 GeV than at 17.3 GeV

Yields dont have time to reach limit hadronic
system? Temperature assumed is incorrect?
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And then at RHIC (200 GeV)...
L not flat any more!
But does it over saturate or ONLY just reach
saturation?
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Rcp of strange particles
Baryons and mesons are different
Rcp
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RAA of strange particles
Phase space suppression in pp vs jet suppression
in AuAu.
h-
Baryons with s quarks scale differently to
non-strange.
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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 more strangeness you add the less it scales
  with Npart.

• The larger strangeness content scales better with
  Nbin.
• Still not perfect.

Nbin scaling
Normalized to unity for 0-5 data
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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.

• K0s 1/2Npart 1/2Nbin
• p Npart
• L 2/3Npart 1/3Nbin
• 1/3Npart 2/3Nbin
• f Nbin
• W Nbin

Pretty good!
Does strangeness see a different correlation
volume?
f Npart
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A theoretical view of the collision
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Chemical freezeout (Tch ) 170 MeV Time between
Tch and Tfo
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Resonance survival probability

• 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

?
lost
K
K
measured
Chemical freeze-out
Kinetic freeze-out
time
Ratio to stable particle reveals information on
behaviour and timescale between chemical and
kinetic freeze-out
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Resonance ratios
Thermal model 1 T 177 MeV
mB 29 MeV
UrQMD 2
K rescatt. gt regen. L rescatt. gt regen. D
rescatt. lt regen. S rescatt. lt regen.
Need gt4fm between Tch and Tfo
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
Small centrality dependence little difference
in lifetime!
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A theoretical view of the collision
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• Chemical freezeout (Tch ) 170 MeV
• Time between Tch and Tfo ? 4fm
• Kinetic freeze-out (Tfo ? Tch) elastic
  scattering stops

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Hydro-dynamical model
Shape of the mT spectrum depends on particle
mass Two Parameters Tfo and b
Lattice QCD Tc 170?10 MeV
Tch
PHENIX Au-Au 200 GeV
E.Schnedermann et al, PRC48 (1993) 2462
?r ?s (r/R)n
STAR Preliminary
Tfo 110 MeV, lt ?? gt 0.8 c
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Multi-strange Kinetic Freeze-out

• ?, K, p Common thermal freeze-out at Tfo 90
  MeV
• lt??gt 0.60 c
• ? Shows different thermal freeze-out behavior
• Tfo 170 MeV
• lt??gt 0.45 c

Blastwave parameterization
Higher temperature Lower transverse flow Probe
earlier stage of collision?

• Hydro does not need different T for multi-strange
• Freeze-out T different Is blastwave realistic?

Are re-interactions till freeze-out realistic
either?
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pp is not trivial
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pT spectra vs multiplicity
1) Re-bin and Divide by min.bias 2) Scale
byltNMBgt/ ltNkgt
L high mult. spectra are more enhanced at high pT
then K0s ? More contribution of Minijets ??
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Summary

• Appear to have strangeness saturation at most
  central top
• RHIC
  energies but not before (gs 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 X and W 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?
p Npart scaling ?p slight increase phase
space suppression of baryons? K0s only small
phase space suppression of strange mesons?
Not flat with centrality
Contains?s and s quark, so not strange should
show no volume dependence
What about the f?
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)0.5Npart (Ns/Nq)Nbin
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SIS energies
KaoS 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)
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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 data
Created a Large System in Local Chemical
Equilibrium
Data Fit (s) Ratio
Do resonances destroy the hypothesis?
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
Nbin scaling
Normalized to unity for 0-5 data
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RAA of strange particles
h-
K, K0s, f and h- all scale similarly
p, L, X show hierarchy.
Phase space suppression in p-p fighting jet
suppression in Au-Au.
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Flow Effect on Spectra
Flow increases as centrality increases
PHENIX, STAR Preliminary 200 GeV
?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 y0
• ?B/B ratio 1
• - Transparent collision
• ?B/B ratio 0
• - Full stopping, little pair production

Preliminary
?L/L

• 2/3 of baryons from pair production
• First time pair production dominates
• Still some baryons from beam

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