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Tatsuya ChujoUniv. of Tsukuba
Soft particle production at RHIC
CNS-RIKEN workshop “Physics of QGP at RHIC” (Feb. 16, 2006)
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Outline• Single particle spectra
– Hadron freeze-out• Kinetic and chemical properties.• Resonance production and time scale.
– Hadron production at intermediate pT
• Baryon-meson effect.• High statistics meson data.• Cu+Cu 200 GeV results and Npart scaling.
– d+Au experiment
• HBT two particle correlation– Systematics of HBT measurements and Hydro.– 1D source imaging.
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Space-Time Evolution of System
1. Hard scattering2. Thermalization and QGP3. Chemical freeze out (particle abundances fixed)4. Kinetic freeze out (elastic Interactions cease)
♦ Hadrons: interact strongly - can probe the evolution
of the system and its medium effect.
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1
3
2
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pT spectra at RHIC
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Strange baryon spectra
200 GeVAu+Au
62.4 GeVAu+Au
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RHIC data set (2000 - 2005)
– p+p @s = 200 GeV (2001, 2003, 2005).– d+Au @sNN = 200 GeV (2003).– A+Au @ sNN = 62.4 GeV(2004), 130 GeV (2000), 200 GeV (2001, 2004).– Cu+Cu @ sNN = 22.5, 62.4, 200 GeV (2005).
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Hadron freeze-out properties
1. Kinetic freeze-out
2. Chemical freeze-out
3. Timescale between chemical and kinetic freeze-out
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Semi-Inclusive soft particle spectra
D.d'Enterria &D. Peressounkonucl-th/0503054
Au+Au 200 GeV central (b < 2.6 fm)
Hydro QCD
• <pT>: < K < p• consistent with radial flow picture.
• 25% () to 40% (p) increase from peripheral to central
PHENIX:PRC 69, 034909 (2004)
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Kinetic freeze-outparticle spectra kinetic freeze-out properties, total collective radial flow.
,K,p: Tkin decreases, increases with centrality.
, (low hadronic x-sections): higher Tkin ≈ Tch (for 200 GeV Au+Au), still significant radial flow.
Blast wave fitTch
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Chemical freeze-out
hadron-chemistry: particle ratios chemical freeze-out properties
short lived
resonances
Tch
s
• Tch ≈ TC ≈ 165 ± 10 MeVChemical freeze-out ≈ hadronization.
• s ~ u, d Strangeness is chemically equilibrated
at RHIC energies.
STAR white paperNucl. Phys A757 (05) 102
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In p+p particle ratios are well described with T=160 MeV.
Resonance ratios in Au+Au are not are well described with
Tch = 16010 MeV, B = 24 5 MeV (O. Barannikova).
Resonance Suppression
STAR Preliminary
p+p 200 GeV Au+Au 200 GeV
c.f.) F. Becattini, Nucl. Phys. A 702, 336 (2002)
But thermal model is not perfect…
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Thermal model [1]:
T = 177 MeVB = 29 MeV
[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. M. Bleicher and Horst Stöcker .Phys.G30 (2004) 111.
Rescattering and regeneration is needed !
UrQMD [2]
Life time [fm/c] :(1020) = 40 (1520) = 13 K(892) = 4 ++ = 1.7
p+p ratios are consistent with thermal model prediction T=160 MeV
Resonance Production in p+p and Au+Au
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1520)p
K
p
K
1520)
Re-scattering
Between chemical and kinetic freeze-out: (shot lived resonances)Rescattering > Regeneration -> Resonance signal loss
Time
chemical freeze-out end of inelastic interactions
T~170 MeVparticle abundance
kinetic freeze-outend of elastic interactions
T~110MeVparticle spectra, HBT
Detector
Regeneration
Resonance Yields:Re-scattering / Regeneration Scenario
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Model includes: • Temperature at chemical freeze-out• Lifetime between chemical and thermal freeze-out• No regeneration included.
results between : T= 160 MeV => > 4 fm/c (lower limit !!!) = 0 fm/c => T= 110-130 MeV
(1520)/ = 0.034 0.011 0.013
K*/K- = 0.20 0.03 at 0-10% most central Au+Au
G. Torrieri and J. Rafelski, Phys. Lett. B509 (2001) 239
Life time:K(892) = 4 fm/c (1520) = 13 fm/c
Temperature, Lifetime and from (1520)/ and K(892)/K
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More Resonances from PHENIX
• From combinations of ±, K±, p,p, and n in PHENIX.
Invariant mass [GeV/c2]
0
K0s pT =1-2 GeV/c
Invariant mass [GeV/c2]
pT =1-2 GeV/c
Invariant mass [GeV/c2]
K*0
pT =1-2 GeV/c
Invariant mass [GeV/c2]
Not enoughstatistics..
pT =1-2 GeV/c
Invariant mass [GeV/c2]
pT =1-2 GeV/c
Invariant mass [GeV/c2]
pT =1-2 GeV/c
Invariant mass [GeV/c2]
pT =1-2 GeV/c
• Demonstration from– Run3 sNN =200 GeV p+p
– ~24M events of Min Bias trigger
From SQM04M. Kaneta
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Physics at intermediate pT
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Baryon Anomaly at RHICMore (anti) baryons than pions at moderate pT (2-5 GeV/c). Does not look like vacuum jet fragmentation.
Factorization assumption of jet fragmentation completely breaks down.
Peripheral
Central
PHENIX: PRL 91, 172301 (2003), PRC 69, 034909 (2004)
(ant
i-) P
roto
n /
Rat
io
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No suppression for protons
• p, pbar : No suppression at intermediate pT (1.5 GeV - 4.5 GeV)• Why. Is it due to strong radial flow or other mechanism?
• RCP ~ RAA
•Shaded boxes : Npart, Ncoll determination errors.
PHENIX: PRL 91, 172301 (2003), PRC 69, 034909 (2004)
Recombination modelFries, et al, nucl-th/0301087Greco, Ko, Levai, nucl-th/0301093
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Other hadrons?
baryon
meson
• The mesons and baryons form two distinct groups, independent of particle mass.
• Diverge at pT ~ 2 GeV/c and come together at 5 GeV/c.• Observed for first time at RHIC.
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More on →K+K- RAA (new Run4 data)
•RAA (high statistics Run4 data) looks like the rather than the proton, even if mass() ~ mass(p)!
• Suggested that it’s not the mass effect (flow).
Nuclear Modification Factor
( ) ( )
( )coll
AA T
yield AuAu NR p
yield pp=
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meson “Rcp“ from STAR
Run-4 :Au+Au 200 GeV
Note: it’s not RAA! Confirmed that high statistics data behaves like meson.Favor: recombination model at intermediate pT.
Rcp
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System size dependence: Cu+Cu @ 200 GeV
Baryon/meson ratio at 2 GeV in Cu+Cu scales as Npart.
Rather is smooth transition from Cu+Cu to Au+Au.
p/ ratio in Cu+Cu/Au+Au
Central Au+Au
Central Cu+Cu
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d+Au experiment
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The Baseline: p+p and d+Au
• p+p and d+Au data from RHIC Run-3 at √sNN=200 GeV
PRELIMINARY
nucl-ex/0601033 (STAR)
• Combination of TOF and TPC info. • High pT p and PID: Multi-Gaussian fit of dE/dx distribution (relativistic rise, TPC).• Charged kaon contaminations can be estimated by K0
s yields
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RdAu and Cronin effect
Phys. Lett. B 586, 244 (2004)
• No suppression at intermediate and high pT at midrapidity.
• Protons have a significant enhancement, traditionally called “the Cronin effect” (~40%).
• Initial Glauber-Eikonal multiple scattering model by Accardi and Gyulassy describes the data well.
CGC: Kharzeev, Levin, McLerranPhys. Lett. B 561, 93 (2003)
PRELIMINARY
1≥AAR
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RdA from STAR
• RdAu (pT = 2 - 5 GeV/c):– Proton ~1.5 (min. bias)– Pion ~1.25 (min. bias)
nucl-ex/0601033 (STAR)
p
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RAuAu vs. RdAuPions suppressed by a factor of ~6 with respect to protons
Proton Cronin effect larger by ~30%
• d+Au collisions can not account for the huge gap between protons and pions in central Au+Au collisions.
PRELIMINARY
PRELIMINARY
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Need something else too…
• Recombination?!
Recombination of shower partons in A+A and p+A: Thermal and shower components.
HWA & YANGPhys.Rev.C70:037901,2004.
“Thermal
Thermal+Shower
Fragmentation (one jet)
Different jets.
“
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HBT measurements
HBT: Femtoscopic radii
• Scaling of R(dNch/dmT, sNN) for data and full hydro calculations.
• New tool: source imaging technique.
• Nice summary paper: “Femtoscopy in RHIC”, Soltz, Lisa, Pratt, Wiedemann, nucl-ex/0505014.
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• Femtoscopy = measurement that provides spatio-temporal information on fm scale (via interactions on MeV scale).
“Femtoscopic” correlations
Statistical InterferenceCoulomb Interaction
Strong Interaction
fermi sized sourceMeV correlationfit to Gaussian model
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A simple (2-particle) source
Can we resolve the contaminations and/or see an exponential tail?
Resonance cloudsub MeV correlation irresolvable
reduces strength
Rlong2 ~ (lifetime)
Rside2 ~ dx2 (geometry)
Rout2~ dx2 + dt2 - 2dxdt
decay
resolvable?
Scaling #1
Npart scaling shows clear dependence
on initial state geometric
overlap
• Rlong obeys dN/d scaling
• Rside shows slight preference
• Rout appears to increase for lower energy systems
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Scaling #2 - Transverse (pair) Mass
• Simple picture of space-time evolution, w/ no room for hadron re-scattering?
• R2 = ?
• R2K+ = R2K
- ?
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The “HBT Puzzle” in Hydro
1. flow effect2. hadronic re-
scattering
1. viscosity2. better EOS
• All solutions partial - break agreement w/ flow, spectra, other radii.• Look again at systemmatics.
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62-200 GeV Hydro vs.
Data• Rlong scaling full
y reproduced• Rout slight incre
ase for lower energy, agreement at mid-centrality
• Rside hydro extrapolates back to dAu
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Source imaging at AGS/RHIC
• 1D image yields excess over angle avg. 3D Gaussian fits• contribution or long duration tail? 3D imaging may answernucl-th/0507015 (Brown) also nucl-th/0501003 Pratt & Danielewicz
PRELIMINARY
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Summary (1)• Kinetic freeze-out
,K,p: Tkin decreases, increases with centrality.
– kinetic freeze-out ≈ chemical freeze-out (~ 160 MeV).
• Chemical freeze-out / Resonances
– Provide a time scale between chemical and kinetic freeze-out.
– Re-scattering and regeneration model: > 4 fm (lower limit).
• Baryon/Meson effect
– High statistics RAA: meson like behavior, favorable recombination model.
– Cu+Cu data: Npart scaling worked.
• d+Au experiment
– Particle type depended of RdAu: p < K < p, but not enough to account for baryon/meson effect in Au+Au.
– Recombination in d+Au?
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Summary (2)
• HBT measurements
– detailed systematics in Npart & dNd vs Hydro
• Rlong (dNd,mT) fully reproduced by hydro
• Rout (dNd,mT) decreasing with increasing sNN
• Rside (dNd,mT) remains a challenge
– Source imaging: evidence for a long tail in pion emission source.
Run-6 (Mar.- Jun., 2006) will start soon! • p+p (62.4 GeV, 200 GeV, 22.5 GeV?)• will provide important reference data for lower energy Au+A
u/Cu+Cu data set.