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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.