Production and Flow of Identified Hadrons at RHIC

Julia Velkovska

XXXIV International Symposium on Multiparticle DynamicsSonoma State University, 2004

July 27,2004, ISMD J.Velkovska 2

RHIC Specifications

3.83 km circumference

Two independent rings 120 bunches/ring 106 ns crossing time

Capable of colliding ~any nuclear species on ~any other species

Energy:

500 GeV for p-p 200 GeV for Au-Au

(per N-N collision)

Luminosity Au-Au: 2 x 1026 cm-2 s-1

p-p : 2 x 1032 cm-2 s-1

)GeV 500(A

Zs

July 27,2004, ISMD J.Velkovska 3

Summary of RHIC runs so far

p+p : 200 GeV , baseline measurementd+Au : 200 GeV , study cold nuclear matter Au+Au : 200 GeV, Run2, Run4

: 130 GeV , Run1

: 62.4 GeV ( match top ISR energy) Run4

: very short 56 GeV, 19 GeV Data in this talk:

mostly from 200 GeV runsMostly from PHENIX

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Particle production at RHIC energies

Bulk of particle production

Collective phenomena

pQCD

Soft (hydro)

0 1 2 3 4 5 6 7 8 9 10 11 12 GeV/c

Hard probesModified by the

mediumJet Quenching

? New physics

This talk is focused at intermediate pT, but to get there we need to review both soft and hard particle production.

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pp and dAu identified hadron spectra: mT

scaling

Idenpendent of mass, strangeness,etc - approximately same mT slope

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Au+Au collisions

Modifications to soft processes from the nuclear medium

1. Slopes depend on particle mass

2. Spectra are NOT exponential in mT

Teff depends on fitting range Best to compare to full hydro calculations

Very low mT data from PHOBOS – constrain the amount of flow needed to describe the data

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Example of Blast wave fits

0-10% centralAu+Au200 GeV

(r) = tanh 1 T r/R

Fit |mT –m0| < 1GeVExtrapolate meson described by same Tfo ,

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Soft processes: Summary

mT “scaling” in pp and dAu collisions

Radial flow in AuAu collisions. Protons and anti-protons spectra significantly affected due to their large mass

Hard probes

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Why study hard scattering ? (in Brief)

The full pallet of QCD probes can be created and measured in the

RHIC experiments

q: fast color triplet

g: fast color octet

Q: slow color triplet

QQbar: slow color singlet/octet

Virtual photon: colorless

Real photon: colorless

Unknown Medium

Inducedgluon radiation?

EnergyLoss?

Dissociation?

Controls

A main goal of relativistic heavy ion physics is to investigate high-temperature, high-density QCD, by creating and then studying the highly-excited medium produced in high-energy nuclear collisions. QCD probe in

QCD probeout

Excited medium(possible quark-gluon plasma?)

Modification?

One method of diagnosing a QCD medium is to shoot a QCD-sensitive probe through it, then look for any modifications due to the medium.(Most obvious possibilities: multiple scatterings, induced radiations, and energy loss.)

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Constrains Fragmentation Function D(Gluon-pi)

Reference for Au+Au spectra

0 production in p+p

Phys. Rev. Let 91, 241803 (2003)

AB hX fa/A(xa,Q

2a) fb/B(xb,Q

2b)

a b cd

Dh/c(zc,Q2

c)

Good agreement with NLO pQCD Factorization theorem:

KKP

Kretzer

data vs pQCD

200 GeV - Run2

July 27,2004, ISMD J.Velkovska 12

If no “effects”: R < 1 in regime of soft physics R = 1 at high-pT where hard scattering dominates A+B = A*B(p+p)

Nuclear Modification Factor RAA/RCP

ddpdT

ddpNdpR

TNN

AA

TAA

TAA /

/)(

2

2

Quantify deviations from expected behaviour in p+p collisions:

<Nbinary>/inelp+p (Nuclear

Geometry)

peripheralbinperipheral

centralbincentral

TCPNYield

NYieldpR

/

/)(

July 27,2004, ISMD J.Velkovska 13

Nuclear Modification factor RAA for @ 200 GeV

strongsuppression

Phys. Rev. Lett. 91, 072301 (2003)

Jet quenching due tothe dense medium

No modification forPeripheral AuAu

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RAA for 0 in Central Collisions: Energy Dependence

A.L.S.Angelis, PLB 185, 213 (1987)

WA98, EPJ C 23, 225 (2002) ,[ Renormalization: D.d'E. nucl-ex/0403055]

PHENIX, PRL 88 022301 (2002) ; PHENIX, PRL 91, 072303 (2003)

Cronin enhancementat 17 GeV

Suppression at 62 And 200 GeVDifferences < 6 GeV/c

Central AA

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Protons are not produced from colorless objects: but

Ncoll scaling !

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Large!!! baryon/meson ratios

Peripheral: consistent with standard fragmentation

Central: a factor ~ 3 higher than peripheral, e+e- and ISR pp data

p and pbar at pT 2-5 GeV/c : SOFT OR HARD ?

Phys. Rev. Lett 91, 172301 (2003).

July 27,2004, ISMD J.Velkovska 17

Scaling properties of (1020)

meson:• Similar mass as proton, but meson. Ideal test particle whether the observed baryon anomaly is a mass effect or not.

proton, pbar: PHENIX: PRL 91, 172301 (2003), PRC 69, 034909 (2004): PHENIX final data, will be submitted to PRC.

p, pbar: low pT (< 1.5 GeV/c): different shape due to the radial flow, intermediate pT: Ncoll scaling

: does not scale with Ncoll

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Rcp of p,

• mesons are heavy, but follow 0, not p+pbar! • Indicates the absence of suppression of proton at

intermediate pT is not a mass effect.

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Compilation on Rcp from STAR

Presented by M. Lamont (QM04)

Two distinct groups in Rcp , i.e. meson and baryon, not by particle mass.

Separate at pT ~ 2 GeV/c and come together at 5 GeV/c.

baryon

meson

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Bulk (Hydrodynamic) Matter

Pressure gradient converts position space

anisotropy to momentum space

anisotropy.

Jet Propagation

Energy loss results anisotropy based on

location of hard scattering in collision

volume.

y

x

y

x

low pT high pT

Azimuthal Anisotropy of Particle Emission

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Elliptic Flow of baryons and mesons

At low pT hydro works remarkably well

Above ~ 2 GeV/c : A split between mesons and baryons

v2 – too large to be attributed to jet absorption (geometric limit for surface emission exceeded)

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Universal behavior in flow per quark

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Recombination of quarks to explain the data

describe Rcp particle ratios , spectra, v2:pT(baryons) >pT(mesons)>pT(quarks)

Duke model, PRC 68, 044902 (2003)

p/Rcp

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Jet correlations with identified mesons and baryons

• jet partner equally likely for trigger baryons & mesons

• flat centrality dependence (within errors)

• expected from purely thermal recombination(nucl-th/0306027)

Need partons from jets to explain the data!!

A. Sickles

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Jet correlations with identified particles: Star

“jettiness” of intermediate pT baryons confirmed!

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SummaryAu+Au collisions at RHIC form a bulk medium which exhibits collective effects Radial flow (mass dependent)

Elliptic flow: descirbed by hydro at low pT , partonic description works at high pT

Hard probes: Dense nuclear medium is responsible for jet quenching

dAu collisions show it is a final state effect At intermediate pT baryons are not suppressed

Is there a new production mechanism at pT = 2-5 GeV ? Recombination: success and challenges

Hadron yields and elliptic flow scale with the number of quarks: Points to partonic degrees of freedom

baryons show jettiness – recombination of shower partons is needed

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EXTRA

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New data: RAA @ 62.4 GeV : Charged hadron and

Common reference p+pcharged+X is used, instead of ISR 0 reference.0 yield is divided by (charged reference)/1.6.

Clear difference between charged and 0 at intermediate pT up to 4 GeV/c.

Suggests a large proton contribution in this pT region, as seen in 200 GeV data.

0

charged

0-10%

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Cronin effect stronger for protons than for pions

Not enough to account for

factor of 3 increase

of p/in central AuAu

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The proton “bump” in the h/ ratios

Expectation (pp, e+e-): h/ 1.6

Above 5 GeV/c

and in peripheral

collisions: recover standard fragmentation

Au+Au @ 200AGeV

nucl-ex/0310005

July 27,2004, ISMD J.Velkovska 31

But what about the Cronin effect ?

Can Cronin effect produce the enhanced p/ ratio in AuAu ?

Usual description: “Initial state multiple

scattering leading to pt broadening.”

Why is it different for protons and pions ?

P.B.Straub et al., Phys.Rev.Lett., 68,452(1992)

P.B. Straub et al., PRL 68 (1992)FNAL experiments measuring R (W / Be) for identified particles at sqrt(s) of 27.4 and 51.3 GeV.

July 27,2004, ISMD J.Velkovska 32

Direct photons: a colorless probe

1 + ( pQCD direct x Ncoll) / ( phenix pp backgrd x Ncoll)

[w/ the real, suppressed background]

PHENIX Preliminary PbGl / PbSc Combined

AuAu 200 GeV Central 0-10%

1 + ( pQCD direct x Ncoll) / phenix backgrd Vogelsang NLO

Built-in control experiment in the AuAu data. Direct photons are described by a curve that includes the measured suppressed production in AuAu.

July 27,2004, ISMD J.Velkovska 33

Strange baryon/meson ratios

The mid-pT anomaly not unique to p/also seen for strange particles

With a little higher pT

reach: K0shas a

peak at ~ 3GeV/c

Height depends on centrality

Peripheral – above pp data

July 27,2004, ISMD J.Velkovska 34

RAA for 0 and charged hadron

pp

AuAubinaryAuAuAA Yield

NYieldR

/

PHENIX AuAu 200 GeV0 data: PRL 91 072301 (2003), nucl-ex/0304022.charged hadron (preliminary) : NPA715, 769c (2003).

July 27,2004, ISMD J.Velkovska 35

p/ in dAu, pp and AuAu

HUGE nuclear effectComing from the

final state (hot nuclear

matter)