Production%20and%20Flow%20of%20Identified%20Hadrons%20at%20RHIC

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Production and Flow of Identified Hadrons at RHIC

• Julia Velkovska

XXXIV International Symposium on Multiparticle
Dynamics Sonoma State University, 2004
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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

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Summary of RHIC runs so far

• pp 200 GeV , baseline measurement
• dAu 200 GeV , study cold nuclear matter
• AuAu 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 runs
• Mostly from PHENIX

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Particle production at RHIC energies
Soft (hydro)
pQCD

• Bulk of particle production
• Collective phenomena

Hard probes Modified by the medium Jet 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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AuAu collisions

• Modifications to soft processes from the nuclear
  medium
• Slopes depend on particle mass
• 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 central AuAu 200 GeV
Fit mT m0 lt 1GeV Extrapolate F meson described
by same Tfo , bT
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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

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Hard probes
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Why study hard scattering ? (in Brief)
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.
The full pallet of QCD probes can be created and
measured in the RHIC experiments
q fast color triplet
QCD probe out
Induced gluon radiation?
QCD probe in
g fast color octet
Modification?
Q slow color triplet
Excited medium (possible quark-gluon plasma?)
Energy Loss?
QQbar slow color singlet/octet
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.)
Dissociation?
Virtual photon colorless
Controls
Real photon colorless
Unknown Medium
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p0 production in pp

• Good agreement with NLO pQCD
• Factorization theorem

200 GeV - Run2
?AB ??hX ? fa/A(xa,Q2a) ??fb/B(xb,Q2b)
???a b ??cd ??Dh/c(zc,Q2c)
data vs pQCD
KKP Kretzer

• Constrains Fragmentation Function D(Gluon-pi)
• Reference for AuAu spectra

Phys. Rev. Let 91, 241803 (2003)
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Nuclear Modification Factor RAA/RCP
Quantify deviations from expected behaviour in
pp collisions
ltNbinarygt/?inelpp
(Nuclear Geometry)

• If no effects
• R lt 1 in regime of soft physics
• R 1 at high-pT where hard scattering dominates
  ? AB AB(pp)

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Nuclear Modification factor RAA for p0 _at_ 200 GeV
No modification for Peripheral AuAu
Jet quenching due to the dense medium

• Phys. Rev. Lett. 91, 072301 (2003)

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RAA for p0 in Central Collisions Energy
Dependence
Central AA
Cronin enhancement at 17 GeV
Suppression at 62 And 200 GeV Differences lt 6
GeV/c
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)
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Protons are not produced from colorless objects
but Ncoll scaling !
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Large!!! baryon/meson ratios
Phys. Rev. Lett 91, 172301 (2003).

• Peripheral consistent with standard
  fragmentation
• Central a factor 3 higher than peripheral,
  ee- and ISR pp data
• p and pbar at pT 2-5 GeV/c SOFT OR HARD ?

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Scaling properties of ?(1020)
proton, pbar PHENIX PRL 91, 172301 (2003), PRC
69, 034909 (2004) ? PHENIX final data, will be
submitted to PRC.

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

p, pbar low pT (lt 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,p,?

• F mesons are heavy, but follow ?0, not ppbar!
• 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)
baryon
meson

• 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.

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Azimuthal Anisotropy of Particle Emission
low pT high pT
Bulk (Hydrodynamic) Matter
Jet Propagation
Pressure gradient converts position space
anisotropy to momentum space anisotropy.
Energy loss results anisotropy based on location
of hard scattering in collision volume.
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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
Rcp
p/?
Duke model, PRC 68, 044902 (2003)
describe Rcp particle ratios , spectra,
v2 pT(baryons) gtpT(mesons)gtpT(quarks)
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Jet correlations with identified mesons and
baryons
A. Sickles
Need partons from jets to explain the data!!
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Jet correlations with identified particles Star
jettiness of intermediate pT baryons confirmed!
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Summary

• AuAu 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 _at_ 62.4 GeV Charged hadron and ?0
0-10
charged
?0

• Common reference pp?chargedX 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.

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Cronin effect stronger for protons than for pions

• Not enough to account for
• factor of 3 increase
• of p/p in central AuAu

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The proton bump in the h/p ratios
AuAu _at_ 200AGeV

• Expectation (pp, ee-) h/p ? 1.6
• Above 5 GeV/c
• and in peripheral
• collisions recover standard fragmentation

nucl-ex/0310005
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But what about the Cronin effect ?

• Can Cronin effect produce the enhanced p/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., PRL 68 (1992) FNAL
experiments measuring R (W / Be) for identified
particles at sqrt(s) of 27.4 and 51.3 GeV.
P.B.Straub et al., Phys.Rev.Lett., 68,452(1992)
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Direct photons a colorless probe
Built-in control experiment in the AuAu data.
Direct photons are described by a curve that
includes the measured suppressed p0 production
in AuAu.
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Strange baryon/meson ratios

• The mid-pT anomaly not unique to p/p also seen
  for strange particles
• With a little higher pT reach L/K0s has a peak
  at 3GeV/c
• Height depends on centrality
• Peripheral above pp data

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RAA for p0 and charged hadron
PHENIX AuAu 200 GeV p0 data PRL 91 072301
(2003), nucl-ex/0304022. charged hadron
(preliminary) NPA715, 769c (2003).
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p/p in dAu, pp and AuAu
HUGE nuclear effect Coming from the final state
(hot nuclear matter)