production and flow of identified hadrons at rhic julia velkovska xxxiv international symposium on...
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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
July 27,2004, ISMD J.Velkovska 4
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.
July 27,2004, ISMD J.Velkovska 5
pp and dAu identified hadron spectra: mT
scaling
Idenpendent of mass, strangeness,etc - approximately same mT slope
July 27,2004, ISMD J.Velkovska 6
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
July 27,2004, ISMD J.Velkovska 7
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
July 27,2004, ISMD J.Velkovska 10
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.)
July 27,2004, ISMD J.Velkovska 11
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 !
July 27,2004, ISMD J.Velkovska 16
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
July 27,2004, ISMD J.Velkovska 18
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.
July 27,2004, ISMD J.Velkovska 19
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
July 27,2004, ISMD J.Velkovska 20
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
July 27,2004, ISMD J.Velkovska 21
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)
July 27,2004, ISMD J.Velkovska 23
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
July 27,2004, ISMD J.Velkovska 24
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
July 27,2004, ISMD J.Velkovska 25
Jet correlations with identified particles: Star
“jettiness” of intermediate pT baryons confirmed!
July 27,2004, ISMD J.Velkovska 26
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
July 27,2004, ISMD J.Velkovska 28
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
July 27,2004, ISMD J.Velkovska 30
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).