Identified hadron spectra at large transverse
momentum in p+p and d+Au collisions at
sNN=200 GeV
Pawan Kumar Netrakanti,VECC, Kolkata
(For STAR Collaboration)
Pawan Kumar Netrakanti
QGP-MEET 2006, VECC,
February 2006
1
Outline
STAR preliminary
 Motivation
STAR preliminary
Pawan Kumar Netrakanti
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Method of analysis
Results from p+p collisions
Results from d+Au collisions
Summary
QGP-MEET 2006, VECC,
February 2006
2
Motivation
High pT PID in TPC
Test predictions (certain aspects) of pQCD
Understanding Nuclear effects in d+Au collisions
Pawan Kumar Netrakanti
QGP-MEET 2006, VECC,
February 2006
3
Method of analysis
 Low pT  Time of Flight (TOF)
 High pT  Time Projection Chamber (TPC)
Coverage: |h|1.8
and f symmetric
Log10(p)
Hadron identification:
STAR Collaboration, nucl-ex/0309012
Intrinsic timing resolution: 85 ps
 Coverage : -1.0 < h< 0.0 and 60o in f
 low pT particle identification ( < 2.5
GeV/c) in this study
Pawan Kumar Netrakanti
High pT : Extend particle identification
in TPC by exploiting the relativistic rise
in ionization energy loss.
Momentum: 3  p10 GeV/c
~
dE/dx of p (K,p) separation: 2s
QGP-MEET 2006, VECC,
February 2006
4
Transverse Momentum Spectra
STAR preliminary
Power-law : ( A/(1 + pT/p0)n)
Levy : (B/(1+(mT-m0)/nT)n)
Power-law function ~ pQCD inspired
Levy ~ exponential + power-law
Power law type behavior for p+p and d+Au collisions at high pT
Pawan Kumar Netrakanti
QGP-MEET 2006, VECC,
February 2006
5
Comparison to NLO pQCD
NLO pQCD with Kretzer
FF inconsistent with data
NLO pQCD with KKP
FF inconsistent with
the p+pbar data
Kretzer differ from KKP, in
the gluon to p fragmentation
Pawan Kumar Netrakanti
NLO pQCD with AKK FF
relatively better than KKP
for the p+pbar data
AKK differ from KKP, in the way
the light flavor FF are obtained
QGP-MEET 2006, VECC,
February 2006
6
p+p collisions and phenomenological model
Phenomenological EPOS
Model are consistent with
pion data, even at low pT.
Phenomenological EPOS
Model are consistent with p
+ pbar data, even at low pT.
K. Werner, F. Liu and T. Pierog, hep-ph/0506232
Pawan Kumar Netrakanti
Interesting to observe that
two different models
(pQCD and EPOS) do a
reasonable job in p+p
collisions
QGP-MEET 2006, VECC,
February 2006
7
Scaling in particle production
e+ and e- does not have a parton
distribution function.
There will be a (sNN )2 multiplied
to cross-section in e+e- collisions.
For p+p collisions n ~ 6.5 for p, p (pbar)
Pawan Kumar Netrakanti
QGP-MEET 2006, VECC,
February 2006
8
d+Au collisions and models
•NLO pQCD calculations
with KKP and AKK FF and
EPOS are consistent with
pion data at high pT (> 4
GeV/c)
•pQCD calculations with
Kretzer FF under predicts
pion data
STAR Preliminary
Parton distribution functions :
L. Frankfurt, et al., Phys. Rev. D 71 (2005) 054001
D. De Florian and R. Sassot, PRD 69 (2004) 074028
Pawan Kumar Netrakanti
• NLO pQCD calculations
with only AKK fragmentation
function consistent with the
p+pbar data
QGP-MEET 2006, VECC,
February 2006
9
Nuclear Modification Factor : d+Au collisions
R AB 
Phys. Rev. Lett. 91
(2003) 072304
STAR preliminary
evt
2
1
N
d
( AB  N AB/dydpT
TAB d 2s pp /dydpT
 RdAu for p > 1, Cronin effect
Absence of high pT suppression
in particle production
 RdAu (p + pbar) > RdAu (p)
Similar dependence has been
observed at lower energies.
Phys. Rev D 19 (1979) 764
STAR preliminary
Pawan Kumar Netrakanti
Qualitative agreement with
recombination model for dAu
collisions. Phys.Rev.Lett.93 (2004) 082302
QGP-MEET 2006, VECC,
February 2006
10
Particle Ratios – p+p collisions
p-/p+ ~ 1 and pbar/p ~ 0.8
PYTHIA predicts a more
prominent pT dependence
p/p+ and pbar/p - increases
with pT ~ 2 GeV/c and then
decreases to ~ 0.2
p/p+ agrees with lower
energy results.
pbar/p - shows a distinct
energy dependence
Pawan Kumar Netrakanti
QGP-MEET 2006, VECC,
February 2006
11
Particle Ratios – d+Au collisions
STAR preliminary
Pawan Kumar Netrakanti
p -/p+ ~ 1- independent of pT
pbar/p decreases with pT
p/p+ and pbar/p - increases
with pT up to 2 GeV/c and
then decreases.
QGP-MEET 2006, VECC,
February 2006
12
Highlight and Summary
 NLO pQCD describes the p+pbar spectrum for the
first time in p+p collisions
 These results show the importance of the significant
improvement of FF for baryons from the light-flavor
separated measurements in e+e- collisions (OPAL)
 The observed xT scaling of p,p(pbar) at high pT also
show dominance of hard processes related to PDF
and FF
 Provide solid reference for effects of jet quenching
and recombination in Nucleus-Nucleus collisions
Details of these results can be found at: arXive: nucl-ex/0601033
Pawan Kumar Netrakanti
QGP-MEET 2006, VECC,
February 2006
13
STAR
The STAR Collaboration
U.S. Labs:
France:
Argonne, Lawrence Berkeley, and
Institut de Recherches Subatomiques
Brookhaven National Labs
Strasbourg, SUBATECH - Nantes
U.S. Universities:
Germany:
UC Berkeley, UC Davis, UCLA,
Max Planck Institute – Munich
Caltech, Carnegie Mellon, Creighton,
University of Frankfurt
Indiana, Kent State, MIT, MSU,
India:
CCNY, Ohio State, Penn State,
Bhubaneswar, Jammu, IIT-Mumbai,
Purdue, Rice, Texas A&M, UT
Panjab, Rajasthan, VECC, Kolkata
Austin, Washington, Wayne State,
Netherlands:
Valparaiso, Yale
NIKHEF/Utrecht
Brazil:
Poland:
Universidade de Sao Paolo
Warsaw University of Technology
China:
Russia:
IHEP - Beijing, IPP - Wuhan, USTC,
MEPHI – Moscow, LPP/LHE JINR –
Tsinghua, SINAP, IMP Lanzhou
Dubna, IHEP – Protvino
Croatia:
South Korea:
Zagreb University
Czech Republic:
Pusan National University
Nuclear Physics Institute
Switzerland:
England:
University
of Bern
Pawan Kumar Netrakanti
QGP-MEET 2006,
VECC,
14
University of Birmingham
February 2006
Scaling of particle production
mT scaling observed for
1 < mT < 2 GeV/c2
STAR preliminary
Pawan Kumar Netrakanti
At high pT : no scaling
Mass effect
Or
baryon-meson effect
QGP-MEET 2006, VECC,
February 2006
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