gábor i. veresquark matter 2006, shanghai, november 14-20, 2006 1 anti-particle to particle ratios...
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Gábor I. Veres Quark Matter 2006, Shanghai, November 14-20, 2006
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Anti-particle to particle ratios in p+p, Cu+Cu and Au+Au collisions at RHIC
Gábor I. VeresEötvös Loránd University, Budapest
Massachusetts Institute of Technology, Cambridge
Quark Matter 2006 Conference, Shanghai, November 19, 2006
for the collaboration
Gábor I. Veres Quark Matter 2006, Shanghai, November 14-20, 2006
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Collaboration
Burak Alver, Birger Back, Mark Baker, Maarten Ballintijn, Donald Barton, Russell Betts, Richard
Bindel,
Wit Busza (Spokesperson), Vasundhara Chetluru, Edmundo García, Tomasz Gburek, Joshua
Hamblen, Conor Henderson, David Hofman, Richard Hollis, Roman Hołyński, Burt Holzman, Aneta
Iordanova, Chia Ming Kuo, Wei Li, Willis Lin, Constantin Loizides, Steven Manly, Alice Mignerey,
Gerrit van Nieuwenhuizen, Rachid Nouicer, Andrzej Olszewski, Robert Pak, Corey Reed, Christof
Roland, Gunther Roland, Joe Sagerer, Peter Steinberg, George Stephans, Andrei Sukhanov,
Marguerite Belt Tonjes, Adam Trzupek, Sergei Vaurynovich, Robin Verdier, Gábor Veres, Peter
Walters, Edward Wenger, Frank Wolfs, Barbara Wosiek, Krzysztof Woźniak, Bolek Wysłouch
ARGONNE NATIONAL LABORATORY BROOKHAVEN NATIONAL LABORATORYINSTITUTE OF NUCLEAR PHYSICS PAN, KRAKOW MASSACHUSETTS INSTITUTE OF TECHNOLOGY
NATIONAL CENTRAL UNIVERSITY, TAIWAN UNIVERSITY OF ILLINOIS AT CHICAGOUNIVERSITY OF MARYLAND UNIVERSITY OF ROCHESTER
9 ongoing PhD thesis studies
Gábor I. Veres Quark Matter 2006, Shanghai, November 14-20, 2006
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Outline
Particle ratios:
PHOBOS detector and PID methods
Particle spectra: • Au+Au PID spectra at 62.4 GeV
• low-pT particle yields
• baryon/hadron ratios
• mT scaling
• centrality dependence of the net proton yield Summary
• ratios in central Au+Au vs. s
• Cu+Cu ratios vs. centrality at 200 and 62 GeV
• comparison of p+p, Cu+Cu and Au+Au ratios vs. Npart
Gábor I. Veres Quark Matter 2006, Shanghai, November 14-20, 2006
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MotivationParticle ratios:
• are influenced by baryon pair production, baryon number transport, andfinal state interactions
• show how close the system is to ideal baryon-free plasma
• provide input to quantitative analysis of chemical equilibrium in thermal models z
-xy
Gábor I. Veres Quark Matter 2006, Shanghai, November 14-20, 2006
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The detector
1m
Spectrometer
Time of Flight
Gábor I. Veres Quark Matter 2006, Shanghai, November 14-20, 2006
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pT (GeV/c)0.03 0.3 3.0
Stoppingparticles
dE/dx TOF
Particle ID from low to high pT
Eloss (MeV)
PHOBOS PID Capabilities
1 2 3 4 50p (GeV/c)
30
40
50
60
70
1/v
(ps/
cm)p+p
K +K + -
++-
p (GeV/c)
Gábor I. Veres Quark Matter 2006, Shanghai, November 14-20, 2006
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Analysis techniques
• Particles identified via dE/dxin the spectrometer
• Monte Carlo studiesto estimate corrections
acceptance in y and pT :
)(
)(
)(
)(
p
p
pa
pa
p
p
p
p
raw
raw
acceptancefficiency,corrections
PID cutsK
pd
e
0 < y < 1.50.2 < pT< 0.8 GeV/c
p [GeV/c]
Gábor I. Veres Quark Matter 2006, Shanghai, November 14-20, 2006
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Controlling systematic uncertainties
)()( BBpapa
Geometrical acceptance drops out of the ratios:
Ratios measured independently for different:
• bending directions
• spectrometer arms
)()( BBpapa
Z Z
B+B–
h+
h–h+
h+ h+
h–
h–h–
by changing the polarity of the magnetic field
Gábor I. Veres Quark Matter 2006, Shanghai, November 14-20, 2006
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pT [GeV/c]
Ab
sorp
tio
n
coef
fici
ent
p
p_
GEANT Monte Carlo(FLUKA+Geisha)/2
Corrections
Absorption• GEANT used• 4% for p/p• 1.5% for K–/K+
_
Secondary particles• GEANT used• 1% for p/p, 2% for –/+
Feed-down• daughters of weakly decaying particles (,, –)• HIJING particle yields are used• track DCA cut (3.5 mm!) keeps correction small• 2% for p/p, <1% for K–/K+ and –/+
_
_
DCA {DCA {
Gábor I. Veres Quark Matter 2006, Shanghai, November 14-20, 2006
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Errors on the ratios
• Statistical errors: 1% (tens of millions of events analyzed)
• Systematic errors (90% C.L.):
beam orbit variations 2% 2% 2%
PID selection cuts 4% 4% 1%
track quality cuts 3% 3% 3%
vertex cuts 1% 1% 1%
DCA cuts 2% 2% 1%
trigger selection cuts 1% 1% 1%
absorption correction 3% 1% 1%
feed-down correction 3% 0% 0%
correction for secondaries 1.5% 0% 2%
Total: 7.5% 6% 4.5%
p K
Gábor I. Veres Quark Matter 2006, Shanghai, November 14-20, 2006
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New results at 62.4 GeV fit smoothly into the energy evolution of antiparticle/particle ratios
Results: energy dependence
arXiv:nucl-ex/0610001submitted to PRCstat.errors only
Gábor I. Veres Quark Matter 2006, Shanghai, November 14-20, 2006
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Cu+Cu ratios, all 3 species vs. Npart
• Integrated over pT and y
• p/p ratios: little, if any, centrality dependence (still not understood theoretically)
_
• Similarly to Au+Au, strong collision energy dependence
200 GeV
62.4 GeV
y0
Gábor I. Veres Quark Matter 2006, Shanghai, November 14-20, 2006
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Comparison of systems at 200 GeV
• p/p ratios do not depend strongly on
- system size- centrality
_
• The study is being currently extended to 62.4 GeV
y0
p+p: Phys.Rev. C71, 021901 (2005)
Gábor I. Veres Quark Matter 2006, Shanghai, November 14-20, 2006
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Ratios of different species
Ratios of different species (like p/) are of significant interest:they are used to study the baryon excess observed at higher RHIC energies in the 2 – 4 GeV/c pT range.
For that, identified spectra of all species were analyzed.
Gábor I. Veres Quark Matter 2006, Shanghai, November 14-20, 2006
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Proton spectra are harder thanthe meson spectra
Time-of-Flight measurementextends the pT reach to 3 GeV/cfor protons
y0
Smooth evolution with centrality
arXiv:nucl-ex/0610001submitted to PRC
Identified particle pT -spectra,
Au+Au at 62.4 GeV
Gábor I. Veres Quark Matter 2006, Shanghai, November 14-20, 2006
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Particle production at very low pT
Low pT spectra carry information about radial flow, possible anomalousenhancement at very low pT, quantum mechanical effects, scaling laws
• Unique low-pT coverage of PHOBOS
T = 1016 MeVsurface = 0.720.02
y0
PHOBOS Au+Au 62.4 GeVarXiv:nucl-ex/0610001submitted to PRC
T = 1026 MeVsurface = 0.760.02
T = 1036 MeVsurface = 0.780.02
Gábor I. Veres Quark Matter 2006, Shanghai, November 14-20, 2006
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mT -scaling in d+Au vs. Au+Au at 200 GeV
Lack of mT scaling in heavy ion collisions
arXiv:nucl-ex/0610001submitted to PRCJ.Phys.G 30 S1143-S1147 (2004 ) PRC 70 (2004) 051901(R)
Gábor I. Veres Quark Matter 2006, Shanghai, November 14-20, 2006
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(Anti)proton/hadron ratiosfor the two charge signs
Baryon excess approached at about pT3 GeV/c
y0
p>++K+
arXiv:nucl-ex/0610001submitted to PRC
PHOBOS
ArXiv:nucl-ex/0610001submitted to PRC
y0
Smooth energy dependenceof pT where p/+1
p
+ c
ross
ing
Central A+A
Gábor I. Veres Quark Matter 2006, Shanghai, November 14-20, 2006
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y0
arXiv:nucl-ex/0610001submitted to PRC
Net protons (p–p)_
The net proton yield is proportional to Npart!p/p centrality independent p and p Npart as well
__
Gábor I. Veres Quark Matter 2006, Shanghai, November 14-20, 2006
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Summary
New results from PHOBOS:
• antiparticle/particle ratios in Cu+Cu collisions• p(p)/h± ratios, identified spectra in 62.4 GeV Au+Au collisions
What have we learned?
• Centrality-independence:• p/p ratios
• net proton, p and p yield per participant
(still not fully understood theoretically)
• baryon excess in Au+Au collisions at 62.4 GeV• mT-scaling holds in d+Au but violated in Au+Au
_
_
_
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