Charged Hadron Spectra and Ratios in d+Au and Au+Au Collisions from PHOBOS Experiment at RHIC
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Transcript of Charged Hadron Spectra and Ratios in d+Au and Au+Au Collisions from PHOBOS Experiment at RHIC
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Charged Hadron Spectra and Ratios in d+Au and
Au+Au Collisions from PHOBOS Experiment at RHIC
Adam TrzupekThe Henryk Niewodniczański Institute of Nuclear Physics
Polish Academy of Sciences
Kraków, Poland
4th Budapest Winter School on Heavy Ion Collisions(December 1st-3rd 2004) in Budapest, Hungary
nucl-ex/0410022, 2004
Birger Back, Mark Baker, Maarten Ballintijn, Donald Barton, Bruce Backer, Russell Betts,
Abigail Bickley, Richard Bindel, Andrzej Budzanowski,Wit Busza (Spokesperson), Alan Carroll,
Zhengwei Chai, Patrick Decowski, Edmundo García, Tomasz Gburek, Nigel George,
Kristjan Gulbrandsen, Steve Gashue, Clive Halliwell, Joshua Hamblen, Adam Harington,
Michael Hauer, George Heintzelman, Conor Henderson, David Hofman, Richard Hollis,
Roman Holynski, Burt Holzman, Aneta Iordanova, Erik Johnson, Jay Kane, Judith Katzy,
Nazim Khan, Wojtek Kucewicz, Piotr Kulinich, Chia Ming Kuo, Jang Wo Lee, Willis Lin,
Steven Manly, Don McLeod, Alice Mignerey, Rachid Nouicer , Gerrit van Nieuwenhuizen,
Andrzej Olszewski, Robert Pak, Inkyu Park, Heinz Pernegger, Corey Reed, Louis Remsberg,
Mike Reuter, Christof Roland, Gunther Roland, Leslie Rosenberg, Joe Sagerer, Pradeep Sarin,
Paweł Sawicki, Helen Seals, Iouri Sedykh, Wojtek Skulski, Chadd Smith, Maciej Stankiewicz,
Peter Steinberg, George Stephans, Andrei Sukhanov, Jaw-Luen Tang, Marguerite Belt Tonjes,
Adam Trzupek, Carla Vale, Robin Verdier, Gábor Veres, Edward Wenger, Frank Wolfs,
Barbara Wosiek, Krzysztof Wozniak, Alan Wuosmaa, Bolek Wyslouch, Jinlong Zhang
ARGONNE NATIONAL LABORATORY BROOKHAVEN NATIONAL LABORATORYINSTITUTE OF NUCLEAR PHYSICS PAN, KRAKÓW MASSACHUSETTS INSTITUTE OF TECHNOLOGY
NATIONAL CENTRAL UNIVERSITY, TAIWAN UNIVERSITY OF ILLINOIS AT CHICAGOUNIVERSITY OF MARYLAND UNIVERSITY OF ROCHESTER
PHOBOS Collaboration
PHOBOS Detector
T0 counter
Spectrometer
SpecTOF
TOF
multiplicity, vertex and calorimeter detectors are not labeled(see Russell Betts talk)
Magnet
Paddle Trigger counter
Paddle Trigger counter
T0 counter
• pT = 0.2 - ~5 GeV/c track curvature in B field => p,charge dE/dx in Si, ToF => mass
• pT = 0.03 - 0.2 GeV/c low-p particles stop in silicon wafers => p, mass
B field negligible => no charge identification
pT and PID Measurement in PHOBOS Spectrometer
10 cm
z
-x
PHOBOS Spectrometer• dipole magnetic field of 2T at maximum• 16 layers of silicon wafers• fine/optimal pixelization, precise dE measurement• collision vertex close to spectrometer• near mid-rapidity coverage
70 cm
0 10 20 Z [cm]
X[c
m]
AB
CD
EF
Be pipe
. .
PID Measurement in PHOBOS Spectrometer<
dE
/dx>
pT > 0.2 GeV/c pT = 0.03 - 0.2 GeV/c
Etot = dEi , i=A, ... ,E
Mpi = Ei dEi/dx
Mp = < Mpi >
/K separation: pT < ~0.6 GeV/cp(p) separation: pT < ~1.2 GeV/c
Kp
Energy Dependence of Antiparticle to Particle Ratios
p/p
K–/K+
A+A central, near mid-rapidity PHOBOS 130 GeV
PRL 87 (2001) 102301
PHOBOS 200 GeV
PRC 67 (2003) 0211901
particle ratios increase with energy
net baryon density is rapidly decreasing
GOOD CONDITIONS FOR QGP FORMATION
at sNN = 200 GeV in Au+Au central collisions:
baryochemical potential: B = 27 2 MeV
energy density: = ~ 5 GeV /fm3 , 0 = 1 fm, nucl-ex/0410022
in AA collisions “BULK” of hadrons is produced at low transverse momentum “TAIL” of transverse momentum distribution at high-pT originates from hard partonic scatterings
0.2<y<1.4
Charged Hadron Transverse Momentum Distributions in Au+Au collisions at sNN = 200 GeV
centrality: 0-15%mid-rapidity
PRC RC in press nuc-ex/0401006 PLB 578 (2004) 297
PLB 578 (2004) 297
TAIL
BULK
invariant yieldsparticle density
parton
nucleus
t = - a few fm/c
parton
t = 0 fm/c
hard partonicscattering
t = + a few fm/c
hadronization
jet of hadrons
leading hadron of high pT
t = + a few fm/c
scattered partons pass throughhot and densemedium
Hard partonic scatterings occur early in AA collision. Scatteredpartons can probe the dense and hot medium created in AA collision
detector
nucleus
if scattered partons loose energy then the numberof leading hadrons will be suppressed (”jet quenching”)
High-pT Probes
RAA
„hard collisions”
„soft collisions”
pT(GeV/c)
Nuclear Modification Factor RAA
ddpNdN
ddpNdidsbpR
TNN
coll
TAA
TAA /
/,...),,,,(
2
2
RAA=1 (Ncoll scaling), lack of nuclear effects, small cross section for hard partonic scattering
Ncoll - number of binary inelastic NN interactions in AA
,m,
NN data:p+ p (UA1) at 200 GeVp+ p (ISR) at 62.4 GeV
RAuAu for Charged Hadrons in Au+Au Collisions at sNN = 200 GeV
Ncoll scaling
suppression of high-pT hadron production is observed
strongest effect is seen in most central collisions
PLB 578 (2004) 297
pT (GeV/c)
45-50% 35-45%
25-35% 15-25%
6-15% 0-6%
RAuAu
mid- peripheral
central
1 d2 NAuAu / dpTd
<Ncoll> d2 NNN / dpTd
RAuAu =
High-pT Suppression
Final state effects?
energy loss in medium
initial state effects possible in d+Auno final state effects
no suppression in d+Au collisions indicates that final state effects are responsible for suppression in Au+Au
central Au+Au:
d +Au:
Initial state effects?
gluon saturation:suppression of high parton density (g+g-> g)Color Glass Condensate
d+Au at 200 GeV is a control experiment
RdAu for Charged Hadrons, sNN = 200 GeV
d+Au control experiment indicates that suppression of particle production in central Au+Au collisions at sNN = 200 GeV
is a consequence of final state effects
PRL 91 (2003) 072302
RdAu
Au+Au
mid-rapidity, 0.2<y<1.4
medium created in Au+Au collisions is strongly interacting
no suppression in d+Au collisions
Low-pT Spectra of Identified Charged Particles in Central Au+Au at sNN = 200 GeV
12
1)/exp(1
21 BET
TT
TmAdydm
Ndm
mT = pT2+mh
2
no enhancement in low-pT yields for pions is observed flattening of (p+p) spectra down to very low pT, consistent with transverse expansion of the system
|T= 229 MeV for (++-) 293 MeV for (K++ K
-)
392 MeV for (p + p)
PRC RC in pressnucl-ex/0401006
medium created in Au+Au collisions is strongly interacting
RAuAu for Charged Hadrons at sNN = 62.4 GeV
nucl-ex/0405003 (Au+Au, 62.4 GeV)
RHIC Physics Run 2004
RAuAu at 62.4 GeV is significantly higher than at 200 GeV for all centralities within the studied pT range
RA
uA
u
Energy Dependence of RAA
nucl-ex/0405003
central Pb+Pb and Au+Au collisions, near mid-rapidity
at high-pT: RAA > 1 at sNN = 17.2 GeV
RAA < 0.2 at sNN = 200 GeV
smooth evolution of RAA with energy
pT(GeV/c)yields normalized by Npart weakly depend on centrality
Nuclear Modification Factor RAANpart
0 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4
Ncoll scaling
45-50% 25-35% 15-25% 0-6%
Npart - number of participating (wounded) nucleons in AA
<Ncoll>
<Npart>
b(fm)
Au+AuGlauber Model
Ncoll ~ Npart 4/3
nucl-ex/0405003, Au+Au: 62.4 GeV, 200 GeV
1 d2 NAA / dpTd <Npart/2> d2 NNN/ dpTdRAA
Npart =
yield per participant (or RAANpart) changes by less than 25% for both
energies in centrality range from 60 to 340 participants.
centrality evolution is the same at both energies:
RAANpart = RPC
Npart (Npart) * f(sNN )
Factorization of Energy and Centrality Dependence of RAA
Npart at sNN = 62.4 and 200 GeV
nucl-ex/0405003
SummaryAu+Au: • almost net-baryon free environment, energy density ~ 5 GeV/fm3
• strong suppression of high-pT charged hadron yields in central collisions at 200 GeV (~ 5 times at pT ~ 5 GeV)
• no evidence for enhanced production of very low-pT pions• flattening of p+p spectra at low-pT, strong radial flow in the system, • RAuAu at 62.4 GeV is significantly higher than RAuAu at 200 GeV• factorization of energy and centrality dependence of RAuAu
Npart
• approximate Npart scaling of hadron yields
d+Au:• no suppression of charged hadron yields at high-pT (at mid-rapidity)
suppression in central Au+Au is final state effect
Conclusions
STRONGLY INTERACTING, HIGH DENSITY AND ALMOST NET-BARYON FREE
MEDIUM IS CREATED AT THE HIGHEST RHIC ENERGY IN CENTRAL Au+Au COLLISIONS
particle ratios high-pT suppression low-pT spectra
Triggering on Collisions & Centrality
• Coincidence between Paddle counters at t = 0 defines a valid collision
• Paddle + ZDC timing reject background
PP
Negative
Paddles
Positive Paddles
Aux
z
PN
Positive ZDC
Negative ZDC
NegativeCerenkov
PositiveCerenkov
Au
Central Peripheral
HIJING +GEANT Glauber calculation Model of paddle trigger
Data Data+MC
RdAu as a Function of Pseudo-rapidity( = - ln tan(/2))
nucl-ex/0406017, PRC in press nucl-ex/0406017, PRC in press
positive is in deuteron direction with increasing , RAA decreasesmodel constraints: Color Glass Condensate
PRC in pressnucl-ex/0401006
d+Au
Scale uncertainty: 15%
Not feed-down corrected
Au+Au Spectra normalized at 2 GeV/c
mT Scaling in d+Au vs Au+Au
RAA at low energy (fixed target experiments)
Initial state effects
RSAu
RPbPb
RpA
Cronin effect
Elab = 200 AGeV, sNN = 19.4GeV
Pb+Pb: Elab =158 AGeV, sNN = 17.3 GeV
RSS
multiple scatterings
pT broadening => RAA
>1
Factorization of RAA(sNN,centrality)
TNNTcollNPC
NAA p,sfp,NRR collcoll For b<10.5 fm:
ddp/Nd
ddp/Nd
N
NR
TcentAA
2TAA
2
coll
centcollN
PCcoll
Centrality Ncoll
62.4 GeV200 GeV
pT (GeV/c)
nucl-ex/0405003
EPS2003 - Aachen 38
Theory Calculations
Cronin Effect:X.N. Wang, Phys. Rev C61, 064910 (2000).
Attributed to initial state multiple scattering.Implemented by Q2(pt) dependent Gaussian kt broadening
Energy loss applied:M. Gyulassy, I. Vitev, X.N Wang and B.W. Zhang; nucl-th/0302007
dE/dxo is the only free parameter.It is determined by fitting toSTAR central RAA(pt)