for the Collaboration
Low-pT Spectra of Identified Charged Particles
in sNN = 200 GeV Au+Au Collisions
from PHOBOS Experiment at RHIC
Adam Trzupek
Institute of Nuclear Physics, Kraków, Poland
International Europhysics Conference on High Energy Physics
EPS (July 17th-23rd 2003) in Aachen, Germany
Adam Trzupek
Au+Au sNN=200 GeV
PHOBOS preliminary
RHIC experiments measured particle spectra at pT > 0.2 GeV/c => jet quenching
PHOBOS has a unique capability to measure particles down to very small transverse momenta << 0.2GeV/c
Particle pT distributions at RHIC
Adam Trzupek
3
2 Th
foeff
mTT
for pT << mh
Enhanced production of low pT particles is expected due to the presence of NEW long wave-length phenomena, e.g. large volume of the system at freeze-out should lead to an increase of low pT particle yields
Why production of particles with very low pT is interesting?
Enhanced yield of pions with pT < 0.2 GeV/c with respect to the B-E distribution may occur when disoriented chiral condensates (DCC) are formed
Mass-dependent suppression at low pT due to the collective transverse expansion of the system is expected
Adam Trzupek
• pT > 0.2 GeV/c track curvature in B field => MOM dE/dx in Si, ToF => PID
• pT = 0.03 - 0.2 GeV/c low pT particles stop in silicon wafers => PID, MOM
B field negligible ( layers A-F )
0 10 20 Z [cm]
X[c
m] A
BC
DEF
Be pipe
. .
pT and PID measurement in PHOBOS spectrometer
z
-x
10 cm
y
70 cm PHOBOS Spectrometer (2001) • two arms at mid rapidity• dipole magnetic field of 2T at maximum• 16 layers of silicon wafers• fine/optimal pixelization, precise dE measurement
(++-)
=> (K++ K-)
(p + p)
Adam Trzupek
Eloss = dEi , i = A, ... ,EMp = < Eloss dE/dx > mh
( mh2) (1/2) Bethe-Bloch function
A B C D E
Ek= 8 MeV
P Ek=21 MeV
K Ek=19 MeV
silicon layer
Candidates should have dE/dx values within dE/dx bands for (+
+-), (K++K-) and (p+p)
Particle identification at very low pT
d
E/d
x [M
eV]
Eloss [MeV]
(+
+-)
(K++K-)
(p+p)
MC
Mp
Correction for energy loss in layer E was applied under the assumption that particle stops in this layer. This correction procedure and energy lossfluctuations in beam pipe and Si lead to a correlation Mp vs Eloss
1 bands
Adam Trzupek
Experimental data sample
Eloss [MeV]
(++-)
(K+
+K-)
(p+p)
DATA
Mp
Sample used for this analysis:
15% most central Au+Au events of sNN = 200 GeV
Number of events used: 400,000 out of 2M availablefor final results
Preliminary
Adam Trzupek
Momentum distributions:
(++-)
(K++K-)
(p+p)
PHOBOS preliminary
pT [GeV/c]
dydpp
Nd
2
1
TT
2
Acceptance & efficiency corrections embedding single MC tracks into experimental events
Background corrections: feeddown, secondaries, misID, ghosts;
(p +p) 41±8%
(K++K-) 16±11%
(++-) 39±3% based on track vertex distributions (DCA) and rescaled HIJING with detector (Geant) simulations
Current systematic errors 20%() ~40%(K) ~50%(p)
Centrality 0-15%sNN=200 GeV Au+Auy= -0.1 — 0.4
Adam Trzupek
Comparison to other RHIC experimentsT. Ullrich Nucl.Phys.A 715,p.399c(2003)
• Yields at lowest pT at RHIC are measured with the PHOBOS spectrometer • Uncertainties in fit extrapolations to pT =0 are reduced• Flattening of proton spectra indicates strong collective radial expansion
Adam Trzupek
Pion low pT yields are well described by Bose - Einstein function extrapolated from higher pT (>0.2GeV/c)
Excess in low pT pion production below 0.2 GeV/c predicted by DCC models is not observed J. Randrup Nucl.Phys. A681 (2001) 100c
B-E fit, pT = 0.2 - 0.7 GeV/c
Pion mT distributions:
12
1)/exp(1
21 BET
TT
TmAdydm
Ndm
Bose - Einstein distribution:
mT = pT2+mh
2
Adam Trzupek
Models constraints
P. Kolb and R. Rapp; PRC 67 (2003) 044903
H
1/(
2m
T)
d2N
/dyd
mT /<
Np
art/2
>HIJING RQMD
HYDRO+THERMALW.Broniowski,W.Florkowski(PRL87,2001,272302)
(p+p)PHOBOS preliminary
Model predictions differ from data by factors 2-6 at loo pT
Hydrodynamic simulation with (initial) transverse boost describes data well from the very low pT up to 1.5 GeV/c
Adam Trzupek
Summary
Algorithm was developed to determine yields of (++-), (K++ K-) and (p + p) at very low pT ( 0.03 - 0.2 GeV/c ) using the PHOBOS
spectrometer No enhancement in low pT yields for pions is observed
Flattening of (p+p) spectra down to very low pT indicates
strong radial flow in the system
Models should account for the dynamics ( rescattering,
expansion ) which has largest effect on low pT (p + p) yields
Adam Trzupek
Collaboration (May 2003)
Birger Back, Mark Baker, Maarten Ballintijn, Donald Barton, Bruce Becker, Russell
Betts,
Abigail Bickley, Richard Bindel, Andrzej Budzanowski, Wit Busza (Spokesperson), Alan
Carroll,
Patrick Decowski, Edmundo Garcia, Tomasz Gburek, Nigel George, Kristjan
Gulbrandsen,
Stephen Gushue, Clive Halliwell, Joshua Hamblen, Adam Harrington, Conor
Henderson,
David Hofman, Richard Hollis, Roman Hołyński, Burt Holzman, Aneta Iordanova, Erik
Johnson,
Jay Kane, Nazim Khan, Piotr Kulinich, Chia Ming Kuo, Jang Woo Lee, Willis Lin, Steven
Manly,
Alice Mignerey, Gerrit van Nieuwenhuizen, Aaron Noell, Rachid Nouicer, Andrzej
Olszewski,
Robert Pak, Inkyu Park, Heinz Pernegger, Corey Reed, Louis Remsberg, Christof
Roland,
Gunther Roland, Joe Sagerer, Pradeep Sarin, Pawel Sawicki, Iouri Sedykh, Wojtek
Skulski,
Chadd Smith, Peter Steinberg, George Stephans, Andrei Sukhanov, Ray Teng,
Marguerite Belt Tonjes, Adam Trzupek, Carla Vale, Robin Verdier, Gábor Veres,
Bernard Wadsworth, Frank Wolfs, Barbara Wosiek, Krzysztof Woźniak, Alan
Wuosmaa, Bolek Wysłouch, Jinlong Zhang
ARGONNE NATIONAL LABORATORY BROOKHAVEN NATIONAL LABORATORYINSTITUTE OF NUCLEAR PHYSICS, KRAKOW MASSACHUSETTS INSTITUTE OF TECHNOLOGYNATIONAL CENTRAL UNIVERSITY, TAIWAN UNIVERSITY OF ILLINOIS AT CHICAGO
UNIVERSITY OF MARYLAND UNIVERSITY OF ROCHESTER
Adam Trzupek
Backup slides
Adam Trzupek
1m
PHOBOS Detector (2001) • Triggering
-Scintillator Paddles- Zero Degree Calorimeter
• 4 Multiplicity Array
- Octagon, Vertex & Ring Si Counters• Two Mid-rapidity Spectrometers• TOF wall for High-Momentum PID
Adam Trzupek
1/(2pT)d2N/dydpT
acceptance & efficiency correctionsembedding single MC tracks into experimental events in phase space cells:
pT, y, Zver ,
(- + +)
Adam Trzupek
PHOBOS preliminary
(++) (K+
+K–) (p+p)
mT – m0
10-2 10-1 1
HIJING RQMD
HYDRO+THERMAL W.Broniowski,W.Florkowski
(PRL87,2001,272302;PRC65,2002,064905)
PHENIX 130 GeV
1/(
2m
T)
d2N
/dyd
mT /<
Np
art/2
>
(Au+Au yields )/<Npart/2>
1
10-1
10
PHOBOS preliminary PHOBOS preliminary
10 10
1 1
10-1 10-1
10-2 10-1 1 10-2 10-1 1
Model Constraints
014.0183.002.061.002.080.0 expexpexp
pHIJKHIJHIJ Y
Y
Y
Y
Y
Y