Transcript Low-p Spectra of Identified Charged Particles in s

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
for the
Collaboration
International Europhysics Conference on High Energy Physics
EPS (July 17th-23rd 2003) in Aachen, Germany
Particle pT distributions at RHIC
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
Adam Trzupek
Why production of particles with very low pT is interesting?
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
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
Teff  Tfo
Adam Trzupek
mh  T  2

3
for pT << mh
pT and PID measurement in PHOBOS spectrometer
10 cm
z
-x
X[cm]
y
B
A
C
E
D
.
Be pipe
0
Adam Trzupek
10
• 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
F
.
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
20 Z [cm]
(++-)
B field negligible
+
=> (K + K )
( layers A-F )
(p + p)
Particle identification at very low pT
Eloss =  dEi , i = A, ... ,E
Mp = < Eloss dE/dx >  mh
( mh2) (1/2)
Bethe-Bloch function
dE/dx [MeV]
Candidates should have dE/dx
values within-dE/dx bands for
+
(++-), (K +K ) and (p+p)
P Ek=21 MeV
1 bands
K Ek=19 MeV
Mp
(p+p)
 Ek= 8 MeV
+
-
(K +K )
(++-)
A
B
C
D
MC
E
silicon layer
Eloss [MeV]
Correction for energy loss in layer E was applied under the assumption
that particle stops in this layer. This correction procedure and energy loss
fluctuations in beam pipe and Si lead to a correlation Mp vs Eloss
Adam Trzupek
Experimental data sample
Sample used for this analysis:
Preliminary
15% most central
Au+Au events
of sNN = 200 GeV
Number of events used:
400,000 out of 2M available
for final results
(p+p)
Mp
+
-
(K +K )
(++-)
DATA
Eloss [MeV]
Adam Trzupek
Momentum distributions:
1 d2N
2 p Tdp Tdy
Acceptance & efficiency
corrections
Centrality 0-15%
sNN=200 GeV Au+Au
y= -0.1 — 0.4
embedding single MC tracks
into experimental events
(++-)
Background corrections:
-
(K++K )
(p+p)
PHOBOS preliminary
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)
pT [GeV/c]
Adam Trzupek
Comparison to other RHIC experiments
T. 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 mT distributions:
Bose - Einstein distribution:
1 1 d 2N
1
 A exp(mT /TBE )  1
2 mT dydmT
mT = pT2+mh2
B-E fit, pT = 0.2 - 0.7 GeV/c
 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
Adam Trzupek
Models constraints
1/(2mT) d2N/dydmT /<Npart/2>
HIJING
RQMD
P. Kolb and R. Rapp; PRC 67 (2003) 044903
HYDRO+THERMAL
W.Broniowski,W.Florkowski
(PRL87,2001,272302)

(p+p)
PHOBOS preliminary
H
Model predictions differ from
data by factors 2-6 at loo pT
Adam Trzupek
Hydrodynamic simulation with
(initial) transverse boost describes
data well from the very low pT up to
1.5 GeV/c
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
INSTITUTE OF NUCLEAR PHYSICS, KRAKOW
NATIONAL CENTRAL UNIVERSITY, TAIWAN
UNIVERSITY OF MARYLAND
Adam Trzupek
BROOKHAVEN NATIONAL LABORATORY
MASSACHUSETTS INSTITUTE OF TECHNOLOGY
UNIVERSITY OF ILLINOIS AT CHICAGO
UNIVERSITY OF ROCHESTER
Backup slides
Adam Trzupek
PHOBOS Detector (2001)
• Triggering
-Scintillator Paddles
- Zero Degree Calorimeter
• 4 Multiplicity Array
- Octagon, Vertex & Ring Si Counters
• Two Adam
Mid-rapidity
Spectrometers
Trzupek
• TOF wall for High-Momentum PID
1/(2pT)d2N/dydpT
acceptance & efficiency
corrections
embedding single MC tracks into
experimental events in phase
space cells:
pT, y, Zver ,
(- + +)
Adam Trzupek
Model Constraints
HIJING
HYDRO+THERMAL W.Broniowski,W.Florkowski
1/(2mT) d2N/dydmT /<Npart/2>
(Au+Au yields )/<Npart/2>
(++)
10
RQMD
(PRL87,2001,272302;PRC65,2002,064905)
(K++K–)
10
(p+p)
10
PHOBOS preliminary
PHOBOS preliminary
1
1
1
10-1
10-1
10-1
PHOBOS preliminary
10-2
10-1
1
10-2
10-1
1
10-2
PHENIX 130 GeV
 Yexp 

  0.80  0.02
 Y Adam

 HIJ  Trzupek
 Yexp

Y
 HIJ

  0.61  0.02

K
 Yexp

Y
 HIJ
10-1
1
mT – m0

  0.183  0.014

p