1. Particle Production at Very Low and Intermediate Transverse Momenta in d+Au and Au+Au Collisions
Adam Trzupek
The Henryk Niewodniczański Institute of Nuclear Physics
Polish Academy of Sciences
Kraków, Poland
for the Collaboration
Quark Matter 2005
18th International Conference on Ultra-Relativistic
Nucleus-Nucleus Collisions, Budapest, Hungary

2. Collaboration (August 2005)
Burak Alver, Birger Back, Mark Baker, Maarten Ballintijn, Donald Barton, Russell Betts, Richard Bindel,
Wit Busza (Spokesperson), Zhengwei Chai, Vasundhara Chetluru, Edmundo García, Tomasz Gburek,
Kristjan Gulbrandsen, Clive Halliwell, Joshua Hamblen, Ian Harnarine, Conor Henderson, David Hofman, Richard Hollis, Roman Hołyński, Burt Holzman, Aneta Iordanova, Jay Kane,Piotr Kulinich,
Chia Ming Kuo, Wei Li, Willis Lin, Constantin Loizides, Steven Manly, Alice Mignerey,
Gerrit van Nieuwenhuizen, Rachid Nouicer, Andrzej Olszewski, Robert Pak, Corey Reed,
Eric Richardson, Christof Roland, Gunther Roland, Joe Sagerer, Iouri Sedykh, Chadd Smith,
Maciej Stankiewicz, Peter Steinberg, George Stephans, Andrei Sukhanov, Artur Szostak,
Marguerite Belt Tonjes, Adam Trzupek, Sergei Vaurynovich, Robin Verdier, Gábor Veres,
Peter Walters, Edward Wenger, Donald Willhelm, Frank Wolfs, Barbara Wosiek, Krzysztof Woźniak,
Shaun Wyngaardt, Bolek Wysłouch
ARGONNE NATIONAL LABORATORY BROOKHAVEN NATIONAL LABORATORY
INSTITUTE OF NUCLEAR PHYSICS PAN, KRAKOW MASSACHUSETTS INSTITUTE OF TECHNOLOGY
NATIONAL CENTRAL UNIVERSITY, TAIWAN UNIVERSITY OF ILLINOIS AT CHICAGO
UNIVERSITY OF MARYLAND UNIVERSITY OF ROCHESTER

3. Particle Production at Very Low pT
Au+Au, 200 GeV
centrality: 0-15%
mid-rapidity
PHOBOS:
 PRC 70 (2004) (R)
 PLB 578 (2004) 297
PHOBOS experiment has a unique capability to measure particles down to very small transverse momenta:
GeV/c
BULK
Enhanced production of low-pT particles was predicted as a consequence of NEW long wave-length phenomena
TAIL
Particle spectra at low pT can be modified due to collective transverse expansion
A recent optical model implies that chiral symmetry restoration can have significant impact on shapes of pion spectra at very low pT
J.Cramer, et al., Phys. Rev. Lett. 94 (2005)

4. pT and PID Measurement in PHOBOS Spectrometer
70 cm
PHOBOS Spectrometer
16 layers of silicon wafers
fine pixelization, precise dE measurement
collision vertex close to spectrometer
near mid-rapidity coverage
dipole magnetic field of 2T at maximum
10 cm z -x
pT > 0.2 GeV/c
track curvature in B field p,charge
dE/dx in Si, ToF mass
pT = GeV/c
low-p particles stop
in silicon wafers p, mass
B field negligible no charge identification
Z [cm]
X[cm] A B C D E F
Be pipe .

5. PHOBOS PID Capabilities
PRC 70 (2004) (R) 1 2 3 4 5
p (GeV/c) 30 40 50 60 70
p+p
1/v (ps/cm)
K +K
++-
Eloss (MeV)
p (GeV/c)
Stopping
particles
dE/dx
TOF
0.5
5.0
0.03
pT (GeV/c)
Particle ID from low to high pT

6. Identified Particle pT -Spectra, Au+Au at 62.4 GeV
These results at 62.4 GeV fit smoothly into the energy evolution of antiparticle/particle ratios

7. Low-pT Spectra of Identified Particles in Au+Au Collisions
at sNN =62.4 GeV
(2pT)1d2N/dydpT[c2/GeV2]
Blast wave fit parameters:
0-15%: Tfo = 99 MeV, <T>=0.51 c
15-30%: Tfo = 98 MeV, <T>=0.51 c
30-50%: Tfo = 97 MeV, <T>=0.49 c
(2pT)1d2N/dydpT[c2/GeV2]
(2pT)1d2N/dydpT[c2/GeV2]

8. Low-pT Spectra of Identified Particles Au+Au at sNN = 200 GeV
B-E fit
PHOBOS, PR C70, (R) (2004) PHENIX, PR C69, (2004)
mT = pT2+mh2 
BWF fit
(2pT)1d2N/dydpT[c2/GeV2]
T= 229 MeV for (++-)
293 MeV for (K++ K-)
392 MeV for (p + p)
Blast Wave Fit:
Tfo= 99 MeV
<T> = 0.54 c
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

9. Invariant Yields of Very Low pT Particles in Central Au+Au Collisions at sNN=200 GeV
(2pT)1d2N/dydpT[c2/GeV2]
(2pT)1d2N/dydpT[c2/GeV2]

10. Low-pT Spectra as Model Constraints
(2pT)1d2N/dydpT[c2/GeV2]
J. Cramer (private comm.,
erratum to be published)
J.Cramer, et al.,
PRL 94 (2005)

11. Identified Particle pT -Spectra, d+Au at sNN= 200 GeV
pT range:
(++-) : > 0.03 GeV/c
(K++ K-): > 0.09 GeV/c
(p + p) : > 0.14 GeV/c
Background corrections:
very low-pT:
(++-) : 20%
(K++ K-): 10%
(p + p) : 20%
intermediate pT
(p + p) : ~20%
Systematic uncertainties:
very low pT: ~30%
intermediate pT : ~15%
Event selection:
described in PRL 93,
(2pT)1d2N/dydpT[c2/GeV2]
Tfo = 152 MeV, <T>=0.37 c

12. mT -Scaling in d+Au at sNN= 200 GeV
(2pT)1d2N/dydpT[c2/GeV2]
(++-), (K++ K-), (p + p)
mT-yields are similar after scaling (K++ K-) yield by a factor 2 (strangeness suppression)
Local slopes of mT -spectra similar
Tloc[GeV/c2]

13. mT -Scaling in d+Au vs. Au+Au at sNN = 200 GeV
PRC 70 (2004) (R)
(2pT)1d2N/dydpT[c2/GeV2]
(2pT)1d2N/dydpT[c2/GeV2]
Tloc[GeV/c2]
Tloc[GeV/c2]
In central Au+Au, larger flattening for of p+p mT spectra at small pT
Low-pT spectra of p+p can constrain models describing collective transverse expansion of the system

14. Summary
No evidence for enhanced production of very low-pT pions iaiiin the mosticentral Au+Au collisions at energy 62.4 and iaii200 GeV
Flattening of p+p mT spectra at low-pT in 15% most central iaiiAu+Au collisions at energy 62.4 and 200 GeV
Approximate mT scaling of particle spectra for d+Au iaiicollisions at low and intermediate transverse momentum
New constraints on models and fits

15. backups

16. PID Measurement in PHOBOS Spectrometer
pT > 0.2 GeV/c
pT = GeV/c
p+p p K
<dE/dx> 
K +K
++-
Etot =  dEi , i=A, ... ,E
Mpi = Ei dEi/dx
Mp = < Mpi >
/K separation: pT < ~0.6 GeV/c
p(p) separation: pT < ~1.2 GeV/c

17. d+Au, Model Comparison