for the Collaboration

Particle Production at Very Low and Intermediate

Transverse Momenta in d+Au and Au+Au Collisions

Adam TrzupekThe Henryk Niewodniczański Institute of Nuclear Physics

Polish Academy of Sciences

Kraków, Poland

Quark Matter 2005

18th International Conference on Ultra-Relativistic

Nucleus-Nucleus Collisions, Budapest, Hungary

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 LABORATORYINSTITUTE OF NUCLEAR PHYSICS PAN, KRAKOW MASSACHUSETTS INSTITUTE OF TECHNOLOGY

NATIONAL CENTRAL UNIVERSITY, TAIWAN UNIVERSITY OF ILLINOIS AT CHICAGOUNIVERSITY OF MARYLAND UNIVERSITY OF ROCHESTER

Particle Production at Very Low pT

Enhanced production of low-pT particles was predicted as a consequence of NEW long wave-length phenomena

PHOBOS experiment has a unique capability to measure particles down to very small transverse momenta: 0.03 - 0.2 GeV/c

Au+Au, 200 GeV centrality: 0-15% mid-rapidity

PHOBOS: PRC 70 (2004) 051901(R) PLB 578 (2004) 297

TAIL

BULK

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) 102302

pT and PID Measurement in PHOBOS Spectrometer

10 cm

z

-x

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

• pT > 0.2 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

70 cm

0 10 20 Z [cm]

X[c

m]

AB

CD

EF

Be pipe

. .

pT (GeV/c)0.03 0.5 5.0

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)

PRC 70 (2004) 051901(R)

p+p

K +K + -

++-

p (GeV/c)

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

Low-pT Spectra of IdentifiedParticles in Au+Au Collisions

at sNN =62.4 GeV

Blast wave fit parameters: 0-15%: Tfo = 99 MeV, <T>=0.51 c15-30%: Tfo = 98 MeV, <T>=0.51 c30-50%: Tfo = 97 MeV, <T>=0.49 c

(2p

T)1

d2 N

/dy

dp

T[c

2 /G

eV

2 ]

(2p

T)1

d2 N

/dy

dp

T[c

2 /G

eV

2 ]

(2p

T)1

d2 N

/dy

dp

T[c

2 /G

eV

2 ]

Low-pT Spectra of Identified Particles Au+Au at sNN = 200 GeV

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

PHOBOS, PR C70, 051901 (R) (2004) PHENIX, PR C69, 034909 (2004)

Blast Wave Fit: Tfo= 99 MeV <T> = 0.54 c

T= 229 MeV for (++-)

293 MeV for (K++ K-)

392 MeV for (p + p)

[ ] 12

1)/exp(1

21 −−= BET

TT

TmAdydm

Ndmπ

mT = pT2+mh

2

B-E fit

BWF fit

(2p

T)1

d2N

/dyd

pT[c

2/G

eV

2]

(2p

T)1

d2N

/dyd

pT[c

2/G

eV

2]

Invariant Yields of Very Low pT Particlesin Central Au+Au Collisions at sNN=200 GeV

(2p

T)1

d2N

/dyd

pT[c

2/G

eV

2]

Low-pT Spectra as Model Constraints

J. Cramer (private comm.,erratum to be published)

J.Cramer, et al., PRL 94 (2005) 102302

(2p

T)1

d2N

/dyd

pT[c

2/G

eV

2]

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, 082301Tfo = 152 GeV, <T>=0.37 c

(2p

T)1

d2N

/dyd

pT[c

2/G

eV

2]

mT -Scaling in d+Au at sNN= 200 GeV

(++-), (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

Tlo

c[G

eV/c

2 ]

mT -Scaling in d+Au vs. Au+Au at sNN = 200 GeVPRC 70 (2004) 051901(R)

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

(2p

T)1

d2 N

/dyd

pT[c

2 /G

eV2 ]

(2p

T)1

d2 N

/dyd

pT[c

2 /G

eV2 ]

T

loc[G

eV

/c2]

Tlo

c[G

eV

/c2]

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