H. ItoUniversity of Kansas

For the BRAHMS Collaboration

The BRAHMS Institutions1 Brookhaven National Laboratory, Upton, NY 11973, U.S.A.2 Institut de Recherches Subatomiques and Université Louis Pasteur, Strasbourg, France3 Institute of Nuclear Physics, Krakow, POLAND4 Jagellonian University, Krakow, POLAND5 Johns Hopkins University, Baltimore, MD 21218, U.S.A.6 New York University, New York, NY 10003, U.S.A.7 Niels Bohr Institute for Astronomy, Physics and GeophysicsUniversity of Copenhagen, Copenhagen Ø, DENMARK8 Texas A&M University, College Station, TX 77843-3366, U.S.A.9 Fysisk institutt, Universitetet i Bergen, Bergen, NORWAY10 University of Bucharest, ROMANIA11 University of Kansas, Lawrence, KS 66045, U.S.A.12 University of Oslo, Oslo, NORWAY+ Deceased

Charged Particle Multiplicities at BRAHMS

I. G. Bearden7, D. Beavis1, C. Besliu10, Y. Blyakhman6, J. Brzychczyk4, B. Budick6,H. Bøggild7, C. Chasman1, C. H. Christensen7, P. Christiansen7, J. Cibor3, R. Debbe1, J. J. Gaardhøje7, K. Grotowski4, K. Hagel8, O. Hansen7, A. Holm7, A. K. Holme12, H. Ito11, E. Jakobsen7, A. Jipa10, J. I. Jørdre9, F. Jundt2, C. E. Jørgensen7, T. Keutgen8, E. J. Kim5, T. Kozik4, T. M. Larsen12, J. H. Lee1, Y. K. Lee5, G. Løvhøiden12, Z. Majka4, A. Makeev8, B. McBreen1, M. Murray8, J. Natowitz8, B. S. Nielsen7, K. Olchanski1, J. Olness1, D. Ouerdane7, R. Płaneta4, F. Rami2, D. Röhrich9+, B. H. Samset12, S. J. Sanders11, R. A. Sheetz1, Z. Sosin4, P. Staszel7, T. F. Thorsteinsen9, T. S. Tveter12, F. Videbæk1, R. Wada8, A. Wieloch4 and I. S. Zgura10

Perspective View of BRAHMS Detectors

Perspective View of Global Detectors

Beam Beam Counter

• 2 Size of Cherenkov Radiators3/4 in x 3 cm and 2 in x 4 cm

• Coverage2.5 < | | < 4.7

• Located 219 cm from the vertex

Left Array

Right Array

Multiplicity ArrayTwo Layers:• 175 Silicon-detector channels

.86 cm x 4 cm x .3 mm

• 38 Scintillator tiles12 cm x 12 cm x .5 cm

• coverage -2.2 < < 2.2

Multiplicity By Beam Beam Counter from Detected Energy

Multiplicity By Beam Beam Counter from Statistics

Assumptions

• Poisson probability distribution

• Good measurement of no hit

Beam Beam Counter Background Correction

Multiplicity Array Energy Calibration

• Using 1 MIP response from data, the detected energy is calibrated for each detector.

•Solid line: experimental data•Dotted line: GEANT simulation

Multiplicity By Multiplicity Array

From the Detected Energy to N

•Model dependence is a few percent (HIJING and FRITIOF)•There is no centrality dependence.

Using GEANT Monte Carlo Simulation, get Nch/EMIP for each detector element

Beam Axis

GEANT MIPE

Sin )(

Centrality DeterminationTwo Methods of Measuring Centrality• Centrality by Multiplicity Array• Centrality by ZDC and BB

Preliminary Results

dN/dPreliminary Results

0-5% 5-10%

10-20% 20-30%

30-40% 40-50%

Beam Beam Counter

Silicon

Tile

T1

TPM1

dN/d with model prediction

Preliminary Results

Fritiof

Hijing

dN/d per Participant PairPreliminary Results

FRITIOF

HIJING

EKRT

Eikonal (Kharzeev and Nardi)

Npart from Glauber Model

Npart from Eikonal Model

PHENIX

Conclusion

• Charged particle multiplicities have been measured over a wide range of .

• Pseudorapidity distributions have been measured with different centralities.

• dN/d per participant pair has been measured with different centralities and pseudorapidities. However, the uncertainty in <Npart> for peripheral collision seems to be too large to detemine a definitive trend.