NA5NA577

Strange particle production from 40 GeV data at the NA57 experiment

Paul Normanof the University of Birmingham, United Kingdom

on behalf of the CERN collaboration NA57

SQM 2003, Atlantic Beach 12th-17th March 2003

SQM 2003, Atlantic Beach P.Norman, University of Birmingham, United Kingdom

NA5NA577Talk contents

• Underlying physics and motivation.

• Reminder of NA57 layout and previous results.

• Yields for Pb-Pb interactions @ 40 A GeV/c.• (new), ,

• Signals for p-Be interactions @ 40 A GeV/c.• (new)

• Energy dependence of results.•40 GeV and 160 GeV, comparison with STAR

• Conclusions and outlook.

SQM 2003, Atlantic Beach P.Norman, University of Birmingham, United Kingdom

NA5NA577Underlying physics and motivation

As one of the main pieces of evidence for deconfinement at the SPS, WA97 showed strangeness enhancements for the strange hyperons, up to a factor of 15 for the .

Aim of NA57 – to study strangeness enhancement in more peripheral collisions and as a function of energy.

Low energy 40 GeV/c data gives us yields of even triply strange particles in Pb-Pb collisions, and doubly strange in p-Be.

More general concepts of NA57 discussed in the plenary talk of L. Sandor. This talk will focus on the 40 GeV/c results.

SQM 2003, Atlantic Beach P.Norman, University of Birmingham, United Kingdom

NA5NA577The NA57 experimental layout

Target: 1% Pb 8% Be

Scintillator Petals: centrality trigger

MSD: Multiplicity Silicon Detector

Tracking device: silicon pixel planes (y-z = 5 x 5 cm2 )

Lever arm: double side strips

SQM 2003, Atlantic Beach P.Norman, University of Birmingham, United Kingdom

NA5NA577Strange particle decays

pBR = 63.9% BR = 99.9% BR = 67.8%

BR = 68.6%

Get strange particles and anti-particles from weak decay topologies.

30 cm

5 cm

5 cm

B

Silicon Pixel T

racker

SQM 2003, Atlantic Beach P.Norman, University of Birmingham, United Kingdom

NA5NA577Yields and inverse slopes in NA57

Inverse slopes are obtained using the formula:

Yield =

Yields are extrapolated so that they are integrated over pT, and over 0.5 units of rapidity either side of mid-rapidity.

dydydmNddm

cm

cmT

T

y

ym

5.0

5.0

2

)exp(Tmm

dmdN T

TT

SQM 2003, Atlantic Beach P.Norman, University of Birmingham, United Kingdom

NA5NA577

and signals at 40 GeV/c

p-Be @ 40 A GeV/c

Pb-Pb @ 40 A GeV/c

SQM 2003, Atlantic Beach P.Norman, University of Birmingham, United Kingdom

NA5NA577Centrality measurement @ 40 GeV

Results on the following plots are for the integrated centrality classes I-IV unless stated otherwise.

For comparison with RHIC data, only classes III+IV are considered,although results are for most central 5% NA57/STAR (our bin IV).

SQM 2003, Atlantic Beach P.Norman, University of Birmingham, United Kingdom

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Energy dependence: and yields @ 40 and 160 GeV

from 40 GeV to 160 GeV:andabout same, up by a factor 3, anti-particles up by a factor 5

Larger baryon density at 40 GeV/c

pT > 0, y-ycm< 0.5

Black bars aresystematic errors

SQM 2003, Atlantic Beach P.Norman, University of Birmingham, United Kingdom

NA5NA577 and yields from SPS to RHIC

from NA57 40 GeV to 160 GeV, and confirmed by STAR:, and yields increase slower than their anti-particles at RHIC about same production rate for hyperon and anti-hyperon

STAR results from: - C. Adler et al. Phys. Rev. Lett. 89:092301 (2002) for - J. Castillo from QM2002 nucl-ex/0210032 for - C. Suire from QM2002 nucl-ex/0211017 for

Most central events:12% for NA57 (bins III+IV)14% for STAR

SQM 2003, Atlantic Beach P.Norman, University of Birmingham, United Kingdom

NA5NA577Y/Y ratios from SPS to RHIC

STARNA57

Ratio Y/Y approaches 1 as energy increases. Energy dependence weaker for higher strangeness (and thus lower light quark) content.

Most central events:12% for NA5714% for STAR

STAR results from: - C. Adler et al. Phys. Rev. Lett. 89:092301 (2002) for - J. Castillo from QM2002 nucl-ex/0210032 for - C. Suire from QM2002 nucl-ex/0211017 for

SQM 2003, Atlantic Beach P.Norman, University of Birmingham, United Kingdom

NA5NA577Conclusions

Yields: From 40 GeV/c data to 160 GeV/c there is an increase in

anti-particle yields (by about a factor 5), while the corresponding particle yields remain almost constant.

As could be expected, the and yields with respect to their anti-particles indicates a larger baryon density @ 40 w.r.t. 160 GeV/c. RHIC data confirms this trend.

Baryon yields show a weak dependence on energy, while anti-baryon yields are strongly dependent from 40 GeV to 160 GeV. RHIC data shows this effect continues.

SQM 2003, Atlantic Beach P.Norman, University of Birmingham, United Kingdom

NA5NA577Outlook

p-Be @ 40 A GeV/c: and yields Enhancements in Pb-Pb relative to p-Be

@ 40 GeV/c. Negatives, K0

Pb-Pb @ 40 A GeV/c: Negatives, K0

SQM 2003, Atlantic Beach P.Norman, University of Birmingham, United Kingdom

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The NA57 Collaboration

Athens University, Athens, Greece; Università di Bari and INFN, Bari, Italy; Universitetet i Bergen, Bergen, Norway; Høgskolen i Bergen, Bergen, Norway; University of Birmingham, Birmingham, UK; Comenius University, Bratislava, Slovakia; Università di Catania and INFN, Catania, Italy; CERN, Geneva, Switzerland; Institute of Experimental Physics SAS, Kosice, Slovakia; P.J. Safárik University, Kosice, Slovakia; Universitetet i Oslo, Oslo, Norway; Università di Padova and INFN, Padua, Italy; Collège de France and IN2P3, Paris, France; Academy of Sciences, Prague, Czech Republic; Università "La Sapienza“ di Roma and INFN, Rome, Italy; Università di Salerno and INFN, Salerno, Italy; State University of St. Petersburg, St. Petersburg, Russia; Insitut de Recherches Subatomiques, IN2P3/ULP, Strasbourg, France; Utrecht University and NIKHEF, Utrecht, The Netherlands.