Strange particle production from 40 GeV data at the NA57 experiment

1. Strange particle production from 40 GeV data at the NA57 experiment PaulNorman of the University of Birmingham, United Kingdom on behalf of the CERN collaboration NA57 SQM 2003, Atlantic Beach 12th-17th March 2003

2. Talk contents • Underlying physics and motivation. • Reminder of NA57 layout and previous results. • Yields for Pb-Pb interactions @ 40 A GeV/c. • L (new),X, W • Signals for p-Be interactions @ 40 A GeV/c. • L, X (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

3. Underlying 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 W. • 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

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

5. 5 cm Silicon Pixel Tracker 5 cm 30 cm L B p- X- Strange particle decays Get strange particles and anti-particles from weak decay topologies. L --> p + p- BR = 63.9% X---> L + p- BR = 99.9% W---> L + K-BR = 67.8% K0--> p+ p- BR = 68.6% SQM 2003, Atlantic Beach P.Norman, University of Birmingham, United Kingdom

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

7. L, X and W signals at 40 GeV/c p-Be @ 40 A GeV/c - L L Pb-Pb @ 40 A GeV/c SQM 2003, Atlantic Beach P.Norman, University of Birmingham, United Kingdom

8. Centrality 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 L results are for most central 5% NA57/STAR (our bin IV). SQM 2003, Atlantic Beach P.Norman, University of Birmingham, United Kingdom

9. Energy dependence: L,X and W yields @ 40 and 160 GeV pT > 0, y-ycm< 0.5 Black bars are systematic errors • from 40 GeV to 160 GeV: L andX-about same,W-up by a factor 3, anti-particles up by a factor 5 Larger baryon density at 40 GeV/c SQM 2003, Atlantic Beach P.Norman, University of Birmingham, United Kingdom

10. L, X and W yields from SPS to RHIC Most central events: • 12% for NA57 (bins III+IV) • 14% for STAR STAR results from: - C. Adler et al. Phys. Rev. Lett. 89:092301 (2002) for L - J. Castillo from QM2002 nucl-ex/0210032 for X - C. Suire from QM2002 nucl-ex/0211017 for W • from NA57 40 GeV to 160 GeV, and confirmed by STAR: • L,X-andW-yields increase slower than their anti-particles • at RHIC about same production rate for hyperon and anti-hyperon SQM 2003, Atlantic Beach P.Norman, University of Birmingham, United Kingdom

11. NA57 STAR Y/Y ratios from SPS to RHIC Most central events: • 12% for NA57 • 14% for STAR STAR results from: - C. Adler et al. Phys. Rev. Lett. 89:092301 (2002) for L - J. Castillo from QM2002 nucl-ex/0210032 for X - C. Suire from QM2002 nucl-ex/0211017 for W Ratio Y/Y approaches 1 as energy increases. Energy dependence weaker for higher strangeness (and thus lower light quark) content. SQM 2003, Atlantic Beach P.Norman, University of Birmingham, United Kingdom

12. Conclusions • 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, theL,XandWyields 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

13. Outlook • p-Be @ 40 A GeV/c: • Land Xyields • 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

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