1.  production from proton to Pb-induced reactions at the CERN SPS SQM03, March 16 th, 2003, Atlantic Beach, North Carolina, USA D.Jouan, IPN Orsay, for the NA50 and NA38 collaborations Muon spectrometer detects  and  mesons through their dimuon decay The centrality of the collision is estimated on an event by event basis

2. NA50 collaboration B.Alessandro 11, C.Alexa 4, R.Arnaldi 11, M.Atayan 13, C.Baglin 2, A.Baldit 3, M.Bedjidian 12, S.Beolé 11, V.Boldea 4, P.Bordalo 7,a, S.R.Borenstein 10,b, G.Borges 7, A.Bussière 2, L.Capelli 12, C.Castanier 3, J.Castor 3, B.Chaurand 10, B.Cheynis 12, E.Chiavassa 11, C.Cicalò 5, T.Claudino 7, M.P.Comets 9, S.Constantinescu 4, P.Cortese 1, J.Cruz 7, A.De Falco 5, N.De Marco 11, G.Dellacasa 1, A.Devaux 3, S.Dita 4, O.Drapier 12, B.Espagnon 3, J.Fargeix 3, P.Force 3, M.Gallio 11, Y.K.Gavrilov 8, C.Gerschel 9, P.Giubellino 11,b, M.B.Golubeva 8, M.Gonin 10, A.A. Grigorian 13, S.Grigorian 13, J.Y.Grossiord 12, F.F.Guber 8, A.Guichard 12, H.Gulkanyan 13, R.Hakobyan 13, R.Haroutunian 12, M.Idzik 11,c, D.Jouan 8, T.L.Karavitcheva 8, L.Kluberg 10, A.B.Kurepin 8, Y.Le Bornec 9, C.Lourenço 6, P.Macciotta, M.Mac Cormick 9, A.Marzari-Chiesa 11, M.Masera 11, A.Masoni 5, M.Monteno 11, A.Musso 11, P.Petiau 10, A.Piccotti 11, J.R.Pizzi 12, W.L.Prado da Silva 11,e, F.Prino 11, G.Puddu 5, C.Quintans 7, L.Ramello 11, S.Ramos 7,a, P.Rato Mendes 7, L.Riccati 11, A.Romana 10, H.Santos 7, P.Saturnini 3, E.Scalas 1, E.Scomparin 11, S.Serci 5, R.Shahoyan 7,f, F.Sigaudo 11, M.Sitta 1, P.Sonderegger 6,a, X.Tarrago 9, N.S.Topilskaya 8, G.L.Usai 5, E.Vercellin 11, L.Villatte 9, N.Willis 9, T.Wu 9. 1) Univ. Del Piemonte Orientale, Alessandria and IFN-Torino, Italy 2) LAPP, CNRS-IN2P3, Annecy-le- Vieux, France 3)LPC, Univ. Blaise Pascal and CNRS-IN2P3, Aubière, France 4) IFA, Bucharest, Romania 5)Univ. di Cagliari and INFN, Cagliari, Italy 6)CERN, Geneva, Switzerland 7)LIP, Lisbon, Portugal 8)INR, Moscow, Russia 9)IPN, Univ. de Paris-Sud and CNRS-IN2P3, Orsay, France 10)LPNHE, Ecole Polytechnique and CNRS-IN2P3, Palaiseau, France 11)Univ. Torino/INFN, Torino, Italy 12)IPN, Univ. Claude Bernard Lyon-I and CNRS-IN2P3, Villeurbanne, France 13)YerPhI, Yerevan, Armenia. a) also at IST, Universidade Técnica de Lisboa, Lisbon, Portugal b) on leave from York College, CUNY, New York, USA c) also at CERN, Geneva, Switzerland d) also at Faculty of Physics and Nuclear Techniques, University of Mining and Metallurgy, Cracow, Poland e) now at UERJ, Rio de Janeiro, Brazil f) on leave of absence from YerPhI, Yerevan, Armenia

3. Physics goals and data Study of strangeness production in heavy ion collisions as strangeness enhancement has been proposed among the QGP formation signatures Strange to non strange production is studied through the ratio Goals Data p - W, d - C, d - U, S - S, S - Cu, S - U 200 GeV/nucleon Pb – Pb (1996, 1998 and preliminary 2000) 158 GeV/nucleon

4. Kinematical domain For Pb-Pb, acceptances in the lowest M T bin considered are  0.3 % (!) Rapidity: 0 < y cm < 1 Angular window: 0 <  -0.5 < cos  cs < 0.5 in Collins-Soper frame Results are given for: M T > 1.5 GeV/c 2, or p T > 0.6 GeV/c or p T > 1.4 GeV/c (Pb-Pb)

5.  and  acceptances M T (GeV/c 2 )  Pb-Pb  S-U  S-U  Pb-Pb Acceptance

6. PbPb 2000: better target identification, in particular for peripheral events: target in vacuum vertex selection with multiplicity detector Last Pb-Pb measurement: improved setup Improved rejection of background Additional min. bias trigger Improved efficiency for low Et measurement (here for min. bias)

7. 1. mass continuum (comb. background, Dalitz decays, etc...) 2.resonances , … and fitted, after combinatorial background subtraction (deduced from like-sign pairs), assuming for production:  Breit-Wigner distributions for the resonances  An exponential: dN/dM  exp(-M/M 0 ) for the continuum Analysis The analysis is based on the opposite sign dimuon invariant mass distribution made of:

8. Opposite-sign dimuon invariant mass raw distribution dN/dM  M   (GeV/c 2 ) Pb-Pb 2000 All E T, all M T total background  

9. Smearing and acceptances Calculated with a Monte Carlo simulation using: dN/dy  exp(-(y-y 0 ) 2 /2   ) dN/dM T  M T 3/2 exp(-M T /T) Flat cos  cs distribution The ratio can be extracted either from  the measured mass distribution (followed by acceptance correction) or from  the mass distribution corrected for smearing and acceptance

10. Mass spectrum analysis Fit of the directly measured spectrum with simulated components Use the simulation to determine a desmearing matrix Fit of the spectrum corrected for smearing and acceptance

11.   In a M T bin  and  have close properties (masses)  is then mostly sensitive to the strangeness content of the   A.Shor) in thermodynamical models, M T is the relevant parameter for the production (  exp(- M T /T)) 1.8< M T <2.2 2.2<Mt<2.5 Pb-Pb 1.5< M T <1.8  the ratio  should be closely related to (  S/  q ) 2  for instance  S /  q = 0.9 should correspond to (    [J.Rafelski QM02 + private comm.+this conference] in M T domains (this is a personal comment)

12. as a function of centrality (1) N part is deduced from the measured E T with the Glauber model Strangeness production increases smoothly with N part (or E T ) and with the size of the interacting nuclei Integrated in p T

13. Pb-Pb S-U d-U d-C M T > 1.5GeV/c 2 as a function of centrality (2)   N part Pb-Pb 2000 data preliminary results Strangeness production increases smoothly with N part (or E T ) and with the size of the interacting nuclei Integrated in M T Stat error only

14. Multiplicities versus centrality  N  is the number of produced particles per Pb-Pb collision, for M T > 1.5 GeV/c 2 Multiplicity/Npart increases for  while constant for 

15. dependence on P T The ratio shows no P T dependence

16. as a function of M T (peripheral) M T (GeV/c 2 ) Pb-Pb 2000 preliminary  

17. M T (GeV/c 2 ) as a function of M T (central) shows no M T dependence and increases with centrality The ratio

18. Central multiplicity Pb-Pb 2000 Et>102 GeV  production In the experimental acceptances (redrawn from plot) preliminary comparison

19. Summary The production of  and  has started to be compared for: p-W, d-C, d-U, S-S, S-Cu, S-U and Pb-Pb. Pb-Pb include data collected in year 2000 with a thin target in vacuum (better Pb target identification) redundant measurement of the minimum bias spectrum  for each of the interacting systems, the ratio  increases as a function of centrality (N part or E t )  the centrality increase pattern is similar for all the systems  the ratio  shows no P T or M T dependence  multiplicity per participant increases for  with centrality, and remains constant for   The data and results of NA38/NA50 on low mass vector mesons should contribute to a better understanding of strangeness production as a possible signal of QGP formation in high-energy heavy ion collisions