# Presentation: 639981

## production from proton to Pb-induced reactions at the CERN SPS 

- SQM03, March 16th, 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

**Notes:**
Spectrometre a muons, en aval deux calorimetres pour mesurer la centralité de la collision
La resolution en masse (70 MeV)ne permet pas de séparer omega et rho

## NA50 collaboration 

** **B.Alessandro11, C.Alexa4, R.Arnaldi11, M.Atayan13, C.Baglin2, A.Baldit3, M.Bedjidian12, S.Beolé11, V.Boldea4, P.Bordalo7,a, S.R.Borenstein10,b, G.Borges7, A.Bussière2, L.Capelli12, C.Castanier3, J.Castor3,  B.Chaurand10, B.Cheynis12, E.Chiavassa11, C.Cicalò5, T.Claudino7, M.P.Comets9, S.Constantinescu4, P.Cortese1 , J.Cruz7 , A.De Falco5,   N.De Marco11, G.Dellacasa1 , A.Devaux3, S.Dita4, O.Drapier12, B.Espagnon3, J.Fargeix3, P.Force3, M.Gallio11, Y.K.Gavrilov8, C.Gerschel9, P.Giubellino11,b, M.B.Golubeva8,  M.Gonin10, A.A. Grigorian13, S.Grigorian13, J.Y.Grossiord12, F.F.Guber8, A.Guichard12, H.Gulkanyan13, R.Hakobyan13, R.Haroutunian12, M.Idzik11,c, D.Jouan8, T.L.Karavitcheva8, L.Kluberg10, A.B.Kurepin8, Y.Le Bornec9, C.Lourenço6, P.Macciotta, M.Mac Cormick9,  A.Marzari-Chiesa11, M.Masera11, A.Masoni5, M.Monteno11, A.Musso11, P.Petiau10, A.Piccotti11, J.R.Pizzi12, W.L.Prado da Silva11,e, F.Prino11, G.Puddu5 ,  C.Quintans7, L.Ramello11, S.Ramos7,a, P.Rato Mendes7, L.Riccati11, A.Romana10, H.Santos7, P.Saturnini3, E.Scalas1, E.Scomparin11 , S.Serci5, R.Shahoyan7,f, F.Sigaudo11, M.Sitta1,  P.Sonderegger6,a, X.Tarrago9, N.S.Topilskaya8, G.L.Usai5, E.Vercellin11, L.Villatte9, N.Willis9 , T.Wu9.
- 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

## 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

**Notes:**
NA38 1ere ligne

## Kinematical domain

- For Pb-Pb,  acceptances in the lowest MT bin considered  are  0.3 %  (!)

- Rapidity:    		0   <    ycm    <   1
- Angular window: 	0   <     
- 		         -0.5  <  cos cs  <   0.5     in Collins-Soper frame

- Results are given for:
-      	MT  > 1.5 GeV/c2,
- or
- 	pT   >  0.6 GeV/c 	  or        pT  >  1.4 GeV/c (Pb-Pb)

## and  acceptances

- and  acceptances

- MT (GeV/c2)

******Pb-Pb**

******S-U**

******S-U******

******   ****Pb-Pb**

- Acceptance

**Notes:**
Acceptances for Pb Pb are smaller due to iron absorber and stronger magnetic field
Domain of comparison between Pb and S is limited to Mt>1.5
Ratio of phi and omega acceptances is uncahnged (<10%)

## Last Pb-Pb measurement: improved setup

-  PbPb **2000: **
- better target identification, in particular for peripheral events:
- target in vacuum
-  vertex selection with  multiplicity detector

- Improved rejection of background

- Additional min. bias trigger

- Improved efficiency for  low Et measurement
- (here for min. bias)

**Notes:**
Preabsorber for phi studies

## Analysis 

-  mass continuum  (comb. background, Dalitz decays, etc...)
- 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/M0)   for  the continuum

- Analysis

- The analysis is based on the opposite sign dimuon invariant mass distribution made of:

##  Opposite-sign dimuon invariant mass raw distribution

-  Opposite-sign dimuon invariant mass raw distribution

- dN/dM

- M(GeV/c2)

- Pb-Pb 2000
- All ET,all MT
-         total
-      background

- 

- 

## Smearing and acceptances

- Calculated with a Monte Carlo simulation using:
- dN/dy  exp(-(y-y0)2/2)
- dN/dMT  MT3/2 exp(-MT/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

## 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

## 

- 

- 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 , MT is  the relevant parameter for the production ( exp(-MT/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  MT domains

*(this is a personal comment)*

**Notes:**
The change of ratio phi/om is an acceptance effect

## as a function of centrality (1)

- Npart is deduced from the measured ET with the Glauber model

- Strangeness production increases smoothly with Npart (or ET) and with the size of the interacting nuclei

**Integrated in p****T**

## as a function of centrality (2)

-   Pb-Pb

-   S-U

-   d-U

-   d-C

- MT > 1.5GeV/c2

- 

- Npart

- Pb-Pb 2000 data  preliminary results

- Strangeness production increases smoothly with Npart (or ET) and with the size of the interacting nuclei

**Integrated in M****T**

- Stat error only

## Multiplicities versus centrality

- Nis the number of produced particles per Pb-Pb collision, for MT > 1.5 GeV/c2

- Multiplicity/Npart
- increases for 
- while
- constant for 

##  dependence on PT

-  dependence on PT

- The ratio           shows no
- PT dependence

##  as a function of MT    (peripheral)

-  as a function of MT    (peripheral)

- MT (GeV/c2)

- Pb-Pb 2000 preliminary

- 

##  as a function of MT    (central)

- MT (GeV/c2)

-  as a function of MT    (central)

- shows no MT  dependence and increases with centrality

- The ratio

## Central multiplicity 

- Central multiplicity

**Pb-Pb 2000**
**Et>102  GeV**

****** ****production**
**In the experimental acceptances **

- (redrawn from plot)

**preliminary comparison**

## 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 (Npart or Et)
-  the centrality increase pattern is similar for all the systems
- the ratio  shows no PT or MT 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

**Notes:**
More to come, unfortunately too late for SQM, about cross sections, in particular the different behaviour of phi in d-induced and ion-induced reactions, multiplicities and comparison with NA49,    Tslopes between systems.
A comprehensive summary of all these results  will be a useful reference for the future studies at phenix that starts giving results.