production in d-C d-U S-U and Pb-Pb reactions in the NA38-NA50 CERN SPS experiments

QM08, February 9h, 2008, Jaipur, India

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

NA50 collaboration

 B.Alessandro10, C.Alexa3, R.Arnaldi10, M.Atayan12, A.Baldit2, S.Beolé10, V.Boldea3, P.Bordalo6,a, G.Borges6, J.Castor2, B.Chaurand9, B.Cheynis11, E.Chiavassa10, C.Cicalò4, M.P.Comets8, S.Constantinescu3, P.Cortese1 , A.De Falco4, N.De Marco10, G.Dellacasa1 , A.Devaux2, S.Dita3, O.Drapier9, J.Fargeix2, P.Force2, M.Gallio10, C.Gerschel8, P.Giubellino10, M.B.Golubeva7, M.Gonin9, A.Grigoryan13, J.Y.Grossiord11, F.F.Guber7, A.Guichard11, H.Gulkanyan12, M.Idzik10,b, D.Jouan8, T.L.Karavitcheva7, L.Kluberg9, A.B.Kurepin7, Y.Le Bornec8, C.Lourenço5, M.Mac Cormick8, A.Marzari-Chiesa10, M.Masera10, A.Masoni4, M.Monteno10, A.Musso10, P.Petiau9, A.Piccotti10, J.R.Pizzi11,d, F.Prino10, G.Puddu4 , C.Quintans6, L.Ramello1, S.Ramos6,a, L.Riccati10, A.Romana9,d, H.Santos6, P.Saturnini2, E.Scomparin10 , S.Serci4, R.Shahoyan6,c, M.Sitta1, P.Sonderegger5,a, X.Tarrago8, N.S.Topilskaya7, G.L.Usai4, E.Vercellin10, L.Villatte8, N.Willis8 , T.Wu8.

1) Univ. Del Piemonte Orientale, Alessandria and IFN-Torino, Italy 2)LPC, Univ. Blaise Pascal and CNRS-IN2P3, Aubière, France 3) IFA, Bucharest, Romania 4)Univ. di Cagliari/INFN, Cagliari, Italy 5)CERN, Geneva, Switzerland 6)LIP, Lisbon, Portugal 7)INR, Moscow, Russia 8)IPN, Univ. de Paris-Sud and CNRS-IN2P3, Orsay, France 9)LLR, Ecole Polytechnique and CNRS-IN2P3, Palaiseau, France 10)Univ. Torino/INFN, Torino, Italy 11)IPN, Univ. Claude Bernard Lyon-I and CNRS-IN2P3, Villeurbanne, France 12)YerPhI, Yerevan, Armenia.

a) also at IST, Universidade Técnica de Lisboa, Lisbon, Portugal b) also at Faculty of Physics and Nuclear Techniques, AGH University of Science ant Technology, Cracow, Poland c) on leave of absence from YerPhI, Yerevan, Armenia d) Deceased

1) Strange to non strange production is studied through the ratio

Physics goals and data

Study of strangeness production in heavy ion collisions as strangeness enhancement has been proposed among the QGP formation signatures

Goals

Data considered in this talk (in red)

p - W , d - C , d - U , S - S , S - Cu , S - U 200 GeV/nucleon

Pb – Pb (1996, 1998 and 2000) 158 GeV/nucleon

( Focus on analyses as a function of MT)

2) Cross sections, multiplicities …

« puzzle »: new NA50 updated contribution

Kinematical domain

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

Rapidity: 0 < ycm < 1 (tuned to beam energy)

Angular window: 0 <

-0.5 < cos cs < 0.5 in Collins-Soper frame

Comparison with Pb-Pb limited to :

MT > 1.5 GeV/c2

S-US-U

Pb-Pb

Pb-Pb

Acc

epta

nce

MT (GeV/c2)

NA50 PbPb setup : magnetic field increased, (w.r.t. NA38) last 0.8 m of 4.8 m absorber changed from C to Fe

WITH UPGRADED SETUP Better target identification, in particular for peripheral events: •single target in vacuum• vertex selection with multiplicity detector

Last Pb-Pb measurement in year 2000

Improved rejection of out of target events

Min bias trigger upgrades:•Additional Beam Hod. MB trigger•Timing from BH for all triggers (µµ and MB (ZDC and BH))

Improved efficiency for low Et measurement

Analysis

1. A dimuon mass continuum (from comb. background, Dalitz decays, etc...)

2. Muon pairs from decays of ,

is fitted, after comb. background subtraction (from like-

sign pairs), assuming for production:

Breit-Wigner for resonances (+c.s.c.s.)

an exponential for the continuum : dN/dM exp(-M/M0)

The MC simulation uses dN/dy exp(-(y-y0)2/2)

dN/dMT MT3/2 exp(-MT/T) and Flat coscs

The opposite-sign muon pair invariant mass distribution made of:

M1

n

Pb-Pb S-U d-U d-C

MT > 1.5GeV/c2

as a function of centrality

Npart

increases smoothly with Npart

and with the size of the interacting nuclei

Integrated in MT

S ~ 0.7

(Dimuons, acceptance corrected)

Meaning of ~1.2 ?

1.8< MT<2.2

Pb-Pb

1.5< MT<1.8

and have close properties (masses)

is then mostly sensitive to the strangeness content A.Shor)

in thermodynamical models , MT is the relevant parameter for the production :

(+ effect of strangeness saturation S ,for s quarks)

closely related to S2

no dependence on MT

in MT domains

)/(2 TMS

T

TedM

dN

Note: here S means S/q

7.05.0

5.02.1)(

2

SS

NO EXTRAPOLATION but Flow, secondary production, could nevertheless play a role

In central Pb-Pb collisions:

In a MT bin

Parameterization: k A*B

d-C vs d-U: Cronin, < 1

0<Y<1

: increase of production (strangeness

enhancement)

2 regimes for ? (Increase of

Projectile or target)

Evolution of cross sectionvsd and AB

MT

S-U vs d-U : >> >1

PbPb vs d-U: ~  similar (assuming dU/dC for U->Pb)

increase or decrease ?• Between systems:

increase

on top of a global increase • With centrality:

increase of multiplicity per participant Nµµ/(NMB* Npart),

~flat for

The increase of is due to an increase of the

mult /npart (a.u.)

mult /npart (a.u.)

Npart

Tao Wu PhDThesis, 2003

MT > 1.5GeV/c2

d induced and w.r.t. other measurementsexp year beam E

GeVtarget

domain ref.

FNAL 76 n ~300 Be, Al, Cu, Pb

.67 ± .05 .62 ± .03 .05±.06 PL>75 PRL 37 1976 571

FNAL CP 77 p

225 C, Sn .77±.04.76±.03

.72±.03

.69±.02.05±.05.05±.05

.15<XFPRL38 1977 1334

Accmor 83 p 100 H, Be .96±.04 .11<XF<.24ZPC 18 1983 1

NA11 84 p

120 Be, Ta .90±.02.86±.02

.11<XF<.24

Pt<1

ZPC 22 1984 125

BIS-2 90 p 30-70

C, Al, Cu .81±.06 0<XFPt>1

CZ JP 40 1990 1216

E672 91 530 Be, Cu .81±.04 .77±.02 .04±.05 PT<1.1<XF<.6

Moriond 22-28 march 1992 p285

NA38 92 d 400 C, U .89±.05 .85±.05 .04±.04 MT>1.2

NA60 02 p 400 Be, In, W .91±.02 .82±.01 .09±.02 EPJCs2005-02206-1

HERA-B 03 p 920 C,Ti,W .96±.02 KK -.7<y<.25 .5<PT<3.5

EPJC50_315

Fair agreement

Very precise comparison should include the increase with PT and Y evolution

T(GeV)

he so-called puzzle (I)MT Slopes measurements disagree between experiments….

he so-called puzzle (II)Multiplicity measurements disagree between experiments….

Central PbPb collisions

Up to most recent papers:[NA45 - PRL 96 (2006) 152301]

Also QM06, SQM07

change in µµ

branching ratio+15%

Times are changing:

NA50: new 2000 measurement: more precise trigger(s) timing, two minimum bias triggers

NA50 Multiplicity is obtained from separate measurement of dimuons and collisions numbers

PDG BR values through the years(PDG « fit » value available since 2001)

BR

*10

4Universality: BRµµ expected to converge towards BRee (=> additional -4% on multiplicity)

Comparison of Pb-Pb multiplicities (I)(Pb-Au (7%) for CERES)CERES: PRL96-152301-2006

NA49: PLB 491 2000 59

/1996

(Pb-Au (7%) for CERES)CERES: PRL96-152301-2006

NA49: PLB 491 2000 59

Comparison of Pb-Pb multiplicities (II)

Comparison of Pb-Pb multiplicities (III)(Pb-Au (7%) for CERES)CERES: PRL96-152301-2006

NA49: PLB 491 2000 59

Branching ratio for μμ change together with upgraded data collection and new sample and analysis lead to a lower multiplicity

Comparison of Pb-Pb multiplicities (IV)(Pb-Au (7%) for CERES)CERES: PRL96-152301-2006

NA49: PLB 491 2000 59

The

updated comparison

plot

Comparison of Pb-Pb multiplicities(Pb-Au (7% c.s.) for CERES)

2 effects for NA50 now lower results:

1) 15% increase of BR

2) New 2000 measurement fluctuates by ~ -8% compared to previous (1996) one

(3%c.s.)The most recent NA50 multiplicity measurement is lower than the previous one but still disagrees by a factor ~2 with CERES and NA49 measurementsin most of the MT domain

CERES: PRL96-152301-2006

NA49: PLB 491 2000 59

Are dilepton results compatible ?

anyway: NA50 and CERES dilepton results are quite compatible within large errors of CERES (e+e-) a difference between K+K- and l+l-

decay channels ?

This leads to a 8% correction

a visible effect

• BRµµ: still -4% compared to BRee Account could have to be taken of small difference:

Eventually: correction for centrality domain: 3% 5%

SummaryAt SPS energies, the production of and have been compared for: d-C, d-U, S-U and Pb-Pb, as a function of MT Pb-Pb 2000 is measured with an upgraded set up.

The ratio increases as a function of centrality (Npart or Et), increases with the size of the interacting nuclei is MT independent

Cross sections and multiplicities increase of is due to increase new measurement of and between d-C and d-U

incompatibilities in puzzle ~solved: the updated puzzle shows: a smaller than previous, but remaining disagreement, a factor ~2, between NA50 (μμ) and CERES (KK), also NA49 (KK) an agreement, within the large CERES (ee) errors, between: NA50 (μμ) and CERES (ee) a difference remains between the hadronic and dilepton decay channels

Back up

Why a specific reference is better

Fair agreement

Very precise comparison should include the increase with PT

exp year beam EGeV

target

domain ref.

FNAL 76 n ~300 Be, Al, Cu, Pb

.67 ± .05 .62 ± .03 .05±.06 PL>75 PRL 37 1976 571

FNAL CP 77 p

225 C, Sn .77±.04.76±.03

.72±.03

.69±.02.05±.05.05±.05

.15<XFPRL38 1977 1334

Accmor 83 p 100 H, Be .96±.04 .11<XF<.24ZPC 18 1983 1

NA11 84 p

120 Be, Ta .90±.02.86±.02

.11<XF<.24

Pt<1BIS-2 90 p 30-

70

C, Al, Cu .81±.06 0<XFPt>1

E672 91 530 Be, Cu .81±.04 .77±.02 .04±.05 PT<1.1<XF<.6

Moriond 22-28 march 1992 p285

NA38 92 d 400 C, U .89±.05 .85±.05 .04±.04 MT>1.2

NA60 02 p 400 Be, In, W .91±.02 .82±.01 .09±.02 EPJCs2005-02206-1

HERA-B 03 p 920 C,Ti,W .96±.02 KK -.7<y<.25 .5<PT<3.5

EPJC50_315

and Y evolution

EPJC50_315 W.Geist QM91