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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