Andrea Dainese

1
Results from NA57

• Andrea Dainese
• Padova University and INFN
• on behalf of the NA57 Collaboration

2
Outline

• The NA57 experiment at the CERN SPS
• Strangeness Enhancement (and energy dep.)
• Expansion dynamics mT spectra
• RCP for at ?sNN 17.3
  GeV

Study the production of strange and multi-strange
hadrons at mid-rapidity in heavy-ion
interactions, as a function of centrality and
c.m.s. energy
NEW

• NA57 Posters at QM05
• Rapidity spectra in Pb-Pb collisions at 160
  GeV/c by G.E.Bruno
• RCP in Pb-Pb collisions at 160 GeV/c by
  G.E.Bruno and A.Dainese
• K0 and L production in p-Be collisions at 40
  GeV/c by I.Kralik

3
Strange Particles Reconstruction

• Use charged decay-tracks measured in the pixel
  telescope to reconstruct
• in
• Pb-Pb, p-Be, p-Pb _at_ p 160A GeV/c
• Pb-Pb, p-Be _at_ p 40A GeV/c

4
Yields and Enhancements

• Double-differential cross section for each
  particle fitted to
• with flat/gaussian(K0 and L) y distribution in
  the selected acceptance
• inverse slope of mT distribution (Tapp) free
  parameter of the fit
• Yield (average particle multiplicity / event)
  extrapolated to a common y-pT region
• Strangeness Enhancement (in Pb-Pb relative to
  p-Be)

5
Collision Centrality

• Determined from charged multiplicity, measured
  from the hits in a dedicated Si-mstrip detector
• Npart and Ncoll from trigger cross section
  (Glauber model calc.)
• strigger ? 60 of Pb-Pb sinel (7.26 b)

Pb-Pb _at_ 160 A GeV/c
WA97 Coll., EPJC18 (2000) 57 NA57 Coll., JPG31
(2005) 321
6
Strangeness Enhancements
160A GeV/c
Factor ? 20 for ?
7
Energy Dependenceof Enhancements

• Steeper increase with centrality at lower energy
• X- in most central class larger enhancement at
  lower energy
• qualitative agreement with theory (canonical
  suppression model)
• but energy and centrality dependence not well
  predicted

8
Transverse DynamicsBlast-wave Fit of mT Spectra
Model thermalization plus hydro-dynamical transv
erse flow description
Pb-Pb 40 A GeV/c
Pb-Pb 160 A GeV/c
NA57, JPG30 (2004) 823 Bruno (NA57), JPG31 (2005)
S127
Schnedermann, Sollfrank, Heinz, PRC48 (1993) 2462
9
Blast-wave Fit Results

• Tkin.f.o. 144 7(stat) 14(syst) MeV
• ltb?gt 0.381 0.013(stat) 0.012(syst)

0-53
11 - 10
Tkin.f.o. 118 5(stat) (syst) MeV
0.011 - 0.013
ltb?gt 0.398 0.010(stat) (syst)

• Tkin.f.o. lower at 40 A GeV/c
• Similar transverse flow

• From central to peripheral
• Tkin.f.o. increses
• ltb?gt decreases
• New analysis of dN/dy in y-ycm 0.5
• ltbLgt ltb?gt 0.4
• (large stopping?)

earlier decoupling in peripheral collisions ?
see poster by G.E.Bruno
10
Central-to-peripheral nuclear modification
factors

• RCP at RHIC
• high-pT parton energy loss
• intermediate pT baryon/meson effect
  (recombination?)

• RCP at SPS?
• p0 suppressed energy loss?
• (see also RAA re-analysis)
• no baryon/meson comparison

WA98, EPJC23 (2002) 225
dEnterria, PLB596 (2004) 32
STAR, PRL92 (2004) 052302 prelim.
11
RCP for h-, K0, L, L (?sNN 17.3 GeV)

• Centrality classes 0-5, 10-20, 20-30, 30-40,
  40-55
• RCP from unweighted dN/dpT (corrections are
  centrality independent within systematics)

NEW!
bars quadratic sum of stat. and pT-dep. syst.
errors
NA57, PLB in print, nucl-ex/0507012
12
RCP Comparisons kaons pions
SPS

• p0WA98 RCP lt K0 RCP

WA98, EPJC23 (2002) 225
13
RCP Comparisons kaons L

• Similar K0-L relative pattern at SPS and RHIC
  energy
• RCP values higher by 0.5 at SPS, no significant
  suppression observed
• RHIC meson/baryon pattern can be explained by
  quark recombination models

NA57
STAR

• Recombination at SPS energy?
• consistent with explanation of multi-strange
  enhancements as due to recombination of s and s
• Note effect may also be due to different
  Cronin for L and K

STAR, PRL92 (2004) 052302
14
RCP Comparisons Models

• Data compared to K0 calculation by X.N.Wang
• Medium dNg/dy scaled down from RHIC according to
  the measured decrease in dNch/dy (factor 2)
• Initial-state intrinsic kT broadening tuned on
  the original Cronin data

• Cross-checked using different model PQM
  (BDMPS-based)
• medium density determined from RHIC data and
  extrapolated down to SPS energy Cronin
  enhancement included

X.N.Wang, PRC68 (2001) 064910 PRL81 (1998) 2655
PLB595 (2004) 165 private comm. PQM Dainese,
Loizides, Paic, EPJC38 (2005) 495 private comm.
15
Conclusions

• Strangeness Enhancements at 160 and 40 GeV/c
• same hierarchy, 160 E(W) gt E(X) gt E(L), 40
  E(X) gt E(L)
• agreement with historic QGP signature
• Transverse and longitudinal expansion described
  by hydro
• Tkin.f.o. ? 120 MeV in central collisions
• earlier decoupling in peripheral collisions?
• ltbLgt ? ltb?gt ? 0.4
• RCP nuclear modification factor
• similar patterns (K0-p0WA98, K0-L) as at RHIC
• SPS higher RCP values, no significant
  suppression
• described by calculations including parton energy
  loss
• Cronin? need RpA measurement

16
The NA57 Collaboration
F. Antinorik, P.A. Bacone, A. Badalàf,
R. Barberaf, A. Belogiannia,  I.J. Bloodworthe,
M. Bombarah, G.E. Brunob, S.A. Bulle,
R. Caliandrob, M. Campbellg, W. Carenag,
N. Carrerg, R.F. Clarkee, A. Dainesek,
D. Di Barib, S. Di Liberton, R. Diviàg, D. Eliab,
D. Evanse, G.A. Feofilovp, R.A. Finib,
P. Ganotia, B. Ghidinib, G. Grellao,
H. Helstrupd, K.F. Hetlandd, A.K. Holmej,
A. Jacholkowskif, G.T. Jonese, P. Jovanovice,
A. Juskoe, R. Kamermansr, J.B. Kinsone,
K. Knudsong, V. Kondratievp, I. Králikh,
A. Kravcákovái, P. Kuijerr, V. Lentib,
R. Lietavae, G. Løvhøidenj, V. Manzarib,
M.A. Mazzonin, F. Meddin, A. Michalonq,
M. Morandok, P.I. Normane, A. Palmerif,
G.S. Pappalardof, B. Pastircákh, R.J. Platte,
E. Quercighk, F. Riggif, D. Röhrichc, G. Romanoo,
K. afaríkg, L. ándorh, E. Schillingsr,
G. Segatok, M. Senél, R. Senél, W. Snoeysg,
F. Soramelk, M. Spyropoulou-Stassinakia,
P. Starobam, R. Turrisik, T.S. Tveterj,
J. Urbáni, P. van de Venr, P. Vande Vyvreg,
A. Vascottog, T. Vikj, O. Villalobos Bailliee,
L. Vinogradovp, T. Virgilio, M.F. Votrubae,
J. Vrlakovai, P. Závadam.
a Athens, b Bari, c Bergen, d Bergen, e
Birmingham, f Catania, g CERN, h Kosice, i
Kosice, j Oslo, k Padova, l Collège de France,
m Prague, n Rome, o Salerno, p St.
Petersburg, q Strasbourg, r Utrecht
17
EXTRA SLIDES
18
Two historic QGP predictions

• restoration of c symmetry -gt increased production
  of s
• mass of strange quark in QGP expected to go back
  to current
  value
• ms 150 MeV Tc
• copious production of ssbar pairs,
• mostly by gg fusion
• Rafelski Phys. Rep. 88 (1982) 331
• Rafelski-Müller P. R. Lett. 48 (1982) 1066
• deconfinement ? stronger effect for multi-strange
• can be built using uncorrelated s quarks produced
  in independent microscopic reactions
• strangeness enhancement increasing with
  strangeness content
• Koch, Müller Rafelski Phys. Rep. 142 (1986)
  167

19
NA57 Experimental Layout
Target 1 Pb Scintillator Petals
centrality trigger MSD Multiplicity Silicon
Detector Tracking device silicon
pixel planes (5 x 5 cm2 ) Lever arm
double-sided mstrips
20
Data Samples

• p-Be 160 A GeV/c 219 M events
• p-Pb 160 A GeV/c 287 M events (WA97)
• Pb-Pb 160 A GeV/c 460 M events (0-60 sPb-Pb)
• Particle statistics for RCP analysis
• K0S 1.8 M
• L 0.7 M
• Lbar 0.1 M
• h- 100 M

21
Invariant Mass Spectra
Pb-Pb 160
FWHM 10 MeV
bkg 0.3
bkg 4
bkg 6
bkg 1.2
bkg 4
bkg 6

• Small residual combinatorial background (few at
  most) subtracted or included in the systematics

22
Invariant Mass Spectra vs pT

• Small residual combinatorial background
  subtracted
• at most 10 for hight pT (gt 2.5 GeV/c) K0 in
  central Pb-Pb collisions

23
Hyperon yield measurement

• Data corrected for acceptance and also for
  detector and reconstruction efficiency by Monte
  Carlo simulation
• In the acceptance window
• Yield
• (i.e. particle per event)
• Transverse mass spectra (Tapp)
• Extrapolation to a common window
• one unit of rapidity about ycm
• full range of pT

24
Transverse mass spectra in Pb-Pb at 160 A GeV/c
53 most central events
Inverse slopes (MeV)
s
25
Transverse mass spectrain Pb-Pb at 160 A GeV/c
26
Inverse slopes at 160 A GeV/c
s

• In central and semi-central Pb-Pb collisions (bin
  1,2,3,4) we
• measure compatible slopes for particle and
  its anti-particle
• This symmetry lost in p-Be

27
Collision Centrality

• Determined from charged multiplicity measurement
• Npart and Ncoll from trigger cross section
  (Glauber model calc.)
• strigger ? 60 of Pb-Pb sinel (7.26 b)

NA57 Coll., JPG31 (2005) 321
28
Collision Centralityfor RCP analysis

• Determined from charged multiplicity measurement
• Npart and Ncoll from trigger cross section
  (Glauber model calc.)
• strigger ? 60 of Pb-Pb sinel (7.26 b)

Systematic errors from variation of multiplicity
fit parameters, variation of Pb Woods-Saxon,
uncertainty on sNNinel (1.5)
NA57 Coll., JPG31 (2005) 321
29
Enhancements w.r.t. number of binary collisions
at 160 A GeV/c

• Going from p-Be to Pb-Pb X and W yields scale
• faster than ltNbingt

30
Hyperon Enhancements at 40A GeV/c

• Only lower limit for X, due to limited
  statistics
• Same hierarchy as for higher-energy data E(L) lt
  E(X)

31
Ratios of Enhancements40 GeV/c / 160 GeV/c
32
Energy Dependence of X Enhancement
Redlich et al., JPG28 (2002) 2095
compiled by B.Hippolyte
33
Canonical vs Grand Canonical

• Energy penalty to create a strange particle
• Canonical computed taking into account also
  energy to create companion to ensure conservation
  of strangeness
• Grand Canonical limit just due to creation of
  particle itself. The rest of the system acts as a
  reservoir and picks up the slack

Canonical suppression increases with decreasing
energy
Canonical suppression increases with increasing
strangeness
Redlich et al., JPG28 (2002) 2095
34
Comparison NA57-NA49 Particle yields per
participant
Similar centrality regions

• about 30 systematics on the absolute value of
  the
• yields (under investigation) but

Refs Physical Review C 66, 054902 (2002),
arXivnucl-ex/0311024, Phys. Lett. B
538 (2002), 275.
35
Comparison NA57-NA49 Particle ratios

• particle ratios compatible within errors
• (no impact on relative yields)

Refs Physical Review C 66, 054902 (2002),
arXivnucl-ex/0311024,
arXivnucl-ex/0305021, arXivnucl-ex/0311029.
36
Blast Wave
Blast-wave description of the spectra
Schnedermann, Sollfrank, Heinz, PRC48 (1993) 2462
37
Blast fit for most central collisions
5 most central events
(a) K, p, L, X-, W-
(b) K-, p, f, L, X, W
NA49 centrality 5 for K , f 10 for p, L, X
20 for W
Ref M van Leeuwen, Nucl. Phys. A715 (2003) 161c
38
Freeze-out parameters multi- vs. singly
strange particles
n1
Fit to singly strange particles

• Fit driven by singly strange particles
• X and W fit well with same parameters

39
Longitudinal DynamicsRapidity Distributions
Pb-Pb, 0-53
Pb-Pb, 0-53
Fitted with thermal model longitudinal flow
(Bjorken) using Tkin.f.o. from blast-wave fit
ltbLgt ltb?gt 0.4
Schnedermann, Solfrank, Heinz, PRC48 (1993)
2462 Mohanty and Alam, PRC68 (2003) 064903
40
Comparison NA57-NA49dN/dy

• Different acceptances
• NA57 y-ycm lt 0.5
• NA49 y-ycm lt 1.5

NA49, PRL93 (2004) 022302 PRC66 (2002) 054902
PLB538 (2002) 275 nucl-ex/0409004
41
Centrality dependence (i)
No centrality dependence in our limited acceptance
42
Centrality dependence (ii)
No centrality dependence in our limited acceptance
43
Analysis of Negatives (h-)

• Negatives selected on the basis of track quality
  and impact parameter cut (reject secondaries)
• Residual contamination from weak-decays feed-down
  estimated from Monte Carlo smaller than 3 for
  most central collisions (even smaller for less
  central)
• negligible effect on RCP

44
Centrality (in)dependence of correction weights

• Corrections for acceptance and efficiency
  calculated by embedding MC particles of given pT
  and y in real events, at the level of hits

45
The Negative Cocktail at SPS
Pb-Pb 160 A GeV/c
Pb-Pb 160 A GeV/c
p
identified particles 2.91 lt ? lt 3.51
p
NA49 very preliminary present
ed by C.Blume at Moriond, March 2005
46
RCP Comparisons WA98
WA98, EPJC23 (2002) 225