Transcript Document

NA57 main results
Giuseppe E Bruno
Università di Bari and INFN - Italy
Prologue
Outline
 NA57
Introduction
was the dedicated experiment at
SPS for the
study of multi-strange
the
experimental
technique
Comparison with
NA49-NA45
production at midrapidity
 particle
Main results
enhancements
 1.hyperon
The analysis
is essentially completed
2.strange particle spectra
 3.nuclear
In this talk
we concentrate
onCPthe
main
modification
factors (R
)
 contributions
Conclusions from NA57
Experimental technique
5 cm
 detect K0S, L, X and W
by reconstructing weak
decay topologies
K0s --> p+ + p-
BR = 69.2%
L --> p + p-
BR = 63.9%
X- --> L + pW- --> L + K-
5 cm
p
p-
BR = 99.9%
BR = 67.8%
L
X-
p-
30 cm
B
Target
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Hyperon signals
background unsubtracted
158 A GeV/c
Pb-Pb
40 A GeV/c
Pb-Pb
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Centrality classes
 Centrality determined from charged particle multiplicity (Nch)
 Nwound , Nbin from Glauber model fit
<Nwound>
Pb-Pb 158 A GeV
0 1
2
3
4
bin % of stot 158
<Nbin>
40
158
40
0
40-53 %
62
57
77
81
1
23-40%
121
119
191
203
2
11-23 %
209
208
395
416
3
5-11 %
290
292
614
644
4
0-5 %
349
346
789
807
NA57, J. Phys. G31 (2005) 321-335
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Comparison NA57-NA49-NA44
dN/dy of K0s and ½(K++K-)
½(K++K-)
NA49 0-5%
scaled to 0-10%
dN
Y 
dy
- 0.5 dy
0.5
K0s
NA57
0-11%
NA49
0-10%
NA45 0-7%
scaled to 0-10%
NA49 Nucl. Phys. A715 (2003) 453c, QM2002
NA49 Phys. Rev. C 66, 054902 (2002)
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NA45 S. Radomski Ph.D. thesis
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1. hyperon enhancements
 confirmation of hyperon enhancements
 centrality dependence
 energy dependence
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Two historic QGP predictions

restoration of c symmetry -> increased production of s

mass of strange quark in QGP expected to go back to current
value


ms ~ 150 MeV ~ Tc
copious production of ss 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]
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Enhancements at 158 GeV
SE
Errors:
systematic
3
2
10
10
Hierarchy of the
2 enhancements
1
1
1
1
1
10
100
1000 1
<Nwound>
statistical
10
100
with strangeness
content
(QGP prediction)
1000
<Nwound>
 hadronic transport models cannot reproduce this
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Centrality dependence
Canonical Suppression
(Hamieh et al.)
 enhancement still large
around NW = 50
 enhancing mechanism
still effective at 25 + 25 !
 effect increases with
centrality (except L)
 enhancing mechanism
more and more effective
as NW increases
 constrain models !
e.g.: “canonical suppression model” predicts quick saturation of effect
with centrality, at odds with data [Hamieh et al.: Phys. Lett. B486 (2000) 61]
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Hyperon enhancements at 40 GeV
 The effect is still present
 enhancing mechanism already effective at low energy
(95 % confidence level)
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Energy dependence
of hyperon enhancements
 roughly same order of magnitude as at 158 GeV
 steeper centrality dependence
 slightly larger than at 158 GeV for most central collisions
10
10
1
1
 energy dep. of enhancements not yet understood theoretically
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 energy dependence also constrains models
 e.g. much weaker than predicted by canonical
suppression model:
Redlich et al., JPG28 (2002) 2095
X40 GeV
10
158 GeV
1
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Other measurements of SE
STAR(√sNN=200GeV) full symbols
versus
NA57(√sNN=17.3GeV) open symbols
NA49 (√sNN=17.3GeV)
L sensitive to
baryon density?
NA49, nucl-ex 0701042 (2007), JPG in print
SE at RHIC...
... similar effect as at SPS

STAR, nucl-ex 07052511 (2007), submitted to PRL
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2. strange particle spectra
 centrality dependence of
 freeze-out temperature T
 radial expansion bT
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Blast wave model
 mT distributions described as combined result of thermal
motion (T) and collective transverse expansion (bT) at
freeze-out
RG
 m cosh    pT sinh  
  Aj mT  K1  T
  I0 
rdr
0
mT dydmT
T
T

 

d2 N j
 (r )  tanh-1 b (r )
 r 
b  (r )  b S  
 RG 
n ( 1)
r  RG
Schnedermann, Sollfrank, Heinz, PRC48 (1993) 2462
 for most central (5%) collisions:
T ~ 120 MeV, bT ~ .45
 confirmation of NA49 results
NA57, JPG 30(2004) 823
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NA57: spectra vs centrality
NA57 JPG 30(2004) 823
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Blast wave vs centrality
peripheral
NA57 158 GeV
Centrality classes:
23-40%
40-53%





11-23%
4.5-11%
0
1
2
3
4





40 to 53 % most central
23 to 40 % most central
11 to 23 % most central
4.5 to 11 % most central
4.5 % most central
0-4.5%

central
158 A GeV/c
For more peripheral:


Transverse flow velocity
decreases
Freeze-out temperature
increases
 fix hydro parameters
NA57, JPG 30(2004) 823
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v2 vs hydro at SPS?
 v2 not at hydro limit?
 v2 well below hydro limit for
Tf = 120 MeV
 but NA57: Tf increases for
peripheral events
1s contours
n=1
[Snellings et al.: nucl-ex/0305001]
 Tf = 146 ± 17 MeV for (11-23)%
centrality; NA45 data (13-26)%
 so hydro limit perhaps not too far...
[NA45: Phys.
Rev. Lett. 92 (2004) 032301]
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3. nuclear modification factors (RCP)
 direct comparison to RHIC high pT
quenching results
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Rcp at RHIC
 high pT: suppression
 interpreted as due
to jet quenching
 medium pT:
meson/baryon effect
 valence quark
recombination?
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RCP in NA57
 bars = quadratic sum of stat. and pT-dependent systematic errors
 no evidence for
high pT suppression
(RCP < 1)
 but similar relative
K0S/L pattern as at
RHIC
NA57, PLB 623(2005) 17
STAR, PRL92 (2004) 052302
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Comparisons to models
 Comparison to K0S calculations
(X.N. Wang; PQM)
 medium density extrapolated
down from RHIC according to
multiplicity
 Cronin effect included
 better agreement with E loss
X.N.Wang, PRC68 (2001) 064910; PRL81 (1998) 2655; PLB595 (2004) 165 + private comm.
PQM: Dainese, Loizides, Paic, EPJC38 (2005) 495 + private comm.
22
Relative L, K0S pattern
 Very similar at
SPS and RHIC
NA57, PLB 623(2005) 17
STAR, PRL92 (2004) 052302
23
Conclusions
 Hyperon enhancements



confirmation of enhancement for central colls
centrality dependence: effect already present at
≈ 25+25 participants
energy dependence: similar effects at √sNN=8.8,
17.3 (and 200) GeV
 Strange particle mt spectra

centrality dependence of kinetic freeze-out
parameters
 Nuclear modification factor Rcp

similar relative L/K0s pattern as at RHIC
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of course we did more …
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NA57 publications in refereed journals








Study of the transverse mass spectra of strange particles in Pb-Pb
collisions at 158 A GeV/c
J. Phys. G 30 (2004) 823-840
Energy dependence of hyperon production in nucleus-nucleus
collisions at SPS
Phys. Lett. B595 (2004) 68-74
Multiplicity of charged particles in Pb-Pb collisions at SPS energies
J. Phys. G31 (2005) 321-335
Central-to-peripheral nuclear modification factors in Pb-Pb collisions
at √ sNN = 17.3 GeV/c
Phys. Lett. B 623 (2005) 17-25
Rapidity distributions around mid-rapidity of strange particles in PbPb collisions at 158 A GeV/c
J. Phys. G 31 (2005) 1345-1357
Enhancement of hyperon production at central rapidity in 158 A
GeV/c Pb-Pb collisions
J. Phys. G 32 (2006) 427-441
Transverse dynamics of Pb-Pb collisions at 40 A GeV/c viewed by
strange hadrons
J. Phys. G 32 (2006) 2065-2080
Expansion dynamics of Pb-Pb collisions at 40 A GeV/c viewed by
negatively charged hadronsJ. Phys. G 34 (2007) 403-429
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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. Kravčákovái,
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. Pastirčákh,
R.J. Platte, E. Quercighk, F. Riggif, D. Röhrichc, G. Romanoo,
R. Romitab, K. Šafaříkg, L. Šándorh, 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
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The NA57 Collaboration
Prague
CERN
Athens
Paris - CdF , Strasbourg
Bari, Catania, Padua, Rome, Salerno
Utrecht
St. Petersburg
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Bergen, Oslo
Bratislava, Košice
Birmingham
Giuseppe E BrunoG.E. BRUNO - NA57
28
Experimental apparatus
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
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Strange Particle reconstruction in NA57
Decay channels:
K S0  p +p -
L p - p
X -  Lp -
W-  LK -
plus c.c. for anti-hyperons
Interactions:
Pb-Pb, p-Be, p-Pb @ p = 158A GeV/c
Pb-Pb, p-Be @ p = 40A GeV/c
Acceptance
Dy  1 around mid-rapidity
pT > 0.5 GeV/c
Hyperon yield measurements
mT 
 Data corrected for
acceptance and also for
detector and
reconstruction efficiency
by Monte Carlo simulation
 In the acceptance window:
 Yield
pT2 + m02
 mT 
d2 N

 AmT exp  T 
dydmT
 app 
(i.e. particle per event)
 Transverse mass
spectra (Tapp)
 Extrapolation to a common
window:
 one unit of rapidity
about ycm
 full range of pT
d2 N
Yextr  
dy  dmT
yCM -0.5
m0
dmT dy
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yCM + 0.5

31
Comparison NA57-NA49
Particle yields per participant
Similar centrality regions:
NA57
NA49*
40 GeV
5%
7%
158 GeV
(K)
5%
5%
158 GeV
(L, X)
11%
10%
For NA49: Ks0 = 0.5*(K++K-)
 about 30% systematics on the absolute value of the
yields but …
*Refs: Physical Review C 66, 054902 (2002), Phys.Rev.Lett. 93 (2004) 022302,
Phys. Lett. B 538 (2002), 275.
Comparison NA57-NA49
Particle ratios
 … particle ratios compatible within errors
(no impact on relative yields)
*Refs: Physical Review C 66, 054902 (2002), Phys.Rev.Lett. 93 (2004) 022302,
arXiv:nucl-ex/0305021, arXiv:nucl-ex/0311029.
Comparison NA57-NA49
dN/dy
Different acceptances:
NA57: ~ |y-ycm| < 0.5
NA49: ~ |y-ycm| < 1.5
Particle
NA57
NA49
Kaon
K0
Gaussian
rms = 0.222
in NA57 acc.
K+/2 Gaussians
rms = 0.219
in NA57 acc.
L
flat
flat
L
Gaussian
s = 0.830.22
Gaussian
s = 0.950.05
X
X
flat / notsensitive
2 Gaussians
Gaussian
flat / notsensitive
Gaussian
s = 1.20.4
s = 1.00.4
W
W
NA49, PRL93 (2004) 022302; PRC66 (2002) 054902; PLB538 (2002) 275; nucl-ex/0409004
Comparison NA57-NA49
dN/dy of K0s
NA57
0-11%
NA49
0-10%
NA49, Nucl. Phys. A715 (2003) 453c, QM2002
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Comparison NA57-NA49-NA44
dN/dy of K0s and ½(K++K-)
½(K++K-)
NA49 0-5%
scaled to 0-10%
dN
Y 
dy
- 0.5 dy
0.5
K0s
NA57
0-11%
NA49
0-10%
NA45 0-7%
scaled to 0-10%
NA49 Nucl. Phys. A715 (2003) 453c, QM2002
NA49 Phys. Rev. C 66, 054902 (2002)
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NA45 S. Radomski Ph.D. thesis
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Comparison NA57-NA49
dN/dy of K0s vs. ½(K++K-)
NA49 Physical Review C 66, 054902 (2002)
30
K+
20
15
Fit function:
   y - y0 
dn
 N exp dy
2s 2
 
2
10
N

  y + y0 
 + exp 2


2
s


2




s
y0
K+
23.4
0.88
±0.6 ±0.04
0.839
±0.012
K-
12.8
0.81
±0.3 ±0.02
0.727
±0.010
KNA57 0-5%
10
NA49 0-5%
5
dN
Statistical
Systematic
dy y - ycm 0.5
errror
+
K
+
K
K s0 
2
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Comparison NA57-NA49
Yield/Nwound of L
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Longitudinal dynamics
0-53% sinel
Yield
Dy=1
Systematic
Statistical
dN
errror
errror
dy y - ycm 0.5


Rapidity distributions (at central rapidity) for all levels of
strangeness
Only K0s and L non-flat within acceptance
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Longitudinal dynamics
 thermal model
without flow
 Thermal model +
Longitudinal flow
(Bjorken) using T
kin.f.out from Blast
wave fit:
 <bL> ~ 0.4 ~ <b>
 almost isotropic
expansion?
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Centrality dependence (i)
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Centrality dependence (ii)
No centrality dependence in our limited acceptance
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Yields and enhancements
Cross section for each particle fitted to
 mT
1 d 2N
 f ( y )  exp  T
mT dmT dy
 app




f(y) flat/Gaussian (for K0 and antilambda)
Yield extrapolated to common y/pT region

ycm + 0.5
m
ycm -0.5
Y   dmT 
d 2N
dy
dmT dy
Strangeness enhancement PbPb relative to p-Be
 Y
E 
 N part

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


 Pb- Pb
 Y

 N part

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


 p - Be
43
Enhancements at 158 (√sNN=17.3) GeV
Errors:
systematic
Factor  20 for W
statistical
3
Enhancement =
2
10
10
Hierarchy of the
enhancements
<Yield> / <Nwound>
2
1
1
with strangeness
(<Yield>
/ <Nwound>)p-B
1 content
(QGP prediction)
No enhancement
1
<Nwound>
1
10
100
1000 1
10
100
1000
 Hierarchical enhancement according to strangeness content
 QGP
prediction*:
to build
W by recombination
Particles
having
quarks in easier
Particles
made X
upand
of newly
common with the nucleon
created quarks only
 Significant centrality dependence, except for L
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* Rafelski and Muller
Enhancements w.r.t. number of binary collisions
at 158 A GeV/c, i.e. pt-integrated RAA
Enhancement =
10
<Yield> / <Nbin>
10
(<Yield> / <Nbin>)p-Be
1
1
<Nbin>
• Going from p-Be to Pb-Pb X and W yields scale
faster than <Nbin>
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Ratios of Enhancements
40 GeV/c / 160 GeV/c
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A parenthesis: canonical aspects of
strangeness enhancement
 Thermal fits in HI work very well:
 relative particle abundances ~ as expected at
thermodynamical equilibrium for grand-canonical
system, even for rare, multi-strange particles
E.g.
A. Andronic et al. Nucl.Phys. A772 (2006) 167-199
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A parenthesis: canonical aspects of
strangeness enhancement
 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”
√sNN=8.8GeV
100
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√sNN=130GeV
10
 removal of canonical suppression*
 increases with strangeness
 detailed centrality dependence
not reproduced (very crude
modelling)
 decrease of enhancements with
√sNN predicted, but ~ order of
magnitude close
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*Tounsi, Redlich et al.
A parenthesis: canonical aspects of
strangeness enhancement
Does this explain the observed enhancements ?
 a system in eq., if it is large enough, is in GC eq., but being
large in itself is not a sufficient condition for being GC!
 if AA colls. were just a superposition of pp, they would have
to be treated canonically all the same!
 the system must also know it is large...
 it must know that an Ω+ generated here can be
compensated by, say, an Ω- on the other side of the fireball!
 what counts is the correlation volume
 how does the system know it is large?
how can information travel so quickly through the system?
 not by conventional hadronic transport (no time!)
 natural if the system is coming back from deconfinement
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Expansion dynamics viewed by
negatively charged hadrons

Ref: Expansion dynamics of Pb–Pb collisions at 40 A GeV/c viewed
by negatively charged hadrons, J. Phys. G 34 (2007) 403-429
HBT
dN/dmt
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blast of
strange
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Expansion dynamics viewed by
negatively charged hadrons

Ref: Expansion dynamics of Pb–Pb collisions at 40 A GeV/c viewed
by negatively charged hadrons, J. Phys. G 34 (2007) 403-429
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Blast wave model
R
 m cosh    pT sinh  
Model : thermalization
  Aj mT  K1  T
  I0 
rdr
0
T
T

 

plus hydro-dynamical mT dydmT
n ( 1)
transverse flow


r
 (r )  tanh-1 b (r )
b  (r )  b S  
r  RG
description
 RG 
d2 N j
Pb-Pb 158 A GeV/c
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G
Pb-Pb 40 A GeV/c
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Schnedermann, Sollfrank, Heinz, PRC48 (1993) 2462
Transverse dynamics
peripheral
23-40%
40-53%
11-23%
4.5-11%
0-4.5%
central
158 A GeV/c
 Tkin.f.out lower at 40 A GeV/c, b similar
 Peripheral  central: Tkin.f.out decreases, b increases
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Schnedermann, Sollfrank, Heinz, PRC48 (1993) 2462
Freeze-out parameters:
multi- vs. singly strange particles
n=1
Fit to singly strange particles
• Fit driven by singly strange particles
• X and W fit well with same parameters
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Transverse dynamics
158 A GeV
40 A GeV
 Higher temperature, lower flow describes «deviating»
particles
 Early decoupling?
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Blast Blast-wave
Wave description of the spectra:
d2 N j
mT dydmT

 (r )  tanh b  (r )
-1
RG
0
 mt cosh    pt sinh  
Aj mT  K1 
  I0 
rdr
T
T

 

 r 

R
 G
b  (r )  b S 
Uniform particle density
n
r  RG
n=0
n=1/2
n=1
n=2
T
158±6
152±6
144±7
151±11
bS
0.396
±0.015
0.493
±0.016
0.571
±0.019
0.633
±0.028
b>
0.396
±0.015
0.394
±0.013
0.381
±0.013
0.316
±0.014
(MeV)
2
 b  >
bS
2+n
c2/ndf
39.6/4 36.9/48 37.2/48 68.0/48
8
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Sollfrank, Heinz, PRC48 (1993)
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Giuseppe
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Blast fit for most central collisions
n
5% most central events
T
(MeV)
b> c2/ndf
NA57 1 1181 0.45
0.0
3
2
53/4
3
NA49 0 1271 0.48 120/
0.0
(a)
43
1
(a) K0+, p,1142
L, X-, W0.50
NA49
91/4
W+
(b)(b) K-, p, f, L, X+,0.0
1
1 ±
NA49 centrality: 5% for K , f
10% for p, L, X ; 20% for W
Ref: M van Leeuwen, Nucl. Phys. A715 (2003) 161c
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Collision centrality
• Determined from charged
particle multiplicity
measured in a Si-strips
multiplicity detector
• Nwound and Ncoll from
(Glauber + WNM) fit
 strigger60% of Pb-Pb sinel (7.26 b)
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Collision Centrality
[for 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%)
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(2005) 321
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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)
feed-down fraction
 negligible effect on RCP
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-
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
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The Negative Cocktail at SPS
Pb-Pb 160 A GeV/c
Pb-Pb 160 A GeV/c
p
identified
particles
p
p
2.91 <  < 3.51
NA49 very
preliminary
p-, K- , p
presented by C.Blume at Moriond, March 2005
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RCP Comparisons: WA98
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WA98, EPJC23
(2002) 225
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The NA57 experimental programme
NA57 Proposal (dated August 1996)
Study of Strange and Multistrange
Particles in Ultrarelativistic NucleusNucleus Collisions
Among the signatories, most of the
local organizers of this Conference:
I. Králik, J. Pišút, E. Quercigh,
K. Šafařík, L. Šándor, J. Urbán
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The NA57 experimental programme
NA57 Proposal
1 Introduction
We propose an experiment to study
the production of strange and multistrange particles in nucleus-nucleus
collisions initiated at the OMEGA
Spectrometer, where three ion
experiments have been performed:
WA85 (S-W collisions at 200 A
GeV/c), WA94 (S-S collisions at 200
A GeV/c) and WA97 (Pb-Pb collisions
at 160 A GeV/c).
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The NA57 experimental programme
NA57 Proposal
1 Introduction
The main purpose of the experiment
is to extend the physics scope of
WA97
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The NA57 experimental programme
NA57 Proposal
1 Introduction
The experimental area and part of
the equipment (magnet, DAQ,
detectors) will be shared with the
ALICE collaboration for detectors
test with hadrons and ion beams
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The NA57 experimental programme
NA57 Proposal
Fig.13
A sketch of the ALICE prototype
silicon pixel, silicon strip dublets to
be used in the experiment when
available
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