v. friese [email protected]
DESCRIPTION
Indications of the Onset of Deconfinement at low SPS Energies Recent Results from NA49 ICPAQGP 5 , Colcatta, February 2005. V. Friese [email protected]. for the collaboration. The NA49 Detector. Hadron spectrometer Large acceptance: 4 π yields PID by dE/dx and TOF - PowerPoint PPT PresentationTRANSCRIPT
Indications of the Onset of Deconfinement
at low SPS Energies
Recent Results from NA49
ICPAQGP5, Colcatta, February 2005
V. Friese
for the collaboration
V. Friese ICPAQGP, Colcatta, February 2005 2
The NA49 Detector
Hadron spectrometer
Large acceptance:4π yields
PID by dE/dx and TOF
Centrality by forward calorimeter
Beam energies: 20, 30, 40, 80, 158 AGeVSystems: p+p, p+A, C+C, Si+Si, Pb+Pb
V. Friese ICPAQGP, Colcatta, February 2005 3
Midrapidity mt spectra (central Pb+Pb)
Simultaneous blast wave fitconstant βt
π, d excluded from fit
SSH, PRC 48 (1993) 2462
Single fireball model with common temperature and flow velocity works
Beware: Resonance feeddown, velocity profile
V. Friese ICPAQGP, Colcatta, February 2005 4
Early freeze out of Ω ?
NA49, nucl-ex/0409004NA49, nucl-ex/0409004
(*) Gorenstein, Bugaev, Gadzicki, PRL 88 (2002) 132301
Linear velocity profile:Ω agrees better with charmonia than with other hadrons
Indication for earlier freeze out?
V. Friese ICPAQGP, Colcatta, February 2005 5
Transverse spectra at lower energies
30 AGeV 20 AGeV
Blast wave fits work at all SPS energies
Kinetic freeze out:T = 120 – 130 MeVβt = 0.4 – 0.5
for constant βt
V. Friese ICPAQGP, Colcatta, February 2005 6
Kaon Slope Parameters
Constant inverse slope at all SPS energiesConstant temperature and pressure? Mixed phase?
Kaon spectra almost perfect exponential → fit dn/dmt ~ mt e-mt/T
V. Friese ICPAQGP, Colcatta, February 2005 7
Average mt
Other particle types: No exponential spectrum → calculate mean mt
Similar behaviour seen for pions; protons less conclusive
V. Friese ICPAQGP, Colcatta, February 2005 8
Longitudinal Distributions (central Pb+Pb)
Gaussianlike rapidity spectra (except p, Λ)
Clear hiearchy of rapidity widths at SPS: π- > K+ > K- > Λexception: φ
V. Friese ICPAQGP, Colcatta, February 2005 9
Strange to Nonstrange Ratios: Kaons
Sharp structure in K+ / π, not reproduced by hadronic models(Full equlibrium) hadron gas model overpredicts kaons at higher SPS energies
V. Friese ICPAQGP, Colcatta, February 2005 10
Strange to Nonstrange Ratios: Λ
Similar structure seen as in K+
(sharp peak at 30 AGeV)
HGM describes overall structure, but location of peak different (?)
UrQMD not far off (not shown)
V. Friese ICPAQGP, Colcatta, February 2005 11
Total Strangeness
Energy dependence changes at 30 AGeV
Peak at 30 AGeV,undersaturation at higher SPS energies
V. Friese ICPAQGP, Colcatta, February 2005 12
Ruling out hadronic equlibirium ?
Features of HGM:
No sharp peak Overprediction of strangeness yields at higher SPS energies Maxima at different positions for K, Λ, Ξ, Ω
If connected with PT, maxima should be at the same energy for all strange species
Ξ at 20, 30 AGeV possibly discriminative → to come
V. Friese ICPAQGP, Colcatta, February 2005 13
… one more Parameter
Becattini et al., PRC 69 (2004) 024905
Introducing γS < 1 gives better description of NA49 4π yields
around 30 AGeV: γS ≈ 1At higher energies: γS ≈ 0.7
what does it mean?
V. Friese ICPAQGP, Colcatta, February 2005 14
Indication for deconfinement PT ?
Gazdzicki, Gorenstein, Act. Phys. Polon. B 30 (1999) 2705
Phase transition at 30 AGeV
Hama et al., Braz. J. Phys. 34 (2004) 322
QGP + hadronic phases
Features in strangeness / pion and kaon slopes can be obtained with models assuming a phase transition
V. Friese ICPAQGP, Colcatta, February 2005 15
Relative Strangeness Fluctuations
preliminaryNA49 preliminaryNA49
Dynamical fluctuations in K/π increase towards low SPS energiesNot reproduced in UrQMDp/π in agreement with hadronic transport (resonance decays)
V. Friese ICPAQGP, Colcatta, February 2005 16
Mean pt Fluctuations
Measured at top SPS as function of system size
Maximum at small Npart ( ≈ 100 )
But: similar pattern observed at RHIC
Interesting: Measure at lower SPS energies (hint taken)
V. Friese ICPAQGP, Colcatta, February 2005 17
System Size: Strangeness Enhancement
Es
Strangeness enhancement canonical suppressionVolume effect on strangeness conservation
But: No quantitative agreement with data (rise too fast) if V ~ Npart
Disagreement between peripheral Pb+Pb and central Si+Si, C+C
Tounsi, Redlich, JPG 28 (2002) 2095
NA49, 158 AGeV
V. Friese ICPAQGP, Colcatta, February 2005 18
Cluster Ansatz bei C. Höhne
Microscopic calculation of overlapping „strings“ (VENUS, UrQMD) → correlation volume as fct. of Npart
Calculate ES ~ η according to statistical model, taking into account the distribution in Vcorr
Describes data perfectly !
Application to fluctuations?
V. Friese ICPAQGP, Colcatta, February 2005 19
Summary
Anomalies at lower SPS energies observed by NA49: sharp peak in strange particles to pion ratio constancy of kaon slopes pion production rate increases (not discussed)
Fluctuation in K/π also increase towards low SPS energies, other signals less convincing / absent
Best explanation by scenario with onset of deconfinement
Low SPS is still interesting: EoI to CERN for SPS running from 2009 on Plans of fixed target experiments at RHIC FAIR at GSI