V. Friese v.friese@gsi.de

Indications of the Onset of Deconfinement

at low SPS Energies

Recent Results from NA49

ICPAQGP5, Colcatta, February 2005

V. Friese

v.friese@gsi.de

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