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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

V. Friese [email protected]

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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 Presentation

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Page 1: 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

[email protected]

for the collaboration

Page 2: V. Friese v.friese@gsi.de

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

Page 3: V. Friese v.friese@gsi.de

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

Page 4: V. Friese v.friese@gsi.de

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?

Page 5: V. Friese v.friese@gsi.de

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

Page 6: V. Friese v.friese@gsi.de

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

Page 7: V. Friese v.friese@gsi.de

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

Page 8: V. Friese v.friese@gsi.de

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

Page 9: V. Friese v.friese@gsi.de

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

Page 10: V. Friese v.friese@gsi.de

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)

Page 11: V. Friese v.friese@gsi.de

V. Friese ICPAQGP, Colcatta, February 2005 11

Total Strangeness

Energy dependence changes at 30 AGeV

Peak at 30 AGeV,undersaturation at higher SPS energies

Page 12: V. Friese v.friese@gsi.de

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

Page 13: V. Friese v.friese@gsi.de

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?

Page 14: V. Friese v.friese@gsi.de

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

Page 15: V. Friese v.friese@gsi.de

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)

Page 16: V. Friese v.friese@gsi.de

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)

Page 17: V. Friese v.friese@gsi.de

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

Page 18: V. Friese v.friese@gsi.de

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?

Page 19: V. Friese v.friese@gsi.de

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