Recent Results from the Experiment

1
Recent Results from the Experiment

• Christoph Blume
• University of Frankfurt
• For the NA49 Collaboration

NATO ASI Structure and Dynamics of Elementary
Matter 22. Sept. - 2. Oct. 2003 Kemer, Turkey
2
Heavy Ion Physics at the CERN SPSExploring the
QCD Phase Diagram

• Study of energy dependence
• Look for onset phenomena
• Hadronic observables covered by NA49
• Rare probes
• ? CBM experiment at future GSI facility

F. Karsch, E. Laermann and A. Peikert, Phys.
Lett. B478 (2000) 447

• Study of system size dependence

3
Heavy Ion Physics at the CERN SPSEnergy Scan
Program

• Evolution of hadronic observables with energy
• Data taken at 20, 30, 40, 80, and 158 AGeV
• Particle species p, K, L, f, W
• Thermal freeze-out
• Transverse mass spectra
• Pion-HBT
• Deuteron coalescence
• Rapidity Spectra
• Evolution of stopping

• Chemical freeze-out
• Particle yields
• Phase diagram
• Collectivity
• Elliptic flow v2
• Initial pressure of system
• Critical phenomena
• Charge fluctuations
• QGP observable?

4
The NA49 ExperimentSetup

• Calorimeter for centrality selection

• Hadron spectrometer
• Large acceptance

5
The NA49 ExperimentParticle Identification

• dE/dx measured in TPCs
• Large acceptance
• Resolution 3-4
• Time-of-flight
• Mid-rapidity
• Resolution 60 ps

Example PbPb _at_ 40 AGeV
6
Thermal Freeze-OutTransverse Mass Spectra
158 AGeV

• Common freeze-out condition for all particles
  (including hyperons!)
• Radial flow fit (Blast Wave)

Pions and deuterons not included in fit
7
Thermal Freeze-OutTransverse Mass Spectra
40 AGeV

• Good fit also at 40 AGeV (and 80 AGeV, not
  shown)
• Similar parameters at all energies

8
Thermal Freeze-OutSlope Parameter L and f
L
Monotonic increase of T for L and f
Increase of radial expansion velocity
9
Thermal Freeze-OutSlope Parameter Kaons
? AGS ? NA49 ? RHIC
Clear step in energy dependence
Latent heat (van Hove)? But cross over
hep-ph/0303041
10
Thermal Freeze-OutTransverse Mass Spectra of
Kaons
No significant change in shape (almost perfectly
exponential)
40, 80, 158 AGeV Phys. Rev. C66 (2002) 054902
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Thermal Freeze-OutSize of the Reaction System

• Pion-HBT
• Correlation function of
• identical bosons
• Information on space-time
• evolution of source

12
Thermal Freeze-Out HBT of h-h- Pairs in Central
PbPb
NA49 preliminary
Clear kt dependence ? expansion No significant
energy dependence at SPS
13
Thermal Freeze-Out Deuteron Coalescence B2
Strong variation of B2 with energy (factor 2 for
SPS data)
Not seen in HBT radii Minimum of HBT
volume around SPS energies
NA49 preliminary
14
Rapidity SpectraPions and Kaons
Spectra get wider with increasing beam energy
p- ? K gt K-
Preliminary
K related to L via associated production
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Rapidity Spectraf, L, L
Spectra get wider with increasing beam energy
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Rapidity SpectraOmega
Central (20) PbPb at 158 AGeV
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Chemical Freeze-OutPion Yields (4p)
Change of energy dependence of pion production at
30 AGeV
30 AGeV preliminary
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Chemical Freeze-OutK/p Ratio
K-/p- Continous rise K/p Prominent maximum
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Chemical Freeze-OutModel Comparisons to K/p
Ratio
Structure not fully explained by hadronic models
, but it only looks like that
(H. Stöcker)

• Hadron Gas
• Equilibrated hadron gas
• Parameter (T, mB) dependend on ?s
• Freeze-out for const. E/N 1GeV ? relation
  between T and mB
• Fix T on pion multiplicities
• Braun-Munzinger, Redlich, Oeschler

20
Chemical Freeze-OutTotal Strangeness
Structure not visible in pp data
Dashed curve M. Gazdzicky and M.I. Gorenstein
Acta Phys. Pol. B9, 2705
21
Chemical Freeze-Outf-Meson Yields
f/p Continous rise f/K- Constant (also as
function of centrality)
22
Chemical Freeze-OutBaryon-Antibaryon Ratios
mid-rapidity
Energy dependence weakens with increasing
strangeness content
Statistical model Variation of mB
Modified by mS
23
Chemical Freeze-OutStatistical Model Fits
Hadron gas model with partial strangeness
saturation (F. Becattini)
24
Chemical Freeze-OutQCD Phase Diagram
Smooth chemical freeze-out curve in T-mB plane
Approaches phase boundary at SPS
cross-over Fodor / Katz, hep-lat 0204029
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CollectivityAnisotropic Flow

• Measurement of pressure in early phase of the
  reaction
• May be sensitive to changes in EOS
• Fourier decomposition of the distribution of
  azimuthal angles of emitted particles relative to
  the event plane
• Alternativ method Cumulants

NA49 publication Phys. Rev. C68, 034903 (2003)
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CollectivityElliptic Flow-Parameter v2
Smooth energy dependence of elliptic flow
mid-rapidity (0 lt y lt 0.6 (0.8)) semi-central
(12-34) pions (NA49) charged (other)
Decreasing effect of spectators Increasing
thermalization
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CollectivityElliptic Flow-Parameter v2
Scaled anisotropy v2/e vs charged particle
density
Area of overlap region S
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Charge FluctuationsBasic Idea

• Basic idea
• Had. phase charge unit 1
• QGP phase charge unit 1/3
• Reduced fluctuations in QGP
• S. Jeon and V. Koch,
• Phys. Rev. Lett. 85 (2000) 2076
• M. Asakawa, U. Heinz, and B. Müller,
• Phys. Rev. Lett. 85 (2000) 2072

• Suitable observable must take into
• account
• Impact parameter fluctuations
• Acceptance effects
• Net charge of the system
• Charge conservation

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Charge Fluctuations?q Energy Dependence

• Generalized ?x
• M. Gazdzicki and S. Mrowczynski, Z. Phys. C54
  (1992) 127
• For charge fluctuations x ? q
• Extreme cases
• ?q 0 independent emission
• ?q -1 local charge conservation
• No energy dependence (central PbPb data)

NA49 preliminary
Fqcc

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Charge Fluctuations??q QGP Model

• Subtract global charge conservation
• Simple QGP model
• J. Zaranek, hep-ph/0111228
• Massless quarks, mB 0
• Multiplicity ratios of q, g from equilibrium QGP
  (ideal gas)
• Entropy and local charge conservation during
  hadronization into

NA49 preliminary

• Data compatible to g.c.c.
• QGP fluctuations obscured by resonance decay
  kinematics

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Summary

• Thermal freeze-out conditions
• Good agreement of all particle spectra (including
  hyperons) to model fit including radial flow
• Slope parameter increase continously with energy,
  except Kaons !
• No signifianct energy dependence of pion-HBT
  Volume minimal at SPS
• Strong decrease of B2 with beam energy

• Rapidity spectra
• Spectra widen with beam energy. Strong effect for
  L
• Chemical freeze-out
• Clear non-monotonic energy dependence of
  strangeness/pion ratio
• T, mB parameter approach phase boundary
• Collectivity
• Continous increase of elliptic flow parameter
  with beam energy

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Outlook

• 20 AGeV data currently being analyzed ? ?
  complete excitation function of hadronic
  observables
• Complete the spectrum of analyzed particle
  species L, X, W, f, and strange resonances at
  all energies
• Energy dependence of fluctuations Multiplicity,
  pt, K/p

• System size dependence

The SPS is not yet dead!
It just smells strange
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NA49 Collaboration

• C. Alt, T. Anticic, B. Baatar, D. Barna, J.
  Bartke, M. Behler, L. Betev,
• H. Bialkovska, A. Billmeier, C. Blume, B.
  Boimska, M. Botje, J. Bracinik,
• R. Bramm, R. Brun, P. Buncic, V. Cerny, O.
  Chvala, J.G. Cramer, P. Csató,
• P. Dinkelaker, V. Eckhardt, P. Filip, H.G.
  Fischer, Z. Fodor, P. Foka, P. Freund,
• V. Friese, J. Gál, M. Gazdzicki, G. Georgopoulos,
  E. Gladysz, S. Hegyi,
• C. Höhne, K. Kadija, A. Karev, S. Kniege, V.I.
  Kolesnikov, T. Kollegger,
• R. Korus, M. Kowalski, I. Kraus, M. Kreps, M. van
  Leeuwen, P. Lévai,
• A.I. Malakhov, C. Markert, B.W. Mayes, G.L.
  Melkumov, C. Meurer,
• A. Mischke, M. Mitrovski, J. Molnár, S.
  Mrowczynski, G. Pálla,
• A.D. Panagiotou, K. Perl, A. Petridis, M. Pikna,
  L. Pinsky, F. Pühlhofer,
• J.G. Reid, R. Renfordt, W. Retyk, C. Roland, G.
  Roland, M. Rybczynski,
• A. Rybicki, A. Sandoval, H. Sann, N. Schmitz, P.
  Seyboth, F. Siklér, B. Sitar,
• E. Skrzypczak, G. Stefanek, R. Stock, H.
  Ströbele, T. Susa, I. Szentpétery,
• J. Sziklai, T.A. Trainor, D. Varga, M.
  Vassiliou, G.I. Veres, G. Vesztergombi,
• D. Vranic, S. Wenig, A. Wetzler, Z. Wlodarczyk,
  I.K. Yoo, J. Zaranek,
• J. Zimányi

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Particle YieldsLambda to Pion Ratios
35
Thermal Freeze-OutOmegas
36
The f PuzzleComparison NA49 and NA50 at 158 AGeV
Strong differences in slope and yield between
hadronic channel (NA49) and dimuon channel (NA50)
Rescattering of kaons in microscopic models
accounts for 30 in total yield and 20 MeV
in slope only
37
The f PuzzleNA49 Measurement in Dielectron
Channel
? ? ee- 158 AGeV PbPb 20 central 3 M
events
No ? signal observed Upper limit estimate lt?gt
lt 40
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Transverse Mass Spektraf-Meson
39
Deuteron CoalescenceProton and Deuteron Spectra
Central PbPb
NA49 preliminary
40
Strange Particle Correlations

• Correlation functions reflect influence of FSI
• Coulomb interaction
• Strong interaction
• Correlations of non identical particles
• Study space-time asymmetries by unlike particle
  correlations
• pp correlations
• R. Lednicky, V.L. Lyuboshitz, B. Erazmus,
  D. Nouais, Phys. Lett. B373 (1996) 30
• Source size determination
• ? Lp correlations
• F. Wang and S. Pratt, Phys. Rev. Lett. 83
  (1999) 3138

• Learn about two particle interaction
• LL correlations
• C. Greiner and B. Müller, Phys. Lett. B219
  (1989) 199
• Variables

(in pair c.m.)
(in pair c.m.)
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Lp Correlation Function
NA49 preliminary

• PbPb _at_ 158 AGeV 20 most central
• 60k pairs with Q lt 0.3 GeV/c
• Correlation due to strong FSI
• No quantum statistics
• No Coulomb interaction
• Fit with theoretical c.f.
• R. Lednicky, V.L. Lyoboshitz,
• Sov. J. Nucl. Phys. 35 (1982) 770
• Effective range approximation s-wave scattering
  length f0 -2.3 / -1.8 fm (singlett/triplett)
• Spherical symmetric and static Gaussian source RG

• Compare
• pp in PbPb _at_ 158 AGeV (NA49) RG 4.0 fm
• Lp in AuAu _at_ 6AGeV (E895)

42
LL Correlation Function

• PbPb _at_ 158 AGeV 20 most central
• 3500 pairs with Q lt 0.3 GeV/c
• Extract information on LL FSI
• Strong interaction Fermi statistics
• Fit parameter
• s-wave scattering length f0
• Fixed
• Gaussian source size RG
• l parameter 0.16 (estimated from feed
  down and PID background)

NA49 preliminary

• Indication for small f0
• Compare nn s-wave f0 ? -20 fm

43
The NA49 ExperimentEnergy Scan Program Analyzed
Data
20 AGeV Analysis in progress

• f Phys. Lett. B491 (2000) 59
• Phys. Lett. B538 (2002) 275
• K,? Phys. Rev. C66 (2002) 054902