recent results from the sps christoph blumeexploring the phase diagram of strongly interacting...

Recent Results from the SPS

Christoph Blume Exploring the PhaseDiagram of StronglyInteracting MatterWorkshop in Stony BrookNov. 17, 2004

Christoph Blume Stony Brook Workshop, 17 November 2004 2

Heavy Ion Physics at the CERN SPSExploring the QCD Phase Diagram

SPS energy regime allows to explore an essential part of the phase diagram– If there is QGP seen at RHIC

the transition is likely to happen at SPS energies

– Ebeam = 20 - 158 AGeV (sNN = 6.3 - 17.3 GeV)

Is a phase transition reflected in hadronic observables?

Systematic studies required: Energy dependence

System size dependence

Cross over linefrom lattice QCD

Critical point

1st ordertransition

Lattice calculations:Fodor and KatzBielefeld-Swansea group


Heavy Ion Physics at the CERN SPS The NA49 Experiment

13m

Particle identification:

Pions, charged Kaons: dEdx in TPCs + TOF (mid-rapidity)

K0s, , , : Decay topology + invariant mass

: Invariant mass of identified Kaons


Heavy Ion Physics at the CERN SPSParticle Identification in NA49

dE/dx measured in TPCs– Large acceptance– Resolution 3-4%

Time-of-flight– Mid-rapidity– Resolution 60 ps

Example:Pb+Pb @ 40 AGeV


Heavy Ion Physics at the CERN SPSObservables

Try to characterize the “basic” features of heavy ion events with as few parameters as possible

Soft physics:– Particle production dominated by pt < 2 GeV/c

Systematic studies important– Vary control parameter like beam energy and system size

Focus of this talk: Energy Dependence + Central Collisions

AGS SPS RHIC


Heavy Ion Physics at the CERN SPSObservables

Rapidity Spectra– Longitudinal expansion

Particle Yields– Strangeness– Chemical freeze-out conditions

Transverse Mass Spectra– Transverse expansion ( EOS?)– Thermal freeze-out conditions

Fluctuations– Critical point of the phase diagram


Rapidity Spectra

Central Pb+Pb7% (20-80)5/10% (158)

Change of shape only for Others: ~ Gaussians


Rapidity SpectraPions

Single Gaussians!

ComparisonAGS, SPS, and RHIC

Central Pb+Pb/Au+Au


Rapidity DistributionsLandau Scenario in p+p

Prediction: dN/dy is Gaussian of a width = 2L given by: (simplified model)

pms

2ln2

L. D. Landau, Izv. Akad. Nauk. SSSR 17 (1953) 52P. Carruthers and M. Duong-Van, Phys. Ref. D8 (1973) 859

Pion production ~ Entropy Isentropic expansionDescription of the pion gas as a 3D relativistic fluid


Rapidity SpectraEnergy Dependence of Widths

Pion widths are closeto Landau prediction,but not perfectly

But: Perfect agreementto linear dependenceon ybeam


Rapidity SpectraEnergy Dependence of Widths

Linear dependenceon ybeam

Clear hierarchy forGaussian-like particles at SPS(p, , excluded):

> K+ > K-, >

Seems to break down at AGS


Rapidity SpectraMass Dependence of Widths

Approx. linear dependence on particle mass

Similar slope at all SPS energies

Thermal component of longitudinal flow

negatives


Rapidity SpectraDependence on Strangeness Content

Central Pb+Pb, 158 AGeV

Net protons: 3 valence quarks (uud )

Omegas: 3 produced quarks (sss )

Net s:1 valence (d ) + 2 produced quarks (ss )

Net s:2 valence (ud ) +1 produced quark (s )


Particle Yields

AGS NA49 BRAHMSCentral Au+Au, Pb+Pb

4 multiplicities only!


Particle YieldsStatistical Hadron Gas Model

Becattini et al., Phys. Ref. C69 (2004) 024905

Assumption of chemicalequilibrium at the freeze-out point

Particle production can be described with a few parameters: V, T, B, s

jsS


Particle YieldsPhase Diagram (II)

Chemical freeze-out pointsapproach phase boundaryat top SPS energies

Does the system cross the phase boundary ?And if yes, where ?


Particle YieldsEnergy Dependence

5.1

K+/+

K-/-

/

/

-/

-++/



5.1

UrQMDHSD

E.L. Bratkovskaya et al.,PRC 69 (2004), 054907

K+/+

K-/-

/

/

-/

-++/


Statistical hadron gasmodel: s = 1

P. Braun-Munzinger,J. Cleymans,H. Oeschler, and K. RedlichNucl. Phys. A697 (2002) 902


5.1

K+/+

K-/-

/

/

-/

-++/


Statistical hadron gasmodel: s free

F. Becattini,M. Gazdzicki,A. Keränen,J. Manninen,R. StockPRC 69 (2004), 024905


5.1

K+/+

K-/-

/

/

-/

-++/



5.1

K+/+

K-/-

/

/

-/

-++/


Particle YieldsComparison s- and s-Carriers

s-quark carriers: K-, K0 (1)

(incl. 0) 0,-, - (2)

± (3)

(1) K0 K+, K0 K- by isospin symmetry

(2) Taken from hadron gas fit by F. Becattini et al., if not measured.

(3) Empirical factor ( + ) / = 1.6 assumed.

s-quark carriers: K+, K0 (1)

(incl. 0) 0,+, + (2)

± (3)

Energy dependenceof strangeness productionchanges at 30 AGeV


Particle Yields(Anti-)Strangeness to Pion Ratio

Maximum in strangeness/pion ratio

Same for s and s quarks

Difficult to model Solid line: Statistical hadron gas model with s = 1 K. Redlich, priv. comm.

Predicted as signal for the onset of deconfinementM. Gazdzicki and M.I. Gorenstein, Acta Phys. Polon. B30 (1999), 2705


Transverse Mass Spectra

20 AGeV 30 AGeV

Central (7%) Pb+Pb

t

ttt

tt T

pI

T

mKm

dydmm

dN

1

01

tanh

sinhcosh

Schnedermann, Sollfrank, and Heinz,Phys. Rev. C46

Radial flow fit (“Blast Wave”)

Here: t independent of r



40 AGeV

80 AGeV

158 AGeV

Central Pb+Pb40+80 AGeV: 7%158 AGeV: 5%, 10%(), 23.5%()


Transverse Mass SpectraInverse Slope Parameters of Kaons

Step in energy dependence p+p compilation from:M. Kliemant, B. Lungwitz, and M. Gazdzicki, PRC 69 (2004) 044903Seems to be absent in p+p and models

How about other particle types?


Transverse Mass SpectraEnergy Dependence of mt-m0

Energy dependence of transverse activity seems to change around 30 AGeV.

General feature for pion, kaons and protons

Resonances or change of EOS?

negatively charged


Transverse Mass SpectraBlast Wave Model

t

ttt

tt T

pI

T

mKm

dydmm

dN

1

01

tanh

sinhcosh

Basic blast wave model: Common freeze-out of all particle types Boost invariant longitudinal expansion Transverse expansion is modelled by a velocity profile “Standard” version:

Schnedermann, Sollfrank, and Heinz,Phys. Rev. C46

Extended version: Resonance contribution included

Baryonic resonances introduce dependence on B

Chemical freeze-out: Tch and B taken from freeze-out curve

Thermal freeze-out: System cools down, therefore assume: Conservation of entropy Conservation of effective particle numbers

U. Wiedemann and U. Heinz, Phys. Rev. C56 (1997) 3265B. Tomasik, nucl-th/0304079



E895: nucl-ex/0306033NA49: Phys. Rev. C66 (2002) 054902, nucl-ex/0403023PHENIX: Phys. Rev. C69 (2004) 024904, nucl-ex/0307022

Convave Resonances

Exponential Shoulder Radial flow

- K- p


Transverse Mass SpectraEnergy Dependence of Fit Parameter

Fit to -, K- and p

Box-shaped source profileand linear velocity profile

Fit range 0.1 < mt-m0 < 0.8 GeV

Energy dependence of Tf seems to change around 30 AGeVThermal and chemical freeze-out different? Single freeze-out model?

Continous increase of T

Tch


FluctuationsSearch for the Critical Point

Endpoint of the first orderphase transition line crossover on left side

Position quite uncertain

But recent lattice calculations by Fodor and Katz predictsposition at B = 360 MeV usingphysical quark masses

If the above it true and the phase boundary is really reached at 30 AGeV, it might be accessible at the SPS

Event-by-event fluctuations


20 GeVpreliminar

y

FluctuationsParticle Ratios

preliminary

160 GeVCompare to mixed eventreference Resolution

Finite number statistics

Extraction of dynamical fluctuations

2dynamic = 2

data - 2mix

= RMS/Mean * 100 [%]

Event-by-event fluctuationsof e.g. K/

NA49

NA49


FluctuationsEnergy Dependence of K/ Fluctuations

preliminary

Clear energy dependenceof K/ fluctuations observed Decrease with energy

Fluctuation from UrQMD independent of energy

Non-zero value due to energy and strangeness conservation

Data wider than mixed eventsreference

Promising, but no clear evidence for critical point yet


Summary

Systematic study of energy dependence (still ongoing)– Rapidity and transverse mass spectra– Particle Yields– Fluctuations

A variety of interesting features have been revealed:– Mass dependence of rapidity widths, seemingly

independent of beam energy at SPS– Clear change of the energy dependence of mt-spectra

at 30 AGeV Evidence for a change of EOS?

– Maximum in the strangeness to pion ratio at 30 AGeV Evidence for deconfinement?

Outlook: Search for critical point– No clear evidence yet

dedicated search with future projects (SPS, FAIR)


The NA49 Collaboration

C. Alt, T. Anticic, B. Baatar, D. Barna, J. Bartke, L. Betev, H. Bialkowska, A. Billmeier, C. Blume, B. Boimska, M. Botje, J. Bracinik, R. Bramm, R. Brun, P. Buncic, V. Cerny, P. Christakoglou, O. Chvala, J.G. Cramer, P. Csató, N. Darmenov, A. Dimitrov, P. Dinkelaker, V. Eckhardt, G. Farantatos, D. Flierl, Z. Fodor, P. Foka, P. Freund, V. Friese, J. Gál, M. Gazdzicki, G. Georgopoulos, E. Gladysz, K. Grebieszkow, S. Hegyi, C. Höhne, K. Kadija, A. Karev, M. Kliemant, S. Kniege, V.I. Kolesnikov, T. Kollegger, E. Kornas, R. Korus, M. Kowalski, I. Kraus, M. Kreps, M. van Leeuwen, P. Lévai, L. Litov, B. Lungwitz, M. Makariev, A.I. Malakhov, C. Markert, M. Mateev, B.W. Mayes, G.L. Melkumov, C. Meurer, A. Mischke, M. Mitrovski, J. Molnár, S. Mrowczynski, G. Pálla, A.D. Panagiotou, D. Panayotov, A. Petridis, M. Pikna, L. Pinsky, F. Pühlhofer, J.G. Reid, R. Renfordt, A. Richard, 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, A. Wetzler, Z. Wlodarczyk, I.K. Yoo, J. Zaranek, and J. Zimányi


The End


Elliptic FlowEnergy Dependence

Mid-rapidity data,pt integrated

Change of energydependence of v2

between AGS and 40 AGeV


Rapidity SpectraRapidty Shift y

yP yT

y0

y y

y0

yP yT

y y y’Py’T

How does the rapidity shift y evolve with beam energy?

Determines the energy available in the produced fireball

Baryon number distributions at

lower energies: higher energies:


Rapidity SpectraEnergy Dependence of y

BRAHMS, I.G. Bearden et al.PRL 93 (2004), 102301

py BB

partp

p

dydy

dNy

Ny

yyy

0

)(2

Seems to increase linearly at AGS and SPS:

y /ybeam 0.27

Rapidity shift:

But: Weaker increaseto RHIC energies!

dyydy

dNmE BBy

y yT

p

p

cosh)(

Energy loss E :

RHIC (sNN = 200 GeV): E/Nucleon = 73 ± 6 GeV


Rapidity Spectra Energy Dependence of Net-Protons

BRAHMS, I.G. Bearden et al.PRL 93 (2004), 102301

The shape of the distributionschanges dramatically with energy

AGS: baryonic system RHIC: mesonic system Large implications in the hadronic sector



Central Pb+Pb/Au+Au

Mid-rapidity ratios


Transverse Mass SpectraThe Omega

Evidence for earlyfreeze-out of the Omega from blast wave fits?

Blast Wave Model

VelocityProfile

Tf (MeV) t

A constant 125 0.5 from fits shown before

(*) M.I. Gorenstein, K. A. Bugaev and M. Gazdzicki, PRL. 88 (2002), 132301.

Fit to K, p, , 0.590linearB1

Fit to J/ and ’ (*)0.2170linearB2

NA49 publication:C. Alt et al., nucl-ex/0409004



Hydro calculation

M. Gazdzicki, M.I. Gorenstein, F. Grassi, Y. Hama, T. Kodama, and O. Socolowski Jr.,Braz. J. Phys. 34 (2004), 322, hep-ph/0309192

Assuming 1st orderphase transition

Initial conditions from NeXus

Pure Landau initial conditions do not allow for simultaneousdescription of all observables (y-, mt-spectra, yields)



Model comparisons

M. Bleicher, SQM04

Additional resonances?UrQMD 2.1

Initial QGP pressure?


Elliptic FlowEnergy Dependence

30 AGeVData shows saturation of scaled v2

High mass resonances like in UrQMD 2.1 can not explainv2 above 40 AGeV

Strong hint for initial QGP pressure from30 AGeV on !M. Bleicher, SQM04


FluctuationsEnergy Dependence of p/ Fluctuations

Clear energy dependenceof p/ fluctuations observed Increase with energy

preliminary

Similar trend seen in UrQMD Resonance contribution changes with beam energy

Data narrower than reference Can be caused by resonances


Rapidity SpectraKaons

Single Gaussian worksreasonably well for K-

Does not really work for K+ at lower SPS energies

Use RMS


Heavy Ion Physics at the CERN SPS NA49 Strangeness measurements

Energy K+ K- - + - +

158 AGeV pub. pub. pub. pub. pub. pub. pub. pub. sub. sub.

80 AGeV pub. pub. pub. prel. pub. pub.

40 AGeV pub. pub. pub. prel. pub. pub. prel. sub. sub.

30 AGeV prel. prel. prel. prel. prel. prel.

20 AGeV prel. prel. prel. prel. prel. prel.

: Phys. Lett. B491 (2000) 59: Phys. Rev. Lett. 93 (2004) 022302: Phys. Lett. B538 (2002) 275: nucl-ex/0409004K, : Phys. Rev. C66 (2002) 054902

Minimum Bias Pb+Pb andC+C, Si+Si at 40 and 158 AGeV

Central Pb+Pb:

recent results from the sps christoph blumeexploring the phase diagram of strongly interacting...

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