sps energy scan results and physics prospects at fair

SPS energy scan results and physics prospects at FAIR

Claudia Höhne, GSI Darmstadt

2 Claudia Höhne Quark Matter 2009, Knoxville

Outline

• SPS energy scan overview

• hadron production and the search for the onset of deconfinement

• hadron production, strangeness, BE correlations

• search for the critical point

• fluctuations

• study of the strongly interacting medium with medium probes

• (mini-)jets, dileptons

• future explorations

• energy scans at RHIC and SPS

• HADES and CBM at FAIR


SPS low energy scan

beam energy

[A GeV]

experiments main observables (energy dep.)

40, 80, 158 NA45/ CERES di-electrons, <pt> fluc., HBT

20, 30, 40, 80, 158 NA49 hadrons, strangeness, fluctuations, HBT, flow, light fragments, correlations

40, 158 NA57 strange hyperons

Proposed by NA49 already in 1997 (CERN/SPSC 97-26)

SPS Pb+Pb runs at energies below top beam energy (158A GeV for Pb):• 40A GeV test in 1998, 5 weeks in 1999• 80A GeV 5 days in 2000• 30A GeV and 20A GeV 7 days each in 2002

• NA50 – 40A GeV: pseudorapidity distributions• NA60 – 20, 30A GeV: commisioning run, pseudorapidity distr.

Very successful program!


Hadron yields

in addition:

• J/ at 158A GeV (NA50, NA60)

• low-mass di-leptons at 158A GeV (CERES, NA60) and 40A GeV (CERES)

• , , at 40 and 158A GeV (NA57)

• lower energies: HADES, FOPI

4 yields

[compilation by C. Blume (NA49)]

• enormous wealth of data

• however: low-energy data are missing for less abundant particles!

• rapid change of B

AGS SPS RHIC


• bag model EoS with a strong 1st order phase transition (UrQMD + hydro)

“step” in transverse momentum

• mixed phase: pressure and T independent of → weak increase of slopes of pt-spectra

• behavior can only be explained assuming a phase transition

[H. Petersen et al., arXiv:0902.4866]

[M. Gazdzicki et al, Braz. J. Phys. 34, 322 (2004)]

[L. van Hove, Phys.Lett.B 118, 138 (1982)][M. Gorenstein et al., Phys. Lett. B 567, 175 (2003)]

• hydrodynamic calculation including a phase transition

• similar behavior in <mt> seen for other particles: , K, p, , ,

• however: low energy data missing

[NA

49:

Ph

ys.R

ev.

C77

:024

903,

200

8]


“kink” in entropy production

41

43

2

NN

pNN

s

msF

increase of <>/Nw (measure of entropy production) in PbPb compared to pp

→ increase of No. of degrees of freedom due to deconfinement

[Gazdzicki, Gorenstein, Acta. Phys. Polon. B30, 2705 (1999)]

[NA

49:

Ph

ys.R

ev.

C77

:024

903,

200

8]

extraction of sound velocity cs2

from the width of rapidity spectra

→ softest point of EOS (minimum of sound velocity) at 30A GeV?!

[H. Petersen and M. Bleicher, PoS CPOD2006:025,2006]


“horn” in relative s-production

• maximum in relative strangeness production – approximated by Es

• different energy dependence than in pp

• data best described assuming a phase transition

23

2 KKES

• not reproduced by hadron gas models (HGM)[J.Cleymans et al, PRC 60, 054908 (1999); P.Braun-Munzinger et al., NPA 697, 902 (2002)]

• nor by UrQMD, HSD[E.L. Bratkovskaya et al., PRC 69, 054907 (2004)]

• but actually predicted for a phase transition (SMES)[Gazdzicki, Gorenstein, Acta. Phys. Polon. B30, 2705 (1999)]

[NA49: Phys.Rev.C77:024903,2008]


Maximum in strangeness production

• in statistical models:clear max. in /- (broad in K+/+) ratio result of increasing (limited) T and decreasing B

• new analysis:improved hadron resonance mass spectrum (, higher masses!)→ enhanced production by e.g. K* excitations

• exp. rising mass spectrum with Hagedorns temperature parameter→ even stronger effect (dashed line)

→ peak sharpened, in particular K+/ ratio lowered at high energies

→ complete explanation?

[A. Andronic et al., Phys. Lett. B 673 (2009) 142]


Temperature saturation in chemical freeze-out

• chemical freeze-out (fit T, B, V): temperature saturates for √sNN > 10 GeV although energy density (and initial T) still increases

→ phase boundary reached, additional energy goes into heating the QGP

• occurs at the same energy at which mesons start to carry the larger part of the entropy – accidentally?

[A. Andronic et al., Phys. Lett. B 673 (2009) 142] [H.Oeschler et al., J.Phys.G 32, 223 (2006)]

s/T

3


Properties of hadronic freeze-out

[A. Andronic et al., arXiv:0901.2909]

• volumes determined from chemical freeze out (statistical model) and BE correlations of pions (collisional freeze-out)

• both volumes show minimum at SPS energies (not to be compared directly!)

line to guide the eye

223

2 sidelongHBT RRV

Combined analysis of BE correlations of pions and pt-spectra:

plateau in the averaged phase-space density at SPS

→ -density transformed into new degrees of freedom, -density from later freeze-out

[S.V.Akkelin and Yu.M.Sinyukov, Phys.Rev.C 73, 034908 (2006)]

HBT results:[NA49: Phys.Rev.C 77, 064908 (2008)][CERES: Nucl.Phys.A 714, 124 (2003)][CERES: D. Antonczyk, talk at WPCF 2008, proc. to be published in Acta Phys.Pol.B]


Universal freeze-out? – Pion mean free path

[compilation by S. Schuchmann (CERES)]

NN

V

N

V

NN

ff

ff

1

• mean free path of pions at freeze out:

• f freeze out density, NN, N at midrapidity

• minimum in Vf correlated with baryon → meson dominance phenomenon

• appr. universal pion freeze out f ~ 1fm

Speculation:

• larger f at lower SPS energies?

→ slower expansion of the system/ more diffusive character

→ softest point (EoS)?

Softest point seen in elliptic flow?

… data at 40A GeV not conclusive

[CERES, Phys.Rev.Lett 90, 022301 (2003)]


Centrality/ System-size dependence

• additional degree of freedom: centrality/ smaller A

• How does the transition between pp and PbPb look like?

[NA49: Phys.Rev.C77:024903,2008]

23

2 KKES


Centrality and energy dependence of hyperons

• enhancement factors of up to 20 for !

• difficult to explain in hadronic models

• ok for hadronization at the phase boundary

[NA57: J.Phys.G 35, 044005 (2008)]

see also:[NA49: Phys.Rev.C 78, 034918 (2008), Phys.Rev.Lett. 94, 192301 (2005)]

[P. Braun-Munzinger et al., Phys.Lett.B 596, 61 (2004)]

40A GeV

158A GeV• top SPS (and RHIC):

strangeness in equilibrium (stat. models, larger B?

multi-s hyperons missing!)


• saturation behavior at different energies? – shape study by comparing <K+>/<-> normalized to 1 in central Pb+Pb/ Au+Au

• different for low and high energies – data at 40A GeV in transition region?

• SIS energies: explained by canonical s-suppression in statistical hadron gas model with V ~ Nw

Change of centrality dep. of rel. s-production

C. Blume, C.H. (NA49), Poster, Topic 5

• top SPS/ RHIC: rise in stat. model from can. s-suppr. with V ~ Nw too fast

→ redefine volume by cluster size from percolation model

→ Core-Corona approach

Speculation:

Volume relevant for strangeness conservation differs at low and high energies (hadronic/ partonic)


Phase Diagram

chemical freeze-out systematics (statistical model fits of hadron yields) versus phase transitions from LQCD

[A. Andronic priv. com., analysis in Phys. Lett. B 673 (2009) 142][CP: Z. Fodor, S.D. Katz, JHEP 0404 (2004) 50]

SPS !

Onset of deconfinement at ~ 30A GeV?!

CP?

Medium properties?

high baryon density,

resonances!

quarkyonic matter?

[quarkyonic matter: L. McLerran arXiv:0808.1057]

•RHIC – crossover at low B

•SPS – finite B: 1st order phase transition, CP?


Event-by-event fluctuations: Critical point?

• experimentally difficult, interpretation: many sources may contribute

• fluctuations studies performed• mean-pt fluctuations• multiplicity fluctuations• net electric charge fluctuations• particle ratio fluctuations

• effects under discussion for explanation• HBT, Coulomb interactions, jets• geometry (smaller systems, percolation)• fluctuations in the number of participants• hadronisation, resonance decays• Number of participants/ accepted particles

K. Grebieszkow (NA49), Thu. April 2, session 4B

[NA49, arXiv:0810.5580,PRC acc.][NA49, Phys.Rev.C 70, 034902 (2004)][CERES, Nucl.Phys.A 727, 97 (2003)][NA49, Phys.Rev.C 78, 034914 (2008)][NA49, Phys.Rev.C 70, 064903 (2004)][NA49, arXiv:0808.1237, PRC acc.]…

[CERES, Nucl.Phys.A 811, 179 (2008)][E.G. Ferreiro, et al., Phys.Rev.C 69, 034901 (2004)][V. Konchakovski et al., Phys.Rev.C73, 034902 (2006)][J. Zaranek, Phys.Rev.C66, 024905 (2002)][D.Kresan, V.Friese, PoS CFRNC2006:017,2006][V. Koch, arXiv:0810.2520]…

• future proposal: baryon number fluctuations!


Medium probes

• investigate observables being sensitive to the high density/ partonic phase

• elliptic flow – unfortunately not conclusive

• J/ – not measured below 158A GeV

• direct photons – not measured below 158A GeV

• Dileptons – spectrum strongly modified by the medium

• Jets – influence of medium on the away side *

→ (mini-)jets at top SPS energies: away side shows medium behavior

Jets at SPS:H. Appelshäuser (CERES), Tue. March 31, session 1AM. Szuba (NA49), Tue. March 31, session 1A


Two particle angular correlations at high pt

M. Szuba (NA49), Tue. March 31, session 1A

• near side correlation disappears at low energies – however: same trigger pt for all

• away side plateau at all energies trigger: 2.5 < pt < 4 GeV/cassociate: 1 < pt < 2.5 GeV/c

158A GeV√sNN = 200 GeV

80A GeV

40A GeV 30A GeV 20A GeV


Dileptons (I)

[CERES: Phys.Rev.Lett. 91, 042301 (2003); Eur.Phys.J.C 41, 475 (2005)]

5.9±1.5 ±1.2 ±1.8

2.31±0.19 ±0.55 ±0.69

• dileptons as direct probe of the high density phase

• NA60! → “melting” of -meson, radial flow of dileptons, thermal radiation

• excess higher at lower energy: importance of baryon density!


preliminary

Dileptons (II)

[CERES: Phys.Lett.B 666, 425 (2008)][R. Rapp, J. Wambach, Eur. Phys. J. A 6 (1999) 415.]

• high energies: main source: +- e+e-

• Strength of dilepton yield at low masses is due to coupling to baryons!

Pb+Au 158A GeV

F. Krizek (HADES), Thu. April 2, session 3C

+

N-1

π

Δ(1232)

>

>

N*(1520)

N-1

N*

N

*

e+

e-

explains C+C!


Status and Future

• evidence for onset of deconfinement

→ distinct changes in the behavior (yields, spectra) of emitted particles

• evidence for softest point?

→ elliptic flow data, BE of pions: indications but not conclusive

• medium properties?

→ medium influences away side of jets, di-leptons: indications but more data and statistics missing!

• evidence for critical point?

→ fluctuation measurements not conclusive

→ after qualitative exploration with SPS energy scan try to quantify the properties of the created media (partonic phase/ hadron gas/ dense baryonic phase)

→ search for first order phase transition, critical point, chiral phase transition


Future explorations

E. Sangaline, (RHIC), Poster, Topic 9 L. Kumar (STAR), Tue. March 31, session 2B

complete scan of the QCD phase diagram with modern, 2nd generation experiments on the horizon!

30A GeV

• RHIC beam energy scan- evolution of medium properties- “turn-off” of established signatures- search for CP and PT

• NA61 at SPS (2007 acc. by SPSC)- search for CP and PT in energy-system size scan

• both essentially limited to high yield observables- RHIC: energy dependent

• FAIR and NICA- new accelerator projects- FAIR: high intensities! → rare probes!

A. Laszlo (NA61), Thu. April 2, session 4BJ. Heuser (CBM), Thu. April 2, session 4B


CBM physics program

Search for signatures of a phase transition (and CP) by scanning carefully excitation functions of bulk and rare observables

• deconfinement phase transition at high B

• energy dependence and flow of strangeness and charm• melting of J/ and ’

• QCD critical endpoint• excitation function of event-by-event fluctuations

Quantify properties of the medium

• equation of state at high B

• collective flow of hadrons• particle production at threshold (charm)

• onset of chiral symmetry restoration at high B

• in medium modifications of hadrons (,,→e+e-(+-), D)

• medium properties (energy density, viscosity, ….)• flow, dileptons, charm propagation, multistrange hyperons,…

“CBM physics book” to be submitted soon


Physics prospects with CBM (I)

• CBM at SIS 300 will start in 2017: 10-45A GeV beam energy, high availability of beam (order of 10 weeks per year), interaction rates up to 10 MHz

• CBM and HADES at SIS 100 in 2015Au beam up to 11A GeV, p beam up to 30 GeV(dileptons, multistrange hyperons, charm production in pA)

• assume 10 weeks beamtime, 25A GeV Au+Au (minbias), no trigger, 25 kHz interaction (and storage) rate:

• “unlimited statistics” of bulk observables, e.g. ~1010-11 kaons, 1010 Λ• low-mass di-electrons with high statistics, 106 , , -mesons (each)

• multistrange hyperons with high statistics, 108 , 106

→ yields, spectra, flow of identified particles, correlations, fluctuations

→ scaling behavior of flow, EOS→ s-equilibrium, precise locations of freeze-out points, kinetic freeze-

out (deviations/ early decoupling?)→ pt-dependent medium modifications (di-electrons)


Physics prospects with CBM (II)

• assume 10 weeks beamtime, 25A GeV Au+Au (minbias), open charm trigger, 100 kHz interaction rate

• open charm with good statistics: D0, D±, DS, Λc – order of 104 each→ yields, spectra, flow?

• assume 10 weeks beamtime, 25A GeV Au+Au (minbias), charmonium trigger, max 10 MHz interaction rate

• charmonium with good statistics: 106 J/ , chance to see ’ (103)

→ yields, spectra, flow


Charm propagation

[HSD: O. Linnyk et al., Int.J.Mod.Phys.E17, 1367 (2008)] [SHM: A. Andronic et al., Phys. Lett. B 659 (2008) 149]

Propagation of produced charm quarks in the dense phase –quark like or (pre-)hadron like?

• charmonium to open charm ratio as indicator• indications of collectivity?


CBM @ FAIR

HADES: di-electrons, hadrons for 2-10A GeV beam energy

CBM: hadrons and leptons including rare probes (charm, dileptons) for 2-45A GeV beam energy

→ high rate and high precision detector system with state-of-the art technology

J. Heuser (CBM), Thu. April 2, session 4BA. Lymanets (CBM), Poster, Topic 9C.H. (CBM), Poster, Topic 9

FAIR: brilliant heavy-ion beams with intensities up to 109/s with extended running periods!

SIS100 – start in 2015SIS300 – 2017


D → K π π, cτ= 317 μm109 centr. ev.

eff = 2.6%

S/B = 2.4 (D-)

1.1 (D+)

D0 → K π, cτ= 123 μm1010 centr. ev.

eff = 4.4%

S/B = 6.4 (D0) 2.1 (D0)

_

Simulation of open charm reconstruction

• STS – 8 double-sided Si micro-strip sensor stations (each 400 m Si equ.)

• MVD – 2 MAPS pixel sensors (300 m, 500 m) at z = 5 cm, 10 cm

• no K, id.; p rejection via TOF; 2ndary vertex resolution ~ 50 m

1012 minbias events25A GeV Au+Au

~ 7k D0 + 20k D0 ~ 12k D+ + 26k D-


CBM feasibility studiesfeasibility studies performed for all major channels including event reconstruction and semirealistic detector setup(UrQMD: central Au+Au collisions, 25A GeV – rare probes embedded)

J/J/

' '

strange hyperons di-electrons di-muons

200 k events

4·1010 events

4·108 events

3.8·1010 events

105 events

4.5∙106 events


Summary

• The SPS low-energy scan – a very successful endeavour:

→ evidence for the onset of deconfinement in A+A collisions at ~ 30A GeV

→ observations and indications of distinct changes:

• kink in <>/Nw

• max. in relative s-production• constant <mt> in SPS energy range• saturating Tchem

→ medium effects seen in (mini-)jets, dileptons

→ observations cannot be explained in purely hadronic models

• Future projects for comprehensive investigations, deeper understanding, search for phase transition and critical point

→ program for many years!

→ SPS and RHIC energy scans for high yield observables

→ FAIR with the CBM and HADES detectors which are designed for systematic studies of bulk and of rare observables with excellent statistics

• A lot of work ahead of us

• collapse of p-flow?• min. in cs

2

• min. in VHBT, larger f?• s-saturation in centrality dep.


The end

Thanks for stimulating discussions and support to

Anton Andronic, Harald Appelshäuser, Christoph Blume, Peter Braun-Munzinger, Marek Gazdzicki, Falk Pühlhofer, Peter Senger, Peter Seyboth, Reinhard Stock, Joachim Stroth

and all the colleagues in the NA49 and CBM collaborations

sps energy scan results and physics prospects at fair

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