What is SO special about strangeness in heavy ion

collisions ?

Rene Bellwied Wayne State University

7th International Conference on Strangeness in Quark Matter

North Beach, March 12-17, 2003

A connection to cosmology

• Essential: Witten’s ‘Cosmic Separation of phases’ (Phys.Rev.D 30 (1984) 272) and his idea of strange quark matter.

• The impact on cosmology might be far reaching and definitely affected the search for strangeness enhancement in general and strange quark matter in particular (see Jack Sandweiss talk).

• Strange Quark Matter is still considered a possibility for stable or metastable matter in the universe.

Two recent examples in astrophysicsFundamental paper on ‘How to identify a strange star’ by Jes Madsen, PRL 81 (1998) 3311Recent measurements by Drake et al. and Helfand et al. in 2002 with the Chandra X-ray telescope (see Markus Thoma’s talk)

These two NASA Chandra X-ray Observatory images show two stars - one too small, one too cold - that reveal cracks in our understanding of the structure of matter. (AFP)

RXJ18563C58

Did quark matter strike the earth ?Two anomalous seismic events occurred in 1993, and were measured independently by 9 monitoring stations.

Strange quark matter should pass through the earth at 400 km/s (40 times the speed of seismic waves), i.e. search for seismic events not connected with traditional seismic disturbances e.g. earth quakes. (Herrin et al., SMU, 2002)

What can we do in the laboratory ?

The idea of strange quark matter did not only initiate strangelet searches (see Jack’s talk) but led also to potential signatures for the QGP phase transition.

Increasing strangeness enhancement as a signal for QGP and strangeness equilibration as a signal for thermalization of the particle emitting source were for years at the forefront of our research.

Re-invent strangeness as a QGP signature

• 2000’s: parton quenching (strange particles as leading jet particles), timescales (strange resonances), fluctuations (strange particles e-by-e), partonic flow (radial and elliptic flow of strange particles)

• 1990’s: Strangeness enhancement (multistrange antibaryons as function of system size and beam energy)

• Early 80’s: Strangeness enhancement (K/ and later anti-baryon/baryon as function of beam energy (Rafelski, Mueller, Koch et al.)

• Late 80’s: Strangeness equilibration (strangeness production in thermal models as signal for phase equilibration and collective flow)

History of strangeness enhancement• K/ – the benchmark for abundant strangeness production:

K/

K+/

[GeV]

The impact of baryon density• K-/ – is a simple function of baryon density

STAR preliminary

STAR preliminary

see talk by M.Velkovsky

NA49: volume effects (saturation ?)• Compare:

different system sizes at common incident energy

• Search for better scaling variable than Npart

• Good measure: mean collision density in space and time

(UrQMD simulation)

See talks by Ingrid Kraus & Jean Cleymans

Wroblewski factor evolution

Wroblewski factor dependent on T and B

dominated by Kaons

Lines of constant S

<E>/<N> = 1 GeV

I. Increase instrange/non-strangeparticle ratiosII. Maximum isreached

III. Ratios decrease(Strange baryonsaffected more stronglythan strange mesons)

Peaks at 30 A GeV in AA collisions due to strong B dependence

mesons

baryons

hidden strangeness mesons

PBM et al., hep-ph/0106066

total

Experimental

4 yieldsmid-rapidity yields

New machines to explore the high density regime

new European ‘can-do-all’ facilitysee talk by H.Gutbrod

A new European heavy-ion and anti-proton machine

A complementary high energyhadron facility in Japan (JHF)

Strangeness enhancement in B/B ratios

• Baryon over antibaryon production can be a QGP signature as long as the baryochemical potential is high (Rafelski & Koch, Z.Phys. 1988)

• With diminishing baryochemical potential (increasing transparency) the ratios approach unity with or without QGP, and thus only probe the net baryon density at RHIC.

New RHIC data of baryon ratios

• The ratios for pp and AA at 130 and 200 GeV are almost indistinguishable. The baryochemical potentials drop from SPS to RHIC by almost an order of magnitude to ~50 MeV at 130 GeV and ~20 MeV at 200 GeV.

STAR p+p 200 GeV

STAR preliminary BRAHMS, PRL

nucl-ex/0207006

See talk by J.H.Lee

Strangeness enhancement in yields

• Enhancement factors up to 20 (!) comparing pp to AA for . Still very large centrality dependence for . See talks by C.Meurer, M.Mitrovski, L.Sandor

STAR Preliminaryequilibration volume ?

Tounsi et al.

Is strangeness still enhanced at RHIC ?

NA49 preliminary

• Anti-strange baryon production is a measure of enhancement, whereas strange baryon production at RHIC is strongly affected by vanishing net baryon density

Strangeness thermalization: Do yields (ratios) agree with the statistical

model picture ?

Are thermal models boring ?

Good success with thermal models in e+e-, pp, and AA collisions.Thermal models generally maketell us nothing about QGP, but (e.g. PBM et al., nucl-th/0112051):

Elementary particle collisions: canonical description, i.e. local quantum number conservation (e.g.strangeness) over small volume.Heavy ion collisions: grand-canonical description, i.e. percolation of strangeness over large volumes, most likely in deconfined phase if chemical freeze-out is close to phase boundary.

Do we understand strangeness production ?

• Chemical (and thermal) equilibrium models describe the data, so do non-equilibrium models ! Is equilibrium an applicable concept ? (see QM round table discussion)

• Even if we assume thermal equilibrium, do we understand production on a microscopic (partonic) level ? Not really.

Radial flow and thermalization ?

see Javier Castillo’s talk

STAR preliminary

STAR preliminary

Common parametrization of flow ?

• Do particles with smaller interaction cross section decouple earlier and still show transverse flow ?

• Blast wave parametrization fits for NA49 & STAR

,

,K,P,

NA49 – PbPb 158 A GeV

STAR preliminary

Particle identified elliptic flow

• v2 measurements: , k, p, flow, do and flow ?

see talk by Paul Sorensen

STAR preliminary

RHIC Particle Spectra at 200 GeV

BRAHMS: 10% centralPHOBOS: 10%PHENIX: 5%STAR: 5%

see PHOBOS talk by Gabor Veres

Strangeness pushing the boundaries of particle identification

One sees the mass dependence of the transverse expansion, which is well described by thermal and hydrodynamics models

preliminary preliminary

Strange jet-like particles• R(AA) & v2 measurements in Au-Au (see talks by Hui Long, Paul Sorensen and Julia Velkovska)

Effects due to:initial state (gluon saturation)or final state (partonic energy loss, quark coalescence, hadronic/partonic flow) ?

Is there a mass dependenceor a flavor dependence ?

Note: show no suppressionout to 3 GeV/c (similar to PHENIXprotons and D-mesons)

Interplay between soft and hard processes (Vitev et al., QM 2002)

+bar/K0s

preliminary

see talks by B.Norman and H.Long

Strange resonances in medium

Short life time [fm/c] K* < *< (1520) < 4 < 6 < 13 < 40

Red: before chemical freeze outBlue: after chemical freeze out

Medium effects on resonance and their decay products before (inelastic) and after chemical freeze out (elastic).

Rescattering vs. Regeneration ?

see talks by:L. GaudichetH. ZhangJ. MaP. FachiniD. Jouan

Resonances come into their own• Resonances tells us about production, rescattering, and

regeneration & medium modifications• Resonances tell us about timescales (together with

balance functions & HBT measurements)

Giorgio Torrieri and Johann RafelskiPhys.Lett.B509:239-245, 2001

STAR preliminary

-measurements at SPS & RHIC• The is interesting in terms of thermal radial flow and in terms of

medium modifications.

• NA50 / NA 49 difference due to different decay channels (i.e. medium modifications) ? PHENIX will do precision measurement in the K+K- and the e+e--channels

see J.Ma’s talk

Some puzzles along the way

Large ratio at AGS (and SPS) still not understood

1.0

2.0

3.0

4.0

/ p

AGS:measured by E864/E878confirmed by E917SPS:measured by NA49RHIC:measured by STAR

Sub-threshold Kaon production (KaOS)

see Andreas Foerster, Laura Tolos & Christoph Hartnack talks

Recent non-RHIC measurement production in Au-Au collisions at 6 A GeV (E895@AGS)

see Paul Chung’s talk

Future measurement of interest • Hyperon polarization in AA: is measured (E896 @ AGS) and in

agreement with pp and pA data, but pp and pA data from FNAL show intriguing differences between and their antiparticles

What did we learn in pp ?

STAR p+p 200 GeV

STAR preliminary

see talks by: A. Billmeier, R. Witt & posters by: M.Heinz and J.Adams

STAR preliminarySTAR preliminary

What is to come in pA ?use particle identifiedstrange particle spectrafrom the RHIC dA run:

a.) as reference forstrangeness enhancement& production mechanisms

b.) as reference for high pt phenomena: (Cronin, jet quenching, quark coalescence)

P.B. Straub et al., PRL 68 (1992)FNAL experiments measuring R (W / Be) for identified particles at s of 27.4 and 51.3 GeV.

Main topics for the ‘new’strangeness

• Can we prove that we have buildup of transverse and elliptic flow in the partonic phase by measuring multistrange baryon elliptic, transverse, and directed flow ?

• Can we show that high pt particle suppression (measured through R(AA), v2, and back-to-back jets) is due to final state effects (e.g. quenching in the QGP) and that these effects are flavor and/or mass dependent by measuring K+,K-,K0, -bar, -bar R(AA) functions ?

• Can we determine timescales for all phases of the collision and quantify medium modifications by precisely measuring the generation, rescattering, and regeneration of strange resonances ?

• We need pp and pA reactions for reference

We have come a long way !

4th SQM 98, Padova,RHIC summary talk:

Yes !?!

Well, maybe ….

Let’s just waitand see !

Yeah !

Heck, YEAH !!

Strangeness is alive & well

• The systematic studies of strangeness production have entered a very sophisticated stage (volume effects, timescales, medium effects)

• We have a program that is relevant at high energies (RHIC,LHC) and high densities (new facilities in Europe and Japan).

• Old ‘smoking guns’ (e.g. strangeness enhancement) get replaced by new ‘smoking guns’ (e.g. strangeness quenching and flow).

There will be plenty more SQM’s to make Jan’s day !!