XXXIII International Symposium on Multiparticle Dynamics, September 7, 2003Kraków, Poland

Manuel Calderón de la Barca Sánchez

STAR Collaboration

Review of Spectra at RHIC

Review of Spectra at RHIC

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Outline First of all, there’s too much data!!

Focus on some recent results and analyses BRAHMS PHOBOS PHENIX STAR

Low, Intermediate, High-pt

Can we understand it? Can at least some of it be synthesised?SpectraFlow

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Particle Spectra in Au+Au, STAR |y|<.5

Hydro inspired “Thermal” Fits (input to Blast-Wave parameterization) (T, t) = (170 MeV, 0.6c) Large transverse flow component in central collisions.

STAR Preliminary

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Hydrodynamics Equation of State

Low pt, 99.5% of particles are below 2 GeV.

Hydrodynamics describes bulk particle momentum distributions

Hydro is limit of zero mean free path…early phase dominated by strong interactions?Calculations too long a system lifetime (still work to do)Enormous initial pressure, but decouples quickly (~10 fm/c)

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Spectra at large y, BRAHMS.

y=3 Thermal fit

T = 0.42

T = 140 MeV

y=0 Thermal fit

T = 0.53

T = 138. MeV

y=3

Radial flow decreasesat large rapidity.Boost invariant region is onlyabout 1 unit wide! 3-D hydro

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Charged hadrons at large , PHOBOS

T. Hirano

Hydrodynamics:Mid-rapidity data is well described, but larger rapidity is not.

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Particle Ratios and Statistical Models

Statistical models do a very good job.Values Tch are very close to expected Tcrit from lattice.

However, this alone cannot prove a phase transition nor that the system is thermal; but coupled with agreement from hydrodynamics (spectra and v2), evidence starts to increase…

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Intermediate pt, spectra for various masses

Yield of p () similar to (K) at ~3 GeV, flow effect for heavierparticle/baryon?

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Compare with scaling by Ncoll…

K0s and 0 show

suppression at 2-3 GeV, p and do not… strong radial flow for heavier particles?

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Particles with Similar Mass

Differ at low pt, similar at ~3 GeV

Reflection of Flow? Rescattering? Recombination?

Rescattering has effect on other observables: resonances! (See Patricia’s talk)

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Wealth of data!

It is very important to try to understand as much of the combined measurements as possibleUnder a single framework!

Many times, predictions work for observable A but fail for observable B. Need a coherent picture!

Some recent ideas:Hydro-inspired Blast-wave (won’t go into it)Recombination+FragmentationSingle Freeze-out

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Fragmentation + Recombination

qq

q

Baryon1

Meson

Fragmentation

q q

q q q

Baryon1

Meson

Recombination

M Q B Q2 3p p p p Bass et al. nucl-th/0306027

Lopez, Parikh, Siemens, PRL 53 (1984) 1216:Net charge and baryon number fluctuations [Asakawa, Heinz, BM, PRL 85 (2000) 2072; Jeon, Koch, PRL 85 (2000) 2076]

Balance functions [Bass, Danielewicz, Pratt, PRL 85 (2000) 2689]

Recombination / coalescence [Fries, BM, Nonaka, Bass, nucl-th/0301087; Greco, Ko, Levai, nucl-th/0301093; Molnar, Voloshin, nucl-th/0302014]

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F+R: Model assumptions

at low pt, quarks and antiquarks recombine into hadrons locally “at an instant”:

hadron momentum P is much larger than average momentum Δp2 of the internal quark wave function of the hadron; features of the parton spectrum are shifted

to higher pt in the hadron spectrum parton spectrum has thermal part (quarks) and

a power law tail (quarks and gluons) from pQCD.

qq M qqq B

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Does it fit the measured spectra?

Teff = 350 MeV blue-shifted temperature

pQCD spectrum shifted by 2.2 GeV

R.J. Fries, B. Müller, C. Nonaka, S.A. Bass; PRL 90 202303 (2003)

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For identified particles…, K

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…p, , , ,

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Ratios vs pt

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High pt suppression.

Reproduces charged hadron suppression, and flavor dependence.Prediction, quenching for protons above 6 GeV, where fragmentation starts to dominate

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What about v2?

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Does v2 reflect partonic flow?

Recombination model suggests that hadronic flow reflects partonic flow (n = number of valence quarks):

2 2v vhad partn

had partT Tp np

Provides measurement of partonic v2 !

P. Sorensen (UCLA – STAR)

Quark v2

See also: Lin & Ko, PRL 89 (2002) 202302; Molnar & Voloshin, nucl-th/0302014

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Identified Particle Spectra at RHIC @ 200 GeV

Feed-down matters !!!

BRAHMS: 10% centralPHOBOS: 15%PHENIX: 5%STAR: 5%

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Single freeze-out model, Tch = Tkin?

W. Broniowski and W. Florkowski, PRC 65 064905 (2002), for 130 GeVA. Baran, W. Broniowski, W. Florkowski nucl-th/0305075 for 200 GeV ratios and spectra.

Very nice feature, includefeeddown in the calculations.

Describe spectra and ratiosvs pt and vs centrality well

Supports the use of thermal approach to heavy ion collisions

If Tch=Tkin, very explosive expansion!

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High-pt: Latest news from the d+Au run

In Au+Au, suppression of high-pt hadrons and of away side jet, not seen in d+Au. Final state effect…consistent with the production of dense matter!!

From cover ofPRL 91 (2003)

072302 Phobos072303 Phenix072304 Star072305 Brahms

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Summary & Conclusions All 4 RHIC experiments have continued their outpour

of measurements. Low pt spectra, hydrodynamic fits, statistical models

taken together yield support (albeit don’t prove) to a high density thermalized phase. Still trouble in the longitudinal direction (HBT, v2 vs y)

We are beginning to see more theoretical efforts that encompass various observables! That is good! Spectra, flow, correlations. Would like to understand in

one picture, pt, y and centrality dependence. Fragmentation + Recombination: aplicability of the

recombination regime to 3-6 GeV, fragmentation dominates at a higher pt than one naïvely expected.

v2 of hadrons reflects v2 of constituent quarks (? and !)

High-pt spectra and correlations: suppression of hadrons and away-side jet is a final state effect.