A probe for hot & dense nuclear matter.

Lake Louise Winter Institute 21 February, 2000

Manuel Calderón de la Barca Sánchez

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Heavy Ions & QGP

• Aims to probe nuclear matter at high energy densities

• Goal is to study the predicted transition from ordinary nuclear matter to quark matter, and to actually create such a state of freely interacting quarks & gluons.– Can we understand nuclear physics with quark

degrees of freedom?

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Heavy Ion Collisions: Background

• Specific to RHIC– Tunable Energy 30 - 200 GeV for Au-Au– Changeable species : p Pb

AGS SPS RHIC

snn4.8 GeV 17 GeV 200 GeV

Mode Fixed Target Fixed Target Collider

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Physics of Heavy Ion Spectra at RHIC

• Particle production increases significantly– ~800-2000 charged

particles per unit rapidity

• Hard scattering is prominent

• Pt distributions allows access to observables related to– temperature

– baryo- and strangeness chemical potential

– energy flow

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• Insight into collision dynamics

• Slopes

– DeviationsHigh-pt, parton

MS & energy lossjet quenching?

Pt Distributions

T

p

edpp

dN

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RHIC Collisions: Environment

TPC y

•Pions (~80%)

•Kaons

•Protons

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Hard Scattering

• High pt particles – jets & single particles calculable in pQCD– allows access to small distances, early times

affected by the dense medium?– dE/dx energy loss softening of pt spectrum

retain information about the collision– fast particles little to no rescattering in hadronic stage

– should be significant in numberexpect ~50% of Et to be produced via partonic

processes

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STAR Detector

• TPC acceptance

– // < 1.5, 0 < < 2

• Bz = 0.5 T

• Particle ID via

– dE/dx

– RICH

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Inside the STAR TPC

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Tracking

• Resolution:

– 1.5% @ 1GeV/c for , K, p

pp

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dE/dx : Truncated Mean

p(GeV/c)

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RICH Particle ID

•Pions•Kaons•Protons

<pt>

= 450 MeV/c

K = 675 MeV/c

p = 840 MeV/c

To 5 GeV/c

RICH PID

RICH PID

pt(GeV/c)

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RHIC Year-1 Data

• May - August, 10 weeks ~ 106 evts

• Central Collision Rates: 100 Hz (12 Mb data/evt)

• Goals

– y and pt distributions for charged tracks.

Can we do a rough characterization of the collision?

– As possible, obtain spectra for specific particles separately using PID information.Will there be differences btw different particle species?

– Particle distributions vs. multiplicity.

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Multiplicity & Centrality

• Study particle distributions as a function of Nch

• Compare to p-p data• Look for deviations

from predicted behavior

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High-Pt Studies

• Single Particle Inclusive Spectra (h+, h-)

• Future studies– Particle Ratios at high pt

pbar/p compared to p+p, insight into jet quenching?

RICH can identify protons up to 5 GeV/c

– J/ Spectra Predicted to be suppressed in QGPL3 Trigger + EM Calorimeter for e+e-

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Summary

• STAR: Ready in May

• TPC, RICH for high-pt Spectra physics.

• Analyses over full impact parameter range out to several GeV/c in pt

– Sensitive to fundamental event characteristics

– Will there be surprises?