PHENIX OVERVIEW

W.A. Zajc

Columbia University

for the PHENIX Collaboration

Special thanks to J. Mitchell (BNL) for animations

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OutlineOutline

Why Nuclear Physics?

Why RHIC?

Why PHENIX?

Where do we go from here?

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Central Truths of Nuclear Physics

Central Truths of Nuclear Physics

We are nothing

We are dust

We don’t matter

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We are nothing (c. 1900)

We are nothing (c. 1900)

Most of “us” is (nearly) empty space 99.9% of the mass of atoms is

contained in the nucleus The nucleus is about one-trillionth

( 1/1,000,000,000,000 ) the size of the atom

ProtonProtonNeutronNeutronQuarksQuarksHeld togetherHeld togetherby gluonsby gluons(not shown)(not shown)

NucleusNucleus(“ion” when alone)(“ion” when alone)

AtomAtom

KeyKey

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We are dust (c. 1950)

We are dust (c. 1950)

Only the lightest elements (Hydrogen and Helium) were created in the Big Bang

The rest of “us” is stardust All heavy elements (like the Carbon and

Nitrogen we’re made of) were “cooked” together inside stars

Explosions of those (early) stars spread the heavier elements throughout the universe.

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We don’t matter (c. 2000)

We don’t matter (c. 2000)

More accurately: We’re not matter

Recall nearly all the mass of each atom is concentrated in the nucleus: Each nucleus consists of

neutrons and protons Each neutron and proton consists

of 3 quarks Each quark has the mass of about

1% of a proton or neutron(!) The rest of the mass of protons

and neutrons (and hence our mass) is “frozen energy” from the Big Bang

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Phase Transitions

Phase Transitions

The “great freeze” took place about 10 millionths of a second after the Big Bang

General name for such phenomena: Phase transitionExamples:

Steam to water to ice

(Free quarks and gluons) to (protons and neutrons) to (??)

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Phase DiagramsPhase Diagrams

Water

Nuclear Matter

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A Silly AnalogyA Silly Analogy Suppose…

You lived in a frozen world where water existed only as ice and ice comes in only quantized sizes ~ ice cubes and theoretical friends tell you there should be a liquid phase and your only way to heat the ice is by colliding two ice cubes So you form a “bunch” containing a billion ice cubes which you collide with another such bunch 10 million times per second which produces about 1000 IceCube-IceCube collisions per

second which you observe from the vicinity of Mars

Change the length scale by about 10 trillion You’re doing physics at RHIC!

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Boiling Neutrons and Protons

Boiling Neutrons and Protons

Fundamental Method:Collide heavy nuclei at the highest

possible energies:

Fundamental Goals: Create (new) dense forms of matter Re-create the quark-gluon phase transition

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In PicturesIn Pictures

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RHIC = Relativistic Heavy Ion Collider Located at Brookhaven National Laboratory

RHICRHIC

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RHIC’s Experiments

RHIC’s Experiments

STAR

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How is RHIC Different?

How is RHIC Different?

It’s a collider Detector systematics independent of ECM (No thick targets!)

It’s dedicated Heavy ions will run 20-30 weeks/year

It’s high energy Access to non-perturbative phenomena

Jets Non-linear dE/dx

Its detectors are comprehensive ~All final state species measured with a

suite of detectors that nonetheless have significant overlap for comparisons

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What is PHENIX?What is PHENIX? Pioneering High Energy Nuclear Interaction

eXperiment Goals:

Broadest possible study of A-A, p-A, p-p collisions to Study nuclear matter under extreme conditions Using a wide variety of probes sensitive to all

timescales Study systematic variations with species and

energy Measure spin structure of the nucleon

These two programs have produced a detector with unparalleled capabilities

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The CollaborationThe CollaborationA strongly international venture:

11 nationsBrazil, China, France, Germany, India,

Israel, Japan, South Korea, Russia, Sweden, United States

51 institutions

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PHENIX at RHICPHENIX at RHIC

2 central spectrometers

2 forward spectrometers

3 global detectors

West

EastSouth

North

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ScheduleSchedule

2 central spectrometers

2 forward spectrometers

3 global detectors

1999

20002001

2002

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24-Jul-9724-Jul-97

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10-Jan-9810-Jan-98

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12-Jan-9912-Jan-99

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23-Dec-9923-Dec-99

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Run-1 Configuration

Run-1 Configuration

Two central arms Mechanically

~complete Roughly half of

aperture instrumented Global detectors

Zero-degree Calorimeters (ZDCs)

Beam-Beam Counters (BBCs)

Multiplicity and Vertex Detector (MVD, engineering run)

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TourTour

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Tour (Particle View)

Tour (Particle View)

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Run-1 Accomplishments

Run-1 Accomplishments

First collisions:15-Jun-00 Last collisions: 04-Sep-00 During this period:

Commissioned Zero-Degree Calorimeters Beam-Beam Counters Multiplicity and Vertex Counter Drift Chambers Pad Chambers Ring Imaging Cerenkov Counter Time Expansion Chamber Time-of-Flight Counters Electromagnetic Calorimeter Muon Identifier Minimum Bias Triggers Data Acquisition System

Recorded ~5M minimum bias events

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Run-1 ResultsRun-1 Results

This is a partial compilation

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Measuring InitialCollision GeometryMeasuring Initial

Collision Geometry

Zero Degree Calorimeters (ZDC) Sensitive to spectator

neutrons common to all four RHIC

experiments Using a combination of

the ZDC’s and BBC’s we can define Centrality Classes

Zero Degree Calorimeter

5-10%10-15%

15-20%

0-5 %

“Spectators”

“Spectators”

“Participants”. n

nnp

pp

Beam-Beam Counter (BBC)Impact Parameter

ZD

CBBC

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R2

Determining Energy DensityDetermining

Energy Density

Bjorken~ 5.0 GeV/fm3

Roughly 1.5 to 2 times higher than any previous experiments

Bjorken formula for thermalized energy density

time to thermalize the system (0 ~ 1 fm/c)~6.5 fm

For the most central events:

PHENIX preliminary

EMCAL

What is the energy density achieved? How does it compare to the expect

phase transition value ? Is this energy density thermalized?

dy

dE

RT

Bj0

2

11

dydz 0

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Have studied growth of Number of particles Energy

versus “centrality” Excellent consistency between two analyses First evidence for new term in growth ~ number

of collisions

PHENIX preliminaryPHENIX preliminary

collpart NBNAddX 0

28.088.0 A

12.034.0 B

First PublicationsFirst Publications

)(24.080.0 GeVA )(09.023.0 GeVB

19.038.0/ AB 18.029.0/ AB

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Fingerprinting Particles

Fingerprinting Particles

Combined Tracking Beam-Beam Counter Time-of-Flight array

provides excellent hadron identification over broad momentum band:

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Anti-proton/proton ratio

Anti-proton/proton ratio

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Approaching the Early Universe

Approaching the Early Universe

Early Universe: Anti-proton/proton = 0.999999999

√s [GeV]

PHENIX preliminary

E866Au+Au

NA44Pb+Pb

pba

r/p

We’ve created “pure” matterapproaching this value

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0 0 spectraspectra0 0 spectraspectra

0

pT >2 GeV,asym<0.8

Systematic errors includedMain sources:

peak extraction PID loss efficiency calculations non-vertex pions pT scale

Centrality ~Nbin ~Npart

10% 800 300 M.B. 125 75 75-92% 10 10 ~1M Min Bias AuAU events

s = 130 GeV

Peripheral

Min bias

Central

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Charged pT SpectraCharged pT Spectra Systematic

trends in high momentum production also studied with charged particles Much greater

statistics Different

systematics

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Comparison to charged spectraComparison to

charged spectra

0 spectra matches identified charged pion spectra –

A very good internal test of our results

(+ +-)/2

0

All charged

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Comparison to Theory

Comparison to Theory

Good agreement with “grazing” collisions

For head-on collisions, clear deficit with respect to “no new physics” calculations

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Central Events – What’s Going On?Central Events – What’s Going On?

“Standard” predictions overestimate the cross-sectionfor 0 by at least 5

dE/dx=0.25 GeV/fm

dE/dx = 0 (pQCD)

Predictions including (plasma-like!)energy loss consistent with 0

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Physics Implications (??)

Physics Implications (??)

Slide fromseminar given lastmonth by M. Gyulassy

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Physics ImpactPhysics Impact

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Composition at high pT

Composition at high pT

Possible complication in comparisons of charged yields to theory:

Particle composition is observed to be a strong function of pT

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Time to PhysicsTime to PhysicsAgain, learn from the past:

First CDF publication:Transverse-Momentum

Distributions of Charged Particles Produced in p-pbar Interactions at 630 and 1800 GeV, F. Abe et al., Phys. Rev. Lett. 61, 1819 (1988).

~One year from data-taking.

Much simpler final state!

We will be hard-pressed to reach this goal

And much harder-pressed to maintain “CDF-like” rate WRONG!(?)

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One Year AgoOne Year AgoFor years we’d been showing pictures of one “central” arm:

21-Jan-00: The real thing moves into place

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Shape of Things to Come

Shape of Things to Come

Completion of Central Arms Significantly

increased aperture Addition of new capabilities

South Muon Arm Di-muon physics

Upgraded Triggers Data Acquisition

The ~5M events recorded in Run-1 represent ~1 day of data-taking for RHIC+PHENIX in Run-2

Insert here

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Shape of Things NowShape of Things Now

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SummarySummary PHENIX detector has provided outstanding data in

first year of RHIC operations Measured

Charged multiplicity Transverse energy Elliptic flow Identified particle spectra HBT parameters High pT spectra Inclusive electron spectrum (much more)

Observed New trends in particle production New behavior in particle yields at high momentum

Ideally positioned to dramatically extend these results in second year of RHIC running