Mark D. Baker

What have we learned from RHIC?

Mark D. BakerChemistry Department

Thanks to: W. Busza, Axel Drees, J. Katzy, B. Lugo,

P. Steinberg, N. Xu, F. Wolfs BSA Lecture Committee

Particle Data Group http://ParticleAdventure.org/

Mark D. Baker

Some of the people

Mark D. Baker

Where they come from • BNL

– Chemistry, Collider-Accelerator, Physics

• >1000 people from around the world– Brazil, Canada, China, Croatia, Denmark, France,

Germany, India, Israel, Japan, Korea, Norway, Poland, Russia, Sweden, Taiwan, UK, US

Mark D. Baker

What is the universe made of?&

What holds it together?

Mark D. Baker

What is the universe made of?

Placeholder

Mark D. Baker

What holds it together?:The Fundamental Forces

Mark D. Baker

Let’s smash some atoms!

+ -

-

u

u u u u u

d

u d u du du d

proton

proton

pion ()

uud

Mark D. Baker

If you can’t smash it, heat it!

Temperature

Plasma

+

---

-+

Pressure

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Sideways slide - How much heat?

Placeholder

Mark D. Baker

Heat is also a window back in time

Mark D. Baker

How do we get to 2 trillion oK?

Collide Gold nuclei at 99.99% of the speed of light

But: Will these fast violent collisions teach us anything?

10-23 seconds, 10-38 liters

Mark D. Baker

The plan of attack

• Collide gold nuclei at high energy– Collider, detectors, computers

• Understand the collision dynamics– Collective motion, equilibrium– Temperature, density

• Learn about the strong interaction– Quark-Gluon Plasma– Confinement

Mark D. Baker

Where?

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Inside the tunnel

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STARSTAR

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RHIC Computing Facility

The detectors can take 7 Gigabytes of data / minute!

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First Collisions

Mark D. Baker

Timeline

CollisionsDelivered

Star & Phobos

Brahms & Phenix

|-----June------|-----July------|----August----|--September--|---October---|---November--| 2000

sNN = 130 GeV

Au-Au

|-December--|--January---|--February--|----March----|-----April-----|

(PHOBOS)

(STAR) (PHENIX)

1st Collisions

Papers (PHENIX)(BRAHMS)(PHOBOS)

(STAR)

Title:

Creator:qcdisplay2.2 Contact prindle@npl.washington.eduPreview:This EPS picture was not savedwith a preview included in it.Comment:This EPS picture will print to aPostScript printer, but not toother types of printers.

Papers

Mark D. Baker

Looking for collective effects...

Is Gold+Gold > 197 * Proton+Proton?

Mark D. Baker

AuAu @ RHIC is something new!

PHOBOS

CERN/SPS

Energy/nucleon (GeV)

Produced Particles/Participating Nucleon Pair

ppPHENIX

BRAHMSprelim.

PRL 85 (2000) 3100

Mark D. Baker

How many produced particles?

Measured # in ahead-on collision:

4100±410

(Simulation)

PHOBOS Preliminary

Mark D. Baker

Elliptic Flow: A collective effect

dN/d(R ) = N0 (1 + 2V1cos (R) + 2V2cos (2(R)) + ... )

Elliptic flow

Beam’s eye view of anon-central collision:

Asymmetric particle distribution:

Particles prefer to be “in-

plane”

Mark D. Baker

Elliptic Flow Expectations

Hydrodynamic model

V2

Normalized Multiplicity

midrapidity : || < 1.0

Preliminary

Particle asymmetry

No collective motion

Hydrodynamic “Flow”

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Elliptic Flow

Hydrodynamic model

V2

Normalized Multiplicity

midrapidity : || < 1.0

Preliminary

PRL 86 (2001) 402Particle asymmetry

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Collective motion largest at RHIC

STAR, PRL 86 (2001) 402

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It even makes sense in detail

Huovinen, Kolb, Heinz

Particle asymmetry

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Plan of attack - where are we?

• Collide gold nuclei at high energy– Collider, detectors, computers

• Understand the collision dynamics– Collective motion, equilibrium

– Temperature, density• Learn about the strong interaction

– Quark-Gluon Plasma

– Confinement

Mark D. Baker

We see the conditions at freezeout(a lower limit to the maximum Temperature)

FreezeoutHottest period

RT

1

Expansion cooling

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Separating Temperature & Expansion

2

2

22

3

c

vmT

N

E

Compare produced particles with different masses!

2

2

. 3c

vmTTeff

Effective Temperature

mass

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1.7 1012 oK

RHIC shows rapid expansion& a high temperature

!3

2

c

vEffectiveTemperature(GeV)

CERN NA49

STAR Preliminary

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Another thermometer

In an equilibrium system, twoparameters are sufficient to predict the “chemical” mix:

(# pions) / (# protons)(# kaons) / (# pions)(# anti-protons)/(# protons) et cetera.

Temperature (T)and “net amount of matter” (B)

Mark D. Baker

Temperature from particle ratios

T = (2.2+0.2) 1012 oK-

STAR Preliminary

23

64

1,5,7

)/( 1. hhK

pp / 2.

KK / 4.

/ 3.

hK / 5. *0

/ 6./ 7. p

Mark D. Baker

Temperature at Freezeout

• Chemical: T = (2.2+0.2) 1012 oK• Kinetic: T = (1.7+0.4) 1012 oK

• We did reach ~ 2 trillion K!

--

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The yields are compared to predictions by Hijing.The SPS data values from NA44, NA49 are plotted as reference.The ~3 measurement converted to y using the accepted mean pt.

Mark D. Baker

What happens before freeze-out?•Energetic particles come from quark or gluon “jets”.•They interact with the dense medium, but can’t thermalize.•Jet energy loss (“quenching”) is predicted.•Jet quenching measures the density early in the collision.

pion

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Jet quenching at RHIC?

Neutral pionsCentral collisions

No quenching

Number

Transverse Momentum (GeV/c)

Neutral pions Peripheral collisions

Quenching

Transverse Momentum (GeV/c)

Preliminary

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More on jet quenching

Details need to be understood before conclusions can be drawn.

Mark D. Baker

Summary

• We’ve learned a lot about the system– We have reached ~2 trillion degrees K– The system is expanding rapidly.– It was probably even hotter and denser

• Possible first evidence of jet quenching!– Should lead to a measure of the density

• No conclusions yet about the strong force.

Mark D. Baker

Outlook

• More analysis• More data (x100 next run)

– Allows new early time probes

• More variety of data– Energy and species scan

• Detector Upgrades

It’s going to get even better!

Stay tuned for news about the strong force!