References to Study the New Matter

Study QGP in different Centrality

Most Central events (highest multiplicity), e.g. top 5% central, i.e. 5% of the events with largest multiplicity

Mid Central events

Most Peripheral events

From most central to most peripheral event, the collision is more like a p+p collisions.

One can also collision smaller size of nuclear, e.g. Cu+Cu, Si+Si, instead of Au+Au to gain more luminosity.

N_coll: 8 N_part: 6

Centrality can be quantified by the number of collisions (N_coll) and number of participants (N_part) through the glauber model calculation with

Cold Nuclear Effect• Mostly referring to initial state effect, i.e. the effect before the hard collision

happens. – Color Glass Condensate: "Color" in the name "color glass condensate" refers to

a type of charge that quarks and gluons carry as a result of the strong nuclear force. The word "glass" is borrowed from the term for silica and other materials that are disordered and act like solids on short time scales but liquids on long time scales. In the "gluon walls," the gluons themselves are disordered and do not change their positions rapidly because of time dilation. "Condensate" means that the gluons have a very high density (from Wikipedia)

– EMC: single nucleons and nucleons inside an nucleus have a different distribution of momentum among their component quarks .

• Shadowing – Initial state energy loss: e.g. gluon fragment into hardons before the hard

collision.– Cronin effect: multiple scatter of projectile partons with the partons in the target

nuclear• There’re also final state effect, e.g.

– co-mover effect, i.e. After QGP freezout into hardonic phase, the signal particle, e.g. J/psi still can be reduced via collision with those hadrons.

Ways to Reveal the QGP properties---RAA

• nuclear modification factor (RAA):

)__()(

)(

tsparticipanorcollisionsNppyield

AuAuyieldRAA

)__()(

)(

tparticipanorcollisionsNppyield

AudyieldRdA

RAA ( or RdA)

No medium effect

pQCD – Single Hadron Production• Add fragmentation to hadrons

– D(z) – fractional momentum dist. of particles created by outgoing quark or gluon (i.e. in a jet)

KKP

Kretzer

data vs pQCD

dt

d

z

QzD

QxQxdxdxdp

dE

c

abcaBbaAaba

ˆ),,(

),,(),,(

2

/

2/

2/3

3

0

Phys. Rev. Lett. 91, 241803 (2003)

a/A

b/B

A

B

ab̂

Slides from B. Cole Talk

Au + Au Experiment (200GeV) d + Au Control Experiment (200GeV)

Preliminary DataFinal Data

Cronin enhancement: parton pT smearing from random kick before collisions (i.e. initial state effect)

Energy loss: parton loss lots of energy (dE/dx = ???GeV/fm) through bremsstrahlung when pass through the new state of matter (final state effect)

PHENIX: Au-Au Final Results from 2002

– Unequivocal observation of strong suppression at high p in central Au-Au collisions.

RA

A

q

q

p (GeV/c)

Slides from B. Cole Talk

– Rather than separating v2, RAA(pT) plot RAA(, pT)

RAA(, pT)

Pair Production from Gluon Field• Suppose we pull quark & anti-quark apart ?

– Store energy in gluon field• Eventually enough energy to produce pair.

– Get two shorter flux tubes.

– Continue until energy of outgoing quarks is exhausted

– “Fragmentation”

– Jet:

q qqq

qq

STAR Experiment: “Jet” Observations

Nu

mb

er o

f p

airs

Angle between high energy particles0º 180º

proton-proton jet event

In Au-Au collisions we see only one “jet” at a time !

How can this happen ? Jet quenching!

q

q

Analyze by measuring (azimuthal) angle between pairs of particles

Slides from B. Cole Talk

trigger

Adler et al., PRL90:082302 (2003), STAR

near-side

away-side

1 < pT (assoc) < 2.5 GeV/c

http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=21

What’s a shock wave?

SHOCK WAVE is a thin transitive area propagating with supersonic speed in which there is a sharp increase of density, pressure and speeds of substance.