What do we study

Nucleosynthesis builds nuclei up to HeNuclear Force…Nuclear Physics

Universe too hot for electrons to bindE-M…Atomic (Plasma) Physics

E/M Plasma

Too hot for quarks to bind!!!Too hot for quarks to bind!!!Standard Model (N/P) Physics

Quark-Gluon

Plasma??

Too hot for nuclei to bindNuclear/Particle (N/P) Physics Hadron

Gas

SolidLiquidGas

Today’s Cold UniverseGravity…Newtonian/General Gravity…Newtonian/General

RelativityRelativity

Structure of matter in the Universe

scale ~ 10-15 m

scale ~ 10-10 m

Huge scale Iron

Wood

3

1

3

1

3

1

3

2

3

2

3

2

UniverseGravitational

Electromagnetic

Strong

Leptons: electron, muon, etc

Current building block

baryon meson

hadrons

Particles

Leptons

pion

u d

Force carriers

GluonsGlue the quark together

Quarks are Confined inside Particles

Strong Interaction (QCD)

•Strong interaction is mediated by gluons

•Both gluons and quarks has “color” charge.

• V(r) = -kV(r) = -k11/r + k/r + k22rr, , kk22 1 GeV / 1 GeV / fm, constant force.fm, constant force.

Electromagnetic Interaction

• Force (r) ~ 1/r2

• Two charges can be broken apart and set free

As two quarks are pulling away, energy increase. Color string fragment into new pairs of quark. Single quarks are confined inside particles. When energy is high enough, it forms a jet.

How to Liberate Quarks and Gluons

Increase Temperature and/or Pressure

Bayon (pressure)pressure

Water molecule is liberated with high T and P

Librated Quarks and Gluons

1,500,000,000,000 K~100,000 times higher temperature than the center of our sun.

One Way to Increase Temperature or Pressure

Small “Bang”

Heavy alien object hits the heavy earth

Tremendous kinetic energy converted into tremendous heat and pressure.

One (Nuclear Physicist’) Way to Increase Temperature or Pressure

Mini “Bang”

Heavy (Au) Nuclei hits the heavy (Au) Nuclei

Tremendous kinetic energy converted into tremendous heat

One (Real Nuclear Physicist’) Way to Increase Temperature or Pressure

Mini “Bang”

Heavy Nuclei hits the heavy Nuclei

Tremendous kinetic energy converted into tremendous heat

Different Stage after the Collision

• Right before the collision.

• Instantly (< 1 fm/c) after the collision. Highest energy density (15GeV/fm3).

• After ~1fm, system thermalized, i.e. thermal equilibrium. Temperature is the same everywhere.

Hadron continue to interact with each other elastically. Hadron is not changed but the momentum distribution does. At Kinetic freezout, the elastic interaction between hadrons stop. Hadron spree out and detected by the experiment

System continue the expension and cool down. Quarks and gluons start to fragment into hadrons. The particle ratio kept on changing due to the chemical reactions. At the point of Chemical Freezout, the chemical reaction ceased

What are the probes.

• soft hadron: Pions, kions, protons, etc

•coming from the fragmentation process after chemical freezout.

•To study their behavior (cross section, correlation, suppression, etc) can leads to the estimation of the QGP properties, e.g. temperature, pressure, energy density.

• Penetrating probes: direct photons, jet, heavy flavor, etc

•Coming from the QGP, i.e. before the chemical freezout. Directly bring the information of the QGP properties.

What are Detected

Detector in Rphi plane

particle tracks

beambeam

• collision vertex

• particle momentum (px, py, pz) right after the collsion through bending curvature in the magnet field.

• particle energy (photon, no bending in the magnet field).

• particle species identification through, e.g. energy loss (dE/dx) and particle speed (time of flight), cerenkov radiation, etc.

How an experiment take data

Take what is necessary: trigger

target

trigger

• soft hadron production ……………………………..…………… Minimum-bias trigger

• Direct photons ………………………………………..…………… photon trigger

• High pT particles (belong to jet). ………………………………….. High pt trigger

•J/psi, D meson production. ………………….…………………… J/psi, D meson trigger

• ………………………..

• One can take all the collision events with enough resources.

• Not every collision is interesting.

• heavy flavor, photon are very rare.

What is needed for the result to be publishable

The result, in principle, need to be independent of a specific experiment.

An experiment is specific in it:

• detector acceptance (Accp):

•N (accepted by the detector)/N (produced from the collision).

•Detector efficiency (Eff).

• HV trip, construction flaw. The efficiency < 100%

•Experiment trigger efficiency (Trg_eff).

•Trigger always biased,

•e.g. photon trigger: only accept events with hits above a certain energy.

pT

accp

x

y

pT

Trg_eff

Example of Publishable Results.

• cross section (σ): a Lorentz invariant measure of the probability of interactions. It has dimension of area (unit cm2 or barn )

• σ x L = N(events), where L is the luminosity, i.e. the intensity of the beams

effTrgEffAccp

photonN

Nppphoton

collision _

)(1)()(

How to Study QGP

• Nuclei is made of protons and neutrons: p+p collision is a natural reference (note: QGP may have already been produced by p+p collisions: ask Rolf and Brijesh)

• Behavior Quarks and gluons in a static nuclei is different from that in proton.

• Cold nuclear effect, or initial state nuclear effect, i.e. before collisions

• p(d)+Au can quantify this effect.

• New matter is produced after the collisions ( hot or final state effect).

time

p+p

d+Au

Au+Au

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

Ways to Reveal the QGP properties---RAA

• nuclear modification factor (RAA):

)__()(

)(

tsparticipanorcollisionsNppyield

AuAuyieldRAA

)__()(

)(

tparticipanorcollisionsNppyield

AudyieldRdA

RAA ( or RdA)

No medium effect

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)

coneRWays to Reveal the QGP properties---Jet correlation

Calculate angle between two jet particles

trigger

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

near-side

away-side

Energy dissipated when parton pass through opaque medium. How?

1 < pT (assoc) < 2.5 GeV/c

Thanks Andy

Particle ratio is determined by Temperature and chemical potential

• abundances in hadrochemical equilibrium

Ways to Reveal the QGP properties---particle ratio

1

1

2 /3

3

22

Tmp

hhBh

e

pdVgN

lesantipartic and

,.......,,,,,,,,,, DdpKKh

>= critical temperature

Ways to Reveal the QGP properties---flow

V1: directed flow

Higher order

V2: elliptic flow

A Movie of Glass Bead Show Liquid Behavior

http://www-news.uchicago.edu/releases/07/071106.liquids.shtml

Decreasing the number of glass beads in the cross section of the jet changes the behavior of the granular stream after hitting the target from liquid-like pattern to one that looks like fireworks. This latter pattern is more characteristic of how individual particles would behave after hitting a wall.

A Movie of Glass Bead Show Liquid Behavior

http://www-news.uchicago.edu/releases/07/071106.liquids.shtml

More Materials

• RHIC white paper: for physics understanding– J. Adams et al., Nucl. Phys. A 757, 102 (2005); K. Adcox et al., Nucl. Phys. A

757, 184 (2005) ; I. Arsene et al., Nucl. Phys. A 757, 1 (2005); B. B. Back et al., Nucl. Phys. A 757, 28 (2005).

• CERN detector and analysis brief book: For nice explanation of jargon in this field. – http://physics.web.cern.ch/Physics/DataAnalysis/BriefBook/

– http://physics.web.cern.ch/Physics/ParticleDetector/BriefBook/