Pizza Talk – Yale - Jan 2005

Hunting for Free Quarks

Helen CainesRelativistic Heavy Ion Group

WNSL - West

Helen Caines

Pizza Talk – Jan 2005 2

The RHI Physics Group

The ActorsFaculty : Helen Caines

John Harris

Thomas Ullrich1

Research Scientists: Jaroslav Bielcik2

Jana Bielcikova

Matthew Lamont

Nikolai Smirnov

Richard Witt3

Grad. Students: Stephen Baumgardt (1)

Betty Bezverkhny (5)

Oana Catu (3)

Jonathan Gans (Ph.D 04)

Michael Miller (Ph,D 04)

Christine Nattrasse (2)

Sevil Salur (5)

1 – Adjunct, Scientist at BNL

2 – Joint appointment with BNL

3 – Visiting, Scientist at University of Bern, Switzerland

Helen Caines

Pizza Talk – Jan 2005 3

quarkshadrons

mesons baryons

pions,kaons,

..

protons,neutrons,

...

nucleons

protons neutrons

partons

quarks gluons

Some Terminology

Helen Caines

Pizza Talk – Jan 2005 4

More About QuarksOrdinary matter made

of up and down quarks

• Quarks interact by exchanging gluons• Nucleons are held together by gluons• Free quarks have never been seen - distinctive non-integer

charge

Helen Caines

Pizza Talk – Jan 2005 5

Why We Don’t See Free Quarks

Compare to gravitational force at Earth’s surface

Quarks exert 16 metric tons of force on each other!

quark quarkgluons The size of a nucleus is 1.2A1/3 fm

where A is the mass number and a fm is 10-15 m

Helen Caines

Pizza Talk – Jan 2005 6

Evolution of the Universe

Reheating Matter ?

?Need temperatures

around1.5·1012 K

(200 MeV)

The universe gets cooler !10-44 sec Quantum Gravity Unification of all 4

forces 1032 K

10-35 sec Grand Unification E-M/Weak = Strong forces

1027 K

10-35 sec ? Inflation universe exponentially expands by 1026

1027 K

2 10-10 sec Electroweak unification

E-M = weak force 1015 K

2·10-6 sec Proton-Antiproton pairs

creation of nucleons 1013 K

6 sec Electron-Positron pairs

creation of electrons 6 x 109 K

3 min Nucleosynthesis light elements formed 109 K

106 yrs Microwave Background

recombination - transparent to photons

3000 K

109 yrs ? Galaxy formation bulges and halos of normal galaxies form

20 K

Helen Caines

Pizza Talk – Jan 2005 7

RHIC @ Brookhaven National Lab

Long Island

Long Island

• 2 concentric rings of 1740 superconducting magnets• 3.8 km circumference• counter-rotating beams of ions from p to Au

STAR

PHENIX

PHOBOSBRAHMS

• Au+Au @ sNN= 200 GeV • p+p @ s = 200 GeV

Helen Caines

Pizza Talk – Jan 2005 8

What Do Those Numbers Mean?

• Energies are measured in electron volts– 1 eV is the energy acquired by a particle with charge 1 accelerated

across a voltage of 1 volt• keV - 1000 eV• MeV - 1,000,000 eV, 1 million eV• GeV - 1,000,000,000 eV, 1 billion eV

• The binding energy of a nucleus is about 8 MeV/nucleon

• Beam energies are often given in GeV/nucleon– RHIC is one nucleus with 100 GeV/nucleon colliding with another

nucleus with 100 GeV/nucleon going the opposite direction

Helen Caines

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• Central Au+Au Collision:

NColl. sNN = 40 TeV ~ 6 Joule

How Much Is That?

Sensitivity of human ear:

10-11 erg = 10-18 Joule = 10-12 Joule

Indeed a pretty “Loud Bang“ if E Sound

Most goes into particle creation

Helen Caines

Pizza Talk – Jan 2005 10

Aftermath of a Collision

As seen by STAR experiment at RHIC

End-on view of high energy gold-gold

collision

• >5000 particles

• Only charged particles seen here (there are also lots of neutral particles)

• Neutrals don’t ionise the gas so are not “seen” by the detector.

Helen Caines

Pizza Talk – Jan 2005 11

Blackbody Radiation

Planck distributiondescribes intensityas a function of thewavelength of theemitted radiation

“Blackbody” radiation is the spectrum of radiation

emitted by an object attemperature T

1/Wavelength Frequency E p

Helen Caines

Pizza Talk – Jan 2005 12

inte

nsity

transverse momentum

Systematic Errors not shown

Phobos Preliminary

Determining the Temperature

From transverse momentum distribution deduce temperature ~

120 MeV

Close to Temperature we needed

Helen Caines

Pizza Talk – Jan 2005 13

What’s the Energy Density?• A typical approach

– use calorimeters to measure energy emitted from collision

– estimate the volume of the collisionThe PHENIX

CalorimeterIn Central Collision:

E ~ 650 GeV

R2

Time it takes to thermalize system (0 ~ 1 fm/c)

R~6.5 fm

dydz 0V ~ 130 fm3

BJ 5.0 GeV/fm3

~30 times normal nuclear density

~ 5 times above critical from

lattice QCD

Helen Caines

Pizza Talk – Jan 2005 14

5 GeV/fm3. Is that a lot?

Last year, the U.S. used about 100 quadrillion BTUs of energy:

At 5 GeV/fm3, this would fit in a volume of:

Or, in other words, in a box of the following dimensions:

mfmfm 5105103.1 93 329

Helen Caines

Pizza Talk – Jan 2005 15

Helen Caines

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One Way To Dig Even Deeper - Jets

hadron

hadron

• Possible for “knock-on” collisions of partons

• Seen in high-energy physics experiments since mid-1970’s

• A real particle physics phenomenon that can be used to probe the trillion degree material we create

Helen Caines

Pizza Talk – Jan 2005 17

Creating a “jet” of particles

• As connection between quarks breaks up, most of the motion stays close to direction of the original quarks

kaon

pion

pion

pion

• The fragmented “bits” appear as “normal” subatomic particles–pions, kaons,etc

pionpion

kaon

• Jets commonly come in

pairs

Helen Caines

Pizza Talk – Jan 2005 18

Case study: opacity of fog

• “is this thing on?”• First beam - least know the

source is on.• Second beam intensity tells you a

lot about matter passed through

Predictions

QGP: the “backwards” jet will be absorbed by the medium

Hadron gas: the “backwards” jet be less affected by the medium

?

Helen Caines

Pizza Talk – Jan 2005 19

Jets in Heavy Ion Collisions?

ee q q (OPAL@LEP)

p-p jet+jet (STAR@RHIC)

Au-Au ??? (STAR@RHIC)

No, but a bit tricky…

Jets in Au-Au hopeless Task?

Helen Caines

Pizza Talk – Jan 2005 20

central Au+Au collisions

trigger Phys Rev Lett 90, 082302

min. bias p+p collisions

Jets & 2-particle Azimuthal Distributions

p+p dijet

• Trigger: highest pT track

• Δ distribution:

0: central Au+Au similar to p+p : strong suppression of back-to-back correlations in central Au+Au

?

Helen Caines

Pizza Talk – Jan 2005 21

Have we found the Quark Gluon Plasma?

• We now know that Au+Au collisions generate a medium that is dense (pQCD theory: many times cold nuclear matter density)

• exhibits behaviour of very hot, thermalized source that is dissipative

• We have yet to prove that:• Dissipation occurs at the partonic stage• The system is deconfined and thermalized • A transition occurs: can we turn the effects off ?

This represents significant progress in our understanding of strongly interacting matter

Not yet, still work to do … (but getting closer)