aaas symposia nuclear matter at the highest energies and densities james nagle columbia university...

James Nagle

Columbia UniversityAAAS Symposia

Nuclear Matter at the Highest Energies and Densities

James Nagle

Lepton and Dilepton Production:

Current Experimental Results

Lepton and Dilepton Production:

Current Experimental Results

AAAS SymposiaNuclear Matter at the Highest Energies and Densities

James Nagle



OutlineOutlineOutlineOutline

What is the nature of nuclear matter at the highest energies and densities?

What are leptons?

How can we study nuclear matter using lepton and dilepton observables?

What are the experimental results?

James Nagle



Forces of NatureForces of Nature

+ +…

Quantum Electrodynamics (QED) Field theory for electromagnetic interactions Exchange particles (photons) do not have electric charge Flux is not confined - U(r) 1/r and F(r) 1/r2

Quantum Chromodynamics (QCD) Field theory for strong (nuclear) interactions Exchange particles (gluons) do have “color” charge Flux is confined - U(r) r and F(r) constant

James Nagle



QCD ConfinementQCD ConfinementQuarks are the fundamental particles carrying color charge.

However, we have never observed free quarks !

cc

cc

cuc u

J/ is a bound state of cc (hidden charm)

Potential energy allows formation of qq pair. Now quarks confined in D mesons (open charm).

Pulling quarks apart is like stretching a spring.

D0 meson

Anti-D0 meson

James Nagle



Studying Quark ConfinementStudying Quark Confinement

Color Screening

cc

In a hot plasma of other quarks and gluons (Quark-Gluon Plasma), we expect a screening of the long range attractive force between quarks.

This screening should suppress bound states such as J/, but not change the total charm production (D mesons).

r

V(r

)/

Lattice QCD calculation

James Nagle



Creating the Hot PlasmaCreating the Hot Plasma

1 2 3 4

Collisions between heavy nuclei (Gold A=197) at relativistic velocities (v = 0.99995 x speed of light) deposit enormous energy and create approximately 10,000 quarks, antiquarks and gluons in a fireball.

These are the highest energy nuclear reactions ever created on earth, but note that these collisions cannot chain react.

James Nagle



With and Without PlasmaWith and Without PlasmaGoal:Fundamental understanding of the confinement of quarks in QCD and its modification at the highest energies and densities. Method:Compare the ratio of J/ to D mesons in a plasma and not in a plasmaProton+Proton collisions are the control with no Quark-Gluon Plasma c

cAu+Au or Pb+Pb collisions produce charm in a Quark-Gluon Plasma

cc

Thus, look for a suppression in the ratio:

pp

AuAu

DmesonsJ

DmesonsJ

/

/

James Nagle



Lepton = = smallLepton = = smallLeptons are point-like particles that carry no color charge, and therefore have no strong interactions.How does this make them useful in studying strongly interacting nuclear matter?Vector mesons , J/, … are unstable and can decay into dileptons.

Once the leptons are created they travel through the dense plasma almost unaffected and carry out crucial information.

J/e+e- or J/+ -

e+

e-

James Nagle



D Meson MeasurementsD Meson Measurements

0eD K

0D K

0 0e eD D e e K K

0 0eD D e K K

0 0D D K K

c c

0D

0D

D mesons decay very quickly. We can only observe them via their decay products. However, complete reconstruction is very difficult.

For example D0 K- +

D mesons can be measured via single leptons (electrons or muons) and also lepton pairs.

K+

K- e+

e

-

D*0

James Nagle



Intriguing Results at CERNIntriguing Results at CERN

“Strong evidence for the formation of a transient quark-gluon phase without color confinement is provided by the observed suppression of the charmonium states J/, c, and ’.”

Maurice Jacob and Ulrich Heinz

NA50 measures dimuons (+-) in Pb-Pb and p-p collisions and

observes

Invariant Mass(GeV/c2)

J/+ -

mass = 3.1 GeV/c2

Open Charm contributionD0D0+-K+K-

CERN Press Release 2000

an open charm enhancement and a suppression in J/production relative to model calculations.

James Nagle



Unprecedented EnergiesUnprecedented EnergiesNew collider facility and four new experiments to study Gold-Gold collisions at over an order of magnitude higher energy than ever before for heavy nuclei.

James Nagle



PHENIX ExperimentPHENIX Experiment

PHENIX is the only RHIC experiment specifically designed to measure leptons and dileptons.

Electrons are measured by the two central spectrometers.

Muons are measured by the two forward spectrometers.

James Nagle



Collect the Data!Collect the Data!

Collect the Data!

Scale of the ProblemScale of the ProblemUncovering nature’s secrets is not easy.PHENIX example: over 500 people, over 10 countries

tons of steel, specialized detectorsthousands of custom signal processors

transmitting over 5 Gigabytes per second

James Nagle



Needle in a HaystackNeedle in a Haystack

Over 5000 charged particles are produced in one Au-Au collision.

Detectors need to find these rare leptons without mistaking other particles for a lepton at the level of one in 10,000.

There is the electron.

James Nagle



Ring Imaging Cherenkov Detector

Ring Imaging Cherenkov Detector

No particle can travel faster than the speed of light in vacuum (v < c).

However, a particle can travel faster than the speed of light in a medium(c/n < v < c) where n=index of refraction.

If it does a cone of light called Cherenkov radiation is produced similar to a sonic boom with the speed of sound.

Since electrons are lighter than pions, at the same momentum, they have a much higher velocity and yield Cherenkov light in our detector.

Giant mirror reflects light onto a array of thousands of photomultiplier tubes.

James Nagle



Electron TrackingElectron TrackingMeasure trajectory of particles that bend through a magnetic field. This allows a momentum determination.

Bvc

e

dt

pd

All tracksThen measure the energy deposit in an electromagnetic calorimeter. Electrons and photons leave full energy, but hadrons (e.g. pions) leave only a small fraction.

Thus check for energy-momentum measurement match for electrons.

Electron enriched sample (using RICH)

Energy/Momentum

James Nagle



Single Electron SpectraSingle Electron Spectra

PHENIX

1.2M Minimum bias events

In August 2000, PHENIX recorded one million Au-Au collisions. With this data we can address charm production via single electrons.

Transverse Momentum (GeV/c)

Electron Yield per Event We are not done yet.

Most of these electrons are not from open charm decays but from other hadron decays (e.g. 0,).

These other contributions must be subtracted away.

James Nagle



0 ee

ee, ee

0ee, 3

0ee, ee

conversion

ee

ee

Extracting the Charm SignalExtracting the Charm SignalAfter accounting for other contributions, we see a clear electron signal most likely from open charm D mesons.


Electron Yield per Event

Systematic Error


ElectronsBackground

ElectronsAllratio

""

.

James Nagle



Both central

and minimum bias data

are consistent with theoretical calculations (PYTHIA) of expected charm production.

Electron PhysicsElectron Physics


Electron Yield per Event

James Nagle



Charm Energy DependenceCharm Energy Dependence

Good agreement with extrapolation from proton-proton collisions at lower energies.

Center-of-Mass Energy (GeV)

Charm Yield per Collision

James Nagle



Run IIRun IIRHIC achieved full energy

RHIC achieved ~50% of designbeam intensities

For example PHENIX recorded ~ 170 million events Days in the run

Integrated Collisions Sampled

James Nagle



Charm via MuonsCharm via Muons

PHENIX Simulation

With a new muon spectrometer, we can measure open charm (D mesons) and open beauty (B mesons) via their single muon decays.


Charm D0 K+ -

Beauty B0 D+ -

James Nagle



J/ MeasurementsJ/ Measurements

In the fall 2001, PHENIX recorded hundreds of J/ decaying to both e+e- and +-. Data analysis is underway.

In the fall 2002, PHENIX will sample billions of Au-Au collisions to collect high statistics. Also, the STAR experiment will make a first measurement.

We can then combine our opencharm (D meson) measurement with our new J/ measurement tounderstand the change in thequark confining potential.

PHENIXSimulation

+- Invariant Mass(GeV/c2)

James Nagle



Thermometer for the PlasmaThermometer for the PlasmaUpsilon (bb) state is more strongly bound than J/ (cc)

RHIC

PHENIXSimulation

+- Invariant Mass(GeV/c2)

Future upgrade to RHIC beam intensities should allow for Upsilon (bb) state measurements.

b

bc

c

Thus, the Upsilon should not be suppressed until much higher energy densities.

James Nagle



ConclusionsConclusionsGoal:Fundamental understanding of the confinement of quarks in QCD and its modification at the highest energies and densities.

Method:Measurement of open charm and hidden charm (J/) production and study yields as a function of collision volume (which nuclei) and energy.

Status:Measurements of charm (D mesons) via electrons are in hand. Critical J/ data analysis is underway.

We are at the start of an exciting area of physics !

aaas symposia nuclear matter at the highest energies and densities james nagle columbia university...

Documents