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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
Columbia UniversityAAAS Symposia
Nuclear Matter at the Highest Energies and Densities
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
Columbia UniversityAAAS Symposia
Nuclear Matter at the Highest Energies and Densities
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
Columbia UniversityAAAS Symposia
Nuclear Matter at the Highest Energies and Densities
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
Columbia UniversityAAAS Symposia
Nuclear Matter at the Highest Energies and Densities
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
Columbia UniversityAAAS Symposia
Nuclear Matter at the Highest Energies and Densities
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
Columbia UniversityAAAS Symposia
Nuclear Matter at the Highest Energies and Densities
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
Columbia UniversityAAAS Symposia
Nuclear Matter at the Highest Energies and Densities
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
Columbia UniversityAAAS Symposia
Nuclear Matter at the Highest Energies and Densities
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
Columbia UniversityAAAS Symposia
Nuclear Matter at the Highest Energies and Densities
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
Columbia UniversityAAAS Symposia
Nuclear Matter at the Highest Energies and Densities
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
Columbia UniversityAAAS Symposia
Nuclear Matter at the Highest Energies and Densities
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
Columbia UniversityAAAS Symposia
Nuclear Matter at the Highest Energies and Densities
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
Columbia UniversityAAAS Symposia
Nuclear Matter at the Highest Energies and Densities
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
Columbia UniversityAAAS Symposia
Nuclear Matter at the Highest Energies and Densities
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
Columbia UniversityAAAS Symposia
Nuclear Matter at the Highest Energies and Densities
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
Columbia UniversityAAAS Symposia
Nuclear Matter at the Highest Energies and Densities
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
Columbia UniversityAAAS Symposia
Nuclear Matter at the Highest Energies and Densities
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.
Transverse Momentum (GeV/c)
Electron Yield per Event
Systematic Error
Transverse Momentum (GeV/c)
ElectronsBackground
ElectronsAllratio
""
.
James Nagle
Columbia UniversityAAAS Symposia
Nuclear Matter at the Highest Energies and Densities
Both central
and minimum bias data
are consistent with theoretical calculations (PYTHIA) of expected charm production.
Electron PhysicsElectron Physics
Transverse Momentum (GeV/c)
Electron Yield per Event
James Nagle
Columbia UniversityAAAS Symposia
Nuclear Matter at the Highest Energies and Densities
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
Columbia UniversityAAAS Symposia
Nuclear Matter at the Highest Energies and Densities
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
Columbia UniversityAAAS Symposia
Nuclear Matter at the Highest Energies and Densities
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.
Transverse Momentum (GeV/c)
Charm D0 K+ -
Beauty B0 D+ -
James Nagle
Columbia UniversityAAAS Symposia
Nuclear Matter at the Highest Energies and Densities
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
Columbia UniversityAAAS Symposia
Nuclear Matter at the Highest Energies and Densities
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
Columbia UniversityAAAS Symposia
Nuclear Matter at the Highest Energies and Densities
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 !
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