1. Probing Quark Matter in the PHENIX Experiment at RHIC
Saskia Mioduszewski
In the presence of a dense strongly interacting
medium, the scattered partons will undergo
soft interactions, suffering energy loss and
resulting in a suppression of the number
of particles observed at large energies
“Jet Quenching”
Heavy Ion Collisions provide a means to heat and
compress normal nuclear matter
Goal is to create a new hot and dense form of matter
-- deconfined quarks and gluons “Quark Gluon Plasma” (QGP)
 Recreate a form of matter in the laboratory as existed in
the early universe, directly after the Big Bang (before cooling).
Benefit to society: understanding the origin of the universe
Au+Au event in the PHENIX detector
Relativistic Heavy Ion Collider
Why Heavy Ion Collisions?
Ordinary nuclear matter
protons and neutrons
Quark-Gluon Plasma
quarks and gluons
Heat and compress
cone of particles “jet”
proton
How do we probe the collisions?
Hard scatterings between partons (quarks/gluons) in nucleon-nucleon collisions produce jets of particles.
A “jet” is a directed spray (or cone) of particles, which can have large energies measured by our detectors
What is the effect of the QGP?
Measurement in Au+Au Collisions
“Control” Experiment: d+Au Collisions
Conclusion:
In Au+Au collisions, the number of particles
produced at large energies is suppressed.
In d+Au collisions, there is no suppression
in the number of particles produced at
large energies.
 Suppression is due to the medium
produced in Au+Au collisions (QGP?).
We have produced very hot and dense
matter in Au+Au collisions at RHIC!
Nucleus +
nucleus
(Au+Au) collision
Proton/deuteron
+ nucleus
(d+Au) collision
Central Au+Au
* p+p scaled by Nbinary(central)
We measure the number of
particles vs. energy in
Au+Au collisions and
compare with the (scaled)
number of particles in p+p
collisions
Large+Large vs.
Small+Small
We find that the number of
particles produced at large
energies in Au+Au collisions
is suppressed relative to
expectation. -- A new effect
first observed at RHIC!
d+Au: (Small+Large) No Produced medium
R~1  no suppression observed
suppression
Au+Au: (Large+Large) Produced medium
R ~ 0.2  factor 5 suppression in number of particles at large energies  “Jet Quenching”