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QCD (Quantum ChromoDynamics)
-QCD describes the
interactions between
quarks and gluons.
-There are six flavors of
quarks, and eight gluons,
all carrying color charge
Finite Size Effects on
Dilepton Properties
in Relativistic Heavy
Ion Collisions
Trent Strong, Texas A&M University
-The force between quarks
is strong and is linear in
distance! (coupling constant
αs≈1)
Advisors: Dr. Ralf Rapp, Dr. Hendrik van Hees
Texas A&M University
-Force weakens at small
distances (or high
energies), so quarks
essentially free within close
distances
(asymptotic freedom)
Development of excess with centrality, broadening of ρ
spectral shape
Time Evolution of Relativistic
Heavy-Ion Collision
-Cocktail: Component from hardscattering processes; surface
contribution
-Colliders accelerate nuclei to
very relativistic speeds!
(RHIC, γ ≈ 10, v=.995c)
At NA60: In-In @ 158
GeV/Nucleon
Total Spectra = a ∙ (Thermal) + b ∙ (Cocktail)
-In this region, QGP and other
forms of exotic matter like a
hadron gas can form
Results: Naive Two-Component
Model
-They allow us to test further
the theory of QCD and explore
the early universe
Electromagnetic Probes:
Dileptons and Photons
Semiperipheral
M [GeV]
M [GeV]
a.) are produced abundantly,
and throughout the history
of the collision.
-Predicted transition temperature is ~
170 MeV, corresponding to a
temperature on the order of 1012 K.
-Quarks and gluons form a hot and
dense soup!
Peripheral
Dileptons and photons good
sources of information from a
hot and dense medium since
they:
-Quark-Gluon Plasma (QGP)- form of
matter predicted by QCD at high
temperature and density.
-As density and temperature become
very large, hadrons formed by quarks
overlap
=> quarks lose their affiliation with
any particular hadron.
Collision Zone
-Thermal or In-Medium:
Components from thermal medium,
such as QGP or hadron gas; bulk
contribution
-Nuclei collide, a hot and dense
region is formed
Quark-Gluon Plasma
Two-Component Model
Idea: Attempt to model spectra
using two contributions…
Relativistic Heavy-Ion Collisions
b
NA60 Dilepton Data:
Invariant Mass Spectra
b.) do not interact strongly
with the
medium.
The ρ meson is the dominant
producer of dileptons.
The particles carry this
information via their invariant
mass and 4-momentum.
Semicentral
M [GeV]
Semicentral
pT < 0.5 GeV
Central
M [GeV]
Semicentral
pT > 1.0 GeV