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