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Upsilon
Particles in
High-Energy
Au+Au
Collisions
Catie Talbert
Austin College
Texas A&M – Cyclotron Institute
REU 2006
Mentor: Saskia Mioduszewski
Grad Student: Matt Cervantes
Outline
• Physics Motivation – QGP
• Background
– The Accelerator – RHIC
– The Detector – STAR
• Theoretical/Experimental Approach
– Suppression/Enhancement of J/Y and Upsilon
– STARsim Program
• Summary and Outlook
Physics Motivation
• Quarks
– 6 flavors
– Interact in
accordance with the
strong force
– Exist only in
triplets (baryons) or
paired with an antiquark (mesons)
– No free quarks
Physics Motivation
• Quark-Gluon Plasma (QGP)
– Phase change that occurs at high energy densities
– Quarks are so densely packed that they no longer
recognize their own boundaries – they become
“free” to move
Physics Motivation
• Where can we find
QGP?
– Thought to have existed
shortly after the Big
Bang
– May also exist in (very
dense) neutron stars
– Re-create QGP at RHIC
The
Detector
–
STAR
The Accelerator – RHIC
•Solenoidal
Tracker
at RHIC
• Relativistic
Heavy-Ion
Collider (RHIC)
– 2.4 mile circumference
– 200 GeV (.99995c)
– Gold (Au) ions and protons
The Detector – STAR
• STAR detector subsystems
•Solenoidal magnet
Provides for a uniform
axial magnetic field
•Time Projection Chamber
Gives complete 3-D
information of the
particle tracks
•Electromagnetic
Calorimeters
Provides information
on the energy
deposited by e+/- and γ
STAR’s Mission
To re-create the QGP and study
the dynamics of quark matter by
observing the particles resulting
from the collisions
Theoretical Approach
• Quarkonium
– Meson made up of
a quark and its own
anti-quark
• Charmonium
– J/Y (cc)
• Bottomonium
– Upsilon (bb)
Theoretical Approach
• Suppression of J/Y
– Compared to p+p collision (multiplied by # of
nucleons)
– During initial collision, charm (bottom) particles
are produced
– In QGP phase, deconfinement, quarkonium no
longer bound, charm prefers to combine with a
light quark
– Suppression of charmonium was thought to be a
signature of the QGP (original idea of Matsui,
Satz)
Theoretical Approach
• Enhancement of J/Y
– RHIC has higher energies than previous
experiments
• Increased initial charm production
• Increased chance to thermalize
• J/Y can recombine
– Possible increased charmonium count after QGP
phase (Grandchamp, Rapp)
• New problem:
– Suppression (deconfinement) and
Enhancement (recombination)
Upsilon Particle
• Bottom (Upsilon) is much more rare than
charm (J/Y)
– Bottom quark is heavier than charm, takes more
energy to make
• Because bottom quark is heavier, difficult to
thermalize ENHANCEMENT not an issue
• Only a measure of suppression, disentangles
new Suppression/Enhancement puzzle
(Grandchamp, Rapp, Lumpkins, van Hees, Sun)
Experimental Approach
• Importance of STARsim Simulation
– Upsilon is very rare particle, difficult to measure
– We can insert simulated Upsilon particles into real
events and then be able to search for them
– This allows for a measure of detector efficiencies
– Simulation allows us to set an upper limit on the
production of Upsilon particles resulting from a
collision
Experimental Approach
STARsim Program
Upsilon Simulation
Decays to electron, positron
J/Y Simulation
Decays to electron, positron
Summary and Outlook
• Goal of RHIC/STAR to create and study QGP
• Because of complications with suppression
and enhancement, Upsilon is important for
understanding J/Y data at RHIC and whether
or not QGP is observed
• Simulation is critical for measurement of
Upsilon
Summary and Outlook
• This summer we got
STARsim up and
running (!) for single
particle generation
• Next step is to embed
simulated Upsilon
particle into real data
from STAR
Acknowledgements
• Dr. Saskia Mioduszewski, Texas A&M
Cyclotron Institute
• Matt Cervantes, Graduate Student, Texas
A&M Cyclotron Institute
• STAR Collaboration