Upsilon Particles in HighEnergy Au Au Collisions

1
Upsilon Particles in High-Energy AuAu Collisions
Catie Talbert Austin College Texas AM
Cyclotron Institute REU 2006 Mentor Saskia
Mioduszewski Grad Student Matt Cervantes
2
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

3
Physics Motivation

• Quarks
• 6 flavors
• Interact in accordance with the strong force
• Exist only in triplets (baryons) or paired with
  an anti-quark (mesons)
• No free quarks

4
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

5
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

6
The Accelerator RHIC

• Relativistic Heavy-Ion Collider (RHIC)
• 2.4 mile circumference
• 200 GeV (.99995c)
• Gold (Au) ions and protons

7
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 ?

8
STARs Mission

• To re-create the QGP and study the dynamics of
  quark matter by observing the particles resulting
  from the collisions

9
Theoretical Approach

• Quarkonium
• Meson made up of a quark and its own anti-quark
• Charmonium
• J/Y (cc)
• Bottomonium
• Upsilon (bb)

10
Theoretical Approach

• Suppression of J/Y
• Compared to pp 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)

11
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)

12
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)

13
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

14
Experimental Approach
Experimental Approach
STARsim Program
15
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

16
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

17
Acknowledgements

• Dr. Saskia Mioduszewski, Texas AM Cyclotron
  Institute
• Matt Cervantes, Graduate Student, Texas AM
  Cyclotron Institute
• STAR Collaboration