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Identification of Upsilon Particles
Using the Preshower Detector in
STAR
Jay Dunkelberger, University of Florida
Outline
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Quarks, Confinement, and QGP
Relativistic Heavy Ion Collider and the STAR
experiment
Heavy Quarkonia
STAR’s Electromagnetic Calorimeter and
Preshower detector
Summary
Quarks
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Building blocks for hadrons
Come in six flavors
Interact via the strong force,
which is mediated by gluons
Are found bound as triplets
in baryons, or pairs in
mesons
Free quarks and gluons are
never observed because of
the nature of the strong
force (confinement)
Deconfinement and QGP
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At extremely high temperatures ( >10¹² K) quarks are no
longer confined to specific baryons or mesons
New deconfined state of matter called Quark-Gluon
Plasma is formed
The QGP is thought to have existed in our universe up
to 10⁻⁵ seconds after the Big Bang
Relativistic Heavy Ion Collider (RHIC)
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Located at Brookhaven
National Laboratory on
Long Island
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Can collide Au nuclei at
energies of up to 200 GeV
per nucleon-nucleon pair
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At these energy densities it
is possible for the QGP to
be formed briefly
The STAR Detector
•Gold nuclei collide in
the center of the
detector
•STAR is able to
record about 100 of
the thousands of
events per second
•Decisions are made at the hardware and
software levels as to which data are
recorded for analysis
STAR Detector Systems
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Solenoid Magnet
Establishes uniform magnetic field parallel to the beam
axis
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Time Projection Chamber
Records hits that are later reconstructed into tracks for charged
particles that can be used to identify particles and determine
their momentum
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Electromagnetic Calorimeter
Measures the energies of electromagnetically interacting
particles, can detect neutral particles (e.g. photons)
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Preshower Detector
Helps distinguish between hadrons and electrons in the
EM calorimeter
Au + Au Collision at STAR
J/ψ Particle
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Neutral meson composed of a charm
anti-charm pair
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Has a rest mass of about 3.1 GeV/c²
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A suppression of J/ψ is expected in
QGP compared to binary scaling of
data from proton-proton collisions
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Suppression has already been
observed at lower energies
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At RHIC energies recombination of
J/ψ is possible
Upsilon Particle
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Consists of a bottom anti-bottom pair
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Rest mass is about 9.5 GeV/c²
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Like J/ψ it is expected that Y production will be
suppressed in the QGP, but Y is much heavier than
J/ψ so recombination is not likely
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Comparing J/ψ and Y yields could provide important
evidence for the formation of QGP
Finding Upsilon Particles
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Look for Y particles that decay to e⁺ e⁻ pair
Combinatorially create opposite-sign pairs and generate invariant
mass plot
Create like sign pairs to generate background
Subtract out the background and look for a peak at the Y mass
(~9.5 GeV/c²)
BEMC Towers
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21 layers of scintillator and
lead
Particles that interact by EM
force start showers in lead
plates which shows up as light
in scintillator
Light signals are carried away
by fiber optic cables, and
converted to digital values
At layer five is the Shower
Maximum Detector
First two layers serve as
Preshower detector
Preshower Detector (BPRS)
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First two layers are read out separately from the rest
of the tower
Using Preshower data we can greatly reduce
hadronic background
About 84% of electrons will shower in the first two
layers of the BEMC, compared to only about 6% of
hadrons
Rough estimates showed a two times improvement
in relative electron yield
BPRS is currently being commissioned as a part of
the STAR detector
Particle Identification
Comparing Yields: No BPRS
dE/dx as measured in TPC (2 GeV/c < p < 3 GeV/c)
Comparing Yields: with BPRS
dE/dx as measured in TPC (2 GeV/c < p < 3 GeV/c)
Commissioning the BPRS
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The BPRS has not yet
been incorporated as a
part of STAR’s analysis
One task was to modify
the preexisting status
table package to include
BPRS data
Status tables are stored
in a database so
analyzers know which
towers are giving good
data for a given run
A graph of the raw ADC values
taken from the BPRS detector
Summary and Future Work
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Heavy quarkonia can be useful in gathering
information about the QGP
STAR’s Preshower detector gives a method
for effectively screening out hadrons from our
data
Need to run our upsilon analysis on a full
data set
Acknowledgements
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Dr. Saskia Mioduszewski
Dr. Rory Clarke
Matt Cervantes
STAR Collaboration
Cyclotron Institute, Texas A&M University