Composites in 28AGev Collisions in E895

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Composites in 2-8AGev Collisions in E895

• Stephen Baumgart
• University of California, Davis
• for the
• E895 Collaboration
• N. Ajitanand(2), J. Alexander(2), M.G.
  Anderson(1), D. Best(4) , F.P. Brady(1), T.
  Case(4), W. Caskey(1) , D. Cebra(1), J.L.
  Chance(1), P. Chung(2), B. Cole(9), K. Crowe(4),
  A. Das(6), J.E. Draper(1), M.L. Gilkes(5), S.
  Gushue(8), M. Heffner(1), A.S. Hirsch(5), E.L.
  Hjort(5), L. Huo(10), M. Justice(3), M.
  Kaplan(7), D. Keane(3), J.C. Kintner(12), J.L.
  Klay(1), D. Krofcheck(11), R. Lacey(2), J.
  Lauret(2), M.A. Lisa(6) , H. Liu(3), Y.M.
  Liu(10), R. McGrath(2), Z. Milosevich(7), G.
  Odyniec(4), D.L. Olson(4), S.Y. Panitkin(3), C.
  Pinkenburg(2), N.T. Porile(5), G. Rai(4), H.G.
  Ritter(4), J.L. Romero(1), R. Scharenberg(5), L.
  Schroeder(4), B. Srivastava(5), N. Stone(8),
  T.J.M. Symons(4), A.H. Tartir(1), R. Wells(6), J.
  Whitfield(7), T. Wienold(4), R. Witt(3), L.
  Wood(1), W.N. Zhang(10)
• (1) University of California,
  Davis, California 95616 (2) State University
  of New York, Stony Brook, New York 11794-3400
  (3) Kent State University, Kent, Ohio 44242
  (4) Lawrence Berkeley National Laboratory,
  Berkeley, California 94717 (5) Purdue
  University, West Lafayette, Indiana 47907-1396
  (6) The Ohio State University, Columbus, Ohio
  43210 (7) Carnegie Mellon University,
  Pittsburgh, Pennsylvania 15213 (8) Brookhaven
  National Laboratory, Upton, New York 11973 (9)
  Columbia University, New York, New York 10027
  (10) Harbin Institute of Technology, Harbin
  150001, P.R. China(11) University of Auckland,
  New Zealand (12) St. Marys College, Moraga,
  California 94575 Feoder Lynen Fellow of the
  Alexander v. Humboldt Foundation

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The TPC Detector
The E895 experiment is a fixed target Au on Au
experiment. Using the AGS at BNL, the experiment
was run at the beam energies of 2,4,6, and 8 A
Gev. After the ions collide the products move
through the detector, ionizing the gas. Their
curvature in the B-field gives their momentum.
The amount of ionization gives the particles
velocity from the Bethe-Bloch parameterization.
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Motivations

• The purpose of heavy ion experiments is to learn
  about hot, dense matter. Questions like What are
  the properties of hot, dense matter? and Are
  there phase transitions at very high temperatures
  and densities? can be answered.
• Using heavy ion accelerators, new regions of
  phase space can be probed.
• To learn about the nuclear equations of state,
  things like temperature, flow, the time evolution
  of the system, density, and other properties must
  be known.
• Because condensates like deuterons, and helions
  form only under certain conditions, by studying
  the condensates, the properties of the hot, dense
  matter of the fireball can be found.

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Fitting Spectra
Particle yields are extracted from fitting
spectra. The raw data from the detector is binned
into a mt-m0 vs. rapidity phase space. Then, the
spectra are fitted by fixing the proton and pion
yields based on temperature and dN/dy parameters
from a previous analysis.
(1/2pmt)(d2N/dydmt)
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Composites
In this project the yields of composites were
analyzed. Composites form in a process called
coalescence.

• Coalescence occurs when two particles are close
  together in phase space and can combine to form a
  new particle. An example of this is when a proton
  and a neutron combine to form a deuteron.
• Tritons are created when a neutron combines with
  a deuteron. Helions are created when a proton
  combines with a deuteron.

Once the spectra are found, one can draw
inferences about hot, dense matter.
The first thing done with the spectra was to fit
them with Boltzmann curves for temperature and
dN/dy parameters.
The rapidity in the beam direction, y, is often
correleated with a particles angle from beam
direction. A phenomena that has an angular
dependence will be noticed by finding dN/dy.
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Deuteron dN/dy
Deuterons form from protons and neutrons. The
process that occurs in a heavy ion collision is
not so much different than what occurred in the
hot, dense early universe.
Gaussian model for 4? yields
34.2 35.6 34.3 35.0
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Triton dN/dy
Tritons must coalesce out of deuterons and
neutrons. There are fewer deuterons than protons
or neutrons so the triton yields are smaller.
Gaussian model for 4? yields
8.5 9.1 8 8
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Helion dN/dY
Helions are rare compared to protons and
deuterons in the E895 experiment but because they
have twice the charge of other common particle
species, they are easier to identify.
5.7 2.8 4 2
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dN/dy for Deuterons ,Tritons, and Helions
We can check to see if we have found all the
protons in these events. The Total yield of
protons will be the sum of the initial protons
plus those neutrons converted into protons
through the delta channel.
The distribution is a Gaussian function with
respect to rapidity. Integration will give the
total number of protons.
Once error propagation is done, the differences
can be checked to make sure they are within
errors.
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Calculating the Gaussian Radius of the Source

• Using the measured proton and deuteron spectra,
  one can calculate a coalescence radius for proton
  emission. A similar technique can be used to find
  a coalescence radius for protons and deuterons.

Llope et. AL. Phys. Rev. C 52, 2004
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Coalescence Radii for Various Rapidities
In order to compare different particles, all
mt-m0s for coalescence radii assume proton mass.
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Coalescence Radii for Various Rapidities
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Radii from Helion Coalescence (ycm 0)
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Interpretation of Gaussian Radii of Source
The coalescence radii give the probability of
particle emission by a Gaussian equation
Where A constant RG coalescence
radius r transverse distance
From the these graphs, one can see how
coalescence radii show a transverse momentum
dependence.
As you can see from the graphs of coalescence
radii for different rapidity, the radii vs. mt
function changes as a function of y. Because y is
correlated with the angle from the beam
direction, this suggests that the source is not
spherical.
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Proton Phase Space Density
Phase Space is defined as the density of
particles per six dimensional momentum-coordinate
space.
Because the radii and the yields in momentum
space are known, the phase space density can be
calculated.
This is a thermal system so the phase space
density is expected to decrease exponentially
with mt.
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Future Goals

• Do error propagation!
• Find source size as a function of rapidity.
• The temperature values from the spectra can be
  used to estimate the blast velocity of the
  fireball.
• Fits to determine chemical potential can be done.
  
• While fitting the spectra with Boltzmann curves,
  it became apparent that flow effects were
  occurring. This deserves further study.