UC Davis June 16-21st 2008 1Rosi Reed
Low Energy Test Run Results
Rosi Reed
University of California at Davis
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Introduction
• Event quality• Beam Pipe Events
– Spectra– HBT
• Beam Profile Analysis
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Summary 9 GeV Test Run
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5.5 % with Vertex
Yellow = cogged at Phenix
3.3% with Vertex r < 2 cm
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Multiplicity – Cut on Events heading into the TPC
30% Central
62.4 GeV points are scaled to match 3.2 GeV points at Nch = 13
Au-AlAu-Al + Alpha-Al
An increased yield in low multiplicity events could be the result of alpha particles from Au break-up hitting the beam pipe
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Au-Al HBT Analysis – Rigidity
π+
π-
pt
d
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Some Calculations – Au-Al Events
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Eta for Au-Al Events
30% Central
All
All
30-100% Central
Events with a Negative Average Eta Flipped for Graphs 2-4
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43
Increase at Eta = 0 from Spectators from Al
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Eta for Au-Al Events
30% Central
Proton
30% Central
Pion
30-100% Central
Proton
30-100% Central
Pion
PID done through nSigma cut
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Pion+ Proton Yield for Au-Al Eventsybin = 0.5 around ycm
No efficiency corrections made
T ~ 80 +/- 2 MeV T ~ 91 +/- 3 MeV T ~ 99 +/- 4 MeV
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Proton/Pion Ratio for Au-Al Events
Increase in p vs pi at y = 0 comes from Al spectators
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Au-Al HBT Analysis (root SNN = 3.2)
• Event quality cuts:– Vr > 2 cm (Not Au+Au collisions)– |Vz| > 75 cm (Not Au+Be collisions)– Vz*TotalEventPz < 0 (Events “into” TPC)– Events with Pz < 0 flipped (pz = pz*-1)– Multiplicity > 10 (30% Central)
• Track Quality cuts:– Assumed all negatively charged tracks were pions– nHits/nPossHits > 0.5 for either TPC or FTPC
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Au-Al pi- HBT Analysis
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Beam profile vs time
• Analyzed Vx vs Vy distributions vs time for – Run 72 (13:26:02 – 28:25)– Run 73 (13:36:10 – 13:37:30)– Run 74 (43:12 – 44:21)
• Binned distributions with the same Vernier scan location
• No Z vertex cuts• Cut on Vr < 2
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Gaussian Multiplication
• Beam is gaussian in shape• Distribution of collisions in xy space is equal
to the beam distributions multiplied by each other– Also gaussian in shape
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Assuming the beams have the same width
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Beam profile vs time Summary
Calculated from Vx vs Vy distributions
# Beam-Beam Events
Blue = Run 72, Yellow Run 73, Grey Run 74
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Beam Sigmas calculated from formula on pg 15
Sigma X = 1.75 mm +/- .20
Sigma Y = 2.40 mm +/- .15
Error bars reflect statistical error only
If our assumptions are correct, these distributions should be flat
Beam Sigmas
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Vernier Scan Versus Average Event Location
Slope should be +/- 0.5 if our assumptions were correct
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Time Decay for Run 97
Empty events fall off exponentially
Beam-Beam and Empty Events have the same time constant
Beam-Pipe events have twice the time constant of Beam-Beam and Empty Events
Run 97 occurred after BBC threshold was lowered
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Events During Vernier Scan
During Vernier Scan it appears the empty event rate follows the beam-beam event rate in runs 72 and 73.
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Conclusion
• We still do not understand why we triggered– Empty events
• BBC threshold changed but the trigger rate still seems to be beam related
– Beam-Pipe Events• Beam Pipe events are a combination of Au-Pipe
Material and Alpha-Pipe Material
• We have a reasonable estimate of the good event rate
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Backup Slides
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Vernier Scan
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Vx Vy Distribution of 1st Primary Vertex at 9 GeV
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Z Axis distributions
Thin Be beam pipe extends from Z = -75 cm to 75 cm. Outside 75 cm there is a thicker Al beam pipe.
3.6 AGeV Au+Be
3.6 AGev Au+Al
3.6 AGev Au+Al
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Number of Vertices per Event
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• 78.9% of events had 1 primary vertex– 81.6% of “beam-beam” events have 1 primary vertex– 71.6% of “beam-pipe” events have 1 primary vertex
(Data taken from runs 97,76,72)
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XY Location of 2nd + 3rd Vertices for Events with Vertex 1 r > 2 cm
Data from Runs 97, 76, 72
Only 8 % of secondary vertices and 8 % of teritary vertices of events labeled as beam pipe events are located in the center
Indicates that most events labeled as beam pipe events are not Au-Au events that have kicked off an energetic particle.
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Average Eta by Event
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Run 97, 76, 72
Eta averaged over primary tracks only
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Vx vs Vy Distributions for Same Vernier Scan Locations
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Vx vs Vy Distributions for Same Vernier Scan Locations
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Track Eta Distribution for Eta Ave > 0
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