low energy test run results
DESCRIPTION
Low Energy Test Run Results. Rosi Reed University of California at Davis. Introduction. Event quality Beam Pipe Events Spectra HBT Beam Profile Analysis. 2. Summary 9 GeV Test Run. 5.5 % with Vertex. 3.3% with Vertex r < 2 cm. Yellow = cogged at Phenix. - PowerPoint PPT PresentationTRANSCRIPT
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
12
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