Low Energy Test Run Results

UC Davis June 16-21st 2008 1Rosi Reed

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

3

5.5 % with Vertex

Yellow = cogged at Phenix

3.3% with Vertex r < 2 cm


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


Au-Al HBT Analysis – Rigidity

π+

π-

pt

d


Some Calculations – Au-Al Events


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


Eta for Au-Al Events

30% Central

Proton

30% Central

Pion

30-100% Central

Proton

30-100% Central

Pion

PID done through nSigma cut


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


Proton/Pion Ratio for Au-Al Events

Increase in p vs pi at y = 0 comes from Al spectators


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


Au-Al pi- HBT Analysis


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


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


Assuming the beams have the same width


Beam profile vs time Summary

Calculated from Vx vs Vy distributions

# Beam-Beam Events

Blue = Run 72, Yellow Run 73, Grey Run 74


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


Vernier Scan Versus Average Event Location

Slope should be +/- 0.5 if our assumptions were correct


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


Events During Vernier Scan

During Vernier Scan it appears the empty event rate follows the beam-beam event rate in runs 72 and 73.


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


Backup Slides


Vernier Scan


Vx Vy Distribution of 1st Primary Vertex at 9 GeV

24


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


Number of Vertices per Event

26

• 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)


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.


Average Eta by Event

28

Run 97, 76, 72

Eta averaged over primary tracks only


Vx vs Vy Distributions for Same Vernier Scan Locations


Track Eta Distribution for Eta Ave > 0

Low Energy Test Run Results

Documents

Transcript of Low Energy Test Run Results