1. Charles F. Maguire Vanderbilt University
Checking Radiation Length Systematic Error Effect on f->KK Reconstruction Efficiency
Charles F. Maguire Vanderbilt University

2. Run2 discrepancy factors for dN/dy 1.69 +/- 0.27 (0 - 10% centrality)
Review Status of the Run2 Discrepancy Looking at the integrated yield numbers dN/dy
Publications from Run2 Au+Au data at 200 GeV
STAR in PL B 612 (April 2005)
PHENIX in PR C 72 (July 2005)
One common centrality bin and minimum bias data can be directly compared using exponential fitting
Both experiments say that their Run4 results agree with their Run2 results
Centrality
STAR dN/dy
PHENIX dN/dy
STAR T
PHENIX T
0 - 10%
/ /- 0.73
/ /- 0.62
357 +/ /- 39
376 +/ /- 20
Mininum Bias
/ /- 0.26
/ /- 0.21
353 +/- 9 +/- 39
366 +/ /- 18
Run2 discrepancy factors for dN/dy / (0 - 10% centrality)
1.79 +/ (minimum bias)
statistical errors only
September 15, 2005
Radiation Length Systematic Effects

3. Minimum Bias Data Comparison I Using same mT range for both data sets
Two data sets are plotted The two sets of data are fitted by exponential functions.
The same mT range is used in both fits,omitting low mT STAR points
No significant change in STAR
results as compared with using their full minimum bias mT range
September 15, 2005
Radiation Length Systematic Effects

4. Radiation Length Systematic Effects
Minimum Bias Data Comparison II
Same data sets are plotted Same mT ranges used but omitting lowest mT PHENIX data point
Slight changes in both dN/dy values, but the discrepancy ratio is still the same at 1.7 +/- 0.2 (statistical)
The fact that STAR and PHENIX disagree at the intermediate pT values means that STAR doesn’t see f suppression but PHENIX does
September 15, 2005
Radiation Length Systematic Effects

5. Radiation Length Issues for f->KK Yield
Absorption
Extra radiation length could increase threshold for Kaon detection
Effect would be most pronounced at lower particle pT values but several f pair mT bins might be effected
Multiple scattering
Extra radiation length would increase multiple scattering
Possible loss of acceptance in real vs MC due to tracking cuts
However, MC tracking cuts are compared with and matched to real cuts
Mass identification
Extra radiation length slows down particle speed due to energy loss
Mass identification based on time-of-flight could be compromised
September 15, 2005
Radiation Length Systematic Effects

6. Method for Checking Radiation Length
Any unknown extra radiation length most likely at or after DC
Run4 has only beam pipe and helium bag before DC
Photon conversion analysis indicates no significant unknown radiation length much before the DC
Test extra radiation length (3%) added in PC1
One inch “hexcell” volume before and after gas gap is replaced with pure Lithium as a tracking medium. Gives approximately 3% more RL.
Location advantage that it is common in East and West arms
Gives longer flight time and multiple scattering effects
Extra radiation length could be more in PC3, or in TEC and PC2 Also studied effect of increasing RL in only PC2 and PC3
Study before and after effects on f->KK at pT = GeV/c
Corresponds to lowest PHENIX mT bin being reported mT - mf = 0.3 GeV/c
Check energy loss absorption, multiple scattering, increased decay-in-flight from longer flight time, and mass identification effects
September 15, 2005
Radiation Length Systematic Effects

7. Effect of 3% Extra RL on Kinetic Energy Loss
For kaons from f->KK at mT = 0.3 GeV/c
K.E.
K.E.
Initial K.E. 60 to 300 MeV for initial pT > 250 MeV/c (= 60 MeV)
Default MC RL
Extra 3% MC RL
DK.E. = ~ 4 MeV
DK.E. = ~ 8 MeV
Mean K.E. loss increases only a few (~4) MeV with 3% extra RL
Total absorption of Kaons not an issue; extra RL doubles energy loss
September 15, 2005
Radiation Length Systematic Effects

8. Radiation Length Systematic Effects
Effect of 3% Extra RL in PC1 on TOF Tracking and Kaon ID For kaons from f->KK at mT = 0.3 GeV/c
Default MC RL
Extra 3% MC RL
Slight effect (broadening) on track matching cuts from extra 3% RL TOF ISKAON variable already high at 0.52 goes to 1.18 with extra 3% RL
September 15, 2005
Radiation Length Systematic Effects

9. Radiation Length Systematic Effects
Effect of 3% Extra RL in PC1 on TOF Kaon ID Variable For kaons from f->KK at mT = 0.3 GeV/c
1.53
0.76
3.10
1.81
Default MC RL
Extra 3% MC RL
0.96
0.42
0.70
0.26
TOF ISKAON variable (before recalibration) is strongly momentum dependent at low pT even without extra RL
September 15, 2005
Radiation Length Systematic Effects

10. NOTES ABOUT REAL DATA ANALYSIS
Real data analysis uses recalibration modules
Recalibrators shift the distributions in particle ID and in track matching to be centered at zero (what about widths?)
MC distributions are matched to the real data distributions
Question as to why the raw MC distributions are off center?
Can we see a momentum dependent effect in the real data?
September 15, 2005
Radiation Length Systematic Effects

11. Effect of 3% Extra PC1 RL on West EMCal Kaon Identification
For kaons from f->KK at mT = 0.3 GeV/c K K
p, m
p, m
Extra 3% MC RL
Default MC RL ? ?
Slight effect (broadening) on track matching cuts from extra 3% RL EMC mass variable already high at goes to with extra 3% RL
September 15, 2005
Radiation Length Systematic Effects

12. Effect of 3% Extra PC1 RL on East EMCal Kaon Identification
For kaons from f->KK at mT = 0.3 GeV/c K K
p, m
p, m
Default MC RL
Extra 3% MC RL ? ?
Slight effect on track matching cuts from extra 3% RL EMC mass variable already high at goes to with extra 3% RL
September 15, 2005
Radiation Length Systematic Effects

13. Effect of 3% Extra RL at PC1 on f->KK Yield
For kaons from f->KK at mT = 0.3 GeV/c
Default MC RL 12.6M f
Extra 3% MC RL 13.3M f
Reconstructed sum = 1322
Reconstructed sum = 1569
Loss of f->KK with 3% RL addition at PC1 = 20 +/- 3% (MC cuts tuned)
September 15, 2005
Radiation Length Systematic Effects

14. Loss = 19 +/- 3%; however the loss is entirely on the West side !
Effect of 3% Extra RL at PC2 and PC3 on f->KK Yield
For kaons from f->KK at mT = 0.3 GeV/c
Extra 3% MC RL PC2, PC3 13.7M f
Default MC RL 12.6M f
Reconstructed sum = 1569
Reconstructed sum = 1298
Loss = 19 +/- 3%; however the loss is entirely on the West side !
September 15, 2005
Radiation Length Systematic Effects

15. Compare PC3 and EMC sf and sz with actual residuals
East PC3 q projection error vs sz distribution
East EMC f projection error vs sf distribution
East EMC q projection error vs sz distribution
East PC3 f projection error vs sf distribution
September 15, 2005
Radiation Length Systematic Effects

16. Summary of Effects of 3% RL Increase
Two simulations of 3% RL increase were done
Simulations used lowest mT bin f->KK mesons (pT = 0.83 GeV/c, mT = 0.3 GeV)
First simulation had 3% RL increase at PC1 East and West
Second had 3% RL increase at both PC2 (West) and PC3 East and West
Each simulation compared to default RL in PISA
First simulation showed that the average increase in energy loss = 4 MeV
3% RL increase effectively doubles the energy loss of the default RL in PISA Mean K.E. is greater than 180 MeV, so total absorption unlikely important
Largest singles observable effect is half a s shift upward of mass ID parameter
First simulation showed a uniform 20% decrease in f->KK pair reconstruction efficiency in both East and West Arms
Second simulation has no decrease in East yield but a 20% decrease in the West Arm
Conclusions
Increased RL will lead to some loss in reconstruction efficiency probably because of multiple scattering tails or increased decay-in-flight (could repeat PISA w.o. mu. sc.)
Radiation length mistake unlikely to be cause of 1.7 factor discrepancy with STAR since we must surely know the RL to at least a factor of 2?
Effective radiation length can be probed with shifts in real data mass peak in TOF
MC tracking dispersions are not zero-centered or normalized for both TOF and EMCal
Need to compare these results with real data (ongoing with Dipali and Debsankar)
September 15, 2005
Radiation Length Systematic Effects