Checking Radiation Length Systematic Error Effect on f->KK Reconstruction Efficiency

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

2. Review Status of the Run2 DiscrepancyLooking at the integrated yield numbers dN/dy • Publications from Run2 Au+Au data at 200 GeV • STAR in PL B 612 (April 2005) 181-189 • PHENIX in PR C 72 (July 2005) 014903 • One common centrality bin and minimum bias datacan be directly compared using exponential fitting • Both experiments say that their Run4 results agree with their Run2 results Run2 discrepancy factors for dN/dy 1.69 +/- 0.27 (0 - 10% centrality) 1.79 +/- 0.13 (minimum bias) statisticalerrors only Radiation Length Systematic Effects

3. Minimum Bias Data Comparison I Using same mT range for both data sets Two data sets are plottedThe 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 Radiation Length Systematic Effects

4. Minimum Bias Data Comparison II Same data sets are plottedSame 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 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 valuesbut 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 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 unknownradiation length much before the DC • Test extra radiation length (3%) added in PC1 • One inch “hexcell” volume before and after gas gap is replaced withpure 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 PC2Also studied effect of increasing RL in only PC2 and PC3 • Study before and after effects on f->KK at pT = 0.82 - 0.84 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 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 MeVfor 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 Radiation Length Systematic Effects

8. Effect of 3% Extra RL in PC1 on TOF Tracking and Kaon IDFor 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% RLTOF ISKAON variable already high at 0.52 goes to 1.18 with extra 3% RL Radiation Length Systematic Effects

9. Effect of 3% Extra RL in PC1 on TOF Kaon ID VariableFor 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 stronglymomentum dependent at low pT even without extra RL 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? 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% RLEMC mass variable already high at 0.271 goes to 0.278 with extra 3% RL 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% RLEMC mass variable already high at 0.273 goes to 0.280 with extra 3% RL Radiation Length Systematic Effects

13. Effect of 3% Extra RL at PC1 on f->KKYield For kaons from f->KK at mT = 0.3 GeV/c Default MC RL 12.6M f Extra 3% MC RL13.3M f Reconstructed sum = 1322 Reconstructed sum = 1569 Loss of f->KK with 3% RL addition at PC1 = 20 +/- 3% (MC cuts tuned) Radiation Length Systematic Effects

14. Effect of 3% Extra RL at PC2 and PC3 on f->KKYield For kaons from f->KK at mT = 0.3 GeV/c Extra 3% MC RLPC2, 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 ! Radiation Length Systematic Effects

15. Compare PC3 and EMC sfandsz with actual residuals East PC3 q projectionerror vs szdistribution East EMC f projectionerror vs sfdistribution East EMC q projectionerror vs szdistribution East PC3 f projectionerror vs sfdistribution 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 PISAMean 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 reconstructionefficiency 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 STARsince 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) Radiation Length Systematic Effects