Answers to Homework

1. Answers to Homework L.C. Bland STAR Review of FMS 2 September 2009

2. Q1. Please provide a description of latency and functionalities for each required level of online monitoring • Answer • Latency 0 : LED response (sums and/or cell-by-cell) in online plots for shift crew • Latency 1 min: Trigger-level bit checking • Latency 5 min: Experts reading trigger data file manually for debugging • Latency 10 min: Online farm monitor • Latency hours: Trigger data files from HPSS accessed at RCAS/fastoffline • Latency 1 day: Iterations on p0 reconstruction at RCAS/feedback to HV

3. Q2. Please provide figures showing the stability of the LED system (i) under stable running conditions; (ii) after events such as a power dip. What is the expectation for the stability across years? First 3 examples of cells with LED response with 2tot < 2000 from north-inner calorimeter under stable running conditions

4. Further Answers to Q2 LED response for the same 3 phototubes for runs before/after massive weather-induced power dip on day=178. Data readily available was from online monitoring, and does not include all runs, since the importance of LED monitoring was fully established during RHIC run 9. Day=178 was missing due to return travel from a workshop. “stable” conditions before/after day=178 power dip PMT <Q>,10169004<run<10175039 <Q>,10177006<run<10179020 5 62 61.7 8 143.6 141.8 12 119 118.1

5. Further Answers to Q2 Multi-year stability is unknown. Likely not a real issue, given ability to cross check versus neutral pion based reconstructions. Conclusion: LED monitoring is robust

6. Q3. What is the expected sensitivity of the LED system-including fiber distribution system-to radiation damage? Experience with optical fibers for BBC readout does not indicate significant transparency loss due to radiation damage versus time (virtually identical positioning of detectors and fibers from RHIC run 2 through RHIC run 9). Basis for this is comparable year-to-year detector resolution to minimum-ionizing particles, and similar HV applied to phototubes. Pulse generator chips may have failure modes associated with radiation damage, or some other cause. East FPD modules have been in place since run 3. East FPD LED system has not run continuously. Nonetheless, the LED pulse generator chips were fully operational in RHIC run 9, after seven years of RHIC operation. Bottom line: sensitivity of LED system to radiation damage is expected to be minimal.

7. Q4. Please provide information on the rates of dead and noisy channels, as a function of time. • Next page reproduces page 16 from a presentation at the spin working group meeting during the September 2008 STAR Analysis Meeting. The page primarily addresses gain spread, but also shows holes from dead and noisy channels for the inner calorimeter of the FMS. • Analyses that led to preliminary results do not reveal signficant time dependence to the number of dead/noisy channels. Final analyses will require better quantification of detector status versus time.

8. Gain Spread • High voltage set points determined from spectral slopes, in comparison to full PYTHIA/GSTAR simulations. Not all detectors could be operated at desired set points. • Offline gains determined from high-tower associated invariant mass. • Comments: • White boxes are holes • corners are detectors with XP2972 phototubes FMS inner calorimeter gains (GeV/count) from p0 peak centroid in high-tower associated invariant mass distributions Plan: perform online analysis of p0 peak centroid in high-tower associated invariant mass, and feedback correction factors into high voltage set points

9. Q5. Please outline kinematic reach and expected timeline to completion for the analyses presented on slide 13 of the introductory talk • Goal 1 – achieved via normalized correlations for p+p/d+Au involving forward p0 • 0.01<x<0.05 (correlated hadron at midrapidity) • ~1 month to complete p+p efficiency study • ~3 months to complete d+Au efficiency study • ~2 months for final normalizations, including luminosity • 0.003<x<0.01 (correlated p0 in interval 2<h<1) • >6 months, later if calibrations/p0 finding developments are required • 0.001<x<0.003 (correlated p0 at large rapidity) • ~1 month to complete d+Au data assessment • ~5 months for efficiency studies and final normalization

10. Further answers to Q5 • Goal 2 – achieved via data/theory comparison for correlations for p+p/d+Au involving forward p0 • Page 6 estimates ~6 months for data analysis for FMS p0 pairs and for correlated hadron at midrapidity. >6 months is estimated for correlated p0 in 1<h<2 range • Comparison to theory is expected to take ~2 months after data is available. Plan is to begin contact with theorists that have quantitative models • Goal 3 – measurements of transverse spin asymmetries… • Present understanding is that p+p data beyond run-8 will be required. Achieving goal 3 at s=500 GeV is more difficult than at s=200 GeV • Present understanding is that full jets rather than just jet surrogates are important

11. Q6. Please outline the distribution of online gains Run 8 p+p gain factors used in analyses • Comments: • Estimate gain spread is ~5 smaller than intrinsic gain spread of PMT operated at fixed voltage. Specification for new PMT purchases typically include tolerance on gain spread. • p0 reconstructions were not available during run due to a simple coding issue that read the mapping data. Their importance was stated at a January 2008 STAR operations meeting. • These gains are used in reconstructions, including trigger emulation, of PYTHIA/GSTAR events and result in good agreement with most data distributions studied to date.