Update on BPRS calibration and its effect on Heavy Quarkonium

1. Matthew Cervantes Texas A&M University Update on BPRS calibration and its effect on Heavy Quarkonium STAR Analysis Meeting: HF

2. Electron identification in STAR Barrel Preshower (BPRS) in STAR BPRS calibration method in AuAu 2007 data BPRS “Re-calibration” BPRS and Heavy Quarkonium Outline STAR Analysis Meeting: HF

3. elec had STAR Analysis Meeting: HF Electron identification in STAR • Time Projection Chamber (TPC) momentum: charged track curvature dE/dx: Ionization Energy loss of charged particles • High momentum trackslead to a convergence of dE/dx particle bands • Project TPC tracks to BEMC and use the energy from BEMC to form ratio p/E • Shower Maximum Detector (SMD) Energy, position and shower profile BPRS

4. STAR Analysis Meeting: HF BEMC and BPRS in STAR • Sampling Pb-scintillator (5-6 mm thick layer ~X0) • Tower ~21 X0 : slightly less than 1 hadronic interaction length • Interaction probability for hadrons (Pb only) is ~ 3% before layer 1 (~ 6% before layer 2) • BPRS: ~63% of electrons will shower before the scintillator layer 1 (~84% before layer 2) 20 Xo Most hadron interactions with nuclear material develop at depths beyond the first 2 layers! 15 Xo BPRS

5. BPRS calibration methods (AuAu MinBias) In principle we can calibrate the BPRS by fitting MIP peaks in the ADC spectrum OR by choosing an ADC region that is displaced far enough above the MIP region; well into the “slope region” of an exponentially falling ADC spectrum. High multiplicity of AuAu at 200 GeV buries the MIP peak under the ADC spectrum and the “slope region” is used. 2007 ProductionMinBias data is used and we require no track associations to the BPRS. After a final set of BPRS gain values are derived from the “un-tracked” data, we then apply these gain values to track associated data (tracks matched to BPRS channels) and perform a MIP cross-check at a ring-by-ring level. BPRS calibration method in AuAu 2007 data STAR Analysis Meeting: HF

6. Pedestal and 5*RMS (values from database) subtracted from the ADC of each BPRS channel; slope region fit (30 <= ADC <= 70). Methods for fitting the ADC slope region Area method Determine the average area of an ADC distribution for each ring, then select a reference channel within this ring whose ADC distribution area is closest to that ring average area. Each of the channel distributions within this ring are then adjusted to the distribution of the selected channel, such that the slope of each channel is adjusted to that of the reference channel slope. BPRS calibration: slope region STAR Analysis Meeting: HF

7. Slope method Determine the ring slope average of a given ring, then select a reference channel within this ring whose slope is closest to that ring slope average. Each of the channel distributions within this ring are then adjusted to the distribution of the selected channel, such that the slope of each channel is adjusted to that of the reference channel slope. The area and slope method were both used to calculate channel-by-channel gain values for the BPRS. Gain values were calculated for each of the methods and were self-consistent. BPRS calibration: slope region (cont.) STAR Analysis Meeting: HF

8. Step 1: Alignment of the slopes of each BPRS channel within a particular ring: example (Ring 10) LH panel: Channel slopes within Ring 10: “uncorrected” RH panel: Channel slopes within Ring 10: “corrected” Distribution of channel slopes in Ring 10 now “tight”. BPRS calibration STAR Analysis Meeting: HF

9. Step 2: After alignment of the slopes of each BPRS channel for each of the 40 rings, we then adjust this “new” slope of each ring to a reference ring slope. These ring slopes need adjustment to a reference ring. We choose to adjust “new” ring slopes to Ring 10 slope. BPRS calibration (cont.) • LHS (slope method) and RHS (area method) consistent STAR Analysis Meeting: HF

10. Step 3: Wanted to check if the gain values from BPRS calibration lined up MIP peaks (using track association) Constraints: Tracks have p > 1 and “ADC isolation cut” LH panel (no gains) and RH panel (yes gains) Note the severe disagreement between East and West MIP cross-check (BPRS) Note the number of counts STAR Analysis Meeting: HF

11. Step 3: I noted in one of the HF meetings (5/13/09) that there was a weird West vs. East MIP peak asymmetry. Asymmetry led to inspecting individual BPRS channels. Wanted to find hot/cold towers possibly missed in calib. I discovered “steps” when developing a “hot/cold” cut. MIP cross-check (cont.) RoPichannel = (Channelcounts – Ringaverage counts) ? STAR Analysis Meeting: HF

12. Step 0: Noting the “steps” present in Rings 21-40, will this explain the East vs. West MIP peak asymmetry? Look at ADC vs. BPRS channels (ped/rms subtr.) Are database (ped/rms) values called properly? How does a good channel vs. bad channel look? A step backwards (BPRS “?”) Here the abundance of counts re-appears STAR Analysis Meeting: HF

13. Compare: Check by hand that database values for PEDASTAL and RMS agree with by-hand fit Fit values agree with what is in the database. I.e. BPRS channels 2900-4100 corrupted. Why? A step backwards (BPRS “?” cont.) The physics-tail is corrupted and effectively buried under the noise STAR Analysis Meeting: HF

14. Step 0’: Necessary to exclude the BPRS channels 2900-4100 and then we re-calibrate the BPRS. Mask the corrupted sector of BPRS: 25% dead 25% BPRS masked: now re-run calib. “Step 1,2” Will this affect the West vs. East “asymmetry”? BPRS “Re-calibration” STAR Analysis Meeting: HF

15. Step 1’: Alignment of the slopes of each BPRS channel within a particular ring: example (Ring 10) LH panel: Channel slopes within Ring 10: “uncorrected” RH panel: Channel slopes within Ring 10: “corrected” Distribution of channel slopes in Ring 10 now “tight”. BPRS “Re-calibration” (cont.) STAR Analysis Meeting: HF

16. Step 2’: After alignment of the slopes of each BPRS channel for each of the 40 rings, we then adjusted this “new” slope of each ring to a reference Ring 10 slope. LH plot is re-calibrated slopes and final gains are saved. How does this look when compared to old-calibration? BPRS “Re-calibration” (cont.) Note: West ends are not “identical” because I removed capacitor 127 during re-calibration. STAR Analysis Meeting: HF

17. Step 3’: A re-check if the gain values from BPRS calibration lined up MIP peaks (using track association) Constraints: Tracks have p > 1 and “ADC isolation cut” MIPs: LH panel (pre-?) and RH panel (post-?) RH panel “agreement“ in East vs. West: buried MIPs MIP cross-re-check (BPRS) STAR Analysis Meeting: HF

18. After removing the BPRS channels 2900-4100, then take another look at the RoPi distribution for West and East. RoPi: LH panel (Ring 21 post-?) and RH panel (all Rings post-?). Use RH plot to kick-out the “hot/cold” BPRS channels. BPRS “RoPi” values post-? RoPichannel = (Channelcounts – Ringaverage counts) STAR Analysis Meeting: HF

19. Calibration of the BPRS for 2007 AuAu 200 GeV data is not quite complete. Possibly 25% of the BPRS appears to be “dead”... some type of corruption. MUST figure this out! Have a tentative list of channels that need to be removed under my “RoPi cut”; will circle back and quantify this list soon. BPRS still needs to be “road tested”. 2007 AuAu looks like a loss; ~90+% operational for 2008 and hopefully 2010. Power of BPRS could be 2010. BPRS: To-do list and Future STAR Analysis Meeting: HF

20. Outlined that a “proof-of-principle” exists for using the BPRS in e- rich data at DNP 2007. Repeat: The use of BPRS in 2007 AuAu for the heavy quarkonium analyses is not promising. Recall we tried to see what the BPRS would do to the Upsilon signal. At the time a “generic BPRS cut” and the “25% dead” was unknown. (Not that the BPRS would have been useful) BPRS still needs the “road-tests” and we are attempting to do this with Daniel Kikola’s J/y. BPRS and Heavy Quarkonium STAR Analysis Meeting: HF

21. Note: The following is an attempt to take the BPRS for a test drive on the 2007 landscape. Perhaps we might learn something from the 2007 data instead of waiting for 2010 data. STAR Analysis Meeting: HF

22. Production 2007 MinBias trigger 20003/20013 Warning: The following are crude cuts relative to Daniel’s and in no way as refined! Currently, only able to pull ~30 million events. Both tracks required to come from vertex. Relic vertex ranking cut still in place from the Upsilon study: 0 < rankvertex <= 1 (need to remove) Track Cuts: nFitPts > 25, nFitPts/nMaxPts > 0.55, |η| < 1 Mimic of the Daniel Kikola J/y STAR Analysis Meeting: HF

23. Track Cuts (cont.): DCA < 1.0 cm (should be 1.5 cm?) Primary tracks PT > 1.2 GeV/c p/E < 2 c-1 |nσe|< 2, |nσk| > 2, |nσp| > 2, nσπ<-3 or nσπ >2.5 E > 0 and center tower of 3x3 cluster highest. Cuts might be too harsh; but this is the best we could piecemeal from Daniel’s presentations… Mimic of the Daniel Kikola J/y (cont.) STAR Analysis Meeting: HF

24. BPRS 25% dead: ~56% di-lepton acceptance!!! Would still like to make BPRSOFF vs. BPRSON comparison, however crude (road-testing). Case 1: “Dead-mask” the BPRS channels and look at the J/y signal with selection BPRSOFF Case 2: Apply the BPRS channels and look at the J/y signal with selection BPRSON A lot of pair production in AuAu 2007 run. Mimic of the Daniel Kikola J/y (cont.) STAR Analysis Meeting: HF

25. J/y “road-test” (Case 1) (Case 2) BPRSADC < 10 Cut on low momentum track of pair! STAR Analysis Meeting: HF

26. BPRS and crude inspection: “Signal” drops from a peak of 140 to 70: factor of 2 down. “Background” drops from a peak of 650 to 200: factor of 3.25 down. Statistic effect? Material effect? Notes from the J/y road-test STAR Analysis Meeting: HF