Minutes of the CALCOM Analysis Meeting, October 3, 1997. ======================================================= Agenda: L. Qin - Drift chamber efficiency studies F.J. Klein - Status of time-based tracking in RECSIS N. Pivnyuk - A first look at straight tracks from the 1.645 GeV data A. Vlassov - Summary of Cherenkov counter efficiency studies using the 1.654GeV data L.C. Smith - Status of the EC calibration M. Battaglieri - Status of the LAEC calibration (no report) From 9/30 meeting : E. Smith - A first look at the TOF data ------------------------------------------------------------- Next meeting: Tuesday October 7, 10:30am in room B207. If you want to make a presentation, let me know by Monday 5pm. ============================================================ Alex Vlassov presented a summary of his extensive studies of the Cherenkov counter efficienies using elastic ep scattered electrons from the 1.645GeV data. About 500k triggers were analysed giving a good coverage at small angles but not enough events at large angles for a detailled analysis of the Chernkov counter response. At small angles, statistics is good enough to measure inefficiencies at the 1-2 percent level with good granularity. The results are globally consistent for all 4 sectors, however, because of the good statistics we an see details of small deviations from a uniform response: sector 1: small, localized island around 20deg with few % inefficiency around midplane sector 4: very uniform response, no visible inefficiencies in active region sector 5: small, localized area around midplane at 17deg with few % inefficiency sector 6: overall slightly enhanced inefficiencies compared to other sectors, thin strip around midplane spanning from 12 - 32 deg with up to 5% inefficiencies With the existing 18M triggers the study can be significantly refined, and should provide a very detailled account of the CC efficiencies with fine granularity. +++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Alex, have a good trip back to Russia, and thank you very much for the excellent work for the CALCOM effort. See you soon again!!! Volker Burkert +++++++++++++++++++++++++++++++++++++++++++++++++++++++++ ============================================================================ Individual reports: Liming Qin: ----------- DC efficiency study and possible problems in RECSIS Liming Qin 10/3/97 DC single layer efficiencies for the six superlayers of all six sectors were obtained from single superlayer track reconstruction. The results from the 2nd HV scan (run 6103-6110) agree with the earlier measurement (run 5870/5874/5877/5881) which didn't cover wide enough ranges to determine the start of the efficiency plateaus for region 1 and 2. The efficiency for electrons were calculated with a cut on Q=-1 and P>1.0GeV/c ("electron"). The results show the nominal HV settings are very close to the starts of the plateaus. Only small adjustments (<50V) are necessary to optimize the settings. The conclusion is based on the results for sector 1/2/3 which do have good electrons under the cut. The results for sector 4/5/6 are very similar to those obtained with a cut on Q=+1 and P<1.0GeV/c ("proton"). The hit position and distribution in the wire chambers indicate we have "protons" survived the "electron" cut. (We have "electrons" survived the "proton' cut as well in sector 4/5/6.) It seems that recsis sometimes misinterprets the charge of particles in these three sectors and therefore miscalculates the momentum. However, if we look at only reconstructed information, such as momentum and scattering angle, they seem to be fine. The problem will show up if low level information such as wire ID is involved. We need to have a careful look on the possible problem in recsis. If we placed an additional cut on the wire number so that only sections where the "electrons" are supposed to be are selected, namely the forward sections, the results from all six sectors agree. Jim Mueller: ----------- While trying to understand some strange effects presented by Liming at the CLACOM meeting yesterday, I found a bug in the ana routine that makes the hit-based-tracking n-tuples from the recsis banks. Specifically, there was a error associating tracks in the HBTR and DCLA bank. This results in an error in the information in ntupole 112 in the /trk/hbt subdirectory of your hbook file in the following manner. Consider an elastic event with an electron in sector one and a proton in sector 4. a) The entry for the lowest sector track (in this case e) will be correct b) The entry for the higher sector track (in this case p) will have hit-level information (sector, number of wires hit, which wires hit) correct, but ... c) the track based information (q, p, theta, phi, etc) will be from the lower sector track. (In this case it will look like you have negative protons at the wrong theta and phi.) I want to stress that this is only a problem with this ntuple, and NOT WITH THE OUTPUT BANKS themselves. However, I know that Rob Feuerbach's analysis of the DC HV scan was based on this ntuple, and the plots presented yesterday by Liming suggest that a similar error may be effecting his code. I have corrected this bug and committed it to the CVS repository. Anyone who uses histograms made by user_ana in the trk/hbt directory, should probably checkout the ana area and rebuild. If you don't use these histograms, you can ignore this. Franz Klein: ----------- Franz Klein reported the status of Time Based Tracking (tbt) in Recsis. The tbt worked quite good for June data but drift chamber timing constants and the time-to-distance relation had to be calibrated for the new data because the timing as well as the gas mixture changed compared to the previous run. Up to now the results (missing mass and momenta resolution) are less accurate than obtained with June run data, due to the time-to-distance relation which is not yet well determined (residua for distance-of-closest-approach: 1.0 to 1.4 mm, depending on the cell size). Nikolai Pivnyuk: --------------- Time Based Reconstruction for Run 6112. --------------------------------------- Goal : - To determine Time-To-Distance-Relation and Spatial Resolution with B-field = 0. - To look for the background. Data : Run 6112 (Big Torus OFF, Mini Torus Current = 1000 A, H2 target, Electron beam : Eo = 1.6 GeV, Current = 0.12 na). Procedure : track reconstruction in the middle plane. Superlayer 5 was taken into account. As a zero approximation Time-to-Distant function was taken as it was calculated for the February Run 0710. Summary : Tracks in the Superlayer 5 were reconstructed roughly - after the first iteration in Time-to-distance-function determination procedure. Resolution is likely to be expected of the same order as it was in February Run 0710 (which is about 200microns, V.B.). Background still continues to exist and needs a more detail study. Cole Smith ---------- Low EC threshold cosmic-ray runs were performed prior to and during the commissioning run. The means of MIP energy loss distributions were used to determine PMT gains. Comparison of these runs show changes in EC PMT gains which appear to be randomly distributed and on the order of +- 5 %. Runs were also taken with the beam on and B=0 to get straight tracks from the target. These runs confirm the gains shifts observed with cosmic muons, but also show systematic gains shifts of +- 10-15% which affect groups of PMTs, usually those belonging to a particular view (UVW). Non-MIP backgrounds from protons and photons which skew the energy loss distributions are the likely explanation for the latter shifts. Other possibilities which need to be investigated are rate-induced PMT gain shifts (can be studied with laser and beam on/off runs) and rate-induced ADC pedestal shifts (take pedestal run with beam on/off). Elton Smith: ---------- First Look at Scintillation Counters. 9/30/97 ES The forward-angle TOF scintillators high voltage settings have not been changed during the current running period. The matching was originally within 20%. The tubes are still matched at that level. However there are exceptions, which have either changed over time or HV settings have been changed by accident. We will go through one more iteration before next week. The large-angle TOF system is matched to within 50%. We will continue updating HV settings as required. We hope to have stable settings before the 2.4 GeV running. At 1.6 GeV, protons from elastic scattering are clearly visible in the energy loss of the large angle scintillators. The energy loss plots show penetrating but highly ionizing protons up to scintillator 36 (about 70 degrees) and then stopping protons up to scintillator number 40 (90 degrees). Data were taken to determine the thresholds for the LeCroy 2313 discriminators (that feed the TDC's) and the VPI Pretrigger boards. A calibration for the pretrigger boards for 1.86 ADC counts/mV was determined from the data. The nominal pretrigger board setting of of 100 mV, corresponding to ADC channel of 186 or 1/3 min ionizing, is quite resonable and was left there. The 2313 discriminator thresholds, showed that the system was efficient for min ionizing particles for a setting of approximately 50 mV. The thresholds were set to 40 mV, based on this observation. [Note added: Due to the relatively low accidental rate in each counter and the fact that the ADCs are firing even when the discriminator does not fire, the thresholds were reset to 20 mV on Friday.] The width of the pretrigger discriminator settings and the ADC gate widths have not yet been studied in detail. Scaler rates of the TOF scintillators indicate that the target full/target empty ratio is approximately 2/1. We have also done preliminary matching of tracks in the drift chambers with energy losss in the scintillators and show good agreement with initial expectations for energy loss of protons in the large-angle counters.