Minutes of CALCOM meeting, February 20, 1998. ============================================ Agenda: H. Egiyan - TOF time calibration procedures and results S.Stepanyan - Usage of RF signal in the PID. Kyung-Yeub Nam - Study of pi-0 detection efficiency/acceptance in the forward EC M. Mestayer - Time-based tracking in RECSIS (no report) G. Gavalian - Detection of nuclear fragments from empty target run using the new CLAS particle id. V. Burkert - Some results from various people B. Niczyporuk - Time-of-flight resolution with elastic protons V. Burkert - Priorities for future CALCOM activities =========================================================================== Individual contributions: ------------------------ V. Burkert: ---------- Near term priorities in the CALCOM effort include the study of the magnetic field, and a better understanding of the drift chamber geometry. A. Drift chamber calibration, especially the drift time to distance relationship need to be urgently improved. Currently we have position resolutions of the order of 0.7 - 1.5mm for region 1 - region 3. B. Magnetic field: (1) We must create a field table using the simulated values and the COLD coil shape. The coil is known to shrink by 2 to 3 cm when cooled down. This should be fairly straight forward to take into account and to compute a new "cold" field table. (2) We should get new coil shapes and positions from the W&M measurements and compute the full field table for the 6 individual coils (no symmetry!). C. We need to continue to improve tracking efficiency, and understand the luminosity and multiplicity dependence. D. We need to use high statistics data to study the detector response IN DETAIL using inclusive cross sections as well as exclusive reactions with well known angular distribution. E. Currently we cannot detect eta -> gg in the calorimeters due the large opening angle of the two photons. We need to combine the analysis of the EC and EC1 detectors to increase the acceptance for such events. H. Egiyan: TOF time calibration procedure and results. --------- The results of the TOF calibration with RF signal were discussed and the automated procedure for the calibration was described. It consists of 4 stages : 1. Alignment with respect to the RF signal ; 2. Alignment of the first ten strips using e-pi events ; 3. Alignment of the 6 sectors with respect to each others ; 4. Alignment of the rest of the TOF strips using e-pi events. The calibration constants of the TOF offsets for december run have been put into the map and they allow us to have ~19 MeV resolution for pion identification and ~24 MeV for protons. The calibration for other runs are going to be done too using the procedure described. The procedure and results of particle identification are described in CLAS note 98-0043. S.Stepanyan - Usage of RF signal in the PID. ----------- After SC TDC's were calibrated using the RF signal, for PID - correction of "event start" time to the RF bunch was used. This technic worked well for the December 2.4 GeV runs (that the ones were used for SC TDC calibration). However when the same calibration constants were applied to 1.6 GeV run data that clearly showed that in some cases there was wrong identification of the RF bunch. It can happen if times for reaching a beam to the target in the different runs (energies) were different and this difference was not multiple of RF structure. It was shown that using RF signal distributions relative to the detected electron SC time one can effectively correct on that time difference. Particularly - the RF distribution from 1.6 GeV Feb. run was shifted approximately 1ns compared to the distribution from the 2.4 GeV run. G.Gavalian ---------- The results of an analysis of empty target run 8766 using current TOF calibration were shown. One can clearly separate contributions from pions, protons, deuterons as well as tritons on the beta vs momentum and the mass spectrum plots. V. Burkert Some results of people who "saw it first". --------- Much progress has been made on particle identification in recent weeks. The meeting thus focussed on the time calibration procedure and results on particle identification using this procedure. Using the method described by Hovanes various people have studied physics reactions: Latifa, Volker and Stepan find a clear omega signal, and hints (2sigma) of an eta' signal requiring a proton and two neutrals (if confirmed with more statistics, I believe this would be the first time the eta' has been seen in electroproduction). Reinhard Schumacher selects the positive kaons and finds a clean Lambda as well as a Sigma^0 signal in the missing mass of ep->eK+X. Kyung-Yeub Nam - Estimation of the pi0 detection efficiency. -------------- Detection efficiency of 2 photons from pi0 decay in the forward EC was studded using the December run data at beam energies 1.6 GeV and 2.4 GeV. Reaction ep=>ep(pi0=>gg) were analysed in the W>1.14 GeV range. As a pi0 detection efficiency ratio of the number of events with final states (epgg) and (epX) was taken,where X was identified as a pi0 by using cuts on the missing mass spectrum of final (ep) system (-0.02 ep at 2.4 GeV (Run 8666), reconstructed with SDA, I have found that the averaged resolution of "delay differences" (between the proton SC slab and electron SC slab) is about 1.5 ns. This resolution is about by factor of 1.5 better then the SDA calibrations. The comparison does not include so far the Time-Walk corrections. Work is in progress. Comment by V.B.: --------------- The time resolution of the rf-based method described by Hovanes is accurate at the level of less than 100psec, with intrinsic resolutions of about 150-250psec. So there is a large discrepancy with the 1.5nsec claimed in Bogdan's study.