Minutes of CALCOM meeting March 20, 1998. ======================================== Agenda: L. Qin - New DC drift-time distance calibration and DC position resolution G. Gavalian - Status of level 2 trigger analysis S. Stepanyan - Event recosntruction and DC geometry V. Burkert - CLAS response to single particles from the e1 data ============================================================ Individual reports: ================== L. Qin: New DC calibration and position resolution ------ CLAS drift chamber resolution was studied using single superlayer track reconstruction. The single cell resolution of Region one was found to be 260 microns. The resolutions for Region two and three were between 360-390 microns. The same drift time for time based tracking in recsis was used for the study. A new x->t function was introduced to recsis (#4). The residual distributions were improved, however, there was no significant improvement to the momentum resolution. Other issue such as geometry may be relevant to the TBT results as well. Study for better x->t conversion including a dependence on the magnetic field is on the way. G.Gavalian: Status of level 2 trigger analysis ---------- The new results of Segment Finder Efficiency study were presented. Comparing with the previous measurments, time characteristics are improved. For some sectors efficiency of segment finding is 100% within angular range 15-45 degree were Segment Finder is implemented. For others there are efficiency fallings in some angular intervals, wich might be a hardware problem. S. Stepanyan: Event reconstruction and DC geometry ------------- Data from December run at different primary energies and torus current settings were analyzed in order to study the source of the momentum shift in the tracking. To do so (ep) events in the elastic scattering region were selected and momenta of scattered electron and recoil proton were calculated from measured angles (electron and proton). Comparison with measured momenta showed that while for negative particles (electrons) we have measured momenta less then it should be, for positives it is higher. This shifts can not be accomplished with simple changes of integral Bdl (field scale), also amount is to big for that. However this can be fixed by introducing a rotation of Region 2 DC around Y axis (in the sector coordinate system) towards to the beam. Studies with rotation 0.5mr (1mm on the position of R2DC) showed significant reduction of differences between measured and calculated momenta for the elastic electrons and protons. V. Burkert: CLAS response to single particles from e1 data ---------- I have looked into the single particle yields of 1.6, 2.4 and 4.0GeV data from the e1 run. The goal has been to evaluate the data w.r.t. the possibility of using the beam data to evaluate relative acceptances for single particles in CLAS. In order for this information to be useful the single particle must not be correlated with the triggering electron as this would introduce a bias into the analysis. Therefore. as a first step I looked into potential correlations between the electron and hadrons. Here are the results: E = 1.645 GeV: ------------- electron - in trigger protons - strongly correlated with electrons for angles up to about 80deg. pi+ - correlated with electrons at forward angles nearly uncorelated at large angles pi- - uncorrelated with electron E = 2.445 GeV: ------------- electron - in trigger protons - strongly correlated with electrons for angles up to about 80deg. - no visible corelation at larger angles pi+ - some small correlation with electrons at forward angles - uncorrelated at large angles pi- - uncorrelated at any angle E = 4.045 GeV: ------------- electron - in trigger protons - strongly correlated with electrons for angles up to about 80deg. - no correlation at larger angles pi+ - uncorrelated with electron at any angles pi- - uncorrelated with electron at any angle The study was based on about 1,000,000 triggers for the two lower energies and about 150,000 triggers at 4.045 GeV. In conclusion, pions accumulated in the e1 data at energies 2.445 GeV and higher show little or no correlation with the triggerring electron. They may therefore be used for acceptance studies for positive and negative particles. Of course, since there is no obvious way for normalization, only relative acceptances may be studied. However, one of the important pieces of information is the phi acceptance for tracks as a function of polar angle and particle momentum. Here one would expect a plateau near the mid-plane and a fall-off near the magnet coils. Studies with considerably higher statistics are needed to map out the single particle acceptances in all sectors, and with sufficient accuracy.