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    User name jpchen

    Entry time Mon May 3 10:25:40 EDT 1999

    Entry number 37

    keyword=Minutes of 4/28 analysis meeting

    Minutes of 4/28 analysis meeting: Present: Alexandre Deur, Pibero Djawotho, Ioannis Kominis, Marat Rvachev, Zhengwei Cai, Luminita Todor, Christophe Jutier, Xiaodong Jiang, Mark Jones, Dave Prout,John LeRose, Jian-ping Chen. Luminita presented the optics study with the VCS optics data. The optics data were taken at 15 and 23 degrees at momentum of 3.5 GeV/c. Twoarm_x-Beam_x has a mean value of 0.01 mm with sigma of 0.7 mm. H_React_Z-E_React_Z has a mean value of 0.05 mm with sigma of 3 mm. Z_react comparing with the surveyed target foil positions, the differences are all less than 1 mm. The missing mass reconstruction has a resolution of 2 MeV. The momentum resolution for 12C elastic has a resolution of FWHM 4X10-4. Also shown are the polarizibility and VCS resonance plots, where the VCS and the pi missing mass peaks as shown can be separated. The database can be accessed from the VCS web page: http://www.jlab.org/~luminita/vcs.html. Mark Jones presented his study of the E94010 optics data. The data were taken at 0.8 GeV/c with seven 12C foils for dp/p of 0, +-2 and +-4%, with sieve slits and with 6msr. Improvement is obvious from the plots of x_sieve vs y_sieve before optimization (using the original data base), with VCS database and after optimization. For electron arm, the database is now in good shape, the difference of z_target comparing the data with calculated target positions are typically about 1 mm (except for the two edge foils). For hadron arm, the original z_target was about 10% off. Mark has to introduce a midplane symmetry breaking term Y100 to get the y_targ (z_target) to be at the right position. A lot of discussion at the meeting on that. Other than that, the database for hadron arm is also in good shape. Copies of both presentations are availble. Marat and Zhengwei are continu with their optics analysis. Expect to have results in one to two weeks. Xiaodong showed the 12C elastic peak for hadron arm. If using John's calculation of P (instead of the HAC input P) then the elastic peak is at the right position (E_x=0). The 2nd foil has wider resolution than the other foils (due to RTD wire in the path of the scattered e?). Alexandre: I am have focus on VDCs. No raster this week. - The problem of 3% of good electrons with 0 track is solve. I used a non optimized database (db_gdh_start) with bad T0. Espace was cuting 3% of good 1 track events because of bad timing. Nilanga gave me a new t0 optimized database (/work/halla//e95001/nilanga/ana/db_opt_tc2) but this one is optimized only for T0. The other detectors numbers are obsolte (that's why I got some no gain matched spectra with hadron shower) - for electron arm (with good T0 numbers) The % of events with 0 track is 6.3 % The % of events with 1 track is 82 % The % of events with 2 track is 8.2 % The % of events with 3 track is 2.5 % The % of good electrons (cut preshoer,shower and cerenkov) with 0 track is 0.08 % The % of good electrons with 1 track is 98.7 % The % of good electrons with 2 track is 1.1 % The % of good electrons with 3 track is 0.08 % These numbers change shlightly with the kinematic but remain of the same magnitude. I am taking care now of the 2 track events (select the good track and reject the other one, the odd to have two good electrons are small: 0.06% ). The efficiency of the electron arm is 99.92 % - For the hadron arm the things are not as clean (no preshower ?). We have a lot of 0, 2 and 3 tracks events looking like bad events but which are not cut by the cerenkov and shower. The are mainly low energy events and have a "pedestal tail shape" (I am not saying the are related to the pedestal, I am just talking about the shape). The % of events with 0 track is 9.5 % The % of events with 1 track is 78 % The % of events with 2 track is 9 % The % of events with 3 track is 2.5 % The % of good electrons (cut shower and cerenkov) with 0 track is 0.2 % The % of good electrons with 1 track is 96 % The % of good electrons with 2 track is 3% % The % of good electrons with 3 track is 0.7 % I think the difference between the electron arm and the hadron arm is mainly coming from these 0, 2 and 3 tracks low energy events. The efficiency of the vdc, with these events, is 99.1 %. If I am puting a low energy cut on shower I get 99.7 % of efficiency. So it's seems the hadron arm will need more work than the electron one. Ioannis: Showed his study of E_arm shower counter effeciecies with Cherenkov cut.