Minutes of the CALCOM meeting September 4, 1998. ================================================ Agenda: Calibration: ------------ K. Mikhailov - Results from straight track analysis of drift chamber alignments A. Stavinsky - Conclusions from empty target data analysis H. Aznauryan - Empty target analysis for low deuterons and low energy protons F. Klein - Effect of magnetic field map grid size on B. Niczyporuk reconstructed momenta (no report). Physics: -------- J. Manak - gamma + p --> p + omega analysis Executive summary: ================== Konstantin Mikhailov presented results of the ITEP analysis using straight tracks from B-Torus = 0 runs. He finds that: (1) the beam line was offset diuring e1 runs vertically by about -5mm (see: also A. Skabelin at CALCOM August 21), (2) that there are sizeable relative misalignments between region I, region II, and region III chambers. (3) He produced a new DC geometry map that will be tested with data before re-processing starts. Alexei Stavinsky showed the history of the empty target run event rates. A linear rise (with time) of the event rate from the downstream window strongly suggests ice buildup. The effect is that in the most extreme case 30% of all events come from the downstream window. Hovannes Aznauryan analyzed the empty target data with an associated deuteron or two protons. He finds that the timing for such events becomes washed out and shifts to larger values. This effect seem qualitatively consistent with being due to energy loss in the target/air/drift chamber system. He will work on defing corrections for these effects which are currently not implemented. Franz Klein and Bogdan Niczyporuk showed results of studies of the effect of the mag. field grid size on the reconstructed kinematics. The grid size was reduced in the (SDA) simulation while the reconstruction was done with the original grid. Small shifts were found at angles around 20-30 deg. However, the effect is too small to explain effects seen in the data which, however, are strongest at angles below 20deg. Some more work is needed to arrive at a final conclusion. Joe Manak showed preliminary results of his analysis of photoproduction of omega mesons. Using reconstruced p/pi+/pi- events and missing mass for pi0 identification a nice omega signal emerges with little background. The events show strong falloff with t indicating strong diffractive-like production mechanism. Volker Burkert --------------------------------------------------------------------- Individual reports: ------------------- K. Mikhailov: ------------- Time based reconstruction of straight tracks for February runs 8935(empty target) and 8936(full target) was used for the drift chamber alignment. These runs have not B-field in Torus and have B-field in minitorus(maximum value, current 6000A). The first step of Drift chamber alignment is matching time to distance function for straight track for each region (superlayer) and for each sector. For this purpose we sampled candidate to electron using EID0(fast electron identification-SC,CC,EC). This candidate should have a 6-hits(or more) cluster in superlayer for which we are finding time to distance function and each layer should have a hit. We are doing a single superlayer straight track fit through 5 ayers (1,2,4,5,6). Layer 3 is not in fit. Third layer is used to calculate residual between circle with center in wire position in layer 3 and the fit. The residual is correction time to distance function R_corr(T_i) = R(T_i) + residual, where T_i is time step depends on cell size. The correction is doing by hand(not automatically). Then we have time to distance function for one sector, and we repeat this procedure for other sectors using the function as start function. For region 3 superlayer 5(axial) we got time to distance function using this procedure and resolution is about 250 mkm for linear part of time to distance. For region 2 superlayer 3 we had a problem with occupancy in mid part of time to distance plot. This hole corresponded to the track which has the biggest TDC in layer 4 and this track didn't included in analysis because one has bad chi-square. This problem was fixed by mixing number of excluded layer(the number changed in loop from 1 to 6). The resolution for superlayer 3(region 2) becomes about 250 mkm. Structure region 1 superlayer 2 is different from region 2 and 3. The electron small angle track is almost parallel to cells and many clusters has more than 6 hits(up to 12). The resolution in this region is worse than overs and equal is about 400 mkm and such clusters may have ambiguous which doesn't compensate the value of stagger 300 mkm. The residual magnetic field( Minitorus current = 6000 ) rotates particles on small angle and the X-vertex position is shifted. The vertex position reconstructed from electron track gives a circle on the plane XY(CLAS coordinate system). The center of this circle is the target position. The analysis showed the target was shifted in Y direction on about -0.5 cm. The alignment was produced in a three steps. First step is the minimization of the angle between parts of a track which are independently fitted in the region 1,2 and 3. The procedure of angle correction is minimization angle difference between couples: region 1 and 2, 2 and 3, 1 and 3 for electron and for proton. On the second step corrections is defined for X for each region. It's supposed that X-vertex(Z=0) of each region gives circle and correction was produced by moving X-vertex of each region to circle by X-shift of each region in 6 sectors. The circle parameters(radius and center) was found before any corrections by fit X-vertex. On the third step we used empty target run and take the tracks from downstream wall for Z corrections. Z-vertex(X=0) should give the circle because downstream wall position is Z=2cm(not in center of coordinate) and residual field in minitorus. The correction was produced by moving Z-vertex of each region to circle. The result of this analysis is preliminary map. map: ~kmikhail/CLAS/PARMS/Maps/run8936_alignment.txt ----------------------------------------------- Preliminary alignment values for survey geometry. X-shifts Z-shifts [cm] DC align sec:1 reg:1 (xz): -0.25(+/-0.1) 0. DC align sec:2 reg:1 (xz): 0. 0. DC align sec:3 reg:1 (xz): 0. 0. DC align sec:4 reg:1 (xz): 0.02(+/-0.1) 0.18(+/-0.04) DC align sec:5 reg:1 (xz): 0.21(+/-0.1) 0. DC align sec:6 reg:1 (xz): -0.30(+/-0.3) 0. DC align sec:1 reg:2 (xz): 0. 0. DC align sec:2 reg:2 (xz): 0. 0. DC align sec:3 reg:2 (xz): 0.1 (+/-0.02) 0. DC align sec:4 reg:2 (xz): 0.06(+/-0.02) 0. DC align sec:5 reg:2 (xz): 0.16(+/-0.03) 0.2 (+/-0.08) DC align sec:6 reg:2 (xz): 0.17(+/-0.05) 0.41(+/-0.09) DC align sec:1 reg:3 (xz): -0.1 (+/-0.04) 0. DC align sec:2 reg:3 (xz): 0. 0. DC align sec:3 reg:3 (xz): 0.1 (+/-0.02) 0. DC align sec:4 reg:3 (xz): -0.17(+/-0.02) -0.85(+/-0.4) DC align sec:5 reg:3 (xz): -0.18(+/-0.02) 0. DC align sec:6 reg:3 (xz): -0.15(+/-0.02) 0. Rotation around the y-axis. [RAD] DC rot sec:1 reg:1 (y): -0.00068 DC rot sec:2 reg:1 (y): 0. DC rot sec:3 reg:1 (y): +0.00034 DC rot sec:4 reg:1 (y): +0.00013 DC rot sec:5 reg:1 (y): -0.0015 DC rot sec:6 reg:1 (y): 0. DC rot sec:1 reg:2 (y): -0.00034 DC rot sec:2 reg:2 (y): -0.00094 DC rot sec:3 reg:2 (y): -0.00017 DC rot sec:4 reg:2 (y): 0. DC rot sec:5 reg:2 (y): 0. DC rot sec:6 reg:2 (y): -0.00068 DC rot sec:1 reg:3 (y): +0.00017 DC rot sec:2 reg:3 (y): 0. DC rot sec:3 reg:3 (y): 0. DC rot sec:4 reg:3 (y): -0.00051 DC rot sec:5 reg:3 (y): 0.00051 DC rot sec:6 reg:3 (y): 0.00034 A. Stavinsky: Empty target analysis -------------- 1.It was shown that the extra material on the downstream window of the cryotarget are likely to be H2O since its thickness is time dependent (ie: window icing). When plotted the ratio of the downstream to the upstream target window as a function of date it increases linearly from 6(run 8657) to 30(run 8938) with slope ~+2 unit/day in (suppose that Al=1 unit). 2.It was also shown based on method discussed at CALCOM two weeks ago(number of events in different regions of vertex position distribution arise from Z_Al, Z_H, and unknown substance with Z_A; Z_H contribution could be removed by cut cos B < 0, where B-angle between proton and virtual gamma) that the ratio of H protons to nuclear protons in the unknown material is 0.29+-0.025 which is comparetible with H2O(0.25). H. Aznauryan: -------------- The problem of deuteron and two proton production where studied using 4 Gev e1 data. Events with two protons or deuterons where chosen by their mass and dE/dX in the scintillator counters. Where found that most of the selected particles coming from the second window of the target and distribution of protons, in two proton production, and deuterons of their vertex position are the same. Then difference of time-of-flights calculated using momentum and particle mass and measured by scintillator counter was studied. This difference was investigated for negative and positive pions, protons from two-proton events and one proton production, as well as deuterons. All these studies showed that for heavy particles with low momentum time-of-flights measured by scintillator counters are bigger then the time-of-flights calculated using momentum and particle's mass. This can happen because of momentum calibration. J. Manak -------- I looked at gamma p -> pi+ pi- pi0 p by observing the pizero in missing mass in 30% and 50% field data. The omega signal was found to be quite clean in both data sets with the signal to bkgnd ratio of approx 3:1. I estimated a yield of 16 thousand of these events for the 30% field data set and approx. 115K for the 50% field data set. Center of mass and t distributions were also examined. Finally, I looked at the tagger energy spectrum for successfully reconstructed events the spectrum was found to be very irregular and difficult to interpert. I and others are investigating the tagger normalization. +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++