Minute of the CDC Group Meeting held on 19-Jul-01 (10:25-12:30 at the Room 425 in the Building No.3) [I] Reports on the present status 1) Kuroiwa-kun a) Influence of oxygen contamination He calibrated the oxygen monitor by himself since according to the specification, guaranteed accuracy of the monitor is +-3% of the full scale, i.e., +-30 ppm for the 1000 ppm range. The calibration was carried out by flowing a span gas (103 ppm) or a zero gas directly to the oxygen monitor. The measured values were 98 ppm and 4 ppm respectively. Thus the accuracy of the monitor was estimated to be +-5 ppm between 0 - 100 ppm range. He is now taking cosmic ray data with 80 ppm of oxygen in order to compare the result with the past measurements by other people. He plans to collect cosmic ray tracks with oxygen contamination as small as possible to see the "real" resolution at large drift distances. * It may be difficult to make the chamber completely gas-tight though it is worth trying. * Increase of gas flow rate is the easiest way to reduce the oxygen level. * The linear dependence of attachment as a function oxygen concentration may have a finite offset if the gas contains other electro-negative molecules such as water vapor (see figure (==>o2x.eps)). Q)Are there any other measurements of the attachment rate to be compared with ours ? => He will look for the papers published after Pack and Phelps (1966). b) NIM paper The latest version of the draft is now on our web site. Please read it and send him comments, corrections or suggestions. * The present procedure used to obtain hit positions is essentially a leading-edge threshold technique. A weighted charge centroid method may be effective to reduce the resolution degradation due to diffusion. This is one of the reasons why FADCs are used. => He will try. * The measurement of two track separation capability will be included in his thesis. 2) Hoshina-san A new bug was found in Geant4. The program can enter an infinite loop when a low momentum track goes across a boundary between two volumes almost tangentially and there exists yet another volume nearby. This does happen in the vicinity of the corners of the sensitive volume of our jet cells. The bug has been fixed by a patch. See http://www-jlc.kek.jp/~hoshina/cdc/geant4/ for details. 3) Hayasaka-kun He is studying the relation between the wire gain and the distance (Xdiff) of two tracks, one reconstructed in the cell placed upstream and another in the cell downstream, using the dE/dx experiment data. First, he estimated the expected Xdiff as a function of reduced field strength (E/N) in the drift region (see figure (==> xdiff_vs_En_theory.ps)). Next, the expected line was translated so as to pass the data point having the smallest value of Xdiff (see figure (==> EPTvsXdiff_1.0GeV_pi_theta0_fit_theory.ps)). Then the effective E/N for each run (data point) was determined from the measured Xdiff and the expected line (E/N at which the expected line gives the measured Xdiff). Finally he plotted ln(Q)/N as a function of effective E/N, where Q is the average charge collected by the sense wires (see figure (==> TPlnG_vs_ENcorrection_1.0GeVpi_theta0.ps)). ln(Q)/N is expected to be a monotonic function of E/N on the sense wire surface (E0/N). The figure shows a correlation between E0/N and the effective E/N in the drift space, as naively expected. It is still necessary, however, to distinguish the contribution of positive ions from that of gas density change, to the gas gain variation. Q) What is the purpose of this study? A) He has two goals: 1) calibration of the collected charge (dE/dx) using both Xdiff and the recorded pressure and temperature; 2) rough estimation of Xdiff caused by the space charge (positive ion) effect alone. Q) The expected line should have been translated so as to pass the data point corresponding to the lowest beam intensity. Which data point on the figure "Xdiff vs. E/N" was obtained with the lowest intensity? A) The data point corresponding to the lowest beam intensity is not included in the figure. He did not have enough time to analyze the data taken with narrower beam slits. 4) Kobayashi a) About gas-density dependence of wire gain He estimated the gas-density dependence of wire gain using the Diethorn formula with the parameters determined with a single wire straw tube (Nucl. Instr. and Meth. A 447(2000)459). The result was dG/G = -7.8 dD/D, with D, the gas density, which gives 2.6% (1.0%) gain variation for 1 degree Celsius (1 torr) change. However this is a rough estimate since the application of the Diethorn formula may be inappropriate in the case where space charge affects the development of avalanche. Furthermore the gain variation coefficient is expected to depend on beam incident angle (theta) since the interference between avalanches can not be ignored in our case. b) About Hayasaka-kun's study One possible way to see the space charge effect on the wire gain is to plot the average collected charge as a function of effective electric field in the drift space. If the plot shows the correlation it is most likely due to the space charge effect. If the correlation is not clear the gas-density correction to the collected charge will be necessary in order to make both the horizontal and vertical axes dependent only on the space charge. Unfortunately, however, we have only a rough estimate of the gain variation coefficient as mentioned above. An optimized value of the coefficient may be obtained as the value which minimizes the chi-square in the linear fitting to the "CORRECTED charge vs. EFFECTIVE electric field". 5) Araya-kun and Hashiguchi-kun a) The prototype of the DAQ GUI frame is completed (see figures (==> Daq1.ps and Daq2.ps)). New functions are expected to be easily added to the prototype if necessary. b) The VME CPU board has arrived while the first module of FADC, which had been expected to be ready by the end of June, will be completed and subjected to tests at the beginning of September. c) There are a lot of things to do for the DAQ system (see the minute of the previous meeting) and they and Watanabe-san are soon going to move the whole setup to TUAT for various tests using a normal ADC. * Please keep in mind that 10 channels of FADC will definitely be needed for the experiment at T1 in November. * In the experiment it will be necessary to monitor the sense-wire currents (event by event) and the gas temperature and pressure (periodically) with (VME) digital voltmeters. 6) Kuboshima-san She personally wants to be an expert of Geant4 while now studying Geant3 under the orders of Norik-san. => She will join the Fuji-B3 mogura (mole) club. II] Others *) Any proposals, ideas, suggestions are still welcome in order to make the beam time at the PS productive. *) The next CDC meeting will be held on August 30th (Thu) from 14:00 at the Room 425 in the Building No.3. The main agenda of the meeting will be individual sharing of the work for the preparation of the experiment at T1. Please think over what should be done and what you can do for it.