Minute of the CDC Group Meeting held on 19-Jul-01 (10:25-12:30 at the Room 425 in the Building No.3)
Japanese version is here
- Date and Place
July 19(Thursday), 2001 at the Room 425 in the Building No.3 (KEK)
- Attendants
M.Kobayashi, K.Fujii, H.Okuno, T.Matsui, O.Nitoh, H.Kuroiwa, K.Hoshina, H.Hashiguchi, T.Hayasaka, M.Araya, R.Kuboshima
- Contents
- 1)Cosmic-ray measurement and analysis(H.Kuroiwa)
- a) 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 this figure.(1 page, PS)
- *) 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) The latest version of the draft is now
here.(9 pages, PS 20kB)
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)Simulation program development based on Geant4(K.Hoshina)
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 here
for details.
- 3)dE/dx data analysis(T.Hayasaka)
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 this figure.(1 page, PS)
Next, the expected line was translated so as to pass the data point
having the smallest value of Xdiff.
See this figure.(1 page, 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 this figure.(1 page, 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.
*) What is the purpose of this study? => 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.
*) 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? => 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)About gas-density dependence of wire gain and Hayasaka-kun's study(M.Kobayashi)
- a) 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) 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 axis 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)VME-based DAQ system(H.Hashiguchi, M.Araya)
- a) The prototype of the DAQ GUI frame is completed.
See this figure. =>
1(1 page, PS)
2(1 page, 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)Others
- *) Kuboshima-san 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.
- *) 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.
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