Bunch Crossing Efficiency and Time Distributions
in Theta Scan Data at H2  

  • Theta Scan at H2 on June 21, 1998 (summary)

    • - The runs cscdata_0030 - cscdata_0040 were analysed to see dependence of the bunch crossing efficiency from Theta angle (Theta = 0,5,10,15,20,25,30,35,40 and 45 degress, see Logbook v.1, pp 80-83).

    - Conditions of the runs according Logbook: "New" gas (Ar+CO2+CF4=40+50+10 and this is in contradiction with A.Korytov's report where he quoted "Old" gas usage), HV nominal = 3.8 kV (pretty high for the "New" gas), thresholds of new anode preamplifiers = 150 (JTAG code), beam - muons 225 GeV.

    -Summary of the results is in Results . This analysis has confirmed with more details the observation made by A.Korytov and F.Petriello - the data at Theta angle of 15 degrees show lower efficiency due to broader time distribution.

    The efficiencies of the "software" bunch crossing identification vs Theta angle at inf. gate and gates of 25 and 20 nsec are given on the page 1 of the Results (top three histograms) together with the parameters of the time distributions for the 1-st and the 2-arrivals from 4 and more planes ON (3 bottom histograms). Sigma 1 and Sigma2 are the fitted parameters of the function made from two halves (left and right) of the gaussians with common center but different variances Sigma1**2 and Sigma2** and RMS is provided by PAW. We see that RMS at the Theta of 15 degrees is more than at Theta of 10 degrees by almost 2 nsec, at 20 degress - by 1 nsec and after that RMS slowly returns to the level of 4 nsec with Theta increasing up to 35-40 degrees.

    Note that the parameters of the time distributions from individual planes also have spectacular dependence from the Theta angle (page 2 of the Results ) with Sigma1 having peak at 15-20 degrees, Sigma2 going down with Theta up to 20 degrees and Sigma = sqrt((Sigma1**2+Sigma2**2)/2) decreasing with Theta after Theta of 10 degrees. The gauss centers (and therefore the means as well) for some planes depend from Theta too (plane 1 has difference of 10 nsec between centers of for Theta=0 and Theta=45 degrees). In the current analysis the time delays were tuned by software for each plane at each angle. Therefore the efficiencies and RMS for the 1-st and the 2-nd arrivals look probably "too good". The hardware bunch crossing identification logic probably will not be biased by such difference because this can be compensated by different delays in the chips (cards).

    Finally the cathode signal is increasing by almost 2 times with the Theta as it is shown on the page 3 of the Results

    - Comments:

    1. P2 geometry - wire spacing of 3.16 mm and cathode anode spacing of 9.52 mm/2 give the angle of diagonal of the rectangular cell to be 18 degrees, e.g. right in the region of anomaly (15-20 degrees). For the tracks with Theta > 18 degress the fraction of the tracks shared by two adjucent anode wires is increasing with the Theta.

    2. If the anode layers are not staggered than for given track at large incident Theta angles the pattern of arrivals is probably specific for each plane and this could contribute to the time resolution of the 1-st and the 2-nd arrivals.

    3. The used high voltage HV=3.80 kV is higher than HV_default for a "new gas" mixture by 250 V, e.g the conditions were not "normal".


  • Theta Scan at H2 (run by run)

    • - cscdata_0030 Theta = 0

    - cscdata_0031 Theta = 5

    - cscdata_0032 Theta = 10

    - cscdata_0033 Theta = 15

    - cscdata_0035 Theta = 20

    - cscdata_0036 Theta = 25

    - cscdata_0037 Theta = 30

    - cscdata_0038 Theta = 35

    - cscdata_0039 Theta = 40

    - cscdata_0040 Theta = 45


  • Time correlation between layers at Theta=0.

    • - The time correlations between the 1-st anode layer and the others were studied. Data from run cscdata_0030 (Theta=0) at H2. The means of the time distributions for layers 2-6 were plotted for 5 nsec wide slices of the time distribution of the 1-st layer( Correlation ). Note the different behaviour of layers 3 and 6. The probable explanation is that the wires of layer 6 are almost against of the wires of the layer 1 for the tracks at Theta=0 while the wires of layer 3 are shifted by the one half of the wire gap. The layers 2,4 and 5 have intermediate positions.


    Last modified: Mon May 31 13:30:00 CST 1999

    teren@fnal.gov