Log entry time 02:22:29 on January 14, 2009

Entry number 256001

The pre-scale factor is ps1=3200,ps2=430,ps3=80,ps4=16777215,ps5=1,ps6=350,ps7=65535,ps8=100

This is corresponding to the rates on each trigger

T1: 40 Hz. T2: 50 Hz T3: 42 Hz T6: 86 Hz

The dead time is about 15%. I have to reduce the rates on other triggers to get the 15% dead time. The online dead time is quite close to the off-line value now.

I did a test by removing RICH, the dead time is about 7%.

The background rate now is listed below.

run bcm C1r C2r C3r tracks multi-tracks

5117 11.5132 3.75935 4.8211 4.51899 0.2 0.0138

5118 13.3244 3.695 4.74527 4.45675 0.220084 0.0166803

5119 12.6404 3.71419 4.76617 4.47552 0.215724 0.0158403

compared to what we have before.

first cell:

C1:C2:C3 = 3.8 MHz: 4.5 MHz : 4.3 MHz

second cell:

C1:C2:C3 = 3.5 : 4.5 : 4.2 MHz

The pressure of the three cells is 8.08, 7.23, 7.87 atms. Thus the rate of first chamber scales. The reason chamber 2 and 3 rates does not scale is probably that I have to run a little bit higher HV to keep efficiency high. The efficiency plot can be seen in Fig. 1, 2, 3, 4.

Fig. 1 3.5V + 5.0 V + 5.0 V

Fig. 2 3.5 V + 4.5 V + 4.5 V

Fig. 3 4.0 V + 5.5V + 5.5V

Fig. 4 4.5 V + 6.0 V + 6.0 V

The current threshold setting is 3.5 V + 4.4 V + 4.4 V to keep the high hitting efficiency. This setting will give a hitting efficiency higher than 98%. This leads to a theoretical tracking efficiency to be above 98%.

I also checked the collimator. The collimator is not mis-placed. The vertex reconstruction is same as what we have before.

Fig.5 shows the vertex comparison with an old run.

Thus, I think the current setting are consistent with the December run in terms of background and number of tracks that we found. It is at the limit, since the dark current is about 190uA. No lost connection to the HV crate are observed and the ROC 9 and 10 are happy.

A copy of this log entry has been emailed to: jpchen@jlab.org,jiang@jlab.org,vasulk@jlab.org,yqiang@jlab.org,brads@jlab.org

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5