Log entry time 08:24:38 on February 15, 2009

Entry number 261267

This entry is a followup to: 261265

Brad and I took a control access from 1:16AM to 5:34AM to inspect trigger non-uniformity on BB spectrometer. Several problems with BigBite trigger have been identified, which could impact both d2n and transversity.

Following is a preliminary description; Brad is going to bring more details.

1^st Problem:

One of the NIM bins, fully installed with BB shower summing modules, is overloaded on its +-12V power supply. This would reduce the shower signal gain by ~1 order of magnitude to both Trigger and DAQ, as well as introduce distortion.

Detail:

If I understand right, this NIM bin is holding summing modules, except shower row 24 25,26,27(which are in another normal working bin). When Brad and I first looked at this bin, its -12V is only outputting -1.5V. During follow tests, its +12V power also dropped to +1.5V in some case.

For our test signal sent to one of the input:

It’s also observed that, if a test signal is sent at PMT signal cable, the read out at T1 trigger discriminator inputs are:

·         -70-90mV for sum#1->15; 17->23; signal is distorted

·         0mV for sum#16, see 2^nd problem

·         -1080mV for sum#24- >26

This could explain “pion punch through at higher BB acceptance” during Transversity. That could be caused by that shower block row 1->23 is not properly amplified (and for broken channels, its ADC signal copy could be amplified more than its trigger discriminator copy).

Temp. Solution:

4 of the summing modules are moved to a new NIM crate, which bring power load to normal. Now gains of row 1-23 summing module are back to normal.

Shower HV gain might need to be recalibrated; threshold need to be reset. We also need to assess its impact to transversity data.

2^nd Problem:

Fan output problem with shower sum #16.

1.     The fan base line is not zero-able (we tried to lower it from +175mV -> +75mV, cannot lower more).

2.     When we try to send a pulse from PMT signal cable, the discriminator of T1 shower sum #16 do not get any signal (other channels are OK except 1^st problem)! This could form a trigger whole for Transversity Coin set up (to be confirmed)

3.     Another fan copy to T6 is OK.

Since T1 is not used, we left it as it was.

3^rd Problem:

T1 trigger, Shower sum #19 has a flippy cable. Replaced by Brad

4^th  Problem:

Brad: “P-26L” 50 Ohm splitter is unplugged”; should be fixed by him.