User name paschke
Log entry time 20:48:43 on June29,2004
Entry number 127415
BCMs were moved around this afternoon. Here I'm looking at data taken
since then (Runs 2531, 2532, 2533, and 2534).
BCM1, BCM3, and BCM8 are all read out from the same ADC.
BCM2 and BCM7 have been moved to another ADC on the other side of
the crate. The question is: can we get a good double difference
from BCMs in different ADCs? The answer: "maybe".
Double Difference (1-2) and DD(7-8) are both about 1.5 sigma from
zero, while DD(1-3) is zero, with nice lack of tails.
DD (3-7) is 3.6 ppm (with ugly tails) and a huge component of apparent
readout helicity pickup (the pairsynch cut select which helicity
came first in the pair).
So, the two downconvertors really don't agree. Helicity pickup
previously reported in bcms 7 and 8 was coming from the bcm
10 kHz electronics (not from the ADC reading those signals out).
And while bcm1, 2 and 3 still bear watching, they at least haven't
been shown to be bad.
Helpful guide to bcm identities:
BCM1 = upstream 1x (1MHz)
BCM2 = downstream 1x (1MHz)
BCM3 = downstream 3x (1MHz)
BCM7 = upstream 3x (10 kHz)
BCM8 = downstream 3x (10 kHz)