X1 Online Crosstalk
Correction
James Gaillard
Imperial College
12th February 2003
X1 Online Crosstalk Correction
• It was decided in December 2002 to go ahead and
implement the new x1 correction for the barrel
proposed at the last collaboration meeting in the
absence of any objections.
• The new x1 correction is based on the same
principle as the old – linearly scale the difference
between the odd or even calibration and the full
calibration and subtract this scaled difference
from the full calibration. This gives the crosstalk
corrected calibration.
X1 Online Crosstalk Correction
• The old x1 correction had two correction methods,
one for odd channels, one for even channels.
• The scaling factor depended on three quantities
for the odd and one for the even.
• For the odd, the scale factor was 1.2 for the
backward, 1.65 for the forward for all channels.
• For the even, the scale factor was
-(0.6*(Full-E [dac20])) + 3.5 for the backward
-(1.2*(Full-E [dac20])) + 4.1 for the backward
X1 Online Crosstalk Correction
• The origin of these numbers remains a mystery.
The original ABin, ABinEven, ABinOdd files taken
at the time of the 2000 crosstalk measurements
no longer exist. They are written over every time a
new electronics calibration is taken. Comparing
Dan’s xtalk measurements with todays
(December’s) calibrations was the only route to go.
• This makes reproduction of the old scaling factors
very difficult, and not knowing how they were
produced (not documented) one cannot reproduce
for different preamps.
X1 Online Crosstalk Correction
• A new method was devised. This basically involved
applying a single scaling factor, which only
depended on the channel number and the type of
preamp (and fwd/bkwd). Only do 7-9 type preamps
have a significant odd-even scaling distinction.
• The assumption that there is a linear relationship
between the full-odd (or even) and the full-single
is only approximately true for ~50% of all
channels. No discernable pattern of linearly
behaved channels was seen. It seems random.
X1 Online Crosstalk Correction
X1 Online Crosstalk Correction
X1 Online Crosstalk Correction
•
7-9 Odd
•
7-9 Even
•
5-2
•
1-6