Calibration
Strategy for EMTiming
Overview
The primary goal of the calibration table is to get
rid of the dependence of timing information on channel to channel
hardware differences. For channel timing information depends on energy
(widely known as slewing corrections) because the system uses analog
to digital signal discriminators (ASD) to convert analog signals from
PMTs into digital LVDS signal.
We plot the timing information for each
channel as a function of energy (more precisely as a function of
total ADC counts), and fit it with empirical function. The
resulting function is applied to the data during
reconstruction.
The most interesting events from physics point of
view probably lie at high energies. Therefore it is important to get
slewing curve right in the high energy region. It poses a problem
because the number of events in the detector drops exponentially with
energy, forcing us to use data averaged over many runs in order to
collect good statistics in each channel at high energy tail.
If one looks at the mean time
dependence on the run number, one can notice that
there are
significant jitter on run by run basis. Therefor we adopt the following
strategy.
Calibration
Strategy
From the mean time page we determine what runs can
be used together for a single calibration slewing table. The selection
is that one can draw a straight horizontal line through the selected
runs. The resulting table is the slewing correction averaged over all
selected run range. If this table is to be applied to the all data form
selected runs, the resulting time distribution will be centered at
zero.
However, it is necessary to take into account
run by run variations. After we apply slewing corrections to all
channels
we plot timing for the whole detector. The difference in the mean of
that distribution from zero is recorded in the secondary table and will
be applied to the data from that run at the reconstruction stage.
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Maintained by: Max
Goncharov