re: R-HRS signs and swap

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User name R. Michaels

Log entry time 11:23:50 on April 27, 2009

Entry number 269075

This entry is a followup to: 269061

keyword=re: R-HRS signs and swap

When the scaler addresses got swapped I was very worried and went into
the hall (Friday, halog 267931) with Bo Zhao and we checked with both
xscaler and scread (on both a-onl and adev) and ... the map was ok
with THOSE codes. What I mean is going from Left to Right in the
crate we know which scaler is which. I cannot, however, vouch for
the gating signals, i.e. is the first one [++] or is it [-+] ?

Next we should make sure it's ok in halla_scaler_process.tcl and
THaScaler/Podd. Note, THaScaler and xscaler use the same scaler.map
file, while halla_scaler_process.tcl is somewhat independent.

I think we should do these sign checks at some point:

1. Target sign check (needs no beam):
Put the target in one state. Then in the other.
I mean just the electronics signal, not necessarily the target spin.
See how the scalers count. Check the flags in datastream.

2. The helicity sign check (needs beam time):
Induce a deliberately large charge asymmetry (2% is feasible) and
measure this with HRS and HAPPEX DAQ and ideally with Moller, Compton
as well. This Qasy can also be observed rapidly in scalers/HAPPEX
(few minutes data), but should also be observed in the event stream
using triggers T1,T3 from a carbon target for example. For event
stream the statistics is important. For example, to get 5% accuracy
for a 1% asymmetry requires 4M events, The asymmetry shows up by
counting events in each helicity state. It would be best to use a
carbon target or something that doesn't change the asymmetry.

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