[Sane-analysis] Helicity dependent lifetimes

[Mark Jones]

Hello all,

Unfortunately, we do not get reasonable results for the
helicity dependent lifetime by using the scalers directly.
This has been known for a long time but I had some
hope that we would figure out a solution.
One problem is that we didn't directly measure the
helicity minus gated scalers for the input rates of
each of the triggers. We only have the helicity plus gated
scalers. We should stiil be able to get the livetime asymmetry,
but the results give asymmetries that are unreasonable.


Below is an example where
I work out the asym_true= asym_meas/lt
where lt= (number of taped triggers)/(number of input triggers)
I suggest that we just use this for correcting
the measured asymmetries.


                      Cheers,
                              Mark




dtime= 0.0002 sec   dead time of system in sec
rate_true_p = 1000  the rate of helicity plus events
asym_true=0.00584   the true asymmetry
rate_true_m         the rate of helicity minus events
rate_true_m = rate_true_p*(1-asym_true)/ (1+asym_true) = 988.39
rate_meas_p = rate_true_p/(1+rate_true_p*dtime) = 833.33
rate_meas_m = rate_true_m/(1+rate_true_m*dtime) = 825.25
asy_meas = (rate_meas_p - rate_meas_m)/rate_meas_p + rate_meas_m)
asy_meas = .00488
lt_p = rate_meas_p/rate_true_p
lt_m = rate_meas_m/rate_true_m
lt_asy = (lt_p - lt_m)/ (lt_p + lt_m) = -0.00097

or
lt_asy = -asy_meas*(1-lt)/lt  can use either lt_p or lt_m
since they are close to each other.

asym_true = asym_meas - lt_asy

So we should be able to just get the correction to the measured
asym from the lifetime as

asym_true = asym_meas +asy_meas*(1-lt)/lt = asym_meas/lt
-- 
				Mark Jones
				757-269-7733
				jones at jlab.org