Now we understand the photon energy correction was already applied when the cooked files for the FROST are made. I will check if we need the tagger sag correction or not. The tagger system of the FROST experiment has some sagging problem. This problem has been experienced by another group and there are already some report .
For g1c, the tagger sag is happened at roughly 0.42 E_e and 0.74 E_e (where E_e = 3.115 GeV).
As the first step, I check the tagger sag positions in double-pion data. The first tagger sag position is 0.69 GeV (0.42 E_e where E_e = 1.645 GeV) and the second is 1.22 GeV (0.74 E_e where E_e = 1.645 GeV). For this checking, I make 2D-Histogram whose x-axis has the energy of the measured photon beam with the unit, GeV and y-axis has the ration of the measured photon beam to the calculated photon beam. This plot is made in the decay mode γ p -> p π+ π-. The momentum information of particles are taken after the eloss correction. That is, the calculated photon beam is from the following equation :
E(calculated photon) = E(proton) + E(π+) + E(π-) - E(target proton) and
E(proton) = sqrt{(proton momentum)^2 + (proton mass)^2}
I have projected the 2D-histogram every 5 MeV Binning and fitted them using the gaussian function. I make the following histogram using the mean values and their errors of the gaussian fitting.
