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Cut-map Efficiency

The cut-maps described in section 3.4 works very well on single tag data, and a purity over 85% in the data can be achieved after the cuts. The double tag case is harder to deal with as the main background is a single tag $\gamma$$\gamma$ plus an off-energy electron. This background is not as confined as the pure off-energy electron background, and the cut-maps will be less effective. Applying the cut-maps on both of the electrons in a double tag event is however the best approach to reject the most of this background.

A purity over 75% in the final sample is desirable in order to get good quality of the data. The cut limit for the outer and inner modules were set to 0.15 and 0.5 respectively (removing all events that hit the cutmap in bins with more than 0.15/0.5 permill of the background signal). An average purity of 75% was then obtained, with only a 36% loss of the $\gamma$$\gamma$ signal (Table 5.3).

Table 5.3: The remaining $\gamma$$\gamma$-signal, its purity, data loss, expected full signal and signal expected from probability calculations

Energy	Events	Exp. Gam	Purity	$\gamma$$\gamma$-loss	Full	Prob.
189	78	56	0.72	0.43	101	97
192	12	8	0.63	0.35	13	14
196	47	34	0.72	0.32	49	53
200	43	35	0.81	0.31	51	51
202	9	6	0.66	0.35	9	23
206	74	58	0.79	0.37	93	89
Tot	263	197	0.75	0.36	317	326

The cuts used on data also have to be used on the Monte Carlo in order to get comparable results. As mention in section 3.4, the cut-maps are run-dependent as the y-position of the off-energy background changes. Monte Carlo has a fixed beam position over the whole year, and therefore an average fixed Y-value had to be used.