# EEmc Gammas via conversion method, improving hadronic veto

*Abstract:*Based on EEmc Gammas via conversion method, losses due to cuts we saw that the hadronic veto cut (sum of all postshower tiles w/ in R<0.3 is less than 0.2 MeV) reduces gamma yields by 50%, with events at higher pT suffering most. Based on EEmc Gammas via conversion method, relaxing the hadronic veto cut, where we relaxed the hadronic veto, we saw odd behaviors in other variables which are suggestive of hadronic backgrounds. In this study we examine using a ratio of postshower energy to candidate energy in place of the absolute cut.

*Event sample:*

### 1.0 The Postshower Ratio Cut

_{post}/ E

_{candidate}) as a discrimination variable (the "discriminant").

1. Require candidate to be w/in the EEMC with pT > 5.0 GeV.

_{T}/ E

_{T}

^{R<0.3 }> 0.9

Figure 1.2 -- Ratio of energy deposited in postshower to energy of candidate, evolution with cuts. Isolation cut (red), preshower-1 cut (yellow), preshower-2 cut (green).

Observations:

A better discriminant could involve the SMD energy instead of the tower energy. Specifically, the backgrounds which I am concerned about at present tend to have small energy deposits in the SMD relative to the tower energy. They tend to be rejected reasonably well by applying the absolute veto on the postshower detector. So perhaps a ratio of postshower to SMD energy would single out these events better.

### 2.0 The Postshower-SMD Ratio Cut

Form a discriminant combining both postshower response and SMD response.

D = Log( E_{post} / ( E_{u}+E_{v}+1.0E-9 GeV) )

Events with large postshower energy relative to the SMD should show up at larger values of the discriminant. The value of 1.0E-9 GeV added to the denominator is there so that zero SMD energy is handled gracefully (i.e. it get cut, likely showing up in the overflow bin of the histogram).

### 3.0 Conversion Method w/ Post-SMD Ratio Cut

*Cuts:*

_{T}/ E

_{T}

^{R<0.3 }> 0.9

Observations:

1. The improvement here is more difficult to see... but the events which show up with no energy in the SMD relative to the gamma candidate are significantly supressed. Although once again, they are not eliminated entirely.

### 4.0 Fit to the Post-SMD ratio distribution

Figure 4.1 -- Fit the postshower-SMD ratio distribution to the sum of two gaussians to estimate the fraction of events which may be due to hadronic showers. (Note: the hadron fraction is calculated over the range [10,-1), not [10,1) as the figure suggests.)

_{photonic}= 92.5% as originally estimated

_{hadronic}= 50.0%, which I "read off" from figure 2.1

_{b}= 0.85 * ε

_{photonic }+ 0.15 * ε

_{hadronic }= 78.7%

### 5.0 Conclusions, questions

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