Start Counter Material Study

We have estimated the effect of the carbon fiber lining for the start counter support structure on the efficiency for detection for protons. Four reactions of the form $\gamma p\rightarrow pX$were studied:

reaction name	generator	photon energy range (GeV)	t-slope (1/GeV)	mX (GeV)	Γ (MeV)
b1pi	genr8	9.0	5.0	2.0	100
bggen1	bggen	?	7.0	0.5	0
bggen2	bggen	?	7.0	1.5	0
bggen3	bggen	?	?	?	0

The material budget is summarized as follows:

For each reaction, two detector conditions were considered:

1. no carbon fiber support
2. nominal (three layer) carbon fiber support

For each reaction, two definitions of "detected" were considered:

1. proton emerges from the start counter, with no requirement on momentum ("appeared")
2. proton emerges from the start counter with at least 200 MeV/c of total momentum ("tracked")

Range and energy loss were calculated using the Range package. All relevant polar angles were considered. The effect of the magnetic field was not included in this estimate.

Two plots are shown for each reaction:

1. momentum vs. polar angle, with the angle dependent cut for each of the following conditions
2. "detection" efficiency with the corresponding angular distribution of events in arbitrary units

The colors indicate the definition of "detected" and the absence/presence of the carbon fiber:

• appeared, no carbon fiber (blue)
• appeared, with carbon fiber (red)
• tracked, no carbon fiber (green)
• tracked, with carbon fiber (black)

reaction	p vs. theta	efficiency
b1pi	momentum vs. polar angle, b1pi	detection efficiency, b1pi
bggen1	momentum vs. polar angle, bggen1	detection efficiency, bggen1
bggen2	momentum vs. polar angle, bggen2	detection efficiency, bggen2
bggen3	momentum vs. polar angle, bggen3	detection efficiency, bggen3

Integrated over all angles, the various definitions of detection and detector configurations give:

reaction	appeared, no carbon fiber (blue)	appeared, with carbon fiber (red)	tracked, no carbon fiber (green)	tracked, with carbon fiber (black)
b1pi	0.9386	0.9252	0.92285	0.90845
bggen1	0.7429	0.725	0.6724	0.6589
bggen2	0.7925	0.7749	0.73	0.7138
bggen3	1	1	1	1