EG1 Run - Count rate calculations

Simple Count Rate Calculation (S. Kuhn)

The following graphs are based on a simple acceptance calculation for CLAS in the configuration where the target is 55 cm upstream from the nominal target point (0,0,0). This corresponds to the target location for EG1 running. The acceptance for a given scattering angle theta and final energy E' was calculated as the range in phi in a given sector for which the scattered electron would travel through the active volume of all three Drift Chamber regions, divided by 60 degrees. Cerenkov, TOF and EGN acceptance and response were ignored.

The histograms were generated by a full simulation of the internally radiated cross section for inclusive electron scattering, based on form factor parametrizations for elastic scattering and quasi-elastic scattering, the Brasse parametrization for resonance scattering, and a smooth interpolation into the DIS region using the NMC parametrization of F₂ and the Whitlow parametrization for R. The cross sections were then multiplied by the acceptance.

In the following 3 histograms, the torus magnetic field was assumed to be 1/2 of the nominal field strength, with inbending electrons.

Cross section times acceptance for p(e,e') at 4 GeV

The cross section is given in units of 10^-35 cm². This corresponds to a rate of about 1 count/100s or 1000 counts/day. Note that the overall count rate will be about 10 times higher due to contributions from other target components (¹⁵N, ⁴He etc.). The total count rate adds up to 700-800 Hz. All rates are based on a total overall luminosity of 10³⁴ nucleons/cm²*electrons/s.

Some examples: The highest count rate is the elastic peak at small theta, with 180 k counts per day. The proton asymmetry in this bin is A|| = 0.15. However, due to dilution and beam and target polarization, the expected measured asymmetry could be 10x smaller and the count rate 6x higher. This would yield a 6% statistical error on A|| in a day, or less than 3% in 5 days. The same relative uncertainty would apply to the extracted product of beam polarization times target polarization times dilution factor.

Cross section times acceptance for d(e,e') at 4 GeV

Again, the cross section is in units of 10^-35 cm². Assuming an overall luminosity of 10³⁴ nucleons/cm2*electrons/s, this corresponds again to about 1 count per 100 s or 1000 counts per day, with the overall rates about a factor 5 higher (dilution factor is 0.2). The integrated rate is once again around 700 Hz.

Cross section times acceptance for p(e,e') at 1.8 GeV

Due to the different bin sizes in this histogram, the unit on the z-axis corresponds to a cross section of only 0.44 10^-35 cm². Also, note the logarithmic scale. Furthermore, the luminosity at 1. 8 GeV will probably have to be a factor 5 smaller than at 4 GeV, which means that the z-scale gives roughly counts per 1000 s. The overall integrated count rate is once more around 700-800 Hz.

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