# Changes

,  14:49, 30 March 2017
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=== Normalization Procedure for Rate Estimates ===

=== Normalization Procedure for Rate Estimates ===

In order to get a realistic estimate of the expected rates due to the beam-gas background, the yields extracted from the thus produced simulations need to be normalized.  The factors that must be known for the normalization include the level of vacuum (or the gas density), the cross section for the p+A interaction, and the proton current in the machine.  The beam-gas collisions is essentially a fixed target collision with a proton hitting a "fixed" gas molecule.  The luminosity for this can be estimated from $L = \Phi \rho l$, where L is the luminosity, &Phi; is the proton flux (obtained by the beam current), &rho; is the (transverse) gas density, and l is the longitudinal length of the gas.  Then the rate can be obtained by multiplying the luminosity by the cross section of the interaction.  This rate can then be used as a scaling factor to the generated per event yields from the previous section.  Then these rates can be compared to the expected rates from physics events to get a feeling for how bad the impact of the background will be on the measurement.

In order to get a realistic estimate of the expected rates due to the beam-gas background, the yields extracted from the thus produced simulations need to be normalized.  The factors that must be known for the normalization include the level of vacuum (or the gas density), the cross section for the p+A interaction, and the proton current in the machine.  The beam-gas collisions is essentially a fixed target collision with a proton hitting a "fixed" gas molecule.  The luminosity for this can be estimated from $L = \Phi \rho l$, where L is the luminosity, &Phi; is the proton flux (obtained by the beam current), &rho; is the (transverse) gas density, and l is the longitudinal length of the gas.  Then the rate can be obtained by multiplying the luminosity by the cross section of the interaction.  This rate can then be used as a scaling factor to the generated per event yields from the previous section.  Then these rates can be compared to the expected rates from physics events to get a feeling for how bad the impact of the background will be on the measurement.
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The macro '''/direct/eic+u/rmpetti/workarea/backgroundStudies/beamGas/macros/makeStoBplots.C''' will produce plots overlaying the expected rate of background in the detector with rate of DIS physics events in the detector as a function of the particle energy.  In addition to taking the output TTrees from the background simulation, the macro will also take in EICTrees produced from a physics Monte Carlo generator (for example PYTHIA), which will also be normalized from the expected luminosity that will be delivered by the machine design multiplied by the cross section.
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