Many times I see plots for expected/measured "event rates", but what's the motivation for this? Why not generate/use plots for expected/measured event numbers/counts instead?
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Actual number of events measured will depend on how long an experiment is run, the efficiency of a detector, the size or thickness of a target, the intensity of an incoming beam among other things. Each of these is unique to a given experiment.
Science is done with the expectation of reproducibility, so these factors which distinguish one experimental setup from another are factored from the analysis. What remains is a rate: of time, of incident particle, of target thickness, etc.
Bill N
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Wait, quick question - what about when quantities are given as "rates" but with respect to, let's say, energy instead of time? For example, many times in particle physics experiments, instead of the the cross section $\sigma$ being calculated, the derivative of the cross-section with respect to energy $\frac{d\sigma}{d E}$ is given. What's the point of doing that? – Arturo don Juan Aug 17 '15 at 02:10
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I'm asking because I've seen stuff like that many times. – Arturo don Juan Aug 17 '15 at 02:11
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Because we like to investigate how a change in the energy affects the interaction rate per incident particle. The cross section, $\sigma$ gives us a total incident rate. \frac{d\sigma}{dE} shows how that changes with a change in energy. – Bill N Aug 17 '15 at 02:23
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Because rate is often the right observable to report.
The number of event depends on how long you observe, but to within statistics (corrected) rates can be compared between similar experiments without correction.
