What is the meaning of weight of events?

Hi friends
I newly joined the high energy physics group. Every time I used to deal with the “weight of events”. Can you please anyone clarify me what does this really mean? Thanks

this kind of questions are best discussed with your supervisor. We try to use the forum for questions how to work with root.

Nevertheless, I will quickly help you out:

  • When we study a distribution of some quantity we measure, we usually fill it in a histogram. A histogram just counts how many events fall in each bin.
  • Particularly when you do some simulations, you need to apply some corrections.
    – The efficiency for detecting events could be lower/higher depending on detector properties
    – Monte Carlo simulators might spit out specific events a bit too rarely or a bit too often, e.g. because the precision of the simulation is not good enough.
    – Any combination or variation of the above
  • In these cases, you apply a weight to an event. That is, instead of increasing the event count in a bin by 1, you increase it by the weight.

Very simple example: Let’s say that the efficiency to detect an event is 80%. You know that, and you want to correct for this. You measure 800 events, but you know that it should have been 1000.
You fill the histogram for each of your 800 events with a weight of 1/0.8. Because the event weight is higher, the histogram will look like it contains 1000 events even though you filled it only 800 times, which is exactly what you need to properly analyse a distribution.

Events weights are usually not constant, though, because efficiencies etc may depend on many quantities.


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