# What exactly is background in terms of data analysis in particle physics? [closed]

I often come across the term "background" in particle physics. Could someone explain what it exactly means?

## closed as too broad by ZeroTheHero, AccidentalFourierTransform, Jon Custer, Yashas, user259412Apr 26 '17 at 0:03

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• Context of how it's used would help – scrappedcola Apr 24 '17 at 16:43
• I am looking at a process where a higgs boson decays into two photons . To analyse the decay five monte carlo background samples were used for the higgs production (gluon gluon Fusion, vector boson fusion, etc.) Now, what exactly is "backround"? – Mark Apr 24 '17 at 16:47
• Background is the events in your selected data sample which aren't your signal. Often they can be just random combinations of final-state particles (combinatorial background) or misidentified processes. – dukwon Apr 24 '17 at 17:17
• And how can someone "identify" the background? – Mark Apr 24 '17 at 17:18
• There isn't really one generic answer for that. Unless you expect zero background or zero signal, you never know on an event-by-event basis whether a particular event is signal or background. We only really care about distributions of events. In $H→\gamma\gamma$, the background is just modelled as a smooth polynomial in $m(\gamma\gamma)$ and the Higgs as a Gaussian or similar peaking shape. – dukwon Apr 24 '17 at 17:23