The European Physical Journal C

, Volume 70, Issue 1, pp 525–530

Trial factors for the look elsewhere effect in high energy physics

Open AccessSpecial Article - Tools for Experiment and Theory

DOI: 10.1140/epjc/s10052-010-1470-8

Cite this article as:
Gross, E. & Vitells, O. Eur. Phys. J. C (2010) 70: 525. doi:10.1140/epjc/s10052-010-1470-8


When searching for a new resonance somewhere in a possible mass range, the significance of observing a local excess of events must take into account the probability of observing such an excess anywhere in the range. This is the so called “look elsewhere effect”. The effect can be quantified in terms of a trial factor, which is the ratio between the probability of observing the excess at some fixed mass point, to the probability of observing it anywhere in the range. We propose a simple and fast procedure for estimating the trial factor, based on earlier results by Davies. We show that asymptotically, the trial factor grows linearly with the (fixed mass) significance.

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© The Author(s) 2010

Authors and Affiliations

  1. 1.Weizmann Institute of ScienceRehovotIsrael