STAMPS@CMU presents:

Testing a sharp null hypothesis versus a continuous alternative: Deep issues regarding this everyday problem in high energy physics

by Robert Cousins (Department of Physics and Astronomy, UCLA)

Online webinar February 12, 2021 at 1:30-2:30 PM ET.
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Abstract
In high energy physics, it is extremely common to test a well-specified null hypothesis (such as the Standard Model of elementary particle physics) that is nested within an alternative hypothesis with unspecified value(s) of parameter(s) of interest (such as the Standard Model plus a new force of nature with unknown strength). As widely discussed in the context of the Jeffreys-Lindley paradox, two experiments with the same p-value for testing the null hypothesis can have differing results for the Bayesian probability that the null hypothesis is true (and for the Bayes factor), since the latter depends on both the sample size and the width of the prior probability density in the parameters(s) of the sought-for discovery. After a reminder of relevant methods for hypothesis testing and the paradox, I will note that the issues are particularly apparent when there are three well-separated independent scales for the parameter of interest, namely (in increasing order) the small (or negligible) width of the null hypothesis, the width of the measurement resolution, and the width of the prior probability density. After giving examples with this hierarchy, I will quote various statements in the statistics literature and discuss their relevance (or not) to usual practice in high energy physics. Much of the talk will draw on arXiv:1310.3791.

Bio

Robert (Bob) Cousins is Distinguished Professor Emeritus in the Department of Physics and Astronomy at UCLA, where he was on the faculty from 1981 through 2020. He completed his A.B from Princeton in 1976, obtained his Stanford Ph.D. under Mel Schwartz while collaborating on a kaon experiment at Fermilab, and then had a position at CERN during 1981 before joining UCLA. Throughout his career, he has worked on experiments measuring or searching for rare processes, at Brookhaven National Lab with kaons, at CERN with neutrinos, and since 2000 on the CMS Experiment at CERN's Large Hadron Collider. This has motivated his career-long interest in statistical data analysis.

Cousins has held various high-level leadership positions in his collaborations, and served on a number of ad hoc and standing advisory and review committees for laboratories and funding agencies. Recent such service included the Particle Physics Project Prioritization Panel (P5) in the U.S. (2013-2014), and CERN’s Scientific Policy Committee (2018-2023).