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. **

** For connection information, join our mailing list here. **

**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).