CMS partners to release Higgs boson discovery data to public

As part of its ongoing commitment to making its science fully open, the CMS Collaboration has just publicly released the CMS portfolio of measurements that contributed to the 2012 discovery of the Higgs boson.

The CERN launch coincides with the release of joint software, a statistical analysis tool developed by CMS during the first run of the Large Hadron Collider (LHC) to search for unique particles, and has been used throughout the collaboration ever since. tool.

Physical measurements based on LHC data are often reported as central values ​​and their corresponding uncertainties. For example, shortly after the Higgs boson was observed in the proton collision data of the Large Hadron Collider, CMS measured its mass as 125.3 plus or minus 0.6 GeV (the proton mass is about 1 GeV). But this number is just a simple summary of the measurements, a bit like the title of a book.

In measurement, the complete information extracted from the data is encoded in a mathematical function (called the likelihood function), which includes the measured value of the quantity and its dependence on external factors. In the case of CMS measurements, these factors include the calibration of the CMS detector, the accuracy of the CMS detector simulation used to facilitate the measurement, and other system effects.

Likelihood functions based on measurements from LHC data can be complex because many aspects need to be determined to fully understand the chaotic collisions that occur at the LHC. For example, the likelihood function of the CMS Higgs boson discovery measurement combination, which CMS has just released in electronic format, has nearly 700 parameters for a fixed value of the Higgs boson mass. Of these, only the number of Higgs bosons found in the data is the physical parameter of interest, while the rest model system uncertainties.

Each of these parameters corresponds to a dimension of the multidimensional abstract space in which the likelihood function can be plotted. It is difficult for humans to imagine a multi-dimensional space, let alone a multi-dimensional space.

The newly released CMS measurement of the Higgs boson discovery is the first likelihood function made public by the collaboration, allowing researchers to address this problem. With publicly accessible likelihood functions, physicists outside the CMS collaboration can now precisely consider the CMS Higgs boson discovery measurements in their studies.

The release of this likelihood function and the Combine software for modeling likelihood and fitting data mark a new milestone in CMS’s decade-long commitment to fully open science. It joins hundreds of open access publications, publishes nearly 5 petabytes of CMS data on the CERN Open Data Portal, and publishes the entire software framework on GitHub.