Physicist from CMS cooperation at CERN just published the combination of CMS measurements that helped establish the discovery of the Higgs boson in 2012.
CMS event display showing a Higgs boson candidate decaying into two photons. It is one of two decay channels that were key to the particle’s discovery. Image credit: CERN.
“Physical measurements based on data from CERN’s Large Hadron Collider (LHC) are typically reported as central values and corresponding uncertainties,” the CMS physicists said.
“For example, shortly after observing the Higgs boson in the LHC’s proton-proton collision data, CMS determined its mass to be 125.3 plus or minus 0.6 GeV (the mass of a proton is about 1 GeV).”
“But this figure is just a quick summary of the measurements, and is like the title of a book.”
In measurement, the complete information extracted from the data is encoded into a mathematical function known as a likelihood function. This function includes measurements of quantities and dependence on external factors.
“For CMS measurements, these factors include the calibration of the CMS detector, the accuracy of the CMS detector simulation used to facilitate the measurements, and other systematic effects,” the researchers said.
“To fully understand the nasty collisions that occur at the LHC, many aspects need to be determined, so the likelihood function for measurements based on LHC data can be complex.”
“For example, the likelihood function for the combined CMS Higgs boson discovery measurement that CMS just released in electronic form has nearly 700 parameters for a fixed value of the Higgs boson mass.”
“Only one of these, the number of Higgs bosons found in the data, is an important physical parameter, and the rest model systematic uncertainties.”
“Each of these parameters corresponds to a dimension of a multidimensional abstract space in which the likelihood function can be drawn.”
“It is difficult for humans to visualize spaces that contain multiple dimensions, much less spaces that contain many dimensions.”
The new release of the CMS Higgs boson discovery measurement likelihood function, the first publicly available likelihood function from this collaboration, allows researchers to avoid this problem.
Using a publicly accessible likelihood function, physicists outside the CMS Collaboration can now accurately incorporate CMS Higgs boson discovery measurements into their studies.
“The release of this likelihood function and the Combine software used to model likelihood and fit data marks another milestone in CMS’s 10-year commitment to fully open science.” said the people.
“This joins hundreds of open access publications, the release of nearly 5 petabytes of CMS data on the CERN Open Data Portal, and the publication of the entire software framework on GitHub.”
Source: www.sci.news
