View of the CMS experiment. Credit: CERN
The CMS team at the LHC performed a new test on a model that was devised to explain the minuscule mass of neutrinos, electrically neutral particles that change type as they travel through space.
The particles that cannot be broken down into smaller parts, like as quarks and electrons, obtain their mass through interactions with a basic field associated with the Higgs boson in the Standard Model of particle physics. The neutrinos, on the other hand, are an exception, as the Higgs process cannot account for their mass. As a result, physicists are looking at alternative explanations for neutrino mass.
A mechanism that links a known light neutrino with a hypothetical heavy neutrino is one such speculative explanation. The heavier neutrino acts as a larger child on a seesaw in this concept, lifting the lesser neutrino to give it a little mass. The neutrinos, on the other hand, would have to be Majorana particles, or their own antimatter particles, for this seesaw scenario to function.
The CMS team recently investigated the seesaw hypothesis by looking for Majorana neutrinos produced through a specific mechanism known as vector-boson fusion in data acquired by the CMS detector from high-energy collisions at the LHC between 2016 and 2018. If these collisions occurred, they would produce two muons (heavier copies of the electron) with the same electric charge, two “jets” of particles with a big total mass that were far apart, and no neutrino.
The CMS researchers found no evidence of Majorana neutrinos in the data after identifying and removing a background of collision events that seem almost identical to the sought-for events. They were, nevertheless, able to place fresh limits on a seesaw model parameter that depicts quantum mixing between a known light neutrino and a hypothetical heavy neutrino.
The results include bounds for a heavy Majorana neutrino with a mass greater than 650 billion electronvolts (GeV) that surpass those obtained in previous LHC searches, as well as the first direct limits for a heavy Majorana neutrino with a mass greater than 2 trillion electronvolts (TeV) and up to 25 TeV.
After a successful restart on April 22, the LHC will be back in collision mode this summer, allowing the CMS team to acquire more data and test out the seesaw once more.
Further information: Probing Majorana neutrinos and the Weinberg operator in the same-charge dimuon channel through vector boson fusion processes in proton-proton collisions at s√=s= 13 TeV. cms-results.web.cern.ch/cms-re … XO-21-003/index.html