A current research study advanced the search for heavy neutral leptons (HNLs), theoretical particles that might address significant questions in particle physics. While traditional LHC experiments focus on quickly decomposing particles, this research study required innovative techniques to identify long-lived HNLs. The items of these decays are generally electrons, photons, hadrons, and muons– well-known particles that the big particle detectors were developed to determine and observe. In the HNL search, a muon is changed by a weakly engaging heavy particle that leaves no trace– until it rots. If it decomposes in the muon system it can produce a shower of particles plainly noticeable in the muon detectors.
The muon system of the CMS experiment. A current study advanced the search for heavy neutral leptons (HNLs), theoretical particles that might answer significant concerns in particle physics. While standard LHC experiments focus on quickly decomposing particles, this study required ingenious methods to detect long-lived HNLs. Credit: CERN
CMS presents results of look for long-lived neutral particles.
The CMS cooperation at CERNs Large Hadron Collider has actually just recently provided new outcomes in look for long-lived heavy neutral leptons (HNLs). Also known as “sterile neutrinos,” HNLs are interesting hypothetical particles that might fix 3 significant puzzles in particle physics: they might explain the smallness of neutrino masses by means of the so-called “see-saw” system, they could describe the matter-antimatter asymmetry of the Universe, and at the same time they might offer a candidate for dark matter.
HNLs are however extremely hard to spot given that they engage really weakly with known particles. The current analysis is an example of scientists having to use significantly imaginative techniques to detect particles that the detectors were not particularly developed to measure.
Studying Particle Decay at the LHC
Many of the particles studied in the large LHC experiments have one thing in typical: they are unstable and decay practically immediately after being produced. The products of these decays are generally electrons, hadrons, photons, and muons– popular particles that the big particle detectors were designed to observe and measure. Studies of the initial temporary particles are carried out based on mindful analysis of the observed decay products. Much of the flagship LHC results were acquired by doing this, from the Higgs boson decaying into photon sets and 4 leptons to studies of the top quark and discoveries of brand-new unique hadrons.
A Different Approach to HNL Analysis
The HNLs studied in this analysis require a different method. They are neutral particles with comparatively long lifetimes that permit them to fly for meters undetected, before rotting somewhere in the detector. The analysis provided here concentrates on cases where an HNL would appear after the decay of a W boson in a proton-proton accident, and would then itself decay somewhere in the muon system of the CMS detector.
Function of the Muon System
The muon system constitutes the outer part of CMS and was developed– as its name recommends– to find muons. Muons produced in the LHC proton-proton accidents traverse the entire detector, leaving a trace in the inner tracking system and after that another one in the muon system. Combining these two traces into the full muon track lets physicists determine muons and measure their properties.
In the HNL search, a muon is replaced by a weakly connecting heavy particle that leaves no trace– up until it decomposes. If it rots in the muon system it can produce a shower of particles clearly noticeable in the muon detectors.
Analysis Procedure and Results
The analysis begun by selecting crash occasions with a reconstructed electron or muon from the decay of the W boson and an isolated cluster of traces in the muon system. The analysis required the elimination of cases where basic procedures could mimic the HNL signal. After the complete analysis, no excess of signal above expectation has actually been observed. As an outcome, a variety of possible HNL specifications was omitted, setting the most strict limits to date for HNLs with masses of 2-3 GeV.
Read more in the CMS publication here.