Scientists from the ATLAS Collaboration at the Large Hadron Collider (LHC) have recorded a very rare Higgs boson decay that has ever been observed on a scientific installation. This is reported on the CERN website.
The phenomenon is known as Dalitz decay, in which the Higgs boson decays into two leptons (electrons or a muon pair with opposite charges) and a photon. For this, ATLAS physicists have aimed at the decay of a boson mediated by a virtual photon. A virtual particle has a very small (but nonzero) mass and almost immediately decays into two leptons. Scientists analyzed the statistics obtained during the Run 2 collider session, looking for events with photons and two leptons with a combined mass of less than 30 gigaelectronvolts.
In this mass region, decays with the participation of virtual particles prevail over other decays that give the same final state. The difference from the null hypothesis, according to which scientists could observe a statistical fluctuation, was three sigma, which indicates the existence of a new decay (a difference of five sigma unambiguously proves the event).
Observing the decay of the Higgs boson into a photon and a lepton pair will allow physicists to study CP symmetry, or combined parity, which means that when particles are replaced by antiparticles and when a system is mirrored, the laws of physics remain invariant or unchanged. It is known that CP symmetry is broken in some weak decay processes. The decay of the Higgs boson into three particles will allow physicists to better understand the causes of parity violation and, possibly, find signs of the existence of New Physics.