According to physicists from the CMS Collaboration at CERN’s Large Hadron Collider (LHC), it is the first time that this process has been seen in proton-proton collisions. It is also the most precise measurement of the tau’s anomalous magnetic moment and offers a new way to constrain the existence of new physics.
The tau, sometimes called tauon, is a peculiar particle in the family of leptons.
In general, leptons, together with quarks, make up the matter content of the Standard Model.
The tau was only discovered in the 1970s and its associated neutrino — the tau neutrino — completed the tangible matter part upon its discovery in 2000 by the DONUT Collaboration at Fermilab.
Precise research for the tau is rather tricky though, as its lifetime is very short — it remains stable for only 290*10-15 seconds.
The two other charged leptons, the electron and the muon, are rather well studied.
A lot is also known about their magnetic moments and their associated anomalous magnetic moments.
The former can be understood as the strength and orientation of an imaginary bar magnet inside a particle.
This measurable quantity, however, needs corrections at the quantum level arising from virtual particles tugging at the magnetic moment, deviating it from the predicted value.
The quantum correction, referred to as anomalous magnetic moment, is of the order of 0.1%.
If the theoretical and experimental results disagree, then this anomalous magnetic moment, al, opens doors to physics beyond the Standard Model.
The anomalous magnetic moment of the electron is one of the most precisely known quantities in particle physics and agrees perfectly with the model.
Its muonic counterpart, on the other hand, is one of the most investigated ones, into which research is ongoing.
Although theory and experiments have mostly agreed so far, recent results give rise to a tension that requires further investigation.
For the tau, however, the race is still going. It is especially hard to…
Read the full article here