Candidate W-boson decay to tau and neutrino in ATLAS
When a W-boson decays into a tau and a neutrino, the tau promptly decays as well. Taus are heavier cousins of electrons and muons. They can decay into one of their cousins plus neutrinos. This event shows a missing energy (39 GeV) from neutrinos which is higher than the energy of the lone electron (29 GeV). The electron is seen as a track seen going to the left in the two event images and as a yellow calorimeter tower in the lego plot at the upper right. There is also a dashed "missing momentum" track in the upper left image from the sum of the three neutrinos.
Credit: ATLAS Experiment© 2010 CERN