Mass and width of the Higgs boson: what ATLAS was and was not built to measure

by Dr Giacomo Artoni (Brandeis University (US))

Wednesday 28 Mar 2018, 17:00 → 18:00 Europe/Rome

MLH (GSSI)

The Standard Model of particle physics is a very successful theory, describing the fundamental constituents of matter and their interactions with great precision. The last example of this great predictive power is the Higgs boson, found only in 2012 by the ATLAS and CMS collaborations after being introduced in 1964 as a fundamental ingredient of the Standard Model. Despite the great success of this theory, there are a number of phenomena that the Standard Model cannot explain: the existence of dark matter or baryon asymmetry in the universe, to give two examples. The Large Hadron Collider has been built with the goal of discovering the Higgs boson and also look at new physics beyond the Standard Model, by testing its predictions with great precision. The mass of the Higgs boson is measured with a precision of about 0.2% and, being linked to other parameters of the Standard Model, can be used to check the internal validity of the theory. The decay width of the Higgs is, instead, perfectly predicted once the mass is known but the challenge at the LHC is that it is too small to be directly measured. A very elegant technique that exploits off-shell production of diboson pairs is used to make this measurement possible.