What’s that ‘fluctuation’ at 120 GeV?

By Hamish Johnston

Last week’s particle-physics conference in Paris began with the news that CERN’s Large Hadron Collider (LHC) may have produced the first glimpse of direct CP violation in a charmed-muon decay.

If that wasn’t enough to get particle physicists mildly excited, Friday’s joint announcement by the ATLAS and CMS experiments should do the trick.

Physicists working on the LHC’s two biggest experiments have pooled their data from 2011 (or at least the bits they have managed to analyse so far) to obtain the best mass exclusion yet for the Higgs boson.

The data reveal that the mass of the Higgs is unlikely to fall in the range 140–480 GeV/c². This is news because most of this energy range had not been excluded by previous colliders, including the Tevatron at Fermilab. When combined with work at other colliders, the ATLAS and CMS data suggest that the Higgs mass falls into a window between about 110–140 GeV/c², or is greater than about 480 GeV/c².

Perhaps the most intriguing feature of the data is a sharp change at about 120 GeV/c². In his blog, Tommaso Dorigo explains the significance of this fluctuation, and argues that it could be the first indication of the Higgs mass, which he believes is 119 GeV/c². You can read Dorigo’s analysis here.

In the video above, physicists from the CMS experiment talk about the mass-exclusion results.

In other LHC news, researchers from the CMS experiment have published a paper in Physical Review Letters detailing the most extensive search for supersymmetry to date. Supersymmetry (or SUSY) is an attractive concept because it offers a solution to the “hierarchy problem” of particle physics, provides a way of unifying the strong and electroweak forces, and even contains a dark-matter particle. An important result of the theory is that every known particle has at least one superpartner particle, or “sparticle”.

Sadly, those waiting for a revolution in particle physics will have to wait a little longer, because no evidence for such sparticles has been found by CMS. You can read the paper here free of charge.

23 November Higgs update from CERN: Physicists on the ATLAS experiment have published a paper in Physical Review Letters that excludes the Standard Model Higgs mass from 340-450GeV/c² at 95% confidence. You can read the paper here.