The Higgs boson is like a tuning fork that rings at a strictly defined note. But physicists have learned to hear it even when the note is off — in the so-called 'off-shell' region. It was there, in the data from the CMS detector, that answers were hiding about what the Higgs mechanism is really made of.
In proton collisions at the record energy of 13 TeV, pairs of Z bosons were produced, and through them, Higgs particles with masses far from the usual 125 GeV. This 'detuned' signal allowed the first direct test of the hypothesis: is the Higgs boson composite, like an atom or a proton? It turned out that if it does have an internal structure, it is hidden below 870 GeV. That's like a tuning fork showing no sign of composite parts even when struck with a hammer seven times harder than usual.
The second surprise came from the light quarks. Previously, their contribution to Higgs production was almost impossible to detect: it was drowned out by the 'noise' of heavier particles. But by combining data from the on-shell and off-shell regions, physicists managed to isolate this faint whisper and place the tightest constraints to date. Along the way, they measured the boson's lifetime: 5.1 MeV in energy units — about 10⁻²² seconds. That's comparable to the time it takes light to travel a distance a hundred times smaller than an atomic nucleus.
The width of the Higgs boson measured in this analysis is about 5 MeV. In more familiar units, that corresponds to a lifetime of roughly 10⁻²² seconds. In that time, light travels a distance a hundred times smaller than the diameter of a proton.
In Liu Cixin's novel 'The Three-Body Problem', an advanced civilization manipulates physical constants — searches like this for a composite nature of the Higgs field could be a first step toward detecting such interference.