Hunting for Higgs Pairs in Four Jets express
At the Large Hadron Collider, protons collide billions of times per second, and only once in a trillion collisions does a pair of Standard Model Higgs bosons (the particles responsible for the mass of everything) emerge. In the CMS experiment, physicists hunted for exactly such events. Both Higgses almost instantly decay into four 'heavy electrons'—bottom quarks — which the detector sees as four narrow jets of particles.
The main challenge is that the same four jets can also be produced by ordinary processes without any Higgses, like a whisper in the roar of a waterfall. To isolate the signal, the scientists improved the trigger (the system that rapidly selects interesting events), learned to separate merging jets, and applied machine learning. The sensitivity more than doubled compared to previous searches on the same data.
Combining data from two run periods (at 13 and 13.6 TeV), the physicists determined that if Higgs pair production occurs, it happens no more than 4.7 times more intensely than the theoretical prediction. This is the most stringent limit for this decay channel. They also constrained the strength of the 'triple contact' of Higgses — a key parameter that determines the shape of the Higgs potential and governs the mass of all particles.
Now this potential has been probed a little deeper. Like geologists who infer the structure of the Earth's interior from seismic waves, physicists reconstruct the invisible landscape where quarks and electrons gain weight from rare pair events.
Original abstract
as written by the authors arXiv:2604.27044
Measurements of Higgs boson pair (HH) production in the four bottom quark (4b) final state are presented using proton-proton (pp) collision data at $$\sqrt{s}$$ = 13.6 TeV collected by the CMS experiment at the CERN LHC, corresponding to an integrated luminosity of 62 fb$$^{-1}$$. Events in which the Higgs boson decays, H$$\mathrm{t\bar{t}}$$, are separately reconstructed as pairs of small-radius jets (resolved), as well as those where they are reconstructed as single large-radius jets (merged), are studied exclusively. Benefiting from new methods in trigger selection, event selection, and signal extraction, the combination of analyses in the resolved and merged topologies gives an observed (expected) upper limit on the HH signal strength, $$\mu_\mathrm{HH}$$, of 4.4 (4.4) at 95% confidence level (CL). Compared to previously published LHC results in the 4b final state, the expected limit with an equivalent integrated luminosity is improved by more than a factor of two in the resolved topology and is better in the merged topology as well. An updated analysis of the resolved topology using 138 fb$$^{-1}$$ of 13 TeV pp collision data yields an observed (expected) 95% CL upper limit on $$\mu_\mathrm{HH}$$ of 10.0 (5.9), an improvement of about 25% in the expected limit compared to the published results using the same data. Results in the 4b final state with 13 and 13.6 TeV are combined, resulting in an observed (expected) 95% CL upper limit on $$\mu_\mathrm{HH}$$ of 4.7 (2.8). The allowed ranges for the Higgs boson trilinear self-coupling and quartic coupling between two Higgs bosons and two vector bosons are also reported. These are the most stringent constraints achieved in the 4b final state to date.
The bottom quark is almost four times more massive than a proton: it's as if a fragment from a collision of two peas weighed more than the pea itself.
In the novel 'The Three-Body Problem,' aliens manipulate measurements to change the properties of particles — much as physicists hope to see deviations in the behavior of the Higgs boson that point to hidden layers of reality.