New results in the search for pairs of Higgs bosons

The Standard Model of particle physics describes the elementary bricks of matter, as well as their interaction. In this Model the particles get their masses through the Higgs mechanism.
The discovery the Higgs boson in 2012 proved that this mechanism exists but we still have to figure out its details, in particular how the Higgs boson interacts with itself.

The ATLAS collaboration has just released a new result, which aims at addressing this question by searching for pairs of Higgs bosons. This process is incredibly rare – around 1000 times rarer than the production of one Higgs boson.

Events where one Higgs boson decays to two photons and the other Higgs boson decays to two bottom quarks provide us with a powerful handle to search for Higgs pair production.

event in ATLAS detector
Candidate HH→bbɣɣ event in ATLAS data taken in 2017. Charged-particle tracks are shown in green, the two candidate b-jets are shown as red cones, and the two candidate photons are shown as cyan towers.

New analysis techniques to search for this rare process were developed (only 12 of those events would have been produced at the LHC so far) by several teams, including the ATLAS team of CPPM, part of the IPhU Particle Physics Group. This result is more than twice as powerful as the previous ATLAS one.

Limits were set on how often pairs of Higgs bosons are produced, at 4.1 times the Standard Model prediction. We also set limits on Higgs pair production via the decay of a hypothetical new scalar particle.

Although this result sets the world’s best limits on the size of the Higgs self-coupling, our work is far from being done. We will need much more data to precisely measure the Higgs self-coupling and to see whether it agrees with the Standard Model prediction. The High-Luminosity upgrade of the LHC plans to deliver a dataset 20 times larger than the one we used for this study. The ATLAS group at CPPM is deeply involved in the upgrade of the detectors for this new phase.

Useful links

Public note ATLAS
Online article CERN
ATLAS video

Contact information
Standard Model
Higgs boson
Particle Physics