The ATLAS experiment at CERN has found new evidence that pairs of Higgs particles may be produced in some proton collisions in the LHC accelerator. This was reported at the ICHEP26 conference in Brazil.
At the biennial international particle physics conference ICHEP, researchers from the ATLAS experiment presented today the results of a search for proton-proton collisions in which two tau particles are specifically produced.
Such pairs of tau particles may indicate that two Higgs particles, shortly after their joint creation, both decayed into b mesons and tau particles. Previously, ATLAS and the competing CMS experiment had jointly searched for Higgs pairs via a process in which they decay into b mesons and photons—the so-called HH>bbjj channel.
For the new analyses, data from the most recent LHC Run 3 were used for the first time. LHC Run 3 concluded early this summer, but a large portion of the experimental data is still awaiting analysis.
No hard evidence for the creation of Higgs particle pairs has yet been found in the data analyzed, but there are indications pointing in that direction. Statistically, the observed effect is approximately 1 sigma, ATLAS reported at ICHEP26. The signals could still be due to chance. In particle physics, a discovery is only considered valid at the 5-sigma level.
We’re not quite there yet with 1 sigma. Nevertheless, it’s an interesting development, says particle physicist Tristan Du Pree, affiliated with ATLAS. Nikhef is a partner in ATLAS. A number of Nikhef Ph.D. students are contributing to the search for double-Higgs events.
Du Pree: “Previously, we reported joint evidence from ATLAS and CMS for double-Higgs with two photons at a 3-sigma significance. This adds to that, and it gives us hope that we’ll make further progress with the full data from Run 3.”
ATLAS physicist Pamela Ferrari, who works for Nikhef at CERN, also calls the new result encouraging. “In general, there is now a sense that we will be able to find an initial signal in all the data up to and including Run 3—especially if ATLAS and CMS combine their measurements.”
This bodes well for the measurements to come in a few years, once the LHC has been upgraded to even higher beam intensity—the HiLumi LHC—says Ferrari.
The simultaneous production of two Higgs particles is, in theory, extremely rare, because Higgs particles are heavy on their own, so a great deal of collision energy must be brought together to create them.
Theoretically, however, interactions between Higgs particles are very valuable, as they provide direct insight into the so-called Higgs potential. Its shape indicates exactly how a Higgs particle influences other particles. The self-interaction of Higgs particles should demonstrate this particularly well.
The Higgs particle, detected in 2012, is part of the universal Higgs field that gives all elementary particles a specific mass. To date, the exact Higgs potential is known only in general terms. As a result, numerous theoretical questions remain unanswered regarding the Higgs mechanism and even the stability of the universe.
