Would the real Higgs boson please stand up?

Many different kinds of Higgs bosons have been hypothesized over the years. Any one of these ideas could be correct—or none at all.

After decades of speculation, the Higgs boson was finally discovered on the fourth of July, 2012 – or was it? Despite the headlines, scientists claimed to have seen not a Higgs boson, but “a new particle” or “a new boson.” As it often happens in science, the eureka moment is an explosion of more questions than answers.

What the experiments actually revealed was an excess of certain types of events. More collisions produced pairs of photons, pairs of Z bosons or pairs of W bosons than would be expected in a world without a Higgs. The photon and the Z boson measurements were precise enough to show that they came from decays of a single particle with a mass of approximately 125 GeV (heavier than all known particles except the top quark). The photon, Z and W are all bosons, which are particles of force, as contrasted with fermions, which are particles of matter. Fermions attract or repel each other by tossing and catching bosons.

In the Standard Model, fermions and bosons both acquire their masses by pushing through the same Higgs field, but the Standard Model may be wrong. Perhaps only bosons interact with the Higgs field. If so, then the fermions would have to get their masses some other way.

A group of CMS physicists considered this possibility, known as a “fermiophobic” Higgs. In this scenario, all of the usual assumptions about how Higgs bosons are produced in collisions and how they decay have to be modified. The physicists were able to reinterpret some existing studies, but others had to be reanalyzed for the fermiophobic case. Their result using last year’s data doesn’t support the idea that a fermiophobic Higgs boson exists, though it is not completely conclusive. The CMS collaboration has released a preliminary result using more data.

This is just one way that the Higgs can be non-standard. Some models, such as those with supersymmetry, require at least five Higgs bosons with complex Higgs-to-Higgs transitions. Rather than a finish line, this summer’s discovery was the start of a new adventure.

—Jim Pivarski

The U.S. physicists pictured above made major contributions to the search for a fermiophobic Higgs boson.

These physicists lead the Computing Operations office, which manages all computing services, sites and workflows that process, store, transfer and analyze data and Monte Carlo simulations.