Evidence of Higgs boson discovered

For the past few months, particle physicists have been very cautious about calling the newly discovered particle, found at the Large Hadron Collider, a “Higgs-like” particle. The Large Hadron Collider at the European Organization for Nuclear Research (CERN) is the largest particle collider on earth, made to smash protons together at velocities near the speed of light in order to learn more about the fundamental particles that describe the universe. The reason that this new particle has been called a “Higgs-like” particle is, simply, that we aren’t entirely sure that it is actually “the Higgs boson” predicted by the Standard Model.

However, many physicists, including some of those here at Hopkins in the Department of Physics and Astronomy, are working to identify this particle. Co-leading the investigation is associate professor Andrei Gritsan, who is a collaborator on the CMS (Compact Muon Solenoid Experiment) detector. Gritsan’s team has been examining the decay of this “Higgs-like” particle into two Z bosons, a particle that mediates the weak nuclear force.

There are two reasons why this particle, also known by individuals outside the scientific community as the “God particle,” is so important. The first is that it explains why all fundamental particles with mass, such as quarks, have mass. The second is that it has the ability to explain why photons, the particles that mediate the electromagnetic force, are massless, while Z and W± bosons, the particles that mediate the weak nuclear force, have mass.

It is strange that photons don’t have mass and Z and W± bosons do, because in the early universe, these forces originated from the same force, called the electroweak force. However, as the universe cooled after the Big Bang, that force separated into the two forces we have recently been able to observe.

The Z and W± bosons have mass because they interact with the Higgs field. According to theory, the stronger the interaction, the greater the mass. However, photons do not interact with the Higgs field at all, and, therefore, are massless.

As of now, we have increasingly credible evidence that the new particle that was discovered, with a mass of 126GeV/c2, is the Higgs boson. However, there is still some work that needs to be done in order to determine if it is. In an interview with The News-Letter, Gritsan explained that determining if this is the Higgs boson involves two parts.

“One, determine if this is ‘a Higgs’ boson. This is something that we are closing in on now: the properties of the discovered boson are consistent with a Higgs boson, such as the measurement of the quantum numbers, something that we are developing here at Hopkins,” Gritsan said.

The second part, explained Gritsan, is “to say that this is ‘the Higgs’ boson exactly as predicted in the Standard Model of particle physics would take much more time, and it may well become not ‘the Higgs’ boson.” This means that there might not be only one Higgs boson. “We have found one Higgs boson, but it is early to say if there are more. It is possible,” he added.

The idea of different Higgs bosons isn’t so different from other particles in the Standard Model — there are different types of quarks, neutrinos, leptons and even different types of bosons for the weak nuclear force. These different Higgs bosons may function in a similar way; they could serve a similar function, but would have slightly different properties.

“Even if we do not find another Higgs boson in the next five years, this would still keep the question open: there could be more with higher masses for example, we just have not reached it, or there may be no more,” Gritsan said.

Gritsan is motivated by revealing the unknown, which has important scientific implications. While the discovery of the Higgs boson does not appear to have many practical implications, the scientific implications of this are phenomenal.

“Since we found a Higgs boson, it must be the manifestation of the Higgs field, which means vacuum is not empty and is filled with this field. There are implications for stability of this field and as a consequence stability of the Universe, among other things,” Gritsan said.

Incredibly, one of the smallest things ever discovered may actually lead to theories about the stability of the Universe. Despite the level of complexity of the subject and the magnitude of the solution, Gritsan notes what is most difficult about his job:

“[There are] too many interesting things to do, so not having enough time for everything is the biggest challenge.”