Six years after its discovery, the first evidence for the decomposition of the Higgs boson opens new doors for particle physics.
The Large Hadron Collider (LHC) discovered in 2012 the Higgs boson, the subatomic particle responsible for giving mass to fundamental subatomic particles.
Today, physicists have another exciting announcement to add to the Higgs saga: They have made the first unequivocal observation of Higgs bosons decomposing into matter-antimatter quarks. Surprisingly, Higgs bosons break down most often in this way.
The new announcement shows strong agreement between theoretical predictions and experimental data, which in turn could place strict restrictions on ideas from more fundamental physics that strive to explain why the Higgs boson exists.
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Higgs bosons are made in high-energy collisions between pairs of particles that have been accelerated to almost the speed of light. These bosons do not live long, only about 10 ^ minus 22 seconds. A particle with that life, traveling at the speed of light, will decompose long before it travels a distance the size of an atom. Therefore, it is impossible to directly observe Higgs bosons. It is only possible to observe its degradation products and use them to infer the properties of the parent boson.
Higgs bosons have a mass of 125 gigaelectrons volts (GeV). Theoretical calculations predict that Higgs bosons decay in pairs of the following particles by the following percentages: lower quarks (58%), W bosons (21%), Z bosons (6%), tau leptons (2.6%), and photons (0.2%). The rest is made up of more exotic configurations.
One of the key results of the recent announcement has been to verify that the prediction was correct for the lower quarks.
When physicists announced the discovery of the Higgs boson in 2012, they relied on its decomposition into Z bosons, W bosons, and photons, but not lower quarks. The reason is extremely simple: those particular decays are much easier to identify. The W and Z bosons are responsible for causing the weak nuclear force and can be broken down in different and easily identifiable ways.
At the collision energies available at the LHC, Higgs bosons occur in only one collision per billion. Because it is difficult or impossible to isolate collisions in which Higgs bosons break down into lower quarks, scientists needed another approach.
The Standard Model of particle physics predicts that about 60% of the time a Higgs boson will break down into a bottom pair of quarks, the second heaviest of the six types of quarks.
The detection of the decomposition of the Higgs boson in a pair of background quarks was carried out by mixing the data obtained by teams at ATLAS and at CMS at the Large Hadron Collider, whose analysis coincided in both teams.
While simply observing this mode of decline is a significant advance in scientific knowledge, it has a much more important result. It turns out that the Higgs boson, proposed in 1964, is not motivated by a fundamental idea. It was simply added to the Standard Model, which describes the behavior of subatomic particles, as an add-on.
In fact, before the Higgs boson was proposed, the standard model predicted massless particles. After including the Higgs field as an ad hoc addition to the standard model, the particles now had mass. Therefore, it is very important to explore predictions of decreasing probabilities and look for clues of a connection to an underlying theory. And there have been more recent and comprehensive theories developed since the 1960s, predicting that perhaps more than one type of Higgs boson exists.
Therefore, it is crucial to understand the rate at which Higgs bosons decay into other particles and compare it to predicted decay rates.
The LHC will continue to operate until early December . Then, it will suspend operations for two years to be restored and updated. In spring 2021, the LHC will resume operations with significantly enhanced capabilities. The throttle and detectors are expected to continue to collect data through the mid-2030s and to record more than 30 times more data than has been recorded so far. With that increased data and improved capabilities, it is quite possible that the Higgs boson still has many stories to tell …
Reference: Observation of Higgs boson decay to bottom quarks. arXiv: 1808.08242 [hep-ex] arxiv.org/abs/1808.08242
