If you have been a science fan in recent years, you are aware of the exciting results of the Large Hadron Collider (LHC), which in 2012 found the Higgs boson, the subatomic particle responsible for giving mass to fundamental subatomic particles.
Today, physicists have another exciting announcement to supplement the Higgs saga: they made the first unambiguous observation that Higgs bosons fall into a matter-antimatter pair of bottom quarks. Surprisingly, the Higgs bosons break down the most in this way.
The new announcement shows a strong correspondence between the theoretical predictions and the experimental data, which in turn could impose stricter restrictions on ideas of more fundamental physics that explain why Higgs boson even exists.
Field of Dreams
In the 1
However, there was a problem. The simplest manifestation of the theory predicted that all particles had no mass. As early as the 1960s, physicists knew that subatomic particles had a mass, which was possibly a fatal flaw.
Several groups of scientists have proposed a solution to this problem: a field pervades the universe and is called a Higgs field. Fundamental subatomic particles interacted with this field, and this interaction gave them their mass. [6 Implications of Finding the Higgs Boson]
The existence of the field also implied the existence of a subatomic particle, the Higgs boson, which was discovered in 2012 by researchers from the Laboratory of the European Organization for Nuclear Research (CERN) in Switzerland. (Disclosure: I am an employee of one of the research groups that made the first discovery, as well as today's announcement.) The British physicist Peter Higgs and the Belgian physicist François Englert shared the 2013 Nobel Prize in Physics for their predictions of the Higgs field ,
Finding the Bottom Quarks
Higgs bosons are formed in high-energy collisions between pairs of particles that have been accelerated to almost the speed of light. These bosons do not live very long – only about 10 ^ minus 22 seconds. A particle with this lifetime, moving at the speed of light, will decay long before it covers a distance the size of an atom. Therefore, it is impossible to directly observe Higgs bosons. It is only possible to observe their decay products and deduce the properties of the parent boson.
Higgs bosons have a mass of 125 gigaelectron volts (GeV), or one that is about 133 times heavier than a proton. Calculations from established theory predict that Higgs' bosons develop into pairs of the following particles in the following percentages: bottom quarks (58 percent), W bosons (21 percent), Z bosons (6 percent), tau leptons (2.6 Percent) and photons (0.2 percent). More exotic configurations do the rest. One of the key findings of today's announcement was to verify that the prediction for bottom quarks was correct. [Strange Quarks and Muons, Oh My! Nature’s Tiniest Particles Dissected]
When physicists announced the discovery of the Higgs boson in 2012, they were based on their decay into Z bosons, W bosons and photons, but not in bottom quarks. The reason is actually extremely simple: these particular decays are much easier to identify.
With the collision energies available at the LHC, Higgs bosons are manufactured in just one collision in every 1 billion. The large number of collisions at the LHC takes place through the interaction of the strong nuclear force, which is (by far) the strongest of the subatomic forces and responsible for keeping the atomic nucleus together.
The Problem is with Interactions With strong power, the production of a matter-antimatter pair of bottom quarks is very common. Thus, the production of bottom quarks by Higgs bosons decaying into bottom quarks is completely overlaid by pairs of bottom quarks made by more common processes. Accordingly, it is essentially impossible to identify those events in which bottom quarks are generated by the decay of Higgs bosons. It's like trying to find a single diamond in a 50-gallon zirconia drum.
Since it is difficult or impossible to isolate collisions in which Higgs bosons decay into bottom quarks, the scientists needed a different approach. Therefore, researchers looked for another class of events – collisions in which a Higgs boson was generated simultaneously with a W or Z boson. Researchers refer to this class of collisions as "associated production".
W and Z bosons are responsible for the weak nuclear power and can decay in various easily recognizable ways. Associated production occurs less frequently than unrelated Higgs production, but the presence of W or Z bosons enhances the ability of researchers to identify events involving a Higgs boson. The technique of associated production of a Higgs boson was developed at the Fermi National Accelerator Laboratory just outside Chicago. Because of the plant's low-energy particle accelerator, the lab could never claim it had discovered the Higgs boson, but its researchers' knowledge played a significant role in today's announcement.
The LHC accelerator hosts two particle physics detectors that can observe Higgs bosons – the Compact Muon Solenoid (CMS) and a Toroidal LHC Apparatus (ATLAS). Both experimental collaborations today announced the observation of the associated production of Higgs bosons, with the specific decay of Higgs bosons into a matter-antimatter pair of bottom quarks.
While the simple observation of this decay mode is a significant advance in scientific knowledge, it has a much more important result. It turns out that the Higgs field proposed in 1964 is not motivated by a more fundamental idea. It was simply added to the standard model, which describes the behavior of subatomic particles as something like a patch. (Before the Higgs field was proposed, the standard model predicted massless particles.) After the Higgs field was added as an ad hoc addition to the standard model, particles now have mass.) Therefore, it is very important to study the predictions of decay probabilities to look for clues to a connection to an underlying theory. And there are newer and more comprehensive theories that have been developed since the 1960s that predict that more than one type of Higgs boson may exist.
It is therefore important to understand the rate at which Higgs bosons break down into other particles and compare them to the predicted decay rates. The simplest way to illustrate the match is to give the observed decay rate divided by the predicted rate. Better agreement between the two gives a ratio close to 1. The CMS experiment finds in today's announcement an excellent match with a ratio of predicted to observed rates of 1.04 plus or minus 0.20, and the ATLAS measurement is similar (1.01 plus or minus 0.20). This impressive consensus is a triumph of current theory, though it does not indicate a direction to a more fundamental origin for the Higgs phenomena.
The LHC will continue to work until the beginning of December. Then it will pause the operation for two years for renovations and upgrades. In the spring of 2021, it will resume operations with greatly expanded capabilities. The accelerator and detectors are expected to continue to record data and record more than 30 times more data than previously recorded until the mid-2030s. With this increase in data and improved abilities, it is quite possible that the Higgs boson still has stories to tell.
Originally published on Live Science.
Don Lincoln shared this article with Live Science Expert Voices: Op-Ed & Insights .