Important discovery: The first decay observation of the Higgs particle

On August 28, 2018, scientists worked at the world's largest particle accelerator project LHC, at the European Nuclear Research Center (CERN - Geneva, Switzerland), announced about the first observation of the decay of the Higgs into a pair of particles and anti-bottom quarks. Surprisingly, the Higgs particle essentially decays in this way.

(Artwork: Shutterstock)

This information shows a high consistency between theoretical predictions and empirical data, which solidifies the theoretical basis for the existence of the Higgs particle.

Higgs - the "seed of God"

In the 1960s, researchers investigated the relationship between weak electromagnetic forces and weak nuclear forces, which are responsible for some types of radioactive decay. Although these two forces seem to be separate, it is finally discovered that both of these forces come from a more general and fundamental force, which we now call the electroweak force.

The most obvious problem of this theory is that it predicts all particles with zero mass. Even in the 1960s, physicists knew that subatomic particles had masses, so this was a serious loophole of this theory.

Some groups of scientists have proposed a solution to this problem: a scalar field permeating the universe from the 'wild pink' is called the Higgs field. Basic subatomic particles (subatomic particles) interact with this field, and this interaction gave them mass. The existence of the Higgs field also implies the existence of a subatomic particle called the Higgs particle or the Higgs boson. The model of elementary particles according to this theory is called the Standard Model.

In the drawing below, the Higgs (H) is shaded in gray, while the other nuts are pink, purple, and blue.

The upper left corner is 6 types of quarks, including: u (initials up - ie up quark), c (charm - charm quark), t (top - top quark), d (down - down quark), s (strange - strange quark) and b (bottom - bottom quark). It is these quarks in this small, pink rectangle that form into protons and neutrons.

A small, blue rectangle in the lower left corner shows only 6 light particles called lepton (spin particles with 1/2): electron - e, muon - µ, tauon - τ, neutrino electron - ϖe, muon neutrino - ϖµ and tauon neutrino - ϖτ.

Quarks and leptons are considered to be physical particles. The small rectangle, purple on the right is only 4 types of force particles, also known as field particles (interactive transmission particles): Z, γ: (photon), W and g (gluon).

These are 16 types of seeds that by early 2012, physicists have discovered and described very carefully and accurately. There is only one seventh elementary particle, ie the Higgs - according to the theory required for the Standard Model to not collapse - until early 2012 no one had "seen" the Higgs particle figure!

Because no one has been able to find it for decades, it is sometimes called the "particle of God" by the Higgs which implies that it is full of mysteries. Many scientists argue that this is just a metaphor for the press, literature, but attractive but not helpful for readers to understand the physical nature of this kind of particles.

Because of nearly half a century of hunting and finding nothing on July 4, 2012, when two large CERN laboratories simultaneously published the results of discovering a new elementary particle, there are properties similar to Higgs, The public opinion of the global scientific community is strong. So that someone likened CERN to detonating a blockbuster in a daylight.

A year later, British physicist Peter Higgs and Belgian physicist François Englert - two people predicted the existence of the Higgs - shared the 2013 Nobel Prize in physics.

The search for the bottom quarks

Large particle accelerator (LHC).(Photo: Flickr).

Higgs particles generated in high-energy collisions between pairs of accelerated particles are close to the speed of light. These particles do not last long, they only exist at 10-22 seconds. A particle with such a lifespan, moving at the speed of light, will decay before it moves enough a distance of one atomic size. Therefore, it is not possible to directly observe the Higgs particle. Only their decay products can be observed and used to deduce the properties of the parent particles.

Higgs particles have a mass of 12 giga electrons vol (GeV) or weigh about 133 times a proton. Calculations from previous theories predict that the Higgs particle decays into pairs of particles as follows: bottom quark (58%), W particle (21%), Z particle (6%) , lepton particles (2.6%) and photons (0.2%). Remaining some other foreign configurations create the rest.

'' ONE OF THE IMPORTANT RESULTS OF THIS TIME DETERMINATION IS CONFIRMATION OF THE ESTIMATES IS ACCURATE FOR QUARK BEADS 'BOTTOM.' '

When physicists announced the discovery of the Higgs in 2012, they were based on the decay of the Higgs particle into Z, W and photon, not the bottom quark. The reason is very simple: these special decays are much easier to identify.

With the colliding energies available at the LHC accelerator, the probability to produce a Higgs is 1 billionth of a billion (1 billion collisions has a collision producing Higgs particles). The large number of collisions at the LHC accelerator occurs through the interaction of the strong nuclear force, which is the strongest force of subatomic forces and plays the role of atomic nuclei together.

The problem is that in strong force-related interactions, creating a particle-antiparticle pair of bottom quarks is actually quite common. Therefore, the creation of bottom quarks by the decay of Higgs particles is completely overwhelmed by pairs of quarks created by other ordinary processes. Accordingly, it is basically impossible to determine the events in which the decay of the Higgs particles produces the bottom quark. It's like trying to find a natural diamond in a large container full of artificial diamonds.

Because it is difficult or even impossible to isolate collisions in which Higgs particles decay into bottom quarks, scientists need a different approach. The researchers looked for another type of event - collisions where Higgs particles were created simultaneously with W and Z particles. The researchers called this type of collision 'combined production' ( liên kết Production).

W and Z particles play a role in creating weak nuclear forces and they can decay in different and recognizable ways. The 'combined production' process appears less frequently than the events that do not involve the Higgs, but the presence of W and Z particles greatly enhances the ability to detect events that contain Higgs particles. .

The combined production technique of the Higgs is first applied in the Fermi National Accelerator Laboratory, located on the outskirts of Chicago. Because the laboratory used a low-energy accelerator, they were unable to claim to have found the Higgs, but the laboratory's knowledge played an important role in this success.

Simulation of proton-proton collision event in CMS's LHC is characterized by a Higgs particle decaying into 2 bottom quarks.While this is a common decay of the Higgs, its sign is difficult to separate from similar events.(Photo: CMS).

The LHC accelerator has two large physical detectors capable of observing the Higgs particles - namely Compact Muon Solenoid (CMS) and A Toroidal LHC Apparatus (ATLAS). Both laboratories collaborated simultaneously on the combined production of Higgs particles, with the specific decay of the Higgs into a pair of particle-bottom and antiparticle quarks.

An important theory

The process of discovering the Higgs in a way that is quite simple is significant progress in science, but it also has a more important result.

It indicates that the Higgs field, referred to in 1964, is not only motivated by a fundamental theory. It has been included in the Standard Model, which describes the behavior of subatomic particles. (Before the Higgs field was proposed, the Standard Model predicted that particles had no mass. After the Higgs field was introduced as a special addition to the Standard Model, the particles now have mass. ). Therefore, it is very important to discover predictions about the probability of decay to find suggestions that link to basic theory. And more recently, more comprehensive theories have been developed since the 1960s, predicting that more than one type of Higgs may exist.

Therefore, it is important to understand the speed at which the Higgs divides into other particles and compare it with the predicted decay rate. The easiest way to illustrate consistency is to report the observed decay rate, divided by the predicted speed. The best consistency between the two speeds will give the value close to 1.

CMS's experiment found great consistency in the recent report, with the ratio between the actual prediction and observation being 1.04 ± 0.2 and the ATLAS measurement results are very similar (1, 01 ± 0.2). This impressive unity is a triumph of the current theory, although it does not indicate a direction for a more fundamental source of phenomena for the Higgs particles.