Researchers from Tel Aviv University were able to describe for the first time a rare physical process that begins with the Higgs boson - the "divine particle" that was first observed about a decade ago - and eventually decays into a pair of rare elementary particles * New observations from the Sarn particle accelerator in Switzerland have helped researchers understand the process more clearly
For decades the Higgs boson has been driving the physics community around the world crazy. Since the discovery of the particle accelerator, there has been a fascinating journey to find "new physics" related to it and to its north.
One of the paths in this journey is led by a team of researchers from Tel Aviv University who are partners in a groundbreaking study aimed at studying a rare decay process that begins with the Higgs boson, and ends with a pair of elementary particles known as magic quarks. As part of the study, the researchers found that it is possible to characterize the rate of decay in a more accurate and complete way than was known until now.
The research was conducted under the leadership of Prof. Erez Etzion and doctoral students Guy Koren, Hadar Cohen and David Reicher - from the School of Physics and Astronomy in the Raymond and Berly Sackler Faculty of Exact Sciences at Tel Aviv University. The study was conducted in collaboration with researchers at the Weizmann Institute and other researchers at the LHC particle accelerator in Geneva.
Higgs - the particle responsible for mass
In the standard model of particle physics there are particles called bosons and their function is to serve as "carriers of force": the best known among them is the photon - a particle that carries the electromagnetic force. Additional bosons carry lesser known forces such as the strong force and the weak force. More than a jubilee years ago, the physicists Prof. Peter Higgs and Prof. Francois Engler (starting in 1984 a Sackler fellow in a special appointment at the School of Physics and Astronomy inTel Aviv University) that there may exist a new particle associated with giving mass to elementary particles in our world. Only in 2012 was it proven in an experiment that took place at the LHC particle accelerator (in which the researchers from Israel are senior partners) that the Higgs boson is a real and measurable particle, and it is quite heavy compared to other known particles. Higgs and Engler won the Nobel Prize the following year.
In the particle accelerator, pairs of protons are made to collide with each other at enormous speeds. In such energetic collisions, all kinds of interesting processes can occur, from which we can learn about the nature of our universe. The way these processes are studied is by placing a complex array of particle detectors around the point of collision, with their help it is possible to reproduce the types of particles formed in collisions as well as their properties.
Many processes may occur in these collisions, and each process has a characteristic "signature" in the detector. In order to extract from rare events and from them to derive new insights about the fundamental forces in nature, it is necessary to collect statistical data in large quantities (that is, to observe a very large number of collisions).
The Higgs is a heavy particle that immediately decays
As mentioned, the Higgs boson is a relatively heavy particle, but it can be created in collisions between protons if the accelerator energy is high enough. Immediately after it is formed it breaks down into lighter particles. "It is interesting to investigate what types of particles it breaks down into and how often the breakdown occurs for each and every particle," says Guy Koren. "To help answer this question, our group is trying to measure the rate at which the Higgs boson decays into particles called charm quarks."
"The thing is, this is not a simple task for two main reasons," Koren adds. "This is a very rare process - only one out of billions of collisions will a Higgs boson be created at all, and only about 3% of the Higgs bosons that are created will decay into magical quarks. In addition to this, there are five other types of quarks, and the problem is that they all leave a similar signature in our detectors. So even when this process is really happening, it is very difficult for us to recognize it."
Of the total number of collisions collected in the accelerator from 2012 until today, the group from Tel Aviv has not yet detected enough decays of the Higgs boson into magical quarks in order to measure the rate of the process with the necessary statistical precision.
However, enough information has been collected to say what the maximum rate of the process is in relation to what the theory predicts. A decay rate greater than the predicted rate will be the first important marker for "new" physics or an extension of the currently accepted model, which is the standard model of elementary particles. From the current measurement, the researchers conclude that there is no chance that the rate of decay of the Higgs into magic quarks is 8 times (or more) than the theory predicts, otherwise enough such decays would have been observed to measure it. "This may not sound like a very exciting statement," Koren quips, "but this is the first time that someone has ever been able to say something significant about the rate of this specific decay from its direct measurement, so in our field this is a very important and significant statement."
What are quarks anyway? These are particles of a certain type with similar properties. They make up, among other things, the protons and neutrons found in the nuclei of the atoms of the substance. There are six different types of quarks, which are usually associated with three different "generations", where each generation contains a pair of quarks of a different type. The first generation contains the pair of quarks with the smallest masses, called "up" and "down". The second generation includes the "strange" and "magical" type quarks, which have larger masses, and the third generation includes the heaviest quarks, of the "top" and "bottom" type.
It usually breaks down into heavy particles
"The theory predicts that the rate of decay of the Higgs boson into the various particles will be proportional to the mass (squared) of the particles into which it decays," adds Prof. Etzion. "Therefore, the expectation is that in most cases it will break down into the heavier particles, and only rarely will it break down into the light particles. In the meantime, the results from the accelerator confirm this explanation, i.e., enough decays to the third generation heavy quarks (and other heavy particles) have been observed in order to confirm the existence of these decays and to measure their rate, and the rate does match what the theory predicts, but that is not the end of the matter, because still Higgs decays to second (or first) generation quarks have not been observed, so we cannot yet be sure that the same 'laws' apply to these generation quarks."
Prof. Etzion intends to explain the possible effects of future discoveries in this context: "If we suddenly discover that the Higgs boson decays into them at a rate that is not proportional to the square of their mass, this could have far-reaching consequences regarding our understanding of the universe, and in particular the way in which elementary particles get their mass . This is also why we put so much effort into characterizing the decay of the Higgs into a magic quark, because it is the heaviest quark whose decay rate has not yet been measured."
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very interesting