Particles Change Identities In The First Potentially Observed Triangle Singularity – Forbes

Scientists discovered a strange interaction of particles during the Compass experiment at CERN.

New research led by scientists at the University of Bonn, published recently in Physical Review Letters, may detail the first time a so-called triangle singularity has been observed, a strange dance in which sub-atomic particles change their identities. Observing this triangle singularity may give insights to the strong force, and why particles such as protons and neutrons are heavier than expected.

Quarks are never seen alone in nature. Instead, they are seen in groupings of twos and threes. These form the building blocks of nature. In addition, each quark has a color charge, which we refer to as red, blue, or green.

A pair of two quarks is called a meson and always consists of a quark and antiquark. These two quarks will have opposite color. For example, a meson could consist of a red and an antired quark. Three quarks are called a baryon, and consist of a red, blue, and green quark, or an antired, antigreen, and antiblue quark.

Protons and neutrons within atomic nuclei are baryons- made of three quarks.

In both of these cases, the color charges cancel out, leaving a particle of zero color charge.

What is not seen is groups of four quarks. This was until 2015, when scientists at CERN in Geneva seemed to see the presence of a tetraquark popping into existence in their data.

Seeing a tetraquark was surprising. But now, scientists think there may be another explanation to the data - and the finding might be even more bizarre than the discovery of a tetraquark.

In the Compass experiment at CERN, high-velocity pions collide with hydrogen nuclei.

In the Compass Experiment at CERN, pions were accelerated to extraordinarily high velocities and smashed into hydrogen nuclei. Pions are mesons, consisting of a quark-antiquark pair. These quarks are held together by the strong force, one of the four fundamental forces of nature. The strong force becomes stronger with distance, sort of like the force of a stretched rubber band - the farther apart the two quarks are, the more that they are drawn to one another. This force holds quarks together, whether they be in pions or hydrogen nuclei.

When a very fast pion crashes into a hydrogen atom, the energy held within this force is released all at once, similar to a snapping rubber band. This energy then goes into creating new particles.

In Einstein's famous formula, energy can be converted into mass, which is what researchers saw in ... [+] the Compass experiment.

Its here that it looked like a four-quark particle - the tetraquark - was created. But another interpretation is that instead, we might be seeing the fabled triangle singularity.

The triangle singularity was postulated in 1950 by Russian physicist Lev Davidovich Landau, but never seen before.

Physicist Lev Landau, who first proposed the existence of triangle singularities. (Photo ITAR-TASS/ ... [+] Valery Gende-Rote)

When the pions collide with the hydrogen nuclei, a flood of particles results. Some of these are another type of meson, kaons. Two kaons can then go on to exchanging quarks between themselves, transforming identities in the process. This is the triangle singularity - triangle from the form this interaction takes on a Feynman diagram, and singularity because during this interaction, the math describing the interaction temporarily breaks down.

Its still unclear as to whether this is an actual triangle singularity, but if it is, it can help address some of the mystery behind the strong force. For example, one unanswered question that physicists have is why particles like protons or neutrons are so much more massive than what they are predicted to be from the Higgs mechanism. Understanding triangle singularities may offer important clues to that puzzle.

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Particles Change Identities In The First Potentially Observed Triangle Singularity - Forbes