Interesting Things Are Happening At CERN

CERN Yasgun
CERN Yasgun

In a paper recently published in Physical Review Letters, the ALICE collaboration used a method known as femtoscopy to study the residual interaction between two-quark and three-quark particles. Thanks to this measurement, an interaction between the ɸ (phi) meson (strange-antistrange quarks) and a proton (two up quarks and one down quark) was observed for the first time.

What is ALICE Mission (Collaboration)?

The ALICE (A Large Ion Collider Experiment) Collaboration has built a detector optimized to study nuclear collisions at ultra-relativistic energies provided by the LHC (Lage Heavy Collider).

The aim is to study the physics of strongly interacting matter at the highest energy densities ever achieved in the laboratory. In such cases, an extreme phase of matter – called the quark-gluon plasma – is formed.

Our universe is thought to have been in a primitive state for the first few millionths of a second after the Big Bang, before quarks and gluons bonded together to form protons and neutrons.

Recreating this primordial state of matter in the lab and understanding how it evolved will shed light on questions about how matter is organized and the mechanisms that constrain quarks and gluons.

To this end, we conduct a comprehensive study of hadrons, electrons, muons and photons produced in collisions of heavy nuclei (208Pb).

ALICE also studies proton-proton and proton-nucleus collisions, both in comparison to nucleus-nucleus collisions and on their own.

If we go back to our article again;

Since the ɸ meson is not electrically charged, an interaction between the proton and ɸ cannot be of electromagnetic origin. There is only strong interaction between the proton and ɸ.

The strong interaction is what holds the quarks together inside the hadrons (like the proton and the ɸ meson), while the strong interaction is now the force acting between the hadrons. This holds the protons and neutrons together in the atomic nucleus.


Proton Phi Interaction
An artistic representation of the interaction between a proton (consisting of two up quarks and a down quark) and a ɸ meson (consisting of a strange-anti-spaced quark pair) as they arise from a proton-proton collision at the LHC, the distance between them. them in the order of a femtometer. Permission: ALICE collaboration

In contrast to the now strong interaction between protons and neutrons, which can be studied in stable bound states such as nuclei, the interaction between unstable hadrons produced in particle collisions is very difficult to observe.

What is Strong Force (Interaction) Now?

The strong force between the quarks in one proton and the quarks in another proton is strong enough to overcome the repulsive electromagnetic force. This is now called strong interaction: it is what "glues" the nuclei together.

Let's Get to Know Hadrons

In particle physics, a composite subatomic particle made up of two or more quarks held together by strong interaction.


They are like molecules held together by electric force. Most of the mass of ordinary matter comes from two hadrons: protons and neutrons, while most of the mass of protons and neutrons is due to the binding energy of the quarks that compose them, due to the strong force.

If we go back to our article;

It was found to be possible at the LHC using an approach known as femtoscopy. Hadrons in LHC collisions are very close together, about 10-15 m is produced at distances (the unit is known as the femtometer, hence the name femtoscopy).

LHC (Large Hadron Collider): Large Hadron Collider. .

This scale now matches the range of the strong force, giving the hadrons a brief chance to interact before flying away. As a result, pairs of hadrons experiencing an attractive interaction move slightly closer together, while the opposite happens for a repulsive interaction.

Both effects can be clearly observed by detailed analysis of the measured relative velocities of the particles.

Knowledge of the p-ɸ (proton-ɸ meson) interaction is of twofold interest in nuclear physics.

First, this interaction is a port for searches for partial restoration of chiral symmetry. The left and right (chiral) symmetry that characterizes the strong interaction has been found to be disrupted in Nature.

This effect is responsible for the much larger masses of hadrons, such as protons and neutrons, relative to the masses of the quarks that make them up.

Therefore, chiral symmetry is linked to the origin of the mass itself!

One possible way to seek restoration of chiral symmetry and to shed light on the mass-forming mechanism is to examine modifications of the properties of ɸ mesons in dense nuclear matter formed in collisions at the LHC.

However, for this purpose it is important to first understand the simple two-body p-ɸ interaction in vacuum.

A second point of interest is that, due to its strange-anti-spaced quark content, the ɸ meson is considered a possible mediator of interaction between baryons (three-quark hadrons) containing one or more strange quarks, called hyperons (Y). ).

What Happens at the Core of Neutron Stars

Depending on the strength of this interaction, hyperons can form the core of neutron stars, which are among the densest and least understood astrophysical objects.

Direct measurement of the Y-ɸ interaction force, although feasible, has not yet been performed, but today this quantity can be estimated on the basis of p-ɸ findings via fundamental symmetries.

Therefore, measuring the p-ɸ interaction provides indirect access to the YY interaction in neutron stars.

The moderate interaction strength measured by ALICE provides a quantitative reference for further studies of ɸ properties in the nuclear medium and also translates into a negligible interaction between hyperons in neutron stars.

More accurate measurements will be made during the upcoming LHC Studies 3 and 4, making it possible to significantly improve the precision of the extracted parameters as well as directly detect the Y-ɸ interaction.

Source: ScienceDaily

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