HomeNewsPhysicsGEM simplifies the interior construction of protons and their collisions

GEM simplifies the interior construction of protons and their collisions


by The Henryk Niewodniczanski Institute of Nuclear Physics Polish Academy of Sciences

When a proton collides with a proton, the gluon emitted by one of many valence quarks can work together with a digital quark from the the quark-antiquark pair inside the opposite proton. According to the GEM mannequin, the results of such an interplay can be a quick proton with an intact construction of valence quarks, and different particles created in processes going down within the interplay area (outlined in white). Credit: IFJ PAN / Dual Color

Inside every proton or neutron there are three quarks sure by gluons. Until now, it has usually been assumed that two of them kind a “stable” pair often known as a diquark. It appears, nonetheless, that it is the finish of the street for the diquarks in physics. This is among the conclusions of the brand new mannequin of proton-proton or proton-nucleus collisions, which takes into consideration the interactions of gluons with the ocean of digital quarks and antiquarks.


In physics, the emergence of a brand new theoretical mannequin usually augurs badly for previous ideas. This can be the case with the outline of collisions of protons with protons or , proposed by scientists from the Institute of Nuclear Physics of the Polish Academy of Sciences (IFJ PAN) in Cracow. In the most recent mannequin, a big function is performed by interactions of gluons emitted by one proton with the ocean of digital quarks and antiquarks, showing and disappearing inside one other proton or neutron.

Gluons are carriers of the sturdy power, one of many 4 elementary forces of nature. This binds quarks into composite constructions, akin to protons or neutrons. In many respects, the sturdy power differs from the others. For instance, it doesn’t weaken, however grows with the gap between the particles. Moreover, in contrast to photons, gluons carry a particular sort of cost (picturesquely often known as colour) and may work together with one another.

The majority of nuclear reactions—together with the majority of collisions of protons with protons or atomic nuclei—are processes by which particles solely “brush against” one another by exchanging gluons. Collisions of this sort are known as “soft” by physicists and trigger them hassle, because the idea describing them is incalculable from first rules. Thus, by necessity, all at the moment’s fashions of sentimental processes are roughly phenomenological.

“In the beginning, we only wanted to see how the existing tool, known as the dual parton model, handles more precise experimental data on proton-proton and proton-carbon nucleus collisions,” recollects Prof. Marek Jezabek (IFJ PAN). “It rapidly turned out that it was not coping well. So we decided, on the basis of the old model which has been under development for over four decades, to try to create something which was on the one hand more precise, and on the other—closer to the nature of the described phenomena.”

GEM simplifies the internal structure of protons and their collisions
One of the attainable collisions of a proton and two protons/neutrons in a carbon nucleus, in line with the GEM mannequin. Two valence quarks of 1 proton change gluons with valence quarks in two protons/neutrons of the carbon nucleus. The three quarks of the incoming proton are not colour impartial. These quarks, proven in purple on the proper, should then catch different particles from the interplay area (proven in white), ensuing within the manufacturing of secondary particles. Credit: IFJ PAN / Dual Color

The gluon change mannequin (GEM) constructed at IFJ PAN can be phenomenological. However, it’s not primarily based on analogies to different , however straight on the existence of quarks and gluons and their elementary properties. Moreover, GEM takes into consideration the existence in protons and neutrons of not solely triplets of the primary (valence) quarks, but additionally the ocean of regularly arising and annihilating pairs of digital quarks and antiquarks. In addition, it takes into consideration the constraints ensuing from the precept of baryon quantity conservation. In simplified phrases, it says that the variety of baryons (i.e., protons and neutrons) current earlier than and after the interplay should stay unchanged. As every carries its personal baryon quantity (equal to 1/3), this precept supplies extra dependable conclusions on what is occurring with the quarks and the gluons exchanged between them.

“GEM has allowed us to explore new scenarios of the course of events involving protons and neutrons,” says Dr. Andrzej Rybicki (IFJ PAN). “Let’s imagine, for example, that in the course of a soft proton-proton collision, one of protons emits a gluon, which hits the other proton—not its valence quark, but a quark from the virtual sea that exists for a fraction of a moment. When such a gluon is absorbed, the sea quark and antiquark forming a pair cease to be virtual and materialize into other particles in specific final states. Note that in this scenario, new particles are formed despite the fact that the valence quarks of one of the protons have remained untouched.”

The Cracow gluon mannequin results in attention-grabbing insights, two of that are notably noteworthy. The first issues the origin of diffractive protons, noticed in proton-proton collisions. These are quick protons that come out of the web site at small angles. Until now, it was believed that they might not be produced by colour change processes and that another bodily mechanism was chargeable for their manufacturing. Now, it seems that the presence of diffractive protons could be defined by the interplay of the gluon emitted by one proton with the ocean quarks of one other proton.

Another commentary can be attention-grabbing. The earlier description of sentimental collisions assumed that two of the three valence quarks of a proton or a neutron are sure collectively in order that they kind a “molecule” known as a diquark. The existence of the diquark was a speculation that not all physicists would vouch for indiscriminately, however the idea was broadly used—one thing that’s now prone to change. The GEM mannequin was confronted with experimental information describing a state of affairs by which a proton collides with a carbon nucleus and interacts with two or extra protons/neutrons alongside the way in which. It turned out that as a way to be according to the measurements, beneath the brand new mannequin, the disintegration of the diquark have to be assumed in no less than half the circumstances.

“Thus, there are many indications that the diquark in a proton or neutron is not a strongly bound object. It may be that the diquark exists only effectively as a random configuration of two quarks forming a so-called color antitriplet—and whenever it can, it immediately disintegrates,” says Dr. Rybicki.

The Cracow of change explains a wider class of phenomena in an easier and extra coherent method than the present instruments for description of sentimental collisions. The present outcomes, introduced in an article revealed in Physics Letters B, have attention-grabbing implications for matter-antimatter annihilation phenomena, by which an antiproton might annihilate on a couple of / within the atomic nucleus. Therefore, the authors have already formulated first, preliminary proposals to carry out new measurements at CERN with an antiproton beam.


Nuclear physicists on the hunt for squeezed protons


More info:
Marek Jeżabek et al, The Gluon Exchange Model for diffractive and inelastic collisions, Physics Letters B (2021). DOI: 10.1016/j.physletb.2021.136200

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The Henryk Niewodniczanski Institute of Nuclear Physics Polish Academy of Sciences

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GEM simplifies the interior construction of protons and their collisions (2021, June 10)
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