The subatomic particles are composed of three lighter particles known as quarks: two up quarks and one down quark. However, scientists have believed for decades that protons may also include “intrinsic” charm quarks, which are more heavy quarks. Physicists announce that a new analysis supports this theory.

Up and down quarks are significantly lighter than charm quarks. Theoretical physicist Juan Rojo of Vrije Universiteit Amsterdam explains, “it is possible to have a component of the proton that is heavier than the proton itself.”

Rojo and coworkers integrated a range of experimental evidence and theoretical computations in an effort to reveal the proton’s fictitious allure. Rojo states that measuring this property is essential for comprehending one of the most significant particles in the universe.

Physicists are aware that the deeper one probes a proton, the more complex it becomes. Protons contain transitory quarks and their antimatter counterparts, antiquarks, when seen at extremely high energies, such as in collisions at particle accelerators like the Large Hadron Collider, or LHC, near Geneva (SN: 4/18/17). These “extrinsic” quarks are produced when gluons, which “glue” the quarks inside protons together, divide into quark-antiquark pairs.

Extrinsic quarks are not vital to the proton’s identity. They are just the outcome of the behavior of gluons at high energy. But charm quarks may exist within protons even at low energy, in a form that is more durable and deeply rooted.

Particles in quantum physics do not acquire a definitive state until they are measured; instead, they are characterized by probabilities. If protons possess inherent charm, there would be a minuscule chance of discovering, in addition to two up quarks and a down quark, a charm quark and antiquark within a proton. Due to the fact that protons are not well-defined collections of separate particles, the mass of a proton is not simply the sum of its constituents (SN: 11/26/18). Due to the modest likelihood, the charm quark and antiquark do not contribute their entire mass to the proton’s weight, which explains how the proton can contain particles heavier than itself.

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Using thousands of measurements from tests at the Large Hadron Collider (LHC) and other particle accelerators, along with theoretical calculations, the team discovered 3 sigma-level evidence for the proton’s intrinsic charm. The inherent charm quarks carry around 0.6% of the proton’s momentum, according to the research.

Typically, however, 5 sigma is necessary for a clear conclusion. “The data and analysis are not yet sufficient… to move from ‘evidence for’ to ‘finding of’ inherent charm,” says Ramona Vogt, a theoretical physicist at Lawrence Livermore National Laboratory in California who authored a commentary for Nature on the paper.

In addition, the definition of “intrinsic charm” is not easy, making it difficult to compare the new discovery with past results from other groups. Wally Melnitchouk, a theoretical physicist at Jefferson Lab in Newport News, Virginia, explains, “Previous investigations have shown varying limits on intrinsic allure due in part to the use of various definitions and schemes.”

Notably, the new analysis integrates observations from the LHCb team, which on February 25 published in Physical Review Letters measurements potentially consistent with intrinsic charm in the proton. C.-P. Yuan, a theoretical physicist at Michigan State University in East Lansing, describes the inclusion of these data in the analysis as “very novel.” However, Yuan has concerns over the type of calculation utilized to interpret the data. It is not completed at the current state-of-the-art analysis.

To better comprehend the results of the LHC and other facilities that smash protons and monitor the resulting particles, scientists must determine the proton’s intrinsic charm content. Researchers must be able to evaluate the interior and exterior of the objects with which they collide.

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Theoretical physicist Tim Hobbs of Fermilab in Batavia, Illinois, suggests that data from future accelerators, such as the proposed Electron-Ion Collider, could be useful. Currently, the proton remains a mystery. The problem persists; it stays extremely difficult.

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