New support for “intrinsic” charm quarks

Q = m vs = 1.51 GeV (orange). The purely intrinsic result (3FNS) obtained using the correspondence N3LO is also displayed (green). On the right, the purely intrinsic end result (3FNS) with full uncertainty (PDFU + MHOU), with the PDFU indicated by a dark band; the predictions of the original BHPS model and the more recent meson/baryon cloud model are also shown for comparison (dashed and dashed curves, respectively). Credit : Nature (2022). DOI: 10.1038/s41586-022-04998-2″ width=”800″ height=”436″/>

The intrinsic charm PDF and comparison with models. On the left, the purely intrinsic (3FNS) result (blue) with PDFU alone, compared to PDF 4FNS, which includes both an intrinsic component and a radiative component, at Q = mvs= 1.51 GeV (orange). The purely intrinsic result (3FNS) obtained using N3The LO match is also displayed (green). On the right, the purely intrinsic end result (3FNS) with full uncertainty (PDFU + MHOU), with the PDFU indicated by a dark band; the predictions of the original BHPS model and the more recent meson/baryon cloud model are also shown for comparison (dashed and dashed curves, respectively). Credit: Nature(2022). DOI: 10.1038/s41586-022-04998-2

A team of researchers from the NNPDF collaboration have found new evidence supporting the “intrinsic” charm quark theory. In their article published in the journal Nature , the group describes how they used a machine learning model to develop a structure of protons, then used it to compare the results of real collisions in particle accelerators and what they learned while doing so. Ramona Vogt, with Lawrence Livermore National Laboratory, published a News & Views article in the same journal issue describing the team’s work on this new effort. Nature also released a podcast where Nick Petrić Howe and Benjamin Thompson discuss the work done by the team.

Previous research involving the use of particle accelerators has suggested that protons contain quarks which are held together by gluons. A reasonable amount of evidence has also shown that there are at least two up quarks and one down quark. There have also been theories suggesting that there is another, the so-called charm quark, but there is little real evidence of their existence. That could change, however, as researchers in this new effort have used a new approach to “prove” they exist.

They found evidence that a small part (0.5%) of a proton’s momentum comes from a charmed quark. The researchers found this new evidence by using a machine learning model to build a hypothetical structure of protons, including different flavors of quarks, and of course the elusive charm quark. They then ran their model and compared the model’s characteristics with real-world data that has been observed from more than 500,000 accelerator collisions over the past decade.

The researchers also found that if a proton does not have a charm-anticharm quark pair, there is only a 0.3% chance that they will see the results found in their comparisons. And that calculation led them to assign their results a confidence level of 3 sigma, a level usually reserved for confidence levels indicating that something interesting was found. A 5-sigma level is necessary for the physics community to recognize that a discovery has been made.


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More information:
The NNPDF collaboration, Proof of quarks with intrinsic charm in the proton, Nature (2022). DOI: 10.1038/s41586-022-04998-2
Ramona Vogt, The proof at last that the proton has an intrinsic charm, Nature (2022). DOI: 10.1038/d41586-022-02186-w

Benjamin Thompson et al, Do Protons Have Intrinsic Charm? New evidence suggests yes,Nature(2022). DOI: 10.1038/d41586-022-02237-2

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Quote: New support for “intrinsic” charm quarks (August 18, 2022) retrieved August 20, 2022 from https://phys.org/news/2022-08-intrinsic-charm-quarks.html

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