The electroweak and gravitational structure of the nucleon
Final Report Abstract
Almost all visible matter in the universe consists of protons and neutrons (nucleons). While it is well known that nucleons are composite particles made up of strongly interacting quarks and gluons (partons), the confining nature of the strong force means uncovering how these fundamental constituents account for the properties of the nucleon poses a significant challenge. Such information is, however, essential. Our current understanding of particle physics, encapsulated in the Standard Model (including QCD, the theory of the strong force), is known to be incomplete due to the failure to explain, for example, the abundance of matter over antimatter, the hierarchy of quark and lepton masses and, notably, to account for the existence of dark matter. Most experimental searches for new physics beyond the Standard Model involve nucleons as probes. This includes collider experiments such as at the Large Hadron Collider at CERN, long baseline neutrino oscillation experiments in the US and Japan and direct dark matter detectors. To uncover the interactions between the underlying elementary particles occurring in these experiments, precise knowledge of nucleon structure, i.e. the distribution of the partons within the nucleon and their response to electroweak (and non-Standard Model) probes is required. This project uses lattice QCD to determine the fraction of the nucleon’s longitudinal momentum carried by the quark and the quark spin contribution to the spin of the nucleon, among other observables. These quantities can be employed as input in phenomenological fits to experimental data, thereby more tightly constraining the parametrizations of the parton distributions. In addition, we calculate the matrix elements necessary for predicting the dark matter nucleon scattering cross-section from beyond the Standard Model theories. These theories can be tested through a comparison of the predictions with the lower bounds on the cross-section determined in the direct dark matter experiments.
Publications
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Octet baryon isovector charges from Nf=2+1 lattice QCD. Physical Review D, 108(3).
Bali, Gunnar S.; Collins, Sara; Heybrock, Simon; Löffler, Marius; Rödl, Rudolf; Söldner, Wolfgang & Weishäupl, Simon
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Scale setting and the light baryon spectrum in Nf = 2 + 1 QCD with Wilson fermions. Journal of High Energy Physics, 2023(5).
Bali, Gunnar S.; Collins, Sara; Georg, Peter; Jenkins, Daniel; Korcyl, Piotr; Schäfer, Andreas; Scholz, Enno E.; Simeth, Jakob; Söldner, Wolfgang & Weishäupl, Simon
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Sigma terms of the baryon octet in $N_\mathrm{f} = 2+1$ QCD with Wilson quarks. Proceedings of The 39th International Symposium on Lattice Field Theory — PoS(LATTICE2022), 112. Sissa Medialab.
Petrak, Pia Leonie Jones; Bali, Gunnar; Collins, Sara; Heitger, Jochen; Jenkins, Daniel & Weishäupl, Simon
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Octet baryon charges with Nf=2+1 non-perturbatively improved Wilson fermions. Proceedings of European network for Particle physics, Lattice field theory and Extreme computing — PoS(EuroPLEx2023), 040. Sissa Medialab.
Weishäupl, Simon; Bali, Gunnar; Collins, Sara & Söldner, Wolfgang
