Nucleon Physics from Lattice QCD

Lead Research Organisation: University of Glasgow
Department Name: School of Physics and Astronomy

Abstract

The goal of this project is to improve our understanding of the structure of protons and neutrons by calculating, with the help of supercomputing clusters, their fundamental properties from Quantum Chromodynamics (QCD). Analytic calculations in low energy QCD are notoriously difficult and require uncontrolled approximations. High performance supercomputing allows us to perform the calculations without making uncontrolled approximations, through a program called Lattice QCD. This project uses Lattice QCD to calculate fundamental properties of the proton and neutron. Specifically, it improves upon how Lattice QCD calculations are done in a way that promises to reveal new information and generate results with greater precision than previously possible.

Planned Impact

We develop new, and improve upon existing, techniques for constructing and analyzing correlation functions in Lattice Quantum Chromodynamics. A technique utilizing spatial moments of correlation functions will reveal new information about the shape of hadronic form factors with respect to momentum transfer. In particular, we are developing a direct approach for calculating the charge radius of any hadron. A technique related to the Feynman-Hellmann Theorem simplifies correlation function analysis and markedly improves the precision of calculations. These developments will benefit the lattice QCD community directly.

The wider nuclear and particle physics communities will benefit from an improved understanding of the fundamental properties of nucleons. Our recent calculation of the nucleon axial charge gA, based on the Feynman-Hellmann-inspired approach, reduced the uncertainty by which gA is know by more than a factor of 3. We plan to combine this approach with spatial moments and calculate the proton charge radius with a precision that will allow ab initio QCD to weigh in on the current experimental discrepancy. We also plan to merge both methods to calculate nucleon form factors relevant to direct dark matter detection experiments and improve our understanding of neutrino interactions with nuclei.
 
Description We have obtained a detailed understanding of the excited state contributions to the axial form factor (Phys.Rev.C 105 (2022) 6, 065203), which allow us to reliably extract the ground state signal needed to determine the axial form factor needed in neutrino oscillation experiments. As a result of this, we have achieved preliminary, sub-percent precision on the nucleon axial form factor over a range of Q^2 from 0 to about 1.4 GeV^2 (arXiv: 2111.06333). This result means we will be able to calculate the axial form factor with sufficient precision to replace the use of experimentally determined form factor values in the Monte Carlo event generator Genie, which is being used by the neutrino experiments, e.g., DUNE.
Exploitation Route The final determination of the axial form factor over low values of Q^2 (0 to about 1 GeV^2) are planned to be incorporated in the event generator Genie being used by neutrino experiments like DUNE. These Standard Model QCD predicted form factors will be used in place of experimentally-determined, model-dependent form factors, meaning a priori, model-independent, and systematically-improvable form factor values are used instead.
Sectors Other
 
Description Improvements in our ability to calculate the nucleon axial form factor impact the ability of neutrino experiments (e.g., DUNE and Hyper-K) to relate measurements to the science questions they wish to answer (the structure of the nucleon, CP violation, and neutrino masses). Answers to these questions directly impact human understanding of the fundamental structure of matter and the observed and as-yet unexplained imbalance between matter and antimatter. Progress in human understanding and the potential for unforeseen technical innovation are of benefit to society at large.
First Year Of Impact 2022
Sector Other
Impact Types Societal
 
Title Modeling space-time dependence of correlation functions 
Description Lattice QCD-generated correlation functions are usually Fourier transformed (spatial components are summed over) to project on specific momenta. We have developed an extended database of correlation functions that includes the unsummed spatial dependence and a modelling approach for extracting information from the spatial dependence. This extracted information offers a novel way of determining the nucleon charge radii. 
Type Of Material Data analysis technique 
Year Produced 2020 
Provided To Others? No  
Impact None yet. We are using this new database/model approach on data currently being generated with plans to publish results and details of the approach in 2020 or 2021. 
 
Description California Lattice (CalLAT) Collaboration 
Organisation Lawrence Berkeley National Laboratory
Country United States 
Sector Public 
PI Contribution Expertise in analyzing lattice QCD data to extract phenomenologically useful quantities. Intellectual input regarding the plans of the collaboration related to our calculation of single nucleon form factors, axial and vector charges, and charge radii. Work on submission (subsequently approved) US DOE INCITE 2020 proposal for access to Summit supercomputer at ORNL. Help writing research papers. With the help of this award, I visiting Lawrence Berkeley Lab 27 July - 12 August, 2019 to facilitate collaboration.
Collaborator Contribution Expertise with running and job management on Summit, particularly related to exploited the hybrid CPU/GPU architecture. Expertise analyzing lattice QCD data. Intellectual input regarding the plans of the collaboration. Help writing research papers. Work on submission (subsequently approved) US DOE INCITE 2020 proposal for access to Summit supercomputer at ORNL.
Impact Several research papers: * https://arxiv.org/abs/1912.08321 * https://arxiv.org/abs/1812.11127 * https://doi.org/10.1038/s41586-018-0161-8 * https://www.epj-conferences.org/articles/epjconf/abs/2018/10/epjconf_lattice2018_01008/epjconf_lattice2018_01008.html * https://arxiv.org/abs/1704.01114 * https://journals.aps.org/prd/abstract/10.1103/PhysRevD.96.054513 * https://journals.aps.org/prd/abstract/10.1103/PhysRevD.96.014504
Start Year 2016
 
Description California Lattice QCD 
Organisation Lawrence Berkeley National Laboratory
Country United States 
Sector Public 
PI Contribution During 27 July - 12 August 2019, financed by this award, I visited Lawrence Berkeley National Laboratory in the US to collaborate with CalLAT. I helped write the conference report https://arxiv.org/abs/1912.08321. Provided intellectual input on the development of research analysis tools.
Collaborator Contribution Helped write the conference report https://arxiv.org/abs/1912.08321. Developed research analysis tools. Submitted jobs to generate data on Summit supercomputer at Oak Ridge National Laboratory.
Impact We anticipate the first publication (since my award) to be in 2020.
Start Year 2016
 
Description "New physics at the low-energy precision frontier" workshop at the Laboratoire de Physique Théorique d'Orsay in Orsay, France. 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact On behalf of the US-based collaboration CalLAT, I attended a workshop on "New physics at the low-energy precision frontier", which took place 16-20 September 2019 in Orsay, France. The workshop attendees were primarily phenomenologists, who are the end-users of the results of lattice QCD calculations like those produced by CalLAT. The workshop organisers requested CalLAT send a representative to review our recent results and discuss future expected improvements.
Year(s) Of Engagement Activity 2019
URL https://indico.cern.ch/event/815529/
 
Description Invited talk at UK Lattice Field Theory 2021 Kickoff Meeting 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact I have been asked to speak about my research on Nucleon Physics, the research covered by this grant, at the first meeting of the newly formed UK Lattice Field Theory consortium, to be held 23 March 2021 (NOTE THIS IS IN FUTURE). The intent is to advertise this activity, which is based in the US, within the UK with the goal of attracting students and/or postdocs and laying groundwork for possible future funding applications to UKRI/STFC.
Year(s) Of Engagement Activity 2021
URL http://generic.wordpress.soton.ac.uk/uklft/2021/01/28/uklft-kick-off-meeting-24-03-2021/