Related Experiment Video
Updated: May 18, 2026
07:46
Setting Limits on Supersymmetry Using Simplified Models
Published on: November 15, 2013
Strangeness contribution to the proton spin from lattice QCD
Gunnar S Bali1, Sara Collins, Meinulf Göckeler
1Institut für Theoretische Physik, Universität Regensburg, 93040 Regensburg, Germany. gunnar.bali@ur.de
Physical Review Letters
|September 26, 2012
Summary
We calculated the strangeness contribution to the proton spin using lattice quantum chromodynamics (QCD). Our results show a small, negative value for this contribution, impacting our understanding of nucleon spin physics.
Area of Science:
- Quantum Chromodynamics (QCD)
- Hadron Physics
- Particle Physics
Background:
- The proton spin puzzle remains a significant challenge in particle physics.
- Understanding the contributions of light quarks (up, down) and strange quarks to nucleon spin is crucial.
- Lattice QCD provides a non-perturbative approach to studying these contributions.
Purpose of the Study:
- To compute the strangeness (Δs) and light-quark (Δu, Δd) contributions to the proton spin.
- To perform calculations within the framework of lattice QCD with specific parameters.
Main Methods:
- Utilized n(f)=2 lattice QCD with a pion mass of ~285 MeV and lattice spacing a≈0.073 fm.
- Employed the nonperturbatively improved Sheikholeslami-Wohlert Wilson action.
- Performed renormalization of matrix elements, accounting for quark flavor mixing.
Main Results:
- The strangeness contribution to the nucleon spin was found to be Δs(MS)(√(7.4) GeV) = -0.020(10)(4).
- A small negative value for Δs indicates a minor role of strange quarks in carrying proton spin.
- The second error term quantifies uncertainty from the lack of physical point extrapolation.
Conclusions:
- The strangeness contribution to the proton spin is small and negative.
- These findings contribute to resolving the proton spin puzzle.
- Further calculations extrapolating to the physical point are needed for a complete picture.
Related Concept Videos
01:08Atomic Nuclei: Nuclear Spin
All atomic particles possess an intrinsic angular momentum, or 'spin'. Electrons, protons, and neutrons each have a spin value of ½, although protons and neutrons in nuclei may have higher half-integer spins owing to energetic factors.
Atomic nuclei have a net nuclear spin, , which can have an integer or half-integer value. In atomic nuclei, the spins of protons are paired against each other but not with neutrons, and vice versa. Consequently, an even number of protons does not contribute to...
Atomic nuclei have a net nuclear spin, , which can have an integer or half-integer value. In atomic nuclei, the spins of protons are paired against each other but not with neutrons, and vice versa. Consequently, an even number of protons does not contribute to...
01:03Atomic Nuclei: Nuclear Spin State Overview
NMR-active nuclei have energy levels called 'spin states' that are associated with the orientations of their nuclear magnetic moments. In the absence of a magnetic field, the nuclear magnetic moments are randomly oriented, and the spin states are degenerate. When an external magnetic field is applied, the spin states have only 2 + 1 orientations available to them. A proton with = ½ has two available orientations. Similarly, for a quadrupolar nucleus with a nuclear spin value of one, the...
00:59Atomic Nuclei: Nuclear Magnetic Moment
All atomic nuclei are positively charged. When they have a nonzero spin, they behave like rotating charges. As a consequence of their charge and spin, these nuclei generate a magnetic field (B). This, in turn, gives rise to a magnetic moment (μ), which is randomly oriented in the absence of an external magnetic field. When an external magnetic field (B0) is applied, the magnetic moment vectors can align with the field or against it in 2 + 1 orientations. A hydrogen nucleus, which is just a...
01:23Atomic Nuclei: Nuclear Relaxation Processes
In the absence of an external magnetic field, nuclear spin states are degenerate and randomly oriented. When a magnetic field is applied, the spins begin to precess and orient themselves along (lower energy) or against (higher energy) the direction of the field. At equilibrium, a slight excess population of spins exists in the lower energy state. Because the direction of the magnetic field is fixed as the z-axis, the precessing magnetic moments are randomly oriented around the z-axis. This...
01:14Atomic Nuclei: Nuclear Spin State Population Distribution
Near absolute zero temperatures, in the presence of a magnetic field, the majority of nuclei prefer the lower energy spin-up state to the higher energy spin-down state. As temperatures increase, the energy from thermal collisions distributes the spins more equally between the two states. The Boltzmann distribution equation gives the ratio of the number of spins predicted in the spin −½ (N−) and spin +½ (N+) states.
01:08NMR Spectroscopy: Spin–Spin Coupling
The spin state of an NMR-active nucleus can have a slight effect on its immediate electronic environment. This effect propagates through the intervening bonds and affects the electronic environments of NMR-active nuclei up to three bonds away; occasionally, even farther. This phenomenon is called spin–spin coupling or J-coupling. Coupling interactions are mutual and result in small changes in the absorption frequencies of both nuclei involved. While nuclei of the same element are involved in...