Related Experiment Video
Updated: May 22, 2026

07:11
ARL Spectral Fitting as an Application to Augment Spectral Data via Franck-Condon Lineshape Analysis and Color Analysis
Published on: August 19, 2021
Measurement of the neutron F2 structure function via spectator tagging with CLAS
N Baillie1, S Tkachenko, J Zhang
1College of William and Mary, Williamsburg, Virginia 23187, USA.
Physical Review Letters
|May 1, 2012
Summary
This study presents the first measurement of the neutron
Area of Science:
- Nuclear physics
- Particle physics
- Quantum chromodynamics
Background:
- Understanding the internal structure of nucleons (protons and neutrons) is fundamental in particle and nuclear physics.
- The neutron structure function, F(2)(n), is crucial for testing theoretical models of nucleon structure, but experimental data is scarce.
- Previous measurements of F(2)(n) have been limited by large nuclear uncertainties.
Purpose of the Study:
- To report the first measurement of the neutron's F(2) structure function using electron-deuterium scattering.
- To determine the ratio of neutron to proton structure functions, F(2)(n)/F(2)(p), with reduced nuclear uncertainties.
- To provide data across the nucleon-resonance and deep-inelastic scattering regions.
Main Methods:
- Semi-inclusive electron scattering off deuterium.
- Detection of low-momentum spectator protons in the backward hemisphere (momentum ≲100 MeV/c, angle ≳100°).
- Analysis of F(2)(n) in the Bjorken x range for 0.65 < Q(2) < 4.52 GeV(2).
Main Results:
- Successful measurement of the neutron F(2) structure function.
- Data covers both nucleon-resonance and deep-inelastic kinematic regions.
- Estimated nuclear corrections are less than a few percent.
Conclusions:
- This experiment provides the first direct measurement of F(2)(n).
- The study yields the first determination of the F(2)(n)/F(2)(p) ratio with minimal nuclear uncertainties in the range 0.2 ≲ x ≲ 0.8.
- The results offer crucial data for refining models of nucleon structure and the behavior of quarks and gluons within neutrons.
Related Concept Videos
Nuclear Binding Energy
The difference between the calculated and experimentally measured masses is known as the mass defect of the atom. In the case of helium-4, the mass defect indicates a “loss” in mass of 4.0331 amu – 4.0026 amu = 0.0305 amu. The loss in mass accompanying the formation of an atom from protons, neutrons, and electrons is due to the conversion of that mass into energy that is evolved as the atom forms. The nuclear binding energy is the energy produced when the atoms’ nucleons are bound together;...
Nuclear Stability
Protons and neutrons, collectively called nucleons, are packed together tightly in a nucleus. With a radius of about 10−15 meters, a nucleus is quite small compared to the radius of the entire atom, which is about 10−10 meters. Nuclei are extremely dense compared to bulk matter, averaging 1.8 × 1014 grams per cubic centimeter. If the earth’s density were equal to the average nuclear density, the earth’s radius would be only about 200 meters.
To hold positively charged protons together in the...
To hold positively charged protons together in the...
Nuclear Fission
Many heavier elements with smaller binding energies per nucleon can decompose into more stable elements that have intermediate mass numbers and larger binding energies per nucleon—that is, mass numbers and binding energies per nucleon that are closer to the “peak” of the binding energy graph near 56. Sometimes neutrons are also produced. This decomposition of a large nucleus into smaller pieces is called fission. The breaking is rather random with the formation of a large number of different...
Atomic Structure
The Greek philosopher Democritus proposed that everything on Earth is made up of tiny particles called atomos, Greek for "indivisible," from which the modern term "atom" is derived. In the 19th century, John Dalton proposed the atomic theory that is still largely correct today. He put forth five postulates to explain how atoms made up the world around us. (1) All matter is composed of infinitely small particles or atoms. (2) All atoms of a given element are identical to one another and (3) are...
Atomic Structure
Overview
Atomic Mass
Atoms — and the protons, neutrons, and electrons that compose them — are extremely small. For example, a carbon atom weighs less than 2 × 10−23 g. When describing the properties of tiny objects such as atoms, we use appropriately small units of measure, such as the atomic mass unit (amu). The amu was originally defined based on hydrogen, the lightest element, then later in terms of oxygen. Since 1961, it has been defined with regard to the most abundant isotope of carbon, atoms of which are...

