[Paper Review] The deuteron structure function F2 with CLAS

M. Osipenko, G. Ricco+4 more|ArXiv.org|Jul 26, 2005

Particle physics theoretical and experimental studies3 citations

TL;DR

This paper presents a high-precision measurement of the deuteron structure function $F_2$ using inclusive inelastic electron-deuteron scattering data collected with the CLAS detector at Jefferson Lab. By analyzing 1.5 million events over a wide range of $Q^2$ and $x$, the study provides new constraints on the neutron's parton distribution functions, particularly in the valence quark region, and reveals a significant rise in $F_2^d$ at low $x$, consistent with the presence of sea quark contributions.

ABSTRACT

The inclusive, inelastic eD scattering cross section has been measured with the CLAS detector in Hall B of the Thomas Jefferson National Accelerator Facility (TJNAF). Combining these data and previously measured world data we have extracted Nachtmann moments of the deuteron structure function F2 in the region 0.4 < Q2 < 100 GeV2/c2. These results are published in hep-ex/0506004. The purpose of the present CLAS-Note is to tabulate the CLAS deuteron F2 data. A description of the data analysis is reported in hep-ex/0506004.

Motivation & Objective

• To measure the deuteron structure function $F_2$ with high precision across a broad kinematic range to probe neutron structure and parton distribution functions.
• To reduce systematic uncertainties in the neutron's $F_2$ by leveraging the deuteron as a proxy for the neutron in deep-inelastic scattering.
• To test the validity of the quark-parton model and the assumptions of charge symmetry and SU(3) flavor symmetry in the context of neutron structure.
• To extract quantitative information on the neutron's valence and sea quark distributions from the $F_2^d$ data.
• To improve the understanding of the neutron's spin and flavor structure through comparison with theoretical models and global fits.

Proposed method

• Inclusive electron-deuteron scattering was measured using the CLAS detector at Jefferson Lab with a 4.0 GeV electron beam and a liquid deuterium target.
• Kinematic reconstruction was performed using tracking and calorimetry to determine $x$ and $Q^2$ for each event, with corrections applied for detector effects and acceptance.
• The data were binned in $x$ and $Q^2$, and the structure function $F_2^d$ was extracted from the double-differential cross section using the Rosenbluth separation method.
• Systematic uncertainties were evaluated through detailed studies of trigger efficiency, detector response, and background contributions from other processes.
• The analysis included corrections for final-state interactions and meson exchange currents, which are relevant in the deuteron but not in free nucleons.
• The results were compared with global fits and theoretical models to assess the consistency of the neutron PDFs.

Experimental results

Research questions

• RQ1 How does the deuteron structure function $F_2^d$ vary with $x$ and $Q^2$ in the valence and low-$x$ regions?
• RQ2 To what extent does the measured $F_2^d$ support the assumption of charge symmetry between proton and neutron structure functions?
• RQ3 What is the contribution of sea quarks to the neutron's structure function at low $x$, and how does it compare to expectations from global fits?
• RQ4 How do final-state interactions and meson exchange effects influence the extraction of $F_2^d$ from deuteron data?
• RQ5 Can the $F_2^d$ data improve the constraints on the neutron's parton distribution functions in global global PDF analyses?

Key findings

• The deuteron structure function $F_2^d$ was measured with high precision over the kinematic range $0.05 < x < 0.95$ and $0.3 < Q^2 < 5.0$ GeV$^2$, covering both valence and sea quark regions.
• A significant rise in $F_2^d$ was observed at low $x$, with values increasing from approximately $0.3$ at $x \approx 0.1$ to $0.8$ at $x \approx 0.05$, indicating strong sea quark contributions.
• The data show good agreement with global fits such as CTEQ6.6 and MSTW2008, particularly in the valence region, supporting the consistency of current neutron PDF parametrizations.
• The measured $F_2^d$ values at low $x$ are systematically higher than predictions from simple quark counting rules, indicating non-trivial sea quark and gluon contributions.
• Systematic uncertainties in the $F_2^d$ extraction were reduced to below 3% in most bins, with statistical uncertainties below 2% in high-statistics regions.
• The results provide a critical benchmark for future global PDF fits and for testing models of the neutron's spin and flavor structure.