Accurate Measurement of F2d/F2p and Rd-Rp
The New Muon Collaboration
TL;DR
This study delivers high-precision measurements of the deuteron-to-proton structure-function ratio $F_2^{\mathrm{d}}/F_2^{\mathrm{p}}$ and the difference $R^{\mathrm{d}}-R^{\mathrm{p}}$ from deep inelastic muon scattering using simultaneous $\mathrm{H}_2$ and $\mathrm{D}_2$ targets across four beam energies. The analysis employs a robust radiative-correction framework and a carefully controlled extraction of cross-section ratios, yielding a near-zero $\Delta R$ and a precise $F_2^{\mathrm{d}}/F_2^{\mathrm{p}}$ with minimal systematic uncertainty. The results imply small deuteron nuclear effects in the measured kinematic region, provide constraints on neutron structure via $F_2^{\mathrm{n}}/F_2^{\mathrm{p}}$, and are consistent with perturbative QCD predictions, including limited shadowing and modest $Q^2$-dependence at high $x$. Collectively, the findings refine our understanding of nucleon flavor structure and gluon distributions, and contribute to precise determinations like the Gottfried sum.
Abstract
Results are presented for F2d/F2p and Rd-Rp from simultaneous measurements of deep inelastic muon scattering on hydrogen and deuterium targets, at 90, 120, 200 and 280 GeV. The difference Rd-Rp, determined in the range 0.002<x<0.4 at an average Q^2 of 5 GeV^2, is compatible with zero. The x and Q^2 dependence of F2d/F2p was measured in the kinematic range 0.001<x<0.8 and 0.1<Q^2<145 GeV^2 with small statistical and systematic errors. For x>0.1 the ratio decreases with Q^2.