Measurement of charged-pion production in deep-inelastic scattering off nuclei with the CLAS detector

S. Morán et al. (CLAS Collaboration)

Phys. Rev. C 105, 015201 – Published 12 January 2022

Abstract

Background: Energetic quarks in nuclear deep-inelastic scattering propagate through the nuclear medium. Processes that are believed to occur inside nuclei include quark energy loss through medium-stimulated gluon bremsstrahlung and intranuclear interactions of forming hadrons. More data are required to gain a more complete understanding of these effects.

Purpose: To test the theoretical models of parton transport and hadron formation, we compared their predictions for the nuclear and kinematic dependence of pion production in nuclei.

Methods: We have measured charged-pion production in semi-inclusive deep-inelastic scattering off D, C, Fe, and Pb using the CLAS detector and the CEBAF 5.014-GeV electron beam. We report results on the nuclear-to-deuterium multiplicity ratio for $π^{+}$ and $π^{-}$ as a function of energy transfer, four-momentum transfer, and pion energy fraction or transverse momentum—the first three-dimensional study of its kind.

Results: The $π^{+}$ multiplicity ratio is found to depend strongly on the pion fractional energy $z$ and reaches minimum values of $0.67 \pm 0.03, 0.43 \pm 0.02$ , and $0.27 \pm 0.01$ for the C, Fe, and Pb targets, respectively. The $z$ dependencies of the multiplicity ratios for $π^{+}$ and $π^{-}$ are equal within uncertainties for C and Fe targets but show differences at the level of $10 %$ for the Pb-target data. The results are qualitatively described by the GiBUU transport model, as well as with a model based on hadron absorption, but are in tension with calculations based on nuclear fragmentation functions.

Conclusions: These precise results will strongly constrain the kinematic and flavor dependence of nuclear effects in hadron production, probing an unexplored kinematic region. They will help to reveal how the nucleus reacts to a fast quark, thereby shedding light on its color structure and transport properties and on the mechanisms of the hadronization process.

Received 25 September 2021
Accepted 23 December 2021

DOI:https://doi.org/10.1103/PhysRevC.105.015201

Physics Subject Headings (PhySH)

Color confinement Deep inelastic scattering Lepton induced nuclear reactions Particle interactions Particle production Quantum chromodynamics Strong interaction

Nuclear PhysicsParticles & Fields

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Vol. 105, Iss. 1 — January 2022

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Images

Figure 1
Multiplicity ratio of $π^{+}$ and $π^{-}$ as a function of $z$ ; the three different panels show results for C, Fe, and Pb targets, respectively. The error bars represent the quadrature sum of systematic and statistical uncertainties, which is dominated by the systematic uncertainties that are partially correlated point to point. The points have a small horizontal shift for better visualization. The lines correspond to model calculations from GiBUU, GK, and the LIKEn21 nFFs. The bands represent the uncertainty of the LIKEn21 nFF set. The numerical values of the data points and associated errors of this figure are shown in Table 2 in the Appendix section of the article.
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Figure 2
Multiplicity ratios of $π^{+}$ as a function of $z$ for various intervals of $ν$ (in different rows) and $Q^{2}$ (different marker colors). The left, middle, and right panels correspond to C, Fe, and Pb, respectively. The error bars represent the quadrature sum of systematic and statistical uncertainties. The numerical values of the data points and associated errors of this figure are shown in Tables 3, 4, 5 in the Appendix section of the article.
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Figure 3
Multiplicity ratios of $π^{-}$ as a function of $z$ for various intervals of $ν$ (in different rows) and $Q^{2}$ (different marker colors). The left, middle, and right panels correspond to C, Fe, and Pb, respectively. The error bars represent the quadrature sum of systematic and statistical uncertainties. The numerical values of the data points and associated errors of this figure are shown in Tables 3, 4, 5, 6, 7, 8 in the Appendix section of the article.
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Figure 4
Multiplicity ratio of $π^{+}$ as a function of $p_{T}^{2}$ for various $z$ intervals; the red, blue, and black markers show the measured results for C, Fe, and Pb targets. The error bars represent the quadrature sum of systematic and statistical uncertainties. Lines of the same colors represent the results from the GiBUU model. The numerical values of the data points and associated errors of this figure are shown in Tables 9 and 10 in the Appendix section of the article.
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Figure 5
Multiplicity ratio of $π^{-}$ as a function of the $p_{T}^{2}$ for various $z$ intervals; the red, blue, and black markers show the measured results for C, Fe, and Pb targets. The error bars represent the quadrature sum of systematic and statistical uncertainties. Lines of the same colors represent the results from the GiBUU model. The last panel is blank, as there is insufficient data for $π^{-}$ at $z > 0.8$ . The numerical values of the data points and associated errors of this figure are shown in Table 11 and 12 in the Appendix section of the article.
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