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Fitting EMC structure functions with intrinsic charm

Luca Rottoli

TL;DR

The paper investigates whether EMC data constrain a charm parton distribution with charm treated as a fitted component, using the NNPDF3IC framework that includes an intrinsic charm possibility. It extends the FONLL heavy-quark scheme to accommodate massive charm-initiated contributions and parameterizes the charm PDF as a neural network at $Q_0$, with $c^-=0$. By analyzing EMC charm data (and additional EMC datasets) under different branching-ratio treatments, the authors find the charm PDF remains robust and largely unaffected, while inclusive EMC data show modest tension. The results support the existence of an intrinsic charm component, as large-$x$ charm structure persists beyond perturbative expectations and remains stable across data variations.

Abstract

A detailed study of the impact of the data collected by the European Muon Collaboration (EMC) on the parton distribution function (PDF) of the charm quark is presented. The analysis is performed in the NNPDF framework, and the charm PDF is freely parametrized on equal footing as light quark and gluon distributions. We find that variations in the treatment of EMC data do not modify the charm PDF and do not affect our previous conclusion on the presence of an intrinsic component in the charm PDF.

Fitting EMC structure functions with intrinsic charm

TL;DR

The paper investigates whether EMC data constrain a charm parton distribution with charm treated as a fitted component, using the NNPDF3IC framework that includes an intrinsic charm possibility. It extends the FONLL heavy-quark scheme to accommodate massive charm-initiated contributions and parameterizes the charm PDF as a neural network at , with . By analyzing EMC charm data (and additional EMC datasets) under different branching-ratio treatments, the authors find the charm PDF remains robust and largely unaffected, while inclusive EMC data show modest tension. The results support the existence of an intrinsic charm component, as large- charm structure persists beyond perturbative expectations and remains stable across data variations.

Abstract

A detailed study of the impact of the data collected by the European Muon Collaboration (EMC) on the parton distribution function (PDF) of the charm quark is presented. The analysis is performed in the NNPDF framework, and the charm PDF is freely parametrized on equal footing as light quark and gluon distributions. We find that variations in the treatment of EMC data do not modify the charm PDF and do not affect our previous conclusion on the presence of an intrinsic component in the charm PDF.

Paper Structure

This paper contains 6 sections, 3 figures.

Table of Contents

  1. Parton distributions with fitted charm
  2. Theory and fitting methodology
  3. The EMC data
  4. The impact of the EMC data
  5. Discussion and oulook
  6. Acknowledgements

Figures (3)

  • Figure 1: Comparison of the NNPDF3IC PDF set to the PDF set obtained with up-to-date branching ratio, for a charm pole mass of $m_c^{\rm{{pole}}} = 1.47$ GeV. Left panel: comparison of the charm PDF at $Q=1.65$ GeV. Right panel: comparison of the charm PDF at $Q=50$ GeV. The comparison at $Q=50$ GeV is shown as a ratio.
  • Figure 2: Same as Fig. \ref{['fig:1']}, now comparing the baseline fit with a fit including the 200 GeV EMC charm structure function data.
  • Figure 3: Same as Fig. \ref{['fig:1']}, now comparing the baseline fit with a fit including the 200 GeV EMC charm structure function data and the inclusive EMC data.