nNNPDF2.0: quark flavor separation in nuclei from LHC data

Abstract

We present a model-independent determination of the nuclear parton distribution functions (nPDFs) using machine learning methods and Monte Carlo techniques based on the NNPDF framework. The neutral-current deep-inelastic nuclear structure functions used in our previous analysis, nNNPDF1.0, are complemented by inclusive and charm-tagged cross-sections from charged-current scattering. Furthermore, we include all available measurements of W and Z leptonic rapidity distributions in proton-lead collisions from ATLAS and CMS at $$ \sqrt{s} $$ s = 5.02 TeV and 8.16 TeV. The resulting nPDF determination, nNNPDF2.0, achieves a good description of all datasets. In addition to quantifying the nuclear modifications affecting individual quarks and antiquarks, we examine the implications for strangeness, assess the role that the momentum and valence sum rules play in nPDF extractions, and present predictions for representative phenomenological applications. Our results, made available via the LHAPDF library, highlight the potential of high-energy collider measurements to probe nuclear dynamics in a robust manner.

Deuteron uncertainties in the determination of proton PDFs

“…Again we see that the PDFs hardly change from one iteration to the next, so the procedure has converged. In addition in this plot we compare our NNLO deuteron PDFs with a recent NLO determination of nuclear PDFs based on the NNPDF methodology, nNNPDF2.0 [37]. These were obtained by fitting a range of nuclear and proton data, and assuming a smooth dependence on the mass and atomic numbers A and Z .…”

“…However the uncertainty in our determination is as large as the correction. For comparison, we also show the same quantity computed using the nNNPDF2.0 deuteron PDFs [37]: these are NLO, but have a smaller uncertainty since, as explained above, in these fits continuity in A/Z is implicitly assumed, which adds a significant constraint. However the reduction in uncertainty due to this constraint is considerably less in the structure function ratio than it was in the PDFs.…”

Nuclear uncertainties in the determination of proton PDFs

“…Specifically we show the average of up and down quark, the average of up and down antiquark, the strange quark, and the gluon distributions: because the deuteron is Figure 6. Comparison between the deuteron-ite1, deuteron-ite2 and nNNPDF2.0 [34] deuteron PDFs. The average of up and down, the average of antiup and antidown, strange and gluon PDFs are shown at Q = 10 GeV.…”

“…Again we see that the PDFs hardly change from one iteration to the next, so the procedure has converged. In addition in this plot we compare our NNLO deuteron PDFs with a recent NLO determination of nuclear PDFs based on the NNPDF methodology, nNNPDF2.0 [34]. These were obtained by fitting a range of nuclear and proton data, and assuming a smooth dependence on the mass and atomic numbers A and Z.…”

“…However the uncertainty in our determination is as large as the correction. For comparison, we also show the same quantity computed using the nNNPDF2.0 deuteron PDFs [34]: these are NLO, but have a smaller uncertainty since, as explained above, in these fits continuity in A/Z is implicitly assumed, which adds a significant constraint. However the reduction in uncertainty due to this constraint is considerably less in the structure function ratio than it was in the PDFs.…”