Nuclear parton distributions from lepton-nucleus scattering and the impact of an electron-ion collider

Abstract

We present a first determination of the nuclear parton distribution functions (nPDF) based on the NNPDF methodology: nNNPDF1.0. This analysis is based on neutral-current deepinelastic structure function data and is performed up to NNLO in QCD calculations with heavy quark mass effects. For the first time in the NNPDF fits, the χ 2 minimization is achieved using stochastic gradient descent with reverse-mode automatic differentiation (backpropagation). We validate the robustness of the fitting methodology through closure tests, assess the perturbative stability of the resulting nPDFs, and compare them with other recent analyses. The nNNPDF1.0 distributions satisfy the boundary condition whereby the NNPDF3.1 proton PDF central values and uncertainties are reproduced at A = 1, which introduces important constraints particularly for low-A nuclei. We also investigate the information that would be provided by an Electron-Ion Collider (EIC), finding that EIC measurements would significantly constrain the nPDFs down to x 5 × 10 −4 . Our results represent the first-ever nPDF determination obtained using a Monte Carlo methodology consistent with that of state-of-the-art proton PDF fits, and provide the foundation for a subsequent global nPDF analyses including also proton-nucleus data.

Open-source QCD analysis of nuclear parton distribution functions at NLO and NNLO

“…Indeed, as shown in Ref. [39], the uncertainty bands for a combination of singlet and octet contributions become comparable to those in Thes distributions in turn are in a reasonable agreement at higher scales, although at the initial scale the KA15 result is considerably above TUJU19. The total valence distributions from TUJU19 are found to be in very good agreement with those of the KA15 analysis.…”

“…The comparison of the TUJU19 NNLO nPDF fit to other NNLO nPDF analyses is shown in figure 20 for the nNNPDF1.0 [39] and in figure 21 for KA15 [38]. The comparison at NNLO is separated into two figures since different information is available for nNNPDF1.0 5 and KA15 6 analyses.…”

“…The comparison at NNLO is separated into two figures since different information is available for nNNPDF1.0 5 and KA15 6 analyses. In case of nNNPDF1.0 we consider lead nPDFs for gluon g and the quark singlet Σ = u +ū + d +d + s +s (as per [39]). The comparisons are shown at two scales, at Q 2 0 = 1.69 GeV 2 and at Q 2 = 100 GeV 2 for the distribution functions, and at the higher scale Q 2 = 100 GeV 2 for the ratios R p/Pb i of PDFs in a proton bound in lead compared to PDFs in a free proton.…”

“…Nuclear parton distribution functions TUJU19 in lead at NNLO compared to the LHAPDF set nNNPDF1.0[39], shown at our initial scale Q 2 0 = 1.69 GeV 2 and at a higher scale Q 2 = 100 GeV 2 for distribution functions xf i , and at higher scale Q 2 = 100 GeV 2 for the ratios R p/Pb i of PDFs in a proton bound in lead compared to PDFs in a free proton. The comparison is presented for the gluon g and for the quark singlet Σ = u +ū + d +d + s +s in a bound proton in lead.…”

Uncertainties due to Nuclear Data in Proton PDF Fits

“…We found no significant impact on associated phenomenology. We will extend this analysis to deuterium data, and in the future we will be able to use nuclear PDFs from NNPDF [19] to estimate uncertainties. These methods can be applied to other sources of theoretical uncertainties, such as higher twist effects, fragmentation functions, and missing higher order uncertainties [20].…”