Investigating nuclear effects in lepton-ion DIS at the LHC

TL;DR

The paper addresses how nuclear effects modify parton distributions in nuclei for lepton–ion DIS at the LHC and whether universality of nPDFs holds across neutrino and charged-lepton probes. It employs a detailed framework combining $d^2\sigma/dx\,dQ^2$, lepton fluxes, and detector acceptance, using POWHEG-BOX-RES at NLO interfaced to PYTHIA8, across multiple nPDF parameterizations (EPPS21, nCTEQ15HQ, nNNPDF3.0(W)) and a proton baseline, for FASER$\nu$ and the proposed FASER$\nu$2 configurations. The results show sizable and $x$-dependent nuclear effects, with charm-tagged channels providing strong sensitivity to gluon and strange PDFs; the ratio of charm-tagged to inclusive events emerges as a robust observable to discriminate between models and test universality, especially at small $x$. The work demonstrates that future far-forward measurements at the LHC can substantially constrain nuclear PDFs, reduce current uncertainties, and improve modeling of nuclear cross sections relevant for beyond-standard-model searches and future collider programs.

Abstract

Recent studies have demonstrated that the far-forward physics program of the Large Hadron Collider (LHC) can be useful to probe the hadron structure with GeV-TeV neutrinos and muons. In particular, these studies indicate that the measurement of the muon-ion and neutrino-ion cross-sections by the same experiment is feasible. In this paper, we investigate the impact of nuclear effects on the muon-tungsten ($μW$) and neutrino-tungsten ($νW$) deep inelastic scattering (DIS) events at FASER$ν$ and its proposed upgrade FASER$ν2$. We estimate the rates associated with the inclusive cross-sections and for events with a charm tagged in the final state considering different parameterizations for the nuclear parton distribution functions. These results point out that muon and neutrino-induced interactions probe complementary kinematical ranges and that a simultaneous analysis of associated events will allow to test the universality (or not) of the nuclear effects. Moreover, we propose the study of the ratio between the charm tagged and inclusive events in order to discriminate between the distinct modeling of the nuclear effects at small-$x$. Our results indicate that a future experimental reconstruction of $μW$ and $νW$ DIS events at the LHC is a promising way to improve our understanding of nuclear effects and decrease the current uncertainties in parton distribution functions.

Figures (8)

• Figure 1: Comparison between the predictions for the up (left), strange (center) and gluon (right) PDFs of tungsten, derived considering the EPPS21 Eskola:2021nhw, nNNPDF 3.0(W) AbdulKhalek:2022fyi and nCTEQ15HQ Duwentaster:2022kpv parameterizations. Results for two values of the boson virtuality: $Q=2$ GeV (upper panels) and $Q=80$ GeV (lower panels). Uncertainty bands correspond to 68% confidence levels.
• Figure 2: Ratio between the predictions with and without nuclear effects for the up (left), strange (center) and gluon (right) PDFs of tungsten, derived considering the EPPS21 Eskola:2021nhw, nNNPDF 3.0(W) AbdulKhalek:2022fyi and nCTEQ15HQ Duwentaster:2022kpv parameterizations. Results for two values of the boson virtuality: $Q=2$ GeV (upper panels) and $Q=80$ GeV (lower panels). Uncertainty bands correspond to 68% confidence levels.
• Figure 3: Predictions for the number of events for muon DIS at FASER$\nu$ binned in $x$ in the inclusive case (upper panels) and with a tagged charm (lower panels) in the final state. Results derived assuming different parameterizations for the nPDFs. The predictions for the ratio between the nuclear and nucleon results are presented in the bottom panels of the plots.
• Figure 4: Predictions for the number of events for neutrino DIS at FASER$\nu$ binned in $x$ in the inclusive case (upper panels) and with a tagged charm (lower panels) in the final state. Results derived assuming different parameterizations for the nPDFs. The predictions for the ratio between the nuclear and nucleon results are presented in the bottom panels of the plots.
• Figure 5: Ratio between events with tagged charm hadron and inclusive for muon (left) and neutrino (right) DIS at FASER$\nu$. Results derived assuming different parameterizations for the nPDFs.