Far-forward neutrinos at the Large Hadron Collider

Abstract

We present a new calculation of the energy distribution of high-energy neutrinos from the decay of charm and bottom hadrons produced at the Large Hadron Collider (LHC). In the kinematical region of very forward rapidities, heavy-flavor production and decay is a source of tau neutrinos that leads to thousands of charged-current tau neutrino events in a 1 m long, 1 m radius lead neutrino detector at a distance of 480 m from the interaction region. In our computation, next-to-leading order QCD radiative corrections are accounted for in the production cross-sections. Non-perturbative intrinsic-k T effects are approximated by a simple phenomenological model introducing a Gaussian k T-smearing of the parton distribution functions, which might also mimic perturbative effects due to multiple initial-state soft-gluon emissions. The transition from partonic to hadronic states is described by phenomenological fragmentation functions. To study the effect of various input parameters, theoretical predictions for D ± s production are compared with LHCb data on double-differential cross-sections in transverse momentum and rapidity. The uncertainties related to the choice of the input parameter values, ultimately affecting the predictions of the tau neutrino event distributions, are discussed. We consider a 3+1 neutrino mixing scenario to illustrate the potential for a neutrino experiment to constrain the 3+1 parameter space using tau neutrinos and antineutrinos. We find large theoretical uncertainties in the predictions of the neutrino fluxes in the far-forward region. Untangling the effects of tau neutrino oscillations into sterile neutrinos and distinguishing a 3+1 scenario from the standard scenario with three active neutrino flavours, will be challenging due to the large theoretical uncertainties from QCD.

Probing light gauge bosons in tau neutrino experiments

“…Finally, let us note once more that the proposed searches rely on an accurate understanding of the SM tau neutrino flux, which currently still has large uncertainties. This therefore motivates the further study of tau neutrino production through direct measurements [65], precision QCD calculations [64], and improved simulators to understand and improve the flux uncertainties.…”

“…1 Following the DONuT analysis [3], we assume a 33% systematic uncertainty for the SM tau neutrino flux in all experiments, which is added in quadrature to the statistical uncertainties. Dedicated theoretical efforts [63,64] or direct measurements of D s -meson production [65,66] will play an important role in further reducing these uncertainties in the future. Also shown is the average energy of the tau neutrinos interacting with the detector.…”

Neutrinos from charm: forward production at the LHC and in the atmosphere

“…Work is in progress [5] to assess the PDF and scale uncertainties in the prediction of the forward ( +¯ ) flux at the LHC [6] using the PROSA 2019 PDF sets as our default PDFs [3]. We evaluate the charm meson production cross sections at next-to-leading order (NLO) in perturbative QCD and compare the results with the LHCb data [4] to find optimal parameters of theoretical calculation.…”

The Forward Physics Facility: Sites, Experiments, and Physics Potential

“…For 3 ab −1 , such a detector will collect hundreds of thousands of muon neutrino/antineutrino CC events, about a hundred thousand electron neutrino events, and thousands of tau neutrino events. These numbers have large uncertainties due to the poorly understood production cross section in the forward region [40]. It is also important to note that this flux of events will have the same time structure as the LHC accelerator with a bunch spacing of 25 ns.…”

“…Right: The differential cross section for the ν τ + ντ energy distribution for different rapidity ranges for 2π azimuthal coverage. The results are evaluated using NLO perturbative QCD with the PROSA PDFs [155] and scale proportional to m T,2 = 4m 2 c + p 2 T for D s production and decay [40,156].…”