Parton distribution function uncertainties in theoretical predictions for far-forward tau neutrinos at the Large Hadron Collider

Abstract

New experiments to measure neutrinos in the far-forward region at the Large Hadron Collider (LHC) are under design or already in preparation. Two of them, Faser-ν and SND@LHC, are expected to be active during Run 3 and have the potential to detect neutrinos that come from high-energy collisions in one of the LHC interaction points, extracted along the direction tangent to the beam line. Tau neutrinos and antineutrinos come predominantly from D ± s production in pp collisions, followed by the leptonic decay of these mesons. Neutrino pseudorapidities in the range of η > 6.9 and η > 8.9 are relevant to these future experiments. At such large pseudorapidities at high energies, theoretical predictions rely on parton distribution functions (PDFs) in a combination of very small and large parton−x values. We evaluate PDF uncertainties in a next-to-leading order (NLO) QCD calculation of the flux of tau neutrinos plus antineutrinos produced by D ± s decay in the far forward region at the LHC. The theoretical uncertainty associated with the 40 PDF sets of the PROSA19 group amount to ±(20 − 30)% for the tau neutrino plus antineutrino number of charged-current events. Scale uncertainties are much larger, resulting into a range of charged-current event predictions from ∼ 70% lower to ∼ 90% higher than the central prediction. A comparison of the predictions with those obtained using as input the central PDFs from the 3-flavour NLO PDF sets of the CT14, ABMP16 and NNPDF3.1 collaborations show that far-forward neutrino energy distributions vary by as much as a factor of ∼ 2 − 4 relative to the PROSA19 predictions at TeV neutrino energies. The Forward Physics Facility in the high luminosity LHC era will provide data capable of constraining NLO QCD evaluations with these PDF sets.

Neutrino Detection without Neutrino Detectors: Discovering Collider Neutrinos at FASER with Electronic Signals Only

“…This is due to an increasing contribution of neutrinos from charmed hadron decay to the overall flux for which the considered generator predictions differ by up to an order of magnitude. Dedicated efforts are needed, and have indeed already begun [11][12][13][14][15][16], to provide more reliable predictions for this forward charm production.…”

“…For these same reasons, however, the detection of collider neutrinos is of great interest [1][2][3][4][5][6][7][8], since, if they are observed, they will have the highest human-made energies ever recorded. Their detection therefore provides a new window into the production, propagation, and interaction of neutrinos with significant implications for new physics, QCD, neutrino properties, and astroparticle physics [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23].…”

Forward production of prompt neutrinos in the atmosphere and at high-energy colliders

“…There are several approaches to evaluate the heavy-flavor production cross sections. In this work, adopting our previous work [22], we use perturbative QCD at next-to-leading order (NLO) with massive charm, QCD scales of (𝜇 𝑅 , 𝜇 𝐹 ) = (1, 2) 𝑚 𝑇 and intrinsic transverse momentum smearing ⟨𝑘 𝑇 ⟩ = 1.2 GeV. Fig.…”

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“…Notably, the number of neutrino-induced events expected in the FPF is highly suppressed in this low-energy regime. This is primarily dictated by the large energy of incident neutrinos produced in the far-forward region of the LHC, typically of order E ν ∼ 200 − 300 GeV, see Refs [90,91,[111][112][113][114] for further discussion. Instead, low-energy neutrinos are produced more isotropically at the LHC.…”