Trident Production Research Articles

Discovering neutrino tridents at the Large Hadron Collider

Neutrino trident production of dilepton pairs is well recognized as a sensitive probe of both electroweak physics and physics beyond the Standard Model. Although a rare process, it could be significantly boosted by such new physics, and it also allows the electroweak theory to be tested in a new regime. We demonstrate that the forward neutrino physics program at the Large Hadron Collider offers a promising opportunity to measure for the first time, dimuon neutrino tridents with a statistical significance exceeding 5σ, improving on the previous claims at the ∼3σ level by the CHARM-II and CCFR collaborations while accounting for additional backgrounds later identified by the NuTeV collaboration. We present predictions for various proposed experiments and outline a specific experimental strategy to identify the signal and mitigate backgrounds, based on “reverse tracking” dimuon pairs in the FASERν2 detector. We also discuss prospects for constraining beyond Standard Model contributions to neutrino trident rates at high energies. Published by the American Physical Society 2024

Correlating the CDF W-mass shift with the muon g − 2 and the b → sℓ+ℓ− transitions

Motivated by the latest CDF W-mass measurement as well as the muon g−2 anomaly and the discrepancies observed in b→sℓ+ℓ− transitions, we propose an extension of the Standard Model (SM) with the SU(2)L-singlet vector-like fermion partners that are featured by additional U(1)′ gauge symmetry. The fermion partners have the same SM quantum numbers as of the right-handed SM fermions, and can therefore mix with the latter after the electroweak and the U(1)′ symmetry breaking. As a result, desirable loop-level corrections to the (g−2)μ, the W-boson mass mW and the Wilson coefficient C9 in b→sμ+μ− transitions can be obtained. The final allowed parameter space is also consistent with the constraints from the Z→μ+μ− decay, the neutrino trident production and the LHC direct searches for the vector-like quarks and leptons.

Results and Perspectives from the First Two Years of Neutrino Physics at the LHC by the SND@LHC Experiment

After rapid approval and installation, the SND@LHC Collaboration was able to gather data successfully in 2022 and 2023. Neutrino interactions from νμs originating at the LHC IP1 were observed. Since muons constitute the major background for neutrino interactions, the muon flux entering the acceptance was also measured. To improve the rejection power of the detector and to increase the fiducial volume, a third Veto plane was recently installed. The energy resolution of the calorimeter system was measured in a test beam. This will help with the identification of νe interactions that can be used to probe charm production in the pseudo-rapidity range of SND@LHC (7.2 < η < 8.4). Events with three outgoing muons have been observed and are being studied. With no vertex in the target, these events are very likely from muon trident production in the rock before the detector. Events with a vertex in the detector could be from trident production, photon conversion, or positron annihilation. To enhance SND@LHC’s physics case, an upgrade is planned for HL-LHC that will increase the statistics and reduce the systematics. The installation of a magnet will allow the separation of νμ from ν¯μ

Differential measurement of trident production in strong electromagnetic fields

Differential measurement of trident production in strong electromagnetic fields

Precision Measurement of Trident Production in Strong Electromagnetic Fields.

We demonstrate experimentally that the trident process e^{-}→e^{-}e^{+}e^{-} in a strong external field, with a spatial extension comparable to the effective radiation length, is well understood theoretically. The experiment, conducted at CERN, probes values for the strong field parameter χ up to 2.4. Experimental data and theoretical expectations using the local constant field approximation show remarkable agreement over almost 3 orders of magnitude in yield.

Elusive muonic WIMP

The Weakly Interacting Massive Particle (WIMP) paradigm is one of the most popular scenarios for Dark Matter (DM) theories that however is strongly constrained, in particular by direct detection experiments. We stick with the WIMP hypothesis and consider a Dirac fermion candidate for DM that interacts with the Standard Model (SM) via a spin-1 $Z'$, arising from the spontaneous breaking of an Abelian $U(1)'_{\mu}$ gauge symmetry, under which only second generation leptons and the DM are appropriately charged. Due to the charge assignment, the model is gauge anomalous and can only be interpreted as an effective field theory (EFT) at low energy. The $Z'$ couples at tree level only to the vector DM current, to the axial muon current and to left-handed muonic neutrinos, so the WIMP-nucleon cross section is beyond the experimental reach of spin-independent (SI) direct detection searches. We study the current bounds on this model coming from direct and indirect detection of DM, collider searches, contributions to $(g-2)_{\mu}$ and to neutrino trident production. We find that large regions of the parameter space remains to be explored. In the context of LHC searches, we study the impact of a muon-exclusive signal region for the $3\mu$ + ${E}^{{\rm miss}}_T$ channel with an invariant mass window around $m_{Z'}$. We show that this search can significantly improve the current collider bounds. Finally, from the anomalous nature of our EFT, there remain at low energy triboson anomalous interactions between the $Z'$ and the electroweak (EW) SM gauge bosons. We explore the possibilities of probing these interactions at the LHC and at a 100 TeV proton collider finding it extremely challenging. On the other hand, for a muon collider the resonant channel $\mu^{+}\mu^{-}\to Z'\to ZZ$ could be discovered in the most promising scenario with luminosity of $\mathcal{O}({\rm few}\; 10)$ ${\rm fb}^{-1}$.

Novel event generator for the automated simulation of neutrino scattering

An event generation framework is presented that enables the automatic simulation of events for next-generation neutrino experiments in the Standard Model or extensions thereof. The new generator combines the calculation of the leptonic current based on an automated matrix element generator and the computation of the hadronic current based on a state-of-the-art nuclear physics model. The approach is validated in Standard Model simulations for electron scattering and neutrino scattering. Furthermore, the first fully differential neutrino trident production results are shown in the quasielastic region.

Fermiophobic Z′ model for simultaneously explaining the muon anomalies RK(*) and (g−2)μ

We discuss a simple renormalisable, gauge invariant model with a fermiophobic $Z'$ boson: it has no couplings to the three Standard Model (SM) chiral families, but does couple to a fourth vector-like (VL) family. The SM Higgs couples to the fourth VL lepton, leading to an enhanced contribution to the muon anomalous magnetic moment $\left(g-2\right)_{\mu}$. The latter contribution requires a non-vanishing coupling of $Z'$ to right-handed muons, which arises within this model due to mixing effects between the SM and VL fermions, along with $Z'$ couplings to the second generation SM lepton doublet and third generation SM quark doublet. This model can simultaneously account for the measured $B$-decay ratios $R_{K^{(*)}}$ and $\left(g-2\right)_{\mu}$. We identify the parameter space where this explanation is consistent with existing experimental constraints coming from $B_{s}-\bar{B}_{s}$ mixing, neutrino trident production and collider searches. We also check that the SM Higgs coupling to the fourth VL lepton does not produce a dangerous contribution to the Higgs diphoton decay.

Rise and fall of laser-intensity effects in spectrally resolved Compton process

The laser intensity dependence of nonlinear Compton scattering is discussed in some detail. For sufficiently hard photons with energy ω′, the spectrally resolved differential cross section dσ/dω′| ω′=const, rises from small toward larger laser intensity parameter ξ, reaches a maximum, and falls toward the asymptotic strong-field region. Such a rise and fall of a differential observable is to be contrasted with the monotonously increasing laser intensity dependence of the total probability, which is governed by the soft spectral part. We combine that hard-photon yield from Compton scattering with the seeded Breit–Wheeler pair production in a folding model and obtain a rapidly increasing e + e − pair number at ξ ≲ 4. Laser bandwidth effects are quantified in the weak-field limit of the related trident pair production.

Prospects for beyond the Standard Model physics searches at the Deep Underground Neutrino Experiment

The Deep Underground Neutrino Experiment (DUNE) will be a powerful tool for a variety of physics topics. The high-intensity proton beams provide a large neutrino flux, sampled by a near detector system consisting of a combination of capable precision detectors, and by the massive far detector system located deep underground. This configuration sets up DUNE as a machine for discovery, as it enables opportunities not only to perform precision neutrino measurements that may uncover deviations from the present three-flavor mixing paradigm, but also to discover new particles and unveil new interactions and symmetries beyond those predicted in the Standard Model (SM). Of the many potential beyond the Standard Model (BSM) topics DUNE will probe, this paper presents a selection of studies quantifying DUNE’s sensitivities to sterile neutrino mixing, heavy neutral leptons, non-standard interactions, CPT symmetry violation, Lorentz invariance violation, neutrino trident production, dark matter from both beam induced and cosmogenic sources, baryon number violation, and other new physics topics that complement those at high-energy colliders and significantly extend the present reach.

Kinematical distributions of coherent neutrino trident production in gauged Lμ−Lτ model

We analyze the distributions of energy, opening angle and invariant mass in muonic neutrino trident production processes, $\nu_\mu \to \nu_\mu \mu \overline{\mu}$, in a minimal gauged $U(1)_{L_\mu - L_\tau}$ model, in which the discrepancy of anomalous magnetic moment of muon can be solved. It is known that the total cross sections of the neutrino trident production are degenerate in new physics parameters, the new gauge coupling and gauge boson mass, and therefore other observables are needed to determine these parameters. From numerical analyses, we find that the muon energy and invariant mass distributions show the differences among the new physics parameter sets with which the total cross sections have the same value, while the anti-muon energy and opening angle distributions are not sensitive to the parameters.

Nonlinear trident in the high-energy limit: Nonlocality, Coulomb field, and resummations

We study nonlinear trident in laser pulses in the high-energy limit, where the initial electron experiences, in its rest frame, an electromagnetic field strength above Schwinger's critical field. At lower energies the dominant contribution comes from the "two-step" part, but in the high-energy limit the dominant contribution comes instead from the one-step term. We obtain new approximations that explain the relation between the high-energy limit of trident and pair production by a Coulomb field, as well as the role of the Weizs\"acker-Williams approximation and why it does not agree with the high-$\chi$ limit of the locally-constant-field approximation. We also show that the next-to-leading order in the large-$a_0$ expansion is, in the high-energy limit, nonlocal and is numerically very important even for quite large $a_0$. We show that the small-$a_0$ perturbation series has a finite radius of convergence, but using Pad\'e-conformal methods we obtain resummations that go beyond the radius of convergence and have a large numerical overlap with the large-$a_0$ approximation. We use Borel-Pad\'e-conformal methods to resum the small-$\chi$ expansion and obtain a high precision up to very large $\chi$. We also use newer resummation methods based on hypergeometric/Meijer-G and confluent hypergeometric functions.

Inelastic fermion dark matter origin of XENON1T excess with muon (g − 2) and light neutrino mass

Motivated by the recently reported excess in electron recoil events by the XENON1T collaboration, we propose an inelastic fermion dark matter (DM) scenario within the framework of a gauged Lμ−Lτ extension of the standard model which can also accommodate tiny neutrino masses as well as anomalous muon magnetic moment (g−2)μ. A Dirac fermion DM, naturally stabilised due to its chosen gauge charge, is split into two pseudo-Dirac mass eigenstates due to Majorana mass term induced by singlet scalar which also takes part in generating right handed neutrino masses responsible for type I seesaw origin of light neutrino masses. The inelastic down scattering of heavier DM component can give rise to the XENON1T excess for keV scale mass splitting with lighter DM component. We fit our model with XENON1T data and also find the final parameter space by using bounds from (g−2)μ, DM relic, lifetime of heavier DM, inelastic DM-electron scattering rate, neutrino trident production rate as well as other flavour physics, astrophysical and cosmological observations. A tiny parameter space consistent with all these bounds and requirements will face further scrutiny in near future experiments operating at different frontiers.

Measuring the Weak Mixing Angle in the DUNE Near-Detector Complex.

The planned DUNE experiment will have excellent sensitivity to the vector and axial couplings of the electron to the Z boson via precision measurements of neutrino-electron scattering. We investigate the sensitivity of DUNE-PRISM, a movable near detector in the direction perpendicular to the beam line, and find that it will qualitatively impact our ability to constrain the weak couplings of the electron. We translate these neutrino-electron scattering measurements into a determination of the weak mixing angle at low scales and estimate that, with seven years of data taking, the DUNE near detector can be used to measure sin^{2}θ_{W} with about 2% precision. We also discuss the impact of combining neutrino-electron scattering data with neutrino trident production at DUNE-PRISM.

Is it possible to explain the muon and electron g−2 in a Z′ model?

In order to address this question, we consider a simple renormalisable and gauge invariant model in which the $Z'$ only has couplings to the electron and muon and their associated neutrinos, arising from mixing with a heavy vector-like fourth family of leptons. Within this model we discuss the contributions to the electron and muon anomalous magnetic moments from $Z'$ exchange, subject to the constraints from $\mu \rightarrow e \gamma$ and neutrino trident production. Using analytic and numerical arguments, we find that such a $Z'$ model can account for either the electron or the muon $g-2$ anomalies, but not both, while remaining consistent with the experimental constraints from $\mu \rightarrow e \gamma$ and neutrino trident production.

W -boson and trident production in TeV–PeV neutrino observatories

Detecting TeV--PeV cosmic neutrinos provides crucial tests of neutrino physics and astrophysics. The statistics of IceCube and the larger proposed IceCube-Gen2 demand calculations of neutrino-nucleus interactions subdominant to deep-inelastic scattering, which is mediated by weak-boson couplings to nuclei. The largest such interactions are W-boson and trident production, which are mediated instead through photon couplings to nuclei. In a companion paper [1], we make the most comprehensive and precise calculations of those interactions at high energies. In this paper, we study their phenomenological consequences. We find that: (1) These interactions are dominated by the production of on-shell W-bosons, which carry most of the neutrino energy, (2) The cross section on water/iron can be as large as 7.5%/14% that of charged-current deep-inelastic scattering, much larger than the quoted uncertainty on the latter, (3) Attenuation in Earth is increased by as much as 15%, (4) W-boson production on nuclei exceeds that through the Glashow resonance on electrons by a factor of $\simeq$ 20 for the best-fit IceCube spectrum, (5) The primary signals are showers that will significantly affect the detection rate in IceCube-Gen2; a small fraction of events give unique signatures that may be detected sooner.

Neutrino-nucleus cross sections for W -boson and trident production

The physics of neutrino-nucleus cross sections is a critical probe of the Standard Model and beyond. A precise understanding is also needed to accurately deduce astrophysical neutrino spectra. At energies above $\sim 5$ GeV, the cross section is dominated by deep inelastic scattering, mediated by weak bosons. In addition, there are subdominant processes where the hadronic coupling is through virtual photons, $\gamma^\ast$: (on-shell) $W$-boson production (e.g., where the underlying interaction is $\nu_\ell + \gamma^\ast \rightarrow \ell^- + W^+$) and trident production (e.g., where it is $\nu + \gamma^\ast \rightarrow \nu + \ell_1^- + \ell_2^+$). These processes become increasingly relevant at TeV--PeV energies. We undertake the first systematic approach to these processes (and those with hadronic couplings through virtual $W$ and $Z$ bosons), treating them together, avoiding common approximations, considering all neutrino flavors and final states, and covering the energy range $10\,$--$10^8$ GeV. In particular, we present the first complete calculation of $W$-boson production and the first calculation of trident production at TeV--PeV energies. When we use the same assumptions as in prior work, we recover all of their major results. In a companion paper, we show that these processes should be taken into account for IceCube-Gen2.

Gauging the accidental symmetries of the standard model, and implications for the flavor anomalies

We explore the possibility that lepton family numbers and baryon number are such good symmetries of Nature because they are the global remnant of a spontaneously broken gauge symmetry. An almost arbitrary linear combination of these symmetries (together with a component of global hypercharge) can be consistently gauged, if the Standard Model (SM) fermion content is augmented by three chiral SM singlet states. Within this framework of $U(1)$ extensions of the SM one generically expects flavour non-universality to emerge in the charged leptons, in such a way that naturally prevents lepton flavour violation, by aligning the mass and weak eigenbases. For quarks, all the SM Yukawa couplings responsible for their observed masses and mixings arise at the renormalisable level. We perform fits to show that models in this class can explain $R_{K^{(\ast)}}$ and the other neutral current $B$ anomaly data if we introduce a heavy vector-like quark to mediate the required quark flavour violation, while simultaneously satisfying other constraints from direct $Z^\prime$ searches at the LHC, $B_s$ meson mixing, a number of electroweak precision observables, and neutrino trident production. Within this symmetry-motivated framework of models, we find interesting implications for the flavour anomalies; notably, any axial couplings of the $Z^\prime$ to electrons and muons must be flavour universal, with the flavour universality violation arising solely from the vector-like couplings. We also comment on the generation of neutrino masses in these models.

Neutrino tridents at DUNE

The DUNE near detector will collect an unprecedented large number of neutrino interactions, allowing the precise measurement of rare processes such as neutrino trident production, i.e. the generation of a lepton-antilepton pair through the scattering of a neutrino off a heavy nucleus. The event rate of this process is a powerful probe to a well-motivated parameter space of new physics beyond the Standard Model. In this paper, we perform a detailed sensitivity study of the DUNE near detector to neutrino tridents. We provide state-of-the-art predictions for the Standard Model cross sections and corresponding event rates at the near detector for the nu_mu -> nu_mu mu^+ mu^-, nu_mu -> nu_mu e^+e^- and nu_mu -> nu_e e^+ mu^- trident interactions (and the corresponding anti-neutrino modes), discussing their uncertainties. We analyze all relevant backgrounds, utilize a Geant4-based simulation of the DUNE-near detector liquid argon TPC (the official DUNE simulation at the time of writing this paper), and identify a set of selection cuts that would allow the DUNE near detector to measure the nu_mu -> nu_mu mu^+ mu^- cross section with a ~25% accuracy after running in neutrino and anti-neutrino modes for ~3 years each. This would lead to the most precise measurement of the trident process, surpassing the previous measurement by the CCFR collaboration. We show that this measurement would be highly sensitive to new physics, and, in particular, we find that the parameter space of models with gauged L_mu - L_tau that can explain the (g-2)_mu anomaly could be covered almost entirely. As a byproduct, a new Monte Carlo tool to generate neutrino trident events is made publicly available.

Light mediators in anomaly free U (1)X models. Part II. Constraints on dark gauge bosons

We consider experimental constraints in the MeV region in order to determine the parameter space for the U(1)X extension of the Standard Model, presented in the first part of our work. In particular, we focus on the model UV-completed by cold WIMPs. We conclude that the electron anomalous magnetic moment and the neutrino trident production provide the most stringent bounds to {g}_X^2 ∼ 10−6 in the mass interval below the di-muon threshold. By allowing the axial-vector coupling of the dark gauge boson Z′, the interference effect with the SM gauge bosons may reduce the bounds coming from the neutrino trident production. At the same time, such coupling allows a region of the parameter space already favored both by the relic abundance and by the discrepancy between experimental result and theoretical prediction for the muon anomalous magnetic moment. We emphasize that light-Z′ interactions, non-universal for the two first lepton families, necessarily create a difference in the proton charge radius measured in the Lamb shift of the e-hydrogen and μ-hydrogen. Finally, we determine the effects of the new gauge boson on the forward-backward asymmetry in e+e−→ overline{f}f = μ, τ, and on the leptonic decays M → jνjl+l−, where M = π, K, D, Ds, B and j, l = e, μ.