Conventional Neutrino Research Articles

The ENUBET experiment

The knowledge of the initial flux in conventional neutrino beams represents the main limitation for a precision (1%) measurement of [Formula: see text] and [Formula: see text] cross-sections. The ENUBET ERC project is studying a facility based on a narrow-band beam capable of constraining the neutrino fluxes normalization through the monitoring of the associated charged leptons in an instrumented decay tunnel. In particular, the identification of large-angle positrons from [Formula: see text] decays at single-particle level can reduce the [Formula: see text] flux uncertainty at the level of 1%. This setup would allow for an unprecedented measurement of the [Formula: see text] cross-section at the GeV scale. Such an experimental input would be highly beneficial to reduce the budget of systematic uncertainties in the next long baseline oscillation experiments. The ENUBET Collaboration presented at ICNFP 2020 the advances in the design and simulation of the hadron beamline, the optimization and performances of a 20 m long focusing transfer line, the design of an horn-based beamline, the results in terms of particle identification in the decay tunnel, and the final design of the ENUBET demonstrator for the instrumented decay tunnel.

Neutrino and Axion Astronomy with Dark Matter Experiments

Sensitive dark matter (DM) experiments can be well exploited beyond their designated targets, allowing to explore a breadth of physics topics. As we discuss, future large direct DM detection experiments constitute impressive telescopes, complementary to conventional neutrino detectors. This opens a new window into neutrino astronomy, including puzzles such as the origin of supermassive black holes and topics like supernova forecast. Furthermore, DM experiments can act as effective instruments for multimessenger astronomy. This is well illustrated by exploration of relativistic axions from transient astrophysical sources (e.g. axion star explosions), providing novel signatures as well as possible insights into the axion potential.

Unified thermal model for photohadronic neutrino production in astrophysical sources

High-energy astrophysical neutrino fluxes are, for many applications, modeled as simple power laws as a function of energy. While this is reasonable in the case of neutrino production in hadronuclear pp sources, it typically does not capture the behavior in photohadronic pγ sources: in that case, the neutrino spectrum depends on the properties of the target photons the cosmic rays collide with and on possible magnetic-field effects on the secondary pions and muons. We show that the neutrino production from known photohadronic sources can be reproduced by a thermal (black-body) target-photon spectrum if one suitably adjusts the temperature, thanks to multi-pion production processes. This allows discussing neutrino production from most known pγ sources, such as gamma-ray bursts, active galactic nuclei and tidal disruption events, in terms of a few parameters. We apply this thermal model to study the sensitivity of different classes of neutrino telescopes to photohadronic sources: we classify the model parameter space according to which experiment is most suitable for detection of a specific source class and demonstrate that different experiment classes, such as dense arrays, conventional neutrino telescopes, or radio-detection experiments, cover different parts of the parameter space. Since the model can also reproduce the flavor and neutrino-antineutrino composition, we study the impact on the track-to-shower ratio and the Glashow resonance.

New Projections for Dark Matter Searches with Paleo-Detectors

Paleo-detectors are a proposed experimental technique to search for dark matter (DM). In lieu of the conventional approach of operating a tonne-scale real-time detector to search for DM-induced nuclear recoils, paleo-detectors take advantage of small samples of naturally occurring rocks on Earth that have been deep underground (≳5 km), accumulating nuclear damage tracks from recoiling nuclei for O(1)Gyr. Modern microscopy techniques promise the capability to read out nuclear damage tracks with nanometer resolution in macroscopic samples. Thanks to their O(1)Gyr integration times, paleo-detectors could constitute nuclear recoil detectors with keV recoil energy thresholds and 100 kilotonne-yr exposures. This combination would allow paleo-detectors to probe DM-nucleon cross sections orders of magnitude below existing upper limits from conventional direct detection experiments. In this article, we use improved background modeling and a new spectral analysis technique to update the sensitivity forecast for paleo-detectors. We demonstrate the robustness of the sensitivity forecast to the (lack of) ancillary measurements of the age of the samples and the parameters controlling the backgrounds, systematic mismodeling of the spectral shape of the backgrounds, and the radiopurity of the mineral samples. Specifically, we demonstrate that even if the uranium concentration in paleo-detector samples is 10−8 (per weight), many orders of magnitude larger than what we expect in the most radiopure samples obtained from ultra basic rock or marine evaporite deposits, paleo-detectors could still probe DM-nucleon cross sections below current limits. For DM masses ≲ 10 GeV/c2, the sensitivity of paleo-detectors could still reach down all the way to the conventional neutrino floor in a Xe-based direct detection experiment.

A Standard Model Neutrino Mechanism

This work argues a new standard model physics approach for neutrino oscillations by allowing neutrinos to have their flavor be entangled amongst all interacting fermions. Specifically, for a flavor conserved system, the effects from entanglement beginning at its origin and continuing through transit can give rise to the same observational outcomes as a flavor oscillation described by mass eigenstates. The implication being that although neutrino flavor is conserved in weak processes, this is argued to hold for all subsequent interactions. In so doing, the conventional neutrino mass propagator is argued to be a dimensional artifact of the oscillation being dependent on the linear density of material along the neutrino trajectory.

Constraint of the MINERν A medium energy neutrino flux using neutrino-electron elastic scattering

Elastic neutrino scattering on electrons is a precisely-known purely leptonic process that provides a standard candle for measuring neutrino flux in conventional neutrino beams. Using a total sample of 810 neutino-electron scatters after background subtraction, the measurement reduces the normalization uncertainty on the muon neutrino NuMI flux between 2 and 20 GeV from 7.5% to 3.9%. This is the most precise measurement of neutrino-electron scattering to date, will reduce uncertainties on MINERvA's absolute cross section measurements, and demonstrates a technique that can be used in future neutrino beams such as LBNF.

Supernova neutrino physics with a nuclear emulsion detector

The existence of the coherent neutrino-nucleus scattering reaction requires to evaluate, for any detector devoted to WIMP searches, the irreducible background due to conventional neutrino sources and at same time, it gives a unique chance to reveal supernova neutrinos. We report here a detailed study concerning a new directional detector, based on the nuclear emulsion technology. A Likelihood Ratio test shows that, in the first years of operations and with a detector mass of several tens of tons, the observation of the supernova signal can be achieved. The determination of the distance of the supernova from the neutrinos and the observation of 8B neutrinos are also discussed.

Sterile neutrino dark matter from right-handed neutrino oscillations

We study a scenario where sterile neutrino (either warm or cold) dark matter (DM) is produced through (nonresonant) oscillations among right-handed neutrinos (RHNs) and can constitute the whole DM in the Universe, in contrast to the conventional sterile neutrino production through its mixing with the left-handed neutrinos. The lightest RHN can be sterile neutrino DM whose mixing with left-handed neutrinos is sufficiently small while heavier RHNs can have non-negligible mixings with left-handed neutrinos to explain the neutrino masses by the seesaw mechanism. We also demonstrate that, in our scenario, the production of sterile RHN DM from the decay of a heavier RHN is subdominant compared with the RHN oscillation production due to the X-ray and small-scale structure constraints.

Non-minimal dark matter search in dark matter colliders

In the scenarios of dark matter (DM) with a non-minimal dark sector, we revisit a new detection strategy of observing two or three simultaneous signals from inelastic scattering of a boosted DM [1]. The relativistically incoming DM can scatter off inelastically to a heavier unstable dark sector particle which decays back in to the DM associated with visible Standard Model particles inside large volume neutrino detectors. The existence of the secondary procedure renders us to separate it from conventional neutrino scattering background. The relativistically incoming DM can come from the universe by the annihilation of heavy DM component in an inelastic boosted DM scenario or produced by the beam bombardments in fixed target experiments.

J-PARC accelerator and neutrino beamline upgrade programme

The 30 GeV proton beam from the J-PARC Main Ring (MR) accelerator is used to produce a world-class conventional neutrino beam – the neutrino source for the J-PARC long-baseline neutrino programme, including the current T2K experiment and proposed future experiments. Planned upgrades to increase the beam power of the MR from the current ∼400 kW to the design power of 750 kW and beyond, to 1.3+ MW, are underway. These include hardware modifications, such as upgrades of the MR magnet power supplies, RF systems, and feedback systems, as well as a change of the MR beam betatron tune point. Upgrades to the neutrino beamline, such as to the proton beam monitoring, horns, and radioactive material handling, will also be required to accommodate the increased proton beam power. An overview of planned J-PARC MR and neutrino facility upgrades is given.

Neutrinos from a pion beam line: nuPIL

We describe a novel configuration for a neutrino beam line that can simultaneously support both long and short baseline experiments. The neutrino beams originate from pions that are first focused by a magnetic horn, as in a conventional neutrino beam. However, in the case of nuPIL, the horn is followed by a magnetic lattice that is used to select the pion charge and then transports the pions in a production straight. This produces extremely pure neutrino and anti-neutrino beams, while minimizing the amount of beam power that is transported underground for the long-baseline physics program. This configuration greatly simplifies the civil construction leading to a large cost reduction. The principles of the design of nuPIL are presented, together with tracking results and the resulting neutrino flux. The potential of the facility for CP-violation searches, in the framework of the DUNE experiment, is discussed and compared to that of an optimized beam from LBNF.

Chiral transport of neutrinos in supernovae

The conventional neutrino transport theory for core-collapse supernovae misses one key property of neutrinos: the left-handedness. The chirality of neutrinos modifies the hydrodynamic behavior at the macroscopic scale and leads to topological transport phenomena. We argue that such transport phenomena should play important roles in the evolution of core-collapse supernovae, and, in particular, lead to a tendency toward the inverse energy cascade from small to larger scales, which may be relevant to the origin of the supernova explosion.

ENUBET: Enhanced NeUtrino BEams from kaon Tagging

A reduction of the neutrino flux uncertainty by one order of magnitude in conventional neutrino beams can be achieved monitoring the positron production in the decay tunnel originating from the Ke3 decays of charged kaons. This novel approach will be developed in the framework of the ERC ENUBET Project. In this talk we present the aims of the project and the ongoing R&D for the instrumentation of the decay tunnel. In particular, we describe a specialized shashlik calorimeter (iron-scintillator) with a compact readout based on small-area silicon photo multipliers that allows for a very effective longitudinal segmentation of the detector to enhance electron/hadron separation. The expected performance of the detector estimated from a full GEANT4 simulation of the neutrino decay tunnel are presented. We also discuss preliminary results on a prototype composed by 12 ultra compact modules exposed to pions and electrons at CERN-PS.

A novel technique to achieve atomic macro-coherence as a tool to determine the nature of neutrinos

The photon spectrum in macro-coherent atomic deexcitation via radiative emission of neutrino pairs has been proposed as a sensitive probe of the neutrino mass spectrum, capable of competing with conventional neutrino experiments. In this paper, we revisit this intriguing possibility, presenting an alternative method for inducing large coherence in a target based on adiabatic techniques. More concretely, we propose the use of a modified version of coherent population return (CPR), namely two-photon CPR, that turns out to be extremely robust with respect to the experimental parameters and capable of inducing a coherence close to 100 % in the target.

New limits on neutrino magnetic moments from low energy neutrino data

Here we give a brief review on the current bounds on the general Majorana transition neutrino magnetic moments (TNMM) which cover also the conventional neutrino magnetic moments (NMM). Leptonic CP phases play a key role in constraining TNMMs. While the Borexino experiment is the most sensitive to the TNMM magnitudes, one needs complementary information from reactor and accelerator experiments in order to probe the complex CP phases.

Search for sphalerons: IceCube vs. LHC

We discuss the observability of neutrino-induced sphaleron transitions in the IceCube detector, encouraged by a recent paper by Tye and Wong (TW), which argued on the basis of a Bloch wave function in the periodic sphaleron potential that such transitions should be enhanced compared to most previous calculations. We calculate the dependence on neutrino energy of the sphaleron transition rate, comparing it to that for conventional neutrino interactions, and we discuss the observability of tau and multi-muon production in sphaleron-induced transitions. We use IceCube 4-year data to constrain the sphaleron rate, finding that it is comparable to the upper limit inferred previously from a recast of an ATLAS search for microscopic black holes at the LHC with ∼ 3/fb of collisions at 13 TeV. The IceCube constraint is stronger for a sphaleron barrier height E Sph ≳ 9 TeV, and would be comparable with the prospective LHC sensitivity with 300/fb of data at 14 TeV if E Sph ∼ 11 TeV.

Longitudinally segmented shashlik calorimeters with SiPM readout

The goal of the INFN SCENTT R&D project is to develop the calorimeter technologies for the instrumentation of decay tunnels in conventional neutrino beams. This instrumentation is required to achieve a substantial improvement in the uncertainty on neutrino fluxes for the next generation cross section experiments. In particular, we are designing a positron tagger based on purely calorimetric techniques that is able to measure the rate and the spectrum of the positrons produced in the K+→e+π0νe decay. The νe flux is inferred from the positron rate in the decay tunnel. Considering the large dimensions of the tagger, the most cost effective technology is based on small modules of Fe/Scintillator shashlik calorimeters, with adequate segmentation and energy resolution to efficiently tag the positrons over the charged pion background. This contribution presents preliminary results obtained with two shashlik calorimeter prototypes readout with an array of Silicon PhotoMultipliers and tested at the CERN PS-T9 beamline.

The LAGUNA-LBNO neutrino observatory in Europe

The LAGUNA and LAGUNA-LBNO consortia have performed two detailed design studies from 2008 to 2014 to define the optimal combination of baseline and detector technology for the next generation neutrino observatory. Starting from seven sites and three detector technologies the options have been prioritized with the primary choice given to the Pyhäsalmi mine in Finland and the liquid Argon (DLAr) TPC detector technology. This led to a proposal for a European-based next-generation long baseline oscillation experiment, LBNO. The deep underground location of 1400 m offered by the mine is essential to explore neutrino astrophysics and look for proton decay. The mine position at 2300 km from CERN allows quickly to resolve neutrino mass hierarchy and measure leptonic CPV phase δCP by disentangling the matter effects from those caused by CPV. We will demonstrate the capability of LBNO to discover the mass hierarchy at the >5σ level within 4 years of operation using a 20 kt DLAr detector and a conventional neutrino beam created with a 400 GeV 750 kW primary proton beam delivered by CERN SPS. Following the discovery of the mass hierarchy LBNO will pursue the determination of the CP-violating phase δCP. We will show the LBNO sensitivity to measure δCP by studying the shape of the electron neutrino appearance oscillation probability over a broad energy range covering both the 1st and 2nd νe appearance maxima.

Conditions for statistical determination of the neutrino mass spectrum in radiative emission of neutrino pairs in atoms

The photon spectrum in macrocoherent atomic deexcitation via radiative emission of neutrino pairs has been proposed as a sensitive probe of the neutrino mass spectrum, capable of competing with conventional neutrino experiments. In this paper we revisit this interesting proposal in order to quantify the requirements for statistical determination of some of the properties of the neutrino spectrum, in particular, the neutrino mass scale and the mass ordering. Our results are shown as the product of the experimental lifetime, the target volume, and the number density of atoms which have to be set in a coherence state with a given electric field in the target, needed for determination of these properties with a given confidence level.

Charm production in the forward region: constraints on the small-x gluon and backgrounds for neutrino astronomy

The recent observation by the IceCube experiment of cosmic neutrinos at energies up to a few PeV heralds the beginning of neutrino astronomy. At such high energies, the conventional neutrino flux is suppressed and the prompt component from charm meson decays is expected to become the dominant background to astrophysical neutrinos. Charm production at high energies is however theoretically uncertain, both since the charm mass is at the boundary of applicability of perturbative QCD, and also because the calculations are sensitive to the poorly-known gluon PDF at small-x. In this work we provide detailed perturbative QCD predictions for charm and bottom production in the forward region, and validate them by comparing with recent data from the LHCb experiment at 7 TeV. Finding good agreement between data and theory, we use the LHCb measurements to constrain the small-x gluon PDF, achieving a substantial reduction in its uncertainties. Using these improved PDFs, we provide predictions for charm and bottom production at LHCb at 13 TeV, as well as for the ratio of cross-sections between 13 and 7 TeV. The same calculations are used to compute the energy distribution of neutrinos from charm decays in pA collisions, a key ingredient towards achieving a theoretically robust estimate of charm-induced backgrounds at neutrino telescopes.