Neutrino Energy Distributions Research Articles

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

New experiments dealing with neutrinos in the far-forward region at the Large Hadron Collider (LHC) are under design or already in preparation. Two of them, FASERν and SND@LHC, are expected to be active during Run 3 and have the potential to detect the interactions of ν and overline{nu} 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^{pm } 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 pseudorapidities at high energies, QCD theoretical predictions for the flux of ντ plus overline{nu} τ rely on parton distribution functions (PDFs) in a combination of very small and large parton−x values. We evaluate PDF un certainties affecting the flux of ντ + overline{nu} τ produced by {D}_s^{pm } decay in the far forward region at the LHC. Next-to-leading order (NLO) QCD uncertainties are included in the calculation of {D}_s^{pm } production and NLO PDF sets are used for consistency. The theoretical uncertainty associated with the 40 PDF sets of the PROSA19 group amounts to ±(20 − 30)% for the (ντ + overline{nu} τ) number of charged-current (CC) events. Scale uncertainties are much larger, resulting in a range of CC 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.

Prompt electron and tau neutrinos and antineutrinos in the forward region at the LHC

Neutrino fluxes at high rapidity and at high energy are sensitive to QCD dynamics of heavy-flavor production in kinematic regions where measurements have not yet been made. The FASERν and SND@LHC experiments scheduled for Run 3 at the Large Hadron Collider (LHC) and the proposed Forward Physics Facility with a suite of experiments during the High-Luminosity LHC phase will probe neutrinos at high pseudorapidity. This short paper reports on recent evaluations of the prompt ντ+ν¯τ and νe+ν¯e double-differential cross sections in pp collisions at the LHC from the production and decays of Ds± and D±, respectively. For s=14 TeV, the double-differential neutrino energy and pseudorapidity distributions are evaluated at NLO QCD. Data tables with these predictions are presented. Future work needed to refine predictions of neutrino and antineutrino fluxes in the forward region at the LHC is discussed.

Second class currents, axial mass, and nuclear effects in hyperon production

We study the properties of the Cabibbo suppressed quasielastic production of $\Lambda$ and $\Sigma$ hyperons in antineutrino interactions with nuclei, including the effects of modified form factor axial mass, the second class current and SU(3) flavour violations. The hyperon and nucleon are subjected to the nuclear potential and the outgoing hyperon can undergo final state interactions. The hyperon potential has a significant effect on their production through absorption. We predict a significant enhancement of $\Lambda$ production compared with other hyperon production channels through $\Sigma \to \Lambda$ conversions. We produce predictions for several experiments by combining realistic neutrino energy distributions with suitable nuclear targets.

ν − ν interactions in supernovae environments as a function of density and temperature

Neutrinos in astrophysical environments, such as Supernovae (SNe), may interact through pair interactions. These interactions are density and temperature-dependent. Under certain conditions, a neutrino-condensate may form. In this work, we have adapted the separable nonlocal pairing interactions to the SN conditions and studied the temperature and density dependence of the pairing gap as well as the collective response with respect to these variables. We have applied the Bogoliubov transformations and solved the Bardeen, Cooper and Schrieffer (BCS) equations to construct the free quasi-particle sector of the Hamiltonian. The residual two-quasi-particle terms have been treated by applying the Tamm–Dancoff approximation (TDA) and random-phase approximation (RPA), suited to the extended neutrino media. With this, we have constructed neutrino energy distributions both in the superfluid and normal regimes and extracted critical values of the density and temperature.

Using high-energy neutrinos as cosmic magnetometers

Magnetic fields are crucial in shaping the non-thermal emission of the TeV-PeV neutrinos of astrophysical origin seen by the IceCube neutrino telescope. The sources of these neutrinos are unknown, but if they harbor a strong magnetic field, then the synchrotron energy losses of the neutrino parent particles---protons, pions, and muons---leave characteristic imprints on the neutrino energy distribution and its flavor composition. We use high-energy neutrinos as "cosmic magnetometers" to constrain the identity of their sources by placing limits on the strength of the magnetic field in them. We look for evidence of synchrotron losses in public IceCube data: 6 years of High Energy Starting Events (HESE) and 2 years of Medium Energy Starting Events (MESE). In the absence of evidence, we place an upper limit of 10 kG-10 MG (95% C.L.) on the average magnetic field strength of the sources.

Indirect search for dark matter from the Galactic Center and halo with the Super-Kamiokande detector

We present a search for an excess of neutrino interactions due to dark matter in the form of Weakly Interacting Massive Particles (WIMPs) annihilating in the galactic center or halo based on the data set of Super-Kamiokande-I, -II, -III and -IV taken from 1996 to 2016. We model the neutrino flux, energy, and flavor distributions assuming WIMP self-annihilation is dominant to $\nu \overline{\nu}$, $\mu^+\mu^-$, $b\overline{b}$, or $W^+W^-$. The excess is in comparison to atmospheric neutrino interactions which are modeled in detail and fit to data. Limits on the self-annihilation cross section $\langle \sigma_{A} V \rangle$ are derived for WIMP masses in the range 1 GeV to 10 TeV, reaching as low as $9.6 \times10^{-23}$ cm$^3$ s$^{-1}$ for 5 GeV WIMPs in $b\bar b$ mode and $1.2 \times10^{-24}$ cm$^3$ s$^{-1}$ for 1 GeV WIMPs in $\nu \bar \nu$ mode. The obtained sensitivity of the Super-Kamiokande detector to WIMP masses below several tens of GeV is the best among similar indirect searches to date.

Far-forward neutrinos at the Large Hadron Collider

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-kT effects are approximated by a simple phenomenological model introducing a Gaussian kT -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^{pm } production are compared with LHCb data on double-differential cross-sections in transverse momentum and rapidity. The uncertain- ties 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.

Active-sterile neutrino oscillations in the early Universe with the complete mixing matrix

In the framework of a 3+1 scheme with an additional inert state, we consider the thermalisation of sterile neutrinos in the early Universe taking into account the full 4 × 4 mixing matrix. The evolution of the neutrino energy distributions is found solving the momentum-dependent kinetic equations with full diagonal collision terms. The degree of thermalisation of the sterile state is shown in terms of the effective number of neutrinos, N eff, and its dependence on the three additional mixing angles (θ 14, θ 24, θ 34) and on the squared mass difference ∆m 2 41 is discussed. Our results are relevant for fixing the contribution of a fourth light neutrino species to the cosmological energy density, whose value is very well constrained by the final Planck analysis. For the preferred region of active-sterile mixing parameters from short-baseline neutrino experiments, we find that the fourth state is fully thermalised (N eff ≃ 4).

Studying supernova neutrinos through nuclear structure calculations

Differential and integrated cross section calculations are performed in the context of the quasi particle random phase approximation (QRPA) by utilizing realistic two- nucleon forces, for the 64,66 Zn isotopes, contents of the COBRA double beta decay detector. For these isotopes the response to supernova neutrinos is of current inter- est. The response of the 66 Zn isotope to the energy-spectra of supernova neutrinos is also explored by convoluting the original results for the differential cross sections by employing: (i) a two-parameter Fermi-Dirac (FD) and (ii) a Power-Law (PL) neutrino energy distribution. Such folded cross sections are useful in low-energy astrophysical-neutrino detection in underground terrestrial experiments.

Thermalisation of sterile neutrinos in the early universe in the 3+1 scheme with full mixing matrix

In the framework of a 3+1 scheme with an additional inert state, we consider the thermalisation of sterile neutrinos in the early Universe taking into account the full 4×4 mixing matrix. The evolution of the neutrino energy distributions is found solving the momentum-dependent kinetic equations with full diagonal collision terms, as in previous analyses of flavour neutrino decoupling in the standard case. The degree of thermalisation of the sterile state is shown in terms of the effective number of neutrinos, Neff, and its dependence on the three additional mixing angles (θ14, θ24, θ34) and on the squared mass difference Δ m241 is discussed. Our results are relevant for fixing the contribution of a fourth light neutrino species to the cosmological energy density, whose value is very well constrained by the final Planck analysis. For the preferred region of active-sterile mixing parameters from short-baseline neutrino experiments, we find that the fourth state is fully thermalised (Neff≃ 4).

Studying the coherent channel of neutral current ν-nucleus interaction

Original cross-sections calculations for neutral current neutrino scattering on 40Ar isotope are performed in the context of the quasi-particle random phase approximation (QRPA) by utilizing realistic two-nucleon forces. The incoming neutrino energy range adopted, εν ≤ 100 MeV, covers the supernova neutrinos, the low-energy beta-beam-neutrinos and the pion-muon stopped neutrino-beams existing or planned to be conducted at future neutron spallation sources. Subsequently, are the original cross sections convoluted with various supernova neutrino-energy distributions such as the two-parameter Fermi-Dirac and the power law distributions. The folded cross sections are obtained for various values of the parameters of these neutrino energy distributions corresponding to different supernova scenarios. One of the main purposes of this work is to explore the response of the 40Ar isotope as supernova neutrino detector.

Normal-mode analysis for collective neutrino oscillations

In an interacting neutrino gas, collective modes of flavor coherence emerge that can be propagating or unstable. We derive the general dispersion relation in the linear regime that depends on the neutrino energy and angle distribution. The essential scales are the vacuum oscillation frequency ω=Δ m2/(2E), the neutrino-neutrino interaction energy μ=√2GF; nν, and the matter potential λ=√2GF ne. Collective modes require non-vanishing μ and may be dynamical even for ω=0 (“fast modes”), or they may require ω¬=0 (“slow modes”). The growth rate of unstable fast modes can be fast itself (independent of ω) or can be slow (suppressed by √|ω/μ|). We clarify the role of flavor mixing, which is ignored for the identification of collective modes, but necessary to trigger collective flavor motion. A large matter effect is needed to provide an approximate fixed point of flavor evolution, while spatial or temporal variations of matter and/or neutrinos are required as a trigger, i.e., to translate the disturbance provided by the mass term to seed stable or unstable flavor waves. We work out explicit examples to illustrate these points.

Mean-field approach to reconstructed neutrino energy distributions in accelerator-based experiments

The reconstruction of the neutrino energy is crucial in oscillation experiments that use interactions with nuclei to detect the neutrino. The common reconstruction procedure is based on the kinematics of the final-state lepton. The interpretation of the reconstructed energy in terms of the real neutrino energy must rely on a model for the neutrino-nucleus interaction. The Relativistic Fermi Gas (RFG) model is frequently used in these analyses. In the Hartree-Fock (HF) model for quasielastic nucleon knockout, the bound nucleon wave functions are obtained using an effective nucleon-nucleon force. The final-state wave function is constructed from continuum states in the same potential which have the correct asymptotic behavior. The Continuum Random Phase Approximation (CRPA) model extends the HF approach taking long range correlations into account in a self-consistent way. Considering only single-nucleon processes, the distributions of reconstructed neutrino energies obtained within the HF-CRPA approach are compared with the results of the RFG, an RPWIA calculation, and the RPA+np-nh model of Martini et al. We find that the distributions of reconstructed energies for a fixed incoming energy in the HF-CRPA display additional strength in the low reconstructed energy tails compared to models without elastic distortion of the outgoing nucleon. This asymmetry redistributes strength from higher to lower values of the reconstructed energy. The mean field description of the nuclear dynamics results in a reshaping of the reconstructed energy distribution that cannot be accounted for in a plane wave impulse approximation model, even by modifying ad hoc parameters such as the binding energy. In particular it is shown that in the RFG calculations there is no value of the binding energy which is able to reproduce the entire T2K $\nu_\mu$ oscillated spectrum as calculated in HF-CRPA.

Neutral-Current Neutrino-Nucleus Scattering off Xe Isotopes

Large liquid xenon detectors aiming for dark matter direct detection will soon become viable tools also for investigating neutrino physics. Information on the effects of nuclear structure in neutrino-nucleus scattering can be important in distinguishing neutrino backgrounds in such detectors. We perform calculations for differential and total cross sections of neutral-current neutrino scattering off the most abundant xenon isotopes. The nuclear-structure calculations are made in the nuclear shell model for elastic scattering and also in the quasiparticle random-phase approximation (QRPA) and microscopic quasiparticle-phonon model (MQPM) for both elastic and inelastic scattering. Using suitable neutrino energy distributions, we compute estimates of total averaged cross sections for ​8B solar neutrinos and supernova neutrinos.

Constraining nuclear data via cosmological observations: Neutrino energy transport and big bang nucleosynthesis

We introduce a new computational capability that moves toward a self-consistent calculation of neutrino transport and nuclear reactions for big bang nucleosynthesis (BBN). Such a self-consistent approach is needed to be able to extract detailed information about nuclear reactions and physics beyond the standard model from precision cosmological observations of primordial nuclides and the cosmic microwave background radiation. We calculate the evolution of the early universe through the epochs of weak decoupling, weak freeze-out and big bang nucleosynthesis (BBN) by simultaneously coupling a full strong, electromagnetic, and weak nuclear reaction network with a multi-energy group Boltzmann neutrino energy transport scheme. The modular structure of our approach allows the dissection of the relative contributions of each process responsible for evolving the dynamics of the early universe. Such an approach allows a detailed account of the evolution of the active neutrino energy distribution functions alongside and self-consistently with the nuclear reactions and entropy/heat generation and 'ow between the neutrino and photon/electron/positron/baryon plasma components. Our calculations reveal nonlinear feedback in the time evolution of neutrino distribution functions and plasma thermodynamic conditions. We discuss the time development of neutrino spectral distortions and concomitant entropy production and extraction from the plasma. These e↑ects result in changes in the computed values of the BBN deuterium and helium-4 yields that are on the order of a half-percent relative to a baseline standard BBN calculation with no neutrino transport. This is an order of magnitude larger e↑ect than in previous estimates. For particular implementations of quantum corrections in plasma thermodynamics, our calculations show a 0.4% increase in deuterium and a 0.6% decrease in 4 He over our baseline. The magnitude of these changes are on the order of uncertainties in the nuclear physics for the case of deuterium and are potentially signi↓cant for the error budget of helium in upcoming cosmological observations.

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.

Effects of neutrino oscillations on nucleosynthesis and neutrino signals for an18M⊙supernova model

In this paper, we explore the effects of neutrino flavor oscillations on supernova nucleosynthesis and on the neutrino signals. Our study is based on detailed information about the neutrino spectra and their time evolution from a spherically-symmetric supernova model for an 18 M progenitor. We find that collective neutrino oscillations are not only sensitive to the detailed neutrino energy and angular distributions at emission, but also to the time evolution of both the neutrino spectra and the electron density profile. We apply the results of neutrino oscillations to study the impact on supernova nucleosynthesis and on the neutrino signals from a Galactic supernova. We show that in our supernova model, collective neutrino oscillations enhance the production of rare isotopes 138La and 180Ta but have little impact on the nu p-process nucleosynthesis. In addition, the adiabatic MSW flavor transformation, which occurs in the C/O and He shells of the supernova, may affect the production of light nuclei such as 7Li and 11B. For the neutrino signals, we calculate the rate of neutrino events in the Super-Kamiokande detector and in a hypothetical liquid argon detector. Our results suggest the possibility of using the time profiles of the events in both detectors, along with the spectral information of the detected neutrinos, to infer the neutrino mass hierarchy.

Right-handed chirality of muon neutrinos in polarized muon decay at rest

In this paper, we analyze the polarized muon decay at rest admitting the non-standard \(V+A\) interaction in addition to the standard \(V-A\) interaction. We show that the angle–energy distribution of Dirac muon neutrinos (\(\nu _{\mu }\)’) is sensitive to the interference terms between the standard \(V-A\) coupling of left-chirality \(\nu _{\mu }\) and exotic \(V+A\) coupling of right-chirality one, which are proportional to the transverse components of \(\nu _{\mu }\) spin polarization. The interferences do not vanish in the limit of massless \(\nu _{\mu }\) and include the relative phases to test the CP violation. It allows one to calculate a neutrino flux for an assumed configuration of detector in the case of standard model prediction, and the upper limits on the neutrino flux for the left–right \(\nu _{\mu }\) mixture. It is also demonstrated that the effects of neutrino mass and mixing are tiny corrections and can be omitted. The most important conclusion is that even in the massless \(\nu _{\mu }\) limit, there are physical effects connected with the mixture of left- and right-handed helicity components in a spin \(1/2\) quantum state, when the exotic interaction \(V+A\) is admitted, contrary to the electron observables, where all the possible interferences vanish.

Application of simulation techniques in supernova physics

In supernova (SN) physics, the responses of nuclear neutrino-detectors to SN neutrino-spectra, are studied by convoluting original theoretical cross sections with well known SN (anti)neutrino-energy distributions (such distributions are the two-parameter Fermi-Dirac and Power-Law distributions). Also, the interpretation of SN neutrino signals, created at various nuclear ν-detectors, is explored by applying simulation techniques in low-energy anti-neutrino spectra of boosted β-radioactive 6He ions (beta-beam neutrinos). In the present paper, we employ simulation techniques to analyze original SN anti-neutrino signals by using synthetic beta-beam spectra (defined as linear combinations of boosted beta-beam spectra of 6He). The quality of the fits, obtained by using the MERLIN optimization package, is in general good. From a nuclear theory point of view, the resulted nuclear responses reflect the effectiveness of some detector materials as SN neutrino detectors (COBRA, CUORE, ICARUS experiments).

Nuclear responses of64,66Zn isotopes to supernova neutrinos

Nuclear responses to energy spectra of supernova (SN) neutrinos are studied by folding original $\ensuremath{\nu}$-nucleus cross sections calculated in the context of the quasiparticle random-phase approximation using realistic two-body forces. To this purpose, we employ two-parameter neutrino-energy distributions of Fermi-Dirac and power-law shapes for various SN neutrino scenarios. As concrete examples of promising neutrino detectors we have chosen the ${}^{64,66}$Zn isotopes, contents of (i) the semiconductor CdZnTe (COBRA experiment) and (ii) the crystal scintillators ZnMoO${}_{4}$ and ZnWO${}_{4}$. These materials are quite advantageous for measuring double-$\ensuremath{\beta}$-decay events and for potential use in studying current neutrino physics issues. We concentrate on the evaluation of folded differential cross sections, ${[d\ensuremath{\sigma}(\ensuremath{\omega})/d\ensuremath{\omega}]}_{\mathrm{fold}}$, and flux-averaged cumulative cross sections, ${[d\ensuremath{\sigma}(\ensuremath{\omega})/d\ensuremath{\omega}]}_{\mathrm{fold}}^{\mathrm{cum}}$, as well as total cross sections, $\ensuremath{\langle}{\ensuremath{\sigma}}_{\mathrm{tot}}\ensuremath{\rangle}$, of the above Zn isotopes by adopting several realistic SN neutrino models parametrized by the neutrino temperature or the mean neutrino energy and the width of the aforementioned distributions.