This paper describes the physics case for a new fixed target facility at CERN SPS. The SHiP (search for hidden particles) experiment is intended to hunt for new physics in the largely unexplored domain of very weakly interacting particles with masses below the Fermi scale, inaccessible to the LHC experiments, and to study tau neutrino physics. The same proton beam setup can be used later to look for decays of tau-leptons with lepton flavour number non-conservation, $\tau \to 3\mu $ and to search for weakly-interacting sub-GeV dark matter candidates. We discuss the evidence for physics beyond the standard model and describe interactions between new particles and four different portals—scalars, vectors, fermions or axion-like particles. We discuss motivations for different models, manifesting themselves via these interactions, and how they can be probed with the SHiP experiment and present several case studies. The prospects to search for relatively light SUSY and composite particles at SHiP are also discussed. We demonstrate that the SHiP experiment has a unique potential to discover new physics and can directly probe a number of solutions of beyond the standard model puzzles, such as neutrino masses, baryon asymmetry of the Universe, dark matter, and inflation.

/pdf/a-facility-to-search-for-hidden-particles-at-the-cern-sps-3pxaggnjt6.pdf

A facility to search for hidden particles at the CERN SPS: the SHiP physics case.

We present an updated global fit of neutrino oscillation data in the simplest three-neutrino framework In the present study we include up-to-date analyses from a number of experiments Concerning the atmospheric and solar sectors, besides the data considered previously, we give updated analyses of IceCube DeepCore and Sudbury Neutrino Observatory data, respectively We have also included the latest electron antineutrino data collected by the Daya Bay and RENO reactor experiments, and the long-baseline T2K and NOνA measurements, as reported in the Neutrino 2020 conference All in all, these new analyses result in more accurate measurements of θ13, θ12, $$ \Delta {m}_{21}^2 $$
 and $$ \left|\Delta {m}_{31}^2\right| $$
  The best fit value for the atmospheric angle θ23 lies in the second octant, but first octant solutions remain allowed at ∼ 24σ Regarding CP violation measurements, the preferred value of δ we obtain is 108π (158π) for normal (inverted) neutrino mass ordering The global analysis still prefers normal neutrino mass ordering with 25σ statistical significance This preference is milder than the one found in previous global analyses These new results should be regarded as robust due to the agreement found between our Bayesian and frequentist approaches Taking into account only oscillation data, there is a weak/moderate preference for the normal neutrino mass ordering of 200σ While adding neutrinoless double beta decay from the latest Gerda, CUORE and KamLAND-Zen results barely modifies this picture, cosmological measurements raise the preference to 268σ within a conservative approach A more aggressive data set combination of cosmological observations leads to a similar preference for normal with respect to inverted mass ordering, namely 270σ This very same cosmological data set provides 2σ upper limits on the total neutrino mass corresponding to Σmν < 012 (015) eV in the normal (inverted) neutrino mass ordering scenario The bounds on the neutrino mixing parameters and masses presented in this up-to-date global fit analysis include all currently available neutrino physics inputs

/pdf/2020-global-reassessment-of-the-neutrino-oscillation-picture-12e52v81dv.pdf

2020 global reassessment of the neutrino oscillation picture

We present a comprehensive review of keV-scale sterile neutrino Dark Matter, collecting views and insights from all disciplines involved - cosmology, astrophysics, nuclear, and particle physics - in each case viewed from both theoretical and experimental/observational perspectives. After reviewing the role of active neutrinos in particle physics, astrophysics, and cosmology, we focus on sterile neutrinos in the context of the Dark Matter puzzle. Here, we first review the physics motivation for sterile neutrino Dark Matter, based on challenges and tensions in purely cold Dark Matter scenarios. We then round out the discussion by critically summarizing all known constraints on sterile neutrino Dark Matter arising from astrophysical observations, laboratory experiments, and theoretical considerations. In this context, we provide a balanced discourse on the possibly positive signal from X-ray observations. Another focus of the paper concerns the construction of particle physics models, aiming to explain how sterile neutrinos of keV-scale masses could arise in concrete settings beyond the Standard Model of elementary particle physics. The paper ends with an extensive review of current and future astrophysical and laboratory searches, highlighting new ideas and their experimental challenges, as well as future perspectives for the discovery of sterile neutrinos.

/pdf/a-white-paper-on-kev-sterile-neutrino-dark-matter-2mp6xfrw9n.pdf

A White Paper on keV Sterile Neutrino Dark Matter

The theory and phenomenology of light sterile neutrinos at the eV mass scale is reviewed. The reactor, gallium and Liquid Scintillator Neutrino Detector anomalies are briefly described and interpreted as indications of the existence of short-baseline oscillations which require the existence of light sterile neutrinos. The global fits of short-baseline oscillation data in 3 + 1 and 3 + 2 schemes are discussed, together with the implications for β-decay and neutrinoless double-β decay. The cosmological effects of light sterile neutrinos are briefly reviewed and the implications of existing cosmological data are discussed. The review concludes with a summary of future perspectives.

http://iopscience.iop.org/article/10.1088/0954-3899/43/3/033001/pdf

Light sterile neutrinos

We present the results of an updated fit of short-baseline neutrino oscillation data in the framework of 3+1 active-sterile neutrino mixing. We first consider ν
 e
 and $$ {\overline{\nu}}_e $$
 disappearance in the light of the Gallium and reactor anomalies. We discuss the implications of the recent measurement of the reactor $$ {\overline{\nu}}_e $$
 spectrum in the NEOS experiment, which shifts the allowed regions of the parameter space towards smaller values of |U
 e4|2. The β-decay constraints of the Mainz and Troitsk experiments allow us to limit the oscillation length between about 2 cm and 7 m at 3σ for neutrinos with an energy of 1 MeV. The corresponding oscillations can be discovered in a model-independent way in ongoing reactor and source experiments by measuring ν
 e
 and $$ {\overline{\nu}}_e $$
 disappearance as a function of distance. We then consider the global fit of the data on short-baseline $$ {}_{\nu_{\mu}}^{\left(-\right)}{\to}_{\nu_e}^{\left(-\right)} $$
 transitions in the light of the LSND anomaly, taking into account the constraints from $$ {}_{\nu_e}^{\left(-\right)} $$
 and $$ {}_{\nu_{\mu}}^{\left(-\right)} $$
 disappearance experiments, including the recent data of the MINOS and IceCube experiments. The combination of the NEOS constraints on |U
 e4|2 and the MINOS and IceCube constraints on |U
 μ4|2 lead to an unacceptable appearance-disappearance tension which becomes tolerable only in a pragmatic fit which neglects the MiniBooNE low-energy anomaly. The minimization of the global χ
 2 in the space of the four mixing parameters Δm
 41
 2
 , |U
 e4|2, |U
 μ4|2, and |U
 τ4|2 leads to three allowed regions with narrow Δm
 41
 2
 widths at Δm
 41
 2
  ≈ 1.7 (best-fit), 1.3 (at 2σ), 2.4 (at 3σ) eV2. The effective amplitude of short-baseline $$ {}_{\nu_{\mu}}^{\left(-\right)}{\to}_{\nu_e}^{\left(-\right)} $$
 oscillations is limited by 0.00048 ≲ sin2 2ϑ
 eμ
 ≲ 0.0020 at 3σ. The restrictions of the allowed regions of the mixing parameters with respect to our previous global fits are mainly due to the NEOS constraints. We present a comparison of the allowed regions of the mixing parameters with the sensitivities of ongoing experiments, which show that it is likely that these experiments will determine in a definitive way if the reactor, Gallium and LSND anomalies are due to active-sterile neutrino oscillations or not.

/pdf/updated-global-3-1-analysis-of-short-baseline-neutrino-32m91nbf9b.pdf

Updated Global 3+1 Analysis of Short-BaseLine Neutrino Oscillations

We performed a search for any sign of an additional neutrino mass state in β-electron spectrum based on data reanalysis of direct electron antineutrino mass measurements in Tritium beta-decay in the Troitsk nu-mass experiment. The existing data set allows us to search for such a state in the mass range up to 100 eV. The lowest value at a 95% C.L. upper limit for the contribution of a heavy eigenstate into electron neutrino is around or less than 1% for masses above 20 eV.

Upper limit on additional neutrino mass eigenstate in 2 to 100 eV region from “Troitsk nu-Mass” data

The results obtained in the Troitsk nu-mass experiment by measuring the electron-antineutrino mass in tritium beta decay are presented. The facility used consists of a gaseous windowless tritium source and an electrostatic electron spectrometer involving an adiabatic magnetic collimation. Runs in which measurement conditions were reliably established were thoroughly selected in analyzing data obtained from 1994 to 2004. All known systematic effects were taken into account. For the square of the electron-antineutrino mass, the treatment of measured spectra yielded the following result: mν2 = −0.67 ± 1.89stat. ± 1.68syst. eV2. The use of the Bayesian method and the Feldman-Cousins unified approach made it possible to obtain the following upper limits on the mass: mν < 2.12 eV (at a 95% C.L.; Bayesian method) and mν < 2.05 eV (at a 95% C.L., Feldman-Cousins method). At the same time, an estimation of the sensitivity limit without allowance for negative values of the square of the mass leads to mν < 2.2 eV (at a 95% C.L.). Measured spectra were analyzed for the possible existence of an additional structure (step) in the electron spectrum near the boundary energy. The conclusion drawn from this analysis was that, within the existing statistical errors, there are no reasons for introducing such a feature.

Measurement of the electron antineutrino mass in tritium beta decay in the Troitsk nu-mass experiment

In this paper we present the details of our previously published results for the search for an additional neutrino mass state in the β-electron spectrum from the Troitsk nu-mass experiment. Here we present the steps of the analysis and show a set of likelihood functions obtained for each additional heavy mass value. We demonstrate how systematic errors were estimated. We also compare our results with those published recently for a similar analysis for Mainz data and try to explain why there is a factor of 2–3 difference in the sensitivity for an additional heavy mass.

The search for an additional neutrino mass eigenstate in the 2–100 eV region from ‘Troitsk nu-mass’ data: a detailed analysis

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Upper limit on additional neutrino mass eigenstate in 2 to 100 eV region from “Troitsk nu-Mass” data

Measurement of the electron antineutrino mass in tritium beta decay in the Troitsk nu-mass experiment

The search for an additional neutrino mass eigenstate in the 2–100 eV region from ‘Troitsk nu-mass’ data: a detailed analysis