The theoretical and experimental issues relevant to neutrinoless double beta decay are reviewed. The impact that a direct observation of this exotic process would have on elementary particle physics, nuclear physics, astrophysics, and cosmology is profound. Now that neutrinos are known to have mass and experiments are becoming more sensitive, even the nonobservation of neutrinoless double beta decay will be useful. If the process is actually observed, we will immediately learn much about the neutrino. The status and discovery potential of proposed experiments are reviewed in this context, with significant emphasis on proposals favored by recent panel reviews. The importance of and challenges in the calculation of nuclear matrix elements that govern the decay are considered in detail. The increasing sensitivity of experiments and improvements in nuclear theory make the future exciting for this field at the interface of nuclear and particle physics.

/pdf/double-beta-decay-majorana-neutrinos-and-neutrino-mass-2tfhqvhys8.pdf

Double Beta Decay, Majorana Neutrinos, and Neutrino Mass

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.

This paper reports on the improved Mainz experiment on tritium $\beta$
 spectroscopy which yields a 10 times higher signal to background ratio than before. The main experimental effects and systematic uncertainties have been investigated in side experiments, and possible error sources have been eliminated. Extensive data taking took place in the years 1997 to 2001. A residual analysis of the data sets yields for the square of the electron antineutrino mass the final result of $m^2(\nu_e) = (-0.6 \pm 2.2_{\mathrm{{stat}}} \pm 2.1_{\mathrm{{syst}}})$
 eV2/c4. We derive an upper limit of $m(\nu_e)\leq 2.3$
 eV/c2 at 95% confidence level for the mass itself.

Final results from phase II of the Mainz neutrino mass searchin tritium ${\beta}$ decay

We present a weak-lensing mass reconstruction of the interacting cluster 1E 0657-558, in which we detect both the main cluster and a subcluster. The subcluster is identified as a smaller cluster that has just undergone initial infall and pass-through of the primary cluster and has been previously identified in both optical surveys and X-ray studies. The X-ray gas has been separated from the galaxies by ram pressure-stripping during the pass-through. The detected mass peak is located between the X-ray peak and galaxy concentration, although the position is consistent with the galaxy centroid within the errors of the mass reconstruction. We find that the mass peak for the main cluster is in good spatial agreement with the cluster galaxies and is offset from the X-ray halo at 3.4 σ significance, and we determine that the mass-to-light ratios of the two components are consistent with those of relaxed clusters. The observed offsets of the lensing mass peaks from the peaks of the dominant visible mass component (the X-ray gas) directly demonstrate the presence, and dominance, of dark matter in this cluster. This proof of dark matter existence holds true even under the assumption of modified Newtonian dynamics (MOND); based on the observed gravitational shear-optical light ratios and the mass peak-X-ray gas offsets, the dark matter component in a MOND regime would have a total mass that is at least equal to the baryonic mass of the system.

https://iopscience.iop.org/article/10.1086/381970/pdf

Weak-lensing mass reconstruction of the interacting cluster 1E 0657-558: Direct evidence for the existence of dark matter

I review the current status of phenomenological programs inspired by quantum-spacetime research. I stress in particular the significance of results establishing that certain data analyses provide sensitivity to effects introduced genuinely at the Planck scale. My main focus is on phenomenological programs that affect the directions taken by studies of quantum-spacetime theories.

https://link.springer.com/content/pdf/10.12942%2Flrr-2013-5.pdf

Quantum-Spacetime Phenomenology

An electron antineutrino mass has been measured in tritium $\ensuremath{\beta}$ decay in the Troitsk $\ensuremath{\nu}$-mass experiment. The setup consists of a windowless gaseous tritium source and an electrostatic electron spectrometer. The whole data set acquired from 1994 to 2004 was reanalyzed. A thorough selection of data with the reliable experimental conditions has been performed. We checked every known systematic effect and obtained the following experimental estimate for neutrino mass squared ${m}_{\ensuremath{\nu}}^{2}=\ensuremath{-}0.67\ifmmode\pm\else\textpm\fi{}2.53\text{ }\text{ }{\mathrm{eV}}^{2}$. This gives an experimental upper sensitivity limit of ${m}_{\ensuremath{\nu}}l2.2\text{ }\text{ }\mathrm{eV}$, 95% C.L. and upper limit estimates ${m}_{\ensuremath{\nu}}l2.12\text{ }\text{ }\mathrm{eV}$, 95% C.L. for Bayesian statistics and ${m}_{\ensuremath{\nu}}l2.05\text{ }\text{ }\mathrm{eV}$, 95% C.L. for the Feldman and Cousins approach.

Upper limit on the electron antineutrino mass from the Troitsk experiment

Direct search for mass of neutrino and anomaly in the tritium beta-spectrum

Results of the “Troitsk ν-mass” experiment on search for the neutrino rest mass in the tritium beta-decay are presented. New data on the time dependence of the anomalous, bump-like structure at the end of the beta spectrum reported earlier are discussed. Possible systematics is considered in view of contradiction of “Troitsk nu-mass” observation with those of “Mainz neutrino” set-up. An upper limit for electron antineutrino rest mass remains at m ν 2.5eV c 2 at 95% C.L.

Direct search for neutrino mass and anomaly in the tritium beta-spectrum: Status of “Troitsk neutrino mass” experiment

Measurements of the energy loss of fast electrons at an energy of 18 keV have been performed on molecules of hydrogen isotopes, gaseous T

 2
 and frozen D

 2
 . Whereas in the case of gaseous T

 2
 the values of total inelastic cross-section (
 cm2 for E
 = 18.6 keV), average energy loss (
 eV) and peak position of the energy loss spectra (
 eV) agree well with the expectations, the corresponding values for quench condensed D

 2
 differ significantly from the ones for gaseous T

 2
 . We observe a significant lower total inelastic cross-section (
 cm2, for E
 = 18.6 keV) larger average energy loss (
 eV) and higher peak position (
 eV). These differences may be interpreted in terms of changes of the final state spectrum. A CI calculation for a D

 2
 cluster shows indeed a clear shift of the excited states in agreement with the observation.

Energy loss of 18 keV electrons in gaseous T  and quench condensed D  films

Results of the “Troitsk ν-mass” experiment on the search for the neutrino rest mass in the tritium beta-decay are presented. Study of time dependence of anomalious, bump-like structure at the end of beta spectrum reported earlier gives indication of periodic shift of the position of the bump with respect to end-point energy with period of 0.5 year. New upper limit for electron antineutrino rest mass m ν eV c 2 is derived after accounting for the bump.

/pdf/direct-search-for-mass-of-neutrino-and-anomaly-in-the-1zdk21p1vd.pdf

V. N. Aseev

Papers

Upper limit on the electron antineutrino mass from the Troitsk experiment

Direct search for mass of neutrino and anomaly in the tritium beta-spectrum

Direct search for neutrino mass and anomaly in the tritium beta-spectrum: Status of “Troitsk neutrino mass” experiment

Energy loss of 18 keV electrons in gaseous T \(\) and quench condensed D \(\) films

Direct search for mass of neutrino and anomaly in the tritium beta-spectrum