Investigation of double beta decay with the NEMO-3 detector

The double beta decay experiment NEMO~3 has been taking data since February 2003. The aim of this experiment is to search for neutrinoless ($0\nu\beta\beta$) decay and investigate two neutrino double beta decay in seven different isotopically enriched samples ($^{100}$Mo, $^{82}$Se, $^{48}$Ca, $^{96}$Zr, $^{116}$Cd, $^{130}$Te and $^{150}$Nd). After analysis of the data corresponding to 3.75 y, no evidence for $0\nu\beta\beta$ decay in the $^{100}$Mo and $^{82}$Se samples was found. The half-life limits at the 90% C.L. are $1.1\cdot 10^{24}$ y and $3.6\cdot 10^{23}$ y, respectively. Additionally for $0\nu\beta\beta$ decay the following limits at the 90% C.L. were obtained, $> 1.3 \cdot 10^{22}$ y for $^{48}$Ca, $> 9.2 \cdot 10^{21}$ y for $^{96}$Zr and $> 1.8 \cdot 10^{22}$ y for $^{150}$Nd. The $2\nu\beta\beta$ decay half-life values were precisely measured for all investigated isotopes.Comment: 12 pages, 4 figures, 5 tables; talk at conference on "Fundamental Interactions Physics" (ITEP, Moscow, November 23-27, 2009

On the Quantitative Impact of the Schechter-Valle Theorem

We evaluate the Schechter-Valle (Black Box) theorem quantitatively by considering the most general Lorentz invariant Lagrangian consisting of point-like operators for neutrinoless double beta decay. It is well known that the Black Box operators induce Majorana neutrino masses at four-loop level. This warrants the statement that an observation of neutrinoless double beta decay guarantees the Majorana nature of neutrinos. We calculate these radiatively generated masses and find that they are many orders of magnitude smaller than the observed neutrino masses and splittings. Thus, some lepton number violating New Physics (which may at tree-level not be related to neutrino masses) may induce Black Box operators which can explain an observed rate of neutrinoless double beta decay. Although these operators guarantee finite Majorana neutrino masses, the smallness of the Black Box contributions implies that other neutrino mass terms (Dirac or Majorana) must exist. If neutrino masses have a significant Majorana contribution then this will become the dominant part of the Black Box operator. However, neutrinos might also be predominantly Dirac particles, while other lepton number violating New Physics dominates neutrinoless double beta decay. Translating an observed rate of neutrinoless double beta decay into neutrino masses would then be completely misleading. Although the principal statement of the Schechter-Valle theorem remains valid, we conclude that the Black Box diagram itself generates radiatively only mass terms which are many orders of magnitude too small to explain neutrino masses. Therefore, other operators must give the leading contributions to neutrino masses, which could be of Dirac or Majorana nature.Comment: 18 pages, 4 figures; v2: minor corrections, reference added, matches journal version; v3: typo corrected, physics result and conclusions unchange

Probing New Physics Models of Neutrinoless Double Beta Decay with SuperNEMO

The possibility to probe new physics scenarios of light Majorana neutrino exchange and right-handed currents at the planned next generation neutrinoless double beta decay experiment SuperNEMO is discussed. Its ability to study different isotopes and track the outgoing electrons provides the means to discriminate different underlying mechanisms for the neutrinoless double beta decay by measuring the decay half-life and the electron angular and energy distributions.Comment: 17 pages, 14 figures, to be published in E.P.J.

Spectral modeling of scintillator for the NEMO-3 and SuperNEMO detectors

We have constructed a GEANT4-based detailed software model of photon transport in plastic scintillator blocks and have used it to study the NEMO-3 and SuperNEMO calorimeters employed in experiments designed to search for neutrinoless double beta decay. We compare our simulations to measurements using conversion electrons from a calibration source of $\rm ^{207}Bi$ and show that the agreement is improved if wavelength-dependent properties of the calorimeter are taken into account. In this article, we briefly describe our modeling approach and results of our studies.Comment: 16 pages, 10 figure

Results of the BiPo-1 prototype for radiopurity measurements for the SuperNEMO double beta decay source foils

The development of BiPo detectors is dedicated to the measurement of extremely high radiopurity in $^{208}$Tl and $^{214}$Bi for the SuperNEMO double beta decay source foils. A modular prototype, called BiPo-1, with 0.8 $m^2$ of sensitive surface area, has been running in the Modane Underground Laboratory since February, 2008. The goal of BiPo-1 is to measure the different components of the background and in particular the surface radiopurity of the plastic scintillators that make up the detector. The first phase of data collection has been dedicated to the measurement of the radiopurity in $^{208}$Tl. After more than one year of background measurement, a surface activity of the scintillators of $\mathcal{A}$($^{208}$Tl) $=$ 1.5 $\mu$Bq/m$^2$ is reported here. Given this level of background, a larger BiPo detector having 12 m$^2$ of active surface area, is able to qualify the radiopurity of the SuperNEMO selenium double beta decay foils with the required sensitivity of $\mathcal{A}$($^{208}$Tl) $<$ 2 $\mu$Bq/kg (90% C.L.) with a six month measurement.Comment: 24 pages, submitted to N.I.M.

Experimental study of the atmospheric neutrino backgrounds for p→e+π0 searches in water Cherenkov detectors

The atmospheric neutrino background for proton decay via p→e+π0 in ring imaging water Cherenkov detectors is studied with an artificial accelerator neutrino beam for the first time. In total, 3.14×105 neutrino events corresponding to about 10 megaton-years of atmospheric neutrino interactions were collected by a 1000 ton water Cherenkov detector (KT). The KT charged-current single π0 production data are well reproduced by simulation programs of neutrino and secondary hadronic interactions used in the Super-Kamiokande (SK) proton decay search. The obtained p→e+π0 background rate by the KT data for SK from the atmospheric neutrinos whose energies are below 3 GeV is 1.63-0.33+0.42(stat)-0.51+0.45(syst)(megaton-year)- 1. This result is also relevant to possible future, megaton-scale water Cherenkov detectors. © 2008 The American Physical Society

Measurement of inclusive π0 production in the charged-current interactions of neutrinos in a 1.3-GeV wide band beam

In this paper, we report on the measurement of the rate of inclusive π0 production induced by charged-current neutrino interactions in a C 8H8 target at a mean energy of 1.3 GeV in the K2K near detector. Out of a sample of 11606 charged-current neutrino interactions, we select 479 π0 events with two reconstructed photons. We find that the cross section for the inclusive π0 production relative to the charged-current quasielastic cross section is σCCπ0σCCQE=0. 426±0.032(stat)±0.035(syst). The energy-dependent cross section ratio is also measured. The results are consistent with previous experiments for exclusive channels on different targets. © 2011 American Physical Society

Measurement of single charged pion production in the charged-current interactions of neutrinos in a 1.3GeV wide band beam

Single charged pion production in charged-current muon neutrino interactions with carbon is studied using data collected in the K2K long-baseline neutrino experiment. The mean energy of the incident muon neutrinos is 1.3 GeV. The data used in this analysis are mainly from a fully active scintillator detector, SciBar. The cross section for single π+ production in the resonance region (W\u3c2GeV/c2) relative to the charged-current quasielastic cross section is found to be 0.734-0.153+0.140. The energy-dependent cross section ratio is also measured. The results are consistent with a previous experiment and the prediction of our model. © 2008 The American Physical Society

Neutrinoless double beta decay in seesaw models

We study the general phenomenology of neutrinoless double beta decay in seesaw models. In particular, we focus on the dependence of the neutrinoless double beta decay rate on the mass of the extra states introduced to account for the Majorana masses of light neutrinos. For this purpose, we compute the nuclear matrix elements as functions of the mass of the mediating fermions and estimate the associated uncertainties. We then discuss what can be inferred on the seesaw model parameters in the different mass regimes and clarify how the contribution of the light neutrinos should always be taken into account when deriving bounds on the extra parameters. Conversely, the extra states can also have a significant impact, cancelling the Standard Model neutrino contribution for masses lighter than the nuclear scale and leading to vanishing neutrinoless double beta decay amplitudes even if neutrinos are Majorana particles. We also discuss how seesaw models could reconcile large rates of neutrinoless double beta decay with more stringent cosmological bounds on neutrino masses.Comment: 34 pages, 5 eps figures and 1 axodraw figure. Final version published in JHEP. NME results available in Appendi

Evidence for muon neutrino oscillation in an accelerator-based experiment

We present results for νμ oscillation in the KEK to Kamioka (K2K) long-baseline neutrino oscillation experiment. K2K uses an accelerator-produced νμ beam with a mean energy of 1.3 GeV directed at the Super-Kamiokande detector. We observed the energy-dependent disappearance of vmu;, which we presume have oscillated to ντ. The probability that we would observe these results if there is no neutrino oscillation is 0.0050% (4.0σ). © 2005 The American Physical Society