Japan-US seminar on "Double Beta Decay and Neutrinos"

The current status of the Daya Bay reactor antineutrino experiment will be presented.

The Daya Bay reactor neutrino experiment aims to measure $\theta_{13}$, the last unknown neutrino mixing angle, to a precision of $\sin^2(2\theta_{13}) < $0.01$ at the 90\% confidence level. A comprehensive calibration program is essential in order to thoroughly understand detector properties and help achieve the desired sensitivity to $\theta_{13}$. In this talk the author will present the current status of the Daya Bay calibration system and discuss the control and reduction of detector-related systematic uncertainties.

The Daya Bay neutrino oscillation experiment has the greatest sensitivity to the neutrino mixing angle $\sin^2 2\theta_{13}$ of all experiments currently under construction. Our goal is to either determine the size of this mixing angle, or to establish a limit of $\sin^2 2\theta_{13} < $0.01$. The first of 8 anti-neutrino detectors is currently being assembled. The detector status and testing program will be presented.

Muon system is important for background rejection for Daya Bay experiment. An overview of the two muon identification systems, the water Cherenkov detector and RPC, will be presented.

Double Chooz is a reactor neutrino oscillation experiment for measuring precisely a neutrino mixing angle of theta_13. Now we are constructing the far detector at Chooz reactor site for starting to measure neutrinos from the reactor core from April in 2010. In this workshop, we report the outline and current status of Double Chooz experiment.

Neutrino oscillation experiments are strongly related to the double beta decay experiments since measured oscillation parameters strongly limit the parameter space of DBD experiments and give it a clear next target. Also NO experiments and DBD experiments are complementary when determining the absolute flavor transition amplitudes of the neutrinos. In this talk, I will describe about future potential of reactor neutrino experiments.

CUORICINO, an experiment searching for neutrinoless double beta decay of $^{130}$Te, collected data between 2003 and 2008 in the underground Gran Sasso National Laboratory in Italy. An observation of neutrinoless double beta decay would establish that neutrinos are Majorana fermions identical to their antiparticles and would constrain the absolute neutrino masses. The CUORICINO detector utilized 62 crystals of TeO$_2$ arranged in a tower-like structure inside a cryostat and cooled to $\sim$8~mK. The detector achieved an excellent energy resolution of $\sim$8~keV FWHM at 2.6~MeV using a bolometric technique whereby the energy deposited in the detector by a radioactive decay was measured via the induced temperature rise. Most of the crystals were made from natural tellurium, which has 33.8\% isotopic abundance of $^{130}$Te!23$ two crystals were enriched in $^{130}$Te, and two were enriched in $^{128}$Te. The total mass of TeO$_2$ was 40.7~kg. In this talk I will discuss the analysis of the complete CUORICINO data set and present an updated limit on the neutrinoless double beta decay half-life of $^{130}$Te, as well as the corresponding limit on the effective Majorana neutrino mass.

CUORE, the Cryogenic Underground Observatory for Rare Events, is a next-generation experiment to search for neutrinoless double beta-decay in $^{130}$Te. Using an array of 988 TeO$_{2}$ crystals at 10~mK with a total mass of $^{130}$Te of 204~kg, CUORE will search for an excess of events above background near the Q-value of 2530~keV and probe the effective neutrino mass with a sensitivity of a few tens of meV. A precise measurement of the event energy with the bolometer array is crucial for the identification of candidate double beta-decay events. A novel, low temperature calibration system with ultra-low background is being developed to perform a precise calibration of the energy response of each of the 988 TeO$_{2}$ crystals in the CUORE bolometer array. We present the design, development, and expected performance of this low-temperature calibration system.

The CUORICINO experiment was designed to search for neutrinoless double beta decay and other rare processes, including double beta decay with two neutrinos (2nuDBD). It consisted of an array of 62 TeO2 crystals operated as cryogenic bolometers. The array included four enriched crystals, two with Te-130 and two with Te-128, to aid in the measurement of the 2nuDBD rate. I will discuss an analysis of the CUORICINO data using the enriched crystals to measure the ground-state-to-ground-state 2nuDBD rate in Te-130.

The understanding of nuclear matrix elements of two-neutrino double-beta decay is important since it helps to establish reliable predictions of the nuclear matrix element of neutrino-less double-beta decay. The nuclear matrix element of two-neutorino mode is described by successive virtual Gamow-Teller (GT) transitions from the mother nucleus to the intermediate nucleus, and then from the intermediate to the daughter nucleus. Therefore the GT strength (B(GT)) distributions, which can be obtained from the charge exchange reactions provide a useful constraint for the theoretical models. The B(GT) distributions of double-beta-decay nuclei, 116Cd and 48Ca, have been studied by the 116Cd(p,n) /116Sn(n,p) and 48Ca(p,n) / 48Ti(n,p) measurements at Research Center for Nuclear Physics, Osaka University. It has been found that for the present theoretical calculations underestimate the GT strength especially in the continuum in the (n,p) channel, which suggests that thecontribution of the GT giant resonance region is underestimated.

Calcium isotopes were actually fluctuated by using dicyclohexano-18-crown-6 and the advantage of our chemical exchange method is verified not only for an ion separation, but also for an isotope separation. Compared with chromatographic method using benzo-18-crown-6 resin, a large separation factor is expected for the direct liquid-liquid extraction, since the absorption of calcium depends on the concentration of 'additional' hydrochloric acid in solution for the solid-liquid case.

Bolometers are ideally detectors for DBD searches!59# they can investigate several interesting nuclei and, key point for future experiments, they show an intrinsic energy resolution that makes the 2-neutrino induced background completely negligible. Nevertheless this kind of detectors show a large background in the region of interest arising from alfa-emitters close to the surfaces.
This background can be easy identified in case of a scintillating bolometer in which the light signal is contemporarily measured. Choosing a double beta emitter with a transition energy above 2615 keV and neglecting the alfa-induced events, the background that can be obtained (in the region of interest) can reach levels of the order of 0.1-0.01 c/keV/ton/y, i.e. 2-3 orders of magnitude smaller with respect to the expected background of the CUORE Experiment. Results obtained on Cd, Se and Mo based scintillating bolometers will be presented.

Double beta experiment using current nuclear emulsion technology;Nuclear Emulsion is a three dimensional tracking detector with submicron position resolution. Beta tracks can be traced and the energy can be measured by measuring the grain information along the tracks. Until today the main motive force to develop this technology is the study of neutrino oscillations. A large scale experiment, OPERA, using 110000 m^2 emulsion films, is going on. In this talk, the current emulsion technology developped for OPERA will be presented and show the possibility to utilize this tecnology to a large scale double beta experiment.

The performance and the advantages of thin NaI(Tl) scinttilator is discussed. A thin (1~5mm thickness) and wide area (15cm~18cm square) NaI(Tl) scintillator has been applied to double beta decay measurement and dark matter seach. The energy resolution and the energy threshold were reported that they were enough good for both double beta decay and dark matter search. Future prospects of thin NaI(Tl) array for nuclear and particle rare processes will be discussed.

Developments towards a gaseous Xenon Time Projection Chamber for Neutrino-less Double Beta Decay;A High-Pressure Gaseous Xenon TPC can provide excellent energy resolution (less than 1% FWHM at Q-value) along with tracking and fiducialization information. In this talk, we will present recent developments of prototype detectors using gaseous Xenon as well as plans for the development of a ton scale experiment.

The observation of neutrinoless double beta decay, at any nonzero level, would imply that lepton number is not conserved, that neutrinos have Majorana masses, and that neutrinos are their own antiparticles. Majorana neutrino masses are physics far outside the Standard Model. Their existence would be evidence in favor of the see-saw model of the origin of neutrino mass, and evidence in favor of leptogenesis as the explanation of the baryon-antibaryon asymmetry of the universe. This talk will explain the physics of neutrinoless double beta decay, discuss what the observation of this process would teach us, and examine the nature of neutrinos that are their own antiparticles.

CANDLES is the project to search for double beta decay (DBD) of $^{48}$Ca by using CaF$_2$ scintillators. The $Q$-value of $^{48}$Ca, which is the highest (4.27~MeV) among potential DBD nuclei, is far above energies of $\gamma$-rays from natural radioactivities (maximum 2.615~MeV from $^{208}$Tl decay), therefore we can naturally expect small backgrounds in the energy region we are interested in. We gave the best lower limit on the half-life of neutrino-less double beta decay of $^{48}$Ca by using CaF$_2$(Eu) detector system, ELEGANT VI though further development is highly desirable to reach the mass region of current interest. We have constructed the prototype detector, CANDLES III in our laboratory (Osaka U.) at sea level and studied the basic performance of the system, including the light collection, position reconstruction and background rejection. We are now moving the detector system to new experimental room (room D) at Kamioka underground laboratory (2700~m.w.e.) to avoid large background originated from cosmic rays. At the same time, we are increasing the total mass of the $^{48}$Ca compared to the one in the prototype detector. 96 (instead of 60 in prototype) CaF$_2$ modules which contains 350~g of $^{48}$Ca are immersed in a liquid scintillator (LS) which acts as an active veto (veto phase). The conversion phase contains wavelength shifter (Bis-MSB) which converts the emission light of CaF$_2$(pure) which has a peak in the UV region to the visible one where the quantum efficiency of the PMTs is high enough (maximum at $\sim400$~nm) and materials at the optical path have good transparencies. Scintillation lights from both the CaF$_2$ modules and the liquid scintillator in veto phase are viewed by large PMTs ($48 \times 13$'' and $14 \times 17$'' tubes). All the detector system described above are contained in a water tank which is 3~m in diameter and 4~m in height. The water tank and a purification system of the LS together with LS storage tanks were installed at room D. The purification system of the LS removes the radioactive impurities especially U and Th using the techniques of water-extraction and N$_2$ purge. Other components including the CaF$_2$ modules, the PMTs, the liquid scintillator vessel and DAQ system will be installed soon.

EXO is a program to develop and operate large neutrino-less double-beta decay experiments and measure Majorana neutrino masses with an ultimate sensitivity below 10 meV. In this talk I will survey the different activities in progress, including the status of the EXO-200 detector that is approaching data taking and the R\&D on Ba tagging and on large detectors in gaseous phase. The talk is given on behalf of the EXO collaboration including scientists from Canada, Russia, Switzerland and the US.

There is, presently, strong evidence from recent neutrino experiments that neutrinos undergo flavor oscillations, and hence must have finite masses. The oscillation results can provide differences between squares of neutrino mass eigenvalues, but cannot determine the absolute mass scale nor its origin. So far only neutrinoless double beta(0$\nu\beta\beta$) decay measurement offers a realistic opportunity to establish the Majorana nature of neutrinos and give the absolute scale of the effective neutrino mass. Global analyses of the oscillation results imply the effective neutrino mass could have a minimum value as large as a few tens of meV for the inverted hierarchy of the neutrino mass spectrum. Next generation 0$\nu\beta\beta$ decay experiments are currently proposed to achieve such mass sensitivity. The KamLAND detector is located in the Kamioka mine, and is filled with 1,000 tons of liquid scintillator. The detector is very sensitive to low energy neutrinos from nuclear reactors and the Earth. We are currently working on reducing backgrounds in the KamLAND to detect very low energy solar neutrinos produced by the $^7$Be reaction in the Sun. We have proposed upgrading the KamLAND detector into a huge 0$\nu\beta\beta$ decay experiment by adding $^136$Xe to the detector volume. Since the sensitivity of the 0$\nu\beta\beta$ experiment is determined by the available source amount and the background rate, the KamLND detector is suitable for this purpose. We mainly present the currect status of the development for upgrading the KamLAND detector toward the 0$\nu\beta\beta$ decay experimnt.

Observation of exotic neutrinoless double-beta decays would indicate that neutrinos are Majorana particles. The rate of the process is sensitive to the effective neutrino mass. Cryogenic Underground Observatory for Rare Events (CUORE), a next-generation large-scale double-beta decay experiment, is currently under construction at the Gran Sasso National Laboratory (LNGS) in Italy. It will be sensitive to the neutrino mass values suggested by recent atmospheric neutrino oscillation experiments in the so-called inverted mass hierarchy. We will review the status of the R\&D and construction efforts and the prospects for the double-beta decay and other measurements with CUORE.

SNO+ is the follow-up experiment to the Sudbury Neutrino Observatory with liquid scintillator replacing the heavy water. The experiment will detect lower energy solar neutrinos, including the pep and CNO solar neutrinos, and geo and reactor antineutrinos. In addition, SNO+ plans to deploy neodymium in the liquid scintillator to conduct a neutrinoless double beta decay search. Status and plans will be presented.

The problem of determination of the nature - Dirac or Majorana, of massive neutrinos is discussed. The physics potential of experiments, searching for $\beta\beta-$decay, for providing information on the type of $\nu$-mass spectrum, absolute scale of $\nu$- masses and on the Majorana phases in the PMNS neutrino mixing matrix $U$, is reviewed. The possibility that the CP-violation necessary for the generation of the baryon asymmetry of the Universe is due exclusively to the Majorana CP-violating phase(s) in the PMNS neutrino mixing matrix $U$, is also briefly discussed.

The {\sc Majorana} collaboration aims to perform a search for neutrinoless double-beta decay (0$\nu\beta\beta$) by fielding arrays of HPGe detectors mounted in ultra-clean electroformed-copper cryostats located deep underground. Recent advances in HPGe detector technology, in particular P-type Point-Contact (PPC) detectors, show great promise for identifying and reducing backgrounds to the 0$\nu\beta\beta$ signal, which should result in improved sensitivity over previous generation experiments. The ultra-low energy threshold possible in PPC detectors also enables a broader physics program including sensitive searches for dark matter and axions. The {\sc Majorana Demonstrator} R\&D program will field three $\sim$20~kg modules of PPC detectors at Sanford Underground Laboratory. Half of the detector mass will be enriched to 86\% in $^{76}$Ge. I will present the motivation, design, recent progress and current status of this R\&D effort, and discuss its physics reach.

NEMO 3 is a double beta decay experiment operating in the Laboratoire de Souterraine de Modane (LSM). We will present the latest results of the neutrinoless double beta decays of 7kg of $^{100}$Mo and 1kg of $^{82}$Se, as well as two neutrino double beta decays of various isotopes in the NEMO 3 experiment with the highest precision measurements. The SuperNEMO project is being designed to the next step of the NEMO 3 double beta decay experiment. We will present the current status of the project.

Momentum analyzers called DCBA (Drift Chamber Beta-ray Analyzer) are being developed at KEK in order to study neutrinoless double-beta decay. DCBA consists of drift chambers interleaving thin decay-source plates and a solenoid magnet serving a uniform magnetic field. The momentum of individual beta-ray is measured from the helical track reconstructed in three dimension. Then its kinetic energy is calculable. As for backgrounds, pair creation events are easily rejected by electric charges in the magnetic field. Alpha particles have so large momenta that they don't make helical tracks. Since the vertex point of a double beta-decay event is clearly identified, a single electron track is easily eliminated, and double Compton scatterings are also identified. A prototype called DCBA-T2 had been operated, and the energy resolution of about 150 keV (FWHM) was obtained for 976 keV electrons, which were the internal conversion electrons from Bi-207. The DCBA-T2 has been in engineering run using natural Mo plates of 45 mg/cm2 thickness to check comprehensive capabilities. New prototype DCBA-T3 is now under construction to improve the energy resolution and to increase the source amount accommodated in drift chambers. The main different points from DCBA-T2 are the pitches of signal wires, which are changed from 6 mm to 3 mm, and the strength of magnetic field, which is done from 0.8 kG to 3 kG maximum. In order to improve the energy resolution with the reduction of the multiple scattering of electron in chamber gas, a stronger magnetic field is produced by a super-conducting solenoid. It makes the helical track radius smaller, and then smaller pitches of signal wires are required to obtain enough sampling point data on the helical track. A detector module temporarily named Magnetic Tracking Detector (MTD) has been designed on the basis of DCBA in order to search for Majorana neutrino mass down to 50 meV. Status of DCBA-T2 and T3 will be presented together with the future project of MTD.

The study of neutrinoless double beta decay (DBD) is the most powerful approach to the fundamental question if the neutrino is a Majorana particle, i.e. its own anti-particle. The observation of neutrinoless DBD would not only establish the Majorana nature of the neutrino but also represent a determination of its effective mass if the nuclear matrix element is given. So far, the most sensitive results have been obtained with Ge-76, and the group of Klapdor-Kleingrothaus has made a claim of discovery. Future experiments have to reduce radioactive backgrounds to increase the sensitivity. The GERmanium Detector Array ``GERDA'' [1] is a new double beta-decay experiment which is currently under construction in the INFN Gran Sasso National Laboratory, Italy. It is implementing a new shielding concept by operating bare Ge diodes---enriched in Ge-76---in high purity liquid argon supplemented by a water shield. The aim of ``GERDA'' is to verify or refute the recent claim of discovery, and, in a second phase, to achieve a two orders of magnitude lower background index than recent experiments. The paper will discuss design, physics reach, and status of construction of ``GERDA,'' and present results from various R\&D efforts including long term stability of bare Ge diodes in cryogenic liquids, material screening, cryostat performance, design and production of enriched Ge diodes, cryogenic precision electronics, safety aspects, and Monte Carlo simulations.\\[4pt] [1] http://www.mpi-hd.mpg.de/GERDA/