In this Technical Design Report (TDR) we describe the NEXT-100 detector that will search for neutrinoless double beta decay (β β 0ν) in 136 Xe at the Laboratorio Subterráneo de Canfranc (LSC), in Spain. The document formalizes the design presented in our Conceptual Design Report (CDR): an electroluminescence time projection chamber, with separate readout planes for calorimetry and tracking, located, respectively, behind cathode and anode. The detector is designed to hold a maximum of about 150 kg of xenon at 15 bar, or 100 kg at 10 bar. This option builds in the capability to increase the total isotope mass by 50% while keeping the operating pressure at a manageable level. The readout plane performing the energy measurement is composed of Hamamatsu R11410-10 photomultipliers, specially designed for operation in low-background, xenon-based detectors. Each individual PMT will be isolated from the gas by an individual, pressure resistant enclosure and will be coupled to the sensitive volume through a sapphire window. The tracking plane consists in an array of Hamamatsu S10362-11-050P MPPCs used as tracking pixels. They will be arranged in square boards holding 64 sensors (8 × 8) with a 1-cm pitch. The inner walls of the TPC, the sapphire windows and the boards holding the MPPCs will be coated with tetraphenyl butadiene (TPB), a wavelength shifter, to improve the light collection.

The Technical Design for the COMET Phase-I experiment is presented in this paper. COMET is an experiment at J-PARC, Japan, which will search for neutrinoless conversion of muons into electrons in the field of an aluminum nucleus ($\mu$–$e$ conversion, $\mu^{-}N \rightarrow e^{-}N$); a lepton flavor-violating process. The experimental sensitivity goal for this process in the Phase-I experiment is $3.1\times10^{-15}$, or 90% upper limit of a branching ratio of $7\times 10^{-15}$, which is a factor of 100 improvement over the existing limit. The expected number of background events is 0.032. To achieve the target sensitivity and background level, the 3.2 kW 8 GeV proton beam from J-PARC will be used. Two types of detectors, CyDet and StrECAL, will be used for detecting the $\mu$–$e$ conversion events, and for measuring the beam-related background events in view of the Phase-II experiment, respectively. Results from simulation on signal and background estimations are also described.

We have measured the pi+-->e+ nugamma branching ratio over a wide region of phase space, based on a total of 65 460 events acquired using the PIBETA detector. Minimum-chi2 fits to the measured (E(e+), E(gamma) energy distributions result in the weak form factor value of F(A)=0.0119(1) with a fixed value of F(V)=0.0259. An unconstrained fit yields F(V)=0.0258(17) and F(A)=0.0117(17). In addition, we have measured a=0.10(6) for the dependence of F(V) on q2, the e+ nu pair invariant mass squared, parametrized as F(V)(q2)=F(V)(0)(1+aq(2)). The branching ratio for the kinematic region E(gamma)>10 MeV and theta(e(+)gamma)>40 degrees is measured to be B(expt)=73.86(54)x10(-8). Earlier deviations we reported in the high-E(gamma)-low-E(e+) kinematic region are resolved without a tensor term. We also derive new values for the pion polarizability alpha(E)=2.78(10)x10(-4) fm3 and neutral pion lifetime tau(pi0)=(8.5+/-1.1)x10(-17) s.

We have studied radiative pion decays π + → e + νγ in three broad kinematic regions using the PIBETA detector and a stopped pion beam. Based on Dalitz distributions of 42,209 events we have evaluated absolute π → eνγ branching ratios in the three regions. Minimum χ 2 fits to the integral and differential (E e + , Eγ ) distributions result in the axial-to-vector weak form factor ratio of γ ≡ FA/FV = 0.443(15), or FA = 0.0115(4) with FV = 0.0259. However, deviations from Standard Model predictions in the high-Eγ/low-E e + kinematic region indicate the need for further theoretical and experimental work.PACS numbers: 11.30. Rd, 13.20.Cz, 14.40.Aq In the Standard Model description of radiative pion decay π + → e + νγ, where γ is a real or virtual photon (e + e − pair), the decay amplitude M depends on the vector V and axial vector A weak hadronic currents [1]. Both currents contribute to the structure-dependent terms SD V and SD A associated with virtual hadronic states, while only the axial-vector current contributes to the inner bremsstrahlung process IB. Thus, it is convenient to write the decay amplitude as a sum:where p, k and q are the pion, electron and photon fourmomenta, respectively, e and m e are the electron charge and mass, G F is the Fermi coupling constant, V ud is the CKM quark mixing matrix element, while f π is the pion decay constant. The structure-dependent amplitude is parameterized by the vector and axial vector form factors, F V and F A :The conserved vector current (CVC) hypothesis [4,5] relates F V to the π 0 lifetime yielding F V = 0.0259(5) [6], which agrees with the relativistic quark model and chiral perturbation theory [7]. Chiral symmetry calculations [7,8,9] yield F A in the range 0.010-0.014.The combined π → eνγ event count of all previously published experiments is less than 1,200 events, while the overall uncertainties of the parameter γ ≡ F A /F V extracted from data range from 12 % to 56 % [10,11,12,13,14,15].In this Letter we present a first analysis of the π + → e + νγ (πe2γ) events recorded with the PIBETA detector in the course of a new measurement of the π + → π 0 e + ν (πβ) branching ratio [16,17] from 1999 to 2001.The measurements were performed in the πE1 channel at the Paul Scherrer Institute (PSI), Villigen, Switzerland. The π + beam with p ≃ 113 MeV/c, ∆p/p ≤ 1.3 %, and 24 mr horizontal and vertical divergence, had an average intensity of 6.8 · 10 5 π + /s, and produced a σ x,y = 9 mm beam spot on target. A total of 2.2 · 10 13 π + stops were recorded during the running period.The beam particles were first registered in a 3 mm thick beam counter (BC) placed ∼395 cm upstream of the detector center. The pions were slowed in a 30 mm thick active degrader (AD) and stopped in a 50 mm long segmented active target detector (AT) positioned in the center of the PIBETA detector. The BC, AD and AT detectors are all made of plastic scintillation material.The e + and µ + beam contaminations determined by the time-of-flight method were small, 0.4 % and 0.2 %, respectively. The bac...

The lowest order radiative corrections to the width and spectra of the radiative e2 decay are calculated. We take into account the virtual photon emission contribution as well as soft and hard real photon emission contributions. The result turns out to be consistent with the standard Drell-Yan picture for the width and spectra in the leading logarithmical approximation which permits us to generalize it to all orders of perturbation theory. Explicit expressions of nonleading contributions are obtained. The contribution of the short distance is found to be in agreement with standard model predictions. It is presented as a general normalization factor. We check the validity of the Kinoshita-Lee-Nauenberg theorem about the cancellation in the total width of the mass singularities at the zero limit of the electron mass. We discuss the results of the previous papers devoted to this problem. The Dalitz plot distribution is illustrated numerically.A rather detailed calculation of the lowest order RC was carried out in Ref. ͓4͔. Nonclear manipulations with a soft