Search

The rare decay $K_L \!\to\! \pi^0 \nu \overline{\nu}$ was studied with the dataset taken at the J-PARC KOTO experiment in 2016, 2017, and 2018. With a single event sensitivity of $( 7.20 \pm 0.05_{\rm stat} \pm 0.66_{\rm syst} ) \times 10^{-10}$, three candidate events were observed in the signal region. After unveiling them, contaminations from $K^{\pm}$ and scattered $K_L$ decays were studied, and the total number of background events was estimated to be $1.22 \pm 0.26$. We conclude that the number of observed events is statistically consistent with the background expectation. For this dataset, we set an upper limit of $4.9 \times 10^{-9}$ on the branching fraction of $K_L \!\to\! \pi^0 \nu \overline{\nu}$ at the 90% confidence level.

The three body pion decays π+→l+νX(l=e,μ), where X is a weakly interacting neutral boson, were searched for using the full data set from the PIENU experiment. An improved limit on Γ(π+→e+νX)/Γ(π+→μ+νμ) in the mass range 0

International audience; In the present work of the PIENU experiment, heavy neutrinos were sought in pion decays \(\pi ^{ + } \to \mu ^{ + }\nu \). No evidence for extra peak was found in the muon kinetic energy spectrum and 90% confidence level upper limits were set on the neutrino mixing matrix \(|U_{\mu i}|^{2}\) in the mass range of 15.7 to 33.8 MeV/c^2, improving an order of magnitude over previous experiments. Current status of lepton universality test is also reported.

We report the first search for the KL→π0γ decay, which is forbidden by Lorentz invariance, using the data from 2016 to 2018 at the J-PARC KOTO experiment. With a single event sensitivity of (7.1±0.3stat±1.6syst)×10−8, no candidate event was observed in the signal region. The upper limit on the branching fraction was set to be 1.7×10−7 at the 90% confidence level.

In the present work of the PIENU experiment, heavy neutrinos were sought in pion decays pi(+) -> mu(+)nu at rest by examining the observed muon energy spectrum for extra peaks in addition to the expected peak for a light neutrino. No evidence for heavy neutrinos was observed. Upper limits were set on the neutrino mixing matrix vertical bar U-mu i vertical bar(2) in the neutrino mass region of 15.7-33.8 MeV/c(2), improving on previous results by an order of magnitude. (C) 2019 The Authors. Published by Elsevier B.V.

A search for the rare decay K_{L}→π^{0}νν[over ¯] was performed. With the data collected in 2015, corresponding to 2.2×10^{19} protons on target, a single event sensitivity of (1.30±0.01_{stat}±0.14_{syst})×10^{-9} was achieved and no candidate events were observed. We set an upper limit of 3.0×10^{-9} for the branching fraction of K_{L}→π^{0}νν[over ¯] at the 90% confidence level (C.L.), which improved the previous limit by almost an order of magnitude. An upper limit for K_{L}→π^{0}X^{0} was also set as 2.4×10^{-9} at the 90% C.L., where X^{0} is an invisible boson with a mass of 135 MeV/c^{2}.

A pulse shape difference between photons and neutrons was observed in the output signals of scintillation light from the un-doped CsI calorimeter of the KOTO experiment for the K L → π 0 ν ν decay. We developed a discrimination method to reject neutrons and to accept photons in the deposited energy range from 0.1 to 2 GeV. The method rejects 67% of neutron-induced single hadronic clusters and 86% of neutron-induced two-cluster events while keeping more than 90% of photon-induced single electromagnetic clusters and two-photon events.

An electromagnetic calorimeter made of undoped CsI crystals is used in the J-PARC KOTO experiment to search for new physics beyond the standard model with the K L → π 0 ν ν decay. The calorimeter is designed to operate in vacuum of 0.1 Pa and in a high-rate environment where the counting rate due to K L decays is O ( 100 ) kHz. A special method to calibrate the calorimeter during the data taking without using a tracking system for charged particles is reported. The energy, position, and timing resolutions of the calorimeter were evaluated in several beam tests, and the resolutions satisfy the required performance. The energy resolution with the total energy E is 0 . 66 ⊕ 1 . 81 ∕ E [ GeV ] % in the inner region of the calorimeter.

The J-PARC KOTO experiment aims to explore new physics beyond the Standard Model through the K L → π 0 ν ν ¯ decay. We installed a new photon-veto detector, named the Inner Barrel (IB), to improve the detection efficiency and the timing resolution for photons in the region transverse to the neutral beam. The IB is a 2.8-m-long cylindrical detector with a 1.5 m inner diameter. The IB is a lead-scintillator sampling shower counter with a 5-radiation-length thickness and with a low mass support structure, and fits inside the 14-radiation-length-thick cylindrical detector. Scintillating light is read out from both ends via wavelength shifting fibers with a short decay time. The design, construction and performance of the IB are presented in this paper.

The tensor analyzing power Γ20 in elastic electron-deuteron scattering has been measured in the four momentum transfer region between 1.4 and 3.2 fm~l using the Internal Target Facility at NIKHEF. Tensor-polarized deuterium is produced in an Atomic Beam Source and injected into a storage cell. Scattered electrons and recoil deuterons were detected in coincidence with two large acceptance nonmagnetic detectors.

A search for massive neutrinos has been made in the decay π+→e+ν. No evidence was found for extra peaks in the positron energy spectrum indicative of pion decays involving massive neutrinos (π→e+νh). Upper limits (90% C.L.) on the neutrino mixing matrix element |Uei|2 in the neutrino mass region 60–135 MeV/c2 were set and are an order of magnitude improvement over previous results.

The PIENU experiment at TRIUMF is aimed at a measurement of the branching ratio R e / μ = Γ ( ( π + → e + ν e ) + ( π + → e + ν e γ ) ) / Γ ( ( π + → μ + ν μ ) + ( π + → μ + ν μ γ ) ) with precision 0.1 % . Incident pions, delivered at the rate of 60 kHz with momentum 75 MeV/c, were degraded and stopped in a plastic scintillator target. Pions and their decay product positrons were detected with plastic scintillators and tracked with multiwire proportional chambers and silicon strip detectors. The energies of the positrons were measured in a spectrometer consisting of a large NaI(Tl) crystal surrounded by an array of pure CsI crystals. This paper provides a description of the PIENU experimental apparatus and its performance in pursuit of R e / μ .

The PIENU experiment at TRIUMF aims to measure the branching ratio of the pion decay modes $R^{\pi}=[{\pi}^+{\rightarrow}e^+{\nu}_e({\gamma})]/[{\pi}^+{\rightarrow}{\mu}^+{\nu}_{\mu}({\gamma})]$ with precision of $

The PIENU experiment aims to measure the branching ratio of the charged pion decay with precision of < 0.1 %. This measurement is much sensitive to search for massive neutrinos coupled to electrons in ${\pi }^{+}{\rightarrow }e^{+}{\nu }_{e}$ decay. The initial analysis was completed and the upper limit on the neutrino mixing parameter |U e i |2 in the neutrino mass range of 0 to 55 MeV/c 2 was improved by a factor of 1.5, and the sensitivity for the mass range of 68 to 129 MeV/c 2 was improve by a factor of up to 4.

This report will summarize contributions made by the ASU group during the grant period. Focus will be given to three areas: (1) Monte Carlo simulations; (2) signal processing in the electronics; and (3) data analysis software. For reference, a drawing of the KOTO detector is shown in Fig. 1. The production target for the neutral beam particles was about 20 meters upstream of the detector.

We describe the K L 0 flux measurements performed at the J-PARC neutral-kaon beam line. This beam line was constructed for an experiment aiming to observe the CP-violating rare decay K L 0 → π 0 ν ν ¯ . The primary proton energy was 30 GeV and the K L 0 production angle was 16°. Prior to the physics run, the K L 0 flux and spectrum were measured by counting K L 0 → π + π − π 0 decays with a simple setup, which was composed of an electromagnetic calorimeter and a hodoscope system. Results from these measurements are presented and compared with various hadron-interaction simulations.

The Data Acquisition (DAQ) for the KOTO detector is designed around a 14-bit 125 MHz ADC module, which measures the energy and the time of photomultiplier pulses from about 4000 readout channels. The Trigger has a two-tiered design, with a first level decision based on the time-aligned energy sum over the entire calorimeter and a second level decision based on clustering and in-time veto signal rejection. Data accepted by the second level trigger are read out via Gigabit Ethernet and passed to a computer farm for event building and data storage.

An extension of the TRIUMF M13 low-energy pion channel designed to suppress positrons based on an energy-loss technique is described. A source of beam channel momentum calibration from the decay pi+ --> e+ nu is also described., 5 pages

A new measurement of the branching ratio R_{e/μ}=Γ(π^{+}→e^{+}ν+π^{+}→e^{+}νγ)/Γ(π^{+}→μ^{+}ν+π^{+}→μ^{+}νγ) resulted in R_{e/μ}^{exp}=[1.2344±0.0023(stat)±0.0019(syst)]×10^{-4}. This is in agreement with the standard model prediction and improves the test of electron-muon universality to the level of 0.1%.

The KOTO ($K^0$ at Tokai) experiment aims to observe the CP-violating rare decay $K_L \rightarrow \pi^0 \nu \bar{\nu}$ by using a long-lived neutral-kaon beam produced by the 30 GeV proton beam at the Japan Proton Accelerator Research Complex. The $K_L$ flux is an essential parameter for the measurement of the branching fraction. Three $K_L$ neutral decay modes, $K_L \rightarrow 3\pi^0$, $K_L \rightarrow 2\pi^0$, and $K_L \rightarrow 2\gamma$ were used to measure the $K_L$ flux in the beam line in the 2013 KOTO engineering run. A Monte Carlo simulation was used to estimate the detector acceptance for these decays. Agreement was found between the simulation model and the experimental data, and the remaining systematic uncertainty was estimated at the 1.4\% level. The $K_L$ flux was measured as $(4.183 \pm 0.017_{\mathrm{stat.}} \pm 0.059_{\mathrm{sys.}}) \times 10^7$ $K_L$ per $2\times 10^{14}$ protons on a 66-mm-long Au target., Comment: 27 pages, 16 figures. To be appeared in Progress of Theoretical and Experimental Physics

The PIENU experiment at TRIUMF aims to measure the branching ratio of pion decays R = Γ(π(+) → e(+)ν(e) + π(+) → e(+) ν(e)γ)/Γ(π(+)→μ(+)ν(μ) + π(+) → μ(+)ν(μ)γ) with precision

A description is given of a framework code that enables Monte Carlo simulations of experiments to be carried out easily and flexibly in geant4 . The structure of the code and a few limitations are discussed.

A code has been developed that enables the geometry of detectors to be specified easily and flexibly in the XML language, for use in the Monte Carlo program geant 4. The user can provide clear documentation of the geometry without being proficient in the C++ language of geant 4. The features and some applications are discussed.

Inclusive charged pion, kaon, proton, and deuteron production in 14.6 GeV/c proton-nucleus collisions measured by BNL experiment E802 is compared with results from the GEANT3, GEANT4, and FLUKA simulation packages. The FLUKA package is found to have the best overall agreement., Comment: 16 pages, 11 figures; improved clarity of figures

Analyzing powers of pion-proton elastic scattering have been measured at PSI with the Low Energy Pion Spectrometer LEPS as well as a novel polarized scintillator target. Angular distributions between 40 and 120 deg (c.m.) were taken at 45.2, 51.2, 57.2, 68.5, 77.2, and 87.2 MeV incoming pion kinetic energy for pi+ p scattering, and at 67.3 and 87.2 MeV for pi- p scattering. These new measurements constitute a substantial extension of the polarization data base at low energies. Predictions from phase shift analyses are compared with the experimental results, and deviations are observed at low energies., 15 pages, 4 figures

Precise new data for the reaction K−p→π0Λ are presented in the c.m. energy range 1565 to 1600 MeV. Our analysis of these data sheds new light on claims for the Σ(1580) 3 2 − resonance, which (if it exists with the specified quantum numbers) must be an exotic baryon because of its very low mass. Our results show no evidence for this state.

We report on the design and performance of compact detector packages currently installed in the four magnetic out-of-plane spectrometers for electron scattering experiments at the MIT-Bates Linear Accelerator Center. The detector packages have been designed to meet the mechanical requirements arising from out-of-plane particle detection. They offer good trajectory and momentum reconstruction, particle identification and time-of-flight measurements for electrons, pions, protons, and deuterons with large momentum bites and in broad kinematical ranges and high luminosities. The detectors have so far been used with great success in out-of-plane measurements of 12 C ( e → , e ′ p ) , 2 H ( e → , e ′ p ) , virtual Compton scattering below pion threshold and in studies of the N → Δ transition in both exclusive reaction channels 1 H ( e → , e ′ p ) π 0 and 1 H ( e → , e ′ π + )n .

We developed and built a new system of readout and trigger electronics, based on the waveform digitization and pipeline readout, for the KOTO experiment at J-PARC, Japan. KOTO aims at observing the rare kaon decay $K_{L}\rightarrow\pi^{0}\nu\bar{\nu}$. A total of 4000 readout channels from various detector subsystems are digitized by 14-bit 125-MHz ADC modules equipped with a 10-pole Bessel filter in order to reduce the pile-up effects. The trigger decision is made every 8-ns using the digitized waveform information. To avoid dead time, the ADC and trigger modules have pipelines in their FPGA chips to store data while waiting for the trigger decision. The KOTO experiment performed the first physics run in May 2013. The data acquisition system worked stably during the run., Comment: 5 pages,12 figures, Transactions on Nuclear Science, Proceedings of the 19th Real Time Conference, Preprint

The branching ratio, Re/μ = Γ(π → eν + eνγ)/Γ(π → μν + μνγ), provides a sensitive test of muon-electron universality in weak interactions. The status of the PIENU experiment at TRIUMF, which aims to improve the precision of the Re/μ measurement by a factor of > 5, is presented.

High precision 1H(e, e'p)pi0 measurements at Q2 = 0.126. (GeV/c)2 are reported, which allow the determination of quadrupole amplitudes in the gamma*N --> Delta transition; they simultaneously test the reliability of electroproduction models. The derived quadrupole-to-dipole (I = 3/2) amplitude ratios, RSM = (-6.5 +/- 0.2stat+sys+/-2.5mod)% and REM = 9-2.1 +/-0.2stat+sys +/-2.0mod)%, are dominated by model error. Previous RSM and REM results should be reconsidered after the model uncertainties associated with the method of their extraction are taken into account.

We report on a measurement ofthe neutron detection efficiency in NaI crystals in the Crystal Ball (CB)

The large growth of flash ADC techniques for processing signals, especially in applications of streaming data, raises issues such as data flow through an acquisition system, long-term storage, and greater complexity in data analysis. In addition, experiments that push the limits of sensitivity need to distinguish legitimate signals from noise. The use of correlation coefficients is examined to address these issues. They are found to be quite successful well into the noise region. The methods can also be extended to Field Programmable Gate Array modules for compressing the data flow and greatly enhancing the event rate capabilities., 9 pages, 2 figures

We report on an investigation of the ({pi}{sup -}, {pi}{sup 0}{pi}{sup 0}) reaction by means of the {pi}{sup 0}{pi}{sup 0} invariant mass distributions from {pi}{sup -} interactions on H, D, C, Al, and Cu targets at {rho}{sub {pi}{sup -}} = 0.408 GeV/c. The sharp, strong peak in the {pi}{sup +}{pi}{sup -} invariant mass near 2m{sub {pi}} reported by the CHAOS Collaboration is not seen in our {pi}{sup 0}{pi}{sup 0} data. However, we do observe a change in the shape of the {pi}{sup 0}{pi}{sup 0} invariant mass spectrum for the different targets, indicating that the {pi}{sup 0}{pi}{sup 0} interaction diminishes in the nuclear medium as represented by nuclei D, C, Al, and Cu, compared to hydrogen.

We present a measurement of the induced proton polarization ${P}_{n}$ in ${\ensuremath{\pi}}^{0}$ electroproduction on the proton around the $\ensuremath{\Delta}$ resonance. The measurement was made at a central invariant mass and a squared four-momentum transfer of $W=1231 \mathrm{MeV}$ and ${Q}^{2}=0.126 {\mathrm{GeV}}^{2}{/c}^{2},$ respectively. We measured a large induced polarization, ${P}_{n}=\ensuremath{-}0.397\ifmmode\pm\else\textpm\fi{}0.055\ifmmode\pm\else\textpm\fi{}0.009.$ The data suggest that the scalar background is larger than expected from a recent effective Hamiltonian model.

A TRIUMF experiment, PIENU, which aims to measure the branching ratio of pion decays, R = Γ(π→eν+eνγ)/Γ(π→μν+μνγ) to a precision of 0.1% or better is described. Such a measurement provides the best test of electron-muon universality in weak interactions and is sensitive to an effective mass scale of up to 1000 TeV in new physics.

We report an absolute measurement of the tensor analyzing powers {ital T}{sub 20} and {ital T}{sub 22} in elastic electron-deuteron scattering at a momentum transfer of 1.6 fm{sup {minus}1}. The novel approach of this measurement is the use of a tensor polarized {sup 2}H target internal to an electron storage ring, with {ital in} {ital situ} measurement of the polarization of the target gas. Scattered electrons and recoil deuterons were detected in coincidence with two large acceptance nonmagnetic detectors. The techniques demonstrated have broad applicability to further measurements of spin-dependent electron scattering. {copyright} {ital 1996 The American Physical Society.}

The branching ratio of pion decays, R = Γ(π+→e+νe+π+→e+νeγ)Γ(π+→μ+νμ+π+→μ+νμγ is one of the most accurately calculated decay processes involving hadrons and has provided one of the most stringent tests of the hypothesis of electron-muon universality in weak interactions. The current experimental branching ratio Rexp = (1.230±0.004)×10−4 is 40 times less precise than the theoretical prediction RSM = 1.2352(1)10−4. The TRIUMF PIENU experiment aims at measuring the pion branching ratio with a precision improved by at least a factor five.

Differential cross sections and analyzing powers have been measured for inelastic proton excitation of states in $^{12}\mathrm{C}$ up to an excitation energy of 20 MeV. Angular distributions are reported for incoming proton energies of 200, 318, 398, 597, 698, and 800 MeV, typically over the momentum transfer range from 0.5 to 2 ${\mathrm{fm}}^{\mathrm{\ensuremath{-}}1}$; some of these data have been published previously. Reaction calculations in the distorted-wave impulse approximation have been carried out for most of the data. Agreement between theory and experiment for both the magnitudes and shapes of the cross-section data is generally good; the analyzing-power distributions are less well described.

A new development in polarized nuclear-target technology has made it possible to measure analyzing power, Ay, in pion elastic scattering from a polarized target.[1] Such measurements provide us with information on the isoscalar spin-flip strength of the nuclear transition which is very difficult to obtain otherwise. Differential cross sections, σ(Θ), for pion elastic scattering from nuclei with non-zero spin are dominated by the spin-independent (∆S = 0) amplitudes. Contributions from the spin-dependent (∆S = 1) amplitudes are usually negligible because σ(Θ) depends on the sum of the squares of those amplitudes. However, the Ay depend on the interference on the spin-independent and spin-dependent scattering amplitudes and are therefore quite sensitive to the spin-dependent forms.

A high precision measurement of the ultra-rare K{sup +} {yields} {pi}{sup +} {nu}{bar {nu}} decay at Fermilab would be one of the most incisive probes of quark flavor physics this decade. Its dramatic reach for uncovering new physics is due to several important factors: (1) The branching ratio is sensitive to most new physics models which extend the Standard Model to solve its considerable problems. (2) The Standard Model predictions for the K{sup +} {yields} {pi}{sup +} {nu}{bar {nu}} and K{sub L}{sup 0} {yields} {pi}{sup 0} {nu}{bar {nu}} branching fractions are broadly recognized to be theoretically robust at the 5-10% level. Only a precious few accessible loop-dominated quark processes can be predicted with this level of certainty. (3) The K{sup +} {yields} {pi}{sup +} {nu}{bar {nu}} branching fraction is highly suppressed in the Standard Model to the level < 10{sup -10} (

The rare decay ${K}_{L}^{0}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}{\ensuremath{\pi}}^{0}\ensuremath{\nu}\overline{\ensuremath{\nu}}$ was studied with the E391a detector at the KEK 12-GeV proton synchrotron. Based on $9.4\ifmmode\times\else\texttimes\fi{}{10}^{9}$ ${K}_{L}^{0}$ decays, an upper limit of $8.1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7}$ was obtained for the branching fraction at 90% confidence level. We also set a limit on the ${K}_{L}^{0}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}{\ensuremath{\pi}}^{0}X$ ($X\ensuremath{\rightarrow}\mathrm{\text{invisible particles}}$) process; the limit on the branching fraction varied from $7.0\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7}$ to $4.0\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$ for the mass of $X$ ranging from $50\text{ }\text{ }\mathrm{MeV}/{c}^{2}$ to $200\text{ }\text{ }\mathrm{MeV}/{c}^{2}$.

We performed a search for the decay K{sub L}{sup 0}{yields}3{gamma} with the E391a detector at KEK. In the data accumulated in 2005, no event was observed in the signal region. Based on the assumption of K{sub L}{sup 0}{yields}3{gamma} proceeding via parity-violation, we obtained the single event sensitivity to be (3.23{+-}0.14)x10{sup -8}, and set an upper limit on the branching ratio to be 7.4x10{sup -8} at the 90% confidence level. This is a factor of 3.2 improvement compared to the previous results. The results of K{sub L}{sup 0}{yields}3{gamma} proceeding via parity-conservation were also presented in this paper.

The first dedicated search for the rare neutral-kaon decay K{sub L}{sup 0{yields}{pi}0{nu}{nu}} has been carried out in the E391a experiment at the KEK 12-GeV proton synchrotron. The final upper limit of 2.6x10{sup -8} at the 90% confidence level was set on the branching ratio for the decay.

The forward angle differential cross sections of ( π + , π − ) reactions on the calcium isotopes to the double-isobaric-analog (DIAS) and ground states (GS) were measured between 25 and 65 MeV. These low-energy cross sections are up to an order of magnitude larger than those at resonance energies. The forward-angle excitation functions of 42 Ca, 44 Ca DIAS and 44 Ca GS transitions peak around 50 MeV. The 48 Ca DIAS cross section exhibits a minimum at about 50 MeV and that for the GS has a peak which is shifted to lower energy with a smaller cross section than that of the other nuclei. The observed behaviour is inconsistent with theoretical expectations.

Measured values of the differential cross sections for pion-nucleon charge exchange, ${\ensuremath{\pi}}^{\ensuremath{-}}p\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}n$, are presented for ${\ensuremath{\pi}}^{\ensuremath{-}}$ momenta of $103,112,120,130,139,152$, and $178$ MeV/$c$. Complete angular distributions were obtained by using the Crystal Ball detector at the Alternating Gradient Synchrotron at Brookhaven National Laboratory. Statistical uncertainties of the differential cross sections vary from $3$ to $6%$ in the backward angle region and from $6$ to about $20%$ in the forward region with the exception of the two most forward angles. The systematic uncertainties are estimated to be about $3%$ for all momenta.

We performed a search for a light pseudoscalar particle X in the decay K{sub L}{sup 0}{yields}{pi}{sup 0}{pi}{sup 0}X, X{yields}{gamma}{gamma} with the E391a detector at KEK. Such a particle with a mass of 214.3 MeV/c{sup 2} was suggested by the HyperCP experiment. We found no evidence for X and set an upper limit on the product branching ratio for K{sub L}{sup 0}{yields}{pi}{sup 0}{pi}{sup 0}X, X{yields}{gamma}{gamma} of 2.4x10{sup -7} at the 90% confidence level. Upper limits on the branching ratios in the mass region of X from 194.3 to 219.3 MeV/c{sup 2} are also presented.

We report the first measurements of the total cross section of the reaction K{sup -}p{yields}{sigma}{sup 0}{gamma} at eight beam momenta from 514 to 750 MeV/c. The data were obtained at the Alternating Gradient Synchrotron (AGS) at Brookhaven National Laboratory using the Crystal Ball detector consisting of 672 NaI crystals. All charged particles were vetoed by a barrel of plastic scintillators, resulting in a study of only the neutral decays of the {sigma}{sup 0}. The prompt photon and the photons from the decay products of {sigma}{sup 0} were detected for each reconstructed event; the neutron was also detected in a small fraction of the events.