The VIP Collaboration is performing high precision tests of the Pauli Exclusion Principle for electrons in the extremely low cosmic background environment of the Underground Gran Sasso Laboratories of INFN (Italy). The experimental technique consists in introducing a DC current in a copper conductor, searching for K-alpha PEP-forbidden atomic transitions when the K shell is already occupied by two electrons. VIP set an upper limit on the PEP-violation probability 1/2 beta(2) <4.7 x 10(-29). The aim of the upgraded VIP-2 experiment is to improve this result at least by two orders of magnitude. The improved experimental setup and the results of a preliminary data analysis, corresponding to the the first run of the VIP-2 data taking (2016-2017), will be presented.

The MEG experiment at PSI searches for the decay μ→eγ at a level of ≈10−13 on the branching ratio BR(μ→eγ/μ→tot), well beyond the present experimental limit (BR≤1.2×10−11) and is sensitive to the predictions of SUSY-GUT theories. To reach this goal the experiment uses one of the most intense continuous surface muon beams available (≈108μ/s) and relies on advanced technology (LXe calorimetry, a gradient-field superconducting spectrometer as well as flexible and powerful trigger and acquisition systems). In order to maintain the highest possible energy, time and spatial resolutions for such detector, frequent calibration and monitoring, using a Cockcroft–Walton proton accelerator, are required. The proton beam is brought to the centre of MEG by a special bellows insertion system and travels in a direction opposite to the one of the normal μ‐beam. Protons interact with a lithium tetraborate (Li2B4O7) nuclear target and produce one γ (17.6 MeV) from the reaction Li(p,γ)37Be48 or two coincident γs (11.67 and 4.4 MeV) from the reaction B(p,γ1)511C⁎612. The 17.6 MeV γ is used for calibrating and monitoring the LXe calorimeter (σEγ/Eγ=3.85±0.15% at 17.6 MeV) while the coincident 11.67 and 4.4 MeV γs are used to measure the relative timing of the calorimeter and the spectrometer timing counters (σΔt=0.450±0.015ns).

The rate of nuclear muon capture by the proton has been measured using a new technique based on a time projection chamber operating in ultraclean, deuterium-depleted hydrogen gas, which is key to avoiding uncertainties from muonic molecule formation. The capture rate from the hyperfine singlet ground state of the microp atom was obtained from the difference between the micro(-) disappearance rate in hydrogen and the world average for the micro(+) decay rate, yielding Lambda(S)=725.0+/-17.4 s(-1), from which the induced pseudoscalar coupling of the nucleon, g(P)(q(2)=-0.88m(2)(micro))=7.3+/-1.1, is extracted.

The rate of nuclear muon capture by the proton has been measured using a new technique based on a time projection chamber operating in ultraclean, deuterium-depleted hydrogen gas, which is key to avoiding uncertainties from muonic molecule formation.The capture rate from the hyperfine singlet ground state of the p atom was obtained from the difference between the ÿ disappearance rate in hydrogen and the world average for the decay rate, yielding S 725:0 17:4 s ÿ1 , from which the induced pseudoscalar coupling of the nucleon, g P q 2 ÿ0:88m 2 7:3 1:1, is extracted.

Experiment 865 at the Brookhaven AGS has observed the decay K+→e+νeμ+μ−. The branching ratio extracted is (1.72±0.37(stat)±0.17(syst)±0.19(model))×10−8 where the third term in the error results from the use of a model to extrapolate into a kinematic region dominated by background.Received 12 May 2005DOI:https://doi.org/10.1103/PhysRevD.73.037101©2006 American Physical Society

Experiment 865 at the Brookhaven AGS has observed the decay K+-> e(+)nu(e)mu(+)mu(-). The branching ratio extracted is (1.72 +/- 0.37(stat)+/- 0.17(syst)+/- 0.19(model))x10(-8) where the third term in the error results from the use of a model to extrapolate into a kinematic region dominated by background.

POLDI (Pulse-OverLap DIffractometer) is a multiple pulse-overlap diffractometer at PSI, which is designed mainly for strain-scanning experiments. The multiple pulse-overlap method made it possible to build a time-of-flight diffractometer at a continuous neutron source with short flight path, high resolution and high intensity. The best achievable resolutions for the relative linewidths of the Bragg reflections are between 1×10−3 and 2×10−3, depending on the lattice spacing. The layout of the instrument and the features of the chopper, the neutron mirror and the 3He detector in time-focusing geometry are presented. The overall performance of the instrument is discussed with examples of strain-field measurements.

Based on results of a search for the lepton-family-number-violating decay K+->pi(+)mu(+)e(-) with data collected by experiment E865 at the Alternating Gradient Synchrotron of Brookhaven National Laboratory, we place an upper limit on the branching ratio at 2.1 x 10(-11) (90% C.L.). Combining the results with earlier E865 data and those of a previous experiment, E777, an upper limit on the branching ratio of 1.3 x 10(-11) (90% C.L.) is obtained.

This status report gives an update of the ongoing activities of the μ → eγ experiment, now called MEG, as of December 2002. Results from Monte Carlo simulations, beam times at PSI and Japan, and technical developments are reported.

We report experimental details and results of a new measurement of the decay K+-->pi(+)pi(-)e(+)nu(e)(K-e4). A sample of more than 400,000 K-e4 events with low background has been collected by Experiment 865 at the Brookhaven Alternate Gradient Synchrotron. From these data, the branching ratio (4.11+/-0.01+/-0.11)x10(-5) and the pipi invariant mass dependence of the form factors F, G, and H of the weak hadronic current as well as the phase shift difference delta(0)(0)-delta(1)(1) for pipi scattering were extracted. Using constraints based on analyticity and chiral symmetry, a new value with considerably improved accuracy for the s-wave pipi scattering length a(0)(0) has been obtained also: a(0)(0)=0.216+/-0.013 (stat)+/-0.002 (syst)+/-0.002 (theor).

E865 at the Brookhaven National Laboratory AGS collected about 70 000 K(+)(e3) events to measure the K(+)(e3) branching ratio relative to the observed K+-->pi(+)pi(0), K+-->pi(0)micro(+)nu, and K+-->pi(+)pi(0)pi(0) decays. The pi(0) in all the decays was detected using the e(+)e(-) pair from pi(0)-->e(+)e(-)gamma decay and no photons were required. Using the 2002 Particle Data Group branching ratios for the normalization decays, we obtain BR(K(+)(e3(gamma)))=(5.13+/-0.02(stat)+/-0.09(syst)+/-0.04(norm))%, where K(+)(e3(gamma)) includes the effect of virtual and real photons. This result is approximately 2.3sigma higher than the current Particle Data Group value. Implications for the V(us) element of the CKM matrix, and the matrix's unitarity are discussed.

Experiment 865 at the Brookhaven Alternating Gradient Synchrotron obtained 410 K+-->e(+)nue(+)e(-) and 2679 K+-->mu(+)nue(+)e(-) events including 10% and 19% background. The branching ratios were measured to be [2.48+/-0.14(stat)+/-0.14(syst)]x10(-8) (m(ee)>150 MeV) and (7.06+/-0.16+/-0.26)x10(-8) (m(ee)>145 MeV), respectively. Results for the decay form factors are presented.

The detector of the E865-collaboration at the Brookhaven-AGS described here combines a magnetic spectrometer for the charged decay products of 6GeV/cK+ with excellent electromagnetic calorimetry and efficient particle identification for electrons and muons. Its high-resolution, large acceptance and high rate capability made it well suited for the study of extremely rare or forbidden decays with multi-leptonic final states such as K+→π+μ+e−, K+→π+l+l−, K+→l+νle−e+ and K+→π+π−e+νe down to branching ratios below 10−11 in an intense K+ beam (≈108 per AGS spill).