M. D. Cooper

Search for the lepton family number nonconserving decay mu+ ---> e+ gamma

The MEGA experiment, which searched for the muon- and electron-number violating decay μ +→e + γ, is described. The spectrometer system, the calibrations, the data taking procedures, the data analysis, and the sensitivity of the experiment are discussed. The most stringent upper limit on the branching ratio, B(μ + →e + γ)l1.2×10 -11 with 90% confidence, is derived from a likelihood analysis.

Search for narrow signals in the γ-spectrum from pp̄ annihilation at rest

The [gamma]-spectrum originating from pp[combining macron] annihilations at rest in liquid hydrogen was measured with two BGO spectrometers. A total of 24 i?œ 106[gamma]’s were accumulated. No narrow peaks indicating exotic states such as baryonium were observed. The upper limit for the branching ratio with 1040 [less-than-or-equals, slant] mx [less-than-or-equals, slant] 1770 MeV/c2 and with [lambda]x [less-than-or-equals, slant] 25 MeV/c2 is less than 10-3 with more than 99.96% confidence.

Measurement of the 3He mass diffusion coefficient in superfluid 4He over the 0.45–0.95 K temperature range

We have directly measured the mass diffusion coefficient D of 3He in superfluid 4He at temperatures lower than were previously possible. The experimental technique utilizes scintillation light produced when neutrons react with 3He nuclei, and allows measurement of the 3He density integrated along the trajectory of a well-defined neutron beam. By measuring the change in 3He density near a heater as a function of applied heat current, we are able to infer values for D with 20% accuracy. At temperatures below 0.7 K and for concentrations of order 10−4, we find D = [2.0+2.4−1.2]T−(6.51.2) cm2/s, in agreement with a theoretical approximation.

Pion non-analog double charge exchange: 16O(π+, π−)16Ne☆

Abstract The non-analog pion double charge exchange reaction 16 O (π + ,π − ) 16 Ne has been observed. The ground-state differential cross section at 0° is found to be 0.87 ± 0.21 μ b/sr at a mean pion energy of 145 MeV. The mass excess obtained for 16 Ne of 24.4 ± 0.5 MeV is in fair agreement with theoretical predictions. The result indicates that cross sections for pion induced non-isobaric-analog double-charge-exchange transitions can be comparable to those for analog transitions.

Design and performance of modularized NaI(Tl) detectors with rectangular crystal elements: An array of 49 and the crystal box

Abstract An array of 49 NaI(Tl) modules each 20 inch in depth and 2.5 inch × 2.5 inch in cross section has been constructed and its properties, especially energy resolution, explored for positrons in the range 20 MeV – 18 GeV. A subsequent much larger detector, the Crystal Box, has also been constructed from 396 modules of the same cross section, but mostly 12 inch in depth, and operated as a γ-ray and positron detector in a search for rare muon decays. The calibration procedure used for the Crystal Box and its characteristic resolutions in energy, impact point and time are described.

A π0 and η spectrometer of lead glass and BGO for momenta up to 1 GeV/c

Abstract A spectrometer consisting of two sets of bismuth germanium oxide (BGO) crystals and a lead-glass array has been used to measure the π 0 and η momentum spectra produced from proton-antiproton annihilations at rest. We describe the test of the BGO sets in electron beams of energies from 50 to 450 MeV. We discuss the method of construction and calibration of the lead-glass array, as well as procedures to extract the energy and position resolutions for detected photons. A momentum resolution (σ) for π 0 s and ηs of 4% and 3%, respectively has been achieved at momenta below 1 GeV/ c .

ENHANCEMENT OF SUPERTHERMAL ULTRACOLD NEUTRON PRODUCTION BY TRAPPING COLD NEUTRONS

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A fast MWPC with cathode strips and utilizing CF4-isobutane

A planar wire chamber has been developed at LAMPF as a prototype for wire chambers of cylindrical configuration for electron detection in the MEGA experiment. Results form tests with the planar cha ...

New Limit for the Lepton-Family-Number Nonconserving Decayμ+→e+γ

The transport properties of a quasi-three-dimensional, 200 layer quantum well structure are investigated at integer filling in the quantum Hall state. We find that the transverse magnetoresistance R xx , the Hall resistance R xy , and the vertical resistance R zz all follow a similar behavior with both temperature and in-plane magnetic field. A general feature of the influence of increasing in-plane field B in is that the Hall conductance quantization first improves, but above a characteristic value B C in , the quantization is systematically removed. We consider the interplay of the chid edge state transport and the bulk (quantum Hall) transport properties. This mechanism may arise from the competition of the cyclotron energy with the superlattice band structure energies. A comparison of the resuIts with existing theories of the chiral edge state transport with in-plane field is also discussed.An experiment has been performed to search for the muon- and electron-number non-conserving decay mu+ to e+_gamma. The upper limit for the branching ratio to be GAMMA(mu+ to e+_gamma)/GAMMA(mu+ to e+_nu_nubar) < 1.2e-11 with 90% confidence.

Construction of the MEGA photon detector

Abstract The construction techniques used in the development of a set of large pair spectrometers for the MEGA detector are discussed. These spectrometers consist of carbon-fiber-composit cylinders on which the conversion foils are mounted, and appropriately spaced wire chambers in each layer which track the conversion leptons. Close tolerances on all dimensions are maintained. The detector has been operating well in the stopped muon beam line at LAMPF.