51 research outputs found
Search for the Hypothetical pi -> mu x Decay
The KARMEN collaboration has reported the possible observation of a hitherto
unknown neutral and weakly interacting particle x, which is produced in the
decay pi -> mu + x with a mass m(x) = 33.9 MeV. We have searched for this
hypothetical decay branch by studying muons from pion decay in flight with the
LEPS spectrometer at the piE3 channel at PSI and find branching ratios BR(pi-
to mu- anti-x) < 4e-7 and BR(pi+ to mu+ x) < 7e-8 (95\% C.L.). Together with
the limit BR > 2e-8 derived in a recent theoretical paper our result would
leave only a narrow region for the existence of x if it is a heavy neutrino.Comment: 10 pages, TeX (uses epsf), 3 Postscript figures uu-encode
The spin-dependent nd scattering length - a proposed high-accuracy measurement
The understanding of few-nucleon systems at low energies is essential, e.g.
for accurate predictions of element abundances in big-bang and stellar fusion.
Novel effective field theories, taking only nucleons, or nucleons and pions as
explicit degrees of freedom, provide a systematic approach, permitting an
estimate of theoretical uncertainties. Basic constants parameterising the short
range physics are derived from only a handful of experimental values. The
doublet neutron scattering length a_2 of the deuteron is particularly sensitive
to a three-nucleon contact interaction, but experimentally known with only 6%
accuracy. It can be deduced from the two experimentally accessible parameters
of the nd scattering length. We plan to measure the poorly known "incoherent"
nd scattering length a_{i,d} with 10^{-3} accuracy, using a Ramsey apparatus
for pseudomagnetic precession with a cold polarised neutron beam at PSI. A
polarised target containing both deuterons and protons will permit a
measurement relative to the incoherent np scattering length, which is know
experimentally with an accuracy of 2.4\times 10^{-4}.Comment: 5 pages LaTeX2e, 1 .eps figure. To be published in Nucl. Inst.
Methods A as part of the Proceedings of the 9th International Workshop on
Polarized Solid Targets and Techniques in Bad Honnef (Germany), 27th - 29th
October 200
Low Energy Analyzing Powers in Pion-Proton Elastic Scattering
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.Comment: 15 pages, 4 figure
TWO STAGE NUCLEAR DEMAGNETIZATION EXPERIMENTS
Nous décrivons les expériences faites avec un appareil de désaimantation nucléaire, qui comprend un réfrigérateur à dilution d'Hélium -3 dans l'hélium -4 et un composé de Van Vleck paramagnetique comme étage de prérefroidissement. Nous décrivons le résultat de désaimantation d'In, PrNi5 et PrIn3 et aussi de mesures d'orientation nucléaire de 95NbPt et 54MnZn.We describe experiments done with a nuclear demagnetization apparatus consisting of a 3He -4He dilution refrigerator and a "Van Vleck" paramagnetic compounds as precooling stages. Demagnetizations of In, PrNi5 and PrIn3 are reported as well as nuclear orientation measurements of 95NbPt and 54MnZn
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