N. Danneberg

An apparatus for the measurement of the transverse polarization of positrons from the decay of polarized muons

Abstract An apparatus for the measurement of the two transverse polarization components P T 1 and P T 2 of the positrons from polarized μ + decay is described. It makes use of a stroboscopic method which cancels many systematic asymmetries and allows one to use muon stop rates in the order of up to 10 8 s −1 . The experiment aims at an accuracy of Δ P T 1 =Δ P T 2 =3×10 −3 and by that at an improvement of the existing limit by nearly one order of magnitude. With these results one will obtain an improved model-independent value for the Fermi coupling constant G F and more stringent limits to possible violations of time reversal invariance in a purely leptonic reaction.

Polarized muon decay: Measurement of the polarization vector of the decay positrons as a test of time reversal invariance

Abstract The μ P T experiment at the Paul Scherrer Institut has determined the three polarization components of positrons from polarized muon decay simultaneously with the same apparatus by making use of three different effects (spatial and temporal dependence of annihilation-in-flight with polarized electrons and muon decay asymmetry). The use of a stroboscopic method greatly reduces systematic errors. The energy dependence of the transverse polarization component P T 1 , which lies in the plane spanned by muon-spin and positron momentum, yields the low energy parameter η and thus an improved model-independent value of the Fermi coupling constant. A non-zero value of the transverse component P T 2 , which is perpendicular to the above mentioned plane, would be the first observation of time reversal violation in a purely leptonic decay. The preliminary results are P T 1 = (5 ± 16) × 10 −3 , P T 2 = (1 ± 16) × 10 −3 and P L = 1.09 ± 0.15.

Measurement of the polarization vector of the e+ from the decay of polarized μ+ as a test of time reversal invariance

The complete polarization vector of the positrons from the decay of polarized muons has been measured for the first time with one experimental setup. The μPT experiment at the Paul Scherrer Institute determines the three polarization components simultaneously with the same apparatus by making use of three different effects (spatial and temporal dependence of annihilation-in-flight with polarized electrons as well as muon decay asymmetry). The use of a stroboscopic method greatly reduces systematic errors. The energy dependence of the transverse polarization component PT1, which lies in the plane spanned by muon spin and positron momentum, yields the low energy parameter η and thus an improved model-independent value of the Fermi coupling constant. A non-zero value of the transverse component PT2, which is perpendicular to the above-mentioned plane, would be the first observation of time reversal violation in a purely leptonic decay. The preliminary results are PT1 = (5 +/- 16) × 10−3, PT2 = (1 +/- 16) × 10−3 and PL = (1.09 +/- 0.15).

A tracking detector for low energy electrons

Abstract A multiwire proportional chamber has been developed to study parameters of a detector for tracking of low-energy electrons (0.1–1 MeV). The geometry and materials used have been optimized to minimize the energy loss and the multiple Coulomb scattering. The detector is equipped with an electronic readout and event selection system, consisting of amplifier/comparator stage, a fast trigger unit and a data multiplexer. The fast trigger system identifies the desired event within 30 ns. Based on this prototype, the full-scale detectors (50×100 cm 2 ) will be constructed to determine the electron tracks in the neutron decay experiments.

Determination of the Polarization of the Decay Positrons in Polarized Muon Decay

The standard model of electroweak interactions predicts that the positrons from the decay of polarized positive muons are mainly longitudinally polarized. The measurement of the two transverse polarization components of the positron PT1 and PT2 is a sensitive tool to look for contributions from additional, exotic interactions and for the violation of time reversal invariance in this purely leptonic decay. The μPT ‐ experiment at the Paul Scherrer Institute determines the three positron polarization components simultaneously with the same apparatus by making use of three different effects. By examining the temporal dependence of annihilation‐in‐flight of the decay positrons with polarized electrons a possible non‐zero value of the transverse polarization is determined. The phase of this transverse polarization can be measured by making use of the decay asymmetry. Using the dependence of annihilation‐in‐flight on the angle between electron polarization and positron momentum leads to the determination of the...

Polarized muon decay: Measurement of the polarization vector of the decay positrons

In the standard model (SM) of electroweak interactions the positron from the decay of polarized positive muons is mainly longitudinally polarized. The measurement of the two transverse polarization components, therefore, is a sensitive tool for contributions from additional, exotic, interactions. The energy dependence of the transverse polarization component PT1, which lies in the plane spanned by muon-spin and positron momentum, yields the low energy parameter η and thus an improved model-independent value of the Fermi coupling constant. A non-zero value of the transverse component PT2, which is perpendicular to the above mentioned plane, would be the first observation of time reversal violation in a purely leptonic decay. The μPT experiment at the Paul Scherrer Institute determines the three polarization components simultaneously with the same apparatus by making use of three different reactions (spatial and temporal dependence of annihilation-in-flight with polarized electrons as well as muon decay asy...

Is time reversal invariance violated in muon decay? A measurement of the transverse positron polarization

In the standard model (SM) of electroweak interactions the positron from the decay of polarized positive muons is mainly longitudinally polarized. However the model also predicts a small transverse polarization component PT1, which lies in the plane spanned by muon-spin and positron momentum. Interference with additional, scalar couplings would result in substantial values for PT1 as well as in a non-zero value of the transverse component PT2 which is perpendicular to the above mentioned plane. A nonzero component PT2, proportional to the imaginary part of a possible scalar coupling, would be the first observation of time reversal violation in a purely leptonic decay. Measuring PT1, which is proportional to the real part, amounts to a model independent determination of the Fermi-coupling constant. The μPT experiment [1] at the Paul Scherrer Institute will improve the current experimental limits PT2=(16±22)×10−3,PT2=(7±23)×10−3 by almost one order of magnitude. First preliminary results of the experiment a...

New facility for fundamental physics with polarized cold neutrons

A new facility for particle physics with polarized cold neutrons has been taken into operation at the spallation source SINQ at PSI. After extraction of the first beam, its intensity and polarization have been measured as a function of the neutron wavelength. The beam characteristics are among the best in the world for studies of neutron decay. An experimental area was constructed with infrastructure support for convenient experimentation. The physics program will focus on detailed investigations of the free neutron decay process, in particular fundamental symmetries of the weak interaction. The first approved experiment is a novel search for time reversal violation.

Physics with polarized cold neutrons at the spallation source SINQ

A new facility for particle physics has been installed at the spallation source SINQ. An experimental area has been constructed for a series of experiments fed by a high intensity, polarized cold neutron beam. The physics program for this new facility will focus on free neutron decay studies addressing mainly the questions of fundamental symmetries (time reversal and parity) in the weak interactions.