R. Openshaw

Etching of anode wire deposits with CF4/isobutane (80:20) avalanches

Abstract An ionization exposure of 0.5 C per cm of wire in a gas mixture of CF 4 /isobutane (80:20) is shown to reverse anode wire damage in single-wire chamb

Tests of wire chamber ageing with CF/sub 4//isobutane (80.20), argon/ethane (50:50), and argon/ethane/CF/sub 4/ (48:48:4)

In a series of parallel tests the ageing characteristics of CF/sub 4/ isobutane (80:20), argon ethane (50:50), and argon ethane/CF/sub 4/ (48:48:4), have been investigated. Parameters such as flow rate, gas gain, anode wire current density and materials in contact with the gas stream have been varied. Some tests have been extended beyond 8 Coulomb/cm of wire. The Ar/Et chambers have shown a high incidence of pulse height degradation, dark currents, cathode foil etching, and deposits on the electrodes. A strong correlation between anode wire current density and rate of damage (%/C/cm) is indicated for Ar/Et chambers. The CF/sub 4//Iso chambers have shown effectively zero pulse height degradation and few other problems to accumulated charges exceeding 5 C/cm, except for one low-flow chamber with some cathode etching and cathode related pulse height degradation. The addition of 4% CF/sub 4/ to the Ar/Et mixture has dramatically improved the ageing performance of the Ar/Et/CF/sub 4/ cells. >

Wire chamber ageing with CF/sub 4//isobutane and argon/ethane mixtures

The ageing characteristics of CF/sub 4//isobutane (80:20) and argon/ethane (50:50) in identical test cells have been investigated. The gas gain and gas flow rate were varied and the measurements extended beyond 6 C/cm of wire. Study of a third gas mixture Ar/eth/CF/sub 4/ (48:48:4) is at an early stage. The Ar/eth mixture has shown a variety of problems including cathode foil etching, anode deposits, dark currents, and pulse-height degradation. In contrast the CF/sub 4//iso mixture produced some cathode etching for low flow velocities and only very minor anode deposits. With very little pulse-height degradation or dark current this mixture is a considered excellent candidate for a high-rate chamber. A small-area multiwire proportional chamber using this mixture has been evaluated in a pion beam with particle fluxes up to 3*10/sup 7/ particles/cm/sup 2/-s. >

Measurement of P(mu)xi in polarized muon decay

The quantity P_{mu}^{pi}xi, where xi is one of the muon decay parameters and

Precise measurement of parity violation in polarized muon decay

P_{\mu}^{\pi}

Precision planar drift chambers and cradle for the TWIST muon decay spectrometer

is the degree of muon polarization in pion decay, has been measured. The value P_{mu}^{pi}xi = 1.0003 +- 0.0006 stat. +- 0.0038 syst. was obtained. This result agrees with previous measurements but is over a factor of two more precise. It also agrees with the Standard Model prediction for P_{mu}^{pi}xi and thus leads to restrictions on left-right symmetric models.

A Precision Measurement of the Muon Decay Parameters

We present a new high precision measurement of parity violation in the weak interaction, using polarized muon decay. The TWIST collaboration has measured

\rho

P_\mu^\pi \xi

and

, where

\delta

P_\mu^\pi