Search

Lepton family number violation is tested by searching for $\mu^+\to e^+X^0$ decays among the 5.8$\times 10^8$ positive muon decay events analyzed by the TWIST collaboration. Limits are set on the production of both massless and massive $X^0$ bosons. The large angular acceptance of this experiment allows limits to be placed on anisotropic $\mu^+\to e^+X^0$ decays, which can arise from interactions violating both lepton flavor and parity conservation. Branching ratio limits of order $10^{-5}$ are obtained for bosons with masses of 13 - 80 MeV/c$^2$ and with different decay asymmetries. For bosons with masses less than 13 MeV/c$^{2}$ the asymmetry dependence is much stronger and the 90% limit on the branching ratio varies up to $5.8 \times 10^{-5}$. This is the first study that explicitly evaluates the limits for anisotropic two body muon decays., Comment: 7 pages, 5 figures, 2 tables, accepted by PRD

We propose to make the first high precision measurements of nearly the entire differential spectrum (in energy and angle) of positrons from the decay of polarized muons. The main goal of the experiment is the precise testing of the ( V - A ) structure of electroweak interactions in the framework of the SU (2) L × U (1) model. Highly polarized “surface” μ + from the TRIUMF M13 beamline will enter a large volume, high field superconducting magnet on axis and will stop in a thin target at its center. The e + from the muon decay will be precisely tracked in the magnetic field using small-cell planar drift chambers. This spectrometer has been simulated with GEANT and EGS4 and has been demonstrated to meet the precision requirements.

The performance of MicroStrip Gas Chambers (MSGC) in BNL Experiment 885, a search for ΛΛ-hypernuclei, is detailed. Chambers with an active area of 80×50 mm2 were instrumented and operated as a vertex detector in the experiment. Furthermore, two distinct types of microstrip prints were utilized in these chambers. Prints manufactured with Integrated Circuit (IC) photolithographic technology have fine tolerances and thin minimum trace widths, but can suffer from a high rate of defects per print and are more costly. Prints constructed with Printed Circuit (PC) photolithographic technology have coarser tolerances but relatively few defects per print, and are extremely cost-effective. Results of bench and beam tests of both IC and PC based MSGCs are presented and their performance in BNL-E885 is discussed. E885 marks the first use of PC based MSGCs in an experiment.

The design and performance of a wire stringing machine for stringing multiwire proportional chambers and planar drift chambers is discussed.

We have studied the properties of a new type of gas microstrip counter built using flexible printed circuit technology. We describe the manufacturing procedures, the assembly of the device, as well as its operation under a variety of conditions, gases and types of radiation. We also describe two new passivation materials, tantalum and niobium, which produce effective surfaces.

We have studied the long-term operation of gas microstrip detectors which have been passivated with a layer of nickel oxide. We have used as the active gas CF4/isobutane (80:20) and three different types of substrates: Tedlar, glass and Upilex. In all three cases we found that the detectors are stable after passivation and can operate for a month without changes in gain at rates of MHz. The total accumulated charge was approximately 100 mC.

The T2K experiment is designed to study neutrino oscillation properties by directing a high intensity neutrino beam produced at J-PARC in Tokai, Japan, towards the large Super-Kamiokande detector located 295 km away, in Kamioka, Japan. The experiment includes a sophisticated near detector complex, 280 m downstream of the neutrino production target in order to measure the properties of the neutrino beam and to better understand neutrino interactions at the energy scale below a few GeV. A key element of the near detectors is the ND280 tracker, consisting of two active scintillator–bar target systems surrounded by three large time projection chambers (TPCs) for charged particle tracking. The data collected with the tracker are used to study charged current neutrino interaction rates and kinematics prior to oscillation, in order to reduce uncertainties in the oscillation measurements by the far detector. The tracker is surrounded by the former UA1/NOMAD dipole magnet and the TPCs measure the charges, momenta, and particle types of charged particles passing through them. Novel features of the TPC design include its rectangular box layout constructed from composite panels, the use of bulk micromegas detectors for gas amplification, electronics readout based on a new ASIC, and a photoelectron calibration system. This paper describes the design and construction of the TPCs, the micromegas modules, the readout electronics, the gas handling system, and shows the performance of the TPCs as deduced from measurements with particle beams, cosmic rays, and the calibration system.

The time dependence of muon spin relaxation has been measured in high purity aluminum and silver samples in a longitudinal 2 T magnetic field at room temperature, using time-differential \musr. For times greater than 10 ns, the shape fits well to a single exponential with relaxation rates of $\lambda_{\textrm{Al}} = 1.3 \pm 0.2\,(\textrm{stat.}) \pm 0.3\,(\textrm{syst.})\,\pms$ and $\lambda_{\textrm{Ag}} = 1.0 \pm 0.2\,(\textrm{stat.}) \pm 0.2\,(\textrm{syst.})\,\pms$.

The T2K experiment is a long-baseline neutrino oscillation experiment. Its main goal is to measure the last unknown lepton sector mixing angle {\theta}_{13} by observing {\nu}_e appearance in a {\nu}_{\mu} beam. It also aims to make a precision measurement of the known oscillation parameters, {\Delta}m^{2}_{23} and sin^{2} 2{\theta}_{23}, via {\nu}_{\mu} disappearance studies. Other goals of the experiment include various neutrino cross section measurements and sterile neutrino searches. The experiment uses an intense proton beam generated by the J-PARC accelerator in Tokai, Japan, and is composed of a neutrino beamline, a near detector complex (ND280), and a far detector (Super-Kamiokande) located 295 km away from J-PARC. This paper provides a comprehensive review of the instrumentation aspect of the T2K experiment and a summary of the vital information for each subsystem., Comment: 33 pages, 32 figures, Submitted and accepted by NIM A. Editor: Prof. Chang Kee Jung, Department of Physics and Astronomy, SUNY Stony Brook, chang.jung@sunysb.edu, 631-632-8108 Submit Edited to remove line numbers

Planar drift chambers will be used in a solenoidal magnetic field to measure the Michel parameters in muon decay. The chamber manufacture procedure uses flat glass tables and precise ceramic glass spacers to provide precise anode– cathode spacing. Results of bench and beam tests of the prototype chambers are discussed. # 2001 Elsevier Science B.V. All rights reserved.

The TWIST Collaboration has completed a new measurement of the energy-angle spectrum of positrons from the decay of highly polarized muons. A simultaneous measurement of the muon decay parameters {rho}, {delta}, and P{sub {mu}}{sup {pi}{xi}} tests the standard model in a purely leptonic process and provides improved limits for relevant extensions to the standard model. Specifically, for the generalized left-right symmetric model |(g{sub R}/g{sub L}){zeta}| 578 GeV/c{sup 2}, both 90% C.L.

We present the first measurement of the energy spectrum up to 70 MeV of electrons from the decay of negative muons after they become bound in $^{27}\mathrm{Al}$ atoms. The data were taken with the TWIST apparatus at TRIUMF. We find a muon lifetime of $(864.6\ifmmode\pm\else\textpm\fi{}1.2)\text{ }\text{ }\mathrm{ns}$, in agreement with earlier measurements. The asymmetry of the decay spectrum is consistent with zero, indicating that the atomic capture has completely depolarized the muons. The measured momentum spectrum is in reasonable agreement with theoretical predictions at the higher energies, but differences around the peak of the spectrum indicate the need for $\mathcal{O}(\ensuremath{\alpha})$ radiative corrections to the calculations. The present measurement is the most precise measurement of the decay spectrum of muons bound to any nucleus.

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

The TWIST Collaboration has performed new measurements of two of the parameters that describe muon decay: {rho}, which governs the shape of the overall momentum spectrum, and {delta}, which governs the momentum dependence of the parity-violating decay asymmetry. This analysis gives the results {rho}=0.750 14{+-}0.000 17(stat){+-}0.000 44(syst){+-}0.000 11({eta}), where the last uncertainty arises from the correlation between {rho} and the decay parameter {eta}, and {delta}=0.750 67{+-}0.000 30(stat){+-}0.000 67(syst). These are consistent with the value of 3/4 given for both parameters in the standard model of particle physics, and are a factor of two more precise than the measurements previously published by TWIST. A new global analysis of all available muon decay data incorporating these results is presented. Improved lower and upper limits on the decay parameter P{sub {mu}}{sup {pi}}{xi} of 0.995 24

The quantity P{sub {mu}}{sup {pi}}{xi}, where {xi} is one of the muon decay parameters and P{sub {mu}}{sup {pi}} is the degree of muon polarization in pion decay, has been measured. The value P{sub {mu}}{sup {pi}}{xi}=1.0003{+-}0.0006(stat.){+-}0.0038(syst.) was obtained. This result agrees with previous measurements but is over a factor of 2 more precise. It also agrees with the Standard Model prediction for P{sub {mu}}{sup {pi}}{xi} and thus leads to restrictions on left-right symmetric models.

We have measured several properties of gas microstrip detectors built with Tedlar substrates and aluminum traces. We used several gases including argon/ethane mixtures as well as CF/sub 4//isobutane. Gain and timing properties were measured, but our principal concern in this paper was the long term stability of these types of detectors. It was found that gain changes and discharges were the main problems. We could solve both by passivating the prints with a thin metal oxide layer. >

The muon decay parameter {delta} has been measured by the TWIST collaboration. We find {delta}=0.74964{+-}0.00066(stat.){+-}0.00112(syst.), consistent with the standard model value of 3/4. This result implies that the product P{sub {mu}}{xi} of the muon polarization in pion decay, P{sub {mu}}, and the muon decay parameter {xi} falls within the 90% confidence interval 0.9960

To measure the muon decay parameters with high accuracy, we require an array of precision drift detector layers whose relative position is known with very high accuracy. This article describes the design, construction and performance of these detectors in the TWIST (TRIUMF Weak Interaction Symmetry Test) spectrometer., 44 pages, 16 Postscript figures, LaTeX2e, uses Elsevier class elsart.cls, package graphicx, submitted to Nuclear Instruments & Methods in Physics Research

The TWIST Collaboration has measured the Michel parameter $\rho$ in normal muon decay, $\mu^+ \to e^+ \nu_e \bar{\nu}_{\mu}$. In the Standard Model, $\rho$ = 3/4. Deviations from this value require mixing of left- and right-handed muon and electron couplings in the muon-decay Lagrangian. We find $\rho$ = 0.75080 $\pm$ 0.00044(stat.) $\pm$ 0.00093(syst.) $\pm$ 0.00023, where the last uncertainty represents the dependence of $\rho$ on the Michel parameter $\eta$. This result sets new limits on the $W_L-W_R$ mixing angle in left-right symmetric models., Comment: 4 pages, 3 figures, submitted to PRL

We have measured the efficiency, timing and pulse heights in several types of microstrip Gas Chambers with plastic substrates passivated with a thin Nickel layer. We used as active gas mixtures Argon/Isobutane and CF/sub 4//Isobutane. We placed the detectors in a secondary beam at TRIUMF tuned to a momentum of 100 MeV/c of pions, muons and electrons. Preliminary results indicate good efficiency for minimum ionizing particles in Argon/Isobutane mixtures but lesser efficiency in CF/sub 4/ based gases indicating the importance of high quality preamplifiers to increase the signal to noise ratio. >

We have studied the properties of a new type of Gas Microstrip Counter built using flexible printed circuit technology. We describe the manufacturing procedures, the assembly of the device, as well as its operation under a variety of conditions, gases and types of radiation. We also describe two new passivation materials, Tantalum and Niobium, which produce effective surfaces.

At TRIUMF we have an ongoing program of detector R&D. For example, small interelectrode very high rate MWPCs have been developed and are now routinely used in secondary channels at TRIUMF. In a related area the characteristics of ageing in a variety of gas mixtures have been intensely studied, with the remarkable performance of CF4/Isobutane (80:20) discovered. Indeed we have found that an ionization exposure of 0.5 Coulombs per cm of wire in this mixture will reverse existing anode wire damage in single‐wire chambers. TRIUMF is also designing a large volume (2×2×6 m) scintillating fiber detector. Consisting of 1.2×107 1 mm fibers, this detector will meet the requirements for many of the neutrino experiments proposed for the TRIUMF/KAON facility.

In several laboratories there is considerable interest in developing proportional chambers that are able to operate at high rate and suffer minimal degradation over an extended period of operation. However, the causes of damage and degradation in these devices are still poorly understood. At TRIUMF we have a continuing program to study ageing effects. Using several identical single wire test cells, we have investigated the ageing characteristics of CF4/Isobutane (80:20), Argon/Ethane (80:20), and Argon/Ethane/CF4 (48:48:4) [1–3]. With our early results [1] showing a superior ageing performance of the CF4/Iso mixture, we decided to test a small admixture (4%) of CF4 to Ar/Et to see if it would inhibit damage. 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 CF4/Iso chambers have shown effectively zero pulse height degradation and few other problems to accumulated charges exceeding 5 C/cm. The addition of 4% CF4 to the Ar/Et mixture has dramatically improved the ageing performance of the Ar/Et/CF4 cells.

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. >

A high-pressure high-repetition-rate pulsed-discharge technique is described. Ultraviolet preionization and voltage switching are integrated using spark-gap switches in a geometry such that they will irradiate the discharge gas. A repetition rate of 4000 pulses per second (pps) has been achieved.

Gas mixtures with high specific ionization allow the use of small interelectrode distances while still maintaining full efficiency. With the short electron drift distances the timing resolution is also improved. We have built and operated two 25 cm2 chambers with small interelectrode distances. Also single wire detector cells have been built to test gas mixture lifetimes. Various admixtures of CF4, DME, Isobutane, Ethane and Argon have been tested. Possible applications of such chambers are as beam profile monitors, position tagging of rare events and front end chambers in spectrometers.

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. >

Horizontal drift chambers of a relatively simple and inexpensive design are described. Four of these, each with an active area of 0.89 × 0.49 m2, constitute the basic detector system for a new focal-plane polarimeter at the medium resolution spectrometer (MRS) at TRIUMF. The inherent left-right ambiguity in the direction of drift was resolved using the ∼ 15% difference in the signals induced on adjacent (odd or even) cathode wires. With separate change integration of the pulses, a normalized and corrected odd-even difference is obtained from which the horizontal drift direction is reliably deduced. The odd-even difference is found to depend sensitively on the accuracy with which the anode wire is centered in the unit cell.

The (V-A) structure of the weak interaction was put into the standard model by hand in order to obtain agreement with experiments. These experiments, however, do not rule out relatively large deviations from this structure. Muon decay provides an ideal laboratory to test this structure, being a purely leptonic process. The TRIUMF Weak Interaction Symmetry Test (TWIST) will measure both the energy and emission-angle distribution of positrons from the decay of polarized muons. This will provide a simultaneous determination of the Michel parameters Pμξ, ρ and δ describing muon decay with a precision of a few parts in 104. Stringent limits may then be placed on the coupling constants, as well as the mass and mixing angle of a possible right-handed W boson (WR). In this paper the formalism for muon decay is presented, TWIST is described, and the expected results are discussed.