arXiv subjects

A. Olin

Publications and source records attributed to A. Olin.

At least 37 records · Page 2Linked to original sources

arXiv2010

Blind analysis results of the TWIST experiment

The TRIUMF Weak Interaction Symmetry Test (TWIST) experiment was designed to test the standard model at high precision in the purely leptonic decay of polarized muons. A general four-fermion interaction model is used to describe the muon decay. TWIST measures three of the four muon decay parameters of this model, $ρ$, $δ$ and $P_μ^π ξ$, from the shape of the momentum-angle spectrum. The results of this model independent approach are compared to the standard model predictions and used to constrain new physics. Our collaboration has finalized the blind analysis of the final experimental data taken in 2006 and 2007. This analysis mostly reached our goal of a precision of an order of magnitude improvement over the pre-TWIST measurements.

hep-ex↗

arXiv2010

Antihydrogen formation dynamics in a multipolar neutral anti-atom trap

Antihydrogen production in a neutral atom trap formed by an octupole-based magnetic field minimum is demonstrated using field-ionization of weakly bound anti-atoms. Using our unique annihilation imaging detector, we correlate antihydrogen detection by imaging and by field-ionization for the first time. We further establish how field-ionization causes radial redistribution of the antiprotons during antihydrogen formation and use this effect for the first simultaneous measurements of strongly and weakly bound antihydrogen atoms. Distinguishing between these provides critical information needed in the process of optimizing for trappable antihydrogen. These observations are of crucial importance to the ultimate goal of performing CPT tests involving antihydrogen, which likely depends upon trapping the anti-atom.

hep-ex↗

arXiv2009

Decay of negative muons bound in $^{27}$Al

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 $^{27}$Al atoms. The data were taken with the TWIST apparatus at TRIUMF. We find a muon lifetime of (864.6 $\pm$ 1.2) ns, in agreement with earlier measurements. The asymmetry of the decay spectrum is consistent with zero, indicating that the atomic capture has completely depolarised 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 \oalpha radiative corrections to the calculations. The present measurement is the most precise measurement of the decay spectrum of muons bound to any nucleus.

hep-ex↗

arXiv2008

A Precision Measurement of the Muon Decay Parameters $ρ$ and $δ$

The TWIST collaboration has performed new measurements of two of the parameters that describe muon decay: $ρ$, which governs the shape of the overall momentum spectrum, and $δ$, which governs the momentum dependence of the parity-violating decay asymmetry. This analysis gives the results $ρ=0.75014\pm 0.00017(\text{stat})\pm 0.00044(\text{syst})\pm 0.00011(η)$, where the last uncertainty arises from the correlation between $ρ$ and the decay parameter $η$, and $δ= 0.75067\pm 0.00030(\text{stat})\pm 0.00067(\text{syst})$. 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 $P_μ^πξ$ of $0.99524 < P_μ^πξ\leq ξ< 1.00091$ at 90% confidence are determined, where $P_μ^π$ is the polarization of the muon when it is created during pion decay, and $ξ$ governs the muon decay asymmetry. These results set new model-independent constraints on the possible weak interactions of right-handed particles. Specific implications for left-right symmetric models are discussed.

hep-ex↗

arXiv2008

A novel antiproton radial diagnostic based on octupole induced ballistic loss

We report results from a novel diagnostic that probes the outer radial profile of trapped antiproton clouds. The diagnostic allows us to determine the profile by monitoring the time-history of antiproton losses that occur as an octupole field in the antiproton confinement region is increased. We show several examples of how this diagnostic helps us to understand the radial dynamics of antiprotons in normal and nested Penning-Malmberg traps. Better understanding of these dynamics may aid current attempts to trap antihydrogen atoms.

physics.atom-ph↗

arXiv2008

Compression of Antiproton Clouds for Antihydrogen Trapping

Control of the radial profile of trapped antiproton clouds is critical to trapping antihydrogen. We report the first detailed measurements of the radial manipulation of antiproton clouds, including areal density compressions by factors as large as ten, by manipulating spatially overlapped electron plasmas. We show detailed measurements of the near-axis antiproton radial profile and its relation to that of the electron plasma.

nucl-ex↗

arXiv2008

Particle Physics Aspects of Antihydrogen Studies with ALPHA at CERN

We discuss aspects of antihydrogen studies, that relate to particle physics ideas and techniques, within the context of the ALPHA experiment at CERN's Antiproton Decelerator facility. We review the fundamental physics motivations for antihydrogen studies, and their potential physics reach. We argue that initial spectroscopy measurements, once antihydrogen is trapped, could provide competitive tests of CPT, possibly probing physics at the Planck Scale. We discuss some of the particle detection techniques used in ALPHA. Preliminary results from commissioning studies of a partial system of the ALPHA Si vertex detector are presented, the results of which highlight the power of annihilation vertex detection capability in antihydrogen studies.

hep-ex↗

arXiv2007

Towards Antihydrogen Confinement with the ALPHA Antihydrogen Trap

ALPHA is an international project that has recently begun experimentation at CERN's Antiproton Decelerator (AD) facility. The primary goal of ALPHA is stable trapping of cold antihydrogen atoms with the ultimate goal of precise spectroscopic comparisons with hydrogen. We discuss the status of the ALPHA project and the prospects for antihydrogen trapping.

nucl-ex↗

arXiv2006

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 $P_μ^π$ 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.

hep-ex↗

arXiv2006

Time expansion chamber system for characterization of TWIST low energy muon beams

A low mass time expansion chamber (TEC) has been developed to measure distributions of position and angle of the TRIUMF low energy surface muon beam used for the TWIST experiment. The experiment is a high precision measurement of muon decay and is dominated by systematic uncertainties, including the stability, reproducibility, and characterization of the beam. The distributions measured by two TEC modules are one essential ingredient of an accurate simulation of TWIST. The uncertainties, which are extracted through comparisons of data and simulation, must be known to assess potential systematic uncertainties of the TWIST results. The design criteria, construction, alignment, calibration, and operation of the TEC system are discussed, including experiences from initial beam studies. A brief description of the use of TEC data in the TWIST simulation is also included.

physics.ins-det↗

arXiv2006

A study of the proton spectra following the capture of $K^-$ in $^6$Li and $^{12}$C with FINUDA

Momenta spectra of protons emitted following the capture of $K^-$ in $^6$Li and $^{12}$C have been measured with 1% resolution. The $^{12}$C spectrum is smooth whereas for $^6$Li a well defined peak appears at about 500 MeV/$c$. The first observation of a structure in this region was identified as a strange tribaryon or, possibly, a $\bar K$-nuclear state. The peak is correlated with a $π^-$ coming from $Σ^-$ decay in flight, selected by setting momenta larger than 275 MeV/$c$. The $Σ^-$ could be produced, together with a 500 MeV/$c$ proton, by the capture of a $K^-$ in a deuteron-cluster substructure of the $^6$Li nucleus. The capture rate for such a reaction is $(1.62\pm 0.23_{stat} ^{+0.71}_{-0.44}(sys))%/K^-_{stop}$, in agreement with the existing observations on $^4$He targets and with the hypothesis that the $^6$Li nucleus can be interpreted as a $(d+α)$ cluster.

nucl-ex↗

arXiv2005

Measurement of the Muon Decay Parameter delta

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 Pmuxi of the muon polarization in pion decay, Pmu, and the muon decay parameter xi falls within the 90% confidence interval 0.9960 < Pmuxi < xi < 1.0040. It also has implications for left-right-symmetric and other extensions of the Standard Model.

hep-ex↗

arXiv2003

Scattering of p$μ$ muonic atoms in solid hydrogen

We present the results of experimental and theoretical study of the scattering of low energy p$μ$ atoms in solid hydrogen cooled to 3 K. The resulting emission of low energy p$μ$ atoms from the hydrogen layer into the adjacent vacuum was much higher than that predicted by calculations which ignored the solid nature of the hydrogen. New differential scattering cross sections have been calculated for the collisions of p$μ$ atoms on solid hydrogen to acount for its quantum crystalline nature. Analysis of the experimental data performed using such cross sections shows the important role of the coherent scattering in p$μ$ atom diffusion. For p$μ$ energies lower than the Bragg cutoff limit (2 meV) the elastic Bragg scattering vanishes which makes the total scattering cross section fall by several orders of magnitude, and thus the hydrogen target becomes transparent allowing the emission of cold p$μ$ atoms to occur.

nucl-ex↗

arXiv2003

The 21Na(p,gamma)22Mg Reaction and Oxygen-Neon Novae

The 21Na(p,gamma)22Mg reaction is expected to play an important role in the nucleosynthesis of 22Na in Oxygen-Neon novae. The decay of 22Na leads to the emission of a characteristic 1.275 MeV gamma-ray line. This report provides the first direct measurement of the rate of this reaction using a radioactive 21Na beam, and discusses its astrophysical implications. The energy of the important state was measured to be E$_{c.m.}$= 205.7 $\pm$ 0.5 keV with a resonance strength $ωγ= 1.03\pm0.16_{stat}\pm0.14_{sys}$ meV.

astro-ph↗

arXiv2001

Resonant Scattering of Muonic Hydrogen Atoms and Dynamics of Muonic Molecular Complex

Resonant scattering of muonic hydrogen atoms via back decay of molecular complex, a key process in the understanding of epithermal muonic molecular formation, is analyzed. The limitations of the effective rate approximation are discussed and the importance of the explicit treatment of the back decay is stressed. An expression of the energy distribution for the back-decayed atoms is given.

nucl-ex↗

arXiv2001

Measurement of the Resonant $dμt$ Molecular Formation Rate in Solid HD

Measurements of muon-catalyzed dt fusion ($dμt \to ^4He+n+μ^-$) in solid HD have been performed. The theory describing the energy dependent resonant molecular formation rate for the reaction $μt$ + HD $\to [(dμt)pee]^*$ is compared to experimental results in a pure solid HD target. Constraints on the rates are inferred through the use of a Monte Carlo model developed specifically for the experiment. From the time-of- flight analysis of fusion events in 16 and 37 $μg\cdot cm^{-2}$ targets, an average formation rate consistent with 0.897$\pm$(0.046)$_{stat}\pm$ (0.166)$_{syst}$ times the theoretical prediction was obtained.

physics.atom-ph↗

arXiv2001

Time-of-Flight Spectroscopy of Muonic Hydrogen Atoms and Molecules

Studies of muonic hydrogen atoms and molecules have been performed traditionally in bulk targets of gas, liquid or solid. At TRIUMF, Canada's meson facility, we have developed a new type of target system using multilayer thin films of solid hydrogen, which provides a beam of muonic hydrogen atoms in vacuum. Using the time-of-flight of the muonic atoms, the energy-dependent information of muonic reactions are obtained in direct manner. We discuss some unique measurements enabled by the new technique, with emphasis on processes relevant to muon catalyzed fusion.

nucl-ex↗

arXiv2000

Using Thin Film Targets for Muonic Atoms and Muon Catalyzed Fusion Studies

Studies of muonic atoms and muon catalyzed fusion have been conventionally done in a bulk target of gas, liquid or solid hydrogen isotopes. The use of thin film targets developed at TRIUMF have notable advantages in tackling some of the most important questions in the field, which could be further exploited at future high intensity muon sources. We review the technique of the thin film method with emphasis on recent results and a future proposal.

hep-ex↗