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B. Plaster

Publications and source records attributed to B. Plaster.

34 records · Page 2Linked to original sources
arXiv2013

Framework for maximum likelihood analysis of neutron beta decay observables to resolve the limits of the V-A law

We assess the ability of future neutron beta decay measurements of up to O(10^{-4}) precision to falsify the standard model, particularly the V-A law, and to identify the dynamics beyond it. To do this, we employ a maximum likelihood statistical framework which incorporates both experimental and theoretical uncertainties. Using illustrative combined global fits to Monte Carlo pseudodata, we also quantify the importance of experimental measurements of the energy dependence of the angular correlation coefficients as input to such efforts, and we determine the precision to which ill-known "second-class" hadronic matrix elements must be determined in order to exact such tests.

hep-ph↗
arXiv2013

Precision Measurement of the Neutron Beta-Decay Asymmetry

A new measurement of the neutron $β$-decay asymmetry $A_0$ has been carried out by the UCNA collaboration using polarized ultracold neutrons (UCN) from the solid deuterium UCN source at the Los Alamos Neutron Science Center (LANSCE). Improvements in the experiment have led to reductions in both statistical and systematic uncertainties leading to $A_0 = -0.11954(55)_{\rm stat.}(98)_{\rm syst.}$, corresponding to the ratio of axial-vector to vector coupling $λ\equiv g_A/g_V = -1.2756(30)$.

nucl-ex↗
arXiv2012

Measurement of the neutron $β$-asymmetry parameter $A_0$ with ultracold neutrons

We present a detailed report of a measurement of the neutron $β$-asymmetry parameter $A_0$, the parity-violating angular correlation between the neutron spin and the decay electron momentum, performed with polarized ultracold neutrons (UCN). UCN were extracted from a pulsed spallation solid deuterium source and polarized via transport through a 7-T magnetic field. The polarized UCN were then transported through an adiabatic-fast-passage spin-flipper field region, prior to storage in a cylindrical decay volume situated within a 1-T $2 \times 2π$ solenoidal spectrometer. The asymmetry was extracted from measurements of the decay electrons in multiwire proportional chamber and plastic scintillator detector packages located on both ends of the spectrometer. From an analysis of data acquired during runs in 2008 and 2009, we report $A_0 = -0.11966 \pm 0.00089_{-0.00140} ^{+0.00123}$, from which we extract a value for the ratio of the weak axial-vector and vector coupling constants of the nucleon, $λ= g_A/g_V = -1.27590 \pm 0.00239_{-0.00377}^{+0.00331}$. Complete details of the analysis are presented.

nucl-ex↗
arXiv2011

Technique for high axial shielding factor performance of large-scale, thin, open-ended, cylindrical Metglas magnetic shields

Metglas 2705M is a low-cost commercially-available, high-permeability Cobalt-based magnetic alloy, provided as a 5.08-cm wide and 20.3-$μ$m thick ribbon foil. We present an optimized construction technique for single-shell, large-scale (human-size), thin, open-ended cylindrical Metglas magnetic shields. The measured DC axial and transverse magnetic shielding factors of our 0.61-m diameter and 1.83-m long shields in the Earth's magnetic field were 267 and 1500, for material thicknesses of only 122 $μ$m (i.e., 6 foil layers). The axial shielding performance of our single-shell Metglas magnetic shields, obtained without the use of magnetic shaking techniques, is comparable to the performance of significantly thicker, multiple-shell, open-ended Metglas magnetic shields in comparable-magnitude, low-frequency applied external fields reported previously in the literature.

physics.atom-ph↗
arXiv2011

Impact of motion along the field direction on geometric-phase-induced false electric dipole moment signals

Geometric-phase-induced false electric dipole moment (EDM) signals, resulting from interference between magnetic field gradients and particle motion in electric fields, have been studied extensively in the literature, especially for neutron EDM experiments utilizing stored ultracold neutrons and co-magnetometer atoms. Previous studies have considered particle motion in the transverse plane perpendicular to the direction of the applied electric and magnetic fields. We show, via Monte Carlo studies, that motion along the field direction can impact the magnitude of this false EDM signal if the wall surfaces are rough such that the wall collisions can be modeled as diffuse, with the results dependent on the size of the storage cell's dimension along the field direction.

nucl-ex↗
arXiv2010

Determination of the Axial-Vector Weak Coupling Constant with Ultracold Neutrons

A precise measurement of the neutron decay $β$-asymmetry $A_0$ has been carried out using polarized ultracold neutrons (UCN) from the pulsed spallation UCN source at the Los Alamos Neutron Science Center (LANSCE). Combining data obtained in 2008 and 2009, we report $A_0 = -0.11966 \pm 0.00089_{-0.00140}^{+0.00123}$, from which we determine the ratio of the axial-vector to vector weak coupling of the nucleon $g_A/g_V = -1.27590_{-0.00445}^{+0.00409}$.

nucl-ex↗
arXiv2010

Flavor Physics in the Quark Sector

One of the major challenges of particle physics has been to gain an in-depth understanding of the role of quark flavor and measurements and theoretical interpretations of their results have advanced tremendously: apart from masses and quantum numbers of flavor particles, there now exist detailed measurements of the characteristics of their interactions allowing stringent tests of Standard Model predictions. Among the most interesting phenomena of flavor physics is the violation of the CP symmetry that has been subtle and difficult to explore. Till early 1990s observations of CP violation were confined to neutral $K$ mesons, but since then a large number of CP-violating processes have been studied in detail in neutral $B$ mesons. In parallel, measurements of the couplings of the heavy quarks and the dynamics for their decays in large samples of $K, D$, and $B$ mesons have been greatly improved in accuracy and the results are being used as probes in the search for deviations from the Standard Model. In the near future, there will be a transition from the current to a new generation of experiments, thus a review of the status of quark flavor physics is timely. This report summarizes the results of the current generation of experiments that is about to be completed and it confronts these results with the theoretical understanding of the field.

hep-ph↗
arXiv2008

Motional Spin Relaxation in Large Electric Fields

We discuss the precession of spin-polarized Ultra Cold Neutrons (UCN) and $^{3}$He atoms in uniform and static magnetic and electric fields and calculate the spin relaxation effects from motional $v\times E$ magnetic fields. Particle motion in an electric field creates a motional $v\times E$ magnetic field, which when combined with collisions, produces variations of the total magnetic field and results in spin relaxation of neutron and $^{3}$He samples. The spin relaxation times $T_{1}$ (longitudinal) and $T_{2}$ (transverse) of spin-polarized UCN and $^{3}$He atoms are important considerations in a new search for the neutron Electric Dipole Moment at the SNS \emph{nEDM} experiment. We use a Monte Carlo approach to simulate the relaxation of spins due to the motional $v\times E$ field for UCN and for $^{3}$He atoms at temperatures below $600,\mathrm{mK}$. We find the relaxation times for the neutron due to the $v\times E$ effect to be long compared to the neutron lifetime, while the $^{3}$He relaxation times may be important for the \emph{nEDM} experiment.

nucl-ex↗
arXiv2008

A solenoidal electron spectrometer for a precision measurement of the neutron $β$-asymmetry with ultracold neutrons

We describe an electron spectrometer designed for a precision measurement of the neutron $β$-asymmetry with spin-polarized ultracold neutrons. The spectrometer consists of a 1.0-Tesla solenoidal field with two identical multiwire proportional chamber and plastic scintillator electron detector packages situated within 0.6-Tesla field-expansion regions. Select results from performance studies of the spectrometer with calibration sources are reported.

nucl-ex↗
arXiv2007

A Multiwire Proportional Chamber for Precision Studies of Neutron Beta Decay Angular Correlations

A new multiwire proportional chamber (MWPC) was designed and constructed for precision studies of neutron beta decay angular correlations. Its design has several novel features, including the use of low pressure neopentane as the MWPC gas and an entrance window made of thin Mylar sheet reinforced with Kevlar fibers. In the initial off-line performance tests, the gas gain of neopentane and the position resolution were studied.

physics.ins-det↗
arXiv2005

New Measurements and Quantitative Analysis of Electron Backscattering in the Energy Range of Neutron Beta-Decay

We report on the first detailed measurements of electron backscattering from plastic scintillator targets, extending our previous work on beryllium and silicon targets. The scintillator experiment posed several additional experimental challenges associated with charging of the scintillator target, and those challenges are addressed in detail. In addition, we quantitatively compare the energy and angular distributions of this data, and our previous data, with electron transport simulations based on the Geant4 and Penelope Monte Carlo simulation codes. The Penelope simulation is found globally to give a superior description of the data. Such information is crucial for a broad array of weak-interaction physics experiments, where electron backscattering can give rise to the dominant detector-related systematic uncertainty.

nucl-ex↗
arXiv2005

Measurements of the neutron electric to magnetic form factor ratio GEn/GMn via the ^2H(\vec{e},e'\vec{n})^1H reaction to Q^2 = 1.45 (GeV/c)^2

We report values for the neutron electric to magnetic form factor ratio, GEn/GMn, deduced from measurements of the neutron's recoil polarization in the quasielastic 2H(\vec{e},e'\vec{n})1H reaction, at three Q^2 values of 0.45, 1.13, and 1.45 (GeV/c)^2. The data at Q^2 = 1.13 and 1.45 (GeV/c)^2 are the first direct experimental measurements of GEn employing polarization degrees of freedom in the Q^2 > 1 (GeV/c)^2 region and stand as the most precise determinations of GEn for all values of Q^2.

nucl-ex↗
arXiv2004

Evidence for Strange Quark Contributions to the Nucleon's Form Factors at $Q^2$ = 0.108 (GeV/c)$^2$

We report on a measurement of the parity violating asymmetry in the elastic scattering of polarized electrons off unpolarized protons with the A4 apparatus at MAMI in Mainz at a four momentum transfer value of $Q^2$ = \Qsquare (GeV/c)$^2$ and at a forward electron scattering angle of 30$^\circ < θ_e < 40^\circ$. The measured asymmetry is $A_{LR}(\vec{e}p)$ = (\Aphys $\pm$ \Deltastat$_{stat}$ $\pm$ \Deltasyst$_{syst}$) $\times$ 10$^{-6}$. The expectation from the Standard Model assuming no strangeness contribution to the vector current is A$_0$ = (\Azero $\pm$ \DeltaAzero) $\times$ 10$^{-6}$. We have improved the statistical accuracy by a factor of 3 as compared to our previous measurements at a higher $Q^2$. We have extracted the strangeness contribution to the electromagnetic form factors from our data to be $G_E^s$ + \FakGMs $G_M^s$ = \GEsGMs $\pm $ \DeltaGEsGMs at $Q^2$ = \Qsquare (GeV/c)$^2$. As in our previous measurement at higher momentum transfer for $G_E^s$ + 0.230 $G_M^s$, we again find the value for $G_E^s$ + \FakGMs $G_M^s$ to be positive, this time at an improved significance level of 2 $σ$.

nucl-ex↗
arXiv2004

Measurement of Strange Quark Contributions to the Nucleon's Form Factors at Q^2=0.230 (GeV/c)^2

We report on a measurement of the parity-violating asymmetry in the scattering of longitudinally polarized electrons on unpolarized protons at a $Q^2$ of 0.230 (GeV/c)^2 and a scattering angle of θ_e = 30^o - 40^o. Using a large acceptance fast PbF_2 calorimeter with a solid angle of ΔΩ= 0.62 sr the A4 experiment is the first parity violation experiment to count individual scattering events. The measured asymmetry is A_{phys} =(-5.44 +- 0.54_{stat} +- 0.27_{\rm sys}) 10^{-6}. The Standard Model expectation assuming no strangeness contributions to the vector form factors is $A_0=(-6.30 +- 0.43) 10^{-6}$. The difference is a direct measurement of the strangeness contribution to the vector form factors of the proton. The extracted value is G^s_E + 0.225 G^s_M = 0.039 +- 0.034 or F^s_1 + 0.130 F^s_2 = 0.032 +- 0.028.

nucl-ex↗
arXiv2003

Measurements of GEn/GMn from the ^2H(vec{e},e'vec{n})^1H Reaction to Q^2=1.45 (GeV/c)^2

We report new measurements of the ratio of the electric form factor to the magnetic form factor of the neutron, GEn/GMn, obtained via recoil polarimetry from the quasielastic ^2H(vec{e},e'vec{n})^1H reaction at Q^2 values of 0.45, 1.13, and 1.45 (GeV/c)^2 with relative statistical uncertainties of 7.6 and 8.4% at the two higher Q^2 points, which were not reached previously via polarization measurements. Scale and systematic uncertainties are small.

nucl-ex↗