Kevin J. Coakley

Strong Loophole-Free Test of Local Realism

We performed an loophole-free test of Bells inequalities. The probability that local realism is compatible with our results is less than 5.9×10^-9.

Novel method to classify aerosol particles according to their mass-to-charge ratio—Aerosol particle mass analyser

A new method to classify aerosol particles according to their mass-to-charge ratio is proposed. This method works by balancing the electrostatic and centrifugal forces which act on particles introduced into a thin annular space formed between rotating cylindrical electrodes. Particles having a mass-to-charge ratio lying in a certain narrow range are taken out continuously as an aerosol suspension. A theoretical framework has been developed to calculate the transfer function which is defined as the ratio of the exiting particle flux to the entering particle flux. A similarity rule has been derived which states that a single nondimensional constant determines the shape of the transfer function. To examine the feasibility of the proposed principle, a prototype classifier was constructed, and the mass distribution of monodisperse particles nominally 0.309 μm in diameter was measured. The peak structures corresponding to singly, doubly, and triply charged particles were identified in the experimental spectra. The difference between theory and experiment in the peak location for the singly charged particles was about 6.5% in terms of mass, or 2.3% in terms of diameter.

Magnetic trapping of neutrons

Accurate measurement of the lifetime of the neutron (which is unstable to beta decay) is important for understanding the weak nuclear force and the creation of matter during the Big Bang. Previous measurements of the neutron lifetime have mainly been limited by certain systematic errors; however, these could in principle be avoided by performing measurements on neutrons stored in a magnetic trap. Neutral-particle and charged-particle traps are widely used for studying both composite and elementary particles, because they allow long interaction times and isolation of particles from perturbing environments. Here we report the magnetic trapping of neutrons. The trapping region is filled with superfluid 4He, which is used to load neutrons into the trap and as a scintillator to detect their decay. Neutrons in the trap have a lifetime of 750+330-200 seconds, mainly limited by their beta decay rather than trap losses. Our experiment verifies theoretical predictions regarding the loading process and magnetic trapping of neutrons. Further refinement of this method should lead to improved precision in the neutron lifetime measurement.

Neutrino detection with CLEAN

Abstract This article describes CLEAN, an approach to the detection of low-energy solar neutrinos and neutrinos released from supernovae. The CLEAN concept is based on the detection of elastic scattering events (neutrino–electron scattering and neutrino–nuclear scattering) in liquified noble gases such as liquid helium, liquid neon, and liquid xenon, all of which scintillate brightly in the ultraviolet. Key to the CLEAN technique is the use of a thin film of wavelength-shifting fluor to convert the ultraviolet scintillation light to the visible, thereby allowing detection by conventional photomultipliers. Liquid neon is a particularly promising medium for CLEAN. Because liquid neon has a high scintillation yield, has no long-lived radioactive isotopes, and can be easily purified by use of cold traps, it is an ideal medium for the detection of rare nuclear events. In addition, neon is inexpensive, dense, and transparent to its own scintillation light, making it practical for use in a large self-shielding apparatus. The central region of a full-sized detector would be a stainless steel tank holding approximately 135 metric tons of liquid neon. Inside the tank and suspended in the liquid neon would be several thousand photomultipliers. Monte Carlo simulations of gamma ray backgrounds have been performed assuming liquid neon as both shielding and detection medium. Gamma ray events occur with high probability in the outer parts of the detector. In contrast, neutrino scattering events occur uniformly throughout the detector. We discriminate background gamma ray events from events of interest based on a spatial maximum likelihood method estimate of event location. Background estimates for CLEAN are presented, as well as an evaluation of the sensitivity of the detector for p–p neutrinos. Given these simulations, the physics potential of the CLEAN approach is evaluated.

Estimating the Magnitude and Phase Response of a 50 GHz Sampling Oscilloscope Using the "Nose-to-Nose" Method

We describe estimation of the magnitude and phase response of a sampling oscilloscope with 50 GHz bandwidth using the nose-to-nose method. The measurements are corrected for the non-ideal properties of the oscilloscope and calibration apparatus, including mismatch and time-base distortion, drift, and jitter. The mean and standard deviation of repeated measurements of an ensemble of three oscilloscope samplers are reported, along with attempts to verify the magnitude calibration using a swept sine-wave method.

A cross-validation procedure for stopping the EM algorithm and deconvolution of neutron depth profiling spectra

The iterative EM (expectation maximization) algorithm is used to deconvolve neutron depth profiling spectra. Because of statistical noise in the data, artifacts in the estimated particle emission rate profile appear after too many iterations of the EM algorithm is stopped using a cross-validation procedure. The data are split into two independent halves. The EM algorithm is applied to one half of the data to get an estimate of the emission rates. The algorithm is stopped when the conditional likelihood of the other half of the data passes through its maximum. The roles of the two halves of the data are then switched to get a second estimate of the emission rates. The two estimates are then averaged. >

Estimation of Q-factors and resonant frequencies

We estimate the quality factor Q and resonant frequency f/sub 0/ of a microwave cavity based on observations of a resonance curve on an equally spaced frequency grid. The observed resonance curve is the squared magnitude of an observed complex scattering parameter. We characterize the variance of the additive noise in the observed resonance curve parametrically. Based on this noise characterization, we estimate Q and f/sub 0/ and other associated model parameters using the method of weighted least squares (WLS). Based on asymptotic statistical theory, we also estimate the one-sigma uncertainty of Q and f/sub 0/. In a simulation study, the WLS method outperforms the 3-dB method and the Estin method. For the case of measured resonances, we show that the WLS method yields the most precise estimates for the resonant frequency and quality factor, especially for resonances that are undercoupled. Given that the resonance curve is sampled at a fixed number of equally spaced frequencies in the neighborhood of the resonant frequency, we determine the optimal frequency spacing in order to minimize the asymptotic standard deviation of the estimate of either Q or f/sub 0/.

Fast neutron detection with 6Li-loaded liquid scintillator

We report on the development of a fast neutron detector using a liquid scintillator doped with enriched 6 Li. The lithium was introduced in the form of an aqueous LiCl micro-emulsion with a di-isopropylnaphthalene-based liquid scintillator. A 6 Li concentration of 0.15 % by weight was obtained. A 125 mL glass cell was lled with the scintillator and irradiated with ssion-source neutrons. Fast neutrons may produce recoil protons in the scintillator, and those neutrons that thermalize within the detector volume can be captured on the 6 Li. The energy of the neutron may be determined by the light output from recoiling protons, and the capture of the delayed thermal neutron reduces background events. In this paper, we discuss the development of this 6 Li-loaded liquid scintillator, demonstrate the operation of it in a detector, and compare its eciency and capture lifetime with Monte Carlo simulations. Data from a boron-loaded plastic scintillator were acquired for comparison. We also present a pulse-shape discrimination method for dierentiating between electronic and nuclear recoil events based on the Matusita distance between a normalized observed waveform and nuclear and electronic recoil template waveforms. The details of the measurements are discussed along with specics of the data analysis and its comparison with the Monte Carlo simulation.

Least-squares estimation of time-base distortion of sampling oscilloscopes

We present an efficient least-squares algorithm for estimating the time-base distortion of sampling oscilloscopes. The method requires measurements of signals at multiple phases and frequencies. The method can accurately estimate the order of the harmonic model that is used to account for the amplitude nonlinearity of the sampling channel. We study several practical problems related to the time-base distortion estimation, such as the effect of averaging and sample size requirements. We also compare the relative performance of various methods for estimating time-base distortion using simulated and measured data.

Alignment of noisy signals

We study the relative performance of various methods for aligning noisy one-dimensional signals. No knowledge of the shape of the misaligned signals is assumed. We simulate signals corrupted by both additive noise and timing jitter noise which are similar in complexity to nose-to-nose oscilloscope calibration signals collected at NIST. In one method, we estimate the relative shift of two signals as the difference of their estimated centroids, We present a new adaptive algorithm for centroid estimation. We also estimate relative shifts from three different implementations of cross-correlation analysis. In a complete implementation, for N signals, relative shifts are estimated from all N(N-1)/2 distinct pairs of signals. In a naive implementation, relative shifts are estimated from just (N-1) pairs of signals. In an iterative adaptive implementation, we estimate the relative shift of each signal with respect to a template signal which, at each iteration, is equated to the signal average of the aligned signals. In simulation experiments, 100 misaligned signals are generated. For all noise levels, the complete cross-correlation method yields the most accurate estimates of the relative shifts. The relative performance of the other methods depends on the noise levels.