Session L14: Fundamental Constants

Status report on the measurement of the Planck constant using the NIST-3 watt balance

The watt balance allows the comparison of virtual mechanical power to virtual electrical power with uncertainties of a few parts in $10^8$. Since electrical power can be determined as the product of known numerical values, two frequencies, and the Planck constant by the virtue of modern quantum metrology, the watt balance is a link between mechanical power and the Planck constant, $h$. The NIST-3 watt balance was used in a 2007 measurement to determine $h$ with a relative uncertainty of $3.6\times10^{-8}$. We have recently started efforts for another high precision determination of $h$ with this instrument. We present the status of the effort, discuss the largest contributions to the uncertainty budget, and share our plans for the future.   

Is the Electron Orbital g-Factor Equal to 1 Exactly?

An important question addressed by Kusch et al in their pioneering experiments may be put as follows: If the electron g-factors are assumed corrected such that $g_L =1+\delta _L $ and$g_S =2+\delta _S $, what are the measurable magnitudes of $\delta _L $and $\delta _S $? To answer this question, Kusch et al used the resonance Zeeman technique with which they measured the quantity$\delta _S -2\delta _L =a_{SL}$. At that time, no independent value of $\delta _S \,\,\mbox{or}\,\,\delta _L $was available, hence it was not possible to separately determine the two unknowns ($\delta _L ,\,\delta _S )$. It was a practical necessity therefore to assume a value for one in order to determine the other, hence it was assumed that $\delta _L =0$. However, six decades have passed since Kusch et al skillfully measured the quantity $a_{SL} =\delta _S -2\delta _L $, carefully eliminating bound state contributions. In sequel, experimentalists have independently of $\delta _L $, measured $\delta _S $ with increasing precision and accuracy. A culmination of these efforts is the recent measurement of $\delta _S $ by Gabrielse et al. In view of the success recorded in the measurement of $\delta _S $, the question posed by Kusch et al will be reopened/discussed: Is it empirically justified to set $\delta _L $ equal to zero exactly? If we combine the recent measurement of $\delta _S $, together with that of $(\delta _S -2\delta _L )$, then it appears that$\delta _L =(-0.6\pm 0.3)\times 10^{-4}$. Does this imply that the electron orbital g-factor is also corrected?   

Progress at the Penning Trap Mass Spectrometer ``THe-Trap''

In 2008, the ``University of Washington Penning-Trap Mass Spectrometer'' (UW-PTMS), originally designed and built by the Van Dyck group, was moved to the Max-Planck-Insitute for Nuclear Physics in Heidelberg, Germany. It was set up in a dedicated laboratory that meets both the radiation-safety requirements, and the environment-stabilization demands for a high-precision measurement of the tritium/helium-3 mass ratio. Our goal is to measure this mass ratio with a relative uncertainty of $10^{-11}$, which would be more than an order of magnitude better than the previous best measurement. It would decrease the uncertainty in the tritium beta decay Q-value (an important parameter in the ongoing search for the neutrino mass by experiments such as KATRIN) by the same factor. In order to emphasize the specialization of our experiment with regard to \textbf{T}ritium and $^3$\textbf{He}lium, it was renamed to ``THe-Trap''. THe-Trap features a double Penning-trap for rapid ion exchange, an external ion source to minimize trap contamination, a novel Zener-based voltage source, and active as well as passive stabilization of temperature, pressure and the magnetic field of the superconducting magnet. An overview of the project and a report on the recent progress will be given.   

Towards a Precision Measurement of the Tritium Helium-3 Mass Difference

Fitting a low-energy beta-decay spectrum near its endpoint is a direct method for determining the absolute mass scale of electron neutrinos. This is the subject of the large-scale tritium beta-decay experiment KATRIN. Besides a value (or a limit) for a sum of squares of neutrino mass eigenvalues, the fit to KATRIN data, with absolute energy calibration, will also produce a value for ``the electron endpoint for zero neutrino mass'' which is closely related to the Q-value for the beta-decay. Hence, an independent value for the tritium beta-decay Q-value, derived from the 3T - 3He mass difference, can provide a strong test of the systematics of KATRIN. The Florida State University precision Penning trap mass spectrometer has previously produced the most precise values of more than 26 atomic masses, many of which have application to neutrinoless double-beta-decay and to determining fundamental constants. The system is currently being modified for measurements of ions with small m/q ratio, and that are radioactive, to enable a precise measurement of the tritium helium-3 mass difference.   

Classical Derivation of Fundamental Physical Constants

Classical derivation of fundamental constants is presented, in which respective fundamental physical constants are expressed entirely in terms of classical physical quantities. Black-body radiation law, Planck's constant, quantum Hall impedance, magnetic flux quantum, and the fine structure constant are derived based on causal, classical physical principles of quantum electrodynamics. Planck's constant is introduced as invariant product of four-vectors, i.e. as Lorentz-invariant physical quantity. Planck's constant as Lorentz-invariant classical physical quantity permits classical derivation of the other three fundamental constants, and attribution of tangible physical meanings based on classical physical principles. The numerical value of the respective fundamental constants is expressed and calculated entirely with classical physical quantities with accuracies within the uncertainties of their highest accuracy CODATA 2010 listed values.   

Testing the Constancy of the Velocity of Light

The constancy of the velocity of light, which is one of the most important postulates of modern physics, assumes that the speed of light is independent of the choice of observer regardless the relative motion between the light source and the observer. However, this postulate has never been directly experimentally tested. We present a measurement system which can directly test this postulate. This system consists of a transmitter and a distant receiver. The transmitter modulates the terrestrial 635 nm, 1550 nm lights and the starlights emitted from Capella, Betelgeuse, and Vega, which have large radial velocities with respect to the earth around the spring Equinox, into pulses simultaneously. These pulses are received by the distant receiver. We employ a terrestrial white light which travels along the exact path of the starlights to calibrate the system. We compare the arrival times of these pulses at the receiver, in which the startlight pulses have different degrees of delays with respect to the terrestrial pulses. The results indicate that the observed speeds of startlights are related to the radial velocities of the stars with respect to the earth.   

Tests and Analysis of Electromagnetic Models for Semiconductor-Metal Quantum-Well Lasers

This work tests the proposed electromagnetic models for quantum-well lasers by using several materials of semiconductors and metals. Different combinations of semiconductors and metals can generate various wavelengths and mode-couplings in such semiconductor waveguide structures with built-in metal-gratings. The numerical results of these models are computed by the photonic approach and verified by the optical approach. Even for the weak mode-coupling cases, the numerical results computed by both approaches have close values. Numerical results with post-analysis can summarize how the key parameters, such as grating geometry, well thickness, and layer thickness, affect the mode-couplings. The above results can be further interpreted by physics intuition and fundamental concepts so as to provide insights into the modeling and design of lasers for more applications.   

A study of a radon gas scrubber

Radon gas and its progeny are critical sources of background for low background experimental devices. The required reduction of radon levels in the air of the experimental area can typically be achieved with a radon scrubbing system. For testing purposes, a single column system has been built at USD to study the radon-adsorption properties of activated charcoal under different conditions. In this paper, we will demonstrate the working principle and test results.   

Measuring fast neutrons with large liquid scintillator for ultra-low background experiments

Characterizing neutron background is extremely important to the success of rare event physics research such as neutrinoless double-beta decay and dark matter searches. Measuring the energy spectrum of fast neutrons for an underground laboratory is difficult and it requires intensive R{\&}D for a given technology. We developed a neutron detector that is constructed using an aluminum tube with one meter in length and 5 inch in diameter filled with 12 liter liquid scintillators. The inner surface of the tube is painted with specular reflector and there are two 5" PMTs(Hamamatsu H4144) attached to both ends. The detector is calibrated with cosmic muons and radioactive sources. Both position independent and position dependent methods are employed to analyze the experimental data. Good neutron/gamma discrimination is found from few MeV to 50MeV above. We report the result for the measurements of fast neutrons on the surface and at underground in Soudan Mine.