At the heart of this search to uncover a violation of time-reversal symmetry by observing a permanent electric dipole moment of the neutron (nEDM) is the $25 million nEDM experiment that Meyer and 60 other researchers from 15 institutes are working on.
But while searching for a non-zero separation of positive and negative charge inside a neutron (the symmetry-violating nEDM), Meyer ran into another mystery scientists have yet to explain.
Working with highly sensitive photomultipliers intended to detect the scintillation light given off during the nEDM experiment as charged particles emerge from reactions between neutrons and a rare isotope of helium, Meyer identified new attributes to a phenomenon called cryogenic electron emission.
In a recent paper in Europhysics Letters (Vol. 89, Issue 5), Meyer presents a thorough experimental investigation of the electron emission rate in the absence of light -- called the dark rate -- in which the rate of electron emission unexpectedly increases as a photomultiplier is cooled to liquid-helium temperature.
Once the temperature hit around -64 F and as it continued down to the lowest temperature measured during the experiment, -452 degrees F, electron emission from the cathode surface of the photomultiplier steadily increased. This is in contrast to the usual behavior of nature where processes tend to slow down as things get colder.Using two different photomultipliers (denoted by triangles and squares), Meyer found that dark rate electron emission decreased as the temperature (noted above in Kelvin) decreased until about -63.4 F (220 K), when the emission rate then began increasing while temperatures continued dropping to -452 F (4 K).
Meyer saw the electrons being emitted in bursts, noted that the burst duration distribution followed a power law and, as the temperature decreased, that both the rate of bursts and their size increased. Furthermore, he found that while the bursts occurred at random times, that within a given burst the emission of electrons obeyed a peculiar pattern in time.
Scientists have known about cryogenic emission for about 50 years. While other types of spontaneous electron emission without light are understood (thermal or heat, electrical field, and penetrating radiation electron emission), Meyer points out, "at this time, regrettably, a quantitative explanation of the observed characteristics of cryogenic emission is still eluding us."
"Most likely, this observation can eventually be explained within the known laws of physics, but there is always a small chance that we are seeing something new, and that this is a real discovery," he said.
Meyer suggests a trapping mechanism may be at work. How the trap is created and how it fills with or empties itself of electrons might be related to the behavior of traps in semiconductors. One clue pointing to a trap mechanism is the longer intervals between emitted electrons, from about three microseconds apart to three milliseconds apart as a given burst evolved.
A trap would hold electrons until full, then empty some electrons that become dark events measured by the photomultiplier, while others would recombine with an electron hole and thus go undetected. As fewer electrons remained, the release rate would slow.
Retired from teaching duties at the IU College of Arts and Sciences' Department of Physics and having graduated his last student two years ago, Meyer is still active in research at the IU Cyclotron Facility's new Center for Matter and Beams. He estimated continuing the experiment would cost about $500,000.
"I would be very pleased if someone younger would take up this investigation," he said.
And if someone else were to take up this mystery, a semi-retired Meyer has some thoughts on how to proceed.
"Ideally you would want to build an apparatus capable of presenting different surfaces of your choice, like copper, carbon or silicon for example, to an electron multiplier," he said. "The apparatus requires ultra-high vacuum, and the surfaces must be cooled to cryogenic temperatures. Such an experiment will tell us whether these trapping events are present only in semiconductors such as the cathode of a photomultiplier, or are of a more general nature."
To speak with Meyer, please contact Steve Chaplin, University Communications, at 812-856-1896 or email@example.com.
Steve Chaplin | EurekAlert!
Gamma ray camera offers new view on ultra-high energy electrons in plasma
28.10.2016 | American Physical Society
Scientists measure how ions bombard fusion device walls
28.10.2016 | American Physical Society
Physicists from the University of Würzburg have designed a light source that emits photon pairs. Two-photon sources are particularly well suited for tap-proof data encryption. The experiment's key ingredients: a semiconductor crystal and some sticky tape.
So-called monolayers are at the heart of the research activities. These "super materials" (as the prestigious science magazine "Nature" puts it) have been...
Ultrafast lasers have introduced new possibilities in engraving ultrafine structures, and scientists are now also investigating how to use them to etch microstructures into thin glass. There are possible applications in analytics (lab on a chip) and especially in electronics and the consumer sector, where great interest has been shown.
This new method was born of a surprising phenomenon: irradiating glass in a particular way with an ultrafast laser has the effect of making the glass up to a...
Terahertz excitation of selected crystal vibrations leads to an effective magnetic field that drives coherent spin motion
Controlling functional properties by light is one of the grand goals in modern condensed matter physics and materials science. A new study now demonstrates how...
Researchers from the Institute for Quantum Computing (IQC) at the University of Waterloo led the development of a new extensible wiring technique capable of controlling superconducting quantum bits, representing a significant step towards to the realization of a scalable quantum computer.
"The quantum socket is a wiring method that uses three-dimensional wires based on spring-loaded pins to address individual qubits," said Jeremy Béjanin, a PhD...
In a paper in Scientific Reports, a research team at Worcester Polytechnic Institute describes a novel light-activated phenomenon that could become the basis for applications as diverse as microscopic robotic grippers and more efficient solar cells.
A research team at Worcester Polytechnic Institute (WPI) has developed a revolutionary, light-activated semiconductor nanocomposite material that can be used...
14.10.2016 | Event News
14.10.2016 | Event News
12.10.2016 | Event News
28.10.2016 | Power and Electrical Engineering
28.10.2016 | Physics and Astronomy
28.10.2016 | Life Sciences