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!
Astronomers release most complete ultraviolet-light survey of nearby galaxies
18.05.2018 | NASA/Goddard Space Flight Center
A quantum entanglement between two physically separated ultra-cold atomic clouds
17.05.2018 | University of the Basque Country
So-called quantum many-body scars allow quantum systems to stay out of equilibrium much longer, explaining experiment | Study published in Nature Physics
Recently, researchers from Harvard and MIT succeeded in trapping a record 53 atoms and individually controlling their quantum state, realizing what is called a...
The historic first detection of gravitational waves from colliding black holes far outside our galaxy opened a new window to understanding the universe. A...
A team led by Austrian experimental physicist Rainer Blatt has succeeded in characterizing the quantum entanglement of two spatially separated atoms by observing their light emission. This fundamental demonstration could lead to the development of highly sensitive optical gradiometers for the precise measurement of the gravitational field or the earth's magnetic field.
The age of quantum technology has long been heralded. Decades of research into the quantum world have led to the development of methods that make it possible...
Cardiovascular tissue engineering aims to treat heart disease with prostheses that grow and regenerate. Now, researchers from the University of Zurich, the Technical University Eindhoven and the Charité Berlin have successfully implanted regenerative heart valves, designed with the aid of computer simulations, into sheep for the first time.
Producing living tissue or organs based on human cells is one of the main research fields in regenerative medicine. Tissue engineering, which involves growing...
A team of scientists of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg investigated optically-induced superconductivity in the alkali-doped fulleride K3C60under high external pressures. This study allowed, on one hand, to uniquely assess the nature of the transient state as a superconducting phase. In addition, it unveiled the possibility to induce superconductivity in K3C60 at temperatures far above the -170 degrees Celsius hypothesized previously, and rather all the way to room temperature. The paper by Cantaluppi et al has been published in Nature Physics.
Unlike ordinary metals, superconductors have the unique capability of transporting electrical currents without any loss. Nowadays, their technological...
02.05.2018 | Event News
13.04.2018 | Event News
12.04.2018 | Event News
18.05.2018 | Power and Electrical Engineering
18.05.2018 | Information Technology
18.05.2018 | Information Technology