Laser pulse compression technology invented in the late 1980s resulted in high-power, short-pulse laser techniques, enhancing laser intensity 10 million-fold in a quarter of a century.
Scientists at Osaka University discovered a novel particle acceleration mechanism they describe as a micro-bubble implosion, in which super-high energy hydrogen ions (relativistic protons) are emitted at the moment when bubbles shrink to atomic size through the irradiation of hydrides with micron-sized spherical bubbles by ultraintense laser pulses. Their research results were published in Scientific Reports.
Read more here
When her ocean liner, the President Hoover, docked in San Francisco in 1936, Wu Chien-Shiung was surprised to find that discrimination against women was par for the course in the United States. She was told that female students at the University of Michigan, where she was soon to begin as a doctoral student, were not even permitted to use the front entrance of a brand-new student center; they had to scuttle quietly through a side door. It was a problem the “First Lady of Physics” would run up against again and again: when UC Berkeley refused to hire her despite an outstanding performance as a student and researcher, when Columbia University took eight years to promote her, and when the Nobel Prize in physics was given to her two male collaborators for their work in parity nonconservation but not to her.
Read the full story here
There is a long-standing discrepancy between the neutron lifetime measured in beam and bottle experiments. We propose to explain this anomaly by a dark decay channel for the neutron, involving one or more dark sector particles in the final state. If any of these particles are stable, they can be the dark matter. We construct representative particle physics models consistent with all experimental constraints.
Read more here
We have used superconducting high-resolution radiation detectors to measure the energy level of metastable 235mU as 76.737 ± 0.018 eV. The 235mU isomer is created from the α decay of 239Pu and embedded directly into the detector. When the 235mU subsequently decays, the energy is fully contained within the detector and is independent of the decay mode or the chemical state of the uranium. The detector is calibrated using an energy comb from a pulsed UV laser. A comparable measurement of the metastable 229mTh nucleus would enable a laser search for the exact transition energy in 229Th−229mTh as a step towards developing the first ever nuclear (baryonic) clock.
Read more here
The quantum Rabi model, involving a two-level system and a bosonic field mode, is arguably the simplest and most fundamental model describing quantum light-matter interactions. Historically, due to the restricted parameter regimes of natural light-matter processes, the richness of this model has been elusive in the lab. Here, we experimentally realize a quantum simulation of the quantum Rabi model in a single trapped ion, where the coupling strength between the simulated light mode and atom can be tuned at will. The versatility of the demonstrated quantum simulator enables us to experimentally explore the quantum Rabi model in detail, including a wide range of otherwise unaccessible phenomena, as those happening in the ultrastrong and deep strong-coupling regimes. In this sense, we are able to adiabatically generate the ground state of the quantum Rabi model in the deep strong-coupling regime, where we are able to detect the nontrivial entanglement between the bosonic field mode and the two-level system. Moreover, we observe the breakdown of the rotating-wave approximation when the coupling strength is increased, and the generation of phonon wave packets that bounce back and forth when the coupling reaches the deep strong-coupling regime. Finally, we also measure the energy spectrum of the quantum Rabi model in the ultrastrong-coupling regime.
Read more here
Today I am simply copying the press release announcing the precision measurement of the proton’s weak charge. For the original publication check this URL
Canadian researchers played a major role in an international collaboration that has gained new insight into the most elusive of the four fundamental forces in nature, the weak force. The Q-weak experiment has revealed the strength of the weak force’s grip on the proton, by measuring the proton’s weak charge to high precision. The research was carried out using the high quality polarized electron beam available at the Continuous Electron Beam Accelerator Facility, at the US Department of Energy’s Thomas Jefferson National Accelerator Facility. The result, published in the May 10 issue of Nature, significantly narrows the search for new particles that could influence the behavior of matter at sub-nuclear distance scales.
The proton’s weak charge is analogous to its more familiar electric charge, a measure of the influence the proton experiences from the electromagnetic force. These two interactions are closely related in the Standard Model of particle physics, a highly successful theory that describes the electromagnetic and weak forces as two different aspects of a single force that interacts with subatomic particles. Despite its success, the Standard Model has a number of shortcomings, such as the large number of parameters that are constrained only by experiment, or the absence of a clear explanation for the existence of dark matter. The proton’s weak charge can be predicted very precisely in the Standard Model, and a precise measurement then can be used to look for hints of new physics, via deviations from the Standard Model prediction.
To measure the proton’s weak charge, an intense beam of electrons was directed onto a target containing cold liquid hydrogen, and the electrons scattered from this target were detected in a precise, custom-built measuring apparatus. The key to the Q-weak experiment is that the electrons in the beam were highly polarized – prepared prior to acceleration to be mostly “spinning” in one direction, parallel or anti-parallel to the beam direction. With the direction of polarization rapidly reversed in a controlled manner, the experimenters were able to latch onto the weak interaction’s unique property of parity (spatial inversion) violation, in order to isolate its tiny effects to high precision: a different scattering rate by about 2 parts in 10 million was measured for the two beam polarization states.
The proton’s weak charge was found to be QWp=0.0719±0.0045, which turned out to be in excellent agreement with predictions of the Standard Model, taking into account all known subatomic particles and the forces that act on them.
“Our new Q-weak result constrains predictions of hitherto unobserved heavy particles, that could play a role in weak interactions, such as those that may be produced by the Large Hadron Collider (LHC) at CERN in Europe or at future high energy particle accelerators”, said Dr. Michael Gericke, a University of Manitoba member of the Canadian research team. “For example, Q-weak has set limits on the possible existence of leptoquarks — hypothetical particles that can reverse the identities of two broad classes of very different fundamental particles – turning quarks (the building blocks of nuclear matter) into leptons (electrons and their heavier counterparts) and vice versa.”
“The Q-weak experiment, initiated in 2001, represents the sustained effort of a large, international team of about 100 scientists from 25 institutions over nearly two decades”, said Dr. Shelley Page, a co-spokesperson and NSERC PI for the experiment. “The Canadian group was a founding member and represents approximately 15% of the Q- weak collaboration; it was a leading contributor to the equipment design and construction, data production, and analysis efforts”, she said.
More than $3M of support has been provided through the NSERC subatomic physics Project Grant program to the Canadian group, which includes scientists from the Universities of Manitoba, Northern BC, Winnipeg, and TRIUMF. These funds were used to build equipment and to support student and postdoctoral researchers’ salaries and travel to carry out the measurements at Jefferson Laboratory. Vital technical and engineering support was provided by TRIUMF, and detector development was carried out in CFI-funded laboratories at the Universities of Manitoba and Winnipeg. The Canadian group’s primary contributions include the design, fabrication, and field mapping of the large spectrometer magnet, the design and construction of the main electron detector package, development of a novel diamond microstrip detector used for precise Compton electron beam polarimetry, design and construction of low noise detector readout electronics, extensive systematic error simulations and data analysis.
The successful completion of the Q-Weak experiment is an important milestone in parity violating electroweak physics and sets the stage for a new measurement of the weak charge of the electron, at even higher precision – the MOLLER experiment – which is currently under development and in which a Canadian subatomic physics group from the University of Manitoba has again a strong position of leadership.
The experiment was funded by the United States Department of Energy, the National
Science Foundation, the Natural Sciences and Engineering Research Council of
Canada, and the Canadian Foundation for Innovation, with matching and in-kind
contributions from a number of the collaborating institutions.
On Aug. 6, 1945, the United States dropped an atomic bomb nicknamed “Little Boy” on Hiroshima, Japan, leading to a nuclear blast that instantly claimed about 45,000 lives. Now, the jawbone of one of those casualties — belonging to a person who was less than a mile from the bomb’s hypocenter — is helping researchers determine how much radiation was absorbed by the bones of the victims, a new study finds.
The amount is staggering: Analyses show that the jawbone’s radiation dose was about 9.46 grays (Gy). A Gy is the absorption of one joule of radiation energy per kilogram of matter, which in this case is bone.
read more here and the original publication in PLOS ONE here
In a laboratory experiment that mimics astrophysical conditions, with cryogenic temperatures in an ultrahigh vacuum, scientists used an electron gun to irradiate thin sheets of ice covered in basic molecules of methane, ammonia and carbon dioxide. These simple molecules are ingredients for the building blocks of life. The experiment tested how the combination of electrons and basic matter leads to more complex biomolecule forms — and perhaps eventually to life forms.
Read more here
The internal structure of the thorium-229m nuclear state has been studied in detail for the first time by physicists in Germany. Thorium-229m is a metastable (or isomer) excited state of thorium-229 that decays via the emission of an ultraviolet (UV) photon. This photon has much lower energy than most nuclear emissions and could form the basis of a “nuclear clock” that would be much more precise than existing atomic clocks.
Read more here
Έχει αναρτηθεί το νέο πρόγραμμα της εξεταστικής Ιουνίου (συν πτυχιακής) 2018
Δείτε το εδώ