Decays B0s → π+π- and B0 → K+K-
1 April 2017
The probabilities of B0s → π+π- and B0 → K+K- decays occurring in weak annihilation transitions were measured to the currently best accuracy in the LHCb experiment. The studies of these decays provide insight into the details of the processes in quantum chromodynamics and are helpful in search for the effects beyond the Standard Model. The B0s → π+π- decay has already been observed, while the B0 → K+K- decay has not yet been reliably registered in spite of its search on various accelerators. The LHCb experiment was carried out at pp center-of-mass collision energies of 7 TeV and 8 TeV. Special event selection criteria were applied allowing identification of the B0 → K+K- decays against the background of the dominating decays B0s → π+π-. The # decay was first observed with statistical significance of 5.8σ. This decay has the lowest probability among all the probabilities of purely hadron decays measured to-date.
Source: Phys. Rev. Lett. 118 081801 (2017)
Quantum clock in a gravitational field
1 April 2017
The researchers from the University of Vienna and the Institute for Quantum Optics and Quantum Information (Austria) E.C. Ruiza, F. Giacominia, and C. Bruknera studied the theoretical issue of the limiting precision of time measurements with allowance for the quantum processes and the effect of the gravitational field of clock on the space-time metrics. It was shown that the field of one clock influences the readings of the neighboring clocks, and the joint accuracy of time measurements along two close world lines has a fundamental limitation independent of the clock constitution. This is explained by the fact that if the time readings of the clock are determined by quantum processes, such quantum clock must be in superposition of the energy eigenstates, and the energy is the source of the gravitational field affecting the time flow at close points. As a result of the above-mentioned interaction the neighboring clocks become quantum entangled. Although today’s measurement precision is insufficient for observation of this effect, it can be essential in quantum gravitation.
Source: PNAS, online publication of March 7, 2017
Bose Einstein condensate in the state of a supersolid
1 April 2017
Supersolidity is the phenomenon combining crystal ordering and superfluidity. The effect had been predicted by A.A. Andreev and I.M. Lifshitz (Soviet Physics JETP, 1969) and independently by G.V. Chester (Phys. Rev. A, 1970) and A.J. Leggett (Phys. Rev. Lett., 1970). However, the recent reports on observation of supersolidity in solid helium-4 were not confirmed in consequent experiments. L.P. Pitaevskii et al. predicted in their theoretical works that this phenomenon can also occur in Bose-Einstein condensate with spin-orbital coupling. W. Ketterle (Massachusetts Institute of Technology, USA) with colleagues reported the first direct observation of supersolidity in Bose-Einstein condensate. The condensate of 105 atoms 23Na in an optical superlattice was investigated at temperatures of the order of nK. In the angular distribution of light scattered on the condensate, a singularity was observed corresponding to the so-called stripe phase, which was the hallmark of ordering. For the same gas parameters, using the free expansion method the gas was established to be in the superfluid state. Thus, the supersolidity was realized. In another independent experiment carried out in the Swiss Federal Institute of Technology in Zurich, the supersolid state in Bose-Einstein condensate was obtained by an alternative method in an optical cavity.
Source: Nature 543 87 (2017), Nature 543 91 (2017)
Magnetic writing on a single atom
1 April 2017
In the IBM Almaden Research Center in (USA) an experiment was performed under the guidance of A. Heinrich that demonstrated the writing and reading of magnetic information on single holmium (Ho) atoms on the surface of magnesium oxide MgO bilayer. The state was recorded – atoms were sent into one of the two directions of the magnetic moment – using current pulses from the needle of the scanning tunnel microscope. For reading the Ho atom state a magnetometer was used consisting of an iron atom located near a Ho atom. The character of the Zeeman splitting of Fe atom levels depended on the magnetic moment of the Ho atom, and the frequency of transition between sublevels shifted upon moment variation. The tunnel current through the Fe atom varied by 2 to 4 %. The magnetization direction of Ho atom was shown to remain unchanged for several hours at a temperature of 1.2 K (and in one experiment at 4.3 K). Moreover, the researchers created a structure including two Ho atoms and the neighboring Fe atom which served as a magnetometer as before. Four possible states were written and read on these atomic bits. The high magnetic stability together with the electric reading and writing method shows that a monatomic magnetic memory is actually possible.
Source: Nature 543 226 (2017)
Galaxies in the epoch of reionization
1 April 2017
The study of the Universe reionization is of great interest for comprehension of the mechanism of occurrence of first stars, galaxies, and quasars. Observed on the red shifts z≥7 are rather many early galaxies whose distribution may cast light on the course of reionization. Researchers from Chili, China, and USA investigated in the LAGER project a part of the sky 3 sq. degrees using a narrow-band filter on a 4-meter telescope. By using the Lyα emission line, 27 galaxies with z≥7 were identified of which 26 were observed for the first time. Their luminosity distribution corresponds to the Schechter function but with a certain excess of bright galaxies. This excess confirms the hypothesis that giant ionized gas bubbles due to inhomogeneous ionization exist in the Universe. A possible reason for the occurrence of inhomogeneities could be active galactic nuclei.
Source: arXiv:1703.02985 [astro-ph.GA]
The Extracts from the Internet is a section of Uspekhi Fizicheskih Nauk (Physics Uspekhi) the monthly rewiew journal of the current state of the most topical problems in physics and in associated fields. The presented News is devoted to the fundamental discoveries of physics and astrophysics.
Permanent editor is Yu.N. Eroshenko.
It is compiled from a multitude of Internet sources.