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| Issue 12, 2024 |
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Extracts from the Internet | ||
New particles containing b-quarks1 February 2012The collaboration Belle of the electron-positron collider ÊÅÊÂ in Japan has for the first time registered resonant states of bottomonium-like particles Zb(1P) and Zb(2P) with masses 10610 MeV and 10650 MeV, respectively, created in decays of bottomonium Υ(5S). The observed particles whose registration confidence was about 10 σ, belong to the family of so-called exotic hadrons consisting of more than three quarks. Like bottomonium, new particles include b and anti-b quarks as component particles but are electrically charged. This means that they contain at least two more quarks, perhaps u and anti-d. The ATLAS experiment running on the Large Hadron Collider discovered the bottomonium χb(3P) which is a pair b-anti-b in the triplet state. Earlier experiments revealed only the states χb(1P,2P) while the existence of χb(3P) was predicted theoretically. The particle χb(3P) with mass 10.54 GeV was detected through its radiative decay to Υ(1S,2S)γ and Υ → μ+μ-became the first new particle which was detected at the Large Hadron Collider with sufficient confidence (at the 6 σlevel). Sources: arXiv:1110.2251v1 [hep-ex], arXiv:1112.5154v2 [hep-ex] Thermodynamics of phase transition to the superfluid state1 February 2012Ì. Zwierlein (Massachusetts Institute of Technology, USA) and his colleagues studied the thermodynamic characteristics of substances in the transition to superfluid state. The gas of fermionic atoms 6Li was a mixture of atoms in the two lowest states of hyperfine splitting in a magnetic field near the Feshbach resonance. The atoms were cooled and confined in a magneto-optical trap. Optical absorption observations have shown that a cloud of superfluid gas builds up at the center of the trap, formed of atoms joined together into bosonic pairs and surrounded by unpaired atoms in the normal state. In this experiment, there was no need in independently measuring temperature since it was obtained in terms of gas density in the areas of traps with different confinement potential. Compressibility, density and pressure were measured with high accuracy using the same approach, which resulted in finding the equation of state of the gas, including that at the phase transition point. The transition occurred at Tc = 0.167(13)TF where TF is the Fermi temperature. Sharp rise in gas compressibility was found in the vicinity of Tc and a Λ-shaped feature appeared on the curve of heat capacity as a function of temperature, which is a characteristic feature of phase transitions of the second kind. Source: Science 335 563 (2011) Transfer of electrons on the surface of superfluid helium1 February 2012Researchers from Princeton University and Sandia National Laboratories developed an efficient technique for achieving controlled transfer of electrons along the surface. An array of 120 parallel microchannels 3 microns in diameter each, filled with superfluid helium at 1.6 Ê, were fabricated lithographically. An array of control electrodes and sensor electrodes which recorded the position of electrons with the accuracy of the distance between channels were arranged underneath the channels at right angles to them. Packages of 1 to 20 electrons were transferred along channels on the surface of helium by means of the running potential created on the electrodes. The structure thus created resembled a CCD matrix: the intersections of channels and control electrodes play the role of “pixels”. The feature noted specially was an exceptionally high efficiency and reliability of electron transfer: there was no loss of electrons from the packets even after the distance covered was ≈ 109 pixels (or 9 km), which stems from high electron mobility on the surface of superfluid helium. One additional channel was arranged at right angles to the rest of channels for electron transfer among the channels, demonstrating feasibility of 2D translations. This method may prove useful in creating and managing qubits (quantum bits). Source: Phys. Rev. Lett. 107 266803 (2011) Tunnelling-diode oscillator operating in THz range1 February 2012Ì. Feiginov (Technological University of Darmstadt, Germany) et al. created a tunneling diode capable of generating radiation at a record frequency of 1.1 THz at room temperature. At the heart of the device is a semiconductor heterostructure with two AlAs barriers and a quantum wall separating them. Each layer is about 1 nm thick. The operating frequency is limited by electron tunneling time and the time of Coulomb relaxation which is the decisive factor at this stage. However, it was possible to weaken the restriction on the relaxation by using special doping. Attached to the diode is the resonance antenna; the total size of the device does not exceed 1 mm2. Teraherz-range emission promises important practical applications, such as nondestructive medical diagnostics or search and detection of dangerous substances in protection and security systems. According to the calculations of the authors, their technology is likely to gradually raise the generated frequency to 3 THz as the parameters of the tunnel diode and the resonator go through optimization process. Source: Appl. Phys. Lett. 99 233506 (2011) Gamma-rays from the Tycho Brahe supernova remnant1 February 2012Gamma-ray emission from the remnant of the Tycho Brahe supernova whose explosion was observed in 1572 was now recorded at the 5 σ confidence level using the LAT gamma-ray telescope aboard Enrico Fermi Space Observatory. The supernova SN 1572 is of type Ià; it was created owing to the thermonuclear explosion of the white dwarf. According to observations, the explosion front continues to freely expand in one of the directions and the reverse shock wave develops, while in the opposite direction the front begins to slow down when it enters the region of high-density interstellar gas. The spectrum of radiation in the range 0.4-100 GeV fits quite well the models of radiation generation by cosmic rays accelerated on shockwaves. According to this model, accelerated protons collide with nuclei of the surrounding gas and produce neutral pions whose decays emit gamma photons. The measured integral flow of radiation in the specified interval is approximately 3.5 × 10-9 cm-2 c-1. Source: Astrophys. J. Lett. 744 2 (2012) |
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. | |
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