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| Issue 12, 2024 |
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Extracts from the Internet | ||
Search for new physics on LHC1 April 2015Rare processes beyond the Standard Model of elementary particles are being sought in CMS and ATLAS experiments performed on Large Hadron Collider (LHC). Events in which hadron jets and lepton-antilepton pairs l anti-l (e+e- or μ+μ-) are involved and the “missing” transverse momentum, i.e., misbalance between the resultant measured momentum of reaction products and the initial momentum of pp is fixed, were selected among the products of pp collisions (with center of mass energy 8 TeV) and investigated. The additional momentum could be carried away by weakly interacting particles not registered in the experiment. In particular, the models of supersymmetry with Z-boson production in squark and gluino decays were verified. For the channel of l anti-l pair production in the decay of one Z-bozon ATLAS obtained a small, at the level of 3 σ, deviation from calculations within the Standard model. This deviation, if it does exist, may be thought of as a manifestation of the effects of supersymmetry. In the case of independent production of l and anti-l leptons no deviations were observed. In the CMS experiment, on the contrary, no deviations were registered for the Z → l anti-l process, and in the second case the excess of the signal over the background was found at the level of 2.6 σ. Since the deviations from the Standard Model are of little statistical significance and the data of the two experiments differ, it is untimely to speak of the new physics, and further studies are needed. Source: arXiv:1502.06031 [hep-ex], arXiv:1503.03290 [hep-ex] Quantum teleportation of two properties of the particle1 April 2015The effect of quantum teleportation has already been demonstrated in a number of experiments, however, the state of only one quantum degree of freedom of the particle was transferred. Researchers from the University of Science and Technology (Heifei, China) were the first to realize quantum teleportation of simultaneously two degrees of freedom of a unit photon, namely, its spin state and orbital angular momentum. Three pairs of photons in quantum-entangled states were used in the experiment. One of the pairs was “hyperentangled”, i.e., entangled in both the polarization states and the states of the orbital angular momentum of photons. This pair served as the quantum channel of teleportation and the other pairs were used for measurement and preparation of quantum states. The results of measurements taken on the initial photon (whose state was teleported) together with the measurement of the state of one of the two photons of the hyperentangled pair were transported to the recipient through the classical channel. Making use of this information, the recipient could bring the second photon of the hyperentangled pair to the quantum state of the initial photon, i.e., teleportation took place. The quantum fidelity confidently exceeded the classical level, which testified to a successful teleportation. Quantum teleportation of simultaneously several properties will possibly find practical applications in quantum communication and quantum calculations. Source: Nature 518 516 (2015) Observation of corpuscular-wave dualism of quasi-particles1 April 2015L. Piazza (Federal Polytechnic School of Lausanne, Switzerland) with colleagues observed wave and corpuscular properties of quasi-particles in one experiment. Surface polaritons (SP) in a metallic nanowire placed on a graphite substrate that served for heat removal was investigated. SP are electromagnetic surface wavesassociated with charge oscillations. Like ordinary particles, these quasi-particles possess corpuscular-wave dualism. A nanowire was exposed to a laser beam which generated itinerant SP. When reflected from the tips of the nanowire SP formed a standing wave along the wire. The structure of this standing wave was observed by the electron beam scattering. At the same time in each individual event the electron interacted with SP like with a particle, and the electron received an additional discrete energy increment ΔE = ± n2πω. As a result, a flow of scattered electrons both carried information on the spatial wave structure of SP and contained electrons with discrete energy increments corresponding to the corpuscular SP properties. Source: Nature Communications 6 6407 (2015) Pressure-induced superconductivity of MnP1 April 2015J.-G. Cheng (Institute of Physics, Chinese Academy of Science, China) and colleagues revealed for the first time that manganese phosphide MnP becomes a superconductor at a temperature below ≈ 1 K and a pressure of about 8 GPa. At low pressures, the magnetic field destroys Couper pairs, but with increasing pressure the magnetic properties weaken, which results in the occurrence of superconductivity in a narrow region of the phase diagram near ≈ 8 GPa where a quantum critical point exists. A similar effect of the occurrence of superconductivity was discovered earlier in the compound CrAs which, the same as MnP, has a spiral magnetic structure. MnP became the first known manganese-based superconductor. Its superconductivity was registered by a decrease in the electrical resistance and a change in the magnetic susceptibility. The close proximity of the magnetic and superconducting states of MnP may be indicative of a nonstandard mechanism of electron pairing due to quantum spin fluctuations. Source: Phys. Rev. Lett. 114 117001 (2015) Search for signals from dark matter annihilation1 April 2015Dwarf spheroidal galaxies are promising objects for the search of signals from dark matter particle annihilation because the relative content of dark matter in them is large and the background radiation is small. The cosmic gamma-ray telescope Fermi-LAT was used for six years to investigate 15 dwarf spheroids – the satellites of our Galaxy in the energy range of 500 MeV to 500 GeV. No statistically significant excess of gamma-ray signals from dwarf spheroids above the background was found. This implies that for dark matter particles of mass less than 100 GeV with the annihilation channel to pairs of quarks b anti-b or leptons τ+τ- the annihilation cross sectionis below the value ⟨σv⟩≈2.2 × 10-26 cm2 s-1 needed for thermal production of these particles in the early Universe. This restriction presents some difficulties for the most popular dark-matter model in the form of WIMP’s (weakly interacting massive particles). However, models with annihilation channels to light leptons are not excluded, for in these cases the restrictions on gamma-ray emission are weaker. Source: arXiv:1503.02641 [astro-ph.HE] |
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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