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| Issue 11, 2024 |
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Extracts from the Internet | ||
Search for supersymmetry effects in rare decays1 December 2012The LHCb Collaboration of the Large Hadron Collider was studying very rare decay channels B0s → μ+μ- and reported certain new constraints on the possible contribution of supersymmetry to the physics of these decays. The theory of supersymmetry, which unites bosons and fermions in a certain unifying version, is able to resolve a number of problems in elementary particle physics and offers several candidates to play the role of dark matter particles. B0s-mesons produced in pp-collisions consist of an s-quark and a b-antiquark and decay in the framework of the Standard Model to μ+μ- at a probability (3.1 ± 0.2) × 10-9. If supersymmetry were a reality, the decays would occur more often (up to twice as often) via the exchange of neutral Higgs bosons. By the beginning of 2012, several events of B0s → μ+μ- decays were detected in the LHCb experiment and a bound from above on the decay probability, < 4.5 × 10-9 at confidence level 95%, was obtained. This result agrees with the prediction of the Standard Model, while the absence of a significant contribution of supersymmetry constrains minimum supersymmetric models that would predict higher probabilities; however, this does not preclude the possibility of more complex models of supersymmetry. Sources: arXiv:1208.3355 [hep-ex]), University of Cambridge Quantum delayed-choice experiment1 December 2012A. Peruzzo (Bristol University, UK) et al have carried out a new version of the quantum experiment with delayed choice (the general idea of such experiment was suggested by John Wheeler), in which the experimenter chooses the method of measurement while the recorded photons manifest themselves as waves or particles depending on the choice made. In this experiment, which was carried out using the “photonic chip”, the triggering of the method of measurement was implemented using a quantum key — a splitter, whose on or off configurations were dictated by the quantum state of the auxiliary control photons. The superposition of two states of the control photon corresponded to the superposition of the measurement types, and therefore, in a certain sense, a simultaneous measurement of corpuscular and wave properties was carried out. Note also that by changing the weights of the states of the control photon it was possible to achieve a continuous transition from measuring the corpuscular to measuring the wave properties. The experiment also studied Bell's inequality for the states of photons at the output. The maximum valuation of these inequalities showed that quantum effects took place which were not reducible to classical effects, e.g. in the form of “hidden parameters”. Source: Science 338 634 (2012) Amplification of quantum bits1 December 2012G.J. Pryde (Griffits University, Australia) and his colleagues demonstrated a technique for amplifying quantum bits, that is, cubits coded into polarisation states of photons. When quantum information is transmitted, we face the problem of state decoherence due to noise, absorption and scattering of photons in transmission lines. To amplify the useful signal, the researchers transferred the photon states that carried the cubit and passed through a noisy line, and the information was transmitted to another photon placed in better environment. It is important that states were transferred through the interferometer in a random manner since otherwise the deterministic transfer would result in quantum decoherence. Using polarisation splitters, independent two-channel amplification of states with orthogonal polarizations was carried out, and these states were again mixed at amplifier output. As a result, it was possible to achieve nearly five-fold improvement in the quality of transmission (the fidelity) of a quantum signal. This technique may prove important for devices designed for quantum calculations and transfer of quantum information. Source: Nature Physics, published online November 11, 2012 ã. Cooper pairs in aromatic hydrocarbons1 December 2012R. Wehlitz (Wisconsin-Madison University, USA) et al found the effect of formation of short-lived pairs of electrons similar to Cooper pairs, under double photoexcitation of molecules of aromatic hydrocarbons by photons of a synchrotron source. To measure the spectra of photoelectrons, they used electrostatic analysers. Pairs of electrons were produced in molecules of benzene, naphthalene, anthracene and coronene, which have the ring structure with one or several carbon-based rings. If the energy of a photon was roughly 40 eV higher than the threshold of double photoexcitation, a situation was possible when oscillations of the wave function of an electric pair corresponded to the periodic structure of atomic arrangement of atoms in the ring, and the ring length was the multiple of the de Broglie wavelength of the pair. This resulted in the formation of a short-lived bound pairs of the electrons which decayed soon after ejection from the molecule. As a rule, the electrons of the decayed pair were not moving in strictly opposite directions because they interacted with the positive ions in the molecule. In molecules of pyrrole and furan, which have 5-atom rings, the change in geometric configuration precluded pairing of electrons. Although, in contrast to Cooper pairs in superconductors, the pairs discovered in hydrocarbons are weakly coupled and easily decay, their study nevertheless can be useful for designing new organic superconductors. Source: Phys. Rev. Lett. 109 193001 (2012) Effect of intergalactic background on blazer spectra1 December 2012The Enrico Fermi Cosmic Gamma Observatory detected specific features in the spectra of blazers (one of the classes of Galaxies with active nuclei) at red shifts up to z = 1.6, that could be explained in terms of absorption of gamma photons in the interaction with the intergalactic background radiation in the optical and ultraviolet ranges in the γ + γ' → e+e- process. The source of the background radiation which also could be significant in re-ionization of the Universe was the aggregate emission by stars in Galaxies beginning from very early epochs, as well as the radiation that was generated in the accretion of matter onto black holes. Measurement of absorption in the spectra of individual blazers is also quite difficult but it was found to be statistically at 6 σ level for an array of 150 blazers. Direct measurement of this flux proved unfeasible due to absorption by dust in our Galaxy. The detected flux of intergalactic background radiation at the frequency of optical and UV ranges is 3( ± 1) nW m-2 sr-1 for z ≈ 1. This quantity is not very different from the flux generated by the active galactic nuclei. The measured flux provides an upper bound on the possible types of sources, for instance, bounds from above for the rate of star formation in the early universe. Source: Science 338 1190 (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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