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| Issue 12, 2024 |
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Extracts from the Internet | ||
Search for Higgs boson at Tevatron accelerator1 September 2008Three rare events of production of pairs of Z bosons in proton-antiproton collisions were identified in the D0 experiment at the E. Fermi Laboratory on the Tevatron accelerator. ZZ pairs are the most massive among a series of the observed pairs of gauge bosons that includes photons, W and Z bosons. The next step may be the observations of a Z boson in a pair with a Higgs boson — the last particle predicted by the Standard model but not yet observed experimentally. The D0 detector recorded electrons and muons created in decays of Z bosons. Evidence of creation of ZZ pairs was obtained earlier by the CDF collaboration but the D0 experiment observed this process at a higher confidence level — at 5.3 σ. By combining D0 and CDF experimental data collected in the Tevatron accelerator it was possible to establish a new bound on the possible parameters of the Higgs boson. The range of masses in the vicinity of 170 GeV is now excluded with 95% probability. These results show that the Tevatron research is now very close to observing the Higgs boson and further progress is possible as statistical data is accumulated. The Higgs boson is also expected to be observed in the Large Hadron Collider which is now going through the test phase. Sources: http://arxiv.org/abs/0808.0703, http://www.physorg.com/news137076565.html Quantum mechanical effects1 September 2008Two groups of researchers at the University of California at Santa Barbara carried out new experiments testing the principles at the foundation of quantum mechanics. Ì. Hofheinz and coworkers demonstrated for the first time the possibility of creating in a controlled manner photons in Fock states within a resonator — quantum states with exactly determined number of particles. This became possible owing to creating a very high quality resonator. Microwave photons were sent into the resonator through a superconducting tunneling junction (SQUID). The state of the electromagnetic field in the resonator was studied with superconducting quantum “qubit” whose response showed quantum jumps corresponding to individual photons; in this way it was possible to record the existence of from one to six photons in the resonator. N. Katz and his colleagues conducted an experiment with a superconducting qubit (a Josephson contact closed by a superconducting loop and bridged by a capacitor) and were able to confirm the theory describing a partial collapse of the wave function and its return to the initial state under “weak” quantum measurements that introduce a very small perturbation into the quantum system under study. The effect of restoration of the initial quantum state was studied in a theoretical paper by A. Jordan and A. Korotkov in 2006. Sources: Nature 454 310 (2008), http://arxiv.org/abs/0806.3547 Inverse cascade in superfluid helium1 September 2008Researchers at the Lancaster University (Great Britain) and the Institute of Solid State Physics (Chernogolovka) studied heat propagation via second sound in superfluid helium. An electric heater with ac power supply was placed at one end of a cylindrical cryostat. Heat waves were transported along the cryostat by second sound at a speed of 20 m s-1. The transfer process was appreciably affected by the nonlinearity of the medium. As predicted by A.N. Kolmogorov's theory, transformation (“cascading”) of long-wavelength to short-wavelength modes and their damping on the small scales were observed. However, an effect of inverse cascading with energy pumped into long-wave perturbations was unexpectedly discovered beginning at a certain amplitude. The researchers point out that the wave equations for second sound in liquid helium resemble those for wave propagation on the surface of water and therefore the discovered inverse cascade may have common features with the buildup of giant waves. Source: Phys. Rev. Lett. 101 065303 (2008) Carbon tubes1 September 2008A group of American and Chinese researchers synthesized new carbon structures: tubes 40-100 µm in diameter and several centimeters in length. These tubes resemble the familiar carbon nanotubes but are thousands of times larger and visible even to the naked eye. The cylindrical walls of the tubes are about 1 µm thick and are formed of several layers of graphene with multiple inner pores on different scales. The average tube density is not very different from that of the carbon “nanofoam”. The tubes show very high mechanical strength and are semiconducting. The carbon tubes were obtained by chemical vapor deposition from a mixture of ethylene and paraffin oil heated to a temperature of 850° C in a quartz tube furnace. The tubes may find numerous useful applications both in production of superstrong fabrics and structures and in microelectronics. Source: http://physicsworld.com/cws/article/news/35364 New evidence in favor of dark energy1 September 2008In 1995 R. Crittenden and N. Turok suggested to use the Integrated Sachs–Wolfe effect to study the dynamics of galactic superclusters. The effect consists in that a cosmic microwave background photon propagating through an expanding supercluster would gain additional energy through its interaction with a nonstationary gravitational field. A group of astrophysicists led by I. Szapudi at the University of Hawaii succeeded in separating this small effect (on the order of 10-6) at a confidence level better than 4 σ. I. Szapudi studied cross-correlations of galaxy superclusters and giant voids of the “Sloan Digital Sky Survey” galaxy survey providing microwave background temperature map. Supeclusters and voids project to warm and cold spots, respectively, on microwave background. This data allowed the researchers to single out the effect of additional accelerated expansion of galaxy superclusters; as follows from General Relativity theory, accelerated expansion is caused by the presence in the Universe of dark energy that creates negative pressure. Sources: http://arxiv.org/abs/0805.2974v2, http://arxiv.org/abs/0805.3695v2 |
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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