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Neutrino oscillations
1 July 2010
A number of experiments studying neutrino oscillations observed a reduction in
the number of muon neutrinos along neutrino beams; this, however, was only an
indirect indication that a different species of the neutrino appeared in the
beam. A qualitatively new result is now reported at the experiment OPERA where
the first appearance of tau neutrinos in the beam of muon neutrinos was
recorded. The OPERA detector at the Gran Sasso National Laboratory (Italy) sits
in a tunnel under a massive mountain. The working substances of the detector are
emulsion films alternating with plates of low-background-noise lead. In 2008 and
2009 the facility monitored the νμ beam with energy of about 17 GeV, sent
into the OPERA detector from the accelerator at CERN at a distance of 730 km
through the body of the Earth. The candidate event involving ντ was
identified by the characteristic topology of the decay of the τ-lepton
which was created in the interaction between the ντ and a lead nucleus.
The detection of the first candidate event of ντ with certainty of 98%
points to appreciable effect of neutrino oscillations νμ → ντ.
The confidence in the reality of neutrino oscillations will be achieved only
after several such events will have been recorded. Neutrino oscillations assume
that neutrinos have mass, which means going beyond the tenets of the
Standard Model of elementary particles. The OPERA experiment it being conducted
by the international team of researchers from 12 countries, which includes
researchers from five research institutions in Russia. In another experiment,
MINOS (being run since 2005 at the E. Fermi National Laboratory), a very accurate
comparison of the effects of neutrino and antineutrino oscillations has been
realized. The MINOS detector is located at a distance of 735 km from the
accelerator which generates the νμ and anti-νμ beam. The process
occurring in the detector is the magnetic separation and recording of muons and
antimuons generated by the interaction of νμ and anti-νμ with the
material of the detector. An unexpected result was obtained: the squared mass
difference of neutrinos, Δ m2, is 40% smaller than for the
corresponding species of antineutrinos. However, the statistical significance
of this result is only about 2 σ which means that further testing is
necessary. New theoretical approaches will have to be worked out in order to
explain this fundamental difference between the neutrino and the antineutrino,
provideded its reality is confirmed.
Sources: arXiv:1006.1623v1 [hep-ex],
physorg.com
Quantum teleportation to a distance of 16 km
1 July 2010
Õ.-Ì. Jin and his coworkers in China performed an experiment on quantum
teleportation of photon states through air at a distance of 16 km. In the
past it was only possible to implement teleportation over a distance of several
tens of meters for photons transmitted through an optical fiber. Quantum
teleportation assumes that a change in the state of one particle of a pair
instantaneously changes the state of the second remote particle which is in
entangled quantum state with the partner particle, i.e. the quantum state has
been teleported. Quantum entanglement of the state of motion of one photon and
the state of polarization of the second photon was produced here in a nonlinear
crystal, after which one of the photons of the pair was sent into the detector
located at a distance of 16 km. The two photons remained entangled with fidelity
of 89%, which is considerably higher than the classical limit equal to 2/3. The
experiment implemented all the main components of the scheme of quantum teleportation,
with the exception of the local unitary operation. Successful quantum teleportation at the
Earth's surface over a distance of 16 km (exceeding the effective thickness of the atmosphere
(≈10 km) has demonstrated the possibility of using this effect in optical communication
channels between ground stations and satellites.
Source: Nature Photonics 4 376 (2010)
Organic compound with metal's properties
1 July 2010
Researchers from the RAS Institute of Problems of Chemical Physics and
Institute of Solid State Physics together with their colleagues in Japan
succeeded in synthesizing N-methyl-ethyldiazobicyclooctane-triptycene-C60
an organic material which contains no metal atoms but possesses metallic
properties. The new crystalline material was obtained by diffusion method and
its structure was studied by X-ray diffraction. The material consists of planar
layers in which C60 anions are arranged in honeycomb pattern, fullerene
layers alternating with layers of molecules containing only atoms of light
elements: hydrogen, carbon and nitrogen. The dense packing structure in the
arrangement of fullerene molecules is supported by ring molecules of aromatic
hydrocarbon triptycene C20H14. Direct measurements using electrical
contacts fixed to specimens show that at temperatures above 1.9 K electric
conductivity of the material is at the level of metallic conductivity.
Source: Angewandte Chemie 49 4829 (2010)
Instantaneous velocity of a Brownian particle
1 July 2010
Ò. Li (University of Texas at Austin, USA) and colleagues studied the Brownian
motion of silica beads SiO2 about 3µm in size in air and for the first
time measured their instantaneous velocity. Typically experiments follow the
diffusive mode of Brownian motion over relatively long stretches of time when
〈(Δ x)2〉 ∝ t. However, over very short intervals of
time shorter than the relaxation time of particle momentum, the particle moves
by inertia, in ballistic mode. A particle of SiO2 was trapped into an optical
tweezer formed by two focused laser beams. The motion of a particle, which is
described by the Langevin equation in harmonic potential, was observed in the
reflected laser light at high time resolution. As expected, over short time
intervals the relation is 〈(Δ x)2〉 ∝ t2.
Furthermore, it has been established that the distribution of Brownian particles
corresponds to the Maxwell – Boltzmann distribution and that the particle energy
conforms with the energy equipartition theorem.
Source: Science 328 1673 (2010)
Anisotropy of cosmic rays in Southern hemisphere
1 July 2010
A number of experiments conducted in the Northern hemisphere detected a slight
anisotropy (of about 10-4 – 10-3) in the distribution of cosmic rays
with energies up to several TeV. Similar measurements of anisotropy in the TeV
region in the Southern hemisphere were first carried out in the IceCube
experiment conducted in Antarctica at the South Pole. The main purpose of the
IceCub experiment was to record neutrino events but it can also measure the flux
of cosmic rays. IceCube is to reach effective volume of 1 km3 and total
functionality in 2011 by which time 5160 optical modules are expected to be
installed on 86 strings in the ice at depths from 1450 to 2450 m. The described
measurements were conducted in 2007-2008 with only 22 strings installed. Among
the recorded data, 4.3 × 109 reliable events of detecting cosmic rays
particles with energies up to 20 TeV were selected, and the directions were
measured with angular resolution of 3°. Careful work was carried out for
removing from the experimental data the effects of asymmetric geometry of the
detector, seasonal variations and other factors that could distort the result.
The distribution of the measured intensity of cosmic rays in the Southern sky
smoothly matches the distribution which was previously obtained in the Northern
hemisphere. One possible explanation of the anisotropy lies in the peculiarities
in the distribution of interstellar magnetic fields in the vicinity of the Sun
on a scale less than one parsec. The nature of this anisotropy will probably be
clarified after the planned IceCube measurements of anisotropy as a function of
energy of particles.
Source: arXiv:1005.2960v1 [astro-ph.HE]
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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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