Rare meson decays
1 May 2004
Among various channels for the K-meson decay, one
possibility is the rare decay into a pion and two neutrinos.
At the Brookhaven National Laboratory in
the US, the E787 and E949 collaborations (involving Russian
scientists from the RAS Institute for Nuclear Research,
Moscow and the Institute for High Energy Physics, Prot-
vino) have measured the probability of such a process to be
(1.47-0.89+1.30)x10-10, which is two times the value following from
the Standard Model. Because only three decay events were
detected in the experiments, there is a large statistical error in
this result. If this discrepancy is not a statistical fluctuation,
then new phenomena or particles beyond the Standard Model
can accept the explanation.
Superfluidity of a degenerate Fermi gas
1 May 2004
J Thomas and his colleagues at Duke University in the US
have for the first time found the evidence for superfluidity in a
degenerate Fermi gas of ultracold 6Li atoms. The team
studied the collective oscillations of a gas cloud confined in
a magneto-optical trap and evaporatively cooled down to the
Feshbach resonance. The oscillations were triggered by
briefly turning off the optical trap (laser). The frequency and
long damping time of the vibrations corresponded to the
vibrations of a superfluid jelly. The transition to the super-
fluid state occurred below the gas degeneracy temperature TF
in the interval 0.2-0.3TF.
Source: Phys. Rev. Lett. 92 150402 (2004)
Superconductivity of diamond
1 May 2004
Researchers from the Institute for High Pressure Physics
(Troitsk, Russia) and Los Alamos National Laboratory
(USA) have discovered superconductivity in diamond doped
with boron. Diamond was obtained through the reaction of
B4C with graphite at pressures of 8-9GPa and temperatures
of 2500-2800K, which lasted a few second. As a result of the
reaction, polycrystalline samples 1-2mm in size appeared at
the interface of the two substances. Thanks to their small size,
boron atoms easily penetrated into the crystal lattice, their
concentration in the diamond reaching a value of
4.9x1021/cm3. Measurements of electrical resistivity, mag-
netic susceptibility, and heat capacity revealed a super-
conducting transition at a temperature of about 4K. Boron-
doped diamond is a type II superconductor with a large
second critical field Hc2> 3.5T. Its properties are well
described by the Bardeen-Cooper-Schrieffer theory.
Source: Nature 428 542 (2004)
Biaxial liquid crystals
1 May 2004
All known to date liquid crystals possess one optical axis.
They consist of thread-like molecules of approximately
circular cross section that are all stretched in a single
direction. Theory has long predicted that for molecules of
flattened cross section bidirectional ordering can be achieved
in a liquid crystal. Now B R Acharya, A Primak, and S Kumar
from Kent State University in Ohio have for the first time
discovered this kind of biaxial crystals. A biaxial nematic
phase was detected in three materials with slightly different
molecular structures using an X-ray diffraction technique.
Ordering along the second molecular axis manifested itself in
the appearance of an additional peak in the diffraction
Source: Phys. Rev.
Lett. 92 145506 (2004)
A classical electron orbit in an atom
1 May 2004
Normally, an electron in an atom does not proceed along a
classical trajectory: whether the electron is present at this or
that point with respect to the nucleus is determined in a
probabilistic way by means of the wave function. However,
the concept of a classical orbit acquires a meaning if the
electron wave function is configured as a compact wave
packet. Earlier, atomic electron wave packets could only be
created for a very short time because of their dispersive
spreading. Now H Maeda and T Gallagher of the University
of Virginia have developed a new stabilization technique
which allows an electron in the form of a wave packet to
have enough time for making up to 15,000 revolutions around
the nucleus before the wave packet spreads out. The electron
trajectory was a highly elongated ellipse resided between the
Rydberg states n=70
and n=78 of the lithium atom. The electron
wave packet was stabilized by microwave radiation whose
frequency was in phase with the electronic nearest level's transitions.
The electrical field vector lay in the orbit plane along the
major axis of the ellipse.
Source: Phys. Rev. Lett. 92 133004 (2004)
The size of the radiating regionin sonoluminescence
1 May 2004
The mechanism of sonoluminescence, the light emission by
gas bubbles imploding under the action of sound in a liquid,
is not yet known (see Phys. Usp. 43 259 (2000) for a review). One important characteristic
which can shed new light upon this problem is the size of
the emitting region in the bubbles. J S Dam and M T Levinsen
have performed an experiment which has yielded an estimate
for the emitter size. Using a detector consisting of optical
fibers and photomultipliers, Dam and Levinsen observed the
way the radiation interfered with solid impurity particles
about 2mkm in size added to water and located at a distance
of 6-10 mm from the imploding (sonoluminescing) bubbles.
The interference pattern would be smoothed out if the
emitting region were large in size. The presence of inter-
ference suggested that the emitter is not more than 200 nm in
size - much smaller than the bubbles. This result, if correct,
rules out models in which radiation is generated uniformly
throughout the volume of an imploding gas bubble. The
absence of an interference pattern in very pure, impurity-free
water furnishes proof that the observed phenomenon is
indeed related to interference.
Rev. Lett. 92 144301 (2004)
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.
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