Search for the Higgs boson at the Tevatron
1 April 2011
The total array of data currently available on the CDF è D0 experiments
at the Tevatron accelerator of the Fermilab indicates that the Higgs boson cannot have a
mass in the range from 156 to 183 GeV. Most of this interval is excluded at confidence level 95%,
although the level achieved in some sub-intervals is only 90%.
Higgs bosons are particles predicted by the Standard Model and are expected to be
produced at the Tevatron in p-anti-p collisions. So far the search for various channels of their decay
yielded negative results. In view of the excluded area, the Higgs boson mass can lie
either in a narrow range of 183-185 GeV or in the lower-mass range of 114-156 GeV.
In the latter case the Higgs boson must decay not into W±- and Z0 bosons but into heavy quarks that significantly complicate the task of identifying it. The
Tevatron accelerator is to accumulate more statistics until the final closing of the accelerator
planned for September 2011. The search for the Higgs boson also started in the ATLAS and CMS
experiments at the Large Hadron Collider.
Source: arXiv:1103.3233v2 [hep-ex]
Experimental verification of the no-hiding theorem
1 April 2011
Indian researchers J.R. Samal, A.K. Pati and A. Kumar demonstrated in their
experiment the validity of the no-hiding theorem formulated by S.L. Braunstein è
A.K. Pati in 2007. According to the no-hiding-theorem, the quantum information
that is bleached from a system cannot be hidden in the quantum correlations
between this system and its environment but is transferred to objects in the
environment. In this experiment the transfer of information in a system of three
quantum qubits, prepared as nuclei of the atoms of hydrogen, fluorine and carbon
in a single molecule of 13CHFBr2 was studied by an NMR technique.
Application of a series of electromagnetic pulses placed the first qubit in a
particular state, which was followed by randomization and a transfer of
information from the first to the other two qubits. Measurement of the qubit
state showed that eventually the entire quantum information has been transferred
to the third qubit, and that correlations between the qubits did not contain
additional information. It was also shown that the information which was on the
first qubit from the start could be restored from the states of the second and
third qubits up to a unitary transformation.
Source: Phys. Rev. Lett. 106 080401 (2011)
Spin-orbit coupling for atoms
1 April 2011
Y.-J. Tin, Ê. Jimenez-Garcia and L.B. Spielman of the Joint Quantum Institute
(JQI, U.S.A.) demonstrated the effect of spin-orbit coupling for atomic
87Rb in Bose – Einstein condensate. Owing to the contribution of internal orbital motions to the total angular momentum, the spin-orbit coupling has a
somewhat different mechanism for atoms than for electrons. In the experiment
described, sublevels mF = -1 and
mF = 0 of the ground state 5S1/2, F = 1 of 87Rb were selected as the two spin states of the atoms. These
sub-levels were linked to the state of the atom by a pair of laser beams
whose frequencies were slightly offset from the Raman resonance using
acousto-optic modulation. The beams intersected at the right angles at the
center of the optical dipole trap containing 1.8 × 105 atoms of the
Bose – Einstein condensate. The properties of the condensate were found from the way the cloud expanded after the trap potential had been switched off. The
spin-orbit coupling in the condensate is effectively given as the sum of equal
Rashba and Dresselhaus contributions, i.å. the corresponding interaction terms
in the Hamiltonian contained only the product kxσy of the wave number and the Pauli matrices, assuming the magnetic field to be directed along the z
axis. The strength of the spin-orbit interaction could be controlled by an
external magnetic field. When it increased beyond a certain critical value,
condensate atoms with mF = -1 and
mF = 0 spatially separated into two
clouds, thus demonstrating the effect of spin-orbit coupling for the atoms of 87Rb.
Source: Nature 471 83 (2011)
Spontaneous quantum transitions in superconducting structure
1 April 2011
R. Vijay and his colleagues at the University of California observed for the
first time spontaneous quantum transitions in so-called “artificial atoms”,
that is, superconducting transmon qubit that has discrete energy levels. The
qubit was an aluminum ring cooled down to 30 mK and was capacitively linked to a
microcavity. Microwave photons are reflected in the cavity receiving a phase
shift of magnitude that depends on the qubit state. This shift was measured
using a low-noise parametric amplifier based on comparator circuit; the reverse
effect of measurements on the qubit was found to be minimal and not perturbing
its state. This last feature is a consequence of the fact that the system was in
the quantum eigenstate of the measurand. The states of the qubit were monitored
every 10 ns, which allowed to establish the excited state of the qubit in real
time (the average lifetime is 320 ns) and record its quantum jump to the ground
state; the distribution of lifetimes decreased exponentially as is expected for
spontaneous decay. In the future this technique may find practical applications
for correcting errors in quantum computations.
Source: Phys. Rev. Lett. 106 110502 (2011)
The origin of giant gamma-ray bubbles above the galactic disk
1 April 2011
In 2010 the Fermi Gamma-ray Space Telescope observed gigantic volumes of space
on both sides of the galactic disk that emit radiation in the gamma range at
energies of 1-100 GeV and power of Fγ ≈ 4 × 1037 erg s-1.
These structures, with diameters of the order of 10 kpc, are also visible on
X-ray images obtained with the satellite ROSAT and in radio observations of the
WMAP detector. It has been suggested earlier that these gamma bubbles have been
generated as a result of energy release at the galactic center. The model in
which energy is released by a large number of supernovae can not explain these
observations, since no multiple residues of such explosions are found. For this
reason the central black hole and events of accretion onto it were proposed as
another plausible energy source. K.S. Cheng (University of Hong Kong),
D.O. Chernyshov and V.A. Dogel (P.N. Lebedev Institute of Physics, RAS, Moscow),
Ñ.-Ì. Ko and W.-H. Ip (Institute of Astronomy, Taiwan) offered a theoretical
explanation positing that energy is pumped into gamma-ray bubbles due to the
destruction of stars passing in the proximity of the supermassive black hole.
Approximately one half of the material of a captured star is injected into the
halo at a velocity of ≈ 109-1010 sm s-1, heats up the plasma in it and causes its luminosity in the x-ray range. The resulting shock waves
accelerate electrons to energies on the order of TeV. Moving in magnetic fields,
these electrons emit synchrotron radio emission, and inverse Compton scattering
of background photons generates gamma radiation. The rate of destruction of stars
required in this model is asymp; 3 × 10-5 yr-1. This model faithfully reproduces both the observed shape of the giant gamma-bubbles, and the spectra
of their radiation in a number of spectral ranges.
Source: Astrophysical Journal Letters (accepted)
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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