4,435 research outputs found
Baryons with two heavy quarks
We consider general physical characteristics of doubly heavy baryons: the
spectroscopy in the framework of potential approach and sum rules of QCD,
mechanisms of production in various interactions on the basis of fragmentation
model with account of preasymptotic corrections caused by higher twists over
the transverse momentum of baryon, inclusive decays and lifetimes in the
operator product expansion over the inverse powers of heavy quark masses as
well as the exclusive decays in the sum rules of QCD. We generalize the methods
developed in the effective theory of heavy quarks towards the description of
systems with two heavy quarks and a single light quark. The calculations are
presented for the masses, decay widths and yields of baryons with two heavy
quarks in the running and planned experimental facilities. We discuss the
prospects of search for the baryons and possibilities of experimental
observation. The most bright physical effects concerning these baryons as well
as their position in the system for the theoretical description of heavy quark
dynamics are considered.Comment: review, LaTeX file, 32 postscript figure
SU(3) Landau - Zener Interferometry
We consider a general theory of Landau-Zener transitions in a three-level
system. Based on a classification of three level crossings we express the
Landau - Zener Hamiltonians in terms of two bases: i) spin S=1 SU(2) operators
and ii) SU(3) Gell - Mann matrices. We show that the generic Hamiltonians being
non-linear in terms of the SU(2) group generators become linear in the SU(3)
basis. If the diabatic states of the SU(3) Landau - Zener Hamiltonian form a
triangle, the interference between two paths results in formation of "beats"
and "steps" pattern in the time-dependent transition probability. The
characteristic time scales describing the "beats" and "steps" depend on a dwell
time through the triangle. These scales are related to the geometric size of
the interferometer. We formulate the SU(3) Landau - Zener problem in terms of
Bloch dynamics of a unit vector and find a solution of eight-dimensional Bloch
equations in the limit of a non-adiabatic transition. Possible experiments in
triangular and linearly arranged triple quantum dots where Landau - Zener
interferometry can be used for finding manifestations of SU(3) symmetry are
discussed.Comment: 6 pages, 3 figure
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