Within the nonrelativistic quantum chromodynamics (NRQCD) factorization formalism, we compute the relativistic corrections to the exclusive decays of bottomonia with even charge conjugation parity into S-wave charmonium pairs at leading order in the strong coupling constant. Relativistic corrections are resummed for a class of color-singlet contributions to all orders in the charm-quark velocity v c in the charmonium rest frame. Almost every process that we consider in this work has negative relativistic corrections ranging from −20 to −35 %. Among the various processes, the relativistic corrections of the next-to-leading order in v c to the decay rate for χ b2 → η c (mS) + η c (nS) with m, n = 1 or 2 are very large. In every case, the resummation of the relativistic corrections enhances the rate in comparison with the next-to-leading-order results. We compare our results with available predictions based on the NRQCD factorization formalism. The NRQCD predictions are significantly smaller than those based on the light-cone formalism by 1 or 2 orders of magnitude.
We study the non-relativistic behavior of a particle with electric dipole moment and interacting with external electromagnetic fields on a noncommutative space (NCS). For a special configuration of the field, the phase of an electric dipole is derived as an application of the Aharonov-Bohm effect to a system composed of two charges. We find that the quantum phase for an electric dipole obtains some corrections, and these corrections depend on the noncommutative parameter explicitly.
The generation and control of high-quality proton bunches using focused intense laser pulse on an inverse cone target is investigated with a set of particle-in-cell simulations. The inverse cone is a high atomic number conical frustum with a thin solid top and open base, where the laser impinges onto the top surface directly, not down the open end of the cone. Results are compared with a simple planar target, where the proton angular distribution is very broad because of transverse divergence of the electromagnetic fields behind the target. For a conical target, hot electrons along the cone wall surface induce a transverse focusing sheath field. This field can effectively suppress the spatial spreading of the protons, resulting in a high-quality small-emittance, low-divergence proton beam. A slightly lower proton beam peak energy than that of a conventional planar target was also found.
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