Ultracold neutron depolarization in magnetic bottles

We analyze the depolarization of ultracold neutrons confined in a magnetic field configuration similar to those used in existing or proposed magneto-gravitational storage experiments aiming at a precise measurement of the neutron lifetime. We use an extension of the semi-classical Majorana approach as well as an approximate quantum mechanical analysis, both pioneered by Walstrom et al. [Nucl. Instr. Meth. Phys. Res. A 599, 82 (2009)]. In contrast with this previous work we do not restrict the analysis to purely vertical modes of neutron motion. The lateral motion is shown to cause the predominant depolarization loss in a magnetic storage trap. The system studied also allowed us to estimate the depolarization loss suffered by ultracold neutrons totally reflected on a non-magnetic mirror immersed in a magnetic field. This problem is of preeminent importance in polarized neutron decay studies such as the measurement of the asymmetry parameter A using ultracold neutrons, and it may limit the efficiency of ultracold neutron polarizers based on passage through a high magnetic field.Comment: 18 pages, 6 figure

Spin flip loss in magnetic storage of ultracold neutrons

We analyze the depolarization of ultracold neutrons confined in a magnetic field configuration similar to those used in existing or proposed magneto-gravitational storage experiments aiming at a precise measurement of the neutron lifetime. We use an approximate quantum mechanical analysis such as pioneered by Walstrom \emph{et al} [Nucl. Instrum. Methods Phys. Res. A 599, 82 (2009)]. Our analysis is not restricted to purely vertical modes of neutron motion. The lateral motion is shown to cause the predominant depolarization loss in a magnetic storage trap.Comment: 12 pages, 3 figures, for Proceedings of Neutron Lifetime Worksho

Calculation of geometric phases in electric dipole searches with trapped spin-1/2 particles based on direct solution of the Schr\"odinger equation

Pendlebury $\textit{et al.}$ [Phys. Rev. A $\textbf{70}$, 032102 (2004)] were the first to investigate the role of geometric phases in searches for an electric dipole moment (EDM) of elementary particles based on Ramsey-separated oscillatory field magnetic resonance with trapped ultracold neutrons and comagnetometer atoms. Their work was based on the Bloch equation and later work using the density matrix corroborated the results and extended the scope to describe the dynamics of spins in general fields and in bounded geometries. We solve the Schr\"odinger equation directly for cylindrical trap geometry and obtain a full description of EDM-relevant spin behavior in general fields, including the short-time transients and vertical spin oscillation in the entire range of particle velocities. We apply this method to general macroscopic fields and to the field of a microscopic magnetic dipole.Comment: 11 pages, 4 figure

Vacancy decay in endohedral atoms: the role of non-central position of the atom

We demonstrate that the Auger decay rate in an endohedral atom is very sensitive to the atom's location in the fullerene cage. Two additional decay channels appear in an endohedral system: (a) the channel due to the change in the electric field at the atom caused by dynamic polarization of the fullerene electron shell by the Coulomb field of the vacancy, (b) the channel within which the released energy is transferred to the fullerene electron via the Coulomb interaction. % The relative magnitudes of the correction terms are dependent not only on the position of the doped atom but also on the transition energy \om. Additional enhancement of the decay rate appears for transitions whose energies are in the vicinity of the fullerene surface plasmons energies of high multipolarity. % It is demonstrated that in many cases the additional channels can dominate over the direct Auger decay resulting in pronounced broadening of the atomic emission lines. % The case study, carried out for Sc$^{2+}$@C$_{80}^{6-}$, shows that narrow autoionizing resonances in an isolated Sc$^{2+}$ within the range \om = 30... 45 eV are dramatically broadened if the ion is located strongly off-the-center. % Using the developed model we carry out quantitative analysis of the photoionization spectrum for the endohedral complex Sc$_3$N@C$_{80}$ and demonstrate that the additional channels are partly responsible for the strong modification of the photoionization spectrum profile detected experimentally by M\"{u}ller et al. (J. Phys.: Conf. Ser. 88, 012038 (2008)).Comment: 32 pages, 11 figure

Simulations of Electron Capture and Low-Mass Iron Core Supernovae

The evolutionary pathways of core-collapse supernova progenitors at the low-mass end of the spectrum are beset with major uncertainties. In recent years, a variety of evolutionary channels has been discovered in addition to the classical electron capture supernova channel of super-AGB stars. The few available progenitor models at the low-mass end have been studied with great success in supernova simulations as the peculiar density structure makes for robust neutrino-driven explosions in this mass range. Detailed nucleosynthesis calculations have been conducted both for models of electron capture supernovae and low-mass iron core supernovae and revealed an interesting production of the lighter trans-iron elements (such as Zn, Sr, Y, Zr) as well as rare isotopes like Ca-48 and Fe-60. We stress the need to explore the low-mass end of the supernova spectrum further and link various observables to understand the diversity of explosions in this regime.Comment: 7 page, 3 figures, proceedings of the conference "The AGB-Supernova Mass Transition", to appear in Memorie della Societ\`a Astronomica Italian

Universal observation of multiple order parameters in cuprate superconductors

The temperature dependence of the London penetration depth \lambda was measured for an untwined single crystal of YBa_2Cu_3O_{7-\delta} along the three principal crystallographic directions (a, b, and c). Both in-plane components (\lambda_a and \lambda_b) show an inflection point in their temperature dependence which is absent in the component along the c-direction (\lambda_c). The data provide convincing evidence that the in-plane superconducting order parameter is a mixture of s+d-wave symmetry whereas it is exclusively s-wave along the c-direction. In conjunction with previous results it is concluded that coupled s+d-order parameters are universal and intrinsic to cuprate superconductors.Comment: 5 pages, 3 figure