Working group report: Flavor physics and model building

This is the report of flavor physics and model building working group at WHEPP-9. While activites in flavor physics have been mainly focused on B-physics, those in model building have been primarily devoted to neutrino physics. We present summary of working group discussions carried out during the workshop in the above fields, and also briefly review the progress made in some projects subsequently.     

Intra-cavity second harmonic generation with Nd:YVO4/BIBO laser at 542 nm

We report, for the first time, an efficient intra-cavity second-harmonic generation (SHG) at 1084 nm in a nonlinear optical crystal, BiB₃O₆(BIBO) at the direction of (θ, ?) = (170.1°, 90°), performed with a LD end-pumped cw Nd:YVO₄ laser. With 590 mW diode pump power, a continuous-wave (cw) SHG output power of 19 mW at 542 nm yellow-green color has been obtained using a 1.5 mm-thick BIBO crystal. The optical conversion efficiency was 3.22%. It was found that the output wavelength could be 532 nm, 537 nm or 542 nm according to regulating the angle of BIBO.     

Integer quantum Hall effect in graphite

We present Hall effect measurements on highly oriented pyrolytic graphite that indicate the occurrence of the integer quantum-Hall-effect. The evidence is given by the observation of regular plateau-like structures in the field dependence of the transverse conductivity obtained in van der Pauw configuration. Measurements with the Corbino-disk configuration support this result and indicate that the quasi-linear and non-saturating longitudinal magnetoresistance in graphite is governed by the Hall effect in agreement with a recent theoretical model for disordered semiconductors.     

Effect of Mn-site vacancies on the magnetic entropy change and the Curie temperature of La0.67Ca0.33Mn1−xO3 perovskite

Single-phase polycrystalline samples of La_0.67Ca_0.33Mn_1−xO₃ (x=0.00, 0.02, 0.04, 0.06) have been prepared using the sol-gel method. The structure, magnetocaloric properties and the Curie temperature of the samples with different Mn vacancy concentrations have been investigated. The experimental results show that vacancy doping at the Mn-sites has a significant influence on the magnetic properties of La_0.67Ca_0.33Mn_1−xO₃. The Curie temperature decreases monotonically with increasing the Mn-site vacancy concentration x. A remarkable enhancement of the magnetic entropy change has been obtained in the La_0.67Ca_0.33Mn_0.98O₃ sample. The entropy change reaches |ΔS_M|=3.10 J kg⁻¹ K⁻¹ at its Curie temperature (264 K) under an applied magnetic field H=10 kOe, which is almost the same value as that of pure Gd.     

Saturation field direction dependence of domain structures in NiFe elements

The domain structures in NiFe elements were studied by magnetic force microscopy measurement and micromagnetic modeling. The remanent states in the elements were dependent on the direction of the saturation field. The “S” and “U” states were observed at remanence by applying the saturation field at different directions. The “S” and “U” states are metastable: magnetic force microscopy tip field-induced switching from the “S” and “U” states to the flux closure configuration was observed.     

THE DESIGNS OF HIGH EFFICIENCY LAUNCHER OF QUASI-OPTICAL MODE CONVERTER FOR HIGH POWER GYROTRONS

A high efficiency launcher of quasi-optical (QO) mode converters for high power gyrotrons have been designed and tested. A helical cut launcher radiates the RF power via its straight cut onto the first phase correcting mirror. The launchers have been optimized for the TE_31.8 mode at 170 GHz and TE_22.6 mode at 110 GHz by numerically optimizing a launcher surface. The helical cut of the launcher has been optimized by taking the taper angle into account. Further more, the amplitude of the surface perturbation have been optimized for improved focusing in order to reduce the diffraction losses at the helical cut. Low power measurement shows a good agreement with the design. High efficiency characteristics of the design have also been calculated on the assumption of frequency downshift due to the thermal expansion of the cavity and stepwise frequency tuning by changing the operating mode. Besides, the possibility of high efficiency launcher for higher mode is discussed, and these results give the prospect to high efficiency long pulse gyrotrons.     

Energy transfer in hyperthermal Xe-graphite surface scattering

The scattering of a hyperthermal Xe from a graphite (0001) surface has been studied using a molecular beam-surface scattering technique and molecular dynamics (MD) simulations. The angular and velocity distributions of scattered Xe atoms were measured at incidence energies from 0.45 to 3.5 eV, three incidence angles of 15°, 35° and 60° and the surface temperatures of 300 K and 550 K. The observed time-of-flight spectra exhibit a sharp velocity distribution with only one velocity component, which is ascribed to the direct inelastic scattering process. The angle-resolved energy ratios of the mean final translational energy over the mean incidence energy E_f/E_i agree well with those predicted based on the assumption of the conservation of the momentum parallel to the surface. The Hard-Cube model, where the mass of the cube is approximately 310 u, has reproduced the angle-resolved flux distributions of scattered Xe atoms. In the Hard-Cube model almost 80% of the normal component of the incidence translational energy is found to be lost in collision. The MD simulations reproduce well the experimental results by using the Brenner potential for intralayer C atoms and a Lennard-Jones potential for interlayer C–C pair interactions.     

Highly efficient in-band pumped Er:YAG laser with 60 W of output at 1645 nm

A high-power Er:YAG laser that is in-band pumped by a high-power cladding-pumped erbium-ytterbium codoped fiber laser operating at 1532 nm is reported. The Er:YAG laser produced 60.3 W of continuous-wave output at 1645.3 nm in a beam with M2 approximately equal to 3 for 82 W of incident pump power and 20 W of TEM00 output with M2 < 1.2 for 32.4 W of incident pump power. The slope efficiency with respect to incident pump power at pump powers of >20 W was approximately 81%. In the Q-switched mode of operation, a slightly modified resonator configuration incorporating an electro-optic Q switch produced pulses of approximately 4 mJ energy and approximately 100 ns (FWHM) duration, corresponding to a peak power of approximately 42 kW at a repetition rate of 1 kHz for an incident pump power of 16.8 W. The prospects for further improvement in continuous-wave and Q-switched performance are discussed.     

Magnetic,electrical transport and electron spin resonance studies of ferromagnetic insulating manganites Nd0.85Na0.15MnO3

We have investigated the magnetic, electrical transport and electron spin resonance (ESR) properties of polycrystalline Nd_0.85Na_0.15MnO₃ prepared by sol–gel method. A ferromagnetic–paramagnetic (FM–PM) transition is observed around 110 K, which is not accompanied by a metal–insulator transition. The sample displays the complete PM state associated with the ESR spectra fitted by single Lorentzian line shape above 130 K. Below 130 K, ESR spectra become distorted and then linewidth increases rapidly, where short-range magnetic order develops and coexists with PM phase due to the inhomogeneous magnetic state. In addition, the large difference between the activation energies obtained from the resistivity and ESR parameters (peak-to-peak linewidth and line intensity) at the frame of adiabatic small polaron hopping model is pointed out for Nd_0.85Na_0.15MnO₃.     

Magneto resistance due to domain wall scattering and magneto size effect of thin Ni and Co films at low temperatures

Nickel and cobalt films illustrate alternative Bloch lines with cap switches. The strip magnetic domains become zigzag and bubbling cells for Ni and Co films, respectively, under an external field of 1.5 T. The magnetoresistances (MR) for currents parallel (CIW) to the domain walls is 15% less than those of the perpendicular (CPW) case. We also studied the magneto size effect by applying the magnetic field normal to the surface, from which the Sondheimer oscillation appears attributing to periodic striking of the surface for electrons traveling in circular motion on a plane canting to the surface. The experiments can be expressed by the magneto size effect inherited with very small specularity parameters.