533 research outputs found
Belle II iTOP Optics: Design, Construction and Performance
The imaging-Time-of-Propogation (iTOP) counter is a new type of ring-imaging
Cherenkov counter developed for particle identification at the Belle II
experiment. It consists of 16 modules arranged azimuthally around the beam
line. Each module consists of one mirror, one prism and two quartz bar
radiators. Here we describe the design, acceptance test, alignment, gluing and
assembly of the optical components. All iTOP modules have been successfully
assembled and installed in the Belle II detector by the middle of 2016. After
installation, laser and cosmic ray data have been taken to test the performance
of the modules. First results from these tests are presented.Comment: Proceedings of TIPP 2017, May 22 - 26, Beijing, China, 2017;
University of Cincinnati preprint UCHEP-17-07. arXiv admin note: text overlap
with arXiv:1709.0993
Cross-talk suppressed multi-anode MCP-PMT
We have developed a 4-channel multi-anode MCP-PMT, SL10, which exhibits a
performance of sigma_TTS ~ 30 ps for single photons with G ~ 10^6 and QE=20%
under a magnetic field of B <= 1.5 T. The cross-talk among anodes has been
extensively studied. We have taken two measures to suppress it: one is to
configure the SL10 to an effectively independent 4 small pieces of MCP-PMT's by
segmenting an electrode of the second MCP-layer; the other is to use a constant
fractional discriminator. Remarkable improvement has been achieved.Comment: 14 pages, 14 figure
Hybridization-Driven Orthorhombic Lattice Instability in URu2Si2
We have measured the elastic constant (C11-C12)/2 in URu2Si2 by means of
high-frequency ultrasonic measurements in pulsed magnetic fields H || [001] up
to 61.8 T in a wide temperature range from 1.5 to 116 K. We found a reduction
of (C11-C12)/2 that appears only in the temperature and magnetic field region
in which URu2Si2 exhibits a heavy-electron state and hidden-order. This change
in (C11-C12)/2 appears to be a response of the 5f-electrons to an orthorhombic
and volume conservative strain field \epsilon_xx-\epsilon_yy with
{\Gamma}3-symmetry. This lattice instability is likely related to a
symmetry-breaking band instability that arises due to the hybridization of the
localized f electrons with the conduction electrons, and is probably linked to
the hidden-order parameter of this compound.Comment: 5 pages, 4 figure
Elastic Properties and Magnetic Phase Diagrams of Dense Kondo Compound Ce0.75La0.25B6
We have investigated the elastic properties of the cubic dense Kondo compound
Ce0.75La0.25B6 by means of ultrasonic measurements. We have obtained magnetic
fields vs temperatures (H-T) phase diagrams under magnetic fields along the
crystallographic [001], [110] and [111] axes. An ordered phase IV showing the
elastic softening of c44 locates in low temperature region between 1.6 and 1.1
K below 0.7 T in all field directions. The phase IV shows an isotropic nature
with regard to the field directions, while the antiferro-magnetic phase III
shows an anisotropic character. A remarkable softening of c44 and a spontaneous
trigonal distortion εyz+εzx+εxy recently reported by Akatsu et
al. [J. Phys. Soc. Jpn. 72 (2003) 205] in the phase IV favor a ferro-quadrupole
(FQ) moment of Oyz+Ozx+Oxy induced by an octupole ordering.Comment: 9 figures, Strongly Correlated Electron
Magnetic phase diagram of antiferroquadrupole ordering in HoB2C2
The magnetic phase diagram for antiferro-quadrupole (AFQ) ordering in
tetragonal HoBC has been investigated by measurements of elastic
constants , and in fields along the basal -
plane as well as the principal [001]-axis. The hybrid magnet (GAMA) in Tsukuba
Magnetic Laboratory was employed for high field measurements up to 30 T. The
AFQ phase is no longer observed above 26.3 T along the principal [001] axis in
contrast to the relatively small critical field of 3.9 T in fields applied
along the basal [110] axis. The quadrupolar intersite interaction of
and/or is consistent with the anisotropy in the magnetic phase diagram
of the AFQ phase in HoBC.Comment: Phys. Rev. B. (2005) in press. approx 8 pages, 10 figure
Tunneling and rattling in clathrate crystal
We present tunneling and rattling motions of an off-center guest atom in cage
referring to a clathrate crystal La_3Pd_{20}Ge_6. The elastic constant C_{44}
of La_3Pd_{20}Ge_6 shows a Debye-type dispersion around 20 K obeying a
relaxation time tau = tau_0exp(E/k_{B}T) with an attempt time tau_0 =
2.0*10^{-12} sec and an activation energy E = 197 K. At low temperatures below
3 K down to 20 mK, the C_{44} shows a softening of C_{44} =
C_{44}^0(T-T_C^0)/(T-Theta) with T_C^0 = -337.970 mK and Theta = -338.044 mK.
These facts are attributed to two different types of the off-center motions
with Gamma_5 symmetry in 4a-site cage of La_3Pd_{20}Ge_6, a thermally activated
rattling motion over the potential hill and a tunneling motion through the
potential hill at low temperatures.Comment: 5 pages, 4 figures, to be published Phys. Rev.
Lattice Distortion and Octupole Ordering Model in CexLa1-xB6
Possible order parameters of the phase IV in CexLa1-xB6 are discussed with
special attention to the lattice distortion recently observed. A
\Gamma_{5u}-type octupole order with finite wave number is proposed as the
origin of the distortion along the [111] direction. The \Gamma_8 crystalline
electric field (CEF) level splits into three levels by a mean field with the
\Gamma_{5u} symmetry. The ground and highest singlets have the same quadrupole
moment, while the intermediate doublet has an opposite sign. It is shown that
any collinear order of \Gamma_{5u}-type octupole moment accompanies the
\Gamma_{5g}-type ferro-quadrupole order, and the coupling of the quadrupole
moment with the lattice induces the distortion. The cusp in the magnetization
at the phase transition is reproduced, but the internal magnetic field due to
the octupole moment is smaller than the observed one by an order of magnitude.Comment: 5 pages, 4 figures, submitted to J. Phys. Soc. Jp
Neutral B Flavor Tagging for the Measurement of Mixing-induced CP Violation at Belle
We describe a flavor tagging algorithm used in measurements of the CP
violation parameter sin2phi_1 at the Belle experiment. Efficiencies and wrong
tag fractions are evaluated using flavor-specific B meson decays into hadronic
and semileptonic modes. We achieve a total effective efficiency of $ 28.8 +-
0.6 %.Comment: 28 pages, 9 figure
Detection of Neutron Scattering from Phase IV of Ce0.7La0.3B6: A Confirmation of the Octupole Order
We have performed a single crystal neutron scattering experiment on
Ce0.7La0.3B6 to investigate the order parameter of phase IV microscopically.
Below the phase transition temperature 1.5 K of phase IV, weak but distinct
superlattice reflections at the scattering vector (h/2,h/2,l/2) (h, l = odd
number) have been observed by neutron scattering for the first time. The
intensity of the superlattice reflections is stronger for high scattering
vectors, which is quite different from the usual magnetic form factor of
magnetic dipoles. This result directly evidences that the order parameter of
phase IV has a complex magnetization density, consistent with the recent
experimental and theoretical prediction in which the order parameter is the
magnetic octupoles Tbeta with Gamma5 symmetry of point group Oh. Neutron
scattering experiments using short wavelength neutrons, as done in this study,
could become a general method to study the high-rank multipoles in f electron
systems.Comment: 4 pages, 4 figure
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