Possible Verification of Tilted Anisotropic Dirac Cone in \alpha-(BEDT-TTF)_2 I_3 Using Interlayer Magnetoresistance

It is proposed that the presence of a tilted and anisotropic Dirac cone can be verified using the interlayer magnetoresistance in the layered Dirac fermion system, which is realized in quasi-two-dimensional organic compound \alpha-(BEDT-TTF)_2 I_3. Theoretical formula is derived using the analytic Landau level wave functions and assuming local tunneling of electrons. It is shown that the resistivity takes the maximum in the direction of the tilt if anisotropy of the Fermi velocity of the Dirac cone is small. The procedure is described to determine the parameters of the tilt and anisotropy.Comment: 4 pages, 4 figures, corrected Fig.

Calibration System with Cryogenically-Cooled Loads for CMB Polarization Detectors

We present a novel system to calibrate millimeter-wave polarimeters for CMB polarization measurements. This technique is an extension of the conventional metal mirror rotation approach, however it employs cryogenically-cooled blackbody absorbers. The primary advantage of this system is that it can generate a slightly polarized signal ($\sim100$ mK) in the laboratory; this is at a similar level to that measured by ground-based CMB polarization experiments observing a $\sim$ 10 K sky. It is important to reproduce the observing condition in the laboratry for reliable characterization of polarimeters before deployment. In this paper, we present the design and principle of the system, and demonstrate its use with a coherent-type polarimeter used for an actual CMB polarization experiment. This technique can also be applied to incoherent-type polarimeters and it is very promising for the next-generation CMB polarization experiments.Comment: 7 pages, 9 figures Submitted to RS

Innovative Demodulation Scheme for Coherent Detectors in CMB Experiments

We propose an innovative demodulation scheme for coherent detectors used in cosmic microwave background polarization experiments. Removal of non-white noise, e.g., narrow-band noise, in detectors is one of the key requirements for the experiments. A combination of modulation and demodulation is used to extract polarization signals as well as to suppress such noise. Traditional demodulation, which is based on the two- point numerical differentiation, works as a first-order high pass filter for the noise. The proposed demodulation is based on the three-point numerical differentiation. It works as a second-order high pass filter. By using a real detector, we confirmed significant improvements of suppression power for the narrow-band noise. We also found improvement of the noise floor.Comment: 3 pages, 4 figure

Development of a low-mass and high-efficiency charged particle detector

We developed a low-mass and high-efficiency charged particle detector for an experimental study of the rare decay $K_L \rightarrow \pi^0 \nu \bar{\nu}$. The detector is important to suppress the background with charged particles to the level below the signal branching ratio predicted by the Standard Model (O(10$^{-11}$)). The detector consists of two layers of 3-mm-thick plastic scintillators with wavelength shifting fibers embedded and Multi Pixel Photon Counters for readout. We manufactured the counter and evaluated the performance such as light yield, timing resolution, and efficiency. With this design, we achieved the inefficiency per layer against penetrating charged particles to be less than $1.5 \times 10^{-5}$, which satisfies the requirement of the KOTO experiment determined from simulation studies.Comment: 20 pages, 18 figure