Pion-induced double pion production on nuclei in the incident momentum range from 0.5 to 1.5 GeV/c

Measurements of the integrated cross sections and differntial cross sections of pion induced double pion production on nuclei Li, C, Al, Cu, In and Pb at the beam momenta of 0.5, 0.7, 0.9, 1.1, 1.3, and 1.5 GeV/c have been made. The following channels were studied: π++A→π＋＋π-+χ(1); π++A →２π++χ(2); π++A→2π-+χ(3). The data were the first systematic one. As for the differential cross sections, the shape of kinetic energy spectra were compared with each other. As for the integrated cross sections, both their mass number dependence and incident energy dependence were discussed. Furthermore the ratio of integrated cross section of channel(1) to that of channel(2) or (3) were examined. All the features observed were understood qualitatively in the following views: (a) Channel(1) and (2) are mainly contributed by single step reaction; (b) Channel(3) is mainly contributed by multi-step reaction.Thesis--University of Tsukuba, D.Sc.(A), no. 734, 1990. 3. 2

A new quadruple gravitational lens from the Hyper Suprime-Cam Survey: the puzzle of HSC~J115252+004733

We report the serendipitous discovery of a quadruply lensed source at $z_{\rm s}=3.76$, HSC~J115252+004733, from the Hyper Suprime-Cam (HSC) Survey. The source is lensed by an early-type galaxy at $z_{\rm l}=0.466$ and a satellite galaxy. Here, we investigate the properties of the source by studying its size and luminosity from the imaging and the luminosity and velocity width of the Ly-$\alpha$ line from the spectrum. Our analyses suggest that the source is most probably a low-luminosity active galactic nucleus (LLAGN) but the possibility of it being a compact bright galaxy (e.g., a Lyman-$\alpha$ emitter or Lyman Break Galaxy) cannot be excluded. The brighter pair of lensed images appears point-like except in the HSC $i$-band (with a seeing $\sim0.5"$). The extended emission in the $i$-band image could be due to the host galaxy underneath the AGN, or alternatively, due to a highly compact lensed galaxy (without AGN) which appears point-like in all bands except in $i$-band. We also find that the flux ratio of the brighter pair of images is different in the Ks-band compared to optical wavelengths. Phenomena such as differential extinction and intrinsic variability cannot explain this chromatic variation. While microlensing from stars in the foreground galaxy is less likely to be the cause, it cannot be ruled out completely. If the galaxy hosts an AGN, then this represents the highest redshift quadruply imaged AGN known to date, enabling study of a distant LLAGN. Discovery of this unusually compact and faint source demonstrates the potential of the HSC survey.Comment: 9 pages, 7 figures, 3 Tables, MNRAS accepted, text reduce

Development of a multi-pixel photon sensor with single-photon sensitivity

A multi-pixel photon sensor with single-photon sensitivity has been developed, based on a technology of a hybrid photo-detector (HPD) consisting of a photocathode and a multi-pixel avalanche diode (MP-AD). The developed HPD has a proximity focused structure, where a photocathode and an MP-AD are facing each other with a small gap of 2.5 mm. The MP-AD, which has an effective area of 16x16 mm2 composed of 8x8 pixels, has been specially designed for the HPD. The gain of the HPD reaches 5x10^4, sufficiently high to detect single photons with a timing resolution better than 100 ps. Number of photoelectrons up to four can be clearly identified in a pulse-height spectrum as distinct peaks, thanks to the low noise characteristics of the HPD. It is also demonstrated that the HPD can be operated with good performance in a magnetic field as high as 1.5 TComment: 39 pages, 22 figures, submitted to Nucl. Intr. and Meth.