Development of a Large-Area Aerogel Cherenkov Counter Onboard BESS

This paper describes the development of a threshold type aerogel Cherenkov counter with a large sensitive area of 0.6 m$^2$ to be carried onboard the BESS rigidity spectrometer to detect cosmic-ray antiprotons. The design incorporates a large diffusion box containing 46 finemesh photomultipliers, with special attention being paid to achieving good performance under a magnetic field and providing sufficient endurance while minimizing material usage. The refractive index of the aerogel was chosen to be 1.03. By utilizing the muons and protons accumulated during the cosmic-ray measurements at sea level, a rejection factor of 10$^4$ was obtained against muons with $\beta \approx 1$, while keeping 97% efficiency for protons below the threshold.Comment: 13 pages, LaTex, 9 eps figures included, submitted to NIM

Reactor Neutrino Experiments with a Large Liquid Scintillator Detector

We discuss several new ideas for reactor neutrino oscillation experiments with a Large Liquid Scintillator Detector. We consider two different scenarios for a measurement of the small mixing angle $\theta_{13}$ with a mobile $\bar{\nu}_e$ source: a nuclear-powered ship, such as a submarine or an icebreaker, and a land-based scenario with a mobile reactor. The former setup can achieve a sensitivity to $\sin^2 2\theta_{13} \lesssim 0.003$ at the 90% confidence level, while the latter performs only slightly better than Double Chooz. Furthermore, we study the precision that can be achieved for the solar parameters, $\sin^2 2\theta_{12}$ and $\Delta m_{21}^2$, with a mobile reactor and with a conventional power station. With the mobile reactor, a precision slightly better than from current global fit data is possible, while with a power reactor, the accuracy can be reduced to less than 1%. Such a precision is crucial for testing theoretical models, e.g. quark-lepton complementarity.Comment: 18 pages, 3 figures, 2 tables, revised version, to appear in JHEP, Fig. 1 extended, Formula added, minor changes, results unchange

The monitoring system for the aerogel Cherenkov counter of the BELLE detector

We report on a design and performances of a monitoring system developed for the aerogel Cherenkov counters (ACC) of the BELLE detector. The system consists of blue LEDs, a diffuser box, and optical distributors which distribute the LED light to the ACC modules. The employed LED (NSPB series) has been observed to have high reliability on the long term stability and the temprature dependence. The diffuser box is employed to reduce the intrinsic non-uniformity of the LED light intensity. The overall performances of the present monitoring system on uniformity and intensity of the light output have been found to satisfy all the requirements for the monitoring.Comment: 24 pages, LaTeX, 13 eps figures, to be published in Nucl. Instrum. and Meth. A. Postscript file (4.5 MB) is available at http://www-hep.phys.saga-u.ac.jp/~murakami/paper/xxx_accmon.p

No evidence yet for hadronic TeV gamma-ray emission from SNR RX J1713.7-3946

Recent TeV-scale gamma-ray observations with the CANGAROO II telescope have led to the claim that the multi-band spectrum of RX J1713.7-3946 cannot be explained as the composite of a synchrotron and an inverse Compton component emitted by a population of relativistic electrons. It was argued that the spectrum of the high-energy emission is a good match to that predicted by pion decay, thus providing observational evidence that protons are accelerated in SNR to at least TeV energies. In this Letter we discuss the multi-band spectrum of RX J1713.7-3946 under the constraint that the GeV-scale emission observed from the closely associated EGRET source 3EG J1714-3857 is either associated with the SNR or an upper limit to the gamma-ray emission of the SNR. We find that the pion-decay model adopted by Enomoto et al. is in conflict with the existing GeV data. We have examined the possibility of a modified proton spectrum to explain the data, and find that we cannot do so within any existing theoretical framework of shock acceleration models.Comment: in press as Letter to Astronomy & Astrophysic

Large-p⊥p_\perp Heavy-Quark Production in Two-Photon Collisions

The next-to-leading-order (NLO) cross section for the production of heavy quarks at large transverse momenta ($p_\perp$) in $\gamma\gamma$ collisions is calculated with perturbative fragmentation functions (PFF's). This approach allows for a resummation of terms $\propto\alpha_s\ln(p_\perp^2/m^2)$ which arise in NLO from collinear emission of gluons by heavy quarks at large $p_\perp$ or from almost collinear branching of photons or gluons into heavy-quark pairs. We present single-inclusive distributions in $p_\perp$ and rapidity including direct and resolved photons for $\gamma\gamma$ production of heavy quarks at $e^+e^-$ colliders and at high-energy $\gamma\gamma$ colliders. The results are compared with the fixed-order calculation for $m$ finite including QCD radiative corrections. The two approaches differ in the definitions and relative contributions of the direct and resolved terms, but essentially agree in their sum. The resummation of the $\alpha_s \ln(p_\perp^2/m^2)$ terms in the PFF approach leads to a softer $p_\perp$ distribution and to a reduced sensitivity to the choice of the renormalization and factorization scales.Comment: 17 pages, Latex, epsf, 7 figures appended as uuencoded file (hardcopy can be obtained upon request from [email protected]

First-Order Melting and Dynamics of Flux Lines in a Model for YBa2_2Cu3_3O7−δ_{7-\delta}

We have studied the statics and dynamics of flux lines in a model for YBCO, using both Monte Carlo simulations and Langevin dynamics. For a clean system, both approaches yield the same melting curve, which is found to be weakly first order with a heat of fusion of about $0.02 k_BT_m$ per vortex pancake at a field of $50 {\rm kG}.$ The time averaged magnetic field distribution experienced by a fixed spin is found to undergo a qualitative change at freezing, in agreement with NMR and $\mu {\rm SR}$ experiments. Melting in the clean system is accompanied by a proliferation of free disclinations which show a clear B-dependent 3D-2D crossover from long disclination lines parallel to the c-axis at low fields, to 2D ``pancake'' disclinations at higher fields. Strong point pins produce a logarithmical $\ln t$ relaxation which results from slow annealing out of disclinations in disordered samples.Comment: 31 pages, latex, revtex, 12 figures available upon request, No major changes to the original text, but some errors in the axes scale for Figures 6 and 7 were corrected(new figures available upon request), to be published in Physical Review B, July 199

Supernova-Remnant Origin of Cosmic Rays?

It is thought that Galactic cosmic ray (CR) nuclei are gradually accelerated to high energies (up to ~300 TeV/nucleon, where 1TeV=10^12eV) in the expanding shock-waves connected with the remnants of powerful supernova explosions. However, this conjecture has eluded direct observational confirmation^1,2 since it was first proposed in 1953 (ref. 3). Enomoto et al.^4 claim to have finally found definitive evidence that corroborates this model, proposing that the very-high-energy, TeV-range, gamma-rays from the supernova remnant (SNR) RX J1713.7-3946 are due to the interactions of energetic nuclei in this region. Here we argue that their claim is not supported by the existing multiwavelength spectrum of this source. The search for the origin(s) of Galactic cosmic ray nuclei may be closing in on the long-suspected supernova-remnant sources, but it is not yet over.Comment: 4 pages, 1 Figur

ss- and dxyd_{xy}-wave components induced around a vortex in dx2−y2d_{x^2-y^2}-wave superconductors

Vortex structure of $d_{x^2-y^2}$-wave superconductors is microscopically analyzed in the framework of the quasi-classical Eilenberger equations. If the pairing interaction contains an $s$-wave ($d_{xy}$-wave) component in addition to a $d_{x^2-y^2}$-wave component, the $s$-wave ($d_{xy}$-wave) component of the order parameter is necessarily induced around a vortex in $d_{x^2-y^2}$-wave superconductors. The spatial distribution of the induced $s$-wave and $d_{xy}$-wave components is calculated. The $s$-wave component has opposite winding number around vortex near the $d_{x^2-y^2}$-vortex core and its amplitude has the shape of a four-lobe clover. The amplitude of $d_{xy}$-component has the shape of an octofoil. These are consistent with results based on the GL theory.Comment: RevTex,9 pages, 6 figures in a uuencoded fil