Belle II Technical Design Report

Source: arXiv


The Belle detector at the KEKB electron-positron collider has collected almost 1 billion Y(4S) events in its decade of operation. Super-KEKB, an upgrade of KEKB is under construction, to increase the luminosity by two orders of magnitude during a three-year shutdown, with an ultimate goal of 8E35 /cm^2 /s luminosity. To exploit the increased luminosity, an upgrade of the Belle detector has been proposed. A new international collaboration Belle-II, is being formed. The Technical Design Report presents physics motivation, basic methods of the accelerator upgrade, as well as key improvements of the detector. Comment: Edited by: Z. Dole\v{z}al and S. Uno

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    • "In the experiment a Geant4 based detector simulation of the Belle II CDC is used. It includes the simulation of physics effects due to material interactions with the inner detector components, the non-linear x − t relation [5] of drift lengths to drift times due to inhomogeneities of the electric field and the wire-sag effect caused by gravitation. With the more realistic physics simulation, the RMS is higher than in the preliminary studies [1], [2], [3], where an idealized perfect detector was assumed using an older version of the simulation software of the Belle II detector. "
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    ABSTRACT: The Belle II experiment will go into operation at the upgraded SuperKEKB collider in 2016. SuperKEKB is designed to deliver an instantaneous luminosity $\mathcal{L}=8\times10^{35}\,\mathrm{cm}^{-2}\,\mathrm{s}^{-1}$. The experiment will therefore have to cope with a much larger machine background than its predecessor Belle, in particular from events outside of the interaction region. We present the concept of a track trigger, based on a neural network approach, that is able to suppress a large fraction of this background by reconstructing the $z$ (longitudinal) position of the event vertex within the latency of the first level trigger. The trigger uses the hit information from the Central Drift Chamber (CDC) of Belle II within narrow cones in polar and azimuthal angle as well as in transverse momentum ("sectors"), and estimates the $z$-vertex without explicit track reconstruction. The preprocessing for the track trigger is based on the track information provided by the standard CDC trigger. It takes input from the 2D track finder, adds information from the stereo wires of the CDC, and finds the appropriate sectors in the CDC for each track. Within the sector, the $z$-vertex is estimated by a specialized neural network, with the drift times from the CDC as input and a continuous output corresponding to the scaled $z$-vertex. The neural algorithm will be implemented in programmable hardware. To this end a Virtex 7 FPGA board will be used, which provides at present the most promising solution for a fully parallelized implementation of neural networks or alternative multivariate methods. A high speed interface for external memory will be integrated into the platform, to be able to store the $\mathcal{O}(10^9)$ parameters required. The contribution presents the results of our feasibility studies and discusses the details of the envisaged hardware solution.
    Full-text · Article · Jun 2014 · IEEE Transactions on Nuclear Science
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    • "HE aerogel-based ring-imaging Cherenkov (A-RICH) counter is one of the particle identification devices for the Belle II experiment [1] that will be performed using the SuperKEKB accelerator at KEK, Japan. The Belle II is a super í µí°µ-factory experiment searching for new physics beyond the standard model of particle physics through flavor physics and precise measurements of í µí° ¶í µí±ƒ violations. "
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    ABSTRACT: This paper describes recent progress in the development of large-area hydrophobic silica aerogel tiles for use as a radiator in the aerogel-based ring-imaging Cherenkov (A-RICH) counter that will be installed in the forward end cap of the Belle II detector. The proximity-focusing A-RICH counter is designed to efficiently identify charged pions and kaons; our goal is a separation capability of more than 4σ at momenta up to 4 GeV/c. We plan to fill the large end-cap area of 3.5 m<sup>2</sup> with 124 segmented dual-layer-focusing aerogel combinations with different refractive indices (n ~ 1.05). It is crucial to minimize the number of aerogel tiles to reduce tile boundaries because the number of detected photoelectrons decreases at the boundaries. As a step toward achieving high performance in the actual detector, we performed test productions of large-area (over 18 × 18 × 2 cm<sup>3</sup>) aerogel tiles using both conventional and pin-drying methods. In view of the crack-free production yield, we have decided to mass-produce both upstream and downstream aerogel tiles by the conventional method in the Belle II program, although the pin-dried aerogels showed excellent transparency. We also used an electron beam at DESY to conduct a beam test for investigating the performance of a prototype A-RICH counter. When we used a basic counter configuration with dual-layer-focusing aerogels having n ~ 1.045 and 1.055 produced by the conventional method, we confirmed a π/K separation capability better than 4σ at a momentum of 4 GeV/c.
    Full-text · Conference Paper · Oct 2013
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    • "Aerogel-based RICH counters have already been used in several experiments [5]–[7]. To develop a proximity focusing RICH counter using a dual-refractiveindex aerogel radiator [8] for the Belle II experiment [9], we have been attempting to produce highly transparent hydrophobic aerogels with high refractive index (n > 1.04). We recently discovered a new technique, the pin-drying method, for producing aerogels with excellent transparency [10]–[12]. "
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    ABSTRACT: We present optical and X-ray radiographical characterization of silica aerogels with refractive index from 1.05 to 1.07 for a Cherenkov radiator. A novel pin-drying method enables us to produce highly transparent hydrophobic aerogels with high refractive index by shrinking wet-gels. In order to investigate the uniformity in the density (i.e., refractive index) of an individual aerogel monolith, we use the laser Fraunhofer method, an X-ray absorption technique, and Cherenkov imaging by a ring-imaging Cherenkov detector in a beam test. We observed an increase in density at the edge of the aerogel tiles, produced by pin-drying.
    Full-text · Article · Oct 2012 · IEEE Transactions on Nuclear Science
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