Restoration of parameters of high-energy cascades in Cherenkov water calorimeter with a dense array of quasispherical mo
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RAYS AND ASTROPHYSICS
Restoration of Parameters of HighEnergy Cascades in Cherenkov Water Calorimeter with a Dense Array of Quasispherical Modules V. A. Khomyakov*, A. G. Bogdanov, V. V. Kindin, R. P. Kokoulin, A. A. Petrukhin, S. S. Khokhlov, V. V. Shutenko, and I. I. Yashin National Research Nuclear University MEPhI (Moscow Engineering Physics Institute), Kashirskoe sh. 31, Moscow, 115409 Russia * email: [email protected] Received February 10, 2015
Abstract—A problem concerning the restoration of the parameters of a cascade shower with an unknown axis originating by muons in a Cherenkov water calorimeter is considered. A method for estimating the direction and geometric position of the cascade’s axis, which is based on the analysis of responses of quasispherical modules, and the criteria of selection of the events with cascades among the events with a large energy liber ation are proposed. The method and the criteria are tested on events with cascades generated by nearhori zontal muons of high energies detected by a DECOR coordinatetrack detector. The preliminary results of measurements of the energy spectrum of cascade showers are presented. Keywords: Cherenkov water calorimeter, cascade shower, cascade curve. DOI: 10.1134/S1063778815130177
INTRODUCTION Cherenkov water calorimeters are widely used for studying muons and neutrinos of superhigh energies. In this case, the energy of these particles is evaluated by cascade showers. The energy of showers is deter mined in large detectors such as ANTARES and IceCube in a point approximation using model calcu lations, which is associated with large distances between the measurement modules [1, 2]. In this work, the cascade showers were studied on a unique scientific setup NEVOD [3, 4] (Fig. 1), whose Cher enkov detector possesses a dense array of measure ment modules, which makes it possible to restore the full cascade curve in individual events; i.e., this detec tor is in fact a calorimeter. The Cherenkov water calorimeter represents a res ervoir 9 × 9 × 26 m3, in which is located a spatial array with quasispherical modules (QSMs) in its nodes which register the Cherenkov radiation from relativis tic charged particles (91 QSMs are in the array in all). Each QSM is composed of six FEU200 photomulti pliers with flat photocathodes, which are oriented along the axes of the orthogonal system of coordinates. The small step of the spatial array (2.5 m along the detector, 2 m across it, and 2 m in its depth) and the wide dynamic range of the registered signals (1–105 photoelectrons for each FEU [5]) make it possible to
study the cascade showers with measurement of the full cascade curve in individual events. RESTORATION OF SHOWERS WITH KNOWN AXIS The problem of restoration of the cascade curve for showers with the known position of the axis was solved earlier [6]. The events selected as a result of actuation of two DECOR supermodules (SMs) located at the opposite short sides of the tank were analyzed. Such muons are registered only in a narrow range of ze
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