Techniques for detecting the Cherenkov light from cascade showers in water
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chniques for Detecting the Cherenkov Light from Cascade Showers in Water 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, 115409 Russia *e-mail: [email protected] Abstract⎯The NEVOD Cherenkov water detector (CWD) features a denser lattice of sensitive elements than the existing large-scale CWDs, whereby the spatial distribution of Cherenkov light from cascade showers is sampled with a superior resolution of ~0.5 m, which is close to one radiation length for water (36 cm). The experimental techniques for investigating the Cherenkov light generated by particle cascades in water is proposed. The dependence of light intensity on the depth of shower development is for the first time measured at different distances from the shower axis. The results are compared with the Cherenkov light distributions predicted by various model descriptions for the scattering of cascade particles. DOI: 10.1134/S1063779618010215
Cherenkov-light spatial distribution with precision of 0.5 m determined by the optical-module size. The spatial distribution of Cherenkov light from cascade showers is analyzed using the cascades produced in water by near horizontal muons whose tracks are reconstructed with the coordinate-tracking detector DECOR [6]. An event is selected for further analysis once the muon has been detected in two DECOR supermodules on opposite small faces of the CWD facility. The zenith angles of thus selected muons lie in the 85°–90° range, and their mean energy is near 100 GeV. In reconstructing the cascade-shower parameters, we rely on the method proposed in [7] assuming that all shower particles travel along the shower axis and radiate photons at the same angle, and that the axis coincides with the parent-muon track. The shower cascade curve is obtained by estimating the number of shower particles from the responses of PMTs in which their Cherenkov light has been detected. To this end, the part of shower axis lying within the detector’s water region is divided into intervals, or bins. The bin size amounts to one radiation length equal to 36.1 g/cm2 for water. For a given bin, we consider the responses of all PMTs for which its radiation is viewed at the Cherenkov angle of 42°, and then recalculate these responses to the number of charged particles populating this bin. Once the bin is monitored by several PMTs, the corresponding results are averaged taking into account their uncertainties. The shower energy is reconstructed by fitting the observed particle-number dependence on the shower depth to the Greisen form [8] in the one-dimensional approximation.
DETECTOR AND DATA ACQUISITION Cherenkov water detectors (CWDs) play an important role in studying the interactions of ultrahigh-energy muons and neutrinos. Since the energies of these particles are estimated as those of the cascade showers they induce in a CWD, studying the distribution of Cherenkov light produced by these showers in water is an
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