S.B. Shaulov

Results on the primary CR spectrum and composition reconstructed with the SPHERE-2 detector

First preliminary results of the balloon-borne experiment SPHERE-2 on the all-nuclei primary cosmic rays (PCR) spectrum and primary composition are presented. The primary spectrum in the energy range 1016–5 1017 eV was reconstructed using characteristics of Vavilov-Cherenkov radiation of extensive air showers (EAS), reflected from a snow surface. Several sources of systematic uncertainties of the spectrum were analysed. A method for separation of the primary nuclei groups based on the lateral distribution function (LDF) steepness parameter is presented. Preliminary estimate of the mean light nuclei fraction f30-150 at energies 3 1016–1.5 1017 eV was performed and yielded f30-150 = (21±11) %.

Experimental indications of an abnormal contribution to cosmic rays from a nearby single source

Experimental data on the fine structure of a cosmic ray spectrum and the characteristics of extensive air showers in the energy range of 1015–1018 eV are presented. The data agree with the model of a nearby single source. Characteristics of muon and hadron components of the showers indicate that quark stars could exist.

Investigation of SPHERE-2 data sensitivity to chemical composition of primary cosmic rays

A new method for assessing the type of particles of primary cosmic rays in the energy range of 10–1000 PeV for individual events recorded by the SPHERE-2 facility is presented. The method is based on comparing images of recorded events and simulated events, while assuming various types of primary particles with allowance for measuring errors. The aim of the study is to find the limits of sensitivity in determining of the chemical composition of ultrahigh-energy primary cosmic rays using the detection of reflected Cherenkov light generated by extensive air showers (EASes).

Status of the SPHERE experiment

Here is presented the current state of the SPHERE-2 balloon-borne experiment. The detector is elevated up to 1 km above the snow surface and registers the reflected Vavilov-Cherenkov radiation from extensive air showers. This method has good sensitivity to the mass-composition of the primary cosmic rays due to its high resolution near the shower axis. The detector consists of a 1500 mm spherical mirror with a 109 PMT cluster in its focus. The electronics record a signal pulse profile in each PMT. In the last 2 years the detector was upgraded: time resolution of pulse registration was enhanced up to 12.5 ns, channel sensitivity was increased by a factor of 3, a new LED-based relative PMT calibration method was introduced, and new hardware and etc. was installed.

The SPHERE experiment: Baikal 2010

The SPHERE-2 detector was lifted above the snow-covered surface of Lake Baikal by a captive balloon several times in 2010. The Vavilov-Cherenkov radiation of extensive air showers was measured. Preliminary results from processing the data of the SPHERE-2 experiment at various altitudes of observation are presented.