The GAMMA-400 gamma-ray telescope is designed to measure the fluxes of gamma rays and cosmic-ray electrons + positrons, which can be produced by annihilation or decay of the dark matter particles, as well as to survey the celestial sphere in order to study point and extended sources of gamma rays, measure energy spectra of Galactic and extragalactic diffuse gamma-ray emission, gamma-ray bursts, and gamma-ray emission from the Sun. The GAMMA-400 covers the energy range from 100 MeV to 3000 GeV. Its angular resolution is ~0.01 deg (E{\gamma} > 100 GeV), the energy resolution ~1% (E{\gamma} > 10 GeV), and the proton rejection factor ~10E6. GAMMA-400 will be installed on the Russian space platform Navigator. The beginning of observations is planned for 2018.

Design and Performance of the GAMMA-400 Gamma-Ray Telescope for the Dark Matter Searches

The field of astroparticle physics started with the discovery of cosmic rays in 1912 by Victor Hess. Cosmic rays, which initially led to important advances in the field of Particle Physics, provide precious information about the violent phenomena in the Universe producing such high-energy particles and the mechanisms of their propagation in the interstellar medium. In the last years, Cosmic Ray Physics has profited from the rise in space research,and space-based experiments are currently providing direct measurements with unprecedent precision. In this context, recent measurements of the spectra of several cosmic ray species cannot be fully explained within the current paradigm of cosmic ray origin and propagation, and constitute an open window into new phenomena. In particular, AMS-02 has provided the most precise measurement of the positron fraction, and the positron and electron fluxes. These results allowed an accurate description of the rise in the positron fraction and led to a plethora of models proposed to explain the so-called positron excess non consistent with the standard secondary origin of antimatter in cosmic rays. For most cases, the observation requires the inclusion of primary sources, which are typically classified into two scenarios: dark matter or astrophysical origin...

Measurement of the large scale anisotropy in cosmic ray electrons, positrons and protons with the AMS-02 detector on the ISS

From the observation of the Universe, it has been demonstrated that the mass associated to visible matter represents only few percent of its energetic budget, while the remaining part is composed by dark energy, responsible to the cosmological expansion, and by some hidden matter, the dark matter. The likeliest particles family used to describe this dark matter is called WIMP (Weakly Interacting Massive Particles). That kind of particles could be directly detected by measuring nuclear recoil during an elastic scattering inside a scintillating material. For this, the XENON Collaboration has developed a detector consisting in a time projection chamber (TPC) using xenon dual phase (liquid and gas) detector, and placed underground. The different ionization density of nuclear recoils induced by WIMPs, and electronic recoils induced by b particles or g rays background source, leads to different ratio between both signals, in the liquid and in the gas phase, and is used to discriminate WIMPs from background. A good knowledge of the ionization signal is strongly required for such a detector. In this context, the XENON100 response to single electron charge signals is investigated. They correspond to very tiny signals emitted in the gas phase by one or few electrons extracted in time coincidence. Thanks to this analysis, an innovative method to establish the extraction yield of electrons from the liquid to the gas phase has been drawn, allowing to explore a key information to reject electronic recoils from nuclear
ones.

Study of the single electron charge signals in the XENON100 direct Dark Matter search experiment

This work presents an investigation on the non-uniformity of the response of the photocathode of two photomultiplier tubes (PMTs) and its potential influence on the results of scintillation measurements. An experimental system was developed which allows studies of the non-uniformity of the photocathode response and its influence on the shape of alpha spectra obtained after pulse-shape discrimination. The system is presented together with tests of Hamamatsu R7600U-200 and H11934-203 PMTs. A degradation of the counting efficiency and a shift of the peak position towards smaller values were identified in the measurements near the edges of the photocathode where the energy resolution is significantly worse compared to the central region of the PMT. Such non-uniformity also affects absolute activity measurements based on the free parameter model, i.e., the Triple to Double Coincidence Ratio and the CIEMAT/NIST efficiency tracing methods. A significant non-uniformity of the response of a PMT would interfere with the assumption of the traditional free parameter model of a Poisson distribution of the number of emitted photons. Experimental results are presented in the paper, together with a discussion of their practical influence on scintillation and absolute activity measurements. 

A study of the non-uniformity of the PMT photocathode response and its influence on the results obtained in different scintillation counting experiments

Calorimetric particle detectors that play an important role in high-energy cosmic-ray balloon and satellite experiments not only have the major task of measuring energy but also face the problem of identifying electrons and protons. This problem is usually solved by measuring the longitudinal and traverse shower profiles and the total energy release in the calorimeter, using the fact that electromagnetic and hadronic showers differ in their spatial and energy distributions. In this paper, electron and proton identification methods for different types of calorimeters used in cosmic-ray balloon- and satellite-borne experiments are discussed.

http://iopscience.iop.org/article/10.3367/UFNe.0179.200909b.0931/pdf

Electron–proton separation in calorimetry experiments directly measuring the composition and energy spectrum of cosmic rays

The electromagnetic calorimeter (ECAL) of the AMS-02 experiment is a 3-dimensional sampling calorimeter, made of lead and scintillating fibers. The detector allows for a high granularity, with 18 samplings in the longitudinal direction, and 72 sampling in the lateral direction. The ECAL primary goal is to measure the energy of cosmic rays up to few TeV, however, thanks to the fine grained structure, it can also provide the separation of positrons from protons, in the GeV to TeV region. A direct measurement of high energy photons with accurate energy and direction determination can also be provided.

The electromagnetic calorimeter of the AMS-02 experiment

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The electromagnetic calorimeter of the AMS-02 experiment