New results on direct CP violation in charged kaon decays by NA48/2

The NA48/2 result, based on the data collected during the 2003 run, on direct CP violation in $K^{\pm}\to\pi^{\pm}\pi^0\pi^0$ decay is presented. The main goal of the experiment is to reach a sensitivity at level of $10^{-4}$ in the measurement of the charge asymmetry parameter $A_g=(g^+-g^-)/(g^++g^-)$, where $g$ is the \emph{linear slope} of the Dalitz plot in the $K\to 3\pi$ decay. Thanks to the simultaneous collection of the two kaon charges and to the high resolution of the main sub-detectors, the systematics uncertainties are kept under the statistical error level. The experimental procedure, the analysis technique and the main systematics are discussed to present the final result $$A_g=(1.8\pm2.6)\times 10^{-4}$$ This result based on more than $45\cdot10^6$ events, correspondig to one half of the whole two year data taking, is about an order of magnitude more precise with respect to the previous measurement.Comment: Talk given to "Rencontres de Moriond 2006 EW" on behalf of NA48/2 collaboratio

Large Size Telescope camera support structures for the Cherenkov Telescope Array

The design of the camera support structures for the Cherenkov Telescope Array (CTA) Large Size Telescopes (LSTs) is based on an elliptical arch geometry reinforced along its orthogonal projection by two symmetric sets of stabilizing ropes. The main requirements in terms of minimal camera displacement, minimal weight, minimal shadowing on the telescope mirror, maximal strength of the structures and fast dynamical stabilization have led to the application of Carbon Fibre Plastic Reinforced (CFPR) technologies. This work presents the design, static and dynamic performance of the telescope fulfilling critical specifications for the major scientific objectives of the CTA LST, e.g. Gamma Ray Burst detection.Comment: In Proceedings of the 33rd International Cosmic Ray Conference (ICRC2013), Rio de Janeiro (Brazil). All CTA contributions at arXiv:1307.223

Xeff analysis method optimization to enhance IACTs performances

The seek of high precision analyses in $\gamma$-ray astronomy leads to the implementation of multivariate combination, benefiting from several reconstruction methods. Such analysis, called $X_{eff}$, was developed for the H.E.S.S. data using three shower reconstruction methods. This paper presents the improvement granted to this analysis by refining the distribution calculation of discriminant variables, considering observation conditions, and adding new variables in the $X_{eff}$ combination. The efficiency of the analysis is presented using simulations and real data. A comparison with the standard analysis (model++), for a typical set of sources, shows a significant gain in sensitivity.Comment: Contribution to the Proceedings of the 34th International Cosmic Ray Conference (ICRC 2015), The Hague, The Netherland

Observations of very high energy gamma-ray galactic sources with H.E.S.S.

International audienc

Sagittarius dwarf spheroidal galaxy observed by H.E.S.S

Dwarf spheroidal galaxies are characterized by a large measured mass-to-light ratio and are not expected to be the site of high-luminosity non-thermal high-energy gamma-ray emissions. Therefore they are among the most promising candidates for indirect searches of dark matter particle annihilation signals in gamma rays. The Sagittarius dwarf spheroidal galaxy has been regularly observed by the High Energy Stereoscopic System (H.E.S.S.) of Cherenkov telescopes for more than 90 hours, searching for TeV gamma-ray emission from annihilation of dark matter particles. In absence of a significant signal, new constraints on the annihilation crosssection of the dark matter particles applicable for Majorana Weakly Interacting Massive Particles (WIMPs) are derived.Comment: In Proceedings of the 33rd International Cosmic Ray Conference (ICRC2013), Rio de Janeiro (Brazil

Optimization of multivariate analysis for IACT stereoscopic systems

Multivariate methods have been recently introduced and successfully applied for the discrimination of signal from background in the selection of genuine very-high energy gamma-ray events with the H.E.S.S. Imaging Atmospheric Cerenkov Telescope. The complementary performance of three independent reconstruction methods developed for the H.E.S.S. data analysis, namely Hillas, model and 3D-model suggests the optimization of their combination through the application of a resulting efficient multivariate estimator. In this work the boosted decision tree method is proposed leading to a significant increase in the signal over background ratio compared to the standard approaches. The improved sensitivity is also demonstrated through a comparative analysis of a set of benchmark astrophysical sources.Comment: 10 pages, 8 figures, 3 tables, accepted for publication in Astroparticle Physic

A multivariate analysis approach for the Imaging atmospheric Cerenkov Telescopes System H.E.S.S.

International audienceWe present a multivariate classification approach applied to the analysis of data from the H.E.S.S. Very High Energy (VHE) gamma-ray IACT stereoscopic system. This approach combines three complementary analysis methods already successfully applied in the H.E.S.S. data analysis. The proposed approach, with the combined effective estimator Xeff, is conceived to improve the signal-to-background ratio and therefore particularly relevant to the morphological studies of faint extended sources