Y. Becherini

A Parameterisation of single and multiple muons in the deep water or ice

Atmospheric muons play an important role in underwater/ice neutrino detectors. In this paper, a parameterisation of the flux of single and multiple muon events, their lateral distribution and of th ...

A new analysis strategy for detection of faint γ-ray sources with Imaging Atmospheric Cherenkov Telescopes

Abstract A new background rejection strategy for γ-ray astrophysics with stereoscopic Imaging Atmospheric Cherenkov Telescopes (IACT), based on Monte Carlo (MC) simulations and real background data from the H.E.S.S. [High Energy Stereoscopic System, see [1] .] experiment, is described. The analysis is based on a multivariate combination of both previously-known and newly-derived discriminant variables using the physical shower properties, as well as its multiple images, for a total of eight variables. Two of these new variables are defined thanks to a new energy evaluation procedure, which is also presented here. The method allows an enhanced sensitivity with the current generation of ground-based Cherenkov telescopes to be achieved, and at the same time its main features of rapidity and flexibility allow an easy generalization to any type of IACT. The robustness against Night Sky Background (NSB) variations of this approach is tested with MC simulated events. The overall consistency of the analysis chain has been checked by comparison of the real γ-ray signal obtained from H.E.S.S. observations with MC simulations and through reconstruction of known source spectra. Finally, the performance has been evaluated by application to faint H.E.S.S. sources. The gain in sensitivity as compared to the best standard Hillas analysis ranges approximately from 1.2 to 1.8 depending on the source characteristics, which corresponds to an economy in observation time of a factor 1.4 to 3.2.

Search for a Lorentz invariance violation contribution in atmospheric neutrino oscillations using MACRO data

The energy spectrum of neutrino-induced upward-going muons in MACRO has been analysed in terms of relativity principles violating effects, keeping standard mass-induced atmospheric neutrino oscillations as the dominant source of v(u) -> v(tau) transitions. The data disfavor these exotic possibilities even at a subdominant level, and stringent 90% C.L. limits are placed on the Lorentz invariance violation parameter vertical bar Delta v vertical bar < 6 x 10(-24) at sin2 theta(v) = 0 and vertical bar Delta(v)vertical bar < 2.5-5 x 10(-26) at sin 2 theta(v) = +/- 1. These limits can also be re-interpreted as upper bounds on the parameters describing violation of the equivalence principle. (c) 2005 Elsevier B.V. All rights reserved.

High energy blazars spectroscopy with X-shooter on the VLT

We present results of observations in the UV to near-IR range for eight blazars, three of which have been recently discovered at Very High Energies (VHE) and five appearing as interesting candidates for VHE {\gamma}-ray detection. We focus in this paper on the search for their redshifts, which are unknown or considered as uncertain.

Performance of HESS-II in multi-telescope mode with a multi-variate analysis

The second phase of H.E.S.S. is being commissioned and will start physics data-taking in Autumn 2012. The 4-telescope configuration is now enriched with a new very-large Cherenkov telescope (VLCT) at the centre of the array. The ∼600m2 mirror area and high-resolution camera of the VLCT will permit to lower the energy threshold to about 30GeV in the single-telescope mode, opening a new observational window to a large number of new high-energy phenomena. Adding the VLCT also enhances the detection sensitivity in the multi-telescope mode. The performance in this latter data-taking mode of HESS-II with the advanced analysis procedure called Paris-MVA has been studied in order to understand the achievable low-energy sensitivity and preliminary results are shown here. The Monte Carlo (MC) simulations, the γ-ray reconstruction procedures and the analysis strategy used to obtain the resulting improvement in sensitivity by adding the VLCT - of about a factor of ∼ 2 at low energy - will be discussed.

Discovery of VHE emission from PKS 0447 439 with H.E.S.S. and MWL studies

Very-high energy (VHE) emission has been detected from PKS 0447-439 with the H.E.S.S. Cherenkov telescope array. This blazar is one of the brightest hard-spectrum extragalactic objects in the Fermi bright source list. Its detection with H.E.S.S. triggered Target of Opportunity observations with the Swift and RXTE telescopes, which show rapid flaring in the X-ray band. The spectrum and light curve measured by H.E.S.S. are presented. Along with the Fermi LAT data it is possible to put an upper limit on the redshift of the source. Implications of the flux evolution are discussed briefly.

Advanced analysis and event reconstruction for the CTA Observatory

The planned Cherenkov Telescope Array (CTA) is a future observatory for very-high-energy (VHE) gamma-ray astronomy composed of one site per hemisphere [1]. It aims at 10 times better sensitivity, a better angular resolution and wider energy coverage than current installations such as H.E.S.S., MAGIC and VERITAS. In order to achieve this level of performance, both the design of the telescopes and the analysis algorithms are being studied and optimized within the CTA Monte-Carlo working group. Here, we present ongoing work on the data analysis for both the event reconstruction (energy, direction) and gamma/hadron separation, carried out within the HAP (H.E.S.S. Analysis Package) software framework of the H.E.S.S. collaboration, for this initial study. The event reconstruction uses both Hillas-parameter-based algorithms and an improved version of the 3D-Model algorithm [2]. For the gamma/hadron discrimination, original and robust discriminant variables are used and treated with Boosted Decision Trees (BDTs) ...

HESS‐II reconstruction strategy and performance in the low‐energy (20‐150 GeV) domain

In mid‐2009 a notable upgrade of the H.E.S.S. telescope system will take place: a new telescope with a 600 m2 mirror area and very‐high‐resolution camera (0.07°) will be positioned at the centre of the present configuration, with the aim of lowering the threshold and enhance its sensitivity in the 100 GeV to several TeV energy range. HESS‐II will permit the investigation of the lower energy γ‐ray spectra in various cosmic accelerators, giving information on the origin of the γ‐rays observed, and will detect AGNs with a redshift greater than 0.2 (being less affected by absorption by Extragalactic Background Light—EBL—in this energy range) and will search for new classes of very high energy γ‐ray emitters (pulsars, microquasars, GRB, and dark matter candidates).

Estimate of the energy of upgoing muons with multiple coulomb scattering

Neutrino oscillations, in a two neutrino mixing scenario, are the most likely solution for the atmospheric neutrino problem [1]. Underground experiments unfold the mass difference Δm 2 = m 2 v2 and the mixing angle θ from the measurement of the survival probability P(v μ → v μ) = 1 − sin 22 θ sin 2(1.27Δm 2 l v /E v ) .

TIME CORRELATIONS OF HIGH ENERGY MUONS IN AN UNDERGROUND DETECTOR

We present the result of a search for correlations in the arrival times of high energy muons collected from 1995 till 2000 with the streamer tube system of the complete MACRO detector at the underground Gran Sasso Lab. Large samples of single muons (8.6 million), double muons (0.46 million) and multiple muons with multiplicities from 3 to 6 (0.08 million) were selected. These samples were used to search for time correlations of cosmic ray particles coming from the whole upper hemisphere or from selected space cones. The results of our analyses confirm with high statistics a random arrival time distribution of high energy cosmic rays.