Astroparticle Physics

We present an up date of our previous study [2] on how ν oscillations affect the signal from a supernova core collapse observed in the LVD detector at LNGS. In this paper we use a recent, more precise determination of the cross section [8] to calculate the expected number of inverse beta decay events, we intro duce in the simulation also the ν -Fe interactions, we include the Earth matter effects and, finally, we study also the inverted mass hierarchy case.

Within the XENON program, we are operating a double-phase time-projection chamber (TPC) using liquid xenon (LXe) as target material. The current phase, XENON100 installed in the LNGS, is in science mode since the beginning of 2010, with a sensitivity goal of 2 × 10 −45 cm 2 for spin-independent WIMP-nucleon scattering. For the next step, we propose to build a detector with a total mass of 2.4 tons of LXe (1.2 fiducial): XENON1T. The goal is to reduce the background by two orders of magnitude with respect to XENON100, reaching a sensitivity of about 5 × 10 −47 cm 2 . Therefore it is crucial to reduce the external backgrounds: gammas and neutrons from the ambient radioactivity and the most dangerous muon-induced neutrons. A study of the shield and muon veto needed by the experiment has been carried on with a full Geant4 Monte Carlo simulation. To shield the experiment at LNGS we plan to build a water tank of 10 m diameter and 10 m height, instrumented with PMTs to act as a Cerenkov muon veto. The results of the simulation show that the gammas and neutrons from rock and concrete radioactivity are reduced at a completely negligible level, and the muon-induced neutrons contribute to mimic the WIMP's signal with 0.07 events per year, which allows to reach the foreseen sensitivity of the experiment.

Many experiments looking for dark matter are aiming to get the ton scale in the future. However, it is well known that scaling dark matter detectors to higher mass is not a sufficient condition for sensitivity and that an equally important condition is to simultaneously keep the background low, in particular the ultimate background, namely the fast neutron background induced by muons. In this study we explore the possibility of using the existing structure of a running experiment, the LVD supernova observatory at the INFN Gran Sasso National Laboratory, as an active shield and veto for the muon-induced background.

The Large Volume Detector (LVD) in the INFN Gran Sasso National Laboratory, Italy, is a ν observatory mainly designed to study low energy neutrinos from the gravitational collapse of galactic objects. The experiment has been monitoring the Galaxy since June 1992, under increasing larger configurations: in January 2001 it has reached its final active mass M = 1 kt. LVD is one of the largest liquid scintillator apparatus for the detection of stellar collapses and, besides SNO, SuperKamiokande and Amanda, it is a charter member of the SNEWS network, that has become fully operational since July 1st, 2005. No gravitational core-collapse has been detected by LVD during 14 years of data acquisition; this allows to put an upper limit of 0.18 events y −1 in our galaxy at the 90% C.L. The LVD tracking system allows the detection and the recontruction of the cosmic muon tracks in a large fraction of the whole solid angle, in particular also horizontal tracks can be reconstructed. The results of the muon depth-intensity relation and of the flux of neutrino-induced muons are presented. Moreover, during 2006, the CNGS beam will start its operation: the performances of LVD as a beam monitor are described.

The Forbush decrease following the large X2 solar flare on mid-February 2011 has been observed by the muon telescopes of the EEE Project, which are located in several Italian sites and at CERN. Data from two different telescopes of the EEE network have been analyzed and compared to those measured by neutron monitor stations. The variation of the muon counting rate during the Forbush decrease was also extracted for different intervals of the azimuthal angle of the incoming muons.

1] For the first time, accurate measurements of electron and positron fluxes in the energy range 0.2 -10 GeV have been performed with the Alpha Magnetic Spectrometer (AMS) at altitudes of 370 -390 km in the geographic latitude interval ±51.7°. We describe the observed under-cutoff lepton fluxes outside the region of the South Atlantic Anomaly. The separation in quasi-trapped, long-lifetime (O(10 s)), and albedo, short-lifetime (O(100 ms)), components is explained in terms of the drift shell populations observed by AMS. A significantly higher relative abundance of positrons with respect to electrons is seen in the quasi-trapped population. The flux maps as a function of the canonical adiabatic variables L, a 0 are presented for the interval 0.95 < L < 3, 0°< a 0 < 90°f or electrons (E < 10 GeV) and positrons (E < 3 GeV). The results are compared to existing data at lower energies. The properties of the observed under-cutoff particles are also investigated in terms of their residence times and geographical origin.

A pulsed nanosecond IR laser diode system to automatically test the Single Event Effects in laboratory is described. The results of Single Event Latchup (SEL) test on two VLSI chips (VA HDR64, 0.8 and 1:2 mm technology) are discussed and compared to those obtained with high-energy heavy ions at GSI (Darmstadt). r 0168-9002/02/$ -see front matter r 2002 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 -9 0 0 2 ( 0 2 ) 0 0 5 5 2 -1

The radiation emitted by 180-GeV/ c volume-reflected electrons and positrons impinging on a bent crystal has been measured by the H8RD22 Collaboration on the H8 beamline at the CERN SPS. A dedicated spectrometer has been developed to measure high-energy photon spectra ͑up to ϳ100 GeV͒ under volume reflection: photon and charged particle beams have been separated by a bending magnet and leptons were detected and tagged by microstrip silicon detectors and a Pb-scintillator sampling calorimeter. A comparison between the experimental and analytical data for the amorphous and volume-reflection cases is presented and the differences are discussed.

The Alpha Magnetic Spectrometer is a large acceptance cosmic-ray detector ð0:5 m 2 srÞ designed to operate at an altitude of 400 km on the International Space Station. The AMS-02 silicon tracker contains 2264 silicon microstrip sensors (total active area 6:75 m 2 ). The internal alignment parameters of the assembled tracker have been determined on the ground with cosmic-ray muons. The alignment procedure is described and results for the alignment precision and position resolution are reported.

Following the decision to maintain the International Space Station (ISS) on orbit until at least 2020 (possibly until 2028) the AMS collaboration decided to correspondingly extend the lifetime of the experiment. Since the limited amount of helium used to cool the superconducting magnet allowed for only a limited run time of the experiment, a change from the superconducting magnet to the permanent magnet used in AMS-01 became necessary. Due to the lower magnetic field, to maintain the resolution the silicon tracker also had to be reconfigured with the installation of a silicon plane on the top of the experiment and a new plane above the electromagnetic calorimeter.

The trend of volume reflection parameters (deflection angle and efficiency) in a bent (110) silicon crystal has been investigated as a function of the crystal curvature with 400 GeV= c protons on the H8 beam line at the CERN Super Proton Synchrotron. This Letter describes the analysis performed at six different curvatures showing that the optimal radius for volume reflection is approximately 10 times greater than the critical radius for channeling.