C. Cecchi

Fermi-LAT Observations of High-energy Behind-the-limb Solar Flares

We report on the Fermi-LAT detection of high-energy emission from the behind-the-limb (BTL) solar flares that occurred on 2013 October 11, and 2014 January 6 and September 1. The Fermi-LAT observations are associated with flares from active regions originating behind both the eastern and western limbs, as determined by STEREO. All three flares are associated with very fast coronal mass ejections (CMEs) and strong solar energetic particle events. We present updated localizations of the >100 MeV photon emission, hard X-ray (HXR) and EUV images, and broadband spectra from 10 keV to 10 GeV, as well as microwave spectra. We also provide a comparison of the BTL flares detected by Fermi-LAT with three on-disk flares and present a study of some of the significant quantities of these flares as an attempt to better understand the acceleration mechanisms at work during these occulted flares. We interpret the HXR emission to be due to electron bremsstrahlung from a coronal thin-target loop top with the accelerated electron spectra steepening at semirelativistic energies. The >100 MeV gamma-rays are best described by a pion-decay model resulting from the interaction of protons (and other ions) in a thick-target photospheric source. The protons are believed to have been accelerated (to energies >10 GeV) in the CME environment and precipitate down to the photosphere from the downstream side of the CME shock and landed on the front side of the Sun, away from the original flare site and the HXR emission.

Preliminary results of the LAT Calibration Unit beam tests

The calibration strategy of the GLAST Large Area Telescope (LAT) combines analysis of cosmic ray data with accelerator particle beams measurements. An advanced Monte Carlo simulation of the LAT, based on the Geant4 package, was set up to reproduce the LAT response to such radiation and to benchmark the event reconstruction and the background rejection strategy before launch and during operation. To validate the LAT simulation, a massive campaign of beam tests was performed between July and November 2006, in parallel with the LAT integration and test, on the LAT Calibration Unit. This is a detector built with spare flight modules and flight‐like readout electronics, which was exposed to a large variety of beams, representing the whole spectrum of the signal that will be detected by the LAT, using the CERN and the GSI accelerator facilities. Beams of photons (0 – 2.5 GeV), electrons (1 – 300 GeV), hadrons (π and p, a few GeV – 100 GeV) and ions (C; Xe, 1.5 GeV/n) were shot through the CU to measure the phys...

1D, 2D, 3D wavelet methods for gamma‐ray source analysis

An example of wavelet transforms applied to data from EGRET and data of the GLAST pre‐launch simulations is reported. 1D wavelet transform can be an useful tool in the analysis of gamma‐ray source variability, while 2D/3D wavelet transform is a potential partner tool of the standard Likelihood analysis, in the frame of gamma‐ray source detection.

Muon-pair and tau-pair production in two-photon collisions at LEP

The QED processes e^+ e^- ->e^+ e^- \mu^+ \mu^- and e^+ e^- ->e^+ e^- \tau^+ \tau^- are studied with the L3 detector at LEP using an untagged data sample collected at centre-of-mass energies 161 GeV<sqrt{s}<209 GeV. The tau-pairs are observed through the associated decay of one tau into e\nu\nu and the other into \pi\pi\nu . The cross sections are measured as a function of sqrt{s}. For muon pairs, the cross section of the \gamma\gamma ->\mu^+\mu^- process is also measured as a function of the two-photon centre-of-mass energy for 3 GeV<W_{\gamma\gamma}<40 GeV. Good agreement is found between these measurements and the O(\alpha^4) QED expectations. In addition, limits on the anomalous magnetic and electric dipole moments of the tau lepton are extracted.

Measurement of the Z-boson mass using e+e- →Zγ events at centre-of-mass energies above the Z pole

Events from the e + e − → Zγ process with hard initial-state radiation collected with the L3 detector at centre-of-mass energies between 183 GeV and 209 GeV are used to measure the mass of the Z boson. Decays of the Z boson into hadrons or muon pairs are considered and the Z mass is determined to be 91.272±0.032 (stat.)± 0.033 (syst.) GeV, in agreement with the value measured at the Z resonance. Alternatively , assuming this measured value of the Z mass, the method determines the LEP centre-of-mass energy, found to be 175 ± 68 (stat.) ± 68 (syst.) MeV lower than the nominal value.

Search for colour singlet and colour reconnection effects in hadronic Z decays at LEP

A search is performed in symmetric 3-jet hadronic Z-decay events for evidence of colour singlet production or colour reconnection effects. Asymmetries in the angular separation of particles are found to be sensitive indicators of such effects. Upper limits on the level of colour singlet production or of colour reconnection effects are established for a variety of models.  2003 Published by Elsevier B.V. Open access under CC BY license. 22 L3 Collaboration / Physics Letters B 581 (2004) 19–30

A LYSO Calorimeter for the SuperB Factory

The SuperB project is an asymmetric e+e? accelerator of 1036cm?2s?1 luminosity, capable of collecting a data sample of 50?75 ab?1 in five years of running. The SuperB electromagnetic calorimeter (EMC), that will be described in this paper, provides energy and direction measurement of photons and electrons, and is used for identification of electrons versus other charged particles. In particular we will present its design, geometry study and related simulations, as well as R&D on LYSO crystals, a project for the mechanical structure and development on readout and electronics. A matrix of 6 crystals has been tested this year June 2010 at the Beam Test Facility of Frascati (BTF) at energies between 200 MeV and 500 MeV, and a beam test with the complete prototype of 25 crystals is foreseen at CERN in October 2010 to cover the energy range between 500 MeV and 7 GeV.

The SuperB factory electromagnetic calorimeter

The SuperB project is an asymmetric e+e− accelerator of 1036 cm−2s−1 luminosity, capable of collecting a 50–75 ab−1 data sample in five years of running. The SuperB electromagnetic calorimeter (EMC) provides energy and direction measurement of photons and electrons and identification versus other charged particles for electrons. A matrix of 25 LYSO crystals has been tested at the Beam Test Facility at Frascati in May 2011 at energies between 100 MeV and 500 MeV. Results from this test will be presented. Design and Monte Carlo studies for the general EMC system will also be presented.

Study of the LAT PSF of the Gamma Ray Large Area Telescope

GLAST is the next generation telescope for the study of the Gamma Ray Universe.The GLAST mission is composed of two instruments: the LAT (Large Area Telescope) exploring the energy range between 20 MeV and 300 GeV and the GBM (Gamma ray Burst Monitor) studying the region from 10 KeV up to 30 MeV.GLAST represents an important step beyond EGRET providing a large improvement in instrument performance: large Field of View (FOV), large energy range extending to unexplored region of energies larger than 10 GeV, large effective area, a factor of 30 improvement in sensitivity, a much smaller dead time and a very good Point Spread Function (PSF).Since GLAST will operate in a continuous scanning mode, for most of the time during the mission, photons from a source will be detected at different angles in the LAT field of view requiring a good PSF in order to disentangle between sources.We will present results on PSF studies performed with various sets of data. The selection criteria and algorithm have been initially ...

Inclusive Lambda production in two-photon collisions at LEP

The reactions e^+e^- ->e^+e^- Lambda X and e^+e^- ->e^+e^- Lambda X are studied using data collected at LEP with the L3 detector at centre-of-mass energies between 189 and 209 GeV. Inclusive differential cross sections are measured as a function of the lambda transverse momentum, p_t, and pseudo-rapidity, eta, in the ranges 0.4 GeV<p_t<2.5 GeV and |\eta|<1.2. The data are compared to Monte Carlo predictions. The differential cross section as a function of p_t is well described by an exponential of the form A exp (- p_t /<p_t>)