Silicon-tungsten Imaging Calorimeter Research Articles

Analysis on H spectral shape during the early 2012 SEPs with the PAMELA experiment

The satellite-borne PAMELA experiment has been continuously collecting data since 2006. This apparatus is designed to study charged particles in the cosmic radiation. The combination of a permanent magnet, a silicon strip tracker and a silicon-tungsten imaging calorimeter, and the redundancy of instrumentation allow very precise studies on the physics of cosmic rays in a wide energy range and with high statistics. This makes PAMELA a very suitable instrument for Solar Energetic Particle (SEP) observations. Not only does it span the energy range between the ground-based neutron monitor data and the observations of SEPs from space, but PAMELA also carries out the first direct measurements of the composition for the highest energy SEP events, including those causing Ground Level Enhancements (GLEs). In particular, PAMELA has registered many SEP events during solar cycle 24, offering unique opportunities to address the question of high-energy SEP origin. A preliminary analysis on proton spectra behaviour during this event is presented in this work.

The PAMELA space mission for antimatter and dark matter searches in space

The PAMELA satellite-borne experiment has presented new results on cosmic-ray antiparticles that can be interpreted in terms of DM annihilation or pulsar contribution. The instrument was launched from the Baikonur cosmodrome and it has been collecting data since July 2006. The combination of a permanent magnet silicon strip spectrometer and a silicon-tungsten imaging calorimeter allows precision studies of the charged cosmic radiation to be conducted over a wide energy range with high statistics. The primary scientific goal is the measurement of the antiproton and positron energy spectrum in order to search for exotic sources. PAMELA is also searching for primordial antinuclei (anti-helium), and testing cosmic-ray propagation models through precise measurements of the antiparticle energy spectrum and precision studies of light nuclei and their isotopes. This talk illustrates the most recent scientific results obtained by the PAMELA experiment.

Results from PAMELA

The PAMELA satellite experiment was launched into low earth orbit on June 15(th) 2006. The combination of a permanent magnet silicon strip spectrometer and a silicon-tungsten imaging calorimeter al ...

Performance of the PAMELA Si-W imaging calorimeter in space

The Payload for Antimatter-Matter Exploration and Light Nuclei Astrophysics (PAMELA), primarily designed to directly measure antiparticles (antiprotons and positrons) in the cosmic radiation, was launched successfully on June 15th, 2006, and, since then, it is in continuous data taking. The calorimeter of the PAMELA apparatus has been designed to identify antiprotons from an electron background and positrons from a background of protons with high efficiency and rejection power. It is a sampling silicon-tungsten imaging calorimeter, which comprises 44 single-sided silicon sensor planes (380 μm thick) interleaved with 22 plates of tungsten absorber (0.74 X0 each). It is the first silicon-tungsten calorimeter to be launched in space. In this work we present the in-orbit performance of the calorimeter, including the measured identification capabilities. The calorimeter provides a proton rejection factor of ∼105 while keeping a high efficiency in selecting electrons and positrons, thus fulfilling the identification power needed to reach the primary scientific objectives of PAMELA. We show also that, after almost two years of operation in space, the calorimeter is still performing nominally.

Space qualification tests of the PAMELA instrument

PAMELA is a satellite-borne experiment which will measure the antiparticle component of cosmic rays over an extended energy range and with unprecedented accuracy. The apparatus consists of a permanent magnetic spectrometer equipped with a double-sided silicon microstrip tracking system and surrounded by a scintillator anticoincidence system. A silicon–tungsten imaging calorimeter, complemented by a scintillator shower tail catcher, and a transition radiation detector perform the particle identification task. Fast scintillators are used for Time-of-Flight measurements and to provide the primary trigger. A neutron detector is finally provided to extend the range of particle measurements to the TeV region. PAMELA will fly on-board of the Resurs-DK1 satellite, which will be put into a semi-polar orbit in 2005 by a Soyuz rocket. We give a brief review of the scientific issues of the mission and report about the status of the experiment few months before the launch.

Qualification tests of the space telescope PAMELA

PAMELA is a satellite-borne experiment which will investigate the matter-antimatter asymmetry of the universe and other cosmological problems through precise cosmic-ray measurements. The apparatus is built around a permanent magnetic spectrometer equipped with a double-sided silicon microstrip tracking system and surrounded by a scintillator anticoincidence system. Several detectors are used in parallel for particle identification: a silicon-tungsten imaging calorimeter, followed by a scintillator shower tail catcher, and a transition radiation detector made up of carbon fibre radiators and proportional straw tubes. Fast scintillators are used for Time-Of-Flight measurements and to provide the primary trigger. A neutron detector is finally provided to extend the range of particle measurements to very high energies. PAMELA will be operated on-board of the Resurs-DK1 satellite, which will be put into a semi-polar orbit in 2004 by a Soyuz rocket. Purpose of this paper is to report about the mechanical, thermal and electro-diagnostic tests aimed to space qualify the PAMELA telescope before the launch.

The space mission PAMELA

Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics (PAMELA) is a satellite-borne experiment which will investigate the matter–antimatter (a)symmetry of the universe and other cosmological problems through precise cosmic-ray measurements. The primary objectives of the PAMELA mission include measurements of the energy spectra of cosmic-ray antiprotons and positrons over a large energy range (up to 190 GeV for antiprotons, 270 GeV for positrons) and with unprecedented accuracy, the search for an antimatter component with a sensitivity of 10 −7 in the He /He ratio, the measurement of the light nuclear components of cosmic rays up to 200 GeV/n and of the electron component up to at least 400 GeV. The apparatus is built around a permanent magnetic spectrometer equipped with a double-sided silicon microstrip tracking system and surrounded by a scintillator anticoincidence system. State-of-the-art detectors are used for particle identification: a silicon–tungsten imaging calorimeter, augmented by a scintillator shower tail catcher, and a transition radiation detector made up of carbon fibre radiators and proportional straw tubes. Fast scintillators are used for time-of-flight measurements and to provide the primary trigger. A neutron detector is finally provided to extend the range of particle measurements to energies as high as 10 11–10 13 eV. PAMELA will be operated on-board of the Resurs-DK1 satellite, which will be put into its semi-polar orbit in 2004. Here we illustrate the main features of the apparatus and its current status.

Performance of the Transition Radiation Detector of the PAMELA space mission

The performance of the Transition Radiation Detector (TRD) of the PAMELA telescope has been studied using beam test data and simulation tools. PAMELA is a satellite—borne magnetic spectrometer designed to measure particles and antiparticles spectra in cosmic rays. The particle identification at high energy will be achieved by combining the measurements by the TRD and a silicon—tungsten imaging calorimeter. The TRD is composed of 9 planes of straw tubes, interleaved with carbon fiber radiators. A prototype of the detector has been exposed to particle beams of electrons, pious and muons of various momenta at the CERN-PS and SPS accelerator facilities. In addition a dedicated Monte Carlo code has been developed to simulate the detector. Here we illustrate both simulation results and experimental data analysis procedures and we will discuss the estimated TRD performance.

The status of the PAMELA experiment

The PAMELA experiment will be launched on-board of a polar orbiting Resurs DK1 satellite in mid-2003. The primary objective of PAMELA is to measure the flux of antiprotons (80 MeV – 190 GeV) and positrons (50 MeV – 270 GeV) in the cosmic radiation. The wide energy range and large statistics (O(10 4) antiprotons and O(10 5) positrons) will allow sensitive tests of cosmic ray propagation models and searches for exotic sources of antiparticles, such as cold dark matter neutralino annihilations. PAMELA is built around a permanent magnet spectrometer equipped with double-sided silicon detectors and surrounded by an active veto shield. This is complemented by a proportional straw tube / carbon fibre radiator transition radiation detector and a silicon-tungsten imaging calorimeter which is augmented by a scintillator shower tail catcher. A time-of-flight system provides the primary experimental trigger. The status of PAMELA is presented along with main results from simulations and test-beam studies.

The PAMELA experiment on satellite and its capability in cosmic rays measurements

The PAMELA equipment will be assembled in 2001 and installed on board the Russian satellite Resurs. PAMELA is conceived mainly to study the antiproton and positron fluxes in cosmic rays up to high energy (190 GeV for p ̄ and 270 GeV for e +) and to search antinuclei, up to 30 GeV/n, with a sensitivity of 10 −7 in the He / He ratio. The PAMELA telescope consists of: a magnetic spectrometer made up of a permanent magnet system equipped with double sided microstrip silicon detectors; a transition radiation detector made up of active layers of proportional straw tubes interleaved with carbon fibre radiators; and a silicon–tungsten imaging calorimeter made up of layers of tungsten absorbers and silicon detector planes. A time-of-flight system and anti-coincidence counters complete the PAMELA equipment. In the past years, tests have been done on each subdetector of PAMELA; the main results are presented and their implications on the anti-particles identification capability in cosmic rays are discussed here.

Measurements of cosmic-ray electrons and positrons by the Wizard/CAPRICE collaboration

Two recent balloon-borne experiments have been performed by the Wizard/CAPRICE collaboration in order to study the electron and positron components in the cosmic radiation. On 1994 August 8-9 the CAPRICE94 experiment flew from norther Canada and on 1998 May 28-29 the CAPRICE98 experiment flew from New Mexico, USA at altitude8 corresponding to 3.9 and 5.5 g/cm2 of average residual atmosphere respectively. The apparatus were equipped with a Ring Imaging Cherenkov (RICH) detector, a time-of-flight system, a superconducting magnet spectrometer with a tracking system and a 7-radiation-length silicon-tungsten imaging calorimeter. The RICH used in 1994 had a solid NaF radiator while in 1998 the RICH had a CbFlO gaseous radiator. We report on the electron and positron spectra and positron fraction at the top of the atmosphere from few hundred MeV to 40 GeV measured by these two experiments.

First Mass-resolved Measurement of High-Energy Cosmic-Ray Antiprotons

We report new results for the cosmic-ray antiproton-to-proton ratio from 3 to 50 GeV at the top of the atmosphere. These results represent the first measurements, on an event-by-event basis, of mass-resolved antiprotons above 18 GeV. The results were obtained with the NMSU-WIZARD/CAPRICE98 balloon-borne magnet spectrometer equipped with a gas-RICH (Ring-Imaging Cerenkov) counter and a silicon-tungsten imaging calorimeter. The RICH detector was the first ever flown that is capable of identifying charge-one particles at energies above 5 GeV. The spectrometer was flown on 1998 May 28-29 from Fort Sumner, New Mexico. The measured p&d1;/p ratio is in agreement with a pure secondary interstellar production.

Cosmic ray antiproton/electron discrimination capability of the CAPRICE silicon-tungsten calorimeter using neural networks

A data analysis based on an artificial neural network classifier is proposed to identify cosmic ray antiprotons detected with the CAPRICE silicon-tungsten imaging calorimeter against electron background in the energy range 1.2–4.0 GeV. A set of new physical variables, describing the events inside the calorimeter on the base of their different patterns, are introduced in order to discriminate between hadronic and electromagnetic showers. The ability of the artificial neural network classifier to perform a careful multidimensional analysis gives the possibility to identify antiprotons with an electron rejection 408±85 (stat) at 95.0±0.2 (stat)% of signal detection efficiency. The high accuracy achieved by this method improves substantially the efficiency in the evaluation of the cosmic ray antiproton spectrum.

Identification of cosmic ray electrons and positrons by neural networks

A data analysis based on artificial neural network classifiers has been done to identify cosmic ray electrons and positrons detected with the balloon-borne NMSU/Wizard-TS93 experiment. The information is provided by two ancillary and independent particle detectors: a transition radiation detector and a silicon-tungsten imaging calorimeter. Electrons and positrons measured during the flight have been identified with background rejection factors of 80 ± 3 and 500 ± 37 at signal efficiencies of 72 ± 3% and 86 ± 2% for the transition radiation detector and silicon-tungsten imaging calorimeter, respectively. The ability of the artificial neural network classifiers to perform a careful multidimensional analysis surpasses the results achieved by conventional methods.

Measurement of the Positron to Electron Ratio in the Cosmic Rays above 5 GeV

As part of a series of experiments to search for antimatter in cosmic rays, the New Mexico State University balloon-borne magnet spectrometer was configured for a flight to study positrons. Two completely new instruments, a transition radiation detector and a silicon-tungsten imaging calorimeter, were added to the magnet spectrometer. These two detectors provided a proton rejection factor better than 3 × 104. This instrument was flown from Fort Sumner, New Mexico, at an average depth of 4.5 g cm-2 of residual atmosphere for a period of 25 hr. We report here the measured fraction of positrons e+/(e+ + e-) from ~5 to 60 GeV at the top of the atmosphere. Our measurements do not show any compelling evidence for an increase in this ratio with energy, and our results are consistent with a constant fraction of 0.078 ± 0.016 over the entire energy region.