Status of the PAMELA silicon tracker

PAMELA is a composite particle detector which will be launched during the first half of 2006 on board the Russian satellite Resurs DK-1 from Baikonur cosmodrome in Kazakhstan. This experiment is mainly conceived for the study of cosmic-ray antiparticles and for the search for light antinuclei, but other issues related to the cosmic-ray physics will be investigated. In this work the structure of the whole apparatus is shortly discussed with particular attention to the magnetic spectrometer, which has been designed and built in Firenze.     

Measurement of the antiproton/proton ratio at TeV energies with the ARGO-YBJ detector

Cosmic ray antiprotons provide an important probe for the study of cosmic-ray propagation in the interstellar space and to investigate the existence of Galactic dark matter. Cosmic rays are hampered by the Moon, therefore a deficit of cosmic rays in its direction is expected (the so-called Moon shadow). The Earth–Moon system acts as a magnetic spectrometer. In fact, due to the geomagnetic field the center of the Moon shifts westward by an amount depending on the primary cosmic ray energy. Paths of primary antiprotons are therefore deflected in an opposite sense in their way to the Earth. This effect allows, in principle, the search of antiparticles in the opposite direction of the observed Moon shadow.The ARGO-YBJ experiment, in stable data taking since November 2007 with an energy threshold of a few 100s of GeV, is observing the Moon shadow with high statistical significance. Using about 1 year data, an upper limit of the flux ratio in the few-TeV energy region is set to a few percent with a confidence level of 90%.     

The track imaging Cherenkov experiment

We describe a dedicated cosmic-ray telescope that explores a new method for detecting Cherenkov radiation from high-energy primary cosmic rays and the large particle air shower they induce upon entering the atmosphere. Using a camera comprising 16 multi-anode photomultiplier tubes for a total of 256 pixels, the Track Imaging Cherenkov Experiment (TrICE) resolves substructures in particle air showers with 0.086° resolution. Cherenkov radiation is imaged using a novel two-part optical system in which a Fresnel lens provides a wide-field optical trigger and a mirror system collects delayed light with four times the magnification. TrICE records well-resolved cosmic-ray air showers at rates ranging between 0.01 Hz and 0.1 Hz.     

PAMELA sub-detectors capability in identifying nuclei: Status of art and perspectives

After almost three years in orbit, the statistic collected by PAMELA detector for what concern nuclei events from cosmic rays is sufficiently relevant to allow a systematic study of such a component. For this scope charge reconstruction from Time-of-Flight system, calorimeter and magnetic spectrometer is used, with different combinations, in order to cover the widest range of inspection in energy and atomic number permitted by the characteristics of the detector. Some results for performances, goals and limits from the different sub-detectors will be presented.     

Study of the IC443 SNR with the Fermi LAT

During the first six months of data taking the Fermi satellite was capable to detect gamma ray emission of the nearby supernova remnant IC443 (G189.1+3.0). IC443 is a shell-type supernova remnant located in the anticenter region where observation can be made clean enough from possible foreground and background overlap, even though care has to be taken due to the vicinity of one of the brightest gamma-ray pulsars, Geminga. IC443 estimated age (20–30 kyr) and the observed two-shell morphology with different radii suggest that the SNR shell has been interacting with surrounding interstellar matter and a neighboring SNR shell. Also the detection of strong molecular emission lines and TeV gamma-ray emission support the idea that the blast has been interacting with dense molecular gas accelerating cosmic-ray particle. After the first year of data taking, Fermi will be surely capable to determine the spatial extension and resolve in much finer details the spectral shape of the gamma-ray emission produced by the accelerated cosmic rays in IC443 distinguished from those of galactic origin.     

PAMELA and electrons

The 15th of June 2006, the PAMELA satellite-borne experiment was launched from the Baikonur cosmodrome and it has been collecting data since July 2006. The apparatus comprises a time-of-flight system, a silicon-microstrip magnetic spectrometer, a silicon–tungsten electromagnetic calorimeter, an anticoincidence system, a shower tail counter scintillator and a neutron detector. The combination of these devices allows precision studies of the charged cosmic radiation to be conducted over a wide energy range (100 MeV–100's GeV) with high statistics. The measurement of the positron to electron fraction and of the electron energy spectrum in order to search for exotic sources, such as dark matter particle annihilations, are within the PAMELA primary scientific goal.     

Up-and-down journeys: The making of Latin America's uniqueness for the study of cosmic rays

In 1942, American Nobel Prize-winning physicist Arthur Compton pointed out that, “Because in this field of cosmic ray studies certain unique advantages are given by their geographical position, this field of physics has been especially emphasized in South America.” This paper seeks to interrogate the making of Latin America's uniqueness with respect to cosmic-ray research through an analysis that considers Compton's geographical argument, but also goes beyond it, referring to the interactions of nature, knowledge, practices, scientific communities, and diplomacy. To begin with, it highlights the place-based strategies and practices associated with cosmic-ray research. Once research in the field at different altitudes demonstrated that cosmic rays traveled from outer space to the Earth surface, their nature was scrutinized by expeditions that covered broad vertical and horizontal expanses. The study of cosmic rays in Latin America displayed the mobilization of that strategy, which reinforced the reliability of certain sites located at high altitudes and close to the geomagnetic equator in projected investigations. Moreover, such analysis of cosmic rays involved research practices in the field, the emergence of (local, regional, or international) research traditions, and the creation of spaces of knowledge at different scales. By centering on the interaction of knowledge and place, this paper shows that an exploration of the “up-and-down journeys” of cosmic-ray research in Latin America expands our understanding of the geographies and practices of 20th-century physics.     

The ToF system for the PAMELA experiment: In flight performances

A Time of Flight (ToF) scintillator system has been developed for the PAMELA satellite-borne cosmic ray experiment. The main scientific goal of the experiment is the measurement of the antiproton and positron fluxes in the cosmic radiation over large energy ranges. The ToF system provides the fast trigger to the experiment, the rejection of albedo particles and the possibility to distinguish electrons from antiprotons up to about 1.5 GeV.In this paper we describe the performances of the ToF system measured on flight data.     

The energy spectrum of cosmic-ray induced neutrons measured on an airplane over a wide range of altitude and latitude

Crews of high-altitude aircraft are exposed to radiation from galactic cosmic rays (GCRs). To help determine such exposures, the Atmospheric Ionizing Radiation Project, an international collaboration of 15 laboratories, made simultaneous radiation measurements with 14 instruments on a NASA ER-2 high-altitude airplane. The primary instrument was a sensitive extended-energy multisphere neutron spectrometer. Its detector responses were calculated for energies up to 100 GeV using the radiation transport code MCNPX 2.5.d with improved nuclear models and including the effects of the airplane structure. New calculations of GCR-induced particle spectra in the atmosphere were used to correct for spectrometer counts produced by protons, pions and light nuclear ions. Neutron spectra were unfolded from the corrected measured count rates using the deconvolution code MAXED 3.1. The results for the measured cosmic-ray neutron spectrum (thermal to >10 GeV), total neutron fluence rate, and neutron dose equivalent and effective dose rates, and their dependence on altitude and geomagnetic cut-off agree well with results from recent calculations of GCR-induced neutron spectra.     

Simulations of a thin sampling calorimeter with GEANT/FLUKA

The Advanced Cosmic-ray Composition Experiment for the Space Station (ACCESS) will investigate the origin, composition and acceleration mechanism of cosmic rays by measuring the elemental composition of the cosmic rays up to 10¹⁵ eV. These measurements will be made with a thin ionization calorimeter and a transition radiation detector. This paper reports studies of a thin sampling calorimeter concept for the ACCESS thin ionization calorimeter. For the past year, a Monte Carlo simulation study of a thin sampling calorimeter (TSC) design has been conducted to predict the detector performance and to design the system for achieving the ACCESS scientific objectives. Simulation results show that the detector energy resolution function resembles a Gaussian distribution and the energy resolution of TSC is about 40%. In addition, simulations of the detector's response to an assumed broken power law cosmic ray spectrum in the region where the ‘knee’ of the cosmic ray spectrum is believed to occur have been conducted and clearly show that a thin sampling calorimeter can provide sufficiently accurate estimates of the spectral parameters to meet the science requirements of ACCESS.     

The relative transit time of high-rigidity and low-rigidity cosmic rays through the solar system

A study of neutron monitor count rates with vertical cut-off rigidities from 0.6 to 13 GV indicates that high-energy and low-energy galactic cosmic rays arrive at earth orbit with small time differences compared to a month. This is in contradiction to the theory of the deceleration potential which states that cosmic-ray particles with rigidities greater than 36 V arrive at earth orbit about three months before cosmic-ray particles with lesses rigidines.     

A massive bolometer on the international space station to measure energy deposition by the space radiation environment

We describe a novel space-based low-temperature radiation detector, the “Particle Heating Detector” (PhD), which was recently selected to be part of the first mission of the Low-Temperature Microgravity Physics Facility, scheduled to fly on the International Space Station in 2008. This massive bolometer will measure total heating induced in an aluminum absorber by the space radiation environment. The use of paramagnetic alloy thermometers with SQUID readout, giving resolution, combined with a large-area absorber, will enable the detector to perform high-resolution, real-time measurement of the low energy deposition levels caused by galactic cosmic rays in low-Earth orbit.     

The spectrum of cosmic-ray electrons measured with H.E.S.S.

The measurement of very-high-energy cosmic-ray electrons is intrinsically difficult due to the very steep electron spectrum with low fluxes and an enormous background of hadronic cosmic rays. The large collection areas needed for such a measurement can be provided by ground-based imaging atmospheric Cherenkov telescopes. The High Energy Stereoscopic System (H.E.S.S.) has performed the first ground-based cosmic-ray electron measurement and thereby extended the measured range of the spectrum to several TeV. Here the H.E.S.S. measurement is presented, as well as an extension of the H.E.S.S. spectrum towards lower energies. At these energies, H.E.S.S. can probe recent ATIC measurements, which have been interpreted in terms of dark matter scenarios.     

The macro detector at the Gran Sasso Laboratory

The MACRO detector is presently under construction, its installation at Gran Sasso being planned to start in September 1987. It is a large area detector, the acceptance for isotropic particle fluxes being around 10 000 m² sr, designed to search for rare phenomena in the cosmic radiation. It makes use of three detection techniques: liquid scintillator counters, plastic streamer tubes, and track-etch. It will perform a search for GUT monopoles (or any supermassive charged penetrating particle), a survey of cosmic point sources of HE gammas and neutrinos, a systematic study of the penetrating cosmic ray muons, and will be sensitive to neutrino bursts from gravitational stellar collapses in the Galaxy.     

Long-term measurements of cosmic ray neutrons by means of a Bonner spectrometer at mountain altitudes - first results

A Bonner multi-sphere spectrometer has been installed in 2005 at the Environmental Research Station 'Schneefernerhaus' (2660 m above sea level) on the Zugspitze mountain, Germany, to measure the energy spectrum of cosmic-ray neutrons at high altitudes continuously. The system can be used to investigate small temporal variations in the cosmic radiation intensity. For example, measurements were done during periods of 2 Forbush decreases of the cosmic radiation intensity in July and September 2005, respectively. The results were compared with those obtained by using neutron monitors, and neutron fluence spectra measured during these events are presented and discussed.     

Results from the first two years of VERITAS observations

The VERITAS observatory is an imaging atmospheric Cherenkov telescope array located in southern Arizona and covers an energy range between 100 GeV and 30 TeV. The VERITAS collaboration pursues a rigorous observing program that targets a range of key science objectives in astrophysics and particle physics; the understanding of the origin of cosmic rays, the search for supersymmetric dark matter self-annihilation, illuminating the connection between black holes and relativistic jets and constraints to the cosmological diffuse infrared background. We provide a summary of results from the first two years of observations with the full 4-telecope array reported at RICAP09.     

Predicting the response of a submillimeter bolometer to cosmic rays

Bolometers designed to detect submillimeter radiation also respond to cosmic, gamma, and x rays. Because detectors cannot be fully shielded from such energy sources, it is necessary to understand the effect of a photon or cosmic-ray particle being absorbed. The resulting signal (known as a glitch) can then be removed from raw data. We present measurements using an Americium-241 gamma radiation source to irradiate a prototype bolometer for the High Frequency Instrument in the Planck Surveyor satellite. Our measurements showed no variation in response depending on where the radiation was absorbed, demonstrating that the bolometer absorber and thermistor thermalize quickly. The bolometer has previously been fully characterized both electrically and optically. We find that using optically measured time constants underestimates the time taken for the detector to recover from a radiation absorption event. However, a full thermal model for the bolometer, with parameters taken from electrical and optical measurements, provides accurate time constants. Slight deviations from the model were seen at high energies; these can be accounted for by use of an extended model.     

Application of the heliocentric potential to aircraft dosimetry

The heliocentric potential is the result of a steady-state solution to the diffusion equation of cosmic rays through the solar wind. The counting rate of any high-latitude, ground-level neutron monitor can be used to determine this potential, which will return cosmic ray spectra in real time. These spectra are routinely used to determine the radiation dose rate to which air crew are exposed during the precise hours of a flight, including the effects of quick decreases and Forbush decreases. Further, it has been used in an effort to calculate the radiation dose rate to air crew during an energetic solar particle event, as the cosmic ray background before the event must be determined. An alternate approach is to use the deceleration potential, which assumes a significant time-dependence of cosmic rays through the heliosphere. However, the theory behind it does not account for the behaviour of ground-level neutron monitors.     

Track-etched detectors for the dosimetry of the radiation of cosmic origin

Cosmic rays contribute to the exposure on the Earth's surface as well as in its surroundings. At the surface and/or at aviation altitudes, there are mostly secondary particles created through the cosmic rays interaction in the atmosphere, which contribute to this type of exposure. Onboard a spacecraft, the exposure comes mostly from primary cosmic rays. Track-etched detectors (TED) are able to characterise both these types of exposure. The contribution of neutrons, of cosmic origin, on the Earth's surface was studied at altitudes from few hundreds to 3000 m using TED in a moderator sphere. The results obtained are compared with other data on this type of natural radiation background. The results of studies performed onboard aircraft and/or spacecraft are presented afterwards. We used TED-based neutron dosemeter, as well as a spectrometer of linear energy transfer based on a chemically etched TED. The results of studies performed onboard aircraft, as well as spacecraft, are presented and discussed, including an attempt to estimate a neutron component onboard the spacecraft. It was found that they correlate with the results of other independent investigations.     

The Time of Flight electronics for the PAMELA experiment in space

PAMELA, a cosmic ray telescope, was launched into space on 15th June 2006 from the Baikonur cosmodrome aboard of a Soyuz-U and it is in continuous data tacking since 11 July 2006. The Time of Flight system of the PAMELA telescope allows both to distinguish electrons to antiprotons up to about 2 GeV and to measure the absolute charge of the particle. In order to perform these goals the requested time resolution for the whole ToF system is . To fulfill the detector requirements the read out electronics is been required to have a time resolution better than 60 ps with wide dynamic range for charge measurements. The peculiarity of the developed electronics arises from the need to obtain such a time resolution operating in a satellite environment, which implies low-power consumption, radiation hardness, redundancy and high reliability.