PAMELA
Encyclopedia
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| Organization | PAMELA group |
|---|---|
| Mission Type | Cosmic Ray Cosmic ray Cosmic rays are energetic charged subatomic particles, originating from outer space. They may produce secondary particles that penetrate the Earth's atmosphere and surface. The term ray is historical as cosmic rays were thought to be electromagnetic radiation... |
| Host Satellite | Resurs DK1 Resurs DK Resurs-DK1 is a commercial Earth observation satellite capable of transmitting high-resolution imagery to the ground stations as it passes overhead... |
| Launch | 15 June 2006 |
| Launch vehicle | Soyuz-FG Soyuz-FG The Soyuz-FG launch vehicle is an improved version of the Soyuz-U, from the R-7 family of rockets, designed and constructed by TsSKB-Progress in Samara... |
| Launch site | Baikonur Cosmodrome Baikonur Cosmodrome The Baikonur Cosmodrome , also called Tyuratam, is the world's first and largest operational space launch facility. It is located in the desert steppe of Kazakhstan, about east of the Aral Sea, north of the Syr Darya river, near Tyuratam railway station, at 90 meters above sea level... |
| Mission duration | 3 years |
| Mission elapsed time | |
| Mass Mass Mass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:... |
470 kg |
| Max length | 1300 mm |
| Power consumption | 335 Watts |
| Webpage | PAMELA homepage |
| Orbital elements (Resurs DK1) | |
| Inclination Inclination Inclination in general is the angle between a reference plane and another plane or axis of direction.-Orbits:The inclination is one of the six orbital parameters describing the shape and orientation of a celestial orbit... |
70 degrees |
| Orbit Orbit In physics, an orbit is the gravitationally curved path of an object around a point in space, for example the orbit of a planet around the center of a star system, such as the Solar System... |
quasi-polar elliptical |
| Min altitude | 360 km |
| Max altitude | 604 km |
| Period | 94.02 min |
PAMELA (Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics) is an operational cosmic ray
Cosmic ray
Cosmic rays are energetic charged subatomic particles, originating from outer space. They may produce secondary particles that penetrate the Earth's atmosphere and surface. The term ray is historical as cosmic rays were thought to be electromagnetic radiation...
research module attached to an Earth orbiting satellite. PAMELA was launched on 15 June 2006 and is the first satellite
Satellite
In the context of spaceflight, a satellite is an object which has been placed into orbit by human endeavour. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon....
-based experiment dedicated to the detection of cosmic rays, with a particular focus on their antimatter
Antimatter
In particle physics, antimatter is the extension of the concept of the antiparticle to matter, where antimatter is composed of antiparticles in the same way that normal matter is composed of particles...
component, in the form of positron
Positron
The positron or antielectron is the antiparticle or the antimatter counterpart of the electron. The positron has an electric charge of +1e, a spin of ½, and has the same mass as an electron...
s and antiproton
Antiproton
The antiproton is the antiparticle of the proton. Antiprotons are stable, but they are typically short-lived since any collision with a proton will cause both particles to be annihilated in a burst of energy....
s. Other objectives include long-term monitoring of the solar modulation of cosmic rays, measurements of energetic particles from the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
, high-energy particles in Earth's magnetosphere
Magnetosphere
A magnetosphere is formed when a stream of charged particles, such as the solar wind, interacts with and is deflected by the intrinsic magnetic field of a planet or similar body. Earth is surrounded by a magnetosphere, as are the other planets with intrinsic magnetic fields: Mercury, Jupiter,...
and Jovian
Gas giant
A gas giant is a large planet that is not primarily composed of rock or other solid matter. There are four gas giants in the Solar System: Jupiter, Saturn, Uranus, and Neptune...
electrons. It is also hoped that it may detect evidence of dark matter
Dark matter
In astronomy and cosmology, dark matter is matter that neither emits nor scatters light or other electromagnetic radiation, and so cannot be directly detected via optical or radio astronomy...
annihilation.
Development and launch
PAMELA is the largest device yet built by the Wizard collaboration, which includes Russia, Italy, Germany and Sweden and has been involved in many satellite and balloon-based cosmic ray experiments such as Fermi-GLAST. The 470 kg, US$32 million (EU€24.8 million, UK£16.8 million) instrument was originally projected to have a three year mission. However, this durable module is still operational and making significant scientific contributions after more than five years.PAMELA is mounted on the upward-facing side of the Resurs-DK1 Russian satellite. It was launched by a Soyuz
Soyuz (rocket)
The Soyuz was a Soviet expendable carrier rocket designed by OKB-1 and manufactured by State Aviation Plant No. 1 in Samara, Russia. It was used to launch Soyuz spacecraft as part of the Soyuz programme, initially on unmanned test flights, followed by the first 19 manned launches of the...
rocket from Baikonur Cosmodrome
Baikonur Cosmodrome
The Baikonur Cosmodrome , also called Tyuratam, is the world's first and largest operational space launch facility. It is located in the desert steppe of Kazakhstan, about east of the Aral Sea, north of the Syr Darya river, near Tyuratam railway station, at 90 meters above sea level...
on 15 June 2006. PAMELA has been put in a polar elliptical orbit at an altitude between 350 and 610 km, with an inclination of 70°.
Design
The apparatus is 1.3 m high, has a total mass of 470 kg and a power consumption of 335 W. The instrument is built around a permanent magnet spectrometer with a silicon microstrip tracker that provides rigidity and dE/dx information. At its bottom is a silicon-tungsten imaging calorimeter, a neutron detector and a shower tail scintillator to perform lepton/hadron discrimination. A Time of Flight (ToF), made of three layers of plastic scintillators, is used to measure the beta and charge of the particle. An anticounter system made of scintillators surrounding the apparatus is used to reject false triggers and albedo particles during off-line analysis.| Particle | Energy Range |
|---|---|
| Antiproton flux | 80 MeV – 190 GeV |
| Positron flux | 50 MeV – 270 GeV |
| Electron flux | up to 400 GeV |
| Proton flux | up to 700 GeV |
| Electron/positron flux | up to 2 TeV |
| Light nuclei (up to Z=6) | up to 200 GeV/n |
| Light isotopes (D, 3He) | up to 1 GeV/n |
| Antinuclei search | sensitivity better than 10−7 antiHe/He |
Results
Preliminary data (released August 2008, ICHEP Philadelphia) indicate an excess of positrons in the range 10–60 GeV. This is thought to be a sign of dark matterDark matter
In astronomy and cosmology, dark matter is matter that neither emits nor scatters light or other electromagnetic radiation, and so cannot be directly detected via optical or radio astronomy...
annihilation:
hypothetical WIMPs colliding with and annihilating each other to form gamma rays, matter and antimatter particles.
The first two years of data were released in October 2008 in three publications. The positron excess was confirmed and found to persist up to 90 GeV. Surprisingly, no excess of antiprotons was found. This is inconsistent with predictions from most models of dark matter sources, in which the positron and antiproton excesses are correlated.
A paper, published on 15 July 2011, confirmed earlier speculation that the Van Allen belt could confine a significant flux of antiproton
Antiproton
The antiproton is the antiparticle of the proton. Antiprotons are stable, but they are typically short-lived since any collision with a proton will cause both particles to be annihilated in a burst of energy....
s produced by the interaction of the Earth's upper atmosphere with cosmic ray
Cosmic ray
Cosmic rays are energetic charged subatomic particles, originating from outer space. They may produce secondary particles that penetrate the Earth's atmosphere and surface. The term ray is historical as cosmic rays were thought to be electromagnetic radiation...
s. The energy of the antiprotons has been measured in the range of 60–750 MeV. Cosmic rays collide with atoms in the upper atmosphere creating antineutron
Antineutron
The antineutron is the antiparticle of the neutron with symbol . It differs from the neutron only in that some of its properties have equal magnitude but opposite sign. It has the same mass as the neutron, and no net electric charge, but has opposite baryon number...
s, which in turn decay to produce the antiprotons. They were discovered in a part of the Van Allen belt closest to Earth. When an antiproton interacts with a normal particle, both are annihilated. Data from PAMELA indicated that these annihilation
Annihilation
Annihilation is defined as "total destruction" or "complete obliteration" of an object; having its root in the Latin nihil . A literal translation is "to make into nothing"....
events occurred a thousand times more often than would be expected in the absence of antimatter
Antimatter
In particle physics, antimatter is the extension of the concept of the antiparticle to matter, where antimatter is composed of antiparticles in the same way that normal matter is composed of particles...
. The data that contained evidence of antimatter were gathered between July 2006 and December 2008.
Sources of error
Between 1 and 100 GeV PAMELA is exposed to one hundred times as many electrons as antiprotons. At 1 GeV there are one thousand times as many protons as positrons and at 100 GeV ten thousand times as many. Therefore, to correctly determine the antimatter abundances, it is critical that PAMELA is able to reject the matter background. The PAMELA collaboration claimed in The electron hadron separation performance of the PAMELA electromagnetic calorimeter that less than one proton in 100,000 is able to pass the calorimeterCalorimeter
A calorimeter is a device used for calorimetry, the science of measuring the heat of chemical reactions or physical changes as well as heat capacity. Differential scanning calorimeters, isothermal microcalorimeters, titration calorimeters and accelerated rate calorimeters are among the most common...
selection and be misidentified as a positron when the energy is less than 200 GeV.
The ratio of matter to antimatter in cosmic rays of energy less than 10 GeV that reach PAMELA from outside the solar system
Solar System
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...
depends on solar activity and in particular on the point in the 22 year solar cycle
Solar cycle
The solar cycle, or the solar magnetic activity cycle, is a periodic change in the amount of irradiation from the Sun that is experienced on Earth. It has a period of about 11 years, and is one component of solar variation, the other being aperiodic fluctuations. Solar variation causes changes in...
. The PAMELA team has invoked this effect to explain the discrepancy between their low energy results and those obtained by CAPRICE, HEAT and AMS-01
Alpha Magnetic Spectrometer
The Alpha Magnetic Spectrometer, also designated AMS-02, is a particle physics experiment module that is mounted on the International Space Station. It is designed to search for various types of unusual matter by measuring cosmic rays. Its experiments will help researchers study the formation of...
, which were collected during that half of the cycle when the solar magnetic field had the opposite polarity. It is important to note that these results are consistent with the series of positron / electron measurements obtain by AESOP, which has spanned coverage over both polarities. Also the PAMELA experiment has contradicted an earlier claim by the HEAT experiment of anomalous positrons in the 6 GeV to 10 GeV range.
See also
- AMS-02Alpha Magnetic SpectrometerThe Alpha Magnetic Spectrometer, also designated AMS-02, is a particle physics experiment module that is mounted on the International Space Station. It is designed to search for various types of unusual matter by measuring cosmic rays. Its experiments will help researchers study the formation of...
is a research module with similar goals that was attached to the International Space StationInternational Space StationThe International Space Station is a habitable, artificial satellite in low Earth orbit. The ISS follows the Salyut, Almaz, Cosmos, Skylab, and Mir space stations, as the 11th space station launched, not including the Genesis I and II prototypes...
in 2011.