* Astronomy

Blobrana · L

RE: Cosmic rays

Blobrana · L

Title: Neutrinos from charm production in the atmosphere
Author: Rikard Enberg

Atmospheric neutrinos are produced in interactions of cosmic rays with Earth's atmosphere. At very high energy, the contribution from semi-leptonic decays of charmed hadrons, known as the prompt neutrino flux, dominates over the conventional flux from pion and kaon decays. This is due to the very short lifetime of the charmed hadrons, which therefore do not lose energy before they decay. The calculation of this process is difficult because the Bjorken-x at which the parton distribution functions are evaluated is very small. This is a region where QCD is not well understood, and large logarithms must be resummed. Available parton distribution functions are not known at such small x and extrapolations must be made. Theoretically, the fast rise of the structure functions for small x ultimately leads to parton saturation. This contribution describes the "ERS" calculation of the prompt neutrino flux, which includes parton saturation effects in the QCD production cross section of charm quarks. The ERS flux calculation is used by e.g. the IceCube collaboration as a standard benchmark background. We are now updating this calculation to take into account the recent LHC data on the charm cross section, as well as recent theoretical developments in QCD. Some of the issues involved in this calculation are described.

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Blobrana · L

Vast cosmic event leaves record in ancient trees

The wooden hearts of two cedar trees hold a 1200-year-old cosmic mystery - evidence of an unexplained event that rocked our planet in the 8th century.
Cosmic rays are subatomic particles that tear through space. When they reach Earth they react with the oxygen and nitrogen in the atmosphere, producing new particles. One of these - carbon-14 - is taken up by trees during photosynthesis and is "fixed" in the tree's annual growth ring.
Fusa Miyake at Nagoya University, Japan, and his colleagues examined the carbon-14 content of two Japanese cedar trees and were surprised to find that there was a 1.2 per cent increase in the amount of the isotope between AD 774 and 775. The typical annual variation is just 0.05 per cent.
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Blobrana · L

An analysis of the rings of two Japanese cedar trees, reported online today in Nature, reveals that from 774 to 775 C.E., the atmospheric level of radioactive carbon-14 jumped by 1.2%. This indicates that cosmic rays bombarded our planet and converted some atmospheric nitrogen-14 into carbon-14. The scientists argue against two logical suspects: solar flares are too weak to do the job, and no supernova explosion was seen at the time, nor do any nearby supernova remnants date back to Charlemagne's time. There's also nothing unusual in the history books. So the cause remains a mystery.
Source

Blobrana · L

The mystery surrounding the source of the highest-energy particles known in the Universe has grown deeper.
The particles, known as cosmic rays, can show up with energies a million times higher than the biggest particle accelerators on Earth can produce.
Astrophysicists believed that only two sources could make them: supermassive black holes in active galaxies, or so-called gamma ray bursts.
A study in Nature has now all but ruled out gamma ray bursts as the cause.
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Blobrana · L

Title: Origin of Cosmic Rays
Authors: Luke O'C. Drury

It is argued that there are three 'origins' of cosmic rays; the origin of the particles, the origin of the energy, and the site of the acceleration. The evidence for each origin is discussed and a plausible synthesis outlined for the particles of Galactic origin where the energy comes mainly (but not exclusively) from supernova explosions, the site of the acceleration is at strong collisionless shock waves, and the accelerated particles come from the interstellar and circumstellar material swept over by these shocks. If these shocks are capable (as indicated by recent observations and theoretical work) of significantly amplifying magnetic fields this picture appears capable of explaining the cosmic ray particles at all energies below the 'ankle' at 3 x 10^{18} eV. The particles above this energy are generally taken to be of extra-galactic origin and possible acceleration sites for these UHE particles are briefly discussed.

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Blobrana · L

The confirmed origin of ordinary cosmic rays may need to be unconfirmed.
New data gathered by an instrument onboard a Russian spacecraft challenge the theory that most cosmic rays are fuelled by supernovas, the explosions created by dying stars.
Magnetic fields in a supernova should accelerate both hydrogen and helium particles in the same way: Graph the mathematical equations describing this push, and the curve for each particle should have the same slope. But in the PAMELA data, Piergiorgio Picozza found a difference in these slopes that a single shock wave can't explain.
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Scientists Prove Cosmic Rays Are Made of Protons

Cosmic rays are made of protons, scientists found as they used a vast array of telescopes arranged across the Utah desert. Each telescope in the 67-unit arrangement sees the sky with a multifaceted eye. It's no wonder they call it Fly's Eye.
Scientists at the High Resolution Fly's Eye detector, nicknamed HiRes, in the Army's Dugway Proving Grounds in Utah, determined that the positively-charged components found in the centre of each atom are what make up cosmic rays. Previously they had not been sure that the high-energy rays hadn't been something heavier, such as the nucleus of an iron atom.
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