The day before yesterday, radio and newspapers - but perhaps I did not hear the TV - a miracle: it seemed at last been found out what is on the famous dark (DM). Having heard the sensational news and odd, are now ongoing to inform me. In fact the front page of the site was Corriere.it the little article where explained that the experiment PAMELA " could have picked up his first concrete evidence" of DM. Even better. But I wanted to know more, so yesterday I went on the website of Nature and I downloaded the article (using services provided by the University Padua - I just discovered, putting the link, the article is available from PAMELA's official website, I put the direct link to PDF: here).
The title already gives me comfort in that it is not like "The discover of the dark matter, but a more enigmatic " An Anomalous positron abundance in cosmic rays with energies 1.5-100 GeV .
For those who are lazy and do not want to read the article, I tell you in simple terms what happened. In 2006 they launched a satellite from the provocatively named Pamela, who had the task of measuring the flows of electrons and positrons, and calculate the ratio flusso_positr. / (+ Flusso_positr. flusso_elettr.). Clearly this ratio is less than 1, since there is much more matter of antimatter. But why antimatter calculate how much is it? And most importantly, what to do with the DM? Now, astrophysicists say (I'm still a student and then have nothing to do, eheheheh) that positrons are emitted in two ways: a) by the interaction of cosmic rays with the interstellar medium and b) emissions from pulsars, microquasars but also dall'annichilazione DM. In the first case we speak of secondary sources, in the second of the primary sources.
During the past years has always believed that these emissions came almost entirely from secondary sources, since - they say - there are a few pulsars and quasars, especially within the positrons which come down to us. It is always left out the hypothesis of DM annihilation, as the energies explored were low plus, with the tools of 90s, it seemed that the relationship between streams of positrons and electrons with diminished energy.
Now this PAMELA plans a bit shocked 'at all, because the increased sensitivity in high-energy range (1.5 to 100 GeV), has allowed to study in detail this relationship: it increases by a order of magnitude, so no peanuts. This is therefore think that high-energy positrons are starting to be many and so it is not explained by secondary processes. Or, if you want to keep that eighth, one must assume that there is some acceleration in cosmic rays, can provide the energies observed. Or, something not so easy to prove, the increase in the abundance of positrons is due to a primary component.
As I said before, since there are few pulsars and quasars even fewer whose electrons and positrons come this far with such energies. It must therefore assume that the anomaly is due to decay or annihilation of DM particles, the famous WIMP, of which I know little except that the best candidates are neutralinos (for models that make use of supersymmetry) and Kaluza-Klein particles (for models that make use of extra dimensions).
But why do you think I wrote all this stuff? Essentially to spend some 'time while I'm installing the updates on the Vista PC. Well, it will be a coincidence, but has just finished.
Regards.
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