Can anybody tell anything me about the highest frequency photons ever observed? I'm struggling to find anything conclusive on the internet, and I've got a bit of a puzzle with photons where the wavelength is approaching 10ֿ¹³ metres.
First things first, are you talking about high frequency (short wavelength), or long wavelength (low frequency)? Assuming you meant high frequency/short wavelength, and that you simply omitted the minus sign in the exponent (i.e., you meant 10[sup]-13[/sup] meters), google "TeV gamma ray".
Sorry, I didn't omit the minus sign in the exponent. It just comes out rather small on this forum. The longer symbol ¯ is a little better. I have looked using tera (and peta) and found things like this: http://www.ast.leeds.ac.uk/research/tev.html "Very High Energy gamma-rays do not occur naturally on Earth. They are associated with the acceleration and interaction of relativistic particles at energies beyond those achievable in man-made accelerators... When a VHE gamma-ray enters the Earth's atmosphere, it generates a shower of secondary charged particles which in turn cause a flash of blue Cherenkov light...
OK. Now that we have that settled, what are you looking for? 10[sup]-13[/sup] meters is not anywhere close to the upper limit of what we can detect. That is only in the 10 MeV range. We can observe gammas with much higher energy.
Hum, i think that photons with ~3.5 trillion electron-volts were recorded by the Milagro Gamma Ray Observatory quite recently. See also http://cat.inist.fr/?aModele=afficheN&cpsidt=4371214
Can you point me towards some actual observations? I'm struggling to find any. I search on VHE gamma and it's all astronomical, it's always secondary particles, and there's things like this to muddy the waters: http://www.ulo.ucl.ac.uk/~diploma/modules/year_one/www.dur.ac.uk/%7Edph0www4/whyare.htm "Although it is relatively easy to detect the flash of Cherenkov radiation, it is not easy to identify gamma rays. The first reason is that there are not very many of them. Also the cosmic rays mentioned above cause a problem; they produce extensive air showers and Cherenkov radiation in the same way as the gamma rays. In fact they produce about 99% of it! This means that only 1% of the Cherenkov light flashes are due to the gamma rays".
First of all, what is wrong with "secondary particles"? What we measure and how we measure it are not necessarily one and the same. Second, even the LHC will not produce gammas with anywhere close to the energies observed by particles coming from outer space. It should be no surprise that most of the work is astronomical. Thirdly, speaking about astronomical observatories, GLAST is scheduled for launch tomorrow. While its detectors won't be quite in the TeV range, but 300 GeV isn't bad.
What's wrong is that I'm scratching my head here thinking there's something unusual about very high energy photons. Either they don't exist, or they don't exist for long, or they ought to exhibit some characteristics that distinguish them from ordinary photons. But I'm not sure, hence I'm asking for information.
Farsight, since this is an Alpha thread (your own fault), you will be hijacking your own thread and violating the Alpha rules if you bring up some Farsighted conjecture on the non-existence of high energy photons. We have observed them; they exist. This thread is about the highest frequency gammas to have been observed and how we can observe them.
They don't exist for long. For instance, at LEP where they would collide electron and positron at the (cosmologically) paltry energies of 100GeV the electron+positron can do into two possible particles, the photon or the Z. As energy increases, it goes more and more into the Z, in a way inline with the standard model and much to your dislike, the Higgs mechanism of spontaneous symmetry breaking. These then turn almost instantly into other particles because it's energetically preferable. They have sufficent energy to produce copius quantities of hadrons and leptons, so they do. Infact, they do it so readily we don't even see the photon or Z track in the detector. Because they are, at those energies, so 'unstable'. Other particles like the proton can hold onto it's energy a bit better but at cosmological energies, even if sheds pions are an alarming rate due to the GZK process and it's respective cut off. All evidence shows that the behaviour for high energy photons is what you'd expect for high energy photons. The decay modes and cross sections of the standard model, which are functions of energy, are found to be valid to a very high accuracy and they take into account all the 'dirty' mixing of the EM, the weak and the strong force processes. It's the business of physicists to work this out. Entire PhDs and even research lives are spent calculating ALL the contributions to these processes to 2 or 3 loop and then doing out and seeing what nature says. If your ideas don't match the Standard Model (and thus spontaneous symmertry breaking due to a Higgs processes) to something like 99.99% then your model is wrong. But you have no working model so it's a failure in that respect. You rest heavily on electron/positron pair production but you ignore it's just one of the methods of photon interactions. EVERY charged particle and it's antiparticle contributes to photon and Z process, especially at high energy, and physicists account for this. You don't. You don't derive pair production from base postulates like QFT does. You don't derive anything from postulates.
Thank you for the information, Alphanumeric. Can I remind all constributors that this is an Alpha thread. Please can we stay focussed on the subject at hand. DH, you say we have observed them and they exist. But I'm still struggling to find evidence. For example, I'd be interested in seeing a detector image which shows an event then a gap followed by a spray, indicating that a very high energy photon had traversed the gap. This old bubble chamber picture is pair production and annihilation is an example of what I mean. The dotted purple line is the path of the photon. In itself it is not observable, but something crossed that gap, and we're satisfied that it's a photon. Please Register or Log in to view the hidden image! (http://teachers.web.cern.ch/teachers/archiv/HST2002/Bubblech/mbitu/electron-positron.htm)
I'm suprised you didn't already know it, what with your claims of knowing so much about mainstream physics. Was there something you didn't understand about the post I just made which gave you an explaination of how we can tell it's a photon but also the reason why it's not seen as a track gap?
No. Photons travel at c, no track gap means that photon was a photon for zero seconds. Now, can you point me towards something like a detector image which shows an event then a gap followed by a spray, indicating that a very high energy photon had traversed the gap? I've spent an hour searching and can't find what I'm looking for.
No, no track gap means the photon was a photon for such a short period of time it's indetectable to the detector. If you'd bothered to look up particle detection methods and results you'd know it's a common thing for high energy colliders. Supermassive/energetic particles don't have time to propogate enough to be noticable in the collider. We have to work out what they where from their decay products. For instance, we know an electron+positron collision cannot directly turn into a tau and an antitau. It must go through a photon or a Z first, due to the interactions of the Standard Model. Therefore, if we see an electron+positron 'instantly' turn into a tau+antitau, then we know the photon or Z produced by the electron+positron was so short lived it didn't propogate. Life time for some particles is less than \(10^{-24}\) seconds. Even at the speed of light, they would propogate about \(3 \times 10^{-15}m\). That's about the width of a nucleus, utterly beyond our ability to detect for typical for weak bosons (otherwise the weak force would be 'long distance' and effect things outside the nucleus). This should have come up in the 'research' you've been doing. If you haven't come across such information then you aren't looking properly, since it's fairly basic knowledge for anyone who understands the Standard Model on even a conceptual level. It would seem you don't.
The GZK limit is 6*10[sup]19[/sup] eV, or 60 million TeV. The photons Farsight talked about in the OP were far less than that: A wavelength of 10[sup]-13[/sup] meters, or roughly 10 MeV in terms of energy. BTW, GLAST launched Wednesday, June 11, 2008. It will for gammas up to 200 GeV (which is 10+ orders of magnitude less energetic than the GZK limit).
Thanks for the information everybody. I'm still puzzling over photons with a wavelength of less than 10¯¹³ metres. As DH says, the energy of ~10MeV is far less than the energy of cosmological gamma rays which have travelled light years, but then Alphanumeric talks about a high-energy photon having a very short lifetime and decaying almost immediately. Alphanumeric, did you actually mean decay? Did you mean to say the high-energy photon has a short lifetime and decays promptly of its own accord, or did it interact with some other particle that is present in the collider but not in interstellar space? If anybody can point me towards some experiment that demonstrates photons propagating with a wavelength of less than 10¯¹³ metres I'd be grateful. I was looking at a scanner website over the weekend which was talking about a 20MeV beam, so the energy is not particularly special, but I still can't find anything that talks about photons with very short wavelengths.
