SunShots

The idea remains the same, but I was not correct in the sense of “gamma ray detection,” but did advance the view to include “neutrinos in observation,” in regards to our view of the universe. Our Sun.

Hopefully, I am not making it confusing for some.

The coolest thing about this device is the extraordinarily wide field of view. The burst monitor can detect bursts basically in any direction that’s not hidden by the Earth, so a little over half the sky. The primary instrument will have maximal sensitivity for “only” around 1/5th of the sky at any given time. It will still detect gamma rays from other directions, but it won’t be nearly as good at pinning down their energies.

Calorimeters measure the collective behavior of particles traveling along approximately the same path, and are thus naturally suited for the measurement of jets-Dorigo Tommaso

I had been following Glast history as well, and the relationship I thought the “PI institute” held in regards to a “time value measurement position” in regards to Phenomenological order to progressing science. This may be a mistaken notion on my part. I thought Lee Smolin was leading in this area and thought the Glast experiment important to his position.

Longitudinal and Transverse Information about the Energy Deposition Pattern

The calorimeter design for GLAST produces flashes of light that are used to determine how much energy is in each gamma-ray. A calorimeter (“calorie-meter”) is a device that measures the energy (heat: calor) of a particle when it is totally absorbed. CsI(Tl) bars, arranged in a segmented manner, give both longitudinal and transverse information about the energy deposition pattern. Once a gamma ray penetrates through the anticoincidence shield, the silicon-strip tracker and lead converter planes, it then passes into the cesium-iodide calorimeters. This causes a scintillation reaction in the cesium-iodide, and the resultant light flash is photoelectrically converted to a voltage. This voltage is then digitized, recorded and relayed to earth by the spacecraft’s onboard computer and telemetry antenna. Cesium-iodide blocks are arranged in two perpendicular directions, to provide additional positional information about the shower.

I have been interested in “calorimetric designs” when I first heard of it in the Glast design.

Understanding this use in the LHC and hearing of the “onion skin metaphor” was a strange thought, but seems indeed to explain this ability to measure?

Calorimeters for High Energy Physics experiments – part 1
Calorimeters for High-Energy Physics – part 2 April 11, 2008

Tammaso Dorigo gave a nice blog posting in that regard that might give greater clarity to the values of these measures, as well, helps one view the “window of the universe” in a new ways. A point here was the the gamma ray view of the sun some time ago by JoAnne in this Blog.

While we have ground based measures this allows us to look back at space, and see it in this different light. It all started with the “Fly’s eye?”:) Pierre Auger history, and John Bachall lead in these directions.

There are hand-waving arguments that LQG should lead to violations of Lorentz invariance that will be testable by GLAST,

I think this may be one place where LQG goes astray. There are some LQG ideas about the speed of light being variable near the Planck length. Yet, the speed of light is just a way of telling us how much space equals how much time. It is a proportion, and variable c amount to loopiness where time depends on space, but where that dependency depends further on space and … . Yuck. The breaking of Lorentz invariance also goes against the grain of symmetry “recovery” at higher energy.

Lawrence B. Crowell

But won’t they be traveling faster in high density areas due to gravity, and thus covering more area/unit time?

miller – Yes, in supersymmetric models neutralinos are their own antiparticles, so if you’ve got a bunch of them in the same place you’re bound to get some annihilations. The mass of the WIMP places a limit on the energy of the annihilation products. The total energy in a system of two annihilating WIMPs is basically just twice the rest mass energy of the particle (kinetic energies are generally negligible in these cases), so the highest energy photon you could get out would be one with an energy equal to the mass of the WIMP. So by looking at the frequency spectrum you would be able to determine the WIMP mass by seeing at what frequency the spectrum cuts off (and the locations of any spectral lines).

And for what it’s worth, I was being silly in my last post. The rarity of annihilations directly to two photons is nothing to do with whether the particles are bosons or fermions, it’s just because they don’t couple to the EM field.

The nicest signal for WIMP detection (the “smoking gun”, as they say), would be a spectral line at the WIMP mass from annihilation of two WIMPs directly into 2 gammas, or a gamma and a Z boson. In the case of supersymmetric dark matter, where the WIMP is (usually) a Majorana fermion (usually the lightest neutralino), annihilation directly into two photons, or a photon and a Z, would be very rare, so the lines would be very faint. I’m not sure to what extent the same is true of, for example, Kaluza-Klein dark matter, where the DM candidate is usually a boson. In any case, the basic signature, aside from the lines, would be a continuous spectrum with a shape that doesn’t look like what you usually expect from astrophysical sources (power laws and similar, for the most part) with a sharp cutoff at the WIMP mass. It would be especially nice if we found a whole bunch of sources with spectra like that, that all looked the same. That would be a pretty clear indicator that they were being produced by the same process, and if the spectrum looked right you could probably make a strong argument for it being dark matter.

Joe, it’s just because you need two particles to bump into each other. So you have a number of particles to consider, times a number of particles for them to bump into, both of which are proportional to density, so it goes as density squared.

Coincidentally, Tim Sumner of the ZEPLIN III DM experiment gave a talk on their project at Trinity College Dublin on Monday night (I have a summary on my blog).
I meant to ask his opinion on the prospect of success of DM detection by gamma ray observation but unfortunately I forgot.. Cormac