Particle Accelerators and Detectors

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Update 2022

Cosmic Rays

		However, this kind of source seems to be unlikely since UHECRs are isotropic, and not affected by magnetic fields. The yellow line in Figure 01b is the observed cosmic ray energy spectrum. The three other lines show how suspected sources possibly contribute to the overall signature of cosmic rays. It is not known what causes the kinks at the "knee" and "ankle". Normally, cosmic rays bombard the Earth at a rate of about 1 particle/km2-sec. At ultra-high energies, above 1019 ev, the rate falls to less than 1 particle/km2-year.
Figure 01a Cosmic Rays, Origins of [view large image]	Figure 01b C-Rays Spectrum

Detection of cosmic rays:


• Low energy cosmic rays don't have enough energy to penetrate the earth's atmospher all the way to the surface. They have to be detected by instruments on satellite (Figure 02a).

Although secondary high-energy cosmic rays still don't have enough energy to reach the surface, they can generate Cerenkov radiation detectable by Cerenkov detector on the ground (Figure 02a). Cerenkov radiation is the bluish light produced by charged particles moving through a transparent medium at a speed greater than the speed of light in the medium. This is the optical equivalent of a sonic boom. The greater than light speed is possible because the speed of light is c/n in the medium, where n is the index of refraction, and is always greater than one. Therefore, the speed of light in the medium is lower than that in the vacuum and could be conceivably lower than that for the high-energy cosmic rays.

Figure 02a Cosmic Rays Detectors [view large image]

The secondary ultra-high energy cosmic rays can be detected on the ground by either the surface detectors, or the fluorescence detectors (Figure 02a). In the surface detector, the secondary particles produce faint

flashes in the purified water. The fluorescence detector measures the glow emitted by nitrogen atoms after colliding with the secondary particles. The picture on the lower right shows both kinds of detectors installed at the Auger Observatory, which will try to shed light on the mysterious UHECRs.

New results from the Pierre Auger Observatory in 2007 indicate that UHECRs have sky directions statistically consistent with the positions of nearby active galactic nuclei (AGN). These galactic centers are known to emit great amounts of light and are likely powered by large black holes. It also concludes that the UHECRs are protons. Figure 02b is an artist's view of a cosmic ray striking the Earth's atmosphere and creating a shower of secondary particles detectable on the surface. The small inserts are the images of the AGN Centaurus A and the detectors of the Pierre Auger Observatory.

Figure 02b UHECR [view large image]

A report in November 2008 reveals that there is an excess of cosmic ray electrons at energies of 300 - 800 Gev. The finding is consistent with other measurements as indicated in Figure 02c, where the new measurement is in red filled circles. It is compared with previous observations in various symbols. The solid curve is calculated with a power-law spectral index of E-3.2 (the new measurement is scaled with an index of -3.0). The dashed curve is the solar modulated electron spectrum. The source of the bump can be ascribed either from nearby astrophysical objects (such as pulsar or micro-quasar) or from the annihilation of dark matter particles (such as a KK particle with a mass of about 620 Gev).

Figure 02c High Energy Electrons [view large image]

Another possibility is via the annihilation of the supersymmetric neutralinos, which is its own anti-particle (Figure 02d) although it doesn't quite fit the observational data.

		Figure 02e shows experiments over the years trying to obtain evidence for dark matter. It reveals a disparate results not fitting to any particular candidate. A theory introducing a new force between the WIMPs has been proposed to resolve the contradiction between theory and observation. It invokes a heavy force carrying boson that weighs about the same as a proton. It claims to reconcile the many facets of the observations:
Figure 02d Neutralino [view large image]	Figure 02e Dark Matter Experiments

1. The new dark force boosts the annihilation rate of slow-moving WIMPs giving a surplus of electrons and positrons. Yet it has no effect on much faster particles that filled the early universe leaving plenty of WIMPs around today.
2. The absence of surplus anti-protons is explained by the heavy mass of the mediating boson, which can decay into electrons and positrons only.
3. The 511 Kev photons observed by INTEGRAL can be identified to the annihilation of the electron-positron pair.
4. The scenario favours the DAMA detectors, which use material with heavier nuclei (e.g., iodine). While much lighter germanium and silicon is inside CDMS, which detects no signal of any WIMP.

Two 2013 reports suggest strongly that the UHECRs were originated from the shock wave associated with supernova explosion. Gamma-ray data on 2 supernova remnants, called IC443 and W44, from NASA's Fermi space telescope found abundance of gamma-ray photons in the range of energies expected from pion decay. The pion is produced by collision of high energy proton with matter. In the other study, the spectrum from supernova remnant 1006 reveals the presence of high energy protons in the shock wave front.

Figure 02f Supernova Shockwave

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