Cherenkov Radiation & Neutrino Detection Nuruzzaman Mississippi State University

Overview Cherenkov Radiation and its properties Mathematical Background Applications Neutrino detection & AMANDA project

Cherenkov Radiation If particle's speed is higher than speed of light in the medium, e.m. radiation is emitted --“Cherenkov light” or Cherenkov radiation, which can be detected; amount of light and angle of emission depend on particle velocity; Electromagnetic radiation emitted when a charged particle (such as a proton) passes through an insulator at a speed greater than the speed of light in that medium

Cherenkov Radiation Moving charge in dielectric medium In the figure, v is the velocity of the particle (red arrow), β; is v/c, n is the refractive index of the medium. The blue arrows are photons. Moving charge in dielectric medium Wave front comes out at certain angle slow fast cosθc = 1/βn

Cherenkov Radiation Emission by a single particle n - 1 is proportional to air density. The Cherenkov opening angle θ is increasing downwards. For a particle moving vertically downwards, the largest ring on the ground near sea level is from 12 to 15 km height.

Cherenkov Radiation The geometry of the Cherenkov wave front is defined by the particle velocity vp= βc and the speed of light in the medium vl=c/n: cos θ = c/nvp For a particle slower than light (vl = c/n), there is no positive interference of any potential radiation by the polarized medium: When the particle is faster than c/n, we have a positive interference: Charged particle polarizing a dielectric medium with index of refraction n :

Cherenkov Radiation While relativity holds that the speed of light in a vacuum is a universal constant (c), the speed of light in a material may be significantly less than c. For example, the speed of light in water is only 0.75c. Matter can be accelerated beyond this speed during nuclear reactions and in particle accelerators. Cherenkov radiation results when a charged particle, most commonly an electron, exceeds the speed of light in a dielectric (electrically insulating) medium through which it passes Moreover, the velocity of light that must be exceeded is the phase velocity rather than the group velocity. The phase velocity can be altered dramatically by employing a periodic medium, and in that case one can even achieve Cherenkov radiation with no minimum particle velocity — a phenomenon known as the Smith-Purcell effect. In a more complex periodic medium, such as a photonic crystal, one can also obtain a variety of other anomalous Cherenkov effects, such as radiation in a backwards direction (whereas ordinary Cherenkov radiation forms an acute angle with the particle velocity).

Cherenkov Radiation As a charged particle travels, it disrupts the local electromagnetic field (EM) in its medium. Electrons in the atoms of the medium will be displaced and polarized by the passing EM field of a charged particle. Photons are emitted as an insulator's electrons restore themselves to equilibrium after the disruption has passed. (In a conductor, the EM disruption can be restored without emitting a photon.) In normal circumstances, these photons destructively interfere with each other and no radiation is detected. However, when the disruption travels faster than the photons themselves travel, the photons constructively interfere and intensify the observed radiation. A common analogy is the sonic boom of a supersonic aircraft or bullet. The sound waves generated by the supersonic body do not move fast enough to get out of the way of the body itself. Hence, the waves "stack up" and form a shock front. Similarly, a speed boat generates a large bow shock because it travels faster than waves can move on the surface of the water. In the same way, a superluminal charged particle generates a photonic shockwave as it travels through an insulator.

Neutrinos generate muons (μ) in the water which produce flashes of Cherenkov Radiation Flashes are picked up by the light detectors

80 Strings Volume: 1 km3 (1 Gt) Slide shows the concept. Our primary responsibility is for the surface air shower array, which we are calling IceTop. It will be big enough to act as a veto shield for IceCube as well as doing cosmic-ray physics with the coincident events. Because of the much larger size, we will be able to go to much higher energy than with SPASE-AMANDA. 80 Strings Volume: 1 km3 (1 Gt) IceCube is designed to detect neutrinos of all flavors at energies from 107 eV (SN) to 1020 eV

References http://en.wikipedia.org/wiki/Cherenkov_radiation http://www.youtube.com/watch?v=Gt4Y7i-h-h4&feature=related http://www.physics.upenn.edu/balloon/cerenkov_radiation.html I’m not here to talk about Space-TD Pike YB n NginR