Cherenkov Radiation from e e pairs

1
Cherenkov Radiation from ee- pairs
Spencer Klein, LBNL with Sourav Mandal, LBNL/UCB

• Cherenkov radiation occurs when the
  electromagnetic fields of a fast particle excites
  a medium ( through dE/dx)
• ee- pairs form dipoles, with fields are smaller
  than for 2 independent particles
• The fields largely cancel at distance d gtgt D (D
  is the pair separation)
• Radiation from the e/e- from g --gtee- may be
  less than from independent particles
• This could affect IceCube observations of ne
  showers

2
Radiation from a Pair
lt 1

• Radiation is suppressed when

J. D. Jackson, private communication, 2004
3
Simulating Pairs

• Pair opening angle 1/g
• Gaussian multiple scattering
• Stochastic bremsstrahlung energy loss
• 1st approximation
• Track particles over 2 X0 or until they drop
  below Cerenkov threshold

Combined tracks of all particles, g energies
from 108 to 1015 eV
4
Radiation from Pairs
Rise above 1 is real
Suppression sindep/spair

• k 108 1015 eV
• Radiation suppressed for kgt 1012 eV
• Total radiation unaffected
• Less radiation from front part of showers
• Change observed location?

5
Conclusions

• Cherenkov radiation from ee- pairs is less than
  for independent particles
• May affect observation of the early development
  of water showers.
• For air, e is close to 1, and the effect is
  small, except at very high pair energies.