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SUMMARY:The Properties of Ultra-High Energy Cosmic Rays and the problems t
 hat these pose - Prof. Alan Watson (Leeds)
DTSTART:20101102T150000Z
DTEND:20101102T160000Z
UID:TALK26094@talks.cam.ac.uk
CONTACT:John Marshall
DESCRIPTION:An introductory overview of the reasons for interest in the hi
 ghest energy cosmic rays\, including the challenge of their acceleration\,
  will be given.  Measurements of the energy spectrum\, arrival direction d
 istribution and mass composition of cosmic rays above 1018 eV\, made recen
 tly at the Pierre Auger Observatory\, will be discussed in some detail.  T
 he flux of cosmic rays is found to be strongly suppressed above 4 x 1019 e
 V and above a similar energy the distribution of the arrival directions of
  the particles indicates an anisotropy of about 40%.  These two conclusion
 s are nearly independent of assumptions about particle physics parameters.
   However\, while the anisotropy is indicative of a substantial fraction o
 f protons in the primary cosmic ray beam\, measurements of the mass compos
 ition suggest that the fraction of heavier nuclei grows as the energy incr
 eases.  This interpretation\, however\, depends on extrapolations of cross
 -sections\, multiplicity and inelasticity to centre-of-mass energies well-
 beyond what will be reached at the LHC.   It is not clear how these confli
 cting results can be reconciled: some suggestions will be offered.
LOCATION:Rutherford Seminar Room B
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