Seminare de DPNC
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Mercredi, 16. avril 1997

17.00 - Auditoire Stuckelberg

Universite de Geneve
Departement de physique
nucleaire et corpusculaire
24, quai Ernest-Ansermet
1211 Geneva 4

Tel. 022 702 6273
Fax. 022 781 2192

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Sujet:		Observation of Events at Very High Q^2 in ep-collisions
          	at HERA

Par:		Dr. Christoph Grab, ETH Zurich

Resume:

  In measurements of electron-proton scattering at HERA,
the two experiments studied events in the unexplored
highest region of squared 4-momentum transfer Q^2 up
to 35000 GeV^2.
  The measurements are compared with the expectation of
the standard deep-inelastic model of lepton-nucleon
scattering (DIS). For very high Q^2 > 15000 GeV^2, the
number of both neutral current and charged current candidate
events observed exceeds the expectations by the theoretical
predictions. This observed difference is mostly due to events
at large masses M = sqrt{xs} in which the positron is
backscattered at large y = Q^2/M^2.