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Abstract:

We report the first observation of diffractively produced W bosons.In a sample of W → eν events produced in pp collisions at √s=1.8TeV, we find an excess of events with a forward rapidity gap, which is attributed to diffraction.The probability that this excess is consistent with nondiffractive production is 1.1×10−4 (3.8σ).The relatively low fraction of W+ jet events observed within this excess implies that mainly quarks from the Pomeron, which mediates diffraction, participate in W production.The diffractive to nondiffractive W production ratio is found to be RW=(1.15±0.55)%.© 1997 The American Physical Society.

Abstract:

Using the ZEUS detector at HERA, we have studied the reaction e+p → e+X for Q2 > 5000 GeV2 with a 20.1 pb-1 data sample collected during the years 1994 to 1996. For Q2 below 15000 GeV2, the data are in good agreement with Standard Model expectations. For Q2 > 35000 GeV2, two events are observed while 0.145 ± 0.013 events are expected. A statistical analysis of a large ensemble of simulated Standard Model experiments indicates that with probability 6.0%, an excess at least as unlikely as that observed would occur above some Q2 cut. For x > 0.55 and y > 0.25, four events are observed where 0.91 ± 0.08 events are expected. A statistical analysis of the two-dimensional distribution of the events in x and y yields a probability of 0.72% for the region x > 0.55 and y > 0.25 and a probability of 7.8% for the entire Q2 > 5000 GeV2 data sample. The observed excess above Standard Model expectations is particularly interesting because it occurs in a previously unexplored kinematic region. © Springer-Verlag 1997.