Search for new phenomena using single photon events at LEP1
Zeitschrift fur Physik C-Particles and Fields 74:4 (1997) 577-586
Abstract:
Data are presented on the reaction e+e- → γ + no other detected particle at centre-of-mass energies of 89.48, 91.26 and 93.08 GeV. The cross-section for this reaction is related directly to the number of light neutrino generations which couple to the Z0 boson, and to several other possible phenomena such as the production of excited neutrinos, the production of any invisible 'X' particle, and the magnetic moment of the tau neutrino. Based on the observed number of single photon events, the number of light neutrinos that couple to the Z0 is measured to be Nν = 2.89 ± 0.38. No evidence is found for anomalous production of energetic single photons, and upper limits at 95% confidence level are determined for excited neutrino production (BR < 4 - 8 × 10-6 depending on its mass), production of an invisible 'X' particle (σ < 0.1 pb for masses below 60 GeV), and the magnetic moment of the tau neutrino (< 5.1 × 10-6μB). © Springer-Verlag 1997.The ZEUS leading proton spectrometer and its use in the measurement of elastic ρ0 photoproduction at HERA
Zeitschrift fur Physik C-Particles and Fields 73:2 (1997) 253-268
Abstract:
The differential cross section dσ/dt for elastic ρ0 photoproduction, γp → ρ0ρ (ρ0 → π+π-), has been measured in ep interactions at HERA. The squared four-momentum exchanged at the proton vertex, t, has been determined directly by measuring the momentum of the scattered proton using the ZEUS Leading Proton Spectrometer (LPS), a large scale system of silicon micro-strip detectors operating close to the HERA proton beam. The LPS allows the measurement of the momentum of high energy protons scattered at small angles with accuracies of 0.4% for the longitudinal momentum and 5 MeV for the transverse momentum. Photoproduction of ρ0 mesons has been investigated in the interval 0.073 < |t| < 0.40 GeV2, for photon virtualities Q2 < 1 GeV2 and photon-proton centre-of-mass energies W between 50 and 100 GeV. In the measured range, the t distribution exhibits an exponential shape with a slope parameter b = 9.8 ± 0.8 (stat.) ± 1.1 (syst.) GeV-2. The use of the LPS eliminates the contamination from events with diffractive dissociation of the proton into low mass states. © Springler-Verlag 1997.Comparison of ZEUS data with standard model predictions for e(+)p->e(+)X scattering at high x and Q(2)
ZEITSCHRIFT FUR PHYSIK C-PARTICLES AND FIELDS 74:2 (1997) 207-220
D* production in deep inelastic scattering at HERA
PHYSICS LETTERS B 407:3-4 (1997) 402-418
Differential cross sections of D*(+/-) photoproduction in ep collisions at HERA
PHYSICS LETTERS B 401:1-2 (1997) 192-206