31 research outputs found
Measurement of the decay η′ →π0π0η at MAMI
An experimental study of the η′→π0π0η→6γ decay has been conducted with the best up-to-date statistical accuracy, by measuring η′ mesons produced in the γp→η′p reaction with the A2 tagged-photon facility at the Mainz Microtron, MAMI. The results obtained for the standard parametrization of the η′→π0π0η matrix element are consistent with the most recent results for η′→ππη decays, but have smaller uncertainties. The available statistics and experimental resolution allowed, for the first time, an observation of a structure below the π+π- mass threshold, the magnitude and sign of which, checked within the framework of the nonrelativistic effective-field theory, demonstrated good agreement with the cusp that was predicted based on the ππ scattering length combination, a0-a2, extracted from K→3π decays
The Nature of the Cold Filaments in the California Current System
Data from the Coastal Transition Zone (CTZ) experiment axe used to describe the velocity
fields and water properties associated with cold filaments in the California Current. Combined
with previous field surveys and satellite imagery, these show seasonal variability with maximum
dynamic height ranges and velocities in summer and minimum values in late winter and early
spring. North of Point Arena (between 39 degrees N and 42 degrees N) in spring-summer the flow field on the
outer edge of the cold water has the character of a meandering jet, carrying fresh, nutrient-poor
water from farther north on its offshore side and cold, salty, nutrient-rich water on its inshore
side. At Point Arena in midsummer, the jet often flows offshore and continues south without
meandering back onshore as strongly as it does farther north. The flow field south of Point Arena
in summer takes on more of the character a field of mesoscale eddies, although the meandering
jet from the north continues to be identifiable. The conceptual model for the May-July period
between 36 degrees N and 42 degrees N is thus of a surface jet that meanders through and interacts with a field
of eddies; the eddies are more dominant south of 39 degrees N, where the jet broadens and where multiple
jets and filaments are often present. At the surface, the jet often separates biological communities
and may appear as a barrier to cross-jet transport, especially north of Point Arena early in the
season (March-May). However, phytoplankton pigment and nutrients are carried on the inshore
flank of the jet, and pigment maxima are sometimes found in the core of the jet. The biological
effect of the jet is to define a convoluted, 100 to 400-km-wide region next to the coast, within
which much of the richer water is contained, and also to carry some of that richer water offshore
in meanders along the outer edge of that region.The CTZ program was funded by the Coastal Sciences Program of the Office of Naval Research (Code 1122CS). Support for PTS was provided by ONR grants N00014-87K0009 and N00014-90J1115, with additional support provided by NASA grants NAGW-869 and NAGW-1251