M. Eckhause

The time-of-flight system for CLAS

The time-of-flight system for the CEBAF Large Acceptance Spectrometer (CLAS) at the Thomas Jefferson National Accelerator Facility is described. The system, covering an area of 206-square-meters, is composed of scintillation counters 5.08 cm thick, 15 and 22 cm wide, and lengths which vary from 32 cm at the most forward angle to 450 cm at larger angles. All of the components of the system have been designed to optimize the time resolution. Event timing, achieved by leading-edge discrimination with time-walk correction, has been measured with cosmic rays, a laser pulser, and known particle interactions. The intrinsic time resolution varies from about 80 ps for the short counters to 160 ps for the longer counters. Reconstruction of interacting particles during the first period of operation yields an average time resolution for electrons of 163 ps.

Negative muon capture in carbon leading to specific final states

Abstract The yields of γ rays from specific final nuclear states excited following negative muon capture in 12 C have been measured. Using the values for the capture rates to excited states in 12 B and the result of an earlier experiment for the total capture to all bound states in 12 B, we obtain for the durect capture rate to the ground state of 12 B, λ( 12 B gs ) = (6.0 ± 0.4) × 10 3 s −1 . This value is in agreement with theoretical predictions, but the theoretical and experimental uncertainties permit extraction of only a rather imprecise value for the weak-magnetism coupling constant in the muon capture Hamiltonian.

New limit on muon and electron lepton number violation from K0(L) ---> mu+- e-+ decay

The most sensitive experiment to date to search for the muon and electron lepton number violating decay

Search for the weak decay of an H dibaryon.

K^0_L \to \mu^\pm e^\mp

Determinations of nuclear level halflives in 85Rb and 237Np and their use as timing standards

has detected no events consistent with this process. Based on this result, the 90% confidence level upper limit on the branching fraction is

Muon capture rates on 16O leading to bound states of 16N

B(K^0_L \to \mu^\pm e^\mp) < 4.7\times10^{-12}

First observation of the rare decay mode K0(L) ---> e+ e-

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Precision measurement of the wavelengths and natural line widths of 3d-2p pionic X-ray transitions in low-Z atoms

We have searched for a neutral {ital H} dibaryon decaying via {ital H}{r_arrow}{Lambda}{ital n} and {ital H}{r_arrow}{Sigma}{sup 0}{ital n}. Our search has yielded two candidate events from which we set an upper limit on the {ital H} production cross section. Normalizing to the inclusive {Lambda} production cross section, we find ({ital d}{sigma}{sub {ital H}}/{ital d}{Omega})/({ital d}{sigma}{sub {Lambda}}/{ital d}{Omega}){lt}6.3{times}10{sup {minus}6} at 90{percent} C.L., for an {ital H} of mass {approx_equal}2.15 GeV/{ital c}{sup 2}. {copyright} {ital 1996 The American Physical Society.}

Precision Measurements of the

Abstract The application of nuclear lifetimes in the nonosecond range to the calibration of nuclear timing systems is discussed. More precise measurements of the lifetimes of the 517 keV level in 85 Rb and the 60 keV level in 237 Np are presented.

K^-

Abstract The partial muon capture rates on 16 O leading to all four particle-stable states in 16 N have been measured. The results obtained are compared to previous measurements and are also used to extract a value for the induced pseudoscalar coupling constant in muon capture.