a b s t r a c tA muon scattering tomography system which uses extruded plastic scintillator bars for muon tracking and a dedicated muon spectrometer that measures scattering through steel slabs has been constructed and successfully tested. The atmospheric muon detection efficiency is measured to be 97% per plane on average and the average intrinsic hit resolution is 2.5 mm. In addition to creating a variety of threedimensional images of objects of interest, a quantitative study has been carried out to investigate the impact of including muon momentum measurements when attempting to detect high-density, high-Z material. As expected, the addition of momentum information improves the performance of the system. For a fixed data-taking time of 60 s and a fixed false positive fraction, the probability to detect a target increases when momentum information is used. This is the first demonstration of the use of muon momentum information from dedicated spectrometer measurements in muon scattering tomography.

We have studied the leptonic decay D + s → τ + ν τ , via the decay channel τ + → e + ν eντ , using a sample of tagged D + s decays collected near the D * ± s D ∓ s peak production energy in e + e − collisions with the CLEO-c detector. We obtain B(D + s → τ + ν τ ) = (5.30 ± 0.47 ± 0.22)% and determine the decay constant f Ds = (252.5 ± 11.1 ± 5.2) MeV, where the first uncertainties are statistical and the second are systematic. * Deceased

Analyzing 600 pb À1 of e þ e À collisions at 4170 MeV center-of-mass energy with the CLEO-c detector, we measure the branching fraction BðD þ s ! þ Þ ¼ ð5:52 AE 0:57 AE 0:21Þ% using the þ ! þ " decay mode. Combining with other CLEO measurements of BðD þ s ! þ Þ we determine the pseudoscalar decay constant f D s ¼ ð259:7 AE 7:8 AE 3:4Þ MeV consistent with the value obtained from our D þ s ! þ measurement of ð257:6 AE 10:3 AE 4:3Þ MeV. Combining these measurements we find a value of f D s ¼ ð259:0 AE 6:2 AE 3:0Þ MeV, that differs from the most accurate prediction based on unquenched lattice gauge theory of ð241 AE 3Þ MeV by 2.4 standard deviations. We also present the first measurements of BðD þ s ! K 0 þ 0 Þ ¼ ð1:00 AE 0:18 AE 0:04Þ%, and BðD þ s ! þ 0 0 Þ ¼ ð0:65 AE 0:13 AE 0:03Þ%, and measure a new value for BðD þ s ! þ Þ ¼ ð8:9 AE 0:6 AE 0:5Þ%.