Micro Pin Array Detector (MIPA): First Test Results

A novel gas proportional detector, consisting of an array of pins immersed into a cathode made out of closely packed hexagonals has been developed. The resulting geometry of the detector is 3 dimensional. Electron multiplication is limited to a region in close proximity to the tip of each pin, where the electric field decreases with distance from the pin at a rate faster than l/r, the rate that exists in a traditional wire chamber. The multiplication region is limited to a small part of the detector volume leading to stability of operation up to high charge gas gains. The amplification region is located far enough from any dielectric surface that the gas gain is insensitive to the charge state of the surface, a significant benefit compared with many other micro-pattern detectors. The microscopic dimensions of the individual pins of the array result in signals whose total duration is about a microsecond. Two identical, but opposite polarity signals are detected, one on the pin and one on the cathode. Both signals can be used by two independent, charge division, read-out systems to obtain unambiguous x-y position information of the primary ionization

Optical properties of pyrochlore oxide Pb2Ru2O7−δPb_{2}Ru_{2}O_{7-{\delta}}

We present optical conductivity spectra for $Pb_{2}Ru_{2}O_{7-{\delta}}$ single crystal at different temperatures. Among reported pyrochlore ruthenates, this compound exhibits metallic behavior in a wide temperature range and has the least resistivity. At low frequencies, the optical spectra show typical Drude responses, but with a knee feature around 1000 \cm. Above 20000 \cm, a broad absorption feature is observed. Our analysis suggests that the low frequency responses can be understood from two Drude components arising from the partially filled Ru $t_{2g}$ bands with different plasma frequencies and scattering rates. The high frequency broad absorption may be contributed by two interband transitions: from occupied Ru $t_{2g}$ states to empty $e_{g}$ bands and from the fully filled O 2p bands to unoccupied Ru $t_{2g}$ states.Comment: 4 pages, 6 figure

A new measurement of K+(e4) decay and the s-wave pi-pi-scattering length a00

A sample of 400000 events from the decay K+->pi+pi-e+nu(e)(K(e4)) has been collected in experiment E865 at the Brookhaven AGS. The analysis of these data yields new measurements of the K(e4) branching ratio (4.11+-0.01+-0.11)*10**(-5)), the s-wave pi-pi scattering length a00=0.228+-0.012+-0.003, and the form factors F, G, and H of the hadronic current and their dependence on the invariant pi-pi mass

First observation of the decay K+ -> e+ nu mu+ mu-

Experiment 865 at the Brookhaven AGS has observed the decay K^+ -> e^+ nu mu^+ mu^-. The branching ratio extracted is (1.72 +/- 0.37(stat) +/- 0.17(syst) +/- 0.19(model)) x 10^{-8} where the third term in the error results from the use of a model to extrapolate into a kinematic region dominated by background.Comment: 4 pages, 6 figures, Revtex4. Correction to figure and minor text change

An Improved upper limit on the decay K^+ -> pi^+ mu^+ e^-

Based on results of a search for the lepton-family-number-violating decay $K^+ \to \pi^+\mu^+ e^-$ with data collected by experiment E865 at the Alternating Gradient Synchrotron of Brookhaven National Laboratory, we place an upper limit on the branching ratio at $2.1 \times 10^{-11}$ (90% C.L.). Combining the results with earlier E865 data and those of a previous experiment, E777, an upper limit on the branching ratio of $1.3 \times 10^{-11}$ (90% C.L.) is obtained.Comment: v2: 13 pages, submitted to the Phys. Rev. D v3: 13 pages, resubmitted to Phys. Rev. D (corrections include: a more detailed overview of the combined analysis of the available experimntal data

New, high statistics measurement of the K+ -> pi0 e+ nu (Ke3) branching ratio

E865 at the Brookhaven National Laboratory AGS collected about 70,000 K+(e3) events with the purpose of measuring the relative K+(e3) branching ratio. The pi0 in all the decays was detected using the e+e- pair from pi0 -> e+e-gamma decay and no photons were required. Using the Particle Data Group branching ratios for the normalization decays we obtain BR(K+(e3(gamma))=(5.13+/-0.02(stat)+/-0.09(sys)+/-0.04(norm))%, where $K+(e3(gamma)) includes the effect of virtual and real photons. This result is 2.3 sigma higher than the current Particle Data Group value. The implications of this result for the$V_{us}$ element of the CKM matrix, and the matrix's unitarity are discussed.Comment: 4 pages, 5 figures; final version accepted by PR

New Results on Pb-Au Collisions at 40 AGeV from the CERES/NA45 Experiment

In 1999 the CERES/NA45 ran at the CERN SPS with a beam energy of 40 GeV/nucleon. The data set comprises about 8.7 millions Pb-Au events with a trigger selection corresponding to approximately the most central 30% of the geometrical cross section. Results on low-mass electron pair analysis are presented. The upgrade of the experimental setup with the radial drift TPC has allowed to enhance hadron physics capabilities of the experiment. New results on hadron spectra (including Lambda) and flow are presented.Comment: Talk at the International Nuclear Physics Conference INPC2001, Berkeley, CA, July 29th - August 3rd 200