D0−Dˉ0D^0 - \bar D^0 Mixing in the Presence of Isosinglet Quarks

We analyse $\Delta C=2$ transitions in the framework of a minimal extension of the Standard Model where either a $Q=2/3$ or a $Q=-1/3$ isosinglet quark is added to the standard quark spectrum. In the case of a $Q=2/3$ isosinglet quark, it is shown that there is a significant region of parameter space where $D^0 - \bar D^0$ mixing is sufficiently enhanced to be observed at the next round of experiments. On the contrary, in the case of a $Q=-1/3$ isosinglet quark, it is pointed out that obtaining a substancial enhancement of $D^0 - \bar D^0$ mixing, while complying with the experimental constraints on rare kaon decays, requires a contrived choice of parameters.Comment: 10 pages plus four figures. The figures are not included but are available upon reques

Initial results of a positron tomograph for prostate imaging

We present the status and initial images of a positron tomograph for prostate imaging that centers a patient between a pair of external curved detector banks (ellipse: 45 cm minor, 70 cm major axis). The distance between detector banks adjusts to allow patient access and to position the detectors as closely as possible for maximum sensitivity with patients of various sizes. Each bank is composed of two axial rows of 20 CTI PET Systems HR+ block detectors for a total of 80 modules in the camera. Compared to an ECAT HR PET system operating in 3D mode, our camera uses about one-quarter the number of detectors and has approximately the same sensitivity for a central point source, because our detectors are close to the patient. The individual detectors are angled in the plane to point towards the prostate to minimize resolution degradation in that region. The detectors are read out by modified CTI data acquisition electronics. We have completed construction of the gantry and electronics, have developed detector calibration and data acquisition software, and are taking coincidence data. We demonstrate that we can clearly visualize a "prostate" in a simple phantom. Reconstructed images of two phantoms are shown

A retrospective on the LBNL PEM project

We present a retrospective on the LBNL Positron Emission Mammography (PEM) project, looking back on our design and experiences. The LBNL PEM camera utilizes detector modules that are capable of measuring depth of interaction (DOI) and places them into 4 detector banks in a rectangular geometry. In order to build this camera, we had to develop the DOI detector module, LSO etching, Lumirror-epoxy reflector for the LSO array (to achieve optimal DOI), photodiode array, custom IC, rigid-flex readout board, packaging, DOI calibration and reconstruction algorithms for the rectangular camera geometry. We will discuss the highlights (good and bad) of these developments

Study of the Rare Hyperon Decay {\boldmath \Omega^\mp \to \Xi^\mp \: \pi^+\pi^-}

The authors report a new measurement of the decay {Omega}{sup -} {yields} {Xi}{sup -} {pi}{sup +}{pi}{sup -} with 76 events and a first observation of the decay {bar {Omega}}{sup +} {yields} {bar {Xi}}{sup +} {pi}{sup +}{pi}{sup -} with 24 events, yielding a combined branching ratio (3.74{sub -0.56}{sup +0.67}) x 10{sup -4}. This represents a factor 25 increase in statistics over the best previous measurement. No evidence is seen for CP violation, with {Beta}({Omega}{sup -} {yields} {Xi}{sup -} {pi}{sup +}{pi}{sup -}) = 4.04{sub -0.71}{sup +0.83} x 10{sup -4} and {Beta}({bar {Omega}}{sup +} {yields} {bar {Xi}}{sup +} {pi}{sup +}{pi}{sup -}) = 3.15{sub -0.89}{sup +1.12} x 10{sup -4}. Contrary to theoretical expectation, they see little evidence for the decays {Omega}{sup -} {yields} {Xi}*{sub 1530}{sup 0} {pi}{sup -} and {bar {Omega}}{sup +} {yields} {bar {Xi}}*{sub 1530}{sup 0} {pi}{sup +} and place a 90% C.L. upper limit on the combined branching ratio {Beta}({Omega}{sup -}({bar {Omega}}{sup +}) {yields} {Xi}*{sub 1530}{sup 0} ({bar {Xi}}*{sub 1530}{sup 0}){pi}{sup {-+}}) < 7.0 x 10{sup -5}

New measurement of ξ- → Λπ- decay parameters

A study on the measurement of φ≡ using a sample of 144×106 ≡- →λπ- decays having an average polarization of 3.7% was presented. The polarized ≡-'s were produced by directing an 800 geV÷c proton beam onto a 2 mm ×2 mm× 60 mm cu target at angles of +3 and -3 mrad. The results were shown to be a 2.9× improvement over the best previous mesurements. It was shown that CP violation in charged ≡→λπ decays are not suppressed by a vanishing final phase shift difference