Measurement of the Charged Multiplicities in b, c and Light Quark Events from Z0 Decays

Average charged multiplicities have been measured separately in $b$, $c$ and light quark ($u,d,s$) events from $Z^0$ decays measured in the SLD experiment. Impact parameters of charged tracks were used to select enriched samples of $b$ and light quark events, and reconstructed charmed mesons were used to select $c$ quark events. We measured the charged multiplicities: $\bar{n}_{uds} = 20.21 \pm 0.10 (\rm{stat.})\pm 0.22(\rm{syst.})$, $\bar{n}_{c} = 21.28 \pm 0.46(\rm{stat.}) ^{+0.41}_{-0.36}(\rm{syst.})$ $\bar{n}_{b} = 23.14 \pm 0.10(\rm{stat.}) ^{+0.38}_{-0.37}(\rm{syst.})$, from which we derived the differences between the total average charged multiplicities of $c$ or $b$ quark events and light quark events: $\Delta \bar{n}_c = 1.07 \pm 0.47(\rm{stat.})^{+0.36}_{-0.30}(\rm{syst.})$ and $\Delta \bar{n}_b = 2.93 \pm 0.14(\rm{stat.})^{+0.30}_{-0.29}(\rm{syst.})$. We compared these measurements with those at lower center-of-mass energies and with perturbative QCD predictions. These combined results are in agreement with the QCD expectations and disfavor the hypothesis of flavor-independent fragmentation.Comment: 19 pages LaTex, 4 EPS figures, to appear in Physics Letters

Production of pi+, pi-, K+, K-, p and p-bar in Light (uds), c and b Jets from Z0 Decays

We present improved measurements of the differential production rates of stable charged particles in hadronic Z0 decays, and of charged pions, kaons and protons identified over a wide momentum range using the SLD Cherenkov Ring Imaging Detector. In addition to flavor-inclusive Z0 decays, measurements are made for Z0 decays into light (u, d, s), c and b primary flavors, selected using the upgraded Vertex Detector. Large differences between the flavors are observed that are qualitatively consistent with expectations based upon previously measured production and decay properties of heavy hadrons. These results are used to test the predictions of QCD in the Modified Leading Logarithm Approximation, with the ansatz of Local Parton-Hadron Duality, and the predictions of three models of the hadronization process. The light-flavor results provide improved tests of these predictions, as they do not include the contribution of heavy-hadron production and decay; the heavy-flavor results provide complementary model tests. In addition we have compared hadron and antihadron production in light quark (as opposed to antiquark) jets. Differences are observed at high momentum for all three charged hadron species, providing direct probes of leading particle effects, and stringent constraints on models.Comment: 44 pages, 14 figs; submitted to Phys. Rev.

The association between murine cytomegalovirus induced hepatitis and the accummulation of oval cells

The accumulation of oval cells is an early event in the development of hepatocellular carcinoma induced by certain experimental regimes involving hepatocarcinogens. Oval cells have also been observed during chronic hepatitis induced by alcohol and iron overload. In this study, livers of murine cytomegalovirus (MCMV) infected mice were examined to determine whether hepatitis induced by this virus could initiate oval cell proliferation. BALB/c and C57BL/6 mice were infected with MCMV and studied 4, 8, 10 and 12 months later, alongside control (uninfected) mice. The livers were examined histochemically, immunocytochemically and by in situ hybridization to identify oval cells, inflammatory cells and proliferating cells. Oval cells were seen in the periportal regions of livers from MCMV infected BALB/c mice. These increased in number from 4 to 12 months after infection in parallel with increases in the numbers of inflammatory cells, even though cells expressing MCMV antigens were no longer evident in these samples. Proliferating oval cells and hepatocytes were identified by PCNA staining, indicating an increased level of liver regeneration in the infected livers. C57BL/6 mice are less susceptible to persistent MCMV hepatitis and had fewer oval cells than BALB/c mice. Thus the study demonstrates an association between MCMV induced hepatitis, inflammation, and presence of oval cells