654 research outputs found

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

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    Average charged multiplicities have been measured separately in bb, cc and light quark (u,d,su,d,s) events from Z0Z^0 decays measured in the SLD experiment. Impact parameters of charged tracks were used to select enriched samples of bb and light quark events, and reconstructed charmed mesons were used to select cc quark events. We measured the charged multiplicities: nˉuds=20.21±0.10(stat.)±0.22(syst.)\bar{n}_{uds} = 20.21 \pm 0.10 (\rm{stat.})\pm 0.22(\rm{syst.}), nˉc=21.28±0.46(stat.)0.36+0.41(syst.)\bar{n}_{c} = 21.28 \pm 0.46(\rm{stat.}) ^{+0.41}_{-0.36}(\rm{syst.}) nˉb=23.14±0.10(stat.)0.37+0.38(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 cc or bb quark events and light quark events: Δnˉc=1.07±0.47(stat.)0.30+0.36(syst.)\Delta \bar{n}_c = 1.07 \pm 0.47(\rm{stat.})^{+0.36}_{-0.30}(\rm{syst.}) and Δnˉb=2.93±0.14(stat.)0.29+0.30(syst.)\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

    Effect of the distal histidine on the peroxidatic activity of monomeric cytoglobin

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    The reaction of hydrogen peroxide with ferric human cytoglobin and a number of distal histidine variants were studied. The peroxidase activity of the monomeric wildtype protein with an internal disulfide bond, likely to be the form of the protein in vivo, exhibits a high peroxidase-like activity above that of other globins such as myoglobin. Furthermore, the peroxidatic activity of wildtype cytoglobin shows increased resistance to radical-based degradation compared to myoglobin. The ferryl form of wildtype cytoglobin is unstable, but is able to readily oxidize substrates such as guaiacol. In contrast distal histidine mutants of cytoglobin (H81Y and H81V) show very low peroxidase activity but enhanced radical-induced degradation. Therefore, the weakly bound distal histidine appears to modulate ferryl stability and limit haem degradation. These data are consistent with a role of a peroxidase activity of cytoglobin in cell stress response mechanisms.</ns4:p

    Search for resonant WZ production in the fully leptonic final state in proton–proton collisions at √s=13 TeV with the ATLAS detector

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    Measurement of exclusive pion pair production in proton–proton collisions at √s=7 TeV with the ATLAS detector