This article describes a determination of the Cabibbo-Kobayashi-Maskawa matrix element $|V_{cb}|$ from the decay $B^0\to D^{*-}\ell^+\nu_\ell$ using 711 fb$^{-1}$ of Belle data collected near the $\Upsilon(4S)$ resonance. We simultaneously measure the product of the form factor normalization $\mathcal{F}(1)$ and the matrix element $|V_{cb}|$ as well as the three parameters $\rho^2$, $R_1(1)$ and $R_2(1)$, which determine the form factors of this decay in the framework of the Heavy Quark Effective Theory. The results, based on about 120,000 reconstructed $B^0\to D^{*-}\ell^+\nu_\ell$ decays, are $\rho^2=1.214\pm 0.034\pm 0.009$, $R_1(1)=1.401\pm 0.034\pm 0.018$, $R_2(1)=0.864\pm 0.024\pm 0.008$ and $\mathcal{F}(1)|V_{cb}|=(34.6\pm 0.2\pm 1.0)\times 10^{-3}$. The branching fraction of $B^0\to D^{*-}\ell^+\nu_\ell$ is measured at the same time/ we obtain a value of $\mathcal{B}(B^0 \to D^{*-}\ell^+ \nu_\ell) = (4.58 \pm 0.03 \pm 0.26) %$. The errors correspond to the statistical and systematic uncertainties. These results give the most precise determination of the form factor parameters and $\mathcal{F}(1)|V_{cb}|$ to date. In addition, a direct, model-independent determination of the form factor shapes has been carried out.
Continuum-subtracted on-resonance data as a function of the $w$ kinematic variable.
Continuum-subtracted on-resonance data as a function of the $\cos\theta_\ell$ variable.
Continuum-subtracted on-resonance data as a function of the $\cos\theta_\nu$ variable.
We present the first model-independent measurement of the helicity of $W$ bosons produced in top quark decays, based on a 1 fb$^{-1}$ sample of candidate $t\bar{t}$ events in the dilepton and lepton plus jets channels collected by the D0 detector at the Fermilab Tevatron $p\bar{p}$ Collider. We reconstruct the angle $\theta^*$ between the momenta of the down-type fermion and the top quark in the $W$ boson rest frame for each top quark decay. A fit of the resulting \costheta distribution finds that the fraction of longitudinal $W$ bosons $f_0 = 0.425 \pm 0.166 \hbox{(stat.)} \pm 0.102 \hbox{(syst.)}$ and the fraction of right-handed $W$ bosons $f_+ = 0.119 \pm 0.090 \hbox{(stat.)} \pm 0.053 \hbox{(syst.)}$, which is consistent at the 30% C.L. with the standard model.
COS(THETA*) distribution for leptonic W decay in lepton+jets events.. Data are read from plots and errors are statistcial (sqrt(N)).
COS(THETA*) distribution for hadronic W decay in lepton+jets events.. Data are read from plots and errors are statistcial (sqrt(N)).
COS(THETA*) distribution for W decay in dilepton events.. Data are read from plots and errors are statistcial (sqrt(N)).
The correlated production of Lambda and Lambdabar baryons has been studied using 4.3 million multihadronic Zo decays recorded with the OPAL detector at LEP. Di-lambda pairs were investigated in the full data sample and for the first time also in 2-jet and 3-jet events selected with the k_t algorithm. The distributions of rapidity differences from correlated Lambda-Lambdabar pairs exhibit short-range, local correlations and prove to be a sensitive tool to test models, particularly for 2-jet events. The JETSET model describes the data best but some extra parameter tuning is needed to improve agreement with the experimental results in the rates and the rapidity spectra simultaneously. The recently developed modification of JETSET, the MOdified Popcorn Scenarium (MOPS), and also HERWIG do not give satisfactory results. This study of di-lambda production in 2- and 3-jet events supports the short-range compensation of quantum numbers.
Average multipicity of LAMBDA pairs in hadronic events.
Average multipicity of LAMBDA pairs in 2-Jet events.
Average multipicity of LAMBDA pairs in 3-Jet events.
A global event shape analysis of the multihadronic final states observed in neutral current deep inelastic scattering events with a large rapidity gap with respect to the proton direction is presented. The analysis is performed in the range $5 \leq Q^2 \leq 185\gev^2$ and $160 \leq W \leq 250\gev$, where $Q^2$ is the virtuality of the photon and $W$ is the virtual-photon proton centre of mass energy. Particular emphasis is placed on the dependence of the shape variables, measured in the $\gamma^*-$pomeron rest frame, on the mass of the hadronic final state, $M_X$. With increasing $M_X$ the multihadronic final state becomes more collimated and planar. The experimental results are compared with several models which attempt to describe diffractive events. The broadening effects exhibited by the data require in these models a significant gluon component of the pomeron.
Measured (uncorrected) polar distribution of the sphericity axis w.r.t. thevirtual photon direction in the (gamma*-pomeron)rest frame Data are in bins of the mass of the final state hadronic system.
Measured (uncorrected) polar distribution of the sphericity axis w.r.t. thevirtual photon direction in the (gamma*-pomeron)rest frame Data are in bins of the mass of the final state hadronic system.
Measured (uncorrected) polar distribution of the sphericity axis w.r.t. thevirtual photon direction in the (gamma*-pomeron)rest frame Data are in bins of the mass of the final state hadronic system.
The electroproduction of rho mesons with proton diffractive dissociation for Q^2 > 7 GeV^2 and the elastic electroproduction of Phi mesons for Q^2 > 6 Gev^2 are studied in e^+ p collisions at HERA with the H1 detector, for an integrated luminosity of 2.8 pb-1. The dependence of the cross sections on P_t^2 and Q^2 is measured, and the vector meson polarisation obtained. The cross section ratio between proton dissociative and elastic production of rho mesons is measured and discussed in the framework of the factorisation hypothesis of diffractive vertices. The ratio of the elastic cross section for Phi and rho meson production is investigated as a function of Q^2.
Corrected PT**2 distribution for RHO production from the proton dissociative sample. Statistical errors only.
Cross sections and ratio of proton dissociative to elastic cross sections.
Cross sections and ratio of proton dissociative to elastic cross sections.
The reaction gamma p -> J/Psi p has been studied in ep interactions using the ZEUS detector at HERA. The cross section for elastic J/Psi photoproduction has been measured as a function of the photon-proton centre of mass energy W in the range 40 < W < 140 GeV at a median photon virtuality Q^2 of 5*10^{-5} GeV^2. The photoproduction cross section, sigma_{gamma p -> J/Psi p}, is observed to rise steeply with W. A fit to the data presented in this paper to determine the parameter $\delta$ in the form sigma_{gamma p -> J/Psi p} \propto W^{\delta} yields the value \delta = 0.92 \pm 0.14 \pm 0.10. The differential cross section dsigma/d|t| is presented over the range |t| < 1.0 GeV^2 where t is the square of the four-momentum exchanged at the proton vertex. d\sigma/d|t| falls exponentially with a slope parameter of 4.6 \pm 0.4 (+0.4-0.6) GeV^{-2}. The measured decay angular distributions are consistent with s-channel helicity conservation.
Data from the electron channel. Second systematic error is that attributed to the uncertainty in the modelof proton dissociation used for background subtraction.
Data from the muon channel. Second systematic error is that attributed to the uncertainty in the modelof proton dissociation used for background subtraction.
Data from the electron channel. Second systematic error is that attributed to the uncertainty in the modelof proton dissociation used for background subtraction.
Deep inelastic scattering (DIS) events, selected from 1993 data taken by the H1 experiment at HERA, are studied in the Breit frame of reference. The fragmentation function of the quark is compared with those of \ee data. It is shown that certain aspects of the quarks emerging from within the proton in \ep interactions are essentially the same as those of quarks pair-created from the vacuum in \ee annihilation. The measured area, peak position and widthof the fragmentation function show that the kinematic evolution variable, equivalent to the \ee squared centre of mass energy, is in the Breit frame the invariant square of the four-momentum transfer. We comment on the extent to which we have evidence for coherence effects in parton showers.
Distribution of the cosine of the Breit frame polar angle for data with the Breit frame energy flow selection. Statistical errors only.
Distribution of the cosine of the Breit frame polar angle for data before the Breit frame energy flow selection. Statistical errors only.
The fragmentation function for the current hemisphere of the Breit frame. Data are Breit frame energy flow selected only. Statistical errors only.
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Data at Parton level.
Ratio data/(Monte Carlo) at Parton level.
Data at Parton level.. Distribution of Ellis-Karliner angle.
We have measured the partial width and forward-backward charge asymmetry for the reaction e + e - →Z 0 →μ + μ - (γ). We obtain a partial width Γ μμ of 83.3±1.3(stat)±0.9(sys) MeV and the following values for the vector and axial vector couplings: g v =−0.062 −0.015 +0.020 and g A =−0.497 −0.005 +0.005 . From our measurement of the partial width and the mass of the Z 0 boson we determine the effective electroweak mixing angle, sin 2 θ w =0.232±0.005, and the neutral current coupling strength parameter, ϱ =0.998±0.016.
No description provided.
Forward backward charge asymmetry.
No description provided.
We present evidence for the non-Abelian nature of QCD from a study of multijet events produced in e+e− annihilations from √s =50 to 57 GeV in the AMY detector at the KEK storage ring TRISTAN. A comparison of the three-jet event fraction at TRISTAN to the fraction of the DESY storage ring PETRA shows that the QCD coupling strength αs decreases with increasing Q2. In addition, measurements of the angular distributions of four-jet events show evidence for the triple-gluon vertex.
No description provided.
No description provided.
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