2,254 research outputs found

    Factorization of the charge correlation function in B0Bˉ0B^0\bar B^0 oscillations

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    Extraction of the mass difference Δm\Delta m from B0Bˉ0B^0\bar B^0 oscillations involves tagging of bottom flavour at production and at decay. We show that the asymmetry between the unmixed and mixed events factorizes into two parts, one depending on the production-tag and the other on the decay-tag.Comment: 6 pages, Latex, no figure

    B Mixing

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    The neutral BB mesons, B0B^0 and BsB_s, can oscillate between their particle and antiparticle states owing to flavor-changing weak interactions. In recent years, techniques to detect these oscillations as a function of the meson's decay time have been developed. In this article the physics of flavor oscillations is reviewed and theoretical predictions are summarized. The many observations that demonstrate the time-dependence of B^0-\B0bar oscillations are presented along with a combined measurement of its frequency, δmd\delta m_d. The attempts to measure the BsB_s oscillation frequency, both directly and indirectly, are then summarized. Finally, values for the CKM elements Vtd|V_{td}| and Vts/Vtd|V_{ts}/V_{td}| are extracted

    ALEPH Tau Spectral Functions and QCD

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    Hadronic τ\tau decays provide a clean laboratory for the precise study of quantum chromodynamics (QCD). Observables based on the spectral functions of hadronic τ\tau decays can be related to QCD quark-level calculations to determine fundamental quantities like the strong coupling constant, quark and gluon condensates. Using the ALEPH spectral functions and branching ratios, complemented by some other available measurements, and a revisited analysis of the theoretical framework, the value \asm = 0.345 \pm 0.004_{\rm exp} \pm 0.009_{\rm th} is obtained. Taken together with the determination of \asZ from the global electroweak fit, this result leads to the most accurate test of asymptotic freedom: the value of the logarithmic slope of αs1(s)\alpha_s^{-1}(s) is found to agree with QCD at a precision of 4%. The value of \asZ obtained from τ\tau decays is \asZ = 0.1215 \pm 0.0004_{\rm exp} \pm 0.0010_{\rm th} \pm 0.0005_{\rm evol} = 0.1215 \pm 0.0012.Comment: 14 pages, 5 figures, invited talk at the Tau06 International Workshop, Pisa, September 19-22 200

    Measurement of the photon structure function at ALEPH

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    The photon structure function F2gamma has been measured with data taken by the ALEPH collaboration at LEP centre-of-mass energies sqrt s = 91 GeV with < Q^2 > of 9.9, 20.7 and 284 GeV^2 and sqrt s = 183 GeV with of 13.7 and 56.5 GeV^2. For the data at sqrt s = 183 GeV a two-dimensional unfolding method employing the principle of maximum entropy is used, which reduces the errors compared to one-dimensional methods.Comment: 5 pages, 5 figures, To be published in proceedings "PHOTON99

    Vector and Axial-Vector Spectral Functions and QCD

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    We present new results of the tau hadronic spectral function analysis using data accumulated by the ALEPH detector at LEP during the years 1991-94. In addition to the vector spectral functions, the axial-vector spectral functions and, separately, the tau --> 3pi nu as well as the tau --> pi 2pi0 nu spectral functions are determined from their respective unfolded, i.e., physical invariant mass spectra. The spectral functions are applied to QCD chiral sum rules in order to extract information about saturation at the tau mass scale. Using the the semi-leptonic tau decay rate for vector and axial-vector currents in addition to spectral moments, we obtain precise measurements of the strong coupling constant alpha_s(M_tau) and the contributing non-perturbative power terms. The evolution to the Z mass yields alpha_s(M_Z) = 0.1219 +/- 0.0019.Comment: 15 pages, 12 figures, LaTex, Talk given at the Fourth International Workshop on Tau Lepton Physics (TAU96), Colorado, September 199

    Chiral-invariant CP-violating Effective Interactions in Z Decays to three Jets

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    Tests of CP violation by appropriate momentum correlations in Z3Z\to 3 jets and in particular in ZbbˉXZ\to b\bar bX probe CP-violating effective couplings -- that manifest themselves as form factors -- which conserve the quark chirality and quark flavour. By giving two examples we show that such couplings can be induced at one-loop order in extensions of the Standard Model with CP violation beyond the Kobayashi-Maskawa phase. In one of the models we compute the chirality-conserving part of the CP-violating ZbbˉZb{\bar b}-gluon amplitude for massless bb quarks, determine the resulting effective dimension d=6d=6 couplings in the local limit, and discuss the possible size of the effects. Finally we show that in models with excited quarks the chiral-invariant CP-violating effective interactions could be quite large if appropriate couplings are of a size characteristic of a strong interactionComment: 14 pages, LaTeX with 4 postscript figures, epsf macro include

    SVD Approach to Data Unfolding

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    Distributions measured in high energy physics experiments are usually distorted and/or transformed by various detector effects. A regularization method for unfolding these distributions is re-formulated in terms of the Singular Value Decomposition (SVD) of the response matrix. A relatively simple, yet quite efficient unfolding procedure is explained in detail. The concise linear algorithm results in a straightforward implementation with full error propagation, including the complete covariance matrix and its inverse. Several improvements upon widely used procedures are proposed, and recommendations are given how to simplify the task by the proper choice of the matrix. Ways of determining the optimal value of the regularization parameter are suggested and discussed, and several examples illustrating the use of the method are presented.Comment: 22 page

    Nucleosynthesis constraints on heavy tau-neutrino in the presence of annihilations to majorons

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    We show that in the presence of sufficiently strong ντ\nu_\tau annihilations to majorons, primordial nucleosynthesis constraints can not rule out any values of the ντ\nu_\tau mass up the present laboratory limit.Comment: Talk given at TAUP 95, Toledo, Sept. 1995; 5 pages, LaTex file + 2 figures, all compressed by uufile
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