3,360 research outputs found

    Hadronic B Decays to Charmless Final States and to J/psi K*

    Get PDF
    Preliminary results from the BABAR experiment on charmless B decays to charged pions or kaons, and the measurement of the B -> J/psi K* decay amplitudes are presented. The data sample, collected at the asymmetric-energy B-factory PEP-II at SLAC, comprises a total number of 22.7 million Y(4S) decays, corresponding to an integrated on-resonance luminosity of approximately 21 fb-1. We measure the following CP-averaged branching fractions: BR(B -> pi+pi-) = (4.1 +- 1.0(stat) +- 0.7(sys))xE-6 BR(B -> K+pi-) = (16.7 +- 1.6(stat) +1.2-1.7(sys))xE-6 and an upper limit of BR(B -> K+K-) < 2.5xE-6, at 90% confidence limit. The measurement of the J/psi K* decay amplitudes results in R_\perp = 0.160 +- 0.032(stat) +- 0.036(sys), and reveals a dominant longitudinal component. The phase of the longitudinal amplitude shows evidence for non-vanishing final state interaction.Comment: 13 pages, 8 postscript figures, submitted to Proceedings for BCP

    Evaluation of \alpha (M^2_Z) and (g-2)_\mu

    Full text link
    This talk summarizes the recent development in the evaluation of the leading order hadronic contributions to the running of the QED fine structure constant \alpha(s), at s=MZ2s=M_{\rm Z}^2, and to the anomalous magnetic moments of the muon (g−2)μ(g-2)_\mu. The accuracy of the theoretical prediction of these observables is limited by the uncertainties on the hadronic contributions. Significant improvement has been achieved in a series of new analyses which is presented historically in three steps: (I), use of τ\tau spectral functions in addition to e^+e^- cross sections, (II), extended use of perturbative QCD and (III), application of QCD sum rule techniques. The most precise values obtained are: Δαhad(M2Z)=(276.3±1.6)×10−4\Delta\alpha_{had} (M_2^Z) =(276.3\pm1.6)\times10^{-4}, yielding α−1(MZ2)=128.933±0.021\alpha^{-1}(M_{\rm Z}^2)=128.933\pm0.021, and aμhad=(692.4±6.2)×10−10a_\mu^{\rm had}=(692.4\pm6.2)\times 10^{-10} with which one finds for the complete Standard Model prediction aμSM=(11659159.6±6.7)×10−10a_\mu^{\rm SM}=(11 659 159.6\pm6.7)\times10^{-10}. For the electron (g−2)e(g-2)_e, the hadronic contribution is aehad=(187.5±1.8)×10−14a_e^{\rm had}=(187.5\pm1.8)\times 10^{-14}.Comment: 9 pages, Talk given at the ICHEP'98 Conference, Vancouver, Canada, July 23-29, 199

    Reply to: ''Improved Determination of the CKM Angle alpha from B -> pipi decays''

    Full text link
    In reply to hep-ph/0701204 we demonstrate why the arguments made therein do not address the criticism exposed in hep-ph/0607246 on the fundamental shortcomings of the Bayesian approach when it comes to the extraction of parameters of Nature from experimental data. As for the isospin analysis and the CKM angle alpha it is shown that the use of uniform priors for the observed quantities in the Explicit Solution parametrization is equivalent to a frequentist construction resulting from a change of variables, and thus relies neither on prior PDFs nor on Bayes' theorem. This procedure provides in this particular case results that are similar to the Confidence Level approach, but the treatment of mirror solutions remains incorrect and it is far from being general. In a second part it is shown that important differences subsist between the Bayesian and frequentist approaches, when following the proposal of hep-ph/0701204 and inserting additional information on the hadronic amplitudes beyond isospin invariance. In particular the frequentist result preserves the exact degeneracy that is expected from the remaining symmetries of the problem while the Bayesian procedure does not. Moreover, in the Bayesian approach reducing inference to the 68% or 95% credible interval is a misconception of the meaning of the posterior PDF, which in turn implies that the significant dependence of the latter to the chosen parametrization cannot be viewed as a minor effect, contrary to the claim in hep-ph/0701204.Comment: 5 pages, 1 figure. Fig. 1 corrected (wrong file

    Improved Determination of alpha_QED(M_Z^2) and the Anomalous Magnetic Moment of the Muon

    Full text link
    We reevaluate the hadronic contribution to the running of the QED fine structure constant alpha(s) at s = M_Z^2. We use data from e+e- annihilation and tau decays at low energy and at the qq-bar thresholds, where resonances occur. Using so-called spectral moments and the Operator Product Expansion (OPE), it is shown that a reliable theoretical prediction of the hadronic production rate R(s) is available at relatively low energies. Its application improves significantly the precision on the hadronic vacuum polarization contribution. We obtain delta_alpha^had = (277.8 +/- 2.6) x 10^-4 yielding alpha^-1(M_Z^2) = 128.923 +/- 0.036$. Inserting this value in a global electroweak fit using current experimental input, we constrain the mass of the Standard Model Higgs boson to be M_Higgs = (129 +103 -62) GeV. Analogously, we improve the precision of the hadronic contribution to the anomalous magnetic moment of the muon for which we obtain a_mu^had = (695.1 +/- 7.5) x 10^-10.Comment: tex, 18 pages and 3 figure

    Stau as the Lightest Supersymmetric Particle in R-Parity Violating SUSY Models: Discovery Potential with Early LHC Data

    Full text link
    We investigate the discovery potential of the LHC experiments for R-parity violating supersymmetric models with a stau as the lightest supersymmetric particle (LSP) in the framework of minimal supergravity. We classify the final states according to their phenomenology for different R-parity violating decays of the LSP. We then develop event selection cuts for a specific benchmark scenario with promising signatures for the first beyond the Standard Model discoveries at the LHC. For the first time in this model, we perform a detailed signal over background analysis. We use fast detector simulations to estimate the discovery significance taking the most important Standard Model backgrounds into account. Assuming an integrated luminosity of 1 inverse femtobarn at a center-of-mass energy of 7 TeV, we perform scans in the parameter space around the benchmark scenario we consider. We then study the feasibility to estimate the mass of the stau-LSP. We briefly discuss difficulties, which arise in the identification of hadronic tau decays due to small tau momenta and large particle multiplicities in our scenarios.Comment: 26 pages, 18 figures, LaTeX; minor changes, final version published in PR

    Weak Phase gamma Using Isospin Analysis and Time Dependent Asymmetry in B_d -> K_s pi^+ pi^-

    Full text link
    We present a method for measuring the weak phase gamma using isospin analysis of three body B decays into K pi pi channels. Differential decay widths and time dependent asymmetry in B_d -> K_s pi^+pi^- mode needs to be measured into even isospin pi pi states. The method can be used to extract gamma, as well as, the size of the electroweak penguin contributions. The technique is free from assumptions like SU(3) or neglect of any contributions to the decay amplitudes. By studying different regions of the Dalitz plot, it is possible to reduce the ambiguity in the value of gamma.Comment: 11 pages, 1 figur

    The global electroweak fit at NNLO and prospects for the LHC and ILC

    Get PDF
    For a long time, global fits of the electroweak sector of the Standard Model (SM) have been used to exploit measurements of electroweak precision observables at lepton colliders (LEP, SLC), together with measurements at hadron colliders (Tevatron, LHC), and accurate theoretical predictions at multi-loop level, to constrain free parameters of the SM, such as the Higgs and top masses. Today, all fundamental SM parameters entering these fits are experimentally determined, including information on the Higgs couplings, and the global fits are used as powerful tools to assess the validity of the theory and to constrain scenarios for new physics. Future measurements at the Large Hadron Collider (LHC) and the International Linear Collider (ILC) promise to improve the experimental precision of key observables used in the fits. This paper presents updated electroweak fit results using newest NNLO theoretical predictions, and prospects for the LHC and ILC. The impact of experimental and theoretical uncertainties is analysed in detail. We compare constraints from the electroweak fit on the Higgs couplings with direct LHC measurements, and examine present and future prospects of these constraints using a model with modified couplings of the Higgs boson to fermions and bosons.Comment: 26 pages, 9 figure

    Can the Renormalization Group Improved Effective Potential be used to estimate the Higgs Mass in the Conformal Limit of the Standard Model?

    Full text link
    We consider the effective potential VV in the standard model with a single Higgs doublet in the limit that the only mass scale μ\mu present is radiatively generated. Using a technique that has been shown to determine VV completely in terms of the renormalization group (RG) functions when using the Coleman-Weinberg (CW) renormalization scheme, we first sum leading-log (LL) contributions to VV using the one loop RG functions, associated with five couplings (the top quark Yukawa coupling xx, the quartic coupling of the Higgs field yy, the SU(3) gauge coupling zz, and the SU(2)×U(1)SU(2) \times U(1) couplings rr and ss). We then employ the two loop RG functions with the three couplings xx, yy, zz to sum the next-to-leading-log (NLL) contributions to VV and then the three to five loop RG functions with one coupling yy to sum all the N2LL...N4LLN^2LL...N^4LL contributions to VV. In order to compute these sums, it is necessary to convert those RG functions that have been originally computed explicitly in the minimal subtraction (MS) scheme to their form in the CW scheme. The Higgs mass can then be determined from the effective potential: the LLLL result is mH=219  GeV/c2m_{H}=219\;GeV/c^2 decreases to mH=188  GeV/c2m_{H}=188\;GeV/c^2 at N2LLN^{2}LL order and mH=163  GeV/c2m_{H}=163\;GeV/c^2 at N4LLN^{4}LL order. No reasonable estimate of mHm_H can be made at orders VNLLV_{NLL} or VN3LLV_{N^3LL}. This is taken to be an indication that this mechanism for spontaneous symmetry breaking is in fact viable, though one in which there is slow convergence towards the actual value of mHm_H. The mass 163  GeV/c2163\;GeV/c^2 is argued to be an upper bound on mHm_H.Comment: 24 pages, 5 figures. Updated version contains new discussion, references, figures, and corrects errors in reference

    A configuration system for the ATLAS trigger

    Full text link
    The ATLAS detector at CERN's Large Hadron Collider will be exposed to proton-proton collisions from beams crossing at 40 MHz that have to be reduced to the few 100 Hz allowed by the storage systems. A three-level trigger system has been designed to achieve this goal. We describe the configuration system under construction for the ATLAS trigger chain. It provides the trigger system with all the parameters required for decision taking and to record its history. The same system configures the event reconstruction, Monte Carlo simulation and data analysis, and provides tools for accessing and manipulating the configuration data in all contexts.Comment: 4 pages, 2 figures, contribution to the Conference on Computing in High Energy and Nuclear Physics (CHEP06), 13.-17. Feb 2006, Mumbai, Indi

    A population-based approach to background discrimination in particle physics

    Full text link
    Background properties in experimental particle physics are typically estimated using control samples corresponding to large numbers of events. This can provide precise knowledge of average background distributions, but typically does not consider the effect of fluctuations in a data set of interest. A novel approach based on mixture model decomposition is presented as a way to estimate the effect of fluctuations on the shapes of probability distributions in a given data set, with a view to improving on the knowledge of background distributions obtained from control samples. Events are treated as heterogeneous populations comprising particles originating from different processes, and individual particles are mapped to a process of interest on a probabilistic basis. The proposed approach makes it possible to extract from the data information about the effect of fluctuations that would otherwise be lost using traditional methods based on high-statistics control samples. A feasibility study on Monte Carlo is presented, together with a comparison with existing techniques. Finally, the prospects for the development of tools for intensive offline analysis of individual events at the Large Hadron Collider are discussed.Comment: Updated according to the version published in J. Phys.: Conf. Ser. Minor changes have been made to the text with respect to the published article with a view to improving readabilit
    • …
    corecore