2,857 research outputs found

    Extracting |V_{ub}| from the Hadronic Mass Spectrum of Inclusive B decays

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    Following a strategy introduced earlier by the authors, we show that it is possible to extract |V_{ub}| from the cut hadronic mass spectrum of B decays without large systematic errors which usually arise from having to model the Fermi motion of the heavy quark. We present a closed form expression for |V_{ub}|/|V_{ts}| which is accurate up to corrections of order \alpha_s^2, \alpha_s \rho, (\Lambda/m_b)^2/\rho, where \rho is the experimental cut (s_c/m_b^2) on the hadronic mass used to veto charmed decays. Modulo duality violation errors, which are intrinsic to all inclusive predictions, we estimate the theoretical error in the extraction to be at the 5% level.Comment: 11 pages, 1 figur

    A Comment on the Extractions of V_{ub} from Radiative Decays

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    We present a model independent closed form expression for |V_{ub}|^2/|V_{tb} V_{ts}^*|^2, which includes the resummation of large endpoint logarithms as well as the interference effects from the operators O2O_2 and O8O_8. We demonstrate that the method to extract |V_{ub}| presented by the authors in hep-ph/9909404, and modified in this letter to include interference effects, is not just a refinement of the method introduced in hep-ph/9312311. We also discuss the model dependence of the latter proposal. Furthermore, we show that the resummation is not negligible and that the Landau pole does not introduce any significant uncertainties.Comment: 10 pages, 3 figures; one figure added, one reference added, expanded discussion

    Enhanced subleading structure functions in semileptonic B decay

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    The charged lepton spectrum in semileptonic BXuνˉB\to X_u \ell\bar\nu decay near maximal lepton energy receives important corrections from subleading structure functions that are formally suppressed by powers of ΛQCD/mb\Lambda_{QCD}/m_b but are enhanced by numerical factors. We investigate the series of higher order terms which smear over a region of width ΔEΛQCD\Delta E_\ell \sim \Lambda_{QCD} near the endpoint the contributions proportional to δ(Emb/2)\delta(E_\ell - m_b/2) times (i) the matrix element of the chromomagnetic operator, and (ii) four-quark operators. These contribute to the total rate at the few percent level, but affect the endpoint region much more significantly. Implications for the determination of Vub|V_{ub}| are discussed.Comment: 12 page

    1/fβ1/f^{\beta} noise for scale-invariant processes: How long you wait matters

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    We study the power spectrum which is estimated from a nonstationary signal. In particular we examine the case when the signal is observed in a measurement time window [tw,tw+tm][t_w,t_w+t_m], namely the observation started after a waiting time twt_w, and tmt_m is the measurement duration. We introduce a generalized aging Wiener-Khinchin theorem which relates between the spectrum and the time- and ensemble-averaged correlation function for arbitrary tmt_m and twt_w. Furthermore we provide a general relation between the non-analytical behavior of the scale-invariant correlation function and the aging 1/fβ1/f^{\beta} noise. We illustrate our general results with two-state renewal models with sojourn times' distributions having a broad tail

    Mutual Enrichment in Ranked Lists and the Statistical Assessment of Position Weight Matrix Motifs

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    Statistics in ranked lists is important in analyzing molecular biology measurement data, such as ChIP-seq, which yields ranked lists of genomic sequences. State of the art methods study fixed motifs in ranked lists. More flexible models such as position weight matrix (PWM) motifs are not addressed in this context. To assess the enrichment of a PWM motif in a ranked list we use a PWM induced second ranking on the same set of elements. Possible orders of one ranked list relative to the other are modeled by permutations. Due to sample space complexity, it is difficult to characterize tail distributions in the group of permutations. In this paper we develop tight upper bounds on tail distributions of the size of the intersection of the top of two uniformly and independently drawn permutations and demonstrate advantages of this approach using our software implementation, mmHG-Finder, to study PWMs in several datasets.Comment: Peer-reviewed and presented as part of the 13th Workshop on Algorithms in Bioinformatics (WABI2013

    Semileptonic Lambda_b decay to excited Lambda_c baryons at order Lambda_{QCD}/m_Q

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    Exclusive semileptonic Lambda_b decays to excited charmed Lambda_c baryons are investigated at order Lambda_{QCD}/m_Q in the heavy quark effective theory. The differential decay rates are analyzed for the J^\pi=1/2^- Lambda_c(2593) and the J^\pi=3/2^- \Lambda_c(2625). They receive 1/m_{c,b} corrections at zero recoil that are determined by mass splittings and the leading order Isgur-Wise function. With some assumptions, we find that the branching fraction for Lambda_b decays to these states is 2.5-3.3%. The decay rate to the helicity \pm 3/2 states, which vanishes for m_Q \to \infty, remains small at order Lambda_{QCD}/m_Q since 1/m_c corrections do not contribute. Matrix elements of weak currents between a Lambda_b and other excited Lambda_c states are analyzed at zero-recoil to order Lambda_{QCD}/m_Q. Applications to baryonic heavy quark sum-rules are explored.Comment: 27 pages, 1 fig., minor changes, version to appear in Phys.Rev.