2,340 research outputs found

    Note on Tests of the Factorization Hypothesis and the Determination of Meson Decay Constants

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    We discuss various tests of the factorization hypothesis making use of the close relationship between semi-leptonic and factorized nonleptonic decay amplitudes. It is pointed out that factorization leads to truely model-independent predictions for the ratio of nonleptonic to semi-leptonic decay rates, if in the nonleptonic decay a spin one meson of arbitrary mass or a pion take the place of the lepton pair. Where the decay constants of those mesons are known, these predictions represent ideal tests of the factorization hypothesis. In other cases they may be used to extract the decay constants. Currently available data on the decays Bˉ0→D+π−, D∗+π−, D+ϱ−, D∗+ϱ−\bar B^0 \to D^+\pi^-,\, D^{*+}\pi^-,\, D^+\varrho^-,\, D^{*+}\varrho^- are shown to be in excellent agreement with the factorization results. A weighted average of the four independent values for the QCD coefficient a1a_1 extracted from the data gives a1=1.15±0.06a_1=1.15\pm 0.06 suggesting that it may be equal to the Wilson coefficient c1(ÎŒ)c_1(\mu) evaluated at the scale ÎŒ=mb\mu = m_b.Comment: (9 pages, ReVTeX, no figures), HD-THEP-92-3

    \Lambda_b \to \Lambda_c P(V) Nonleptonic Weak Decays

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    The two-body nonleptonic weak decays of \Lambda_b \to \Lambda_c P(V) (P and V represent pseudoscalar and vector mesons respectively) are analyzed in two models, one is the Bethe-Salpeter (B-S) model and the other is the hadronic wave function model. The calculations are carried out in the factorization approach. The obtained results are compared with other model calculations.Comment: 18 pages, Late

    Lattice QCD calculation of Bˉ→DlΜˉ\bar{B}\to Dl\bar{\nu} decay form factors at zero recoil

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    A lattice QCD calculation of the Bˉ→DlΜˉ\bar{B}\to Dl\bar{\nu} decay form factors is presented. We obtain the value of the form factor h+(w)h_+(w) at the zero-recoil limit w=1w=1 with high precision by considering a ratio of correlation functions in which the bulk of the uncertainties cancels. The other form factor h−(w)h_-(w) is calculated, for small recoil momenta, from a similar ratio. In both cases, the heavy quark mass dependence is observed through direct calculations with several combinations of initial and final heavy quark masses. Our results are h+(1)=1.007(6)(2)(3)h_+(1) = 1.007(6)(2)(3) and h−(1)=−0.107(28)(04)(3010)h_-(1)=-0.107(28)(04)(^{10}_{30}). For both the first error is statistical, the second stems from the uncertainty in adjusting the heavy quark masses, and the last from omitted radiative corrections. Combining these results, we obtain a precise determination of the physical combination FB→D(1)=1.058(1720)F_{B\to D}(1)=1.058(^{20}_{17}), where the mentioned systematic errors are added in quadrature. The dependence on lattice spacing and the effect of quenching are not yet included, but with our method they should be a fraction of FB→D−1F_{B\to D}-1.Comment: 32 pp, 10 figs; final, published versio

    Bˉ0→π+X\bar B^0 \to \pi^+ X in the Standard Model

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    In this paper we investigate the possibility of studying B→πB\to \pi form factor using the semi-inclusive decays Bˉ0→π++Xq\bar B^0 \to \pi^+ + X_q. In general B→PXB\to PX semi-inclusive decays involve several hadronic parameters. But for Bˉ0→π+Xq\bar B^0 \to \pi^+ X_q decays we find that in the factorization approximation, the only unknown hadronic parameters are the form factors F0,1B→πF^{B\to \pi}_{0,1}. Therefore these form factors can be studied in Bˉ0→π+Xq\bar B^0 \to \pi^+ X_q decays. Using theoretical model calculations for the form factors the branching ratios for Bˉ0→π+Xd(ΔS=0)\bar B^0 \to \pi^+ X_d(\Delta S = 0) and Bˉ0→π+Xs(ΔS=−1)\bar B^0 \to \pi^+ X_s (\Delta S = -1), with the cut Eπ>2.1E_{\pi} > 2.1 GeV, are estimated to be in the ranges of (3.1∌4.9)×10−5(F1B→π(0)/0.33)2(3.1\sim 4.9) \times 10^{-5}(F^{B\to \pi}_1(0)/0.33)^2 and (2.5∌4.2)×10−5(F1B→π(0)/0.33)2(2.5\sim 4.2)\times 10^{-5}(F_1^{B\to \pi}(0)/0.33)^2, respectively, depending on the value of Îł\gamma. The combined branching ratio for Bˉ0→π+(Xd+Xs)\bar B^0 \to \pi^+ (X_d+ X_s) is about 7.4×10−5(F1B→π(0)/0.33)27.4\times 10^{-5} (F^{B\to \pi}_1(0)/0.33)^2 and is insensitive to Îł\gamma. We also discuss CP asymmetries in these decay modes.Comment: RevTex 8 pages and two figure

    Non-perturbatively Improved Heavy-Light Mesons: Masses and Decay Constants

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    We present a study of the heavy-light spectrum and of the D- and B-meson decay constants. The results wer e obtained in the quenched approximation, by using the non-perturbatively improved Clover lattice action at beta=6.2, with a sample of 100 configurations, on a 24^3 x 64 lattice. After a careful analysis of th e systematic errors present in the extraction of the physical results, by assuming quite conservative discretization errors, we find f_Ds=231 +/- 12^{+6}_{-1} MeV, f_D = 211 +/- 14^{+0}_{-12} MeV, f_Ds/f_D=1.10(2), f_Bs = 204 +/- 16^{+28}_{-0} MeV, f_B = 179 +/- 18^{+26}_{-9} MeV, f_Bs/f_B=1.14(3)^{+0}_{-1}. Our results, which have smaller discretization errors than many previous estimates at fixed value of the lattice spacing aa, support a large value of f_B in the quenched approximation.Comment: 26 pages, 9 Postscript figure

    Exploring CP Violation with BcB_c Decays

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    We point out that the pure ``tree'' decays Bc±→Ds±DB_c^\pm\to D^\pm_s D are particularly well suited to extract the CKM angle Îł\gamma through amplitude relations. In contrast to conceptually similar strategies using B±→K±DB^\pm\to K^\pm D or Bd→K∗0DB_d\to K^{\ast0} D decays, the advantage of the BcB_c approach is that the corresponding triangles have three sides of comparable length and do not involve small amplitudes. Decays of the type Bc±→D±DB_c^\pm\to D^\pm D -- the UU-spin counterparts of Bc±→Ds±DB_c^\pm\to D^\pm_s D -- can be added to the analysis, as well as channels, where the Ds±D^\pm_s- and D±D^\pm-mesons are replaced by higher resonances.Comment: 9 pages, LaTeX, 3 figures, reference adde

    The CP violating phase Îł\gamma from global fit of rare charmless hadronic B decays

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    We study constraints on the CP violating phase Îł\gamma in the Kobayashi-Maskawa model using available experimental data. We first follow the conventional method to up date the constraint on Îł\gamma by performing a χ2\chi^2 analysis using data from âˆŁÏ”K∣|\epsilon_K|, ΔmBd,s\Delta m_{B_{d,s}} and ∣Vub/Vcb∣|V_{ub}/V_{cb}|. We also include the recent information on sin⁥2ÎČ\sin2\beta in the analysis. We obtain the best fit for Îł\gamma to be 66∘66^\circ and the 95% C.L. allowed range to be 42∘∌87∘42^\circ \sim 87^\circ. We then develop a method to carry out a χ2\chi^2 analysis based on SU(3) symmetry using data from B→ππB\to \pi \pi and B→KπB\to K \pi. We also discuss SU(3) breaking effects from model estimate. We find that present data on B→ππ,KπB\to \pi\pi, K \pi can also give some constraint on Îł\gamma although weaker than the earlier method limited by the present experimental errors. Future improved data will provide more stringent constraint. Finally we perform a combined fit using data from âˆŁÏ”K∣|\epsilon_K|, ΔmBd,s\Delta m_{B_{d,s}}, ∣Vub/Vcb∣|V_{ub}/V_{cb}|, sin⁥2ÎČ\sin2\beta and rare charmless hadronic B decays. The combined analysis gives Îł=67∘\gamma=67^\circ for the best fit value and 43∘∌87∘43^\circ \sim 87^\circ as the 95% C.L. allowed range. Several comments on other methods to determine Îł\gamma based on SU(3) symmetry are also provided.Comment: Revised verion with the new experimental data from Belle and Babar included in the analysis to obtain the global fit for the CP violating phase gamma. RevTex, 32 pages and 8 figure

    1/m_Q Corrections to the Bethe-Salpeter Equation for \Lambda_{Q} in the Diquark Picture

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    Corrections of order 1/m_Q (Q=b or c) to the Bethe-Salpeter (B-S) equation for \Lambda_Q are analyzed on the assumption that the heavy baryon \Lambda_Q is composed of a heavy quark and a scalar, light diquark. It is found that in addition to the one B-S scalar function in the limit m_Q -> \infty, two more scalar functions are needed at the order 1/m_Q. These can be related to the B-S scalar function in the leading order. The six form factors for the weak transition \Lambda_b -> \Lambda_c are expressed in terms of these wave functions and the results are consistent with heavy quark effective theory to order 1/m_Q. Assuming the kernel for the B-S equation in the limit m_Q -> \infty to consist of a scalar confinement term and a one-gluon-exchange term we obtain numerical solutions for the B-S wave functions, and hence for the Λb→Λc\Lambda_b \to \Lambda_c form factors to order 1/m_Q. Predictions are given for the differential and total decay widths for \Lambda_b -> \Lambda_c l \bar{\nu}, and also for the nonleptonic decay widths for \Lambda_b -> \Lambda_c plus a pseudoscalar or vector meson, with QCD corrections being also included.Comment: Latex, 24 pages, two figure

    Weak Decays in the light--front Quark Model

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    We study the form factors of heavy--to--heavy and heavy--to--light weak decays using the light--front relativistic quark model. For the heavy--to--heavy B \ra D^{(\ast)} semileptonic decays we calculate the corresponding Isgur--Wise function for the whole kinematic region. For the heavy--to--light B\ra P and B\ra V semileptonic decays we calculate the form factors at q2=0q^2 = 0; in particular, we have derived the dependence of the form factors on the bb--quark mass in the m_b \ra \infty limit. This dependence can not be produced by extrapolating the scaling behavior of the form factors at qmax2q^2_{max} using the single--pole assumption. This shows that the q2q^2 dependence of the form factors in regions far away from the zero--recoil could be much more complicated than that predicted by the single--pole assumption.Comment: 24 pages, Latex, Postscript figure included at the en

    Combining CP Asymmetries in B→KπB \to K \pi Decays

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    We prove an approximate relation, to leading order in dominant terms, between CP-violating rate differences in B0/Bˉ0→K±π∓B^0/\bar{B}^0 \to K^{\pm}\pi^{\mp} and B±→K±π0B^{\pm} \to K^{\pm}\pi^0. We show how data from these two processes may be combined in order to enhance the significance of a nonzero result.Comment: 9 pages, latex, no figures, submitted to Phys. Rev. Letters, revise
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