Strange quark mass from e+e- revisited and present status of light quark masses

We reconsider the determinations of the strange quark mass m_s from e+e- into hadrons data using a new combination of FESR and revisiting the existing tau-like sum rules by including non-resonant contributions to the spectral functions. To order alpha_s^3 and including the tachyonic gluon mass lambda^2 contribution, which phenomenologically parametrizes the UV renormalon effect into the PT series, we obtain the invariant mass m_s=(119 +- 17)MeV leading to: m_s(2 GeV)=(104+- 15)MeV. Combining this value with the recent and independent phenomenological determinations from some other channels, to order alpha_s^3 and including lambda^2, we deduce the weighted average: m_s (2 GeV)=(96.1 +- 4.8)MeV . The positivity of the spectral functions in the (pseudo)scalar [resp. vector] channels leads to the lower [resp. upper] bounds of m_s(2 GeV): (71 +- 4) MeV < m_s(2 GeV) < (151 +- 14) MeV, to order alpha_s^3. Using the ChPT mass ratio r_3 = 2m_s/(m_u+m_d)=24.2 +- 1.5, and the average value of m_s, we deduce: (m_u+m_d)(2 GeV)=(7.9 +- 0.6) MeV, consistent with the pion sum rule result, which, combined with the ChPT value for m_u/m_d, gives: m_d(2 GeV)=(5.1 +- 0.4)MeV and m_u(2 GeV)=(2.8 +- 0.2)MeV. Finally, using (m_u+m_d) from the pion sum rule and the average value of m_s (without the pion sum rule), the method gives: r_3= 23.5 +- 5.8 in perfect agreement with the ChPT ratio, indicating the self-consistency of the sum rule results. Using the value: m_b(m_b)=(4.23 +- 0.06) GeV, we also obtain the model-building useful scale-independent mass ratio: m_b/m_s=50 +- 3.Comment: Updated and improved average values. Version to appear in Phys. Rev.

QSSR estimate of the BBB_B parameter at next-to-leading order

We compute the leading $\alpha_s$ corrections to the two-point correlator of the $O_{\Delta B=2}$ operator which controls the $B^0 \bar B^0$ mixing. Using this result within the QCD spectral sum rules approach and some phenomenologically reasonable assumptions in the parametrization of the spectral function, we conclude that the vacuum saturation values $B_B\simeq B_{B^*}\simeq 1$ are satisfied within 15\%.Comment: 8 pages, LaTeX, CERN-TH.7140/94, PM 93/16, and KEK Preprint 93-184, two figures appended as a PS fil

Mass-splittings of doubly heavy baryons in QCD

We consider (for the first time) the ratios of doubly heavy baryon masses (spin 3/2 over spin 1/2 and SU(3) mass-splittings) using double ratios of sum rules (DRSR), which are more accurate than the usual simple ratios often used in the literature for getting the hadron masses. In general, our results agree and compete in precision with potential model predictions. In our approach, the alpha_s corrections induced by the anomalous dimensions of the correlators are the main sources of the Xi^*_{QQ}- Xi_{QQ} mass-splittings, which seem to indicate a 1/M_Q behaviour and can only allow the electromagnetic decay Xi^*_{QQ} to Xi_{QQ}+ gamma but not to Xi_{QQ}+ pi. Our results also show that the SU(3) mass-splittings are (almost) independent of the spin of the baryons and behave approximately like 1/M_Q, which could be understood from the QCD expressions of the corresponding two-point correlator. Our results can improved by including radiative corrections to the SU(3) breaking terms and can be tested, in the near future, at Tevatron and LHCb.Comment: 8 pages, 12 figures, 2 tables, improved version including radiative corrections, some additional references and a new summary tabl

Isospin violating decay of ψ(3770)→J/ψ+π0\psi(3770)\rightarrow J/\psi + \pi^0

The strong-isospin violation in $\psi(3770)\rightarrow J/\psi + \pi^0$ via intermediate $D$ meson loops is investigated in an effective Lagrangian approach. In this process, there is only one $D$-meson loop contributing to the absorptive part, and the uncertainties due to the introduction of form factors can be minimized. With the help of QCD spectral sum rules (QSSR), we extract the $J/\psi DD^*$ form factor as an implement from the first principle of QCD. The $DD^*\pi^0$ form factor can be well determined from the experimental data for $D\rightarrow\pi l\nu$. The exploration of the dispersion relation suggests the dominance of the dispersive part via the intermediate $D$ meson loops even below the open charm threshold. This investigation could provide further insights into the puzzling question on the mechanisms for $\psi(3770)\to$ non-$D\bar{D}$ transitions.Comment: more discussions and references are added, accepted by Physical Review

Dominance of the light-quark condensate in the heavy-to-light exclusive decays

Using the QCD {\it hybrid} (moments-Laplace) sum rule, we show $semi$-$analytically$ that, in the limit M_b \rar \infty, the $q^2$ and $M_b$ behaviours of the heavy-to-light exclusive (\bar B\rar \rho~(\pi) semileptonic as well as the B\rar \rho\gamma rare) decay--form factors are $universally$ dominated by the contribution of the soft light-quark condensate rather than that of the hard perturbative diagram. The QCD-analytic $q^2$ behaviour of the form factors is a polynomial in $q^2/M^2_b$, which mimics quite well the usual pole parametrization, except in the case of the $A_1^B$ form factor, where there is a significant deviation from this polar form. The $M_b$-dependence of the form factors expected from HQET and lattice results is recovered. We extract with a good accuracy the ratios: $V^B(0)/A^B_1(0) \simeq A^B_2(0)/A^B_1(0) \simeq 1.11\pm 0.01$, and $A^B_1(0)/F^B_1(0) \simeq 1.18 \pm 0.06$; combined with the ``world average" value of $f^B_+(0)$ or/and $F^B_1(0)$, these ratios lead to the decay rates: $\Gamma_{\bar B\rar \pi e\bar \nu} \simeq (4.3 \pm 0.7)Comment: 10 pages, CERN-TH 7237/94 (the previous version contains numerical errors). Latex file (run twice) 3 ps.figures available by mai

B∗Bπ(γ)B^*B\pi(\gamma) couplings and D^*\rar D\pi(\gamma) -decays within a 1/M1/M-expansion in fullfull QCD

To leading order in $\alpha_s$, we evaluate the leading and non-leading $1/M_b$ corrections to the $B^*B\pi$ and $B^*B\gamma$ couplings using QCD spectral moment sum rules in the full theory. We find that, for large $M_b$ and contrary to the heavy-to-light B\rar \pi(\rho) l\bar \nu form factors, which are dominated by the $soft$ light quark vacuum condensate, these couplings are governed by the $hard$ perturbative graph, like other heavy-to-heavy transitions. We also find that for the B^{*}\rar B\gamma, the $1/M_b$ correction is mainly due to the perturbative and light quark condensate contributions originating from the graphs involving the heavy quark part of the electromagnetic current, which are essential for explaining the large charge dependence in the observed D^{*-}\rar D^-\gamma and D^{*0}\rar D^0\gamma decays. Our $best$ numerical predictions {\it without any free parameters} for the $B^*$-meson are: $g_{B^{*-}B^0\pi^-}\simeq 14\pm 4$, \Gamma_{B^{*-}\rar B^-\gamma}\simeq (0.10\pm 0.03) keV and the large charge dependence of the ratio: {\Gamma_{B^{*-}\rar B^- \gamma}}/ {\Gamma_{B^{*0}\rar B^0 \gamma}}\simeq 2.5~. For the $D^*$-meson, we find: \Gamma_{D^{*-}\rar D^0\pi^-}\simeq 1.54\Gamma_{D^{*0}\rar D^0\pi^0} \simeq (8\pm 5) keV, \Gamma_{D^{*-}\rar D^-\gamma}\simeq (0.09^{+0.40}_{-0.07} ) keV and \Gamma_{D^{*0}\rar D^0\gamma}\simeq (3.7\pm 1.2) keV, where the branching ratios agree within the errors with the present data, while the total widths \Gamma_{D^{*0}\rar all} \simeq (11\pm 4) keV and \Gamma_{D^{*-}\rar all}\simeq (12\pm 7) keV are much smaller than the present experimental upper limits.Comment: published version to appear in Phys. Lett. B (minor modifications compared with the previous version

The B_{s0} meson and the B_{s0}B K coupling from QCD sum rules

We evaluate the mass of the $B_{s0}$ scalar meson and the coupling constant in the $B_{s0} B K$ vertex in the framework of QCD sum rules. We consider the $B_{s0}$ as a tetraquark state to evaluate its mass. We get m_{B_s0}=(6.04\pm 0.08) \GeV, which is bigger than predictions supposing it as a $b\bar{s}$ state or a $B\bar{K}$ bound state with $J^{P}=0^+$. To evaluate the $g_{B_{s0}B K}$ coupling we use the three point correlation functions of the vertex, considering $B_{s0}$ as a normal $b\bar{s}$ state. The obtained coupling constant is: g_{B_{s0} B K} =(16.3 \pm 3.2) \GeV. This number is in agreement with light-cone QCD sum rules calculation. We have also compared the decay width of the \BS\to BK process considering the \BS to be a $b\bar{s}$ state and a $BK$ molecular state. The width obtained for the $BK$ molecular state is twice as big as the width obtained for the $b\bar{s}$ state. Therefore, we conclude that with the knowledge of the mass and the decay width of the \BS meson, one can discriminate between the different theoretical proposals for its structure.Comment: revised version to appear in Phys. Rev.

Upsilon \bar BB Couplings, Slope of the Isgur-Wise Function and Improved Estimate of \boldmath{V_{cb}$}}

We estimate the sum of the $\Upsilon \bar BB$ couplings using QCD Spectral Sum Rules (QSSR). Our result implies the phenomenological bound $\xi'(vv'=1) \geq -1.04$ for the slope of the Isgur-Wise function. An analytic estimate of the (physical) slope to two loops within QSSR leads to the accurate value $\xi'(vv'=1) \simeq -(1.00 \pm 0.02)$ due to the (almost) complete cancellations between the perturbative and non-perturbative corrections at the stability points. Then, we deduce, from the present data, the improved estimate \vert V_{cb} \vert \simeq \ga 1.48 \mbox{ps}/\tau_B \dr ^{1/2}(37.3 \pm 1.2 \pm 1.4)\times 10^{-3} where the first error comes from the data analysis and the second one from the different model parametrizations of the Isgur-Wise function.Comment: {{\bf $\bf 10 pages, Latex, (1 Figure on request), CERN-TH-7103/93 (Phys. Lett. B in press