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Stephan Narison

Publications and source records attributed to Stephan Narison.

79 records · Page 5Linked to original sources
arXiv1996

Heavy quarkonia mass-splittings in QCD: test of the $1/m$-expansion and estimates of $<α_s G^2>$ and $α_s$

I present a more refined analysis of the mass-splittings between the different heavy quarkonia states, using {\it new double ratios} of exponential moments of different two-point functions. Then, I test the validity of the $1/m$-expansion, extract $α_s(M_Z)=0.127\pm 0.011$ from $M_{χ_c(P^1_1)} - M_{χ_c(P^3_1)}$, and provide a new estimate of the gluon condensate from $M_ψ-M_{η_c}$ and $M_{χ_b}-M_Υ$, which combined with the recent estimate from the $τ$-like decay sum rules in $e^+e^-\rar I=1$ hadrons data, leads to the {\it update average value} $\laα_s G^2\ra = (7.1\pm 0.9)\times 10^{-2}$ GeV$^4$ from the light and heavy quark systems. I also find $M_Υ-M_{η_b}\approx 63^{-29}_{+51}$ MeV implying the possible observation of the $η_b$ in the $Υ$-radiative decay.

hep-ph↗
arXiv1996

Heavy quarkonia mass-splittings in QCD: test of the $1/m$-expansion and estimates of $<α_s G^2>$ and $α_s$

New double ratios of exponential moments of different two-point functions, which are less sensitive to the heavy quark mass and to the continuum effects than the commonly used ratio of moments, are presented for a more refined analysis of the mass-splittings between the different heavy quarkonia states. We show that at the $c$ and $b$ quark mass scales the $1/m$-expansion does not converge for these quarkonia channels, while a connection of our mass and width formulae, with the potential model ones is done. Using the present value of the QCD coupling $α_s$, we deduce the value: $<α_s G^2> = (7.5\pm 2.5)\times 10^{-2}$ GeV$^4$ of the gluon condensate from $M_ψ- M_{η_c}$ and $M_{χ_b} - M_Υ$, which we compare with the ones from different fits of the heavy and light quark channels. We also find that $M_{χ_c(P^1_1)} - M_{χ_c(P^3_1)}$ is gouverned by the radiative corrections and gives $α_s$(1.3 GeV) = 0.64$^{+0.36}_{-0.18}$ for 4 flavours, implying $α_s(M_Z) = 0.127\pm 0.011$. Our predictions for the splittings of different heavy quarkonia states are summarized in Table 2, where, in particular, we find $M_Υ-M_{η_b}\approx 63^{-29}_{+51}$ MeV implying the possible observation of the $η_b$ in the $Υ$-radiative decay.

hep-ph↗
arXiv1995

Heavy flavours from QCD spectral sum rules

We present a summary update of the QCD spectral sum rule (QSSR) results for the running and {\it perturbative pole} quark masses, the $f_D$ and $f_B$ leptonic decay constants, the heavy-to-light and heavy-to-heavy exclusive transition-form factors. Analytic expressions of these latter quantities are presented, which give a deeper understanding of their $q^2$- and infinite mass-behaviours. A short comparison of the QSSR results with alternative approaches is done.

hep-ph↗
arXiv1995

Alpha_s from Tau Decays

We review the present status in the determination of the $accurate$ value of $α_s$ from $τ$-decays, where we discuss in detail the different sources of theoretical errors.

hep-ph↗
arXiv1995

QCD SPECTRAL SUM RULES FOR HEAVY FLAVOURS

Recent developments in the uses of QCD spectral sum rules (QSSR) for heavy flavours are summarized and updated. QSSR results are compared with the existing data and with the ones from alternative approaches.

hep-ph↗
arXiv1995

How reliable are the HQET-sum rule predictions?

We test the internal consistencies and the reliability of the existing estimates of the decay constant $f_B$ in the static limit, the meson-quark mass gap $\bar Λ$ and the kinetic energy $K$ of a heavy quark obtained from the heavy quark effective theory (HQET)-sum rules. Finite energy local duality sum rules (FESR) have also been used to fix $approximatively$ the value of the continuum energy and to study the correlations among these different parameters. Then, we deduce to two-loop accuracy: $\bl=(0.65\pm 0.05)$ GeV, $K=-(0.5 \pm 0.2)$GeV^2$, implying the value of the pole mass in HQET: $M_b= (4.61 \pm 0.05)$ GeV. By combining the results from the sum rules in HQET and in the full theory, we obtain $f_B^\infty=(1.98 \pm 0.31)f_π$ and the quadratic mass dependence of the pseudoscalar decay constant: $f_P\sqrt{M_P}=(0.33 \pm 0.06)$GeV$^{3/2}\als^{1/β_1}2}\als^{1/β_1 1-2\als/3π-1.1/M_Q +0.7/M_Q^2 .$

hep-ph↗