arXiv subjects

S. Narison

Publications and source records attributed to S. Narison.

68 records · Page 4Linked to original sources

arXiv1995

$B^Bπ(γ)$ couplings and $D^\rar Dπ(γ) $-decays within a $1/M$-expansion in $full$ QCD

To leading order in $α_s$, we evaluate the leading and non-leading $1/M_b$ corrections to the $B^*Bπ$ and $B^*Bγ$ 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 $B\rar π(ρ) l\bar ν$ 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 $B^{*}\rar Bγ$, 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 $D^{*-}\rar D^-γ$ and $D^{*0}\rar D^0γ$ decays. Our $best$ numerical predictions {\it without any free parameters} for the $B^*$-meson are: $g_{B^{*-}B^0π^-}\simeq 14\pm 4$, $Γ_{B^{*-}\rar B^-γ}\simeq (0.10\pm 0.03)$ keV and the large charge dependence of the ratio: ${Γ_{B^{*-}\rar B^- γ}}/ {Γ_{B^{*0}\rar B^0 γ}}\simeq 2.5~$. For the $D^*$-meson, we find: $Γ_{D^{*-}\rar D^0π^-}\simeq 1.54Γ_{D^{*0}\rar D^0π^0} \simeq (8\pm 5)$ keV, $Γ_{D^{*-}\rar D^-γ}\simeq (0.09^{+0.40}_{-0.07} )$ keV and $Γ_{D^{*0}\rar D^0γ}\simeq (3.7\pm 1.2)$ keV, where the branching ratios agree within the errors with the present data, while the total widths $Γ_{D^{*0}\rar all} \simeq (11\pm 4)$ keV and $Γ_{D^{*-}\rar all}\simeq (12\pm 7)$ keV are much smaller than the present experimental upper limits.

hep-ph↗

arXiv1995

Model-independent determination of $\overline{m}_s$ from $τ$-like inclusive decays in $e^+e^-$ and implications for the $χSB$-parameters

We determine the strange quark running mass of the $\overline{MS}$-scheme by $simulating$ $τ$-$like$ inclusive processes for the $old$ Das-Mathur-Okubo sum rule relating the $e^+e^-$ into $I=0$ and $I=1$ hadrons total cross-sections data. We obtain to three-loop accuracy: $\overline{m}_s$(1 GeV)=($196.7\pm 29.1$) MeV. By combining this result with the pseudoscalar sum rule estimate of $(\overline{m}_d +\overline{m}_u)$ and the standard current algebra values of the light quark mass ratios, we deduce the $average$: $\overline{m}_d$(1 GeV)=$(10.3\pm 1.5)$ MeV, $\overline{m}_u$(1 GeV)=$(5.0\pm 1.5)$ MeV and $\frac{1}{2}\la \bar uu +\bar dd \ra$ (1 GeV) $ \simeq -[(228.6\pm 9.1) \mbox{MeV}]^3$. Using also our value of $m_s$, we update the estimates of the $K'(1.46)$ and $K^*_0(1.43)$ decay constants and of the (pseudo)scalar two-point correlator subtraction constants. Then, we deduce a deviation of about 34\% from kaon PCAC and the ratio of the {\it normal-ordered} condensates: $\la \bar ss \ra /\la \bar uu \ra = 0.68^{+0.15}_{-0.29}$, which confirm previous findings from QCD spectral sum rules. Finally, using the recent value of the $\overline{m}_b$ from the $Υ$-sum rules, we deduce the scale independent quark-mass ratio: $m_b/m_s=34\pm 4$.

hep-ph↗

arXiv1995

QCD tests from $e^+e^- \rar I=1~$ hadrons data and implication on the value of $α_s$ from $τ$-decays

We re-examine the estimate of $\als$ and of the QCD condensates from $e^+e^-\rar I=1$ hadrons data. We conclude that $e^+e^-$ at low energies gives a value of $Λ$ compatible with the one from LEP and from tau inclusive decay. Using a $τ$-like inclusive process and QCD spectral sum rules, we estimate the size of the $D$=4 to 9 condensates by a fitting procedure {\it without invoking stability criteria}. We find $\la \als G^2 \ra =(7.1\pm 0.7)10^{-2}$ GeV$^4$, $ρ\als\la \bar uu\ra^2= (5.8\pm 0.9)10^{-4}$ GeV$^6$, which confirm previous sum rules estimate based on stability criteria. The corrections due to the $D=8$ condensates and to instantons on the vector component of $τ$-decay are respectively $δ^{(8)}_1= -(1.5\pm 0.6)10^{-2}(1.78/M_τ)^8$ and $δ^{(9)}_1=-(7.0\pm 26.5)10^{-4}(1.78/M_τ)^9 $, which indicate that the $δ^{(8)}_1$ is one order magnitude higher than the vacuum saturation value, while the $D\geq 9$ instanton-like contribution to the the vector component of the $τ$-decay width is a negligible correction. We also show that, due to the correlation between the $D=4$ and $1/M^2_τ$ contributions in the ratio of the Laplace sum rules, the present value of the gluon condensate already excludes the recent estimate of the $1/M^2_τ$-term from FESR in the axial-vector channel. Combining our non-perturbative results with the resummed perturbative corrections to the $τ$-width $R_τ$, we deduce from the present data $α_s(M_τ)= 0.33\pm 0.03$.

hep-ph↗

arXiv1994

{$K^0$}-{$\overline{K}^0$} mixing and the CKM parameters $(ρ,η)$ from the Laplace sum rules

Using the Laplace sum rule (LSR) approach, which is less affected by the contribution of the higher mass hadronic states than the Finite Energy Sum Rule (FESR), we test the reliability of the existing estimate of the $K^0$-$\overline {K}^0$ mixing parameter from the four-quark two-point correlator. We obtain, for the renormalization group invariant $B$-parameter $\Big[ f_K/(1.2f_π)\Big]^2 \hat {B}_K$, the upper bound: 0.83 and the $best$ estimate: $0.55 \pm 0.09$. Combining the previous estimate with the updated value of $f_B\sqrt{B_B}=(1.49\pm 0.14)f_π$ obtained from the same LSR method, one can deduce the $best$ fitted values $(ρ,η)\approx (0.41,0.09)$ of the CKM parameters.

hep-ph↗

arXiv1994

A fresh look into the heavy quark-mass values

Using the recent {\it world average} $α_s(M^2_Z)= 0.118 \pm 0.006$, we give the {\it first direct extraction} from the $Ψ$ and $Υ$ data of the values of the {\it running heavy quark masses} within QCD spectral sum rules to two-loops in the $\overline {MS}$-scheme: $\mr_b(M^{PT2}_b)$ = $(4.23~^{+0.03}_{-0.04} \pm 0.02)$ GeV and $\mr_c(M^{PT2}_c)$ = $(1.23~^{+ 0.02}_{-0.04} \pm 0.03)$ GeV, (the errors are respectively due to $\alf$ and to the gluon condensate), and the corresponding value of the {\it short-distance perturbative pole masses to two-loops}: $M^{PT2}_b=(4.62 \pm 0.02)$ GeV, $M^{PT2}_c= (1.41\pm 0.03)$ GeV, which we compare with the updated values of the {\it non-relativistic pole masses} re-extracted {\it directly} from the two-loop non-relativistic sum rules: $M^{NR}_b= (4.69~^{-0.01}_{+0.02} \pm 0.02)$ GeV and $M^{NR}_c=(1.44\pm 0.02\pm 0.03)$ GeV. It is also informative to compare the {\it three-loop} values of the short-distance pole masses: $M^{PT3}_b=(4.87\pm 0.05 \pm 0.02)$ GeV and $M^{PT3}_c= (1.62\pm 0.07 \pm 0.03)$ GeV, with the {\it dressed mass} $M^{nr}_b = (4.94 \pm 0.10 \pm 0.03)$ GeV, entering into the {\it non-relativistic Balmer formula} including higher order $\alf$ corrections. The $small$ mass-differences $M^{NR}_b-M^{PT2}_b \simeq M^{nr}_b-M^{PT3}_b \simeq 70$ MeV and $M_c^{NR}-M_c^{PT2} \simeq (30 \pm 20)$ MeV {\it can measure the size} of the non-perturbative effect induced by {\it renormalon} type-singularities. An analogous analysis is pursued for the heavy-light mesons, where a simultaneous {\it re-fit} of the $B$ and $B^*$ masses from relativistic sum rules leads to: $M_b^{PT2}= (4.63 \pm 0.08)$ GeV,

hep-ph↗

arXiv1994

{$SU(3)$} breaking in {$\bar{B}/D\rar Kl\bar ν$} decays and value of {$V_{cd}/V_{cs}$}}

We determine the $SU(3)$-breaking effects in the $\bar{B}/D \rar Kl\bar ν$ decays from the ratio of the $\bar{B}/D\rar Kl\bar ν$ over the $\bar{B}/D \rar πl\bar ν$ semileptonic form factors using a {\it semi-analytic} expression based on QCD spectral sum rules. We obtain $f_+^{\bar{B}\rar K}(0)/f_+^{\bar{B} \rar π}(0)$ = $1.007\pm 0.020$ and $f_+^{D\rar K}(0)/f_+^{D \rar π}(0)$ = $1.102 \pm 0.007$, which combined with the present CLEO data, leads to $V_{cd}/V_{cs}$ = $ 0.323 \pm 0.058$ and then, to: $\vert V_{cs}\vert = 0.72\pm 0.10$. The prediction on the ratio of mixing angle is (surprisingly) much higher than the value $0.226 \pm 0.004$ derived from the unitarity constraint on the CKM matrix, while the corresponding value of $ V_{cs}$ is lower. These results can open a window for new physics, though a stringent conclusion needs data with much higher statistics (from e.g tau-charm factory) or/and alternative QCD-based estimates of the ratio of the semileptonic form factors.

hep-ph↗

arXiv1994

Heavy Quarks from QCD Spectral Sum Rules

This is a short review of the present status of the dynamics of the heavy quarks extracted from QCD spectral sum rules. We discuss the determination of the ``perturbative" quark mass, the decay constants of the $D$ and $B$ mesons, the form factors of the semileptonic and radiative decays of the $B$ mesons, the slope of the Isgur--Wise function and the emerged value of $V_{cb}$. We mention shortly some properties of the hybrid and $B_c$ mesons.

hep-ph↗

arXiv1994

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 ($\bar B\rar ρ~(π)$ semileptonic as well as the $ B\rar ργ$ 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: $Γ_{\bar B\rar πe\bar ν} \simeq (4.3 \pm 0.7)

hep-ph↗

arXiv1994

Simple But Efficient Tests of QCD from Tau Decays$^{*)}$

We review the determinations of the QCD coupling $α_s$ from the inclusive and exclusive modes of $τ$-decays. The most recent $τ$-data provide the average value $ α_ s \left(M^2_τ\right)\simeq 0.347\pm 0.030 $ corresponding to $ α_ s \left(M^2_Z \right) \simeq 0.121\pm 0.003 \pm 0.001.$ The values of the QCD vacuum condensates extracted from the inclusive weighted-moment distributions are consistent with the ones from QCD spectral sum rules. Accurate estimates and further precision tests should be reached in the next $τ$C/B-factory machines. The $M_τ$-stability test from the $ e^+e^- \longrightarrow I=1 $ hadron data is also discussed.

hep-ph↗

arXiv1994

Target Independence of the Emc-SMC Effect

An approach to deep inelastic scattering is described in which the matrix elements arising from the operator product expansion are factorised into composite operator propagators and proper vertex functions. In the case of polarised $\m p$ scattering, the composite operator propagator is identified with the square root of the QCD topological susceptibility $\sqrt{χ^{\prime}(0)}$, while the corresponding proper vertex is a renormalisation group invariant. We estimate $χ^{\prime}(0)$ using QCD spectral sum rules and find that it is significantly suppressed relative to the OZI expectation. Assuming OZI is a good approximation for the proper vertex, our predictions, $\int_{0}^{1}dx g_1^p (x;Q^2=10\GV^2)= 0.143 \pm 0.005$ and $G^{(0)}_A \equiv ΔΣ= 0.353 \pm 0.052$, are in excellent agreement with the new SMC data. This result, together with one confirming the validity of the OZI rule in the $\hp$ radiative decay, supports our earlier conjecture that the suppression in the flavour singlet component of the first moment of $g_1^p$ observed by the EMC-SMC collaboration is a target-independent feature of QCD related to the $U(1)$ anomaly and is not a property of the proton structure. As a corollary, we extract the magnitude of higher twist effects from the neutron and Bjorken sum rules.

hep-ph↗

arXiv1994

$B \rar K^* \ γ$} from Hybrid Sum Rule

Using the {\it hybrid} moments-Laplace sum rule (HSR), which is well-defined for $M_b \rar \infty$, in contrast with the $popular$ double Borel (Laplace) sum rule (DLSR), which blows up in this limit when applied to the heavy-to-light processes, we show that the form factor of the $B \rar K^* \ γ$ radiative transition is dominated by the light-quark condensate for $M_b \rar \infty$ and behaves like $\sqrt M_b$. The form factor is found to be $ F^{B\rar K^*}_1(0) \simeq (30.8 \pm 1.3 \pm 3.6 \pm 0.6)\times 10^{-2}, $ where the errors come respectively from the procedure in the sum rule analysis, the errors in the input and in the $SU(3)_f$-breaking parameters. This result leads to $Br(B\rar K^* \ γ) \simeq (4.45 \pm 1.12) \times 10^{-5}$ in agreement with the recent CLEO data. Parametrization of the $M_b$-dependence of the form factor including the $SU(3)_f$-breaking effects is given in (26), which leads to $F^{B\rar K^*}_1(0)/ F^{B\rar ρ}_1(0) \simeq (1.14 \pm 0.02)$.

hep-ph↗

arXiv1994

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

We estimate the sum of the $Υ\bar BB $ couplings using QCD Spectral Sum Rules (QSSR). Our result implies the phenomenological bound $ξ'(vv'=1) \geq -1.04$ 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 $ξ'(vv'=1) \simeq -(1.00 \pm 0.02)$ 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 $\vert V_{cb} \vert \simeq \ga 1.48 \mbox{ps}/τ_B \dr ^{1/2}(37.3 \pm 1.2 \pm 1.4)\times 10^{-3}$ where the first error comes from the data analysis and the second one from the different model parametrizations of the Isgur-Wise function.

hep-ph↗

arXiv1994

Precise Determination of {$f_{P_{s}}/f_P$}} {\bf and Measurement of the ``Perturbative'' Pole Mass from {$f_P$}}

We present a compact analytic two-loop expression of the $SU(3)_f$ breaking effects on the ratio of the pseudoscalar decay constants $R_P \equiv f_{P_S}/f_P$ ($P \equiv D,B $), from which, we extract the precise values : $R_D = 1.15 \pm .04$, $R_B = 1.16 \pm .05 $, where the errors are mainly due to the uncalculated $α_s^2$-corrections. We also scan carefully the $M_c$ (resp. $M_b$) mass dependence of $f_D$ (resp. $f_B$) in view of precise measurements of the ``perturbative'' c and b pole quark masses from the future data of the decay constants $f_P$.

hep-ph↗

arXiv1994

QSSR estimate of the $B_B$ parameter at next-to-leading order

We compute the leading $α_s$ corrections to the two-point correlator of the $O_{ΔB=2}$ 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\%.

hep-ph↗