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Silvano Simula

Publications and source records attributed to Silvano Simula.

At least 91 records · Page 5Linked to original sources
arXiv2013

Mass of the $b$ Quark from QCD Sum Rules for $f_{B_{(s)}}$

We demonstrate that Borel QCD sum rules for heavy-light currents entail a very strong correlation between the $b$-quark mass $m_b$ and the $B$-meson decay constant $f_B,$ that is, $δf_B/f_B\approx-8δm_b/m_b.$ By starting from $f_B$ as input, this observation allows for an accurate sum-rule determination of $m_b.$ Employing precise lattice QCD results for $f_B$ in our sum-rule study based on the three-loop $O(α_s^2)$ heavy-light correlation function implies $\bar{m}_b(\bar{m}_b)=(4.247\pm0.034)$ GeV for the $b$-quark $\bar{\rm MS}$ mass.

hep-ph↗
arXiv2013

Decay Constants of Heavy Pseudoscalar Mesons: Reconciling QCD Sum Rules and Lattice QCD

Exploiting recently proposed novel improvements of the techniques used for extracting from QCD sum rules pivotal hadron characteristics, including their systematic errors, we succeed to achieve a conspicuous agreement of the predictions of QCD sum rules for the decay constants $f_B$ and $f_{B_s}$ of the heavy pseudoscalar mesons $B$ and $B_s,$ which before tended to be slightly too large, with corresponding results from lattice QCD. Adopting for the crucial $b$-quark $\bar{\rm MS}$ mass the value $\bar{m}_b(\bar{m}_b)=(4.247\pm0.034)$ GeV, we get $f_B=(192.0\pm14.6)$ MeV and $f_{B_s}=(228.0\pm19.8)$ MeV; clearly, this may be also viewed as a determination of the $b$-quark mass from sufficiently precise decay constants.

hep-ph↗
arXiv2013

Accurate bottom-quark mass from Borel QCD sum rules for $f_B$ and $f_{B_s}$

We prove that Borel QCD sum rules for heavy-light currents yield very strong correlations between the $b$-quark mass $m_b$ and the $B$-meson decay constant $f_B$, namely, $δf_B/f_B\approx -8\,δm_b/m_b$. This fact opens the possibility of an accurate sum-rule extraction of $m_b$ by using $f_B$ as input. Combining precise lattice QCD determinations of $f_B$ with our sum-rule analysis based on the three-loop $O(α_s^2)$ heavy-light correlation function leads to $\bar{m}_b(\bar{m}_b)=(4.247\pm0.034)\;\mbox{GeV}$.

hep-ph↗
arXiv2012

Quark mass and chiral condensate from the Wilson twisted mass lattice quark propagator

In this work, we report about the determination of nonperturbative OPE parameters from fits of continuum perturbation theory to the Landau gauge quark propagator. The propagators are computed numerically using lattice QCD with Nf=2 dynamical Wilson twisted mass fermions. We use four different values of the lattice spacing ranging from about 0.1 fm to about 0.05 fm as well as several quark masses per lattice spacing. This allows us to obtain continuum results for the chiral condensate and the average up/down quark mass. The main results are the average up/down quark mass m_q = 3.0(4)(2) MeV at the physical point and a value of the chiral condensate of -(299(26)(29) MeV)^3 in the chiral limit, both in the MSbar scheme at 2 GeV. We have also studied nonperturbative contaminations of our results at small values of the momenta, which are often interpreted as the contribution of the gluon condensate A^2. We do see contributions from such terms, which are, however, not stable over the order in perturbation theory.

hep-lat↗
arXiv2012

Charmed-Meson Decay Constants from Improved QCD Sum Rules

The decay constants of the charmed heavy pseudoscalar D and D_s mesons are revisited within a recently developed novel approach to dispersive QCD sum rules which relies on an unprejudiced implementation of quark-hadron duality. The proposed modification of the conventional sum-rule techniques is assessed by applying our prescriptions to quantum mechanics, where exact solutions may be easily obtained by simply solving the Schrödinger equation. The very striking similarity of the extraction procedures of bound-state parameters in potential models and in QCD gives us great confidence in the reliability of our improvements of the sum-rule formalism and their applicability to hadron phenomenology. The implications of one's chosen definition of the heavy-quark masses are scrutinized and the MS-bar quark-mass scheme is identified as the optimal choice for our purposes. Our ideas turn out to reconcile QCD sum-rule predictions for the charmed-meson decay constants (which before tended to be markedly too low) with the findings of both lattice QCD and experiment.

hep-ph↗
arXiv2012

D-meson decay constants and a check of factorization in non-leptonic B-decays

We compute the vector meson decay constants fD*, fDs* from the simulation of twisted mass QCD on the lattice with Nf = 2 dynamical quarks. When combining their values with the pseudoscalar D(s)-meson decay constants, we were able (i) to show that the heavy quark spin symmetry breaking effects with the charm quark are large, fDs*/fDs = 1.26(3), and (ii) to check the factorization approximation in a few specific B-meson non-leptonic decay modes. Besides our main results, fD* = 278 \pm 13 \pm 10 MeV, and fDs* = 311 \pm 9 MeV, other phenomenologically interesting results of this paper are: fDs*/fD* = 1.16 \pm 0.02 \pm 0.06, fDs*/fD = 1.46 \pm 0.05 \pm 0.06, and fDs/fD* = 0.89 \pm 0.02 \pm 0.03. Finally, we correct the value for B(B0 \rightarrow D+ pi-) quoted by PDG, and find B(B0 \rightarrow D+ pi-) = (7.8 \pm 1.4) \times 10-7. Alternatively, by using the ratios discussed in this paper, we obtain B(B0 \rightarrow D+ pi-) = (8.3 \pm 1.0 \pm 0.8)\times10-7.

hep-lat↗
arXiv2011

Improved QCD Sum-Rule Approach to Heavy-Meson Decay Constants

A visible improvement of the QCD sum-rule framework, achieved only recently by a slightly more sophisticated consideration of the hadron excitations and continuum, is applied to the extraction of the decay constants of heavy-light pseudoscalar mesons from two-point correlators of heavy-light pseudoscalar currents. This analysis is carried out entirely in terms of the running heavy-quark mass, for which the perturbative expansion exhibits a passable convergence. Our main concern is to gain control over both statistical and systematic uncertainties of the extracted decay constants, the former being induced by the QCD parameter values requested for input, the latter arising from the intrinsically limited accuracy of the QCD sum-rule techniques.

hep-ph↗
arXiv2011

Unprejudiced Look at Effective Continuum Thresholds in Borel Dispersive Sum Rules

Dispersive sum rules constitute long-standing tools for extracting hadron features from QCD. We estimate the systematic uncertainties induced by assuming quark-hadron duality and improve the accuracy of the resulting predictions by elevating the effective thresholds involved in this approximation from constants to functions of momenta and a parameter entering upon Borel transformation. A rigorous scrutiny of the applicability of our proposed sum-rule modifications to QCD gives us great confidence that our sum-rule alterations will prove to be fruitful for hadron phenomenology.

hep-ph↗
arXiv2011

Review of lattice results concerning low energy particle physics

We review lattice results relevant for pion and kaon physics with the aim of making them easily accessible to the particle physics community. Specifically, we review the determination of the light-quark masses, the form factor f_+(0), relevant for the semileptonic K -> pi transition at zero momentum transfer as well as the ratio f_K/f_pi of decay constants and discuss the consequences for the elements V_{us} and V_{ud} of the CKM matrix. Furthermore, we describe the results obtained on the lattice for some of the low-energy constants of SU(2)_LxSU(2)_R and SU(3)_LxSU(3)_R Chiral Perturbation Theory and review the determination of the B_K parameter of neutral kaon mixing. We introduce quality criteria and use these when forming averages. Although subjective and imperfect, these criteria may help the reader to judge different aspects of current lattice computations. Our main results are summarized in section 1.2, but we stress the importance of the detailed discussion that underlies these results and constitutes the bulk of the present review.

hep-lat↗
arXiv2011

OPE, charm-quark mass, and decay constants of D and D_s mesons from QCD sum rules

We present a sum-rule extraction of the decay constants of the charmed mesons D and D_s from the two-point correlator of pseudoscalar currents. First, we compare the perturbative expansion for the correlator and the decay constant performed in terms of the pole and the running MSbar masses of the charm quark. The perturbative expansion in terms of the pole mass shows no signs of convergence whereas reorganizing this very expansion in terms of the MSbar mass leads to a distinct hierarchy of the perturbative expansion. Furthermore, the decay constants extracted from the pole-mass correlator turn out to be considerably smaller than those obtained by means of the MSbar-mass correlator. Second, making use of the OPE in terms of the MSbar mass, we determine the decay constants of both D and D_s mesons with an emphasis on the uncertainties in these quantities related both to the input QCD parameters and to the limited accuracy of the method of sum rules.

hep-ph↗
arXiv2010

Heavy-Quark Mass and Heavy-Meson Decay Constants from QCD Sum Rules

We present a sum-rule extraction of heavy-meson decay constants from the two-point correlator of heavy-light pseudoscalar currents. Our main concern is to control the uncertainties of the decay constants, induced by both input QCD parameters and limited accuracy of the sum-rule method. Gaining this control is possible by applying our novel procedure for the extraction of hadron observables utilizing Borel-parameter-depending dual thresholds. For the charmed mesons, we obtain f_D = 206.2 \pm 7.3 (OPE) \pm 5.1 (syst) MeV and f_{D_s} = 245.3 \pm 15.7 (OPE) \pm 4.5 (syst) MeV. For the beauty mesons, the decay constants prove to be extremely sensitive to the exact value of the b-quark MS-bar mass m_b(m_b). Matching our sum-rule prediction for f_B to the lattice findings, the very accurate b-mass value m_b(m_b) = 4.245 \pm 0.025 GeV is found, which yields f_B = 193.4 \pm 12.3 (OPE) \pm 4.3 (syst) MeV and f_{B_s} = 232.5 \pm 18.6 (OPE) \pm 2.4 (syst) MeV.

hep-ph↗
arXiv2010

OPE, Heavy-Quark Mass, and Heavy-Meson Decay Constants from QCD Sum Rules

We present a sum-rule extraction of the decay constants of heavy-light mesons from the two-point correlator of pseudoscalar currents. To this end, we compare the perturbative expansions for the correlator and the decay constant performed in terms of either the pole mass or the running MS-bar mass of the heavy quark. The perturbative expansion expressed in terms of the pole mass exhibits no sign of convergence whereas reorganizing this very expansion in terms of the MS-bar mass yields a rather clear hierarchy of the perturbative contributions. Accordingly, the decay constants extracted from the pole-mass correlator turn out to be considerably smaller than those extracted from its MS-bar-mass counterpart. Then, making use of the OPE in terms of the MS-bar mass we derive the decay constants of heavy mesons with emphasis on acquiring control over the uncertainties in the decay constants, related both to the input QCD parameters and to the limited accuracy of the method of sum rules. Gaining this control has become possible due to the application of our novel procedure for extracting hadron observables based on dual thresholds which depend on the Borel parameter.

hep-ph↗
arXiv2010

Quark-Hadron Duality and Effective Continuum Thresholds in Dispersive Sum Rules

A novel procedure for extracting hadron characteristics from QCD sum rules, based on effective continuum thresholds (necessary for the implementation of quark-hadron duality) which may depend on the involved momenta and on the Borel parameter(s), enables us to quantify the uncertainties induced by the quark-hadron duality approximation and to achieve a significantly higher accuracy of our predictions for the properties of hadronic bound states.

hep-ph↗
arXiv2010

Heavy-meson decay constants from QCD sum rules

We sketch a recent sum-rule extraction of the decay constants of the heavy pseudoscalar mesons D, D_s, B, and B_s from the two-point correlator of heavy-light pseudoscalar currents [1]. Our main emphasis lies on the control over all the uncertainties in the decay constants, related both to the input QCD parameters and to the limited accuracy of the method of sum rules. Gaining this control has become possible by application of our new procedure of extracting hadron observables based on a dual threshold depending on the Borel parameter. For the charmed-meson decay constants, we find f_D=206.2\pm 7.3(OPE) \pm 5.1(syst) MeV, f_Ds=245.3\pm 15.7(OPE) \pm 4.5(syst) MeV. For the beauty mesons, the decay constants turn out to be extremely sensitive to the precise value of the MSbar mass of the b-quark, mb(mb). By requiring our sum-rule estimate to match the average of the lattice determinations of f_B, we extract the rather accurate value mb(mb)=(4.245\pm 0.025) GeV. Feeding this parameter value into our sum-rule formalism leads to the beauty-meson decay constants f_B = 193.4 \pm 12.3(OPE) \pm 4.3(syst) MeV, f_Bs =232.5 \pm 18.6(OPE) \pm 2.4(syst) MeV.

hep-ph↗
arXiv2010

Decay constants of heavy mesons from QCD sum rules

We present a sum-rule extraction of the decay constants of the D, Ds, B, and Bs mesons from the two-point correlator of heavy-light pseudoscalar currents [1]. Our main emphasis is laid on the control over the uncertainties in the decay constants, related both to the input QCD parameters and to the limited accuracy of the method of sum rules. Gaining this control has become possible due to the application of our novel procedure for extracting hadron observables based on a dual threshold depending on the Borel parameter. For charmed mesons, we obtain f_D=206.2\pm 7.3 (OPE)\pm 5.1 (syst) MeV and f_Ds=245.3\pm 15.7 (OPE) \pm 4.5 (syst) MeV. For beauty mesons, the decay constants turn out to be extremely sensitive to the precise value of the MSbar mass of the b-quark, mb(mb). By requiring our sum-rule estimate to match the average of lattice determinations of f_B, a very accurate value is extracted, mb(mb)=4.245\pm 0.025 GeV, yielding f_B = 193.4 \pm 12.3 (OPE) \pm 4.3 (syst) MeV and f_Bs = 232.5 \pm 18.6 (OPE) \pm 2.4 (syst) MeV.

hep-ph↗
arXiv2010

Decay constants of heavy pseudoscalar mesons from QCD sum rules

We revisit the sum-rule extraction of the decay constants of the D, Ds, B, and Bs mesons from the two-point correlator of heavy-light pseudoscalar currents. We use the operator product expansion for this correlator expressed in terms of the MSbar heavy-quark mass, for which the perturbative expansion exhibits a reasonable convergence. Our main emphasis is laid on the control over the uncertainties in the decay constants, related both to the input QCD parameters and to the limited accuracy of the method of sum-rules. This becomes possible due to the application of our procedure of extracting hadron observables that involves as novel feature dual thresholds depending on the Borel parameter. For charmed mesons, we find the decay constants f_D=206.2\pm 7.3(OPE)\pm 5.1(syst) MeV and f_Ds=245.3\pm 15.7(OPE)\pm 4.5(syst) MeV. For beauty mesons, the decay constants turn out to be extremely sensitive to the precise value of mb(mb). By requiring our sum-rule estimate to match the average of the lattice results for f_B, a very accurate value mb(mb)=4.245\pm 0.025 GeV is extracted, leading to f_B=193.4\pm 12.3(OPE)\pm 4.3(syst) MeV and f_Bs=232.5\pm 18.6(OPE)\pm 2.4(syst) MeV.

hep-ph↗
arXiv2010

Effective Continuum Thresholds for Quark-Hadron Duality in Dispersive Sum Rules

Modifying the standard approaches to nonperturbative QCD based on Borel-transformed dispersive sum rules by allowing the effective continuum thresholds required for the implementation of quark-hadron duality to depend on the Borel parameters and on any relevant momentum promises to provide higher accuracy and reliable error estimates for the extracted predictions of hadron characteristics. A careful analysis reveals that the exact effective continuum thresholds do indeed exhibit dependence on the Borel parameter (and on external momenta) and that they are not universal but vary with the correlators under consideration. The striking similarity of our hadron-parameter extraction procedures in QCD, on the one hand, and quantum-theoretical potential models, on the other hand, calls for application of the proposed techniques in QCD.

hep-ph↗