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V. Gimenez

Publications and source records attributed to V. Gimenez.

72 records · Page 4Linked to original sources
arXiv1998

New Results From Lattice QCD: Non-Perturbative Renormalization and Quark Masses

For the first time, we compute non-perturbatively, i.e. without lattice perturbation theory, the renormalization constants of two-fermion operators in the quenched approximation at $β=6.0$, 6.2 and 6.4 using the Wilson and the tree-level improved SW-Clover actions. We apply these renormalization constants to fully non-perturbatively estimate quark masses in the $\bar{MS}$ scheme from lattice simulations of both the hadron spectrum and the Axial Ward Identity in the quenched approximation. Some very preliminary unquenched Wilson results obtained from the gluon configurations generated by the T$χ$L Collaboration at $β=5.6$ and $N_{f}=2$ are also discussed.

hep-ph↗
arXiv1998

B-parameters for $ΔS = 2$ SUSY Operators

We present the first lattice measurement, using Non Perturbative Renormalization Method, of the B-parameters of the dimension-six four-fermion operators relevant for the supersymmetric corrections to the $ΔS=2$ transitions.

hep-lat↗
arXiv1998

Quark masses and the chiral condensate with a non-perturbative renormalization procedure

We determine the quark masses and the chiral condensate in the MSbar scheme at NNLO from Lattice QCD in the quenched approximation at beta=6.0, beta=6.2 and beta=6.4 using both the Wilson and the tree-level improved SW-Clover fermion action. We extract these quantities using the Vector and the Axial Ward Identities and non-perturbative values of the renormalization constants. We compare the results obtained with the two methods and we study the O(a) dependence of the quark masses for both actions.

hep-lat↗
arXiv1998

Non-perturbative Renormalization of Quark bilinears

We compute non-perturbatively the renormalization constants of quark bilinears on the lattice in the quenched approximation at three values of the coupling beta=6/g_0^2=6.0,6.2,6.4 using both the Wilson and the tree-level improved SW-Clover fermion action. We perform a Renormalization Group analysis at the next-to-next-to-leading order and compute Renormalization Group invariant values for the constants. The results are applied to obtain a fully non-perturbative estimate of the vector and pseudoscalar decay constants.

hep-lat↗
arXiv1997

Lattice B-parameters for $ΔS = 2$ and $ΔI = 3/2$ Operators

We compute several matrix elements of dimension-six four-fermion operators and extract their B-parameters. The calculations have been performed with the tree-level Clover action at $β= 6.0$. The renormalization constants and mixing coefficients of the lattice operators have been obtained non-perturbatively. In the $\MSbar$ renormalization scheme, at a renormalization scale $μ\simeq 2$ GeV, we find $B_K (B_9^{3/2}) = 0.66(11), B_7^{3/2} = 0.72(5)$ and $B_8^{3/2} = 1.03(3)$. The result for $B_8^{3/2}$ has important implications for the calculation of $ε^\prime / ε$.

hep-lat↗
arXiv1997

Non-perturbative Renormalization of the Complete Basis of Four-fermion Operators and B-parameters

We present results on the B-parameters $B_K$, $B^{3/2}_7$ and $B^{3/2}_8$, at $β=6.0$, with the tree-level Clover action. The renormalization of the complete basis of dimension-six four-fermion operators has been performed non-perturbatively. Our results for $B_K$ and $B^{3/2}_7$ are in reasonable agreement with those obtained with the (unimproved) Wilson action. This is not the case for $B^{3/2}_8$. We also discuss some subtleties arising from a recently proposed modified definition of the B-parameters.

hep-lat↗
arXiv1997

Matrix elements of four-fermion operators in the HQET

The B-$\bar B$ mixing, B-meson lifetimes, the $B_{s}$-$\bar{B}_{s}$ lifetime difference and SUSY FCNC effects in $ΔB=2$ processes are very important measurable quantities in B-meson phenomenology whose theoretical predictions depend on unknown matrix elements of several four-fermion operators. We present preliminary results for the matrix elements of the relevant four-fermion operators computed on a sample of 600 lattices of size $24^3\times 40$ at $β=6.0$, using the SW--Clover action for light quarks with rotated light quark propagators and the lattice version of the HQET for heavy quarks. As a necessary ingredient of the calculation, we also present results for the next-to-leading order matching of the full theory to the lattice HQET (one- and two-loop anomalous dimensions, one-loop QCD-HQET matching coefficients and one-loop continuum-lattice HQET matching coefficients).

hep-lat↗
arXiv1997

$B - \bar B$ Mixing in the HQET

We present a high statistics, quenched lattice calculation of the B-parameters $B_{B_d}$ and $B_{B_s}$, computed at lowest order in the HQET. The results were obtained using a sample of 600 quenched gauge field configurations, generated by Monte Carlo simulation at $β=6.0$ on a $24^{3}\times 40$ lattice. For the light quarks the SW-Clover action was used; the propagator of the lattice HQET was also tree-level improved. Our best estimate of the renormalization scale independent B-parameter is $\hat{B}_{B_d} = 1.03 \pm 0.06 \pm 0.18$. $\hat{B}_{B_d}$ has been obtained by using ``boosted'' perturbation theory to calculate the renormalization constants which relate the matrix elements of the lattice operators to the corresponding amplitudes in the continuum. Due to the large statistics, the errors in the extraction of the matrix elements of the relevant bare operators are rather small. The main systematic error, corresponding to $\pm 0.18$ in the above result, comes from the uncertainty in the evaluation of the renormalization constants, for which the one-loop corrections are rather large. The non-perturbative evaluation of these constants will help to reduce the final error. We also obtain $\hat{B}_{B_s}/\hat{B}_{B_d} = 1.01 \pm 0.01$ and $f^2_{B_s}\hat{B}_{B_s}/f^2_{B_d}\hat{B}_{B_d} = 1.38 \pm 0.07$.

hep-lat↗
arXiv1996

Light Quenched Hadron Spectrum and Decay Constants on different Lattices

In this paper we study O(2000) (quenched) lattice configurations from the APE collaboration, for different lattice volumes and for 6.0 \le beta \le 6.4 using both the Wilson and the SW-Clover fermion actions. We determine the light hadronic spectrum and meson decay constants and study the mesonic dispersion relation. We extract the hadronic variable J and the strange quark mass in the continuum at the next-to-leading order obtaining m_s^{MSbar}(mu=2 GeV) = 122 +/- 20 MeV. A study is made of their dependence on lattice spacing. We implement a newly developed technique to extract the inverse lattice spacing using data at the simulated values of the quark mass (i.e. at masses around the strange quark mass).

hep-lat↗
arXiv1996

Light Quenched Hadron Spectrum and Decay Constants on different Lattices

We present a study of ${\cal O}(2000)$ (quenched) lattice configurations from the APE collaboration, for $6.0\leβ\le 6.4$ using both the Wilson and the SW-Clover fermion action. We determine the light hadronic spectrum and meson decay constants. We extract the inverse lattice spacing using data at the simulated values of the quark mass. We find an agreement with the experimental data of $\sim 5%$ for mesonic masses and $\sim 10%-15%$ for baryonic masses and pseudoscalar decay constants. A larger deviation is present for the vector decay constants.

hep-lat↗
arXiv1996

B Physics on the Lattice: $\overlineΛ$, $λ_{1}$, $\overline{m}_{b}(\overline{m}_{b})$, $λ_2$, $B^{0}-\bar{B}^{0}$ mixing, $\fb$ and all that

We present a short review of our most recent high statistics lattice determinations in the HQET of the following important parameters in B physics: the B--meson binding energy, $\overlineΛ$ and the kinetic energy of the b quark in the B meson, $λ_1$, which due to the presence of power divergences require a non--perturbative renormalization to be defined; the $\overline{MS}$ running mass of the b quark, $\overline{m}_{b}(\overline{m}_{b})$; the $B^{*}$--$B$ mass splitting, whose value in the HQET is determined by the matrix element of the chromo--magnetic operator between B meson states, $λ_2$; the B parameter of the $B^{0}$--$\bar{B}^{0}$ mixing, $B_{B}$, and the decay constant of the B meson, $f_{B}$. All these quantities have been computed using a sample of $600$ gauge field configurations on a $24^{3}\times 40$ lattice at $β=6.0$. For $\overlineΛ$ and $\overline{m}_{b}(\overline{m}_{b})$, we obtain our estimates by combining results from three independent lattice simulations at $β=6.0$, $6.2$ and $6.4$ on the same volume.

hep-lat↗
arXiv1996

A High-Statistics Lattice Calculation of $λ_1$ and $λ_2$ in the $B$ meson

We present a high-statistics lattice calculation of the kinetic energy $-λ_1/2 m_b$ of the heavy quark inside the $B$-meson and of the chromo-magnetic term $λ_2$, related to the $B^*$--$B$ mass splitting, performed in the HQET. Our results have been obtained from a numerical simulation based on 600 gauge field configurations generated at $β=6.0$, on a lattice volume $24^3 \times 40$ and using, for the meson correlators, the results obtained with the SW-Clover $O(a)$ improved lattice action for the light quarks. For the kinetic energy we found $-λ_1=\langle B \vert \bar h (i\vec{D})^{2} h \vert B \rangle /(2 M_B )=-(0.09 \pm 0.14)$~GeV$^2$, which is interesting for phenomenological applications. We also find $λ_2= 0.07 \pm 0.01$ GeV$^2$, corresponding to $M^2_{B^*}-M^2_B= 4 λ_2= 0.280 \pm 0.060 $ GeV$^2$, which is about one half of the experimental value. The origin of the discrepancy with the experimental number needs to be clarified.

hep-lat↗
arXiv1996

A High Statistics Lattice Calculation of The B-meson Binding Energy

We present a high statistics lattice calculation of the B--meson binding energy $\overlineΛ$ of the heavy--quark inside the pseudoscalar B--meson. Our numerical results have been obtained from several independent numerical simulations at $β=6.0$, $6.2$ and $6.4$, and using, for the meson correlators, the results obtained by the APE group at the same values of $β$. Our best estimate, obtained by combining results at different values of $β$, is $\overlineΛ=180^{+30}_{-20}$ MeV. For the $\overline{MS}$ running mass, we obtain $\overline{m}_{b}(\overline{m}_{b})=4.15 \pm 0.05 \pm 0.20$ GeV, in reasonable agreement with previous determinations. The systematic error is the truncation of the perturbative series in the matching condition of the relevant operator of the Heavy Quark Effective Theory.

hep-lat↗
arXiv1995

Non-perturbative renormalization of the $ΔS=2$ operator and the heavy-light axial current

We apply a recently introduced non-perturbative renormalization method to two types of lattice operators: the $ΔS=2$ four fermion operator and the heavy-light static axial current, which are relevant for the physics of $K$ and $B$ mesons respectively. The results of the non-perturbative calculations of the renormalization constants are compared with the corresponding perturbative ones.

hep-lat↗
arXiv1995

First Lattice Calculation of The B-meson Binding and Kinetic Energies

We present the first lattice calculation of the B-meson binding energy $\labar$ and of the kinetic energy $-λ_1/2 m_Q$ of the heavy-quark inside the pseudoscalar B-meson. This calculation has required the non-perturbative subtraction of the power divergences present in matrix elements of the Lagrangian operator $\bar h D_4 h$ and of the kinetic energy operator $\bar h \vec D^2 h$. The non-perturbative renormalisation of the relevant operators has been implemented by imposing suitable renormalisation conditions on quark matrix elements, in the Landau gauge. Our numerical results have been obtained from several independent numerical simulations at $β=6.0$ and $6.2$, and using, for the meson correlators, the results obtained by the APE group at the same values of $β$. Our best estimate, obtained by combining results at different values of $β$, is $\labar =190 \err{50}{30}$ MeV. For the $\overline{MS}$ running mass, we obtain $\overline {m}_b(\overline {m}_b) =4.17 \pm 0.06$ GeV, in reasonable agreement with previous determinations. From a subset of 36 configurations, we were only able to establish a loose upper bound on the $b$-quark kinetic energy in a $B$-meson, $λ_1=\langle B \vert \bar h \vec{D}^{2} h \vert B \rangle /(2 M_B )<$~1\, GeV$^2$. This shows that a much larger statistical sample is needed to determine this important parameter.

hep-ph↗
arXiv1995

Renormalization of the effective theory for heavy quarks at small velocity

The slope of the Isgur-Wise function at the normalization point, $ξ^{(1)}(1)$,is one of the basic parameters for the extraction of the $CKM$ matrix element $V_{cb}$ from exclusive semileptonic decay data. A method for measuring this parameter on the lattice is the effective theory for heavy quarks at small velocity $v$. This theory is a variant of the heavy quark effective theory in which the motion of the quark is treated as a perturbation. In this work we study the lattice renormalization of the slow heavy quark effective theory. We show that the renormalization of $ξ^{(1)}(1)$ is not affected by ultraviolet power divergences, implying no need of difficult non-perturbative subtractions. A lattice computation of $ξ^{(1)}(1)$ with this method is therefore feasible in principle. The one-loop renormalization constants of the effective theory for slow heavy quarks are computed to order $v^2$ together with the lattice-continuum renormalization constant of $ξ^{(1)}(1)$ . We demonstrate that the expansion in the heavy-quark velocity reproduces correctly the infrared structure of the original (non-expanded) theory to every order. We compute also the one-loop renormalization constants of the slow heavy quark effective theory to higher orders in $v^2$ and the lattice-continuum renormalization constants of the higher derivatives of the $ξ$ function. Unfortunately, the renormalization constants of the higher derivatives are affected by ultraviolet power divergences, implying the necessity of numerical non-perturbative subtractions. The lattice computation of higher derivatives of the Isgur-Wise function seems therefore problematic.

hep-lat↗
arXiv1994

Renormalons on the Lattice

We present the first lattice calculation of the B-meson binding energy $\labar$ and of the kinetic energy $λ_1/2 m_Q$ of the heavy-quark inside the pseudoscalar B-meson. In order to cancel the ambiguities due to the ultraviolet renormalons present in the operator matrix elements, this calculation has required the non-perturbative subtraction of the power divergences present in the Lagrangian operator $\energy$ and in the kinetic energy operator $\kkinetic$. The non-perturbative renormalization of the relevant operators has been implemented by imposing suitable renormalization conditions on quark matrix elements in the Landau gauge.

hep-lat↗