ArcAdiA

First lattice QCD Study of the Σ- --> n axial and vector form factors with SU(3) breaking corrections

2006-12-31T23:00:00Z

First lattice QCD Study of the Σ- --> n axial and vector form factors with SU(3) breaking corrections Guadagnoli, Diego; Lubicz, Vittorio; Papinutto, Mauro; Simula, Silvano 2007 Nuclear Physics B 761 63-91 We present the first quenched lattice QCD study of the form factors relevant for the hyperon semileptonic decay Σ−→nℓν. The momentum dependence of both axial and vector form factors is investigated and the values of all the form factors at zero-momentum transfer are presented. Following the same strategy already applied to the decay K0→π−ℓν, the SU(3)-breaking corrections to the vector form factor at zero-momentum transfer, f1(0), are determined with great statistical accuracy in the regime of the simulated quark masses, which correspond to pion masses above ≈0.7 GeV. Besides f1(0) also the axial to vector ratio g1(0)/f1(0), which is relevant for the extraction of the CKM matrix element Vus, is determined with significant accuracy. Due to the heavy masses involved, a polynomial extrapolation, which does not include the effects of meson loops, is performed down to the physical quark masses, obtaining f1(0)=−0.948±0.029 and g1(0)/f1(0)=−0.287±0.052, where the uncertainties do not include the quenching effect. Adding a recent next-to-leading order determination of chiral loops, calculated within the Heavy Baryon Chiral Perturbation Theory in the approximation of neglecting the decuplet contribution, we obtain f1(0) = −0.988 ± 0.029(lattice) ± 0.040(HBChPT). Our findings indicate that SU(3)-breaking corrections are moderate on both f1(0) and g1(0). They also favor the experimental scenario in which the weak electricity form factor, g2(0), is large and positive, and correspondingly the value of |g1(0)/f1(0)| is reduced with respect to the one obtained with the conventional assumption g2(q2)=0 based on exact SU(3) symmetry.

Dynamical twisted mass fermions with light quarks: simulation and analysis details

2008-11-14T23:00:00Z

Dynamical twisted mass fermions with light quarks: simulation and analysis details ETM Collaboration; Boucaud, Ph.; Dimopoulos, P.; Farchioni, F.; Frezzotti, R.; Gimenez, V.; Herdoiza, G.; Jansen, K.; Lubicz, Vittorio; Michael, C.; Munster, G.; Palao, D.; Rossi, G.C.; Scorzato, L.; Shindler, A.; Simula, Silvano; Sudmann, T.; Urbach, C.; Wenger, U. 2008-11-15 Computer Physics Communications 179 695-715 In a recent paper [ETMC, P. Boucaud et al., Phys. Lett. B 650 (2007) 304, hep-lat/0701012] we presented precise lattice QCD results of our European Twisted Mass Collaboration (ETMC). They were obtained by employing two mass-degenerate flavours of twisted mass fermions at maximal twist. In the present paper we give details on our simulations and the computation of physical observables. In particular, we discuss the problem of tuning to maximal twist, the techniques we have used to compute correlators and error estimates. In addition, we provide more information on the algorithm used, the autocorrelation times and scale determination, the evaluation of disconnected contributions and the description of our data by means of chiral perturbation theory formulae.

Kaon oscillations in the Standard Model and Beyond using Nf=2 dynamical quarks

2008-12-31T23:00:00Z

Kaon oscillations in the Standard Model and Beyond using Nf=2 dynamical quarks Bertone, Valerio; Dimopoulos, Petros; Frezzotti, Roberto; Gimenez, Vicent; Lubicz, Vittorio; Mescia, Federico; Palao, David; Papinutto, Mauro; Rossi, Giancarlo; Simula, Silvano; Vladikas, Anastassios 2009 1-7 We compute non-perturbatively the B-parameters of the complete basis of four-fermion operators needed to study the Kaon oscillations in the SM and in its supersymmetric extension. We perform numerical simulations with two dynamical maximally twisted sea quarks at three values of the lattice spacing on configurations generated by the ETMC. Unwanted operator mixings and O(a) discretization effects are removed by discretizing the valence quarks with a suitable Osterwalder-Seiler variant of the Twisted Mass action. Operators are renormalized non-perturbatively in the RI/MOM scheme. Our preliminary result for BK(RGI) is 0.73(3)(3).

O(a^2) corrections to the one-loop propagator and bilinears of clover fermions with Symanzik improved gluons

2008-12-31T23:00:00Z

O(a^2) corrections to the one-loop propagator and bilinears of clover fermions with Symanzik improved gluons Constantinou, Martha; Lubicz, Vittorio; Panagopoulos, Haralambos; Stylianou, Fotos 2009 Journal of High Energy Physics 10 1-28 We calculate corrections to the fermion propagator and to the Green's functions of all fermion bilinear operators of the form PsibarGammaPsi, to one-loop in perturbation theory. We employ the Wilson/clover action for fermions and the Symanzik improved action for gluons. The novel aspect of our calculations is that they are carried out to second order in the lattice spacing, O(a^2). Consequently, they have addressed a number of new issues, most notably the appearance of loop integrands with strong IR divergences (convergent only beyond 6 dimensions). Such integrands are not present in O(a^1) improvement calculations; there, IR divergent terms are seen to have the same structure as in the O(a^0) case, by virtue of parity under integration, and they can thus be handled by well-known techniques. We explain how to correctly extract the full O(a^2) dependence; in fact, our method is generalizable to any order in a. The O(a^2) corrections to the quark propagator and Green's functions computed in this paper are useful to improve the nonperturbative RI-MOM determination of renormalization constants for quark bilinear operators. Our results depend on a large number of parameters: coupling constant, number of colors, lattice spacing, external momentum, clover parameter, Symanzik coefficients, gauge parameter. To make these results most easily accessible to the reader, we have included them in the distribution package of this paper, as an ASCII file named: Oa2results.m; the file is best perused as Mathematica input.

A proposal for B-physics on current lattices

2010-04-11T22:00:00Z

A proposal for B-physics on current lattices Blossier, Benoit; Dimopoulos, Petros; Frezzotti, Roberto; Herdoiza, Gregorio; Jansen, Karl; Lubicz, Vittorio; Martinelli, Guido; Michael, Chris; Rossi, Giancarlo; Shindler, Andrea; Simula, Silvano; Tarantino, Cecilia; Urbach, Carsten 2010-04-12 JHEP 2010 1-25 A method to extract B-physics parameters (b-quark mass and fB, fBs decay constants) from currently available lattice data is presented and tested. The approach is based on the idea of constructing appropriate ratios of heavy-light meson masses and decay constants, respectively, possessing a precisely known static limit, and evaluating them at various pairs of heavy quark masses around the charm. Via a smooth interpolation in the heavy quark mass from the easily accessible charm region to the asymptotic point, B-physics parameters are computed with a few percent (statistical + systematic) error using recently produced Nf = 2 maximally twisted Wilson fermions data.

An improved Standard Model prediction of BR(B →τν) and its implicationsfor New Physics

2010-02-24T23:00:00Z

An improved Standard Model prediction of BR(B →τν) and its implicationsfor New Physics Bona, Marcella; Ciuchini, Marco; Franco, Enrico; Lubicz, Vittorio; Martinelli, Guido; Parodi, Fabrizio; Pierini, Maurizio; Schiavi, Carlo; Silvestrini, Luca; Sordini, Viola; Stocchi, Achille; Tarantino, Cecilia; Vagnoni, Vincenzo 2010-02-25 Physics Letters B 687 61-69 The recently measured B →τν branching ratio allows to test the Standard Model by probing virtual effects of new heavy particles, such as a charged Higgs boson. The accuracy of the test is currently limited by the experimental error on BR(B → τν) and by the uncertainty on the parameters f B and |Vub|. The redundancy of the Unitarity Triangle fit allows to reduce the error on these parameters and thus to perform a more precise test of the Standard Model. Using the current experimental inputs, we obtain BR(B →τν)SM = (0.84±0.11)×10−4, to be compared with BR(B →τν)exp = (1.73±0.34)×10−4. The Standard Model prediction can be modified by New Physics effects in the decay amplitude as well as in the Unitarity Triangle fit. We discuss how to disentangle the two possible contributions in the case of minimal flavour violation at large tan β and generic loop-mediated New Physics. We also consider two specific models with minimal flavour violation: the Type-II Two Higgs Doublet Model and the Minimal Supersymmetric Standard Model.

fB and fBs with maximally twisted Wilson fermions

2009-12-31T23:00:00Z

fB and fBs with maximally twisted Wilson fermions Blossier, Benoit; Dimopoulos, Petros; Frezzotti, Roberto; Herdoiza, Gregorio; Jansen, Karl; Lubicz, Vittorio; Martinelli, Guido; Michael, Chris; Rossi, Giancarlo; Sanfilippo, Francesco; Shindler, Andrea; Simula, Silvano; Tarantino, Cecilia; Urbach, Carsten; Wagner, Marc 2010 151-158 We present a lattice QCD calculation of the heavy-light decay constants fB and fBs performed with Nf = 2 maximally twisted Wilson fermions, at four values of the lattice spacing. The decay constants have been also computed in the static limit and the results are used to interpolate the observables between the charmand the infinite-mass sectors, thus obtaining the value of the decay constants at the physical b quark mass. Our preliminary results are fB = 191(14)MeV, fBs = 243(14)MeV, fBs/ fB = 1.27(5). They are in good agreement with those obtained with a novel approach, recently proposed by our Collaboration (ETMC), based on the use of suitable ratios having an exactly known static limit.

Status of the Unitarity Triangle Analysis

2008-12-31T23:00:00Z

Status of the Unitarity Triangle Analysis Bona, Marcella; Ciuchini, Marco; Franco, Enrico; Lubicz, Vittorio; Martinelli, Guido; Parodi, Fabrizio; Pierini, Maurizio; Schiavi, Carlo; Silvestrini, Luca; Sordini, Viola; Stocchi, Achille; Tarantino, Cecilia; Vagnoni, Vincenzo 2009 160-163 We present an update of the Unitarity Triangle (UT) analysis, within the Standard Model (SM) and beyond. Within the SM the main novelties are the inclusion in eK of the contributions of x and fe 6= p /4 pointed out by A. J. Buras and D. Guadagnoli, and an accurate prediction of BR(B→tn), by using the indirect determination of |Vub| from the UT fit, which can be compared to the present experimental result. In the generalization of the UT analysis to investigate New Physics (NP) effects, the estimate of x is more delicate and only the effect of fe 6= p /4 has been included. We confirm an hint of NP in the Bs-¯Bs mixing at the 2.9s level, which makes a comparison with new experimental data certainly desired.

Dynamical twisted mass fermions with light quarks

2007-07-04T22:00:00Z

Dynamical twisted mass fermions with light quarks Boucaud, Ph.; Dimopoulos, P.; Farchioni, F.; Frezzotti, R.; Gimenez, V.; Herdoiza, G.; Jansen, K.; Lubicz, Vittorio; Martinelli, G.; McNeile, C.; Michael, C.; Montvay, I.; Palao, D.; Papinutto, Mauro; Pickavance, J.; Rossi, G.C.; Scorzato, L.; Shindler, A.; Simula, Silvano; Urbach, C.; Wenger, U. 2007-07-05 Physics Letters B 650 304-311 We present results of dynamical simulations with 2 flavours of degenerate Wilson twisted mass quarks at maximal twist in the range of pseudo scalar masses from 300 to 550 MeV. The simulations are performed at one value of the lattice spacing a <~ 0.1 fm. In order to have O(a) improvement and aiming at small residual cutoff effects, the theory is tuned to maximal twist by requiring the vanishing of the untwisted quark mass. Precise results for the pseudo scalar decay constant and the pseudo scalar mass are confronted with chiral perturbation theory predictions and the low energy constants F, l3 and l4 are evaluated with small statistical errors.

Vector and scalar form factors for K- and D-mesonsemileptonic decays from twisted mass fermionswith Nf = 2

2008-12-31T23:00:00Z

Vector and scalar form factors for K- and D-mesonsemileptonic decays from twisted mass fermionswith Nf = 2 Di Vita, Stefano; Haas, Benjamin; Lubicz, Vittorio; Mescia, Federico; Simula, Silvano; Tarantino, Cecilia 2009 257-264 We present lattice results for the formfactors relevant in the K→p ℓnℓ and D→p ℓnℓ semileptonic decays, obtained from simulations with two flavors of dynamical twisted-mass fermions and pion masses as light as 260 MeV. For K →p ℓn decays we discuss the estimates of the main sources of systematic uncertainties, including the quenching of the strange quark, leading to our final result f+(0) = 0.9560(57)stat.(62)syst.. Combined with the latest experimental data, our value of f+(0) implies for the CKMmatrix element |Vus| the value 0.2267(5)exp.(20) f+(0) consistent with the first-row CKM unitarity. For D →p ℓnℓ decays the application of Heavy Meson Chiral Perturbation Theory allows to extrapolate our results for both the scalar and the vector form factors at the physical point with quite good accuracy, obtaining a nice agreement with the experimental data. In particular at zero-momentumtransfer we obtain f+(0) = 0.64(5). A preliminary analysis of the discretization effects is presented and discussed.

First evidence of new physics in b ↔ s transitions

2009-11-30T23:00:00Z

First evidence of new physics in b ↔ s transitions Bona, Marcella; Ciuchini, Marco; Franco, Enrico; Lubicz, Vittorio; Martinelli, Guido; Parodi, Fabrizio; Pierini, Maurizio; Schiavi, Carlo; Silvestrini, Luca; Sordini, Viola; Stocchi, Achille; Vagnoni, Vincenzo 2009-12 PMC Physics A 3 We combine all the available experimental information on Bs mixing, including the very recent tagged analyses of Bs → J/Ψϕ by the CDF and DØ collaborations. We find that the phase of the Bs mixing amplitude deviates more than 3σ from the Standard Model prediction. While no single measurement has a 3σ significance yet, all the constraints show a remarkable agreement with the combined result. This is a first evidence of physics beyond the Standard Model. This result disfavours New Physics models with Minimal Flavour Violation with the same significance.

Light quark masses and pseudoscalar decay constants from Nf=2 lattice QCD with twisted mass fermions

2008-04-06T22:00:00Z

Light quark masses and pseudoscalar decay constants from Nf=2 lattice QCD with twisted mass fermions Blossier, B.; Boucaud, Ph.; Dimopoulos, P.; Farchioni, F.; Frezzotti, R.; Gimenez, V.; Herdoiza, G.; Jansen, K.; Lubicz, Vittorio; Michael, C.; Palao, D.; Papinutto, M.; Shindler, A.; Simula, Silvano; Tarantino, C.; Urbach, C.; Wenger, U. 2008-04-07 Journal of High Energy Physics 020 We present the results of a lattice QCD calculation of the average up-down and strange quark masses and of the light meson pseudoscalar decay constants with Nf=2 dynamical fermions. The simulation is carried out at a single value of the lattice spacing with the twisted mass fermionic action at maximal twist, which guarantees automatic O(a)-improvement of the physical quantities. Quark masses are renormalized by implementing the non perturbative RI-MOM renormalization procedure. Our results for the light quark masses are mud(MSbar,2 GeV) = 3.85 ± 0.12 ± 0.40 MeV, ms(MSbar,2 GeV) = 105 ± 3 ± 9 MeV and ms/mud = 27.3 ± 0.3 ± 1.2. We also obtain fK = 161.7 ± 1.2 ± 3.1 MeV and the ratio fK/fπ = 1.227 ± 0.009 ± 0.024. From this ratio, by using the experimental determination of Γ(K → μbar nuμ(γ))/Γ(π → μbar nuμ(γ)) and the average value of |Vud| from nuclear beta decays, we obtain |Vus| = 0.2192(5)(45), in agreement with the determination from Kl3 decays and the unitarity constraint.

Improved determination of the CKM Angle α from B --> π π decays

2007-06-30T22:00:00Z

Improved determination of the CKM Angle α from B --> π π decays UTfit Collaboration; Bona, M.; Ciuchini, Marco; Franco, E.; Lubicz, Vittorio; Martinelli, G.; Parodi, F.; Pierini, M.; Roudeau, P.; Schiavi, C.; Silvestrini, L.; Sordini, V.; Stocchi, A.; Vagnoni, V. 2007-07 Physical Review D 76 014015-014015-10 Motivated by a recent paper that compares the results of the analysis of the CKM angle alpha in the frequentist and in the Bayesian approaches, we have reconsidered the information on the hadronic amplitudes, which helps in constraining the value of alpha in the standard model. We find that the Bayesian method gives consistent results irrespective of the parametrization of the hadronic amplitudes and that the results of the frequentist and Bayesian approaches are equivalent when comparing meaningful probability ranges or confidence levels. We also find that from B-->pipi decays alone the 95% probability region for alpha is the interval [80°, 170°], well consistent with recent analyses of the unitarity triangle where, by using all the available experimental and theoretical information, one gets alpha=(93±4)°. Last but not least, by using simple arguments on the hadronic matrix elements, we show that the unphysical region alpha~0, present in several experimental analyses, can be eliminated.

K ->pi l nu semileptonic form factors from two-flavor lattice QCD

2009-11-30T23:00:00Z

K ->pi l nu semileptonic form factors from two-flavor lattice QCD Lubicz, Vittorio; Mescia, Federico; Simula, Silvano; Tarantino, Cecilia 2009-12 Physical review D 80 111502 We present new lattice results of the K ->pi l nu semileptonic formfactors obtained from simulations with two flavors of dynamicaltwisted-mass fermions, using pion masses as light as 260 MeV. Our mainresult is f(+)(0)=0.9560(84), which, combined with the latestexperimental data for K-l3 decays, leads to|V-us|=0.2267(5)(exp)(20)(f+)(0). Using the PDG(2008) determinations of|V-ud| and |V-ub| our result implies for the unitarity relation|V-ud|(2)+|V-us|(2)+|V-ub|(2)=1.0004(15). For the O(p(6)) term of thechiral expansion of f(+)(0) we get Delta f equivalent tof(+)(0)-1-f(2)=-0.0214(84).

An estimate of the B --> K* γ Decay Form Factor

2007-03-31T22:00:00Z

An estimate of the B --> K* γ Decay Form Factor Becirevic, Damir; Lubicz, Vittorio; Mescia, Federico 2007-04 Nuclear Physics B 769 31-43 We present the results of a lattice QCD calculation of the form factor relevant to B→K*γ decay. Our final value, T(0) = 0.24 +/- 0.03 (+0.04/-0.01), is obtained in the quenched approximation, and by extrapolating T(q2=0;H--> K*)MH^(3/2) from the directly accessed H-heavy mesons to the meson B. We also show that the extrapolation from B→K*γ* (q2≠0) to B→K*γ (q2=0), leads to a result consistent with the one quoted above. On the other hand, our results are not accurate enough to solve the SU(3) flavor breaking effects in the form factor and we quote TB→K*(0)/TB→ρ(0)=1.2(1), as our best estimate.

Electromagnetic Form Factor of the Pion from Twisted-mass Lattice QCD at Nf=2

2009-03-31T22:00:00Z

Electromagnetic Form Factor of the Pion from Twisted-mass Lattice QCD at Nf=2 Frezzotti, Roberto; Lubicz, Vittorio; Simula, Silvano 2009-04 Physical Review D 79 074506 We present a lattice calculation of the electromagnetic form factor of the pion obtained using the tree-level Symanzik improved gauge action with two flavors of dynamical twisted Wilson quarks. The simulated pion masses range approximately from 260 to 580 MeV, and the lattice box sizes are chosen in order to guarantee that Mpi*L>~4. Accurate results for the form factor are obtained using all-to-all quark propagators evaluated by a stochastic procedure. The momentum dependence of the pion form factor is investigated up to values of the squared four-momentum transfer Q^2~=0.8 GeV^2 and, thanks to the use of twisted boundary conditions, down to Q^2~=0.05 GeV^2. Volume and discretization effects on the form factor appear to be within the statistical errors. Our results for the pion mass, decay constant and form factor are analyzed using (continuum) chiral perturbation theory at next-to-next-to-leading order. The extrapolated value of the pion charge radius is _phys=0.456±0.030(stat)±0.024(syst) in nice agreement with the experimental result. The extrapolated values of the pion form factor agree very well with the experimental data up to Q^2~=0.8 GeV^2 within uncertainties which become competitive with the experimental errors for Q^2>~0.3 GeV^2. The relevant low-energy constants appearing in the chiral expansion of the pion form factor are extracted from our lattice data, which come essentially from a single lattice spacing, adding the experimental value of the pion scalar radius in the fitting procedure. Our findings are in nice agreement with the available results of chiral perturbation theory analyses of pi-pi scattering data as well as with other analyses of our collaboration.

O (a(2)) corrections to the one-loop propagator and bilinears of cloverfermions with Symanzik improved gluons

2009-09-30T22:00:00Z

O (a(2)) corrections to the one-loop propagator and bilinears of cloverfermions with Symanzik improved gluons Constantinou, Martha; Lubicz, Vittorio; Panagopoulos, H.; Stylianou, F. 2009-10 Journal of high energy physics 12 001-067 We calculate corrections to the fermion propagator and to the Green'sfunctions of all fermion bilinear operators of the form (Psi) over barGamma Psi, to one-loop in perturbation theory.We employ the Wilson/clover action for fermions and the Symanzikimproved action for gluons.The novel aspect of our calculations is that they are carried out tosecond order in the lattice spacing, O (a(2)). Consequently, they haveaddressed a number of new issues, most notably the appearance of loopintegrands with strong IR divergences (convergent only beyond 6dimensions). Such integrands are not present in O (a(1)) improvementcalculations; there, IR divergent terms are seen to have the samestructure as in the O (a(0)) case, by virtue of parity underintegration, and they can thus be handled by well-known techniques. Weexplain how to correctly extract the full O (a(2)) dependence; in fact,our method is generalizable to any order in a.The O (a(2)) corrections to the quark propagator and Green's functionscomputed in this paper are useful to improve the nonperturbative RI-MOMdetermination of renormalization constants for quark bilinear operators.Our results depend on a large number of parameters: coupling constant,number of colors, lattice spacing, external momentum, clover parameter,Symanzik coefficients, gauge parameter. To make these results mosteasily accessible to the reader, we have included them in thedistribution package of this paper, as an ASCII file named: Oa2results.m; the file is best perused as Mathematica input.

Kaon physics from lattice QCD

2008-12-31T23:00:00Z

Kaon physics from lattice QCD Lubicz, Vittorio 2009 013 I review lattice calculations and results for hadronic parameters relevant for kaon physics, in particular the vector form factor f+(0) of semileptonic kaon decays, the ratio fK/fp of leptonic decay constants and the kaon bag parameter BK. For each lattice calculation a colour code rating is assigned, by following a procedure which is being proposed by the Flavianet Lattice Averaging Group (FLAG), and the following final averages are obtained: f+(0) = 0.962(3)(4), fK/ fp =1.196(1)(10) and BK = 0.731(7)(35). In the last part of the talk, the present status of lattice studies of non-leptonic K -> pipi decays is also briefly summarized.

K ->pi l nu semileptonic form factors from two-flavor lattice QCD

2009-12-29T23:00:00Z

K ->pi l nu semileptonic form factors from two-flavor lattice QCD Lubicz, Vittorio; Mescia, Federico; Simula, Silvano; Tarantino, Cecilia 2009-12-30 Physical Review D 80 111502 We present new lattice results of the K ->pi l nu semileptonic form factors obtained from simulations with two flavors of dynamicaltwisted-mass fermions, using pion masses as light as 260 MeV. Our main result is f(+)(0)=0.9560(84), which, combined with the latest experimental data for Kl3 decays, leads to |Vus|=0.2267(5)(exp)(20)(f+(0)). Using the PDG(2008) determinations of|Vud| and |Vub| our result implies for the unitarity relation |Vud|^2+|Vus|^2+|Vub|^2=1.0004(15). For the O(p^6) term of the chiral expansion of f+(0) we get Delta f = f+(0)-1-f2=-0.0214(84).

Pseudoscalar decay constants of kaon and D-mesons from Nf=2 twisted mass Lattice QCD

2009-06-30T22:00:00Z

Pseudoscalar decay constants of kaon and D-mesons from Nf=2 twisted mass Lattice QCD ETM, Collaboration; Blossier, Benoit; Dimopoulos, Petros; Frezzotti, Roberto; Haas, Benjamin; Herdoiza, Gregorio; Jansen, Karl; Lubicz, Vittorio; Mescia, Federico; Palao, David; Shindler, Andrea; Simula, Silvano; Tarantino, Cecilia; Urbach, Carsten 2009-07 Journal of High Energy Physics 07 043 We present the results of a lattice QCD calculation of the pseudoscalar meson decay constants fπ, fK, fD and fDs, performed with Nf=2 dynamical fermions. The simulation is carried out with the tree-level improved Symanzik gauge action and with the twisted mass fermionic action at maximal twist. We have considered for the final analysis three values of the lattice spacing, a = 0.10 fm, 0.09 fm and 0.07 fm, with pion masses down to mπ = 270 MeV. Our results for the light meson decay constants are fK = 158.1(2.4) MeV and fK/fπ = 1.210(18). From the latter ratio, by using the experimental determination of Γ(K → μbar nuμ(γ))/Γ(π → μbar nuμ(γ)) and the average value of |Vud| from nuclear beta decays, we obtain |Vus| = 0.2222(34), in good agreement with the determination from semileptonic Kl3 decays and the unitarity constraint. For the D and Ds meson decay constants we obtain fD = 197(9) MeV, fDs = 244(8) MeV and fDs/fD = 1.24(3). Our result for fD is in good agreement with the CLEO experimental measurement. For fDs our determination is smaller than the PDG 2008 experimental average but in agreement with a recent improved measurement by CLEO at the 1.4 σ level.

O(a^2) corrections to 1-loop matrix elements of 4-fermion operators with improved fermion/gluon actions

2008-12-31T23:00:00Z

O(a^2) corrections to 1-loop matrix elements of 4-fermion operators with improved fermion/gluon actions Constantinou, Martha; Lubicz, Vittorio; Panagopoulos, Haralambos; Skouroupathis, Apostolos; Stylianou, Fotos 2009 260 We calculate the corrections to the amputated Green's functions of 4-fermion operators, in 1-loop Lattice Perturbation theory. The novel aspect of our calculations is that they are carried out to second order in the lattice spacing, O(a^2). We employ the Wilson/clover action for massless fermions (also applicable for the twisted mass action in the chiral limit) and the Symanzik improved action for gluons. Our calculations have been carried out in a general covariant gauge. Results have been obtained for several popular choices of values for the Symanzik coefficients (Plaquette, Tree-level Symanzik, Iwasaki, TILW and DBW2 action). We pay particular attention to Delta F=2 operators, both Parity Conserving and Parity Violating (F stands for flavour: S, C, B). We study the mixing pattern of these operators, to O(a^2), using the appropriate projectors. Our results for the corresponding renormalization matrices are given as a function of a large number of parameters: coupling constant, clover parameter, number of colors, lattice spacing, external momentum and gauge parameter. The O(a^2) correction terms (along with our previous O(a^2) calculation of Z_Psi) are essential ingredients for minimizing the lattice artifacts which are present in non-perturbative evaluations of renormalization constants with the RI'-MOM method. A longer write-up of this work, including non-perturbative results, is in preparation together with members of the ETM Collaboration.

f_B and f_Bs with maximally twisted Wilson fermions

2008-12-31T23:00:00Z

f_B and f_Bs with maximally twisted Wilson fermions ETM Collaboration; Blossier, Benoit; Dimopoulos, Petros; Frezzotti, Roberto; Herdoiza, Gregorio; Jansen, Karl; Lubicz, Vittorio; Martinelli, Guido; Michael, Chris; Rossi, Giancarlo; Sanfilippo, Francesco; Shindler, Andrea; Simula, Silvano; Tarantino, Cecilia; Urbach, Carsten; Wagner, Marc 2009 151 We present a lattice QCD calculation of the heavy-light decay constants f_B and f_Bs performed with Nf=2 maximally twisted Wilson fermions, at four values of the lattice spacing. The decay constants have been also computed in the static limit and the results are used to interpolate the observables between the charm and the infinite-mass sectors, thus obtaining the value of the decay constants at the physical b quark mass. Our preliminary results are f_B=191(14) MeV, f_Bs=243(14) MeV, f_Bs/f_B=1.27(5). They are in good agreement with those obtained with a novel approach, recently proposed by our Collaboration (ETMC), based on the use of suitable ratios having an exactly known static limit.

Pseudoscalar decay constants of kaon and D-mesons from N-f=2 twisted mass Lattice QCD

2009-06-30T22:00:00Z

Pseudoscalar decay constants of kaon and D-mesons from N-f=2 twisted mass Lattice QCD Blossier, Benoît; Dimopoulos, Pedro; Frezzotti, Roberto; Haas, Benjamin; Herdoiza, Gregorio; Jansen, Karl; Lubicz, Vittorio; Mescia, Federico; Palao, David; Shindler, Andrea; Simula, Silvano; Tarantino, Cecilia; Urbach, Carsten; Wenger, Urs 2009-07 Journal of high energy physics 2009 043 We present the results of a lattice QCD calculation of the pseudoscalar meson decay constants f(pi), f(K), f(D) and f(Ds), performed with N-f =2 dynamical fermions. The simulation is carried out with the tree-level improved Symanzik gauge action and with the twisted mass fermionic action at maximal twist. We have considered for the final analysis three values of the lattice spacing, a similar or equal to 0.10 fm, 0.09 fm and 0.07 fm, with pion masses down to m(pi) similar or equal to 270 MeV. Our results for the light meson decay constants are f(K) =158.1(2.4) MeV and f(K)/f(pi) = 1.210(18). From the latter ratio, by using the experimental determination of Gamma(K -> munu(mu)(gamma))/Gamma(pi -> mu nu(mu)(gamma)) and the average value of vertical bar V-ud vertical bar from nuclear beta decays, we obtain vertical bar V-us vertical bar = 0.2222(34), in good agreement with the determination from semileptonic K-13 decays and the unitarity constraint. For the D and D-s meson decay constants we obtain f(D) =197(9) MeV, f(Ds) = 244(8) MeV and f(Ds)/f(D) = 1.24(3). Our result for f(D) is in good agreement with the CLEO experimental measurement. For f(Ds) our determination is smaller than the PDG 2008 experimental average but in agreement with a recent improved measurement by CLEO at the 1.4 sigma level.