Searcharxiv⌕ Search

arXiv subjects

G. Herdoiza

Publications and source records attributed to G. Herdoiza.

At least 37 records · Page 2Linked to original sources
arXiv2009

First results of ETMC simulations with Nf=2+1+1 maximally twisted mass fermions

We present first results from runs performed with Nf=2+1+1 flavours of dynamical twisted mass fermions at maximal twist: a degenerate light doublet and a mass split heavy doublet. An overview of the input parameters and tuning status of our ensembles is given, together with a comparison with results obtained with Nf=2 flavours. The problem of extracting the mass of the K- and D-mesons is discussed, and the tuning of the strange and charm quark masses examined. Finally we compare two methods of extracting the lattice spacings to check the consistency of our data and we present some first results of ChiPT fits in the light meson sector.

hep-lat↗
arXiv2009

Light Meson Physics from Maximally Twisted Mass Lattice QCD

We present a comprehensive investigation of light meson physics using maximally twisted mass fermions for two mass-degenerate quark flavours. By employing four values of the lattice spacing, spatial lattice extents ranging from 2.0 fm to 2.5 fm and pseudo scalar masses in the range 280 MeV to 650 MeV we control the major systematic effects of our calculation. This enables us to confront our data with chiral perturbation theory and extract low energy constants of the effective chiral Lagrangian and derived quantities, such as the light quark mass, with high precision.

hep-lat↗
arXiv2009

f_B and f_Bs with maximally twisted Wilson fermions

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.

hep-lat↗
arXiv2009

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

We present the results of a lattice QCD calculation of the pseudoscalar meson decay constants fpi, 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 mpi~270 MeV. Our results for the light meson decay constants are fK=158.1(2.4) MeV and fK/fpi=1.210(18). From the latter ratio, by using the experimental determination of Gamma(K-->mu nu_mu (gamma))/ Gamma(pi--> mu nu_mu (gamma)) 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 sigma level.

hep-lat↗
arXiv2008

Dynamical Twisted Mass Fermions with Light Quarks: Simulation and Analysis Details

In a recent paper [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.

hep-lat↗
arXiv2008

Scaling and chiral extrapolation of pion mass and decay constant with maximally twisted mass QCD

We present an update of the results for pion mass and pion decay constant as obtained by the ETM collaboration in large scale simulations with maximally twisted mass fermions and two mass degenerate flavours of light quarks. We discuss the continuum, chiral and infinite volume extrapolation of these quantities as well as the extraction of low energy constants, and investigate possible systematic uncertainties.

hep-lat↗
arXiv2008

Light baryon masses with dynamical twisted mass fermions

We present results on the mass of the nucleon and the Delta using two dynamical degenerate twisted mass quarks and the tree-level Symanzik improved gauge action. The evaluation is performed at four quark masses corresponding to a pion mass in the range of about 300-600 MeV on lattices of 2.1-2.7 fm. We check for cut-off effects by evaluating these baryon masses on lattices of spatial size 2.1 fm at beta=3.9 and beta=4.05 and on a lattice of 2.4 fm at beta=3.8. The values we find are compatible within our statistical errors. Lattice results are extrapolated to the physical limit using continuum chiral perturbation theory. Performing a combined fit to our lattice data at beta=3.9 and beta=4.05 we find a nucleon mass of 964\pm 28 (stat.) \pm 8 (syst.) MeV. The nucleon mass at the physical point provides an independent determination of the lattice spacing. Using heavy baryon chiral perturbation theory at O(p^3) we find a_{β=3.9}=0.0890\pm 0.0039(stat.) \pm 0.0014(syst.) fm, and a_{β=4.05}= 0.0691\pm 0.0034(stat.) \pm 0.0010(syst.) fm, in good agreement with the values determined from the pion decay constant. Isospin violating lattice artifacts in the Delta-system are found to be compatible with zero for the values of the lattice spacings used in this work. Performing a combined fit to our lattice data at beta=3.9 and beta=4.05 we find for the masses of the Delta^{++,-} and Delta^{+,0} 1316 \pm 60 (stat.) MeV and 1330 \pm 74 (stat.) MeV respectively. We confirm that in the continuum limit they are also degenerate.

hep-lat↗
arXiv2007

Non-perturbative renormalisation of Delta F=2 four-fermion operators in two-flavour QCD

Using Schroedinger Functional methods, we compute the non-perturbative renormalisation and renormalisation group running of several four-fermion operators, in the framework of lattice simulations with two dynamical Wilson quarks. Two classes of operators have been targeted: (i) those with left-left current structure and four propagating quark fields; (ii) all operators containing two static quarks. In both cases, only the parity-odd contributions have been considered, being the ones that renormalise multiplicatively. Our results, once combined with future simulations of the corresponding lattice hadronic matrix elements, may be used for the computation of phenomenological quantities of interest, such as B_K and B_B (the latter also in the static limit).

hep-lat↗
arXiv2007

Non-perturbative renormalisation of four-fermion operators in N_f=2 QCD

We present results for the non-perturbative renormalisation of four-fermion operators with two flavours of dynamical quarks. We consider both fully relativistic left current-left current operators, and a full basis for $ΔB=2$ operators with static heavy quarks. The renormalisation group running of the operators to high energy scales is computed in the continuum limit for a family of Schroedinger Functional renormalisation schemes, via standard finite size scaling techniques. The total renormalisation factors relating renormalisation group invariant to bare operators are computed for a choice of lattice regularisations.

hep-lat↗
arXiv2007

Twisted mass QCD in the charm sector

We present preliminary results for the charm quark mass $m_c$ and the $D$ and $D_s$ mesons decay constants $f_D$ and $f_{D_s}$ from a lattice QCD calculation with ${\rm N_f}$ = 2 dynamical fermions. We use the twisted mass fermionic action defined at maximal twist so that physical quantities are automatically ${\cal O}(a)$ improved. Two lattice spacings are considered. The charm quark mass has been renormalised in the RI-MOM scheme. After a matching to the $\msb$ scheme, we obtain from the simulation at a fine lattice ($a \sim 0.09$ fm) $m_c^{\msb}(m_c) = 1.481 \pm 0.022 \pm 0.092$ GeV, $f_D = 205 \pm 13 \pm 17$ MeV, $f_{D_s} = 271 \pm 6 \pm 6$ MeV and from the simulation at the finer lattice ($a \sim 0.07$ fm) $m_c^{\msb}(m_c) = 1.474 \pm 0.041 \pm 0.132$ GeV, $f_D = 230 \pm 31 \pm 8$ MeV and $f_{D_s} = 264 \pm 5 \pm 8$ MeV. We chose three renormalisation conditions to determine $m_c$: the spread between the final results contributes to the systematic error. At both lattice spacings, particularly at the finer one, the error on $m_c$ is dominated by present uncertainty on the renormalisation constant $Z_P$, which should be reduced before performing a reliable continuum limit.

hep-lat↗
arXiv2007

Renormalisation of quark bilinears with Nf=2 Wilson fermions and tree-level improved gauge action

We present results for the renormalisation constants of bilinear quark operators, using the Nf=2 twisted mass Wilson action at maximal twist (which guarantees automatic O(a) improvement) and the tree-level Symanzik improved gauge action. The scale-independent renormalisation constants are computed with a new method, which makes use of both standard twisted mass and Osterwalder-Seiler fermions. Moreover, the results from an RI-MOM calculation are presented for both scale independent and scale dependent renormalisation constants.

hep-lat↗
arXiv2007

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

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 m_ud^{msbar}(2 GeV)= 3.85 +- 0.12 +- 0.40 MeV, m_s^{msbar}(2 GeV) = 105 +- 3 +- 9 MeV and m_s/m_ud = 27.3 +- 0.3 +- 1.2. We also obtain fK = 161.7 +- 1.2 +- 3.1 MeV and the ratio fK/fpi=1.227 +- 0.009 +- 0.024. From this ratio, by using the experimental determination of Gamma(K-> mu nu (gamma))/Gamma(pi -> mu nu (gamma)) 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.

hep-lat↗
arXiv2007

Dynamical Twisted Mass Fermions with Light Quarks

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 \lesssim 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, \bar{l}_3 and \bar{l}_4 are evaluated with small statistical errors.

hep-lat↗
arXiv2006

Non-perturbative scale evolution of four-fermion operators in two-flavour QCD

We apply finite-size recursion techniques based on the Schrodinger functional formalism to determine the renormalization group running of four-fermion operators which appear in the Delta S=2 effective weak Hamiltonian of the Standard Model. Our calculations are done using O(a) improved Wilson fermions with N_f=2 dynamical flavours. Preliminary results are presented for the four-fermion operator which determines the B_K parameter in tmQCD.

hep-lat↗
arXiv2006

Decay constants of P-wave heavy-light mesons from unquenched lattice QCD

We review some decays that require knowledge of the decay constants of $0^{+}$ heavy-light mesons. We compute the decay constants of P-wave heavy-light mesons from unquenched lattice QCD, with two degenerate flavours of sea quarks, at a single lattice spacing. The lightest sea quark mass used in the calculation is a third of the strange quark mass. For the charm-strange meson we obtain the decay constant: $f_{D_{s 0^+}} = 340(110)$ MeV using our normalisation conventions. We obtain the $f_{P_s}^{static}$ (static-strange P-wave) decay constant as $302(39)$ MeV.

hep-lat↗
arXiv2004

Lattice measurement of the Isgur-Wise functions tau_1/2 and tau_3/2

We propose a method to compute the Isgur-Wise form factors tau_1/2(1) and tau_3/2(1) for the decay of B mesons into orbitally excited (P wave) D** charmed mesons on the lattice in the static limit. We also present the result of an exploratory numerical simulation which shows that the signal/noise ratio allows for a more dedicated computation. We find tau_1/2(1)=0.38(5) and tau_3/2(1)= 0.53(8), with yet unknown systematic errors. These preliminary numbers agree fairly well with theoretical expectation.

hep-lat↗
arXiv2004

Lattice measurement of the couplings g_infinity and g_Bstar_B_pi

We present the results of a quenched lattice QCD study of the coupling g_hat, in the static heavy quark limit. After combining this with our previous results obtained by using propagating heavy quarks with a mass around the physical charm quark, we are able to interpolate to the b-quark sector. Our results are g_hat_infinity = 0.48 +/- 0.03 +/- 0.11, g_hat_b = 0.58 +/- 0.06 +/- 0.10, and g_Bstar_ B_p = 47 +/- 5 +/- 8.

hep-lat↗