43 research outputs found
Twisted mass QCD at finite temperature
No full textWe discuss the use of Wilson fermions with twisted mass for simulations of QCD thermodynamics. As a prerequisite for a future analysis of the finite-temperature transition making use of automatic O(a) improvement, we investigate the phase structure in the space spanned by the hopping parameter kappa, the coupling beta, and the twisted mass parameter mu. We present results for N_f=2 degenerate quarks on a 16^3x8 lattice, for which we investigate the possibility of an Aoki phase existing at strong coupling and vanishing mu, as well as of a thermal phase transition at moderate gauge couplings and non-vanishing mu.Ernst-Michael Ilgenfritz, Michael Müller-Preußker, Marcus Petschlies, Karl Jansen, M. Paola Lombardo, Owe Philipsen, Lars Zeidlewicz and André Sternbec
Lattice calculation of the short and intermediate time-distance hadronic vacuum polarization contributions to the muon magnetic moment using twisted-mass fermions
No full textWe present a lattice determination of the leading-order hadronic vacuum
polarization (HVP) contribution to the muon anomalous magnetic moment,
, in the so-called short and intermediate time-distance
windows, and , defined by the RBC/UKQCD
Collaboration [1]. We employ gauge ensembles produced by the Extended Twisted
Mass Collaboration (ETMC) with flavors of Wilson-clover
twisted-mass quarks with masses of all the dynamical quark flavors tuned close
to their physical values. The simulations are carried out at three values of
the lattice spacing equal to and fm with spatial
lattice sizes up to ~fm. For the short distance window we obtain
, which is consistent
with the recent dispersive value of [2]. In the case of the intermediate window we get the value
, which is consistent
with the result [3] by
the BMW collaboration as well as with the recent determination by the CLS/Mainz
group of [4].
However, it is larger than the dispersive result of [2] by approximately standard deviations.
The tension increases to approximately standard deviations if we average
our ETMC result with those by BMW and CLS/Mainz. Our accurate lattice results
in the short and intermediate windows point to a possible deviation of the cross section data with respect to Standard Model predictions in the low
and intermediate energy regions, but not in the high energy region.Comment: 78 pages, 22 figures, 14 tables. Analysis improved with more data and
fits, presentation reorganized, more material in appendices, fixed typo
Isospin-0 ππ scattering from twisted mass lattice QCD
No full textWe present results for the isospin-0 s-wave scattering length
calculated in twisted mass lattice QCD. We use three ensembles with
unitary pion mass at its physical value, 240~MeV and 330~MeV respectively. We
also use a large set of ensembles with unitary pion masses
varying in the range of 230~MeV - 510~MeV at three different values of the
lattice spacing. A mixed action approach with the Osterwalder-Seiler action in
the valence sector is adopted to circumvent the complications arising from
isospin symmetry breaking of the twisted mass quark action. Due to the
relatively large lattice artefacts in the ensembles, we do not
present the scattering lengths for these ensembles. Instead, taking the
advantage of the many different pion masses of these ensembles, we
qualitatively discuss the pion mass dependence of the scattering properties of
this channel based on the results from the ensembles. The
scattering length is computed for the ensembles and the chiral
extrapolation is performed. At the physical pion mass, our result agrees reasonably well with various
experimental measurements and theoretical predictions
Isospin-0 s-wave scattering length from twisted mass lattice QCD
No full textWe present results for the isospin-0 ππ s-wave scattering length calculated with Osterwalder-Seiler valence quarks on Wilson twisted mass gauge configurations. We use three Nf=2 ensembles with unitary (valence) pion mass at its physical value (250 MeV), at 240 MeV (320 MeV) and at 330 MeV (400 MeV), respectively. By using the stochastic Laplacian Heaviside quark smearing method, all quark propagation diagrams contributing to the isospin-0 ππ correlation function are computed with sufficient precision. The chiral extrapolation is performed to obtain the scattering length at the physical pion mass. Our result Mπa0I=0=0.198(9)(6) agrees reasonably well with various experimental measurements and theoretical predictions. Since we only use one lattice spacing, certain systematics uncertainties, especially those arising from unitary breaking, are not controlled in our result
Lattice calculation of the R-ratio smeared with Gaussian kernels
No full textThe ratio R(E) of the cross-sections for e+e−→ hadrons and e+e−→μ+μ− is a valuable energy-dependent probe of the hadronic sector of the Standard Model. Moreover, the experimental measurements of R(E) are the inputs of the dispersive calculations of the leading hadronic vacuum polarization contribution to the muon g−2 and these are in significant tension with direct lattice calculations and with the muon g−2 experiment. In this talk we discuss the results of our first-principles lattice study of R(E). By using a recently proposed method for extracting smeared spectral densities from Euclidean lattice correlators, we have calculated R(E) convoluted with Gaussian kernels of different widths σ and central energies up to 2.5 GeV. Our theoretical results have been compared with the KNT19 [1] compilation of experimental results smeared with the same Gaussian kernels and a tension (about three standard deviations) has been observed for σ∼600 MeV and central energies around the ρ-resonance peak
Quark masses with Nf=2 twisted mass lattice QCD
No full textWe present the results of the recent high precision lattice calculation of the average up/down, strange and charm quark masses performed by ETMC with Nf=2 twisted mass Wilson fermions. The analysis includes data at four values of the lattice spacing and pion masses as low as ~270 MeV, allowing for accurate continuum limit and chiral extrapolation. The strange and charm masses are extracted by using several methods, based on different observables: the kaon and the eta_s meson for the strange quark and the D, D_s and eta_c mesons for the charm. The quark mass renormalization is carried out non-perturbatively using the RI-MOM method. The results for the quark masses in the MSbar scheme read: m_ud(2 GeV)= 3.6(2) MeV, m_s(2 GeV)=95(6) MeV and m_c(m_c)=1.28(4) GeV. We have also obtained the ratios m_s/m_ud=27.3(9) and m_c/m_s=12.0(3). Moreover, we provide the updated result for the bottom quark mass, m_b(m_b)=4.3(2) GeV, obtained using the method presented in 0909.3187 [hep-lat]
Probing the energy-smeared R-ratio on the lattice
No full textWe present a first-principles lattice QCD investigation of the -ratio
between the cross-section into hadrons and that into muons. By using
the method of Ref.[1], that allows to extract smeared spectral densities from
Euclidean correlators, we compute the -ratio convoluted with Gaussian
smearing kernels of widths of about MeV and central energies from
MeV up to GeV. Our theoretical results are compared with the
corresponding quantities obtained by smearing the KNT19 compilation [2] of
-ratio experimental measurements with the same kernels and, by centring the
Gaussians in the region around the -resonance peak, a tension of about
three standard deviations is observed. From the phenomenological perspective,
we have not included yet in our calculation QED and strong isospin-breaking
corrections and this might affect the observed tension. From the methodological
perspective, our calculation demonstrates that it is possible to study the
-ratio in Gaussian energy bins on the lattice at the level of accuracy
required in order to perform precision tests of the Standard Model.Comment: Version accepted for publication on PRL. Results unchange
Extraction of the isovector magnetic form factor of the nucleon at zero momentum
No full text© Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence. The extraction of the magnetic form factor of the nucleon at zero momentum transfer is usually performed by adopting a parametrization for its momentum dependence and fitting the results obtained at finite momenta. We present position space methods that rely on taking the derivative of relevant correlators to extract directly the magnetic form factor at zero momentum without the need to assume a functional form for its momentum dependence. These methods are explored on one ensemble using Nf = 2+1+1 Wilson twisted mass fermions
Topological susceptibility and η′ meson mass from Nf = 2 lattice QCD at the physical point
No full textIn this paper we explore the computation of topological susceptibility and η' meson mass in Nf = 2 flavor QCD using lattice techniques with a physical value of the pion mass as well as larger pion mass values. We observe that the physical point can be reached without a significant increase in the statistical noise. The mass of the η' meson can be obtained from both fermionic two point functions and topological charge density correlation functions, giving compatible results. With the pion mass dependence of the η' mass being flat we arrive at Mη' = 772(18) MeV without an explicit continuum limit. For the topological susceptibility we observe a linear dependence on M²π, however, with an additional constant stemming from lattice artifacts
The Muon Anomalous Magnetic Moment: A Probe for Physics beyond the Standard Model of High Energy Physics
No full textThe search for physics beyond the standard model, either in direct collider or in high precision low energy experiments is a most active endeavour in particle physics. A prime candidate for the detection of this new physics is the anomalous magnetic moment of the muon. In this project, we present a lattice QCD calculation of the leading order hadronic contribution of the lepton anomalous magnetic moments, i.e. for the electron, the muon and the tau. Such lattice calculations are indispensable as input for the non-perturbative contributions as required in newly planned experiments for measuring these anomalous magnetic moments
