Twisted Mass Lattice QCD Research Articles

Lattice calculation of χ c0 → 2γ decay width * *Support by NSFC of China (12070131001) and also the support by CAS Interdisciplinary Innovation Team and NSFC of China (11935017), NSFC of China (12047505) and State Key Laboratory of Nuclear Physics and Technology, Peking University

We perform a lattice QCD calculation of the decay width using a model-independent method that does not require the momentum extrapolation of corresponding off-shell form factors. The simulation is performed on ensembles of twisted mass lattice QCD gauge configurations with three different lattice spacings. After the continuum extrapolation, the decay width is obtained to be . Regardless of this large statistical error, our result is compatible with the experimental results within 1.3σ. Potential improvements of the lattice calculation in the future are also discussed.

ππ scattering in partially-quenched twisted-mass chiral perturbation theory

We study pion-pion scattering in partially-quenched twisted-mass lattice QCD using chiral perturbation theory. The specific partially-quenched setup corresponds to that used in numerical lattice QCD calculations of the $I=0$ scattering length. We study the discretization errors proportional to $a^2$, with $a$ the lattice spacing, and the errors that arise due to the use of L\"uscher's two-particle quantization condition in a theory that is not unitary. We argue that the former can be as large as $\sim 100\%$, but explain how they can be systematically subtracted using a calculation of the $I=2$ scattering amplitude in the same partially-quenched framework. We estimate the error from the violation of unitarity to be $\sim 25\%$, and argue that this error will be difficult to reduce in practice.

Mathcal{N} = 1 Super-Yang-Mills theory on the lattice with twisted mass fermions

Super-Yang-Mills theory (SYM) is a central building block for supersymmetric extensions of the Standard Model of particle physics. Whereas the weakly coupled subsector of the latter can be treated within a perturbative setting, the strongly coupled subsector must be dealt with a non-perturbative approach. Such an approach is provided by the lattice formulation. Unfortunately a lattice regularization breaks supersymmetry and consequently the mass degeneracy within a supermultiplet. In this article we investigate the properties of mathcal{N} = 1 supersymmetric SU(3) Yang-Mills theory with a lattice Wilson Dirac operator with an additional parity mass, similar as in twisted mass lattice QCD. We show that a special 45° twist effectively removes the mass splitting of the chiral partners. Thus, at finite lattice spacing both chiral and supersymmetry are enhanced resulting in an improved continuum extrapolation. Furthermore, we show that for the non-interacting theory at 45° twist discretization errors of order mathcal{O}(a) are suppressed, suggesting that the same happens for the interacting theory as well. As an aside, we demonstrate that the DDαAMG multigrid algorithm accelerates the inversion of the Wilson Dirac operator considerably. On a 163× 32 lattice, speed-up factors of up to 20 are reached if commonly used algorithms are replaced by the DDαAMG.

Lattice study of two-photon decay widths for scalar and pseudo-scalar charmonium * * This work is supported in part by the National Science Foundation of China (NSFC) (11335001, 11275169, 11405178, 11935017, 11575196, 11875169, 11775229). It is also supported in part by the DFG and the NSFC (11261130311) through funds provided to the Sino-Germen CRC 110 symmetries and the Emergence of

This exploratory study computes two-photon decay widths of pseudo-scalar ( ) and scalar ( ) charmonium using two ensembles of twisted mass lattice QCD gauge configurations. The simulation is performed using two lattice ensembles with lattice spacings fm with size and fm with size . The decay widths for the two charmonia are obtained within the expected ballpark, but are however smaller than the experimental ones. Possible reasons for these discrepancies are discussed.

Transversal and Longitudinal Gluon Spectral Functions from Twisted Mass Lattice QCD with Nf = 2 + 1 + 1 Flavors

I report on the first application of a novel, generalized Bayesian reconstruction (BR) method for spectral functions to the characterization of QCD constituents. These spectral functions find applications in off-shell kinetics of the quark-gluon plasma and in calculations of transport coefficients. The new BR method is applied to Euclidean propagator data, obtained in Landau gauge on lattices with $N_f=2+1+1$ dynamical flavors by the "twisted mass at finite temperature" (tmfT) collaboration. The deployed reconstruction method is designed for spectral functions that can exhibit positivity violation (opposed to that of hadronic bound states). The transversal and longitudinal gluon spectral functions show a robust structure composed of quasiparticle peak and a negative trough. Characteristic differences between the hadronic and the plasma phase and between the two channels become visible. We obtain the temperature dependence of the transversal and longitudinal gluon masses.

Nucleon Structure and the Neutron Electric Dipole Moment from Twisted Mass Lattice QCD

Recent results on nucleon structure using twisted mass lattice QCD simulated with a quark mass yielding the physical pion mass are presented. Namely, the nucleon axial charges and moments of parton distribution functions are discussed as well as the implication of these results on the decomposition of the nucleon spin. Results on the electromagnetic structure are also presented, including a recent study of the neutron Electric Dipole Moment using simulations with pion mass of 370 MeV.

Properties of flavour-singlet pseudoscalar mesons from lattice QCD

We report on the status of the determination of properties of flavour-singlet pseudoscalar mesons using Wilson twisted mass lattice QCD at maximal twist. As part of project C7 , a large number of phenomenologically relevant quantities could be extracted from first principle, from η and η′ masses to decay widths of pseudoscalar mesons to two photons.

Continuum limit of the D meson, Ds meson, and charmonium spectrum from Nf=2+1+1 twisted mass lattice QCD

We compute masses of $D$ meson, ${D}_{s}$ meson, and charmonium states using ${N}_{f}=2+1+1$ Wilson twisted mass lattice QCD. All results are extrapolated to physical light quark masses, to physical strange and charm quark masses, and to the continuum. Our analysis includes states with spin $J=0$, 1, 2, parity $\mathcal{P}=\ensuremath{-},+$, and in case of charmonium also charge conjugation $\mathcal{C}=\ensuremath{-},+$. Computations are based on a large set of quark-antiquark meson creation operators. We investigate and quantify all sources of systematic errors, including fitting range uncertainties, finite volume effects, isospin breaking effects, and the choice of the fitting ansatz for the combined chiral and continuum extrapolation such that the resulting meson masses can be compared directly and in a meaningful way to experimental results. Within combined statistical and systematic errors, which are between below 2 per mille and 3%, our results agree with available experimental results for most of the states. In the few cases where we observe discrepancies, we discuss possible reasons.

Two-photon decays of $$\eta _c$$ η c from lattice QCD

We present an exploratory lattice study for the two-photon decay of $\eta_c$ using $N_f=2$ twisted mass lattice QCD gauge configurations generated by the European Twisted Mass Collaboration. Two different lattice spacings of $a=0.067$fm and $a=0.085$fm are used in the study, both of which are of physical size of 2$fm$. The decay widths are found to be $1.025(5)$KeV for the coarser lattice and $1.062(5)$KeV for the finer lattice respectively where the errors are purely statistical. A naive extrapolation towards the continuum limit yields $\Gamma\simeq 1.122(14)$KeV which is smaller than the previous quenched result and most of the current experimental results. Possible reasons are discussed.

Leading-order hadronic contributions to the lepton anomalous magnetic moments from the lattice

The hadronic leading-order (hlo) contribution to the lepton anomalous magnetic moments $a_l^\mathrm{hlo}$ of the Standard Model leptons still accounts for the dominant source of the uncertainty of the Standard Model estimates. We present the results of an investigation of the hadronic leading order anomalous magnetic moments of the electron, muon and tau lepton from first principles in twisted mass lattice QCD. With lattice data for multiple pion masses in the range $230 \mathrm{~MeV} \lesssim m_{PS} \lesssim 490 \mathrm{~MeV}$, multiple lattice volumes and three lattice spacings we perform the extrapolation to the continuum and to the physical pion mass and check for all systematic uncertainties in the lattice calculation. As a result we calculate $a_{l}^\mathrm{hlo}$ for the three Standard Model leptons with controlled statistical and systematic error in agreement with phenomenological determinations using dispersion relations and experimental data. In addition, we also give a first estimate of the hadronic leading order anomalous magnetic moments from simulations directly at the physical value of the pion mass.

Masses ofDmesons,Dsmesons, and charmonium states from twisted-mass lattice QCD

We compute masses of $D$ mesons, $D_s$ mesons and charmonium states using Wilson twisted mass lattice QCD. We present results for spin $J = 0,1,2,3$, parity $\mathcal{P} = -,+$ and in case of charmonium also charge conjugation $\mathcal{C} = -,+$. Computations are based on quark-antiquark creation operators and performed at three different unphysically heavy $u/d$ quark masses allowing an extrapolation to the physical $u/d$ quark mass. Within combined statistical and systematic errors, which are around $2 \% \ldots 3 \%$, our results agree with available experimental results. Particular focus is put on the $J^\mathcal{P} = 1^+$ mesons $D_1(2430)$ and $D_1(2420)$. We separate and classify these close-by states according to the total angular momentum of their light degrees of freedom, $j \approx 1/2$ and $j \approx 3/2$. This is a first important step to study decays $B^{(\ast)} \rightarrow D_1 + l + \nu$, for which a long-standing conflict between theory and experiment exists.

Hadron-hadron interactions from N f = 2 + 1 + 1 lattice QCD: isospin-2 ππ scattering length

We present results for the $I=2$ $\pi\pi$ scattering length using $N_f=2+1+1$ twisted mass lattice QCD for three values of the lattice spacing and a range of pion mass values. Due to the use of Laplacian Heaviside smearing our statistical errors are reduced compared to previous lattice studies. A detailed investigation of systematic effects such as discretisation effects, volume effects, and pollution of excited and thermal states is performed. After extrapolation to the physical point using chiral perturbation theory at NLO we obtain $M_\pi a_0=-0.0442(2)_\mathrm{stat}(^{+4}_{-0})_\mathrm{sys}$.

Renormalization of quark propagator, vertex functions, and twist-2 operators from twisted-mass lattice QCD atNf=4

We present a precise nonperturbative determination of the renormalization constants in the mass independent RI'-MOM scheme. The lattice implementation uses the Iwasaki gauge action and four degenerate dynamical twisted-mass fermions. The gauge configurations are provided by the ETM Collaboration. Renormalization constants for scalar, pseudoscalar, vector and axial operators, as well as the quark propagator renormalization, are computed at three different values of the lattice spacing, two volumes and several twisted-mass parameters. The method we developed allows for a precise cross-check of the running, thanks to the particular proper treatment of hypercubic artifacts. Results for the twist-2 operator ${O}_{44}$ are also presented.

Mass spectra of Ds meson from Nf = 2 twisted mass lattice QCD

In this paper, we study the mass spectra of Ds mesons, such as Ds, [Formula: see text] and Ds1. In the simulation, we use Nf = 2 twisted mass lattice QCD gauge configurations generated by the European Twisted Mass Collaboration (ETMC). The simulation is performed on lattices with lattice spacings a = 0.067 fm and lattice size 323×64, and a = 0.085 fm and lattice size 243×48, respectively. Our numerical results for the mass spectra of Ds mesons reached impressive agreement with the experimental data.

The hadronic vacuum polarization and automatic O a $$ \mathcal{O}(a) $$ improvement for twisted mass fermions

The vacuum polarization tensor and the corresponding vacuum polarization function are the basis for calculations of numerous observables in lattice QCD. Examples are the hadronic contributions to lepton anomalous magnetic moments, the running of the electroweak and strong couplings and quark masses. Quantities which are derived from the vacuum polarization tensor often involve a summation of current correlators over all distances in position space leading thus to the appearance of short-distance terms. The mechanism of O(a) improvement in the presence of such short-distance terms is not directly covered by the usual arguments of on-shell improvement of the action and the operators for a given quantity. If such short-distance contributions appear, the property of O(a) improvement needs to be reconsidered. We discuss the effects of these short-distance terms on the vacuum polarization function for twisted mass lattice QCD and find that even in the presence of such terms automatic O(a) improvement is retained if the theory is tuned to maximal twist.

Charmless chiral perturbation theory forNf=2+1+1twisted mass lattice QCD

The chiral Lagrangian describing the low-energy behavior of N_f=2+1+1 twisted mass lattice QCD is constructed through O(a^2). In contrast to existing results the effects of a heavy charm quark are consistently removed, leaving behind a charmless 3-flavor Lagrangian. This Lagrangian is used to compute the pion and kaon masses to one loop in a regime where the pion mass splitting is large and taken as a leading order effect. In comparison with continuum chiral perturbation theory additional chiral logarithms are present in the results. In particular, chiral logarithms involving the neutral pion mass appear. These predict rather large finite volume corrections in the kaon mass which roughly account for the finite volume effects observed in lattice data.

Determination of low-energy constants of Wilson chiral perturbation theory

Abstract By matching Wilson twisted mass lattice QCD determinations of pseudoscalar meson masses to Wilson Chiral Perturbation Theory we determine the low-energy constants $ W_6^{\prime } $ , $ W_8^{\prime } $ and their linear combination c 2. We explore the dependence of these low-energy constants on the choice of the lattice action and on the number of dynamical flavours.

Scalar Mesons and Tetraquarks from Twisted Mass Lattice QCD

1 Goethe-Universitat Frankfurt am Main, Institut fur Theoretische Physik, Max-von-Laue-Strase 1, D-60438 Frankfurt am Main, Germany 2 Department of Physics, University of Cyprus, P.O. Box 20537, 1678 Nicosia, Cyprus 3 Computation-based Science and Technology Research Center, Cyprus Institute, 20 Kavafi Str., Nicosia 2121, Cyprus 4 Helmholtz-Institut fur Strahlenund Kernphysik (Theorie) and Bethe Center for Theoretical Physics, Universitat Bonn, D-53115 Bonn, Germany 5 School of Mathematics, Trinity College, Dublin 2, Ireland 6 ECT⋆, Strada delle Tabarelle, 286, I-38123, Trento, Italy 7 NIC, DESY Zeuthen, Platanenallee 6, D-15738 Zeuthen, Germany 8 Humboldt-Universitat zu Berlin, Institut fur Physik, Newtonstrase 15, D-12489 Berlin, Germany

Masses of Mesons with Charm Valence Quarks from 2+1+1 Flavor Twisted Mass Lattice QCD

We present preliminary results of an ongoing lattice QCD computation of the spectrum of $D$ mesons and $D_s$ mesons and of charmonium using 2+1+1 flavors of twisted mass sea and valence quarks.

η and η′ mesons from N f = 2 + 1 + 1 twisted mass lattice QCD

We determine mass and mixing angles of eta and eta' states using Nf=2+1+1 Wilson twisted mass lattice QCD. We describe how those flavour singlet states need to be treated in this lattice formulation. Results are presented for three values of the lattice spacing, a=0.061 fm, a=0.078 fm and a=0.086 fm, with light quark masses corresponding to values of the charged pion mass in a range of 230 to 500 MeV and fixed bare strange and charm quark mass values. We obtain 557(15)(45) MeV for the eta mass (first error statistical, second systematic) and 44(5) degrees for the mixing angle in the quark flavour basis, corresponding to -10(5) degrees in the octet-singlet basis.