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Chris Michael

Publications and source records attributed to Chris Michael.

At least 19 recordsLinked to original sources
arXiv2013

η and η' masses and decay constants from lattice QCD with 2+1+1 quark flavours

We investigate the masses and decay constants of eta and eta' mesons using the Wilson twisted mass formulation with N_f=2+1+1 dynamical quark flavours based on gauge configurations of ETMC. We show how to efficiently subtract excited state contributions to the relevant correlation functions and estimate in particular the eta' mass with improved precision. After investigating the strange quark mass dependence and the continuum and chiral extrapolations, we present our results for masses and mixing angle(s) at the physical point. Using chiral perturbation theory we also extract the decay constants f_l and f_s and use them to estimate the decay widths of eta,η' to gamma gamma and the transition form factor in the limit of large momentum transfer.

hep-lat↗
arXiv2013

η and η' mixing from Lattice QCD

We present a lattice QCD computation of $η$ and $η^\prime$ masses and mixing angles, for the first time controlling continuum and quark mass extrapolations. The results for the eta mass 551(8)(6) MeV (first error statistical, second systematic) and the eta' mass 1006(54)(38)(+61) MeV (third error from our method) are in excellent agreement with experiment. Our data show that the mixing in the quark flavour basis can be described by a single mixing angle of 46(1)(3) degree indicating that the eta' is mainly a flavour singlet state.

hep-lat↗
arXiv2013

Properties of pseudoscalar flavour-singlet mesons from 2+1+1 twisted mass lattice QCD

We study properties of pseudoscalar flavour-singlet mesons from Wilson twisted mass lattice QCD with Nf=2+1+1 dynamical quark flavors. Results for masses are presented at three values of the lattice spacing and light quark masses corresponding to values of the pion mass from 230 MeV to 500 MeV. We briefly discuss scaling effects and the light and strange quark mass dependence of the eta mass. In addition we present an exploratory study using Osterwalder-Seiler type strange and charm valence quarks. This approach avoids some of the complications of the twisted mass heavy doublet. We present first results for matching valence and unitary actions and a comparison of statistical uncertainties.

hep-lat↗
arXiv2013

Determination of Low-Energy Constants of Wilson Chiral Perturbation Theory

By matching Wilson twisted mass lattice QCD determinations of pseudoscalar meson masses to Wilson Chiral Perturbation Theory we determine the low-energy constants $W'_6$, $W'_8$ 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.

hep-lat↗
arXiv2011

Eta and eta' meson masses from Nf=2+1+1 twisted mass lattice QCD

We determine mass and flavour content 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 two values of the lattice spacing, a~0.08 fm and a~0.09 fm, with a range of light quark masses corresponding to values of the pion mass from 270 to 500 MeV and fixed bare strange and charm quark mass values.

hep-lat↗
arXiv2010

Kaon and D meson masses with N_f = 2+1+1 twisted mass lattice QCD

We discuss the computation of the kaon and D meson masses in the N_f = 2+1+1 twisted mass lattice QCD setup, where explicit heavy flavor and parity breaking occurs at finite lattice spacing. We present three methods suitable in this context and verify their consistency.

hep-lat↗
arXiv2010

Computing K and D meson masses with N_f = 2+1+1 twisted mass lattice QCD

We discuss the computation of the mass of the K and D mesons within the framework of N_f = 2+1+1 twisted mass lattice QCD from a technical point of view. These quantities are essential, already at the level of generating gauge configurations, being obvious candidates to tune the strange and charm quark masses to their physical values. In particular, we address the problems related to the twisted mass flavor and parity symmetry breaking, which arise when considering a non-degenerate (c,s) doublet. We propose and verify the consistency of three methods to extract the K and D meson masses in this framework.

hep-lat↗
arXiv2010

Light hadrons from lattice QCD with light (u,d), strange and charm dynamical quarks

We present results of lattice QCD simulations with mass-degenerate up and down and mass-split strange and charm (N_f = 2+1+1) dynamical quarks using Wilson twisted mass fermions at maximal twist. The tuning of the strange and charm quark masses is performed at two values of the lattice spacing a~0.078 fm and a~0.086 fm with lattice sizes ranging from L~1.9 fm to L~2.8 fm. We measure with high statistical precision the light pseudoscalar mass m_PS and decay constant f_PS in a range 270 < m_PS < 510 MeV and determine the low energy parameters f_0, l_3 and l_4 of SU(2) chiral perturbation theory. We use the two values of the lattice spacing, several lattice sizes as well as different values of the light, strange and charm quark masses to explore the systematic effects. A first study of discretisation effects in light-quark observables and a comparison to N_f=2 results are performed.

hep-lat↗
arXiv2010

The continuum limit of the static-light meson spectrum

We investigate the continuum limit of the low lying static-light meson spectrum using Wilson twisted mass lattice QCD with N_f = 2 dynamical quark flavours. We consider three values of the lattice spacing a ~ 0.051 fm, 0.064 fm, 0.080 fm and various values of the pion mass in the range 280 MeV < m_PS < 640 MeV. We present results in the continuum limit for light cloud angular momentum j = 1/2, 3/2, 5/2 and for parity P = +, -. We extrapolate our results to physical quark masses, make predictions regarding the spectrum of B and B_s mesons and compare with available experimental results.

hep-lat↗
arXiv2008

The static-light meson spectrum from twisted mass lattice QCD

We compute the static-light meson spectrum with N_f = 2 flavours of sea quarks using Wilson twisted mass lattice QCD. We consider five different values for the light quark mass corresponding to 300 MeV < m_PS < 600 MeV and we present results for angular momentum j = 1/2, j = 3/2 and j = 5/2 and for parity P = + and P = -. We extrapolate our results to physical quark masses and make predictions regarding the spectrum of B and B_s mesons.

hep-lat↗
arXiv2008

Static-light meson masses from twisted mass lattice QCD

We compute the static-light meson spectrum using two-flavor Wilson twisted mass lattice QCD. We have considered five different values for the light quark mass corresponding to 300 MeV < m_PS < 600 MeV. We have extrapolated our results, to make predictions regarding the spectrum of B and B_s mesons.

hep-lat↗
arXiv2007

Neutral mesons and disconnected diagrams in Twisted Mass QCD

We evaluate properties of neutral mesons in Nf=2 dynamical simulations of TMQCD at maximal twist. The pion is explored - establishing the size of the isospin splitting (an order a^2 effect). We investigate the eta' (the Nf=2 flavour singlet pseudoscalar meson) and neutral rho and scalar mesons. We show that disconnected diagrams can be evaluated very efficiently in TMQCD using variance reduction methods.

hep-lat↗
arXiv2006

Hadronic decays from the lattice

I review the lattice QCD approach to determining hadronic decay transitions. Examples considered include rho to pi pi; b_1 to pi omega; hybrid meson decays and scalar meson decays. I discuss what lattices can provide to help understand the composition of hadrons.

hep-lat↗
arXiv2004

Phenomenology of static-light mesons from unquenched lattice QCD calculations

We present results for the static-light meson from unquenched lattice QCD. The unquenched gauge configurations were generated using the non-perturbatively improved clover action. At the fixed lattice spacing of 0.1 fm the lightest sea quark mass used is a third of the strange quark mass. A comparison is made between heavy-light chiral perturbation theory and the f_B^(static) decay constant. The mass of the bottom quark is also reported: m_b(m_b) = 4.25(2)(11) GeV, where the first error is statistical and the last error is the systematic uncertainty.

hep-lat↗
arXiv2003

Hadronic transitions from the lattice

I discuss strategies to determine hadronic decay couplings from lattice studies. As a check of the methods, I explore the decay of a vector meson to two pseudoscalar mesons with $N_f=2$ flavours of sea quark. Although we are working with quark masses that do not allow a physical decay, I show how the transition rate can be evaluated from the amplitude for $ρ\to ππ$ and from the annihilation component of $ππ\to ππ$. I explore the decay amplitude for two different pion momenta and find consistent results. The coupling strength found is in agreement with experiment. I also find evidence for a shift in the $ρ$ mass caused by mixing with two pion states. I also present results for the decay of a hybrid meson, for the case of heavy valence quarks.

hep-lat↗
arXiv2001

An Exploratory Lattice Study of Spectator Effects in Inclusive Decays of the Lambda_b Baryon

A possible explanation of the apparent disrepency between the theoretical prediction and experimental measurement of the ratio of lifetimes $τ(Λ_b)/τ(B_d)$ is that ``spectator effects'', which appear at $O(1/m_b^3)$ in the heavy quark expansion, contribute significantly. We investigate this possibility by computing the corresponding operator matrix elements in a lattice simulation. We find that spectator effects are indeed significant, but do not appear to be sufficiently large to account for the full discrepency. We stress, however, that this is an exploratory study, and it is important to check our conclusions on a larger lattice and using a larger sample of gluon configurations.

hep-lat↗
arXiv2001

Hadron spectroscopy of twisted mass lattice QCD at beta = 6.0

Simulations that use the clover action in quenched QCD calculations have a lower limit to the quark mass that can be reached, because of the fluctuations caused by exceptional configurations. From this low statistics study, we find that the twisted clover action, recently introduced by the ALPHA collaboration, can be used to simulate quenched QCD at quark masses below those attainable by simulations that use the clover action.

hep-lat↗