Determination of the up/down-quark mass within QCD sum rules in the scalar channel

In this work, we determine up/down-quark mass $$m_{q=u/d}$$ m q = u / d in the isoscalar scalar channel from both the Shifman–Vainshtein–Zakharov (SVZ) and the Monte-Carlo-based QCD sum rules. The relevant spectral function, including the contributions from the $$f_0(500)$$ f 0 ( 500 ) , $$f_0(980)$$ f 0 ( 980 ) and $$f_0(1370)$$ f 0 ( 1370 ) resonances, is determined from a sophisticated U(3) chiral study. Via the traditional SVZ QCD sum rules, we give the prediction to the average light-quark mass $$m_q(2 ~\text {GeV})=\frac{1}{2}(m_u(2 ~\text {GeV}) + m_d(2 ~\text {GeV}))=(3.46^{+0.16}_{-0.22} \pm 0.33) ~\text {MeV}$$ m q ( 2 GeV ) = 1 2 ( m u ( 2 GeV ) + m d ( 2 GeV ) ) = ( 3 . 46 - 0.22 + 0.16 ± 0.33 ) MeV . Meanwhile, by considering the uncertainties of the input QCD parameters and the spectral functions of the isoscalar scalar channel, we obtain $$m_q (2~\text {GeV}) = (3.44 \pm 0.14 \pm 0.32) ~\text {MeV}$$ m q ( 2 GeV ) = ( 3.44 ± 0.14 ± 0.32 ) MeV from the Monte-Carlo-based QCD sum rules. Both results are perfectly consistent with each other, and nicely agree with the Particle Data Group value within the uncertainties.

Isospin-1/2 Dπ scattering and the lightest $$ {D}_0^{\ast } $$ resonance from lattice QCD

Isospin-1/2 Dπ scattering amplitudes are computed using lattice QCD, working in a single volume of approximately (3.6 fm)3 and with a light quark mass corresponding to mπ ≈ 239 MeV. The spectrum of the elastic Dπ energy region is computed yielding 20 energy levels. Using the Lüscher finite-volume quantisation condition, these energies are translated into constraints on the infinite-volume scattering amplitudes and hence enable us to map out the energy dependence of elastic Dπ scattering. By analytically continuing a range of scattering amplitudes, a $$ {D}_0^{\ast } $$ D 0 ∗ resonance pole is consistently found strongly coupled to the S-wave Dπ channel, with a mass m ≈ 2200 MeV and a width Γ ≈ 400 MeV. Combined with earlier work investigating the $$ {D}_{s0}^{\ast } $$ D s 0 ∗ , and $$ {D}_0^{\ast } $$ D 0 ∗ with heavier light quarks, similar couplings between each of these scalar states and their relevant meson-meson scattering channels are determined. The mass of the $$ {D}_0^{\ast } $$ D 0 ∗ is consistently found well below that of the $$ {D}_{s0}^{\ast } $$ D s 0 ∗ , in contrast to the currently reported experimental result.

Meson decay studies from MAMI A2

Decays of the light mesons π0, η, ω, and η’ provide a unique laboratory to test fundamental aspects of hadron physics. Precision studies of such diverse topics as the light quark mass ratio, π−π scattering lengths, and searches for physics beyond the Standard Model are possible. Additionally, Dalitz decays of light mesons provide a way of measuring the electromagnetic meson transition formfactors in the time-like region. The A2 tagged photon facility at the Mainz Microtron provides a high yield of light mesons produced by photo-induced reactions on protons, which makes the experiment ideal for high precision measurements of meson decays. Presented here are the contributions made by the A2 collaboration to such studies.

Bs → Kℓv form factors with 2+1 flavors

Using the MILC 2+1 flavor asqtad quark action ensembles, we are calculating the form factors f0 and f+ for the semileptonic Bs → Kℓv decay. A total of six ensembles with lattice spacing from ≈ 0.12 to 0.06 fm are being used. At the coarsest and finest lattice spacings, the light quark mass m’l is one-tenth the strange quark mass m’s. At the intermediate lattice spacing, the ratio m’l/m’s ranges from 0.05 to 0.2. The valence b quark is treated using the Sheikholeslami-Wohlert Wilson-clover action with the Fermilab interpretation. The other valence quarks use the asqtad action. When combined with (future) measurements from the LHCb and Belle II experiments, these calculations will provide an alternate determination of the CKM matrix element |Vub|.

Towards leading isospin breaking effects in mesonic masses with O(a) improved Wilson fermions

We present an exploratory study of leading isospin breaking effects in mesonic masses using O(a) improved Wilson fermions. Isospin symmetry is explicitly broken by distinct masses and electric charges of the up and down quarks. In order to be able to make use of existing isosymmetric QCD gauge ensembles we apply reweighting techniques. The path integral describing QCD+QED is expanded perturbatively in powers of the light quark’ mass deviations and the electromagnetic coupling. We employ QEDL as a finite volume formulation of QED.