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Register a new userCharm and bottom quark masses on the lattice
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Andrew T. Lytle
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Lattice determinations of quark mass have made significant progress in the last few years. I will review recent advances in calculations of charm and bottom mass, which are near to achieving percent-level precision and with fully controlled systematics. Precise knowledge of these parameters is of particular interest for precision Higgs studies at future accelerators.
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We calculate the up-, down-, strange-, charm-, and bottom-quark masses using the MILC highly improved staggered-quark ensembles with four flavors of dynamical quarks. We use ensembles at six lattice spacings ranging from $aapprox0.15$~fm to $0.03$~fm and with both physical and unphysical values of the two light and the strange sea-quark masses. We use a new method based on heavy-quark effective theory (HQET) to extract quark masses from heavy-light pseudoscalar meson masses. Combining our analysis with our separate determination of ratios of light-quark masses we present masses of the up, down, strange, charm, and bottom quarks. Our results for the $overline{text{MS}}$-renormalized masses are $m_u(2~text{GeV}) = 2.130(41)$~MeV, $m_d(2~text{GeV}) = 4.675(56)$~MeV, $m_s(2~text{GeV}) = 92.47(69)$~MeV, $m_c(3~text{GeV}) = 983.7(5.6)$~MeV, and $m_c(m_c) = 1273(10)$~MeV, with four active flavors; and $m_b(m_b) = 4195(14)$~MeV with five active flavors. We also obtain ratios of quark masses $m_c/m_s = 11.783(25)$, $m_b/m_s = 53.94(12)$, and $m_b/m_c = 4.578(8)$. The result for $m_c$ matches the precision of the most precise calculation to date, and the other masses and all quoted ratios are the most precise to date. Moreover, these results are the first with a perturbative accuracy of $alpha_s^4$. As byproducts of our method, we obtain the matrix elements of HQET operators with dimension 4 and 5: $overline{Lambda}_text{MRS}=555(31)$~MeV in the minimal renormalon-subtracted (MRS) scheme, $mu_pi^2 = 0.05(22)~text{GeV}^2$, and $mu_G^2(m_b)=0.38(2)~text{GeV}^2$. The MRS scheme [Phys. Rev. D97, 034503 (2018), arXiv:1712.04983 [hep-ph]] is the key new aspect of our method.
This report discusses some recent investigations of the heavy hadron spectra using lattice QCD. The first half addresses multiple precision determinations of the masses of charm (and bottom) baryons. Recent lattice results in the tetraquark and the dibaryon sectors are also presented. The second half focuses on new exploratory studies of the excited charmonium spectra in the vector and scalar channels. Along the way, lattice results are compared with the experimental results, wherever they are available.
We use overlap fermions as valence quarks to calculate meson masses in a wide quark mass range on the $2+1$-flavor domain-wall fermion gauge configurations generated by the RBC and UKQCD Collaborations. The well-defined quark masses in the overlap fermion formalism and the clear valence quark mass dependence of meson masses observed from the calculation facilitate a direct derivation of physical current quark masses through a global fit to the lattice data, which incorporates $O(a^2)$ and $O(m_c^4a^4)$ corrections, chiral extrapolation, and quark mass interpolation. Using the physical masses of $D_s$, $D_s^*$ and $J/psi$ as inputs, Sommers scale parameter $r_0$ and the masses of charm quark and strange quark in the $overline{rm MS}$ scheme are determined to be $r_0=0.465(4)(9)$ fm, $m_c^{overline{rm MS}}(2,{rm GeV})=1.118(6)(24)$ GeV (or $m_c^{overline{rm MS}}(m_c)=1.304(5)(20)$ GeV), and $m_s^{overline{rm MS}}(2,{rm GeV})=0.101(3)(6),{rm GeV}$, respectively. Furthermore, we observe that the mass difference of the vector meson and the pseudoscalar meson with the same valence quark content is proportional to the reciprocal of the square root of the valence quark masses. The hyperfine splitting of charmonium, $M_{J/psi}-M_{eta_c}$, is determined to be 119(2)(7) MeV, which is in good agreement with the experimental value. We also predict the decay constant of $D_s$ to be $f_{D_s}=254(2)(4)$ MeV. The masses of charmonium $P$-wave states $chi_{c0}, chi_{c1}$ and $h_c$ are also in good agreement with experiments.
We determine the mass of the charm quark ($m_c$) from lattice QCD with two flavors of dynamical quarks with a mass around the strange quark. We compare this to a determination in quenched QCD which has the same lattice spacing (0.1 fm). We investigate different formulations of the quark mass, based on the Vector Ward Identity, PCAC relation and the FNAL heavy quark formalism. Based on these preliminary results we find no effects due to sea quarks with a mass around strange.
Working with a pion mass $m_pi approx 150$ MeV, we study $pipi$ and $Kpi$ scattering using two flavours of non-perturbatively improved Wilson fermions at a lattice spacing $aapprox 0.071$ fm. Employing two lattice volumes with linear spatial extents of $N_s=48$ and $N_s=64$ points and moving frames, we extract the phase shifts for p-wave $pipi$ and $Kpi$ scattering near the $rho$ and $K^*$ resonances.Comparing our results to those of previous lattice studies, that used pion masses ranging from about 200 MeV up to 470 MeV, we find that the coupling $g_{rhopipi}$ appears to be remarkably constant as a function of $m_{pi}$.
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