Toward the determination of the gluon helicity distribution in the nucleon from lattice quantum chromodynamics
Not Available
73 NUCLEAR PHYSICS AND RADIATION PHYSICSβ
Engineering topics
Monahan, Christopher J.
Publications and source records attributed to Monahan, Christopher J..
Detailed analysis of excited-state systematics in a lattice QCD calculation of π π΄
Excited state contamination remains one of the most challenging sources of systematic uncertainty to control in lattice QCD calculations of nucleon matrix elements and form factors: early time separations are contaminated by excited states and late times suffer from an exponentially bad signal-to-noise problem. High-statistics calculations at large time separations β³ 1 fm are commonly used to combat these issues. In this work, focusing on g A , we explore the alternative strategy of utilizing a large number of relatively low-statistics calculations at short to medium time separations (0.2β1 fm), combined with a multistate analysis. On an ensemble with a pion mass of approximately 310 MeV and a lattice spacing of approximately 0.09 fm, we find this provides a more robust and economical method of quantifying and controlling the excited state systematic uncertainty. A quantitative separation of various types of excited states enables the identification of the transition matrix elements as the dominant contamination. The excited state contamination of the Feynman-Hellmann correlation function is found to reduce to the 1% level at approximately 1 fm while, for the more standard three-point functions, this does not occur until after 2 fm. Critical to our findings is the use of a global minimization, rather than fixing the spectrum from the two-point functions and using them as input to the three-point analysis. We find that the ground state parameters determined in such a global analysis are stable against variations in the excited state model, the number of excited states, and the truncation of early-time or late-time numerical data.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDSβ
A novel nonperturbative renormalization scheme for local operators
The gradient flow exponentially suppresses ultraviolet field fluctuations and removes ultraviolet divergences (up to a multiplicative fermionic wavefunction renormalization). It can be used to describe real-space Wilsonian renormalization group transformations and determine the corresponding beta function. We propose a new nonperturbative renormalization scheme for local composite fermionic operators that uses the gradient flow and is amenable to lattice QCD calculations. We present preliminary nonperturbative results for the running of quark bilinear operators in this scheme and outline the calculation of perturbative matching to the MS-bar scheme.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICβ
One-loop matching for quark dipole operators in a gradient-flow scheme
The quark chromoelectric dipole (qCEDM) operator is a CP-violating operator describing, at hadronic energies, beyond-the-standard-model contributions to the electric dipole moment of particles with nonzero spin. In this paper we define renormalized dipole operators in a regularization-independent scheme using the gradient flow, and we perform the matching at one loop in perturbation theory to renormalized operators of the same and lower dimension in the more familiar MS scheme. We also determine the matching coefficients for the quark chromo-magnetic dipole operator (qCMDM), which contributes for example to matrix elements relevant to CP-violating and CP-conserving kaon decays. The calculation provides a basis for future lattice QCD computations of hadronic matrix elements of the qCEDM and qCMDM operators.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDSβ
Unpolarized gluon distribution in the nucleon from lattice quantum chromodynamics
Not Available
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDSβ
Scale setting the MΓΆbius domain wall fermion on gradient-flowed HISQ action using the omega baryon mass and the gradient-flow scales π‘ 0 and π€ 0
We report on a subpercent scale determination using the omega baryon mass and gradient-flow methods. The calculations are performed on 22 ensembles of π π =2 +1 +1 highly improved, rooted staggered sea-quark configurations generated by the MILC and CalLat Collaborations. The valence quark action used is MΓΆbius domain wall fermions solved on these configurations after a gradient-flow smearing is applied with a flowtime of π‘ gf = 1 in lattice units. The ensembles span four lattice spacings in the range 0.06 β² π β²0.15 fm, six pion masses in the range 130 β² π π β² 400 MeV and multiple lattice volumes. On each ensemble, the gradient-flow scales π‘ 0 /π 2 and π€ 0 /π and the omega baryon mass πβ’π Ξ© are computed. The dimensionless product of these quantities is then extrapolated to the continuum and infinite volume limits and interpolated to the physical light, strange and charm quark mass point in the isospin limit, resulting in the determination of $\sqrt{t}_0$ = 0.1422β’(14) fm and π€ 0 = 0.1709β’(11) fm with all sources of statistical and systematic uncertainty accounted for. The dominant uncertainty in both results is the stochastic uncertainty, though for $\sqrt{t}_0$ there are comparable continuum extrapolation uncertainties. For π€ 0 , there is a clear path for a few-per-mille uncertainty just through improved stochastic precision, as recently obtained by the Budapest-Marseille-Wuppertal Collaboration.
73 NUCLEAR PHYSICS AND RADIATION PHYSICSβ