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arXiv · 1602.07737

Controlling Excited-State Contamination in Nucleon Matrix Elements

Boram Yoon·Rajan Gupta·Tanmoy Bhattacharya·Michael Engelhardt·Jeremy Green·Bálint Joó·Huey-Wen Lin·John Negele·Kostas Orginos·Andrew Pochinsky·David Richards·Sergey Syritsyn·Frank Winter
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Abstract

We present a detailed analysis of methods to reduce statistical errors and excited-state contamination in the calculation of matrix elements of quark bilinear operators in nucleon states. All the calculations were done on a 2+1 flavor ensemble with lattices of size $32^3 \times 64$ generated using the rational hybrid Monte Carlo algorithm at $a=0.081$~fm and with $M_\pi=312$ MeV. The statistical precision of the data is improved using the all-mode-averaging method. We compare two methods for reducing excited-state contamination: a variational analysis and a two-state fit to data at multiple values of the source-sink separation $t_{\rm sep}$. We show that both methods can be tuned to significantly reduce excited-state contamination and discuss their relative advantages and cost-effectiveness. A detailed analysis of the size of source smearing used in the calculation of quark propagators and the range of values of $t_{\rm sep}$ needed to demonstrate convergence of the isovector charges of the nucleon to the $t_{\rm sep} \to \infty $ estimates is presented.

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Boram Yoon, Rajan Gupta, Tanmoy Bhattacharya, Michael Engelhardt, Jeremy Green, Bálint Joó, Huey-Wen Lin, John Negele, Kostas Orginos, Andrew Pochinsky, David Richards, Sergey Syritsyn, Frank Winter. 2016-02-24. Controlling Excited-State Contamination in Nucleon Matrix Elements. https://doi.org/10.1103/physrevd.93.114506

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