[Paper Review] Progress in Simulations with Twisted Mass Fermions at the Physical Point

Abdou Abdel-Rehim, Urs Wenger+9 more|arXiv (Cornell University)|May 7, 2016

Quantum Chromodynamics and Particle Interactions11 citations

TL;DR

This study presents Nf = 2 lattice QCD simulations using twisted mass fermions with a clover term at the physical pion mass, achieving a key result of 20(20) MeV for the charged-neutral pion mass splitting. It reports the first clover twisted mass measurement of the pion's average momentum fraction and determines quark mass ratios and decay constants without finite-volume or discretization corrections, with errors dominated by lattice spacing uncertainty.

ABSTRACT

In this contribution, results from Nf = 2 lattice QCD simulations at one lattice spacing using twisted mass fermions with a clover term at the physical pion mass are presented. The mass splitting between charged and neutral pions (including the disconnected contribution) is shown to be around 20(20) MeV. Further, a first measurement using the clover twisted mass action of the average momentum fraction of the pion is given. Finally, an analysis of pseudoscalar meson masses and decay constants is presented involving linear interpolations in strange and charm quark masses. Matching to meson mass ratios allows the calculation of quark mass ratios: ms=ml = 27:63(13), mc=ml = 339:6(2:2) and mc=ms = 12:29(10). From this mass matching the quantities fK = 153:9(7:5) MeV, fD = 219(11) MeV, fDs = 255(12) MeV and MDs = 1894(93) MeV are determined without the application of finite volume or discretization artefact corrections and with errors dominated by a preliminary estimate of the lattice spacing.

Motivation & Objective

• To investigate the mass splitting between charged and neutral pions in Nf = 2 lattice QCD with twisted mass fermions at the physical pion mass.
• To measure the average momentum fraction of the pion using the clover twisted mass action for the first time.
• To determine quark mass ratios and meson decay constants using linear interpolations in strange and charm quark masses.
• To extract physical observables such as fK, fD, fDs, and MDs without applying finite volume or discretization corrections.
• To provide preliminary estimates of hadronic quantities with errors primarily from lattice spacing uncertainty.

Proposed method

• Employing Nf = 2 lattice QCD simulations with twisted mass fermions and a clover term at a single lattice spacing.
• Using the clover twisted mass action to compute the pion's average momentum fraction via matrix element evaluation.
• Performing linear interpolations in strange and charm quark masses to extract meson masses and decay constants.
• Matching results to experimental meson mass ratios to determine quark mass ratios ms/ml, mc/ml, and mc/ms.
• Calculating physical observables like fK, fD, fDs, and MDs from the matched quark mass ratios.
• Estimating uncertainties primarily from a preliminary lattice spacing determination, with no finite volume or discretization corrections applied.

Experimental results

Research questions

• RQ1 What is the size of the charged-neutral pion mass splitting, including disconnected contributions, in Nf = 2 twisted mass lattice QCD at the physical pion mass?
• RQ2 What is the first lattice QCD measurement of the pion's average momentum fraction using the clover twisted mass action?
• RQ3 What are the quark mass ratios ms/ml, mc/ml, and mc/ms obtained via matching to meson mass ratios in this framework?
• RQ4 What are the resulting values of the kaon, D-meson, and Ds-meson decay constants and mass without finite volume or discretization corrections?
• RQ5 How do the uncertainties in these observables scale, particularly in relation to the lattice spacing estimate?

Key findings

• The charged-neutral pion mass splitting is measured as 20(20) MeV, including disconnected contributions.
• The first measurement of the pion's average momentum fraction using the clover twisted mass action is reported.
• The quark mass ratio ms/ml is determined to be 27.63(13) from matching to meson mass ratios.
• The quark mass ratio mc/ml is found to be 339.6(2.2), and mc/ms is 12.29(10).
• The kaon decay constant is calculated as fK = 153.9(7.5) MeV without finite volume or discretization corrections.
• The Ds-meson mass is determined as MDs = 1894(93) MeV, with errors dominated by the lattice spacing uncertainty.