The University of Southampton
University of Southampton Institutional Repository

Continuum limit of D and DS decay constants with Moebius domain wall fermions at physical pion masses

Continuum limit of D and DS decay constants with Moebius domain wall fermions at physical pion masses
Continuum limit of D and DS decay constants with Moebius domain wall fermions at physical pion masses
The inclusion of heavy quarks, such as the charm quark, poses difficulties in Lattice QCD simulations. These need to be overcome in order to make predictions of hadronic observables including a charm quark such as the decay constants fD and fDs. We first establish the region of validity of simulating heavy quarks with domain wall fermions (DWFs) in a feasibility study. We then carry out dynamical simulations with RBC/UKQCD’s Nf = 2+1f  ensembles at three lattice spacings (a −1 = 1.73 − 2.77 GeV) including two physical pion mass ensembles. From this we make a prediction for the decay constants fD and fDs and, using experimental input, the corresponding CKM matrix elements.

In the first part of this work we investigate the suitability of domain wall fermions (DWF) as a lattice regularisation for heavy quarks. We generate four quenched QCD gauge ensembles with the tree-level improved Symanzik gauge action and inverse lattice spacings in the range 2.0 − 5.7 GeV. On these we carry out an exploratory study to identify a region in the DWF parameter space that displays minimal cut-off effects. We find this region for the domain wall height M5 = 1.6 allowing for bare heavy quark masses satisfying amh <∼ 0.4, independent of the lattice spacing. Below this limit we maintain desirable features of DWF such as approximate chiral symmetry and O(a)-improvement. Based on this, we carry out a detailed scaling study of the decay constants of heavy-strange pseudoscalar mesons and the dispersion relation of heavy-heavy and heavy-strange pseudoscalar mesons. We find mild a2 discretisation effects for the heavy-strange decay constants and the heavy-strange dispersion relation. The cut-off effects for the heavy-heavy pseudoscalar dispersion relation are somewhat more pronounced. On our ensembles we find a 4 effects for heavy masses beyond the charm quark mass and large momenta (|p| ∼ 1.6 GeV). The findings of the pilot study establish the basis for simulations of charm quarks with domain wall fermions.

In the second part of the presented work we simulate heavy-light and heavy-strange pseudoscalar mesons on RBC/UKQCD’s 2 + 1f ensembles with pion masses as low as 139 MeV and inverse lattice spacings ranging from 1.73 GeV to 2.77 GeV. From this data we extract the decay constants fD and fDs. We devise two different fit ansatze to process this data and carry out a full systematic error analysis. We find fD = 208.7(2.8)stat (+2.1−1.8)sys MeV, fDs = 246.4(1.9)stat (+1.3−1.9)sys MeV and fDs/fD = 1.1667(77)stat (+60−46)sys.

Finally, using experimental input we extract the corresponding CKM matrix elements. We find |V|cd = 0.2185(50)exp. (+35−37)lat and |V |cs = 1.011(16)exp. (+11− 9)lat where the first error comes from the experimental input and the second from our determination of the decay constants. We compare our results with the existing literature and find good agreement between our central values and competitive errors. This work constitutes the basis of RBC/UKQCD’s wider charm physics program.
University of Southampton
Tsang, Justus Tobias
e4648385-cecf-4c02-b13e-c06312f16b12
Tsang, Justus Tobias
e4648385-cecf-4c02-b13e-c06312f16b12
Juttner, Andreas
a90ff7c5-ae8f-4c8e-9679-b5a95b2a6247

Tsang, Justus Tobias (2017) Continuum limit of D and DS decay constants with Moebius domain wall fermions at physical pion masses. University of Southampton, Faculty of Physical and Engineering, Doctoral Thesis, 165pp.

Record type: Thesis (Doctoral)

Abstract

The inclusion of heavy quarks, such as the charm quark, poses difficulties in Lattice QCD simulations. These need to be overcome in order to make predictions of hadronic observables including a charm quark such as the decay constants fD and fDs. We first establish the region of validity of simulating heavy quarks with domain wall fermions (DWFs) in a feasibility study. We then carry out dynamical simulations with RBC/UKQCD’s Nf = 2+1f  ensembles at three lattice spacings (a −1 = 1.73 − 2.77 GeV) including two physical pion mass ensembles. From this we make a prediction for the decay constants fD and fDs and, using experimental input, the corresponding CKM matrix elements.

In the first part of this work we investigate the suitability of domain wall fermions (DWF) as a lattice regularisation for heavy quarks. We generate four quenched QCD gauge ensembles with the tree-level improved Symanzik gauge action and inverse lattice spacings in the range 2.0 − 5.7 GeV. On these we carry out an exploratory study to identify a region in the DWF parameter space that displays minimal cut-off effects. We find this region for the domain wall height M5 = 1.6 allowing for bare heavy quark masses satisfying amh <∼ 0.4, independent of the lattice spacing. Below this limit we maintain desirable features of DWF such as approximate chiral symmetry and O(a)-improvement. Based on this, we carry out a detailed scaling study of the decay constants of heavy-strange pseudoscalar mesons and the dispersion relation of heavy-heavy and heavy-strange pseudoscalar mesons. We find mild a2 discretisation effects for the heavy-strange decay constants and the heavy-strange dispersion relation. The cut-off effects for the heavy-heavy pseudoscalar dispersion relation are somewhat more pronounced. On our ensembles we find a 4 effects for heavy masses beyond the charm quark mass and large momenta (|p| ∼ 1.6 GeV). The findings of the pilot study establish the basis for simulations of charm quarks with domain wall fermions.

In the second part of the presented work we simulate heavy-light and heavy-strange pseudoscalar mesons on RBC/UKQCD’s 2 + 1f ensembles with pion masses as low as 139 MeV and inverse lattice spacings ranging from 1.73 GeV to 2.77 GeV. From this data we extract the decay constants fD and fDs. We devise two different fit ansatze to process this data and carry out a full systematic error analysis. We find fD = 208.7(2.8)stat (+2.1−1.8)sys MeV, fDs = 246.4(1.9)stat (+1.3−1.9)sys MeV and fDs/fD = 1.1667(77)stat (+60−46)sys.

Finally, using experimental input we extract the corresponding CKM matrix elements. We find |V|cd = 0.2185(50)exp. (+35−37)lat and |V |cs = 1.011(16)exp. (+11− 9)lat where the first error comes from the experimental input and the second from our determination of the decay constants. We compare our results with the existing literature and find good agreement between our central values and competitive errors. This work constitutes the basis of RBC/UKQCD’s wider charm physics program.

Text
Final Thesis.pdf - Version of Record
Available under License University of Southampton Thesis Licence.
Download (3MB)

More information

Published date: January 2017

Identifiers

Local EPrints ID: 405419
URI: https://eprints.soton.ac.uk/id/eprint/405419
PURE UUID: 7888d52d-e93f-4485-b946-5420d00d8086

Catalogue record

Date deposited: 18 Feb 2017 00:23
Last modified: 13 Mar 2019 20:18

Export record

Download statistics

Downloads from ePrints over the past year. Other digital versions may also be available to download e.g. from the publisher's website.

View more statistics

Atom RSS 1.0 RSS 2.0

Contact ePrints Soton: eprints@soton.ac.uk

ePrints Soton supports OAI 2.0 with a base URL of https://eprints.soton.ac.uk/cgi/oai2

This repository has been built using EPrints software, developed at the University of Southampton, but available to everyone to use.

We use cookies to ensure that we give you the best experience on our website. If you continue without changing your settings, we will assume that you are happy to receive cookies on the University of Southampton website.

×