Physics Letters B 767 (2017) 193–198
Contents lists available at ScienceDirect
Physics Letters B
www.elsevier.com/locate/physletb
Lattice QCD with N
f
=2 +1 +1 domain-wall quarks
TWQCD Collaboration
Yu-Chih Chen
a
, Ting-Wai Chiu
a,b,c,∗
a
Physics Department, National Taiwan University, Taipei 10617, Taiwan
b
Center for Quantum Science and Engineering, National Taiwan University, Taipei 10617, Taiwan
c
Physics Department, National Taiwan Normal University, Taipei 11677, Taiwan
a r t i c l e i n f o a b s t r a c t
Article history:
Received
11 January 2017
Accepted
23 January 2017
Available
online 3 February 2017
Editor: M.
Cveti
ˇ
c
We perform hybrid Monte Carlo simulation of (2 +1 + 1)-flavors lattice QCD with the optimal domain-
wall
fermion (which has the effective 4D Dirac operator exactly equal to the Zolotarev optimal rational
approximation of the overlap Dirac operator). The gauge ensemble is generated on the 32
3
× 64 lattice
with the extent N
s
=16 in the fifth dimension, and with the plaquette gauge action at β = 6/g
2
=6.20.
The lattice spacing (a 0.063 fm) is determined by the Wilson flow, using the value
√
t
0
=0.1416(8) fm
obtained
by the MILC Collaboration for the (2 +1 +1)-flavors QCD. The masses of s and c quarks are fixed
by the masses of the vector mesons φ(1020) and J /ψ (3097) respectively; while the mass of the u/d
quarks
is heavier than their physical values, with the unitary pion mass M
π
280 MeV (and M
π
L 3).
We compute the point-to-point quark propagators, and measure the time-correlation functions of meson
and baryon interpolators. Our results of the mass spectra of the lowest-lying hadrons containing s and c
quarks
are in good agreement with the high energy experimental values, together with the predictions
of the charmed baryons which have not been observed in experiments.
© 2017 The Author. Published by Elsevier B.V. This is an open access article under the CC BY license
(http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP
3
.
1. Introduction
Since the discovery of the Higgs scalar in 2012, the Standard
Model (SM) emerged in mid 1970s looks to be complete in the
sense that all major predictions of the SM have been realized
in high energy experiments, and almost all high energy experi-
mental
data can be understood in the framework of SM, except
the matter-antimatter asymmetry and the origin of the neutrino
masses. Currently, the challenge of high energy physics is to find
out whether there is any new physics beyond the SM, in view of
the generation puzzle and the large number of parameters in the
SM, which suggest that the SM is an effective theory at the scale
probed by the present generation of high energy accelerators. In
order to identify any discrepancies between the high energy ex-
perimental
results and theoretical values derived from the SM, the
latter have to be obtained in a framework which preserves all es-
sential
features of the SM. Otherwise, it is difficult to determine
whether such a discrepancy is due to new physics, or just the
approximations (or models) one has used. So far, the largest un-
*
Corresponding author.
E-mail
address: twchiu@phys.ntu.edu.tw (T.-W. Chiu).
certainties in the theoretical predictions of the SM stem from the
sector of the strong interaction, namely, QCD. Theoretically, lattice
QCD is the most viable framework to tackle QCD nonperturba-
tively
from the first principles. However, in practice, it is difficult
to simulate dynamical u, d, s, c, and b quarks at their physical
masses (ranging from ∼ 3–4500 MeV), in a sufficiently large vol-
ume
and small enough lattice spacing such that the finite-volume
and discretization errors are both well under control. Note that the
t quark can be neglected in QCD simulations since it is extremely
short-lived and it decays to W-boson and b/s/d quarks before it
can interact with other quarks through the gluons. Even after ne-
glecting
the t quark, to simulate u, d, s, c, and b quarks at their
physical masses is still a very challenging problem. For example, if
one designs the simulation close to the physical pion mass with
M
π
140 MeV and M
π
L > 6(to keep finite-volume error under
control), then it would require a lattice of size ∼ 100
4
to accom-
modate
physical c quark with sufficiently small discretization error,
not to mention the much heavier b quark. The current generation
of supercomputers with ∼ 100 Petaflops seems to be marginal for
this purpose, and the next generation of supercomputers with Ex-
aflops
is required to simulate (u, d, s, c, b ) quarks at their physical
masses.
http://dx.doi.org/10.1016/j.physletb.2017.01.068
0370-2693/
© 2017 The Author. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by
SCOAP
3
.
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