Physics Letters B 798 (2019) 134993
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Physics Letters B
www.elsevier.com/locate/physletb
Quark fragmentation as a probe of dynamical mass generation
Alberto Accardi
a,b
, Andrea Signori
c,d,e,b,∗
a
Hampton University, Hampton, VA 23668, USA
b
Theory Center, Thomas Jefferson National Accelerator Facility, 12000 Jefferson Avenue, Newport News, VA 23606, USA
c
Physics Division, Argonne National Laboratory, 9700 S. Cass Avenue, Lemont, IL 60439, USA
d
Dipartimento di Fisica, Università di Pavia, via Bassi 6, I-27100 Pavia, Italy
e
INFN, Sezione di Pavia, via Bassi 6, I-27100 Pavia, Italy
a r t i c l e i n f o a b s t r a c t
Article history:
Received
16 June 2019
Received
in revised form 17 September
2019
Accepted
30 September 2019
Available
online 3 October 2019
Editor:
A. Ringwald
Keywords:
Quarks
Hadronization
Fragmentation
functions
Mass
Chiral
symmetry
QCD
We address the propagation and hadronization of a struck quark by studying the gauge invariance of the
color-averaged cut quark propagator, and by relating this to the single inclusive quark fragmentation
correlator by means of new sum rules. Using suitable Wilson lines, we provide a gauge-invariant
definition for the mass of the color-averaged dressed quark and decompose this into the sum of a
current and an interaction-dependent component. The latter, which we argue is an order parameter
for dynamical chiral symmetry breaking, also appears in the sum rule for the twist-3
˜
E fragmentation
function, providing a specific experimental way to probe the dynamical generation of mass in Quantum
Chromo Dynamics.
© 2019 The Authors. 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
One of the crucial properties of the strong force is confinement,
namely the fact that partons cannot exist as free particles outside
of hadrons. As a consequence, any individual parton struck in a
high-energy scattering process and freed from its parent hadron
must transform into at least one hadron. During this hadronization
process, the colored and much lighter parton interacts with the
surrounding matter and the vacuum to produce massive and col-
orless
hadrons. Hadronization is thus tightly connected to the dy-
namical
generation of the mass, the spin, and the size of hadrons,
but the details of the quark-to-hadron transition are still unknown.
Unraveling hadronization dynamics is not only of fundamental im-
portance
to understand the nature of visible matter, but also to
tackle hadron tomography studies at current and future facilities,
such as the 12 GeV upgrade at Jefferson Lab [1] and a future US-
based
Electron-Ion Collider [2], where measuring the transverse
momentum of one final state hadron is crucial to provide a han-
dle
into the transverse motion of quarks and gluons in the hadron
target [3–10].
*
Corresponding author.
E-mail
addresses: accardi@jlab.org (A. Accardi), asignori@jlab.org (A. Signori).
In this letter, we address the propagation and hadronization
of a struck quark by studying the gauge invariance properties of
the “inclusive jet correlator” defined in Ref. [11–14], i.e., the color-
averaged
cut quark propagator supplemented by suitable Wilson
lines, and by relating this by means of sum rules to the fragmenta-
tion
correlator [15]utilized in Quantum Chromo Dynamics (QCD)
to describe the semi-inclusive transition of a quark into a single
hadron.
In
particular, through the Dirac decomposition of the jet corre-
lator,
we provide a gauge-invariant definition of the jet mass M
j
that was previously introduced in Ref. [14]. In this letter, we elu-
cidate
for the first time its nature and properties, recognizing that
M
j
can be decomposed into the sum of the current quark mass
and of an interaction-dependent “correlation mass”. Thus the jet
correlator can also be interpreted as a color-averaged propagator
for a dressed quark.
We
find that the jet mass and the correlation mass are experi-
mentally
accessible through sum rules for the unpolarized collinear
twist-3 E and
˜
E fragmentation functions (FFs). A similar sum rule
for the
˜
D
⊥
FF also supplies information on the average transverse
momentum of the produced hadrons. This letter focuses on those
FFs whose sum rules encode in a quantitative way the intimate
connection between hadronization and the dynamical generation
of mass and momentum, providing one with a novel way to quan-
https://doi.org/10.1016/j.physletb.2019.134993
0370-2693/
© 2019 The Authors. 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
.