984 research outputs found
QCDQED evolution of TMDs
We consider for the first time the QED corrections to the evolution of
(un)polarized quark and gluon transverse-momentum-dependent distribution and
fragmentation functions (TMDs in general). By extending their operator
definition to QCDQED, we provide the mixed new anomalous dimensions up
to and the pure QED ones up to .
These new corrections are universal for all TMDs up to the flavor of the
considered parton, i.e., the full flavor universality of TMD evolution found in
pure QCD is broken in QCDQED by the presence of the electric charge. In
addition, we provide the leading-order QED corrections to the matching
coefficients of the unpolarized quark TMD parton distribution function onto its
integrated counterparts at .Comment: 9 pages, 3 figures. v2: minor corrections, accepted for publication
in Phys. Lett.
Soft and Collinear Factorization and Transverse Momentum Dependent Parton Distribution Functions
In this work we consider how a parton distribution function, with an explicit
transverse momentum dependence can be properly defined in a
regularization-scheme independent manner. We argue that by considering a
factorized form of the transverse momentum dependent spectrum for the
production of a heavy lepton pair in Drell-Yan reaction, one should first split
the relevant soft function into two boost invariant contributions. When those
soft contributions are added to the pure collinear contributions, well-defined
hadronic matrix elements emerge, i.e., the transverse momentum dependent
distributions. We also perform a comparison with Collins' definition.Comment: 9 pages, 3 figures. We modified the discussion about the equivalence
between Collins (JCC) and Echevarria-Idilbi-Scimemi (EIS) definitions of
TMDPDF. The results remain intact. Version to appear in Phys. Lett.
Non-perturbative QCD effects in spectra of Drell-Yan and -boson production
The factorization theorems for transverse momentum distributions of
dilepton/boson production, recently formulated by Collins and
Echevarria-Idilbi-Scimemi in terms of well-defined transverse momentum
dependent distributions (TMDs), allows for a systematic and quantitative
analysis of non-perturbative QCD effects of the cross sections involving these
quantities. In this paper we perform a global fit using all current available
data for Drell-Yan and -boson production at hadron colliders within this
framework. The perturbative calculable pieces of our estimates are included
using a complete resummation at next-to-next-to-leading-logarithmic accuracy.
Performing the matching of transverse momentum distributions onto the standard
collinear parton distribution functions and recalling that the corresponding
matching coefficient can be partially exponentiated, we find that this
exponentiated part is spin-independent and resummable. We argue that the
inclusion of higher order perturbative pieces is necessary when data from lower
energy scales are analyzed. We consider non-perturbative corrections both to
the intrinsic nucleon structure and to the evolution kernel and find that the
non-perturbative part of the TMDs could be parametrized in terms of a minimal
set of parameters (namely 2-3). When all corrections are included the global
fit so performed gives a and a very precise
prediction for vector boson production at the Large Hadron Collider (LHC).Comment: 24 pages, 11 figures. v2: new subsection added, discussion on the
stability of the calculations and on higher order contributions improved,
results unchange
Single spin asymmetries from a single Wilson loop
We study the leading-power gluon transverse momentum dependent distributions
(TMDs) of relevance to the study of asymmetries in the scattering off
transversely polarized hadrons. Next-to-leading-order perturbative calculations
of these TMDs show that at large transverse momentum they have common dynamical
origins, but that in the limit of small longitudinal momentum fraction only
one origin remains. We find that in this limit only the dipole-type gluon TMDs
survive and become identical to each other. At small they are all given by
the expectation value of a single Wilson loop inside the transversely polarized
hadron, the so-called spin-dependent odderon. This universal origin of
transverse spin asymmetries at small is of importance to current and future
experimental studies, paving the way to a better understanding of the role of
gluons in the three-dimensional structure of spin-polarized protons.Comment: 5 pages, 1 figure. Various changes to the text, additional
references, conclusions unchanged, version accepted for publication in
Physical Review Letter
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