11,285 research outputs found
Single-spin asymmetries and Qiu-Sterman effect(s)
I discuss the relation between the Qiu-Sterman effects on one hand and the
Collins, Sivers and Boer-Mulders effects on the other hand. It was suggested
before that some of these effects are in fact the same, thus providing
interesting connections between transverse-momentum dependent twist-2 functions
and collinear twist-3 functions. Here I propose an alternative way to reach
similar conclusions.Comment: Contribution to the proceedings of "The International Workshop on
Transverse Polarisation Phenomena in Hard Processes" (Transversity 2005),
Como, Italy, 7-10th September 2005. (1 ref. added in v2
Models for transverse-momentum distributions and transversity
I present a short review of models for transverse-momentum distributions and
transversity, with a particular attention on general features common to many
models. I compare some model results with experimental extractions. I discuss
the existence of relations between different functions, their limits of
validity, their possible use.Comment: Talk delivered at the "Third International Workshop on Transverse
Polarization Phenomena in Hard Scattering" (Transversity 2011), 29 Aug. - 2
Sep. 2011, Veli Losinj (Croatia
Twist Three Distribution f_\perp(x,k^\perp) in Light-front Hamiltonian Approach
We calculate the twist three distribution f_\perp(x,k^\perp) contributing to
Cahn effect in unpolarized semi-inclusive deep inelastic scattering. We use
light-front Hamiltonian technique and take the state to be a dressed quark at
one loop in perturbation theory. The 'genuine twist three' contribution comes
from the quark-gluon interaction part in the operator and is explicitly
calculated. f_\perp(x,k^\perp) is compared with f_1(x,k^\perp).Comment: Two figures added, one author added, some parts rewritten for
clarificatio
Modeling dihadron fragmentation functions
We present a model for dihadron fragmentation functions, describing the
fragmentation of a quark into two unpolarized hadrons. We tune the parameters
of our model to the output of the PYTHIA event generator for two-hadron
semi-inclusive production in deep inelastic scattering at HERMES. Once the
parameters of the model are fixed, we make predictions for other unknown
fragmentation functions and for a single-spin asymmetry in the azimuthal
distribution of pi+ pi- pairs in semi-inclusive deep inelastic scattering on a
transversely polarized target at HERMES and COMPASS. Such asymmetry could be
used to measure the quark transversity distribution function.Comment: 16 pages, 10 figure
Accessing the nucleon transverse structure in inclusive deep inelastic scattering
We revisit the standard analysis of inclusive Deep Inelastic Scattering off
nucleons taking into account the fact that on-shell quarks cannot be present in
the final state, but they rather decay into hadrons - a process that can be
described in terms of suitable "jet" correlators. As a consequence, a spin-flip
term associated with the invariant mass of the produced hadrons is generated
non perturbatively and couples to the target's transversity distribution
function. In inclusive cross sections, this provides an hitherto neglected and
large contribution to the twist-3 part of the g2 structure function, that can
explain the discrepancy between recent calculations and fits of this quantity.
It also provides an extension of the Burkhardt-Cottingham sum rule, putting
constraints on the small-x behavior of the transversity function, as well as an
extension of the Efremov-Teryaev-Leader sum rule, suggesting a novel way to
measure the tensor charge of the proton.Comment: 10 pages, 3 figures. Extended discussion on small-x transversity
asymptotics. References adde
First Extraction of Transversity from a Global Analysis of Electron-Proton and Proton-Proton Data
We present the first extraction of the transversity distribution in the
framework of collinear factorization based on the global analysis of pion-pair
production in deep-inelastic scattering off transversely polarized targets and
in proton-proton collisions with one transversely polarized proton. The
extraction relies on the knowledge of di-hadron fragmentation functions, which
are taken from the analysis of electron-positron annihilation data. For the
first time, the chiral-odd transversity is extracted from a global analysis
similar to what is usually done for the chiral-even spin-averaged and helicity
distributions. The knowledge of transversity is important for, among other
things, detecting possible signals of new physics in high-precision low-energy
experiments.Comment: version identical to published one; supplemental material available
at http://link.aps.org/supplemental/10.1103/PhysRevLett.120.19200
Transversity and dihadron fragmentation functions
The observation of the quark transversity distribution requires another soft
object sensitive to the quark's transverse spin. Dihadron fragmentation
functions represent a convenient tool to analyze partonic spin, which can
influence the angular distribution of the two hadrons. In particular, the
so-called interference fragmentation functions can be used to probe
transversity both in semi-inclusive deep inelastic scattering as well as
proton-proton collisions. We discuss two single-spin asymmetries sensitive to
transversity in the these two processes, at leading twist and leading order in
alpha_S.Comment: 4 pages, to appear in proceedings of SPIN2004, Trieste, 10-16 Oct
200
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.
Final State Interactions and the Transverse Structure of the Pion
In the factorized picture of semi-inclusive deep inelastic scattering the
naive time reversal-odd parton distributions exist by virtue of the gauge link
which is intrinsic to their definition. The link structure describes
initial/final-state interactions of the active parton due to soft gluon
exchanges with the target remnant. Though these interactions are
non-perturbative, calculations of final-state interaction have been performed
in a perturbative one-gluon approximation. We include higher-order
contributions by applying non-perturbative eikonal methods to calculate the
Boer-Mulders function of the pion. Using this framework we explore under what
conditions the Boer-Mulders function can be described in terms of factorization
of final state interactions and a spatial distortion.Comment: 13 pages, 5 figures; Proceedings of the workshop, "Recent Advances in
Perturbative QCD and Hadronic Physics" ECT*, Trento (Italy), in Honor of
Anatoli V. Efremov on the occasion of his 75th Birthday, to appear in Mod.
Phys. Lett.
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