8,720 research outputs found
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
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.
Semi-inclusive structure functions in the spectator model
We establish the relationship between distribution and fragmentation
functions and the structure functions appearing in the cross section of
polarized 1-particle inclusive deep-inelastic scattering. We present spectator
model evaluations of these structure functions focusing on the case of an
outgoing spin-1/2 baryon. Distribution functions obtained in the spectator
model are known to fairly agree at low energy scales with global
parameterizations extracted, for instance, from totally inclusive DIS data.
Therefore, we expect it to give good hints on the functional dependence of the
structure functions on the scaling variables x(Bjorken), z and on the
transverse momentum of the observed outgoing hadron, P_{h\perp}. Presently,
this dependence is not very well known, but experiments are planned in the near
future.Comment: 19 pages, 16 figures, submitted to Eur. Phys. J.
The Dihadron fragmentation functions way to Transversity
Observations of the transversity parton distribution based on an analysis of
pion-pair production in deep inelastic scattering off transversely polarized
targets are presented. This extraction relies on the knowledge of dihadron
fragmentation functions, which are obtained from electron-positron annihilation
measurements. This is the first attempt to determine the transversity
distribution in the framework of collinear factorization.Comment: To appear in the proceedings of XIX International Workshop on
Deep-Inelastic Scattering and Related Subjects (DIS 2011), April 11-15, 2011,
Newport News, VA USA ; AIP style files include
Estimate of the Collins function in a chiral invariant approach
We estimate the Collins function at a low energy scale by calculating the
fragmentation of a quark into a pion at the one-loop level in the chiral
invariant model of Manohar and Georgi. We give a useful parametrization of our
results and we briefly discuss different spin and/or azimuthal asymmetries
containing the Collins function and measurable in semi-inclusive DIS and e+ e-
annihilationComment: 5 pages, 4 figures, to appear in Proceedings of 10th International
Workshop on Deep Inelastic Scattering (DIS 2002), Cracow, Poland, 30 Apr-4
May 200
Generalized Universality for TMD Distribution Functions
Azimuthal asymmetries in high-energy processes, most pronounced showing up in
combination with single or double (transverse) spin asymmetries, can be
understood with the help of transverse momentum dependent (TMD) parton
distribution and fragmentation functions. These appear in correlators
containing expectation values of quark and gluon operators. TMDs allow access
to new operators as compared to collinear (transverse momentum integrated)
correlators. These operators include nontrivial process dependent Wilson lines
breaking universality for TMDs. Making an angular decomposition in the
azimuthal angle, we define a set of universal TMDs of definite rank, which
appear with process dependent gluonic pole factors in a way similar to the sign
of T-odd parton distribution functions in deep inelastic scattering or the
Drell-Yan process. In particular, we show that for a spin 1/2 quark target
there are three pretzelocity functions.Comment: 9 pages, updated references and minor corrections, to appear in the
proceedings of the QCD Evolution Workshop 2012 (May 14-17, JLAB
Reviewing model calculations of the Collins fragmentation function
The Collins fragmentation function describes a left/right asymmetry in the
fragmentation of a transversely polarized quark into a hadron in a jet. Four
different model calculations of the Collins function have been presented in the
literature. While based on the same concepts, they lead to different results
and in particular to different signs for the Collins function. The purpose of
the present work is to review the features of these models and correct some
errors made in previous calculations. A full study of the parameter dependence
and the possible modifications to these models is beyond the scope of the
paper. However, some general conclusions are drawn
Probing the transverse spin of quarks in deep inelastic scattering
To identify some way to measure the quark transversity, this thesis analyzes
one-particle and two-particle inclusive deep inelastic scattering, where one
and two of the outgoing hadrons are detected in coincidence with the electron.
It is shown that transversity can be measured in the above processes, in
connection with three different fragmentation functions: the first one requires
the observation of an unpolarized final state hadron with transverse momentum
(Collins function), the second requires the observation of the interference
between the s- and p-wave production of two hadrons, the third requires the
observation of pure p-wave two-hadron production, or equivalently of a spin-one
resonance. All these fragmentation functions fall in the category of T-odd
fragmentation functions: they require the presence of final state interactions,
or else they are forbidden by time-reversal invariance. The last part of the
thesis looks at the possibility of modeling this kind of fragmentation
functions and investigates whether they can be large enough to allow the
extraction of transversity.Comment: PhD thesis, defended on Oct 4th, 2002. About 140 pages. The layout is
slightly different from the original version, which can be found at
http://www.nat.vu.nl/~bacchett/research/thesis.pd
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