8,142 research outputs found
First glances at the transversity parton distribution through dihadron fragmentation functions
We present first observations of the transversity parton distribution based
on an analysis of pion-pair production in deep inelastic scattering off
transversely polarized targets. The extraction of transversity relies on the
knowledge of dihadron fragmentation functions, which we take from
electron-positron annihilation measurements. This is the first attempt to
determine the transversity distribution in the framework of collinear
factorization.Comment: Minor changes in text and reference
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
Single spin asymmetries in hadron-hadron collisions
We study weighted azimuthal single spin asymmetries in hadron-hadron
scattering using the diagrammatic approach at leading order and assuming
factorization. The effects of the intrinsic transverse momenta of the partons
are taken into account. We show that the way in which -odd functions, such
as the Sivers function, appear in these processes does not merely involve a
sign flip when compared with semi-inclusive deep inelastic scattering, such as
in the case of the Drell-Yan process. Expressions for the weighted scattering
cross sections in terms of distribution and fragmentation functions folded with
hard cross sections are obtained by introducing modified hard cross sections,
referred to as gluonic pole cross sections.Comment: 22 pages, 4 figures; minor text modifications and some additional
reference
Renormalization-group anatomy of transverse-momentum dependent parton distribution functions in QCD
The ultraviolet and rapidity divergences of transverse-momentum dependent
parton distribution functions with lightlike and transverse gauge links is
studied, also incorporating a soft eikonal factor. We find that in the
light-cone gauge with -independent pole prescriptions extra divergences
appear which amount, at one-loop, to a cusp-like anomalous dimension. We show
that such contributions are absent when the Mandelstam-Leibbrandt prescription
is used. In the first case, the soft factor cancels the anomalous-dimension
defect, while in the second case its ultraviolet-divergent part reduces to
unity.Comment: 10 pages, 3 figures; needs ws-mpla-hep.cls (supplied). Talk presented
by the first author at Workshop on "Recent Advances in Perturbative QCD and
Hadronic Physics", 20--25 July 2009, ECT*, Trento, Italy, in Honor of Prof.
Anatoly Efremov's 75th birthda
Effects of TMD evolution and partonic flavor on annihilation into hadrons
We calculate the transverse momentum dependence in the production of two
back-to-back hadrons in electron-positron annihilations at the medium/large
energy scales of BES-III and BELLE experiments. We use the parameters of the
transverse-momentum-dependent (TMD) fragmentation functions that were recently
extracted from the semi-inclusive deep-inelastic-scattering multiplicities at
low energy from HERMES. TMD evolution is applied according to different
approaches and using different parameters for the nonperturbative part of the
evolution kernel, thus exploring the sensitivity of our results to these
different choices and to the flavor dependence of parton fragmentation
functions. We discuss how experimental measurements could discriminate among
the various scenarios.Comment: 33 pages, 10 composite figures, JHEP style fil
Emotional crisis in a naturalistic context: characterizing outpatient profiles and treatment effectiveness.
Crisis happens daily yet its understanding is often limited, even in the field of psychiatry. Indeed, a challenge is to assess the potential for change of patients so as to offer appropriate therapeutic interventions and enhance treatment program efficacy. This naturalistic study aimed to identify the socio-demographical characteristics and clinical profiles at admission of patients referred to a specialized Crisis Intervention Center (CIC) and to examine the effectiveness of the intervention.
The sample was composed of 352 adult outpatients recruited among the referrals to the CIC. Assessment completed at admission and at discharge examined psychiatric symptoms, defense mechanisms, recovery styles and global functioning. The crisis intervention consisted in a psychodynamically oriented multimodal approach associated with medication.
Regarding the clinical profiles at intake, patients were middle-aged (M = 38.56, SD = 10.91), with a higher proportion of women (62.22%). They were addressed to the CIC because they had attempted to commit suicide or had suicidal ideation or presented depressed mood related to interpersonal difficulties. No statistical differences were found between patients dropping out (n = 215) and those attending the crisis intervention (n = 137). Crisis intervention demonstrated a beneficial effect (p < 0.01) on almost all variables, with Effect Sizes (ES) ranging from small to large (0.12 < ES < 0.75; median = 0.49). However, the Reliable Change Index indicated that most of the issues fall into the undetermined category (range 41.46 to 96.35%; median = 66.20%).
This study establishes the profile of patients referred to the CIC and shows that more than half of the patients dropped out from the crisis intervention before completion. Our findings suggest that people presenting an emotional crisis benefit from crisis intervention. However, given methodological constraints, these results need to be considered with caution. Moreover, the clinical significance of the improvements is not confirmed. Thus, the effectiveness of crisis intervention in naturalistic context is not fully determined and should be more rigorously studied in future research
On the contribution of twist-3 multi-gluon correlation functions to single transverse-spin asymmetry in SIDIS
We study the single spin asymmetry (SSA) induced by purely gluonic
correlation inside a nucleon, in particular, by the three-gluon correlation
functions in the transversely polarized nucleon, . This
contribution is embodied as a twist-3 mechanism in the collinear factorization
framework and controls the SSA to be observed in the -meson production with
large transverse-momentum in semi-inclusive DIS (SIDIS), . We define the relevant three-gluon correlation functions in
the nucleon, and determine their complete set at the twsit-3 level taking into
account symmetry constraints in QCD. We derive the single-spin-dependent cross
section for the -meson production in SIDIS, taking into account all the
relevant contributions at the twist-3 level. The result is obtained in a
manifestly gauge-invariant form as the factorization formula in terms of the
three-gluon correlation functions and reveals the five independent structures
with respect to the dependence on the azimuthal angle for the produced
meson. We also demonstrate the remarkable relation between the twist-3
single-spin-dependent cross section and twist-2 cross sections for the
-meson production, as a manifestation of universal structure behind the SSA
in a variety of hard processes.Comment: 8 pages, 2 figures. To appear in the proceedings of the 19th
International Spin Physics Symposium (SPIN2010), Juelich, Germany, Sept.27 -
Oct.2, 201
Estimate of the Collins fragmentation function in a chiral invariant approach
We predict the features of the Collins function, which describes the
fragmentation of a transversely polarized quark into an unpolarized hadron, by
modeling the fragmentation process at a low energy scale. We use the chiral
invariant approach of Manohar and Georgi, where constituent quarks and
Goldstone bosons are considered as effective degrees of freedom in the
non-perturbative regime of QCD. To test the approach we calculate the
unpolarized fragmentation function and the transverse momentum distribution of
a produced hadron, both of which are described reasonably well. In the case of
semi-inclusive deep-inelastic scattering, our estimate of the Collins function
in connection with the transversity distribution gives rise to a transverse
single spin asymmetry of the order of 10%, supporting the idea of measuring the
transversity distribution of the nucleon in this way. In the case of e+ e-
annihilation into two hadrons, our model predicts a Collins azimuthal asymmetry
of about 5%.Comment: 12 pages, 15 figures. Figs. 11-14 changed, minor changes in
discussion, few typos fixed and some references added. Final version to
appear in PR
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