834 research outputs found
Azimuthal distributions of pions inside a jet in hadronic collisions
Using a generalized parton model approach including spin and intrinsic parton
motion effects, and assuming the validity of factorization for large pT jet
production in hadronic collisions, we study the azimuthal distribution around
the jet axis of leading pions, produced in the jet fragmentation process. We
identify the observable leading-twist azimuthal asymmetries, which are
generated by all the physically allowed combinations of transverse momentum
dependent (TMD) parton distribution and fragmentation functions. In particular,
we show how one can isolate the Collins and Sivers contributions, and suggest a
test of the process dependence of the Sivers function by considering the effect
of color-gauge invariant initial and final state interactions.Comment: 6 pages, 3 figures, to appear in the proceedings of Third
International Workshop on Transverse Polarization Phenomena in Hard
Scattering (Transversity 2011), Veli Lo\v{s}inj (Croatia), 29 August-2
September 201
Azimuthal distributions of pions inside jets at RHIC
We evaluate the azimuthal asymmetries for the distributions of leading pions
inside a jet, produced in high-energy proton-proton collisions, in kinematic
configurations currently under active investigation at RHIC. Adopting a
transverse momentum dependent approach, which assumes the validity of a
perturbative QCD factorization scheme and takes into account all the spin and
intrinsic parton motion effects, we show how the main mechanisms underlying
these asymmetries, namely the Sivers and the Collins effects, can be
disentangled. Furthermore, we consider the impact of color-gauge invariant
initial and final state interactions and suggest a method for testing the
universality properties of the Sivers function for quarks.Comment: 4 pages, 3 figures, to appear in the proceedings of the 3rd Workshop
on the QCD structure of the nucleon (QCD-N'12), Bilbao (Spain), 22-26 October
201
Testing the universality of the Collins function in pion-jet production at RHIC
By adopting a generalised parton model approach at leading order in QCD,
including spin and intrinsic parton motion effects, we study the Collins
azimuthal asymmetries for pions within a large- jet produced at
mid-rapidity in polarised hadronic collisions. Using available information on
the quark transversity distributions and the pion Collins functions, as
extracted from semi-inclusive deeply inelastic scattering and processes, we compute estimates for the Collins asymmetries in
kinematical configurations presently investigated at RHIC by the STAR
Collaboration. Collins-like asymmetries, involving linearly polarised gluons,
are also considered. Our predictions, compared against available preliminary
data, show a very good agreement, even if some discrepancies, to be further
scrutinized both theoretically and experimentally, appear in the transverse
momentum dependence of the Collins asymmetry. These results are in favour of
the predicted universality of the Collins function and of a mild, if any,
evolution with the hard scale of the asymmetries.Comment: 10 pages, 5 figures (10 plots); v2: discussion on jet kT dependence
of the SSAs extended and one plot on the corresponding unpolarized cross
section added (Fig. 3, right panel); few comments on factorization breaking
effects and on the universality issue of the Collins function added; three
references added; results unchanged; matches the published versio
Probing the gluon Sivers function in and
We present a study of transverse single-spin asymmetries (SSAs) in
and within the framework of
the generalized parton model (GPM), which includes both spin and transverse
momentum effects, and show how they can provide useful information on the still
almost unknown gluon Sivers function. Moreover, by adopting a modified version
of this model, named color gauge invariant (CGI) GPM, we analyze the impact of
the initial- and final-state interactions on our predictions. As a consequence,
we find that these two processes are sensitive to different gluon Sivers
functions, which can be expressed as linear combinations of two distinct,
universal gluon distributions. We therefore define proper observables which
could allow for a separate extraction of these two independent Sivers
functions. At the same time, we show how it would be possible to discriminate
between the GPM and the CGI-GPM approaches by comparing the corresponding
estimates of SSAs with present and future experimental results at RHIC.Comment: 19 pages, 8 figures, 1 table; v2: minor changes, matches the
published versio
Unraveling the Gluon Sivers Function in Hadronic Collisions at RHIC
We study the transverse single-spin asymmetries for
and within the so-called color gauge invariant
generalized parton model (CGI-GPM) which, in addition to spin and transverse
momentum effects, includes initial and final state interactions with the
polarized proton remnants. We compute all relevant contributions, focusing in
particular on the process dependence of the gluon Sivers function, which, for
these processes, can always be expressed as a linear combination of two
independent, universal terms. This study extends and completes a previous one,
where only quark initiated partonic processes were considered. We then perform
a combined phenomenological analysis of RHIC data on transverse single-spin
asymmetries in and , putting
the first preliminary constraints on these two gluon Sivers functions. We show
how their size can be estimated by means of these data, and use our results to
provide predictions for the process , comparing them
with data, and , for which experimental information
will soon become available. Corresponding estimates within the simpler GPM
approach, without initial and final state interactions and with a single
universal gluon Sivers function, are also given, showing that a clear
discrimination between these two models is, for the moment, not possible.Comment: 17 pages, 9 figures (19 plots), 4 table
Azimuthal asymmetries for hadron distributions inside jets in hadronic collisions
Using a generalized parton model approach including spin and intrinsic parton
motion effects, and assuming the validity of factorization for large p_T jet
production in hadronic collisions, we study the azimuthal distribution around
the jet axis of leading pions, produced in the jet fragmentation process. We
identify the observable leading-twist azimuthal asymmetries for the unpolarized
and single-polarized case related to both quark and gluon-originated jets. We
account for all physically allowed combinations of the transverse momentum
dependent (TMD) parton distribution and fragmentation functions, with special
attention to the Sivers, Boer-Mulders, and transversity quark distributions,
and to the Collins fragmentation function for quarks (and to the analogous
functions for gluon partons).Comment: 8 pages, 5 figures, to appear in the proceedings of 19th
International Spin Physics Symposium (SPIN2010), Sep 27-Oct 2, 2010, Juelich
(Germany
Collins and Sivers effects in p(transv. polarized) p --> jet pion X: Universality and process dependence
In this paper we briefly review the transverse momentum dependent generalized
parton model and its application to the study of azimuthal asymmetries in the
distribution of leading hadrons (mainly pions) inside large transverse momentum
jets inclusively produced in polarized proton-proton collisions. We put
particular emphasis on the phenomenological interest of these observables, in
combination with similar asymmetries measured in semi-inclusive deeply
inelastic scattering, Drell-Yan processes and e+e- collisions, for the study of
the universality properties of the transverse momentum dependent parton
distribution and fragmentation functions. We present results for RHIC
kinematics at center-of-mass energies sqrt{s} = 200 and 500 GeV, for central
and mainly forward jet rapidities, in particular for the Sivers distribution
and the Collins fragmentation function, that are believed to be responsible of
many of the largest asymmetries measured in the last years. We also briefly
discuss the case of inclusive jet production and recent phenomenological
applications of other theoretical approaches, like the colour gauge invariant
generalized parton model and the collinear twist-three approach, aiming at
clarifying the issues of the universality and process dependence of transverse
momentum dependent functions.Comment: RevTeX, 16 pages, 9 figures with 19 eps files; Invited mini-review
contribution to the Special Issue on "Path Dependence in Quantum Physics:
From High-Order QCD to Wilson Lines and the Breakdown of Universality", to be
published in Physics of Particles and Nucle
Azimuthal asymmetries in
We study the azimuthal asymmetries for the distributions of leading pions
inside a jet produced inclusively in high-energy proton-proton collisions
within the framework of the transverse momentum dependent generalized parton
model. We present results for the RHIC center-of-mass energies = 200
and 500 GeV, mainly for forward jet rapidities, in particular for the two
mechanisms which dominate such asymmetries: the Sivers and the Collins effects.
We also briefly discuss the case of inclusive jet production and, adopting the
so-called colour gauge invariant parton model, we propose a phenomenological
analysis of the process dependence of the quark Sivers function.Comment: 6 pages, 6 figures, to appear in the Proceedings of the Fourth
International Workshop on Transverse Polarisation Phenomena in Hard Processes
(Transversity 2014), Chia, Cagliari (Italy), 9-13 June 201
Grossly delayed massive subcutaneous emphysema following laparoscopic left hemicolectomy: A case report
AbstractINTRODUCTIONSurgical emphysema is a known early complication of laparoscopic surgery, common during upper gastrointestinal and gynaecological surgery; the authors present the first case of delayed subcutaneous emphysema following a laparoscopic left hemicolectomy.PRESENTATION OF CASEA 52-year-old woman underwent a laparoscopic left hemicolectomy for a sigmoid malignancy; on the third post-operative day after an uneventful procedure, she developed a massive surgical emphysema involving her face, neck and chest with associated pneumoperitoneum but without any evidence of pneumothorax. A gastrograffin enema ruled out an anastomotic leak. Apart from a borderline tachycardia, mildly low saturations and an area of erythema in her right flank, she was totally asymptomatic. The emphysema resolved spontaneously around the 6th post-operative day.DISCUSSIONMassive subcutaneous surgical emphysema after laparoscopic colorectal surgery is a rare complication and can me managed conservatively with a good outcome.CONCLUSIONTo our knowledge, this represents the first case of delayed massive surgical emphysema following colorectal surgery, the aetiology of which has still not been clearly explained, after exclusion of the most common causes
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