92,841 research outputs found
Theoretical aspects of transversity observables
Theoretical aspects of transversity observables are reviewed. The main focus
is on two leading twist transversity single spin asymmetries, one arising from
the Collins effect and one from the interference fragmentation functions.
Electron-positron annihilation experiments which are required to obtain these
fragmentation functions are discussed, as well as the issues of factorization,
evolution and Sudakov factors for the relevant observables. These theoretical
considerations pinpoint the most realistic scenarios towards measurements of
transversity.Comment: 4 pages, uses espcrc2.sty, Talk presented at the "International
Workshop on the Spin Structure of the Proton and Polarized Collider Physics",
ECT*, Trento, Italy, July 23-28, 200
Theoretical aspects of spin physics
A summary is given of how spin enters in collinearly factorizing processes.
Next, theoretical aspects of polarization in processes beyond collinear
factorization are discussed in more detail, with special focus on recent
developments concerning the color gauge invariant definitions of transverse
momentum dependent distribution and fragmentation functions, such as the Sivers
and Collins effect functions. This has particular relevance for azimuthal
single spin asymmetries, which currently receive much theoretical and
experimental attention.Comment: 10 pages, 11 eps figures; Talk presented at the Ringberg Workshop
`New Trends in HERA Physics 2003', Ringberg Castle, Tegernsee, Germany,
September 28 - October 3, 200
Gluon TMD studies at EIC
A high-energy Electron-Ion Collider (EIC) would offer a most promising tool
to study in detail the transverse momentum distributions of gluons inside
hadrons. This applies to unpolarized as well as linearly polarized gluons
inside unpolarized protons, and to left-right asymmetric distributions of
gluons inside transversely polarized protons, the so-called gluon Sivers
effect. The inherent process dependence of these distributions can be studied
by comparing to similar, but often complementary observables at LHC.Comment: 6 pages, no figures, contribution to the proceedings of the 6th
International conference on Physics Opportunities at an ElecTron-Ion Collider
(POETIC VI), \'Ecole Polytechnique, Palaiseau, France, September 7-11, 201
Overview of TMD evolution
Transverse momentum dependent parton distributions (TMDs) appear in many
scattering processes at high energy, from the semi-inclusive DIS experiments at
a few GeV to the Higgs transverse momentum distribution at the LHC. Predictions
for TMD observables crucially depend on TMD factorization, which in turn
determines the TMD evolution of the observables with energy. In this
contribution to SPIN2014 TMD factorization is outlined, including a discussion
of the treatment of the nonperturbative region, followed by a summary of
results on TMD evolution, mostly applied to azimuthal asymmetries.Comment: 6 pages, no figures, contribution to the proceedings of the 21st
International Symposium on Spin Physics (Spin2014), Beijing, China, October
20-24, 201
Single Hadronic-Spin Asymmetries in Weak Interaction Processes
We show that measurements of single-spin asymmetries (SSAs) in charged
current weak interaction processes such as deep inelastic neutrino scattering
on a polarized target and inclusive production in polarized hadron-hadron
collisions discriminate between the two fundamental QCD mechanisms (the Sivers
and Collins effects) which have been proposed to explain such time-reversal-odd
asymmetries. It has recently been shown that QCD final-state interactions due
to gluon exchange between the struck quark and the proton spectators in
semi-inclusive deep inelastic lepton scattering will produce non-zero
Sivers-type single-spin asymmetries which survive in the Bjorken limit. We show
that this QCD final-state interaction produces identical SSAs in charged and
neutral current reactions. Furthermore, the contribution of each quark to the
SSA from this mechanism is proportional to the contribution of that quark to
the polarized baryon's anomalous magnetic moment. In contrast, the Collins
effect contribution to SSAs depends on the transversity distribution of quarks
in the polarized target. Since the charged current only couples to quarks of
one chirality, it cannot sense the transversity distribution of the target, and
thus it gives no Collins-type contribution to single-spin correlations.Comment: 12 pages, 1 figur
Average transverse momentum quantities approaching the lightfront
In this contribution to Light Cone 2014, three average transverse momentum
quantities are discussed: the Sivers shift, the dijet imbalance, and the
broadening. The definitions of these quantities involve integrals over all
transverse momenta that are overly sensitive to the region of large transverse
momenta, which conveys little information about the transverse momentum
distributions of quarks and gluons inside hadrons. TMD factorization naturally
suggests alternative definitions of such integrated quantities, using
Bessel-weighting and rapidity cut-offs, with the conventional definitions as
limiting cases. The regularized quantities are given in terms of integrals over
the TMDs of interest that are well-defined and moreover have the advantage of
being amenable to lattice evaluations.Comment: 6 pages, no figures, contribution to the proceedings of Light Cone
2014, Raleigh, North Carolina, May 26-30, 201
Gluon TMDs in quarkonium production
Quarkonium production offers good possibilities to study gluon TMDs. In this
proceedings contribution this topic is explored for the linearly polarized
gluons inside unpolarized hadrons and unpolarized gluons inside transversely
polarized hadrons. It is argued that and production at
LHC are best to study the effects of linearly polarized gluons in hadronic
collisions, by means of angular independent ratios of ratios of cross sections.
This can be directly compared to asymmetries in heavy quark pair
and dijet production in DIS at a future high-energy Electron-Ion Collider
(EIC), which probe the same TMDs. In the small- limit this corresponds to
the Weizs\"acker-Williams (WW) gluon distributions, which should show a change
in behavior for transverse momenta around the saturation scale. Together with
investigations of the dipole (DP) gluon distributions, this can provide
valuable information about the polarization of the Color Glass Condensate if
sufficiently small are reached. Quarkonia can also be useful in the study
of single transverse spin asymmetries. For transversely polarized hadrons the
gluon distribution can be asymmetric, which is referred to as the Sivers
effect. It leads to single spin asymmetries in for instance (pair)
production at AFTER@LHC, which probe the WW or -type gluon Sivers TMD. It
allows for a test of a sign-change relation w.r.t. the gluon Sivers TMD probed
at an EIC in open heavy quark pair production. Single spin asymmetries in
backward inclusive -odd quarkonium production, such as production,
may offer probes of the DP or -type gluon Sivers TMD at small -values in
the polarized proton, which in that limit corresponds to a correlator of a
single Wilson loop, describing the spin-dependent odderon.Comment: 9 pages, no figures, contribution to the proceedings of the ECT*
Workshop: New Observables in Quarkonium Production (Quarkonium2016), Trento,
Italy, 28 February - 4 March 201
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