985 research outputs found
Three-gluon contribution to the single spin asymmetry in Drell-Yan and direct-photon processes
We derive the single-spin-dependent cross section for the Drell-Yan
lepton-pair production and the direct-photon production in the -collision
induced by the twist-3 three-gluon correlation functions in the transversely
polarized nucleon in the leading order with respect to the QCD coupling
constant. Combined with the contribution from the twist-3 quark-gluon
correlation functions in the literature, this completes the twist-3 cross
section for these processes. We also present a model calculation of the
asymmetry for the direct photon production at the RHIC energy, demonstrating
the sensitivity of the asymmetry to the form of the three-gluon correlation
functions. In particular, we show that the asymmetry in the backward direction
of the polarized nucleon is determined by the small- behavior of the
correlation functions.Comment: 15 pages, 3 figure
Master Formula for the Three-Gluon Contribution to Single Spin Asymmetry in Semi-Inclusive Deep Inelastic Scattering
We derive a "master formula" for the contribution of the three-gluon
correlation function in the nucleon to the twist-3 single-spin-dependent cross
section for semi-inclusive deep-inelastic scattering, ep^\uparrow\to eDX. This
is an extension of the similar formula known for the so-called soft-gluon-pole
contribution induced by the quark-gluon correlation function in a variety of
processes. Our master formula reduces the relevant interfering partonic
subprocess with the participation of the three gluons to the Born cross
sections for the \gamma^*g\to c\bar{c} scattering, which reveals the new
structure behind the twist-3 single spin asymmetry and simplifies the actual
calculation greatly. A possible extension to higher order corrections is also
discussed.Comment: 23 pages, 4 figures. Final version to appear in Phys. Rev. D.
Presentation changed slightl
QCD evolution of naive-time-reversal-odd fragmentation functions
We study QCD evolution equations of the first transverse-momentum-moment of
the naive-time-reversal-odd fragmentation functions - the Collins function and
the polarizing fragmentation function. We find for the Collins function case
that the evolution kernel has a diagonal piece same as that for the
transversity fragmentation function, while for the polarizing fragmentation
function case this piece is the same as that for the unpolarized fragmentation
function. Our results might have important implications in the current global
analysis of spin asymmetries.Comment: 8 pages,4 figure
Contribution of Twist-3 Multi-Gluon Correlation Functions to Single Spin Asymmetry in Semi-Inclusive Deep Inelastic Scattering
As a possible source of the single transverse spin asymmetry, we study the
contribution from purely gluonic correlation represented by the twist-3
``three-gluon correlation" functions in the transversely polarized nucleon. We
first define a complete set of the relevant three-gluon correlation functions,
and then derive its contribution to the twist-3 single-spin-dependent cross
section for the -meson production in semi-inclusive deep inelastic
scattering, which is relevant to determine the three-gluon correlations. Our
cross-section formula differs from the corresponding result in the literature,
and the origin of the discrepancy is clarified.Comment: 29 pages, 3 figures minor corrections; version to appear in Phys.
Rev.
Quark-gluon correlation functions relevant to single transverse spin asymmetries
We investigate the relative size of various twist-3 quark-gluon correlation
functions relevant to single transverse spin asymmetries (SSAs) in a
quark-diquark model of the nucleon. We calculate the quark-gluon correlation
function that is responsible for the gluonic pole contribution
to the SSAs, as well as and
responsible for the fermionic pole contributions. We find in both cases of a
scalar diquark and an axial-vector diquark that at the first nontrivial order
only the \tq(x, x) is finite while all other quark-gluon correlation
functions vanish. Using the same model, we evaluate quark Sivers function and
discuss its relation to the \tq(x, x). We also discuss the implication of our
finding to the phenomenological studies of the SSAs.Comment: 12 pages, 5 figure
Collinear Factorization for Single Transverse-Spin Asymmetry in Drell-Yan Processes
We study the scattering of a single parton state with a multi-parton state to
derive the complete results of perturbative coefficient functions at leading
order, which appear in the collinear factorization for Single transverse-Spin
Asymmetry(SSA) in Drell-Yan processes with a transversely polarized hadron in
the initial state. We find that the factorization formula of SSA contains
hard-pole-, soft-quark-pole- and soft-gluon-pole contributions. It is
interesting to note that the leading order perturbative coefficient functions
of soft-quark-pole- and soft-gluon-pole contributions are extracted from parton
scattering amplitudes at one-loop, while the functions of hard-pole
contributions are extracted from the tree level amplitudes at tree-level. Our
method to derive the factorization of SSA is different than the existing one in
literature. A comparison of our results with those obtained by other method is
made.Comment: 27 pages, 14 figures, text improved, to appear in Phys. Rev.
Accessing tri-gluon correlations in the nucleon via the single spin asymmetry in open charm production
We calculate the single transverse-spin asymmetry for open charm production
in collisions within the QCD collinear factorization approach. We include
contributions from both twist-three quark-gluon and tri-gluon correlation
functions. We find that the quark-gluon correlation functions alone generate
only a very small asymmetry for open charm production in the kinematic region
of current interest at RHIC, so that the observation of any significant
single-spin asymmetry would be a clear indication of the presence of tri-gluon
correlations inside a polarized proton. We furthermore demonstrate that the
tri-gluon contribution could be very different for the production of and
mesons. These features make the single spin asymmetry in open charm
production in polarized collisions at RHIC an excellent probe of tri-gluon
correlation functions.Comment: 10 pages, 7 figure
Hierarchical Star Formation from the Time-Space Distribution of Star Clusters in the Large Magellanic Cloud
The average age difference between pairs of star clusters in the Large
Magellanic Clouds increases with their separation as the ~0.35 power. This
suggests that star formation is hierarchical in space and time. Small regions
form stars quickly and large regions, which often contain the small regions,
form stars over a longer period. A similar result found previously for Cepheid
variables is statistically less certain than the cluster result.Comment: 8 pages, 8 figures, accepted by Monthly Notices of the Royal
Astronomical Societ
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