10,209 research outputs found
Asymmetric Di-jet Production in Polarized Hadronic Collisions
Using the collinear QCD factorization approach, we study the
single-transverse-spin dependent cross section Delta sigma(S_perp) for the
hadronic production of two jets of momenta P_1=P+q/2 and P_2=-P+q/2. We
consider the kinematic region where the transverse components of the momentum
vectors satisfy P_perp >> q_perp >> Lambda_QCD. For the case of initial-state
gluon radiation, we show that at the leading power in q_perp/P_perp and at the
lowest non-trivial perturbative order, the dependence of Delta sigma(S_perp) on
q_perp decouples from that on P_perp, so that the cross section can be
factorized into a hard part that is a function only of the single scale P_perp,
and into perturbatively generated transverse-momentum dependent (TMD) parton
distributions with transverse momenta k_perp = O(q_perp).Comment: 11 pages, 2 figure
Master Formula for Twist-3 Soft-Gluon-Pole Mechanism to Single Transverse-Spin Asymmetry
Perturbative QCD relates the single transverse-spin asymmetries (SSAs) for
hard processes at large transverse-momentum of produced particle to partonic
matrix elements that describe interference between scattering from a coherent
quark-gluon pair and from a single quark, generated through twist-3 quark-gluon
correlations inside a hadron. When the coherent gluon is soft at the gluonic
poles, its coupling to partonic subprocess can be systematically disentangled,
so that the relevant interfering amplitude can be derived entirely from the
Born diagrams for the scattering from a single quark. We establish a new
formula that represents the exact rules to derive the SSA due to soft-gluon
poles from the knowledge of the twist-2 cross section formula for unpolarized
processes. This single master formula is applicable to a range of processes
like Drell-Yan and direct-photon production, and semi-inclusive deep inelastic
scattering, and is also useful to manifest the gauge invariance of the results.Comment: 20 pages, 6 figures; [v2] a paragraph with new Eq. (30) added, minor
modifications, typos corrected; [v3] Erratum added, and minor change
Valley Carrier Dynamics in Monolayer Molybdenum Disulphide from Helicity Resolved Ultrafast Pump-probe Spectroscopy
We investigate the valley related carrier dynamics in monolayer MoS2 using
helicity resolved non-degenerate ultrafast pump-probe spectroscopy at the
vicinity of the high-symmetry K point under the temperature down to 78 K.
Monolayer MoS2 shows remarkable transient reflection signals, in stark contrast
to bilayer and bulk MoS2 due to the enhancement of many-body effect at reduced
dimensionality. The helicity resolved ultrafast time-resolved result shows that
the valley polarization is preserved for only several ps before scattering
process makes it undistinguishable. We suggest that the dynamical degradation
of valley polarization is attributable primarily to the exciton trapping by
defect states in the exfoliated MoS2 samples. Our experiment and a
tight-binding model analysis also show that the perfect valley CD selectivity
is fairly robust against disorder at the K point, but quickly decays from the
high-symmetry point in the momentum space in the presence of disorder.Comment: 15 pages,Accepted by ACS Nan
Single-Transverse Spin Asymmetry in Semi-Inclusive Deep Inelastic Scattering
We study the single-transverse spin asymmetry in semi-inclusive hadron
production in deep inelastic scattering. We derive the leading contribution to
the asymmetry at moderate transverse momentum of the produced
hadron in terms of twist-three quark-gluon correlation functions, and compare
with the approach based on the factorization at fixed transverse momentum
involving the asymmetric transverse-momentum and spin-dependent quark
distribution. We verify that the two approaches yield identical results in this
regime. By a comparison with our earlier calculations for the single-spin
asymmetry in the Drell-Yan process we recover the well-established
process-dependence of the time-reversal-odd transverse-momentum-dependent quark
distributions that generate single-spin phenomena.Comment: 17 pages, 3 figure
Chiral-Odd Contribution to Single-Transverse Spin Asymmetry in Hadronic Pion Production
A formula for the single transverse spin asymmetry in the large- pion
production in the nucleon-nucleon collision is derived. We focuss on the
chiral-odd contribution where the transversity distribution and the chiral-odd
spin-independent twist-3 distribution contributes. This contribution is
expected to give rise to a large effect at .Comment: Latex file 10 pages + 2 figures attached as PS and EPS files. A minor
correction is include
Development of adaptive control methodologies and algorithms for nonlinear dynamic systems based on u-control framework
Inspired by the U-model based control system design (or called U-control system design), this study is mainly divided into three parts. The first one is a U-model based control system for unstable non-minimum phase system. Pulling theorems are proposed to apply zeros pulling filters and poles pulling filters to pass the unstable non-minimum phase characteristics of the plant model/system. The zeros pulling filters and poles pulling filters derive from a customised desired minimum phase plant model. The remaining controller design can be any classic control systems or U-model based control system. The difference between classic control systems and U-model based control system for unstable non-minimum phase will be shown in the case studies.Secondly, the U-model framework is proposed to integrate the direct model reference adaptive control with MIT normalised rules for nonlinear dynamic systems. The U-model based direct model reference adaptive control is defined as an enhanced direct model reference adaptive control expanding the application range from linear system to nonlinear system. The estimated parameter of the nonlinear dynamic system will be placement as the estimated gain of a customised linear virtual plant model with MIT normalised rules. The customised linear virtual plant model is the same form as the reference model. Moreover, the U-model framework is design for the nonlinear dynamic system within the root inversion.Thirdly, similar to the structure of the U-model based direct model reference adaptive control with MIT normalised rules, the U-model based direct model reference adaptive control with Lyapunov algorithms proposes a linear virtual plant model as well, estimated and adapted the particular parameters as the estimated gain which of the nonlinear plant model by Lyapunov algorithms. The root inversion such as Newton-Ralphson algorithm provides the simply and concise method to obtain the inversion of the nonlinear system without the estimated gain. The proposed U-model based direct control system design approach is applied to develop the controller for a nonlinear system to implement the linear adaptive control. The computational experiments are presented to validate the effectiveness and efficiency of the proposed U-model based direct model reference adaptive control approach and stabilise with satisfied performance as applying for the linear plant model
Motions of Hard X-ray Sources During an Asymmetric Eruption
Filament eruptions and hard X-ray (HXR) source motions are commonly observed
in solar flares, which provides critical information on the coronal magnetic
reconnection. This Letter reports an event on 2005 January 15, in which we
found an asymmetric filament eruption and a subsequent coronal mass ejection
together with complicated motions of HXR sources during the GOES-class X2.6
flare. The HXR sources initially converge to the magnetic polarity inversion
line (PIL), and then move in directions either parallel or perpendicular to the
PIL depending on the local field configuration. We distinguish the evolution of
the HXR source motion in four phases and associate each of them with distinct
regions of coronal magnetic fields as reconstructed using a non-linear
force-free field extrapolation. It is found that the magnetic reconnection
proceeds along the PIL toward the regions where the overlying field decreases
with height more rapidly. It is also found that not only the perpendicular but
the parallel motion of the HXR sources correlates well with the HXR lightcurve.
These results are discussed in favor of the torus instability as an important
factor in the eruptive process.Comment: 6 pages, 5 figures, accepted to the Astrophysical Journal Letter
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