4,675 research outputs found
Single spin asymmetry in high energy QCD
We present the first steps in an effort to incorporate the physics of
transverse spin asymmetries into the saturation formalism of high energy QCD.
We consider a simple model in which a transversely polarized quark scatters on
a proton or nuclear target. Using the light-cone perturbation theory the hadron
production cross section can be written as a convolution of the light-cone wave
function squared and the interaction with the target. To generate the single
transverse spin asymmetry (STSA) either the wave function squared or the
interaction with the target has to be T-odd. In this work we use the
lowest-order q->qG wave function squared, which is T-even, generating the STSA
from the T-odd interaction with the target mediated by an odderon exchange. We
study the properties of the obtained STSA, some of which are in qualitative
agreement with experiment: STSA increases with increasing projectile x_F and is
a non-monotonic function of the transverse momentum k_T. Our mechanism predicts
that the quark STSA in polarized proton--nucleus collisions should be much
smaller than in polarized proton--proton collisions. We also observe that the
STSA for prompt photons due to our mechanism is zero within the accuracy of the
approximation.Comment: 10 pages, 6 figures, proceedings of the QCD Evolution Workshop, May
14 - 17, 2012, Thomas Jefferson National Accelerator Facility, Newport News,
V
Sivers Function in the Quasi-Classical Approximation
We calculate the Sivers function in semi-inclusive deep inelastic scattering
(SIDIS) and in the Drell-Yan process (DY) by employing the quasi-classical
Glauber-Mueller/ McLerran-Venugopalan approximation. Modeling the hadron as a
large "nucleus" with non-zero orbital angular momentum (OAM), we find that its
Sivers function receives two dominant contributions: one contribution is due to
the OAM, while another one is due to the local Sivers function density in the
nucleus. While the latter mechanism, being due to the "lensing" interactions,
dominates at large transverse momentum of the produced hadron in SIDIS or of
the di-lepton pair in DY, the former (OAM) mechanism is leading in saturation
power counting and dominates when the above transverse momenta become of the
order of the saturation scale. We show that the OAM channel allows for a
particularly simple and intuitive interpretation of the celebrated sign flip
between the Sivers functions in SIDIS and DY.Comment: 44 pages, 14 figures; v2: typos corrected, figure modifie
Small- Asymptotics of the Quark Helicity Distribution: Analytic Results
In this Letter, we analytically solve the evolution equations for the
small- asymptotic behavior of the (flavor singlet) quark helicity
distribution in the large- limit. These evolution equations form a set of
coupled integro-differential equations, which previously could only be solved
numerically. This approximate numerical solution, however, revealed simplifying
properties of the small- asymptotics, which we exploit here to obtain an
analytic solution. We find that the small- power-law tail of the quark
helicity distribution scales as with , in excellent agreement with the numerical estimate obtained previously. We then
verify this solution by cross-checking the predicted scaling behavior of the
auxiliary "neighbor dipole amplitude" against the numerics, again finding
excellent agreement.Comment: 5 pages, 2 figure
Theoretical study of production of unique glasses in space
The potential of producing the glassy form of selected materials in the weightless, containerless nature of space processing is examined through the development of kinetic relationships describing nucleation and crystallization phenomena. Transformation kinetics are applied to a well-characterized system (SiO2), an excellent glass former (B2O3), and a poor glass former (Al2O3) by conventional earth processing methods. Viscosity and entropy of fusion are shown to be the primary materials parameters controlling the glass forming tendency. For multicomponent systems diffusion-controlled kinetics and heterogeneous nucleation effects are considered. An analytical empirical approach is used to analyze the mullite system. Results are consistent with experimentally observed data and indicate the promise of mullite as a future space processing candidate
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