478 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
Jets in evolving matter within the opacity expansion approach
In a recent study [1] we have extended the opacity expansion approach to
describe jet-medium interactions including medium motion effects in the context
of heavy-ion collisions. We have computed color field of the in-medium sources,
including the effects of the transverse field components and the energy
transfer between the medium and jet. The corresponding contributions are
sub-eikonal in nature, and were previously ignored in the literature. Here we
discuss how our approach can be applied to describe the medium motion effects
in the context of Deep Inelastic Scattering.Comment: 6 pages, 1 figure, DIS2021 proceeding
A New Mechanism for Generating a Single Transverse Spin Asymmetry
We propose a new mechanism for generating a single transverse spin asymmetry
(STSA) in polarized proton-proton and proton-nucleus collisions in the
high-energy scattering approximation. In this framework the STSA originates
from the q->q G splitting in the projectile (proton) light-cone wave function
followed by a perturbative (C-odd) odderon interaction, together with a C-even
interaction, between the projectile and the target. We show that some aspects
of the obtained expression for the STSA of the produced quarks are in
qualitative agreement with experiment: STSA decreases with decreasing
projectile x_F and is a non-monotonic function of the transverse momentum k_T.
In our framework the STSA peaks at k_T near the saturation scale Q_s. Our
mechanism predicts that the quark STSA in proton-nucleus collisions should be
much smaller than in proton-proton collisions. We also observe that in our
formalism the STSA for prompt photons is zero.Comment: 28 pages, 17 figues; v2: minor corrections, a subsection, discussion
and references added; v3: minor corrections and a new figure added; v4: minor
corrections; v5: minor corrections in figure
Fluid flow stimulates chemoautotrophy in hydrothermally influenced coastal sediments
© The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Sievert, S. M., Buehring, S., Gulmann, L. K., Hinrichs, K.-U., Ristova, P. P., & Gomez-Saez, G. Fluid flow stimulates chemoautotrophy in hydrothermally influenced coastal sediments. Communications Earth & Environment, 3(1), (2022): 96, https://doi.org/10.1038/s43247-022-00426-5.Hydrothermalism in coastal sediments strongly impacts biogeochemical processes and supports chemoautotrophy. Yet, the effect of fluid flow on microbial community composition and rates of chemoautotrophic production is unknown because rate measurements under natural conditions are difficult, impeding an assessment of the importance of these systems. Here, in situ incubations controlling fluid flow along a transect of three geochemically distinct locations at a shallow-water hydrothermal system off Milos (Greece) show that Campylobacteria dominated chemoautotrophy in the presence of fluid flow. Based on injected 13C-labelled dissolved inorganic carbon and its incorporation into fatty acids, we constrained carbon fixation to be as high as 12 µmol C cm−3 d−1, corresponding to areal rates up to 10-times higher than previously reported for coastal sediments, and showed the importance of fluid flow for supplying the necessary substrates to support chemoautotrophy. Without flow, rates were substantially lower and microbial community composition markedly shifted. Our results highlight the importance of fluid flow in shaping the composition and activity of microbial communities of shallow-water hydrothermal vents, identifying them as hotspots of microbial productivity.Open Access funding enabled and organized by Projekt DEAL
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