123 research outputs found
Transverse single-spin asymmetries in proton-proton collisions at the AFTER@LHC experiment
We present results for transverse single-spin asymmetries in proton-proton
collisions at kinematics relevant for AFTER, a proposed fixed-target experiment
at the Large Hadron Collider. These include predictions for pion, jet, and
direct photon production from analytical formulas already available in the
literature. We also discuss specific measurements that will benefit from the
higher luminosity of AFTER, which could help resolve an almost 40-year puzzle
of what causes transverse single-spin asymmetries in proton-proton collisions.Comment: 10 pages, 4 figures; more details/discussion added to the text,
references added/updated, version to appear in Advances in High Energy
Physics for the Special Issue "Physics at a Fixed-Target Experiment Using the
LHC Beams
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
Connections between collinear and transverse-momentum-dependent polarized observables within the Collins-Soper-Sterman formalism
We extend the improved Collins-Soper-Sterman (iCSS) construction
recently presented in~\cite{Collins:2016hqq} to the case of polarized
observables, where we focus in particular on the Sivers effect in
semi-inclusive deep-inelastic scattering. We further show how one recovers the
expected leading-order collinear twist-3 result from a (weighted)
-integral of the differential cross section. We are also able to
demonstrate the validity of the well-known relation between the (TMD) Sivers
function and the (collinear twist-3) Qiu-Sterman function within the iCSS
framework. This relation allows for their interpretation as functions yielding
the average transverse momentum of unpolarized quarks in a transversely
polarized spin- target. We further outline how this study can be
generalized to other polarized quantities.Comment: 14 pages, Version to be published in PL
Single-spin asymmetries in the leptoproduction of transversely polarized hyperons
We analyze single-spin asymmetries (SSAs) in the leptoproduction of
transversely polarized hyperons within the collinear twist-3
formalism. We calculate both the distribution and fragmentation terms in two
different gauges (lightcone and Feynman) and show that the results are
identical. This is the first time that the fragmentation piece has been
analyzed for transversely polarized hadron production within the collinear
twist-3 framework. In lightcone gauge we use the same techniques that were
employed in computing the analogous piece in , which
has become an important part to that reaction. With this in mind, we also
verify the gauge invariance of the formulas for the transverse SSA in the
leptoproduction of pions.Comment: 12 pages, 1 figure, reference added, version to appear in Phys. Lett.
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