Yuji Koike

Towards an explanation of transverse single-spin asymmetries in proton-proton collisions: the role of fragmentation in collinear factorization

We study the transverse single-spin asymmetry for single-hadron production in proton-proton collisions within the framework of collinear twist-3 factorization in Quantum Chromodynamics. By taking into account the contribution due to parton fragmentation we obtain a very good description of all high transverse-momentum data for neutral and charged pion production from the Relativistic Heavy Ion Collider. Our study may provide the crucial step towards a final solution to the longstanding problem of what causes transverse single-spin asymmetries in hadronic collisions within Quantum Chromodynamics. We show for the first time that it is possible to simultaneously describe spin/azimuthal asymmetries in proton-proton collisions, semi-inclusive deep-inelastic scattering, and electron-positron annihilation by using collinear twist-3 factorization in the first process along with transverse momentum dependent functions extracted from the latter two reactions.

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.

Operator constraints for twist-3 functions and Lorentz invariance properties of twist-3 observables

We investigate the behavior under Lorentz transformations of perturbative coefficient functions in a collinear twist-3 formalism relevant for high-energy observables including transverse polarization of hadrons. We argue that those perturbative coefficient functions can, a priori, acquire quite different yet Lorentz-invariant forms in various frames. This somewhat surprising difference can be traced back to a general dependence of the perturbative coefficient functions on light cone vectors which are introduced by the twist-3 factorization formulas and which are frame-dependent. One can remove this spurious frame dependence by invoking so-called Lorentz invariance relations (LIRs) between twist-3 parton correlation functions. Some of those relations for twist-3 distribution functions were discussed in the literature before. In this paper we derive the corresponding LIRs for twist-3 fragmentation functions. We explicitly demonstrate that these LIRs remove the light cone vector dependence by considering transverse spin observables in the single-inclusive production of hadrons in lepton-nucleon collisions,

Hyperon polarization from the twist-3 distribution in unpolarized proton-proton collision

ensuremath{ell}Nensuremath{rightarrow}hX

Twist-3 asymmetries in proton-proton collisions

. With the LIRs in hand, we also show that twist-3 observables in general can be written solely in terms of three-parton correlation functions.

Twist-3 approach to hyperon polarization in unpolarized proton-proton collision

We investigate the transverse polarization of a hyperon produced in the high-energy unpolarized proton-proton collision,

Transverse Single-Spin Asymmetries in Proton-Proton Collisions Within Collinear Factorization

pptoLambda^uparrow X

The role of three-gluon correlation functions in the single spin asymmetry

, based on the collinear twist-3 factorization formalism. We focus on the contribution from the twist-3 distribution in one of the unpolarized proton and the transversity fragmentation function for the final hyperon. Utilizing the master formula for the soft-gluon-pole cross section, we clarify the reason for why it receives only the derivative term of the twist-3 distribution. We also present the first computation of the soft-fermion-pole cross section and found that it vanishes. This means that the derivative of the soft-gluon-pole function is the only source for the twist-3 cross section from the unpolarized twist-3 distribution, which provides a useful basis for a phenomenological analysis.

Lorentz invariance relations for twist-3 functions and frame-independence of twist-3 cross sections

We discuss two twist-3 spin asymmetries in

Transverse Single-Spin Asymmetries in Pion and Photon Production from Proton-Proton Collisions

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