Collins effect in semiinclusive deeply inelastic scattering and in electron-positron-annihilation

Abstract

1 Previously, the preliminary result [15] and longitudinal target SSA [28][29][30][31] data were used to extract H ⊥ 1 from SIDIS [32,33]. However, in these studies twist-3 effects [34] were not or only partially considered. Still earlier attempts to learn about the Collins effect from SSA in the hadronic processespp ↑ or pp ↑ → πX [35] were made in [36], but recent studies indicate that the Collins effect is not likely to be the dominant source of SSA in these processes [37] as it was assumed in [36].

Update on transversity and Collins functions from SIDIS and data

“…The extracted Collins FFs are well constrained and much smaller than their positivity bounds, with the unfavoured Collins function large in size and negative, consistently with other extractions [42,43,20]. A word of caution has to be added here since SIDIS data (HERMES and COMPASS) are collected at a much smaller scale (Q 2 2.5 GeV 2 ) compared to the Belle data (Q 2 = 110 GeV 2 ).…”

Measurement of Collins asymmetries in inclusive production of charged pion pairs ine+e−annihilation atBABAR

“…VI. An analysis of Belle data, under the assumption sign opposite to the favored one [31], as also suggested by the HERMES experiment [13].…”

“…[31,46] and references therein). The new precise data presented here can be used to improve the tuning of the various models and possibly discriminate among the different assumptions.…”

“…The measured U=L and U=C double ratios can be used to derive information about the relative sign and magnitude of favored and disfavored fragmentation functions [31]. Analogous expressions can be obtained in the RF0 reference frame, with modulations in cosð2ϕ 0 Þ instead of cosðϕ 1 þ ϕ 2 Þ.…”

Towards a first estimate of the gluon Sivers function from A N data in pp collisions at RHIC

“…Much phenomenological information has been by now collected on quark TMDs; in particular the Sivers distribution [42,43] and the Collins fragmentation function [44] have been extracted from SIDIS and e + e − data by different groups [25,[45][46][47][48][49][50][51][52][53]. Even if to a lesser extent some information on the Boer-Mulders function [54] has been also gathered [55][56][57][58][59][60][61].…”