The Polarising Fragmentation Function and the Lambda polarisation in e+ e- processes

Abstract

The surprising polarisation of Lambdas and other hyperons measured in many unpolarised hadronic processes, p N --> Lambda X, has been a long standing challenge for QCD phenomenology. One possible explanation was suggested, related to non perturbative properties of the quark hadronisation process, and encoded in the so-called Polarising Fragmentation Function (PFF). Recent Belle data have shown a non zero Lambda polarisation also in unpolarised e+ e- processes, e+ e- --> Lambda X and e+ e- --> Lambda h X. We consider the single inclusive case and the role of the PFFs. Adopting a simplified kinematics it is shown how they can originate a polarisation P_Lambda different from 0 and give explicit expressions for it in terms of the PFFs. Although the Belle data do not allow yet, in our approach, an extraction of the PFFs, some clear predictions are given, suggesting crucial measurements, and estimates of P_Lambda are computed, in qualitative agreement with the Belle data.

arXiv comment8 pages, 4 figures. Version accepted for publication in PRD; minor changes, ackowledgements and references added

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Cited by in corpus (11)

• Extracting the Transverse Momentum Dependent Polarizing Fragmentation Functions
• Diffractive production of $\Lambda$ hyperons in the high-energy limit of strong interactions
• Transverse spin effects in hard semi-inclusive collisions
• First extraction of the $\Lambda$ polarising fragmentation function from Belle $e^{+}{e}^{-}$ data
• Isospin Symmetry of Fragmentation Functions
• Several Topics on Transverse Momentum-Dependent Fragmentation Functions
• Probing the longitudinal spin transfer via dihadron polarization correlations in unpolarized $e^{+}{e}^{-}$ and $pp$ collisions
• The transverse polarization of $\Lambda$ hyperons in $e^{+}{e}^{-}\to {\Lambda }^{\uparrow }hX$ processes within TMD factorization
• Observation of $\Lambda$ hyperon local polarization in pPb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 8.16 TeV
• $\sin ({\varphi }_{\Lambda }-{\varphi }_S)$ azimuthal asymmetry in transversely polarized $\Lambda$ production in SIDIS within TMD factorization at EIC
• Transverse spin polarization as a novel probe of medium-induced transverse-momentum-broadening effect