- Physical Review Journals
All JournalsPhysics Magazine

Physical Review D

Reuse & Permissions

It is not necessary to obtain permission to reuse this article or its components as it is available under the terms of the Creative Commons Attribution 4.0 International license. This license permits unrestricted use, distribution, and reproduction in any medium, provided attribution to the author(s) and the published article's title, journal citation, and DOI are maintained. Please note that some figures may have been included with permission from other third parties. It is your responsibility to obtain the proper permission from the rights holder directly for these figures.

Export citation

Export citation

Choose format for download:

Download Citation
  • Open Access

Model for baryon production in spin-dependent string fragmentation

A. Kerbizi1,* and X. Artru2,†

  • *Contact author: albi.kerbizi@ts.infn.it
  • †Contact author: xavier.artru@orange.fr
PDF

Phys. Rev. D 113, 034007 – Published 5 February, 2026

DOI: https://doi.org/10.1103/7dd2-61z8

Abstract

We introduce spin-1/2 baryons in the string+P30 model of hadronization, previously restricted to the production of pseudoscalar and vector mesons. Baryons are modeled as quark–diquark bound states, and baryon production is described by the tunneling of diquark–antidiquark pairs at string breaking points. Diquarks can be scalar or pseudovector, the latter being produced in the relative D50 state. Introducing the quark–baryon–diquark coupling, the relevant splitting amplitudes for the emission of baryons are constructed and used to explore analytically the model predictions. We find a Collins effect for baryon production in the fragmentations of transversely polarized quarks or diquarks as well as a baryon spontaneous pT-dependent transverse polarization. The model is presented in a form suitable for implementation in a Monte Carlo event generator. The hadronic decays of polarized hyperons are also included.

View figure in article

Physics Subject Headings (PhySH)

Article Text

References (47)

  1. J. C. Collins, Fragmentation of transversely polarized quarks probed in transverse momentum distributions, Nucl. Phys. B396, 161 (1993).
  2. A. Airapetian et al. (HERMES Collaboration), Azimuthal single- and double-spin asymmetries in semi-inclusive deep-inelastic lepton scattering by transversely polarized protons, J. High Energy Phys. 12 (2020) 010.
  3. C. Adolph et al. (COMPASS Collaboration), Collins and Sivers asymmetries in muonproduction of pions and kaons off transversely polarised protons, Phys. Lett. B 744, 250 (2015).
  4. R. Seidl et al. (Belle Collaboration), Measurement of azimuthal asymmetries in inclusive production of hadron pairs in e+e− annihilation at s=10.58-GeV, Phys. Rev. D 78, 032011 (2008); 86, 039905(E) (2012).
  5. H. Li et al. (Belle Collaboration), Azimuthal asymmetries of back-to-back π±−(π0,η,π±) pairs in e+e− annihilation, Phys. Rev. D 100, 092008 (2019).
  6. J. P. Lees et al. (BABAR Collaboration), Measurement of Collins asymmetries in inclusive production of charged pion pairs in e+e− annihilation at BABAR, Phys. Rev. D 90, 052003 (2014).
  7. J. P. Lees et al. (BABAR Collaboration), Collins asymmetries in inclusive charged KK and Kπ pairs produced in e+e− annihilation, Phys. Rev. D 92, 111101 (2015).
  8. M. Ablikim et al. (BESIII Collaboration), Measurement of azimuthal asymmetries in inclusive charged dipion production in e+e− annihilations at s=3.65  GeV, Phys. Rev. Lett. 116, 042001 (2016).
  9. J. C. Collins, S. F. Heppelmann, and G. A. Ladinsky, Measuring transversity densities in singly polarized hadron hadron and lepton—hadron collisions, Nucl. Phys. B420, 565 (1994).
  10. A. Bianconi, S. Boffi, R. Jakob, and M. Radici, Two hadron interference fragmentation functions. Part I. General framework, Phys. Rev. D 62, 034008 (2000).
  11. A. Airapetian et al. (HERMES Collaboration), Effects of transversity in deep-inelastic scattering by polarized protons, Phys. Lett. B 693, 11 (2010).
  12. C. Adolph et al. (COMPASS Collaboration), A high-statistics measurement of transverse spin effects in dihadron production from muon–proton semi-inclusive deep-inelastic scattering, Phys. Lett. B 736, 124 (2014).
  13. A. Vossen et al. (Belle Collaboration), Observation of transverse polarization asymmetries of charged pion pairs in e+e− annihilation near s=10.58  GeV, Phys. Rev. Lett. 107, 072004 (2011).
  14. M. Anselmino, A. Mukherjee, and A. Vossen, Transverse spin effects in hard semi-inclusive collisions, Prog. Part. Nucl. Phys. 114, 103806 (2020).
  15. A. D. Panagiotou, Λ0 polarization in hadron—nucleon, hadron—nucleus and nucleus-nucleus interactions, Int. J. Mod. Phys. A 05, 1197 (1990).
  16. A. Airapetian et al. (HERMES Collaboration), Transverse polarization of Λ hyperons from quasireal photoproduction on nuclei, Phys. Rev. D 90, 072007 (2014).
  17. Y. Guan et al. (Belle Collaboration), Observation of transverse Λ/Λ¯ hyperon polarization in e+e− annihilation at Belle, Phys. Rev. Lett. 122, 042001 (2019).
  18. J. Felix, On Theoretical studies of Λ0 polarization, Mod. Phys. Lett. A 14, 827 (1999).
  19. B. Andersson, G. Gustafson, and G. Ingelman, A semiclassical model for the polarization of inclusively produced Λ0 particles at high-energies, Phys. Lett. 85B, 417 (1979).
  20. B. Andersson, G. Gustafson, G. Ingelman, and T. Sjostrand, Parton fragmentation and string dynamics, Phys. Rep. 97, 31 (1983).
  21. P. J. Mulders and R. D. Tangerman, The complete tree level result up to order 1/Q for polarized deep inelastic leptoproduction, Nucl. Phys. B461, 197 (1996); B484, 538(E) (1997).
  22. M. Anselmino, D. Boer, U. D’Alesio, and F. Murgia, Λ polarization from unpolarized quark fragmentation, Phys. Rev. D 63, 054029 (2001).
  23. U. D’Alesio, F. Murgia, and M. Zaccheddu, First extraction of the Λ polarizing fragmentation function from Belle e+e− data, Phys. Rev. D 102, 054001 (2020).
  24. D. Callos, Z.-B. Kang, and J. Terry, Extracting the transverse momentum dependent polarizing fragmentation functions, Phys. Rev. D 102, 096007 (2020).
  25. U. D’Alesio, L. Gamberg, F. Murgia, and M. Zaccheddu, Transverse Λ polarization in e+e− processes within a TMD factorization approach and the polarizing fragmentation function, J. High Energy Phys. 12 (2022) 074.
  26. A. Kerbizi, X. Artru, Z. Belghobsi, F. Bradamante, and A. Martin, Recursive model for the fragmentation of polarized quarks, Phys. Rev. D 97, 074010 (2018).
  27. A. Kerbizi, X. Artru, Z. Belghobsi, and A. Martin, Simplified recursive P03 model for the fragmentation of polarized quarks, Phys. Rev. D 100, 014003 (2019).
  28. A. Kerbizi, X. Artru, and A. Martin, Production of vector mesons in the String+P30 model of polarized quark fragmentation, Phys. Rev. D 104, 114038 (2021).
  29. D. Amati, A. Stanghellini, and S. Fubini, Theory of high-energy scattering and multiple production, Nuovo Cimento 26, 896 (1962).
  30. C. Bierlich et al., A comprehensive guide to the physics and usage of pythia 8.3, SciPost Phys. Codebases 8 (2022).
  31. A. Kerbizi and L. Lönnblad, stringspinner—adding spin to the pythia string fragmentation, Comput. Phys. Commun. 272, 108234 (2022).
  32. A. Kerbizi and L. Lönnblad, Extending stringspinner to handle vector-meson spin, Comput. Phys. Commun. 292, 108886 (2023).
  33. A. Kerbizi and X. Artru, String fragmentation of a quark pair with entangled spin states: Application to e+e− annihilation, Phys. Rev. D 109, 054029 (2024).
  34. A. Kerbizi, L. Lönnblad, and A. Martin, Quark spin effects in e+e− annihilation: A Monte Carlo event generator study, Phys. Rev. D 110, 074029 (2024).
  35. B. Andersson, G. Gustafson, and T. Sjostrand, A model for baryon production in quark and gluon jets, Nucl. Phys. B197, 45 (1982).
  36. B. Andersson, G. Gustafson, and B. Soderberg, A general model for jet fragmentation, Z. Phys. C 20, 317 (1983).
  37. X. Artru, Correspondences between the symmetric Lund model and the dual resonance model, Z. Phys. C 26, 83 (1984).
  38. A. Casher, H. Neuberger, and S. Nussinov, Chromoelectric flux tube model of particle production, Phys. Rev. D 20, 179 (1979).
  39. A. Bacchetta, F. Conti, and M. Radici, Transverse-momentum distributions in a diquark spectator model, Phys. Rev. D 78, 074010 (2008).
  40. R. Jakob, P. J. Mulders, and J. Rodrigues, Modeling quark distribution and fragmentation functions, Nucl. Phys. A626, 937 (1997).
  41. X. Artru, M. Elchikh, J.-M. Richard, J. Soffer, and O. V. Teryaev, Spin observables and spin structure functions: Inequalities and dynamics, Phys. Rep. 470, 1 (2009).
  42. M. G. Alexeev et al. (COMPASS Collaboration), Probing transversity by measuring Λ polarisation in SIDIS, Phys. Lett. B 824, 136834 (2022).
  43. R. L. Workman et al. (Particle Data Group), Review of particle physics, Prog. Theor. Exp. Phys. 2022, 083C01 (2022).
  44. J. C. Collins, Spin correlations in Monte Carlo Event generators, Nucl. Phys. B304, 794 (1988).
  45. I. G. Knowles, Spin correlations in parton—parton scattering, Nucl. Phys. B310, 571 (1988).
  46. B. Assi, C. Bierlich, P. Ilten, T. Menzo, S. Mrenna, M. Szewc, M. K. Wilkinson, A. Youssef, and J. Zupan (MLhad Collaboration), Post-hoc reweighting of hadron production in the Lund string model, SciPost Phys. 19, 104 (2025).
  47. B. Andersson, G. Gustafson, and T. Sjostrand, Baryon production in jet fragmentation and ϒ decay, Phys. Scr. 32, 574 (1985).

Outline

Information

Phys. Rev. D 113, 034007– Published 5 February, 2026
  • Received 2 October 2025
  • Accepted 9 January 2026
Crossmark - Check for updates button
Creative Commons Logo

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.

Published by the American Physical Society

Sign In to Your Journals Account

Filter

Filter

Article Lookup

Enter a citation