Energy dependence of the differences between the quark and gluon jet fragmentation

  • DELPHI Collaboration
Article
First Online:
Received:

Abstract

Three jet events arising from decays of the Z boson, collected by the DELPHI detector, were used to measure differences in quark and gluon fragmentation. Gluon jets were anti-tagged by identifying b quark jets. Unbiased quark jets came from events with two jets plus one photon. Quark and gluon jet properties in different energy ranges were compared for the first time within the same detector. Quark and gluon jets of nearly the same energy in symmetric three jet event topologies were also compared. Using three independent methods, the average value of the ratio of the mean charged multiplicities of gluon and quark jets is $$< r >=1.241 pm 0.015 (stat.)pm 0.025 (syst.).$$ Gluon jets are broader and produce fragments with a softer energy spectrum than quark jets of equivalent energy. The string effect has been observed in fully symmetric three jet events. The measured ratio Rγ of the charged particle flow in the qq̅ inter-jet region of the qq̅g and qq̅γ samples agrees with the perturbative QCD expectation. The dependence of the mean charged multiplicity on the hadronic center-of-mass energy was analysed in photon plus n-jet events. The value for αs(M Z) determined from these data using a QCD prediction with corrections at leading and next-to-leading order is $$←pha_s(M_Z)=0.116pm 0.003 (stat.)pm 03009 (syst.).$$

This is a preview of subscription content, log in to check access.

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. 1.
    JADE Coll., W. Bartel et al., Z. Phys. C21 (1983) 37; JADE Coll., W. Bartel et al., Phys. Lett. B123 (1983) 460; UA2 Coll., P. Bagnaia et al., Phys. Lett. B144 (1984) 291; MARK II Coll., A. Peterson et al., Phys. Rev. Lett. 55 (1985) 1954; HRS Coll., M. Derrick et al., Phys. Lett. B165 (1985) 449; UA1 Coll., G. Arnison et al., Nucl. Phys. B276 (1986) 253; AMY Coll., Y.K. Kim et al., Phys. Rev. Lett. 63 (1989) 1772; TASSO Coll., W. Braunschweig et al., Z. Phys. C45 (1989) 1; AMY Coll., M. Ye et al., Proc. 25th Int. Conf. on High Energy Physics, August 1990, Singapore, Vol. II, Eds. K.K. Phua, Y. Yamaguchi, Pub. South East Asia Theoretical Physics Association and the Physical Society of Japan (1991) p. 889; DELPHI Coll., P. Abreu et al., Z. Phys. C56 (1992) 63; CLEO Coll., M.S. Alam et al., Phys. Rev. D46 (1992) 4822; TOPAZ Coll., Y. Ohnishi et al., Phys. Lett. B313 (1993) 475; VENUS Coll., H. Takaki et al., Phys. Rev. Lett. 71 (1993) 38.Google Scholar
  2. 2.
    OPAL Coll., G. Alexander et al., Phys. Lett. B265 (1991) 462; OPAL Coll., P.D. Acton et al., Z. Phys. C58 (1993) 387; OPAL Coll., R. Akers et al., Z. Phys. C68 (1995) 179.Google Scholar
  3. 3.
    ALEPH Coll., D. Buskulic et al., Phys. Lett. B346 (1995) 389.CrossRefGoogle Scholar
  4. 4.
    M. L. Mangano, P. Nason, Phys. Lett. B285 (1992) 160; M. H. Seymour, Z. Phys. C63 (1994) 99; M. H. Seymour, Nucl. Phys. B436 (1995) 163.CrossRefGoogle Scholar
  5. 5.
    Y.L. Dokshitzer, V.A. Khoze, A.H. Mueller, S.I. Troyan, “Basics of perturbative QCD”, Editions Frontiers, 1991.Google Scholar
  6. 6.
    Ya.I. Azimov, Yu.L. Dokshitzer, V.A. Khoze, S.I. Troyan, Phys. Lett. B165 (1985) 147; Ya.I. Azimov, Yu.L. Dokshitzer, V.A. Khoze, S.I. Troyan, Yad. Fiz. 43 (1986) 149. T. Sjöstrand, ‘Z0 Physics’, Cargèse 1990, Eds. M. Lévy et al., Pub. Plenum Press, New York (1991) 367; CERN-TH.5902/90 “QCD and Jets at LEP”.CrossRefGoogle Scholar
  7. 7.
    TPC Coll., H. Aihara et al.: Phys. Rev. Lett. 57 (1986) 945; MARK II Coll., P.D. Seldon et al.: Phys. Rev. Lett. 57 (1986) 1398; JADE Coll., F. Ould Saada et al.: Z. Phys. C39 (1988) 1.CrossRefGoogle Scholar
  8. 8.
    OPAL Coll., M. Z. Akrawy et al., Phys. Lett. B261 (1991) 334; OPAL Coll., R. Akers et al., Z. Phys. C68 (1995) 531.CrossRefGoogle Scholar
  9. 9.
    L3 Coll., M. Acciarri et al., Phys. Lett. B345 (1995) 93–102; D. Duchesneau, Ph. D. Thesis, “Etude du rayonnement électromagnétique des quarks primaires produits dans les désintégrations hadroniques du Z avec le détecteur L3 au LEP”, Thèse No. 2644, Université de Genève 1993.CrossRefGoogle Scholar
  10. 10.
    ALEPH Coll., D. Buskulic et al., Contribution to the 27th International Conference on High Energy Physics, Glasgow, Scotland, July, 1994. ICHEP94 ref. 0543.Google Scholar
  11. 11.
    DELPHI Coll., P. Aarnio et al., Nucl. Instr. Meth. A303 (1991) 233.Google Scholar
  12. 12.
    DELPHI Trigger Group (V. Bocci, et al.), Architecture and Performance of the Delphi Trigger System, Nucl. Instr. Meth. A362 (1995) 361.CrossRefGoogle Scholar
  13. 13.
    W. Adam et al., Design and Performance of the Delphi Data Acquisition System, IEEE Trans. Nucl. Sci. 39 (1992) 166.CrossRefGoogle Scholar
  14. 14.
    N. Bingefors et al., Nucl. Instr. Meth. A328 (1993) 447.CrossRefGoogle Scholar
  15. 15.
    DELPHI Coll., P. Abreu et al., Phys. Lett. B307 (1993) 221.CrossRefGoogle Scholar
  16. 16.
    S. Bethke, Z. Kunszt, D. Soper, W.J. Stirling, Nucl. Phys. B370 (1992) 310.CrossRefGoogle Scholar
  17. 17.
    S. Catani et al., Phys. Lett. B269 (1991) 432; N. Brown, W.J. Stirling, Z. Phys. C53 (1992) 629.CrossRefGoogle Scholar
  18. 18.
    JADE Coll., W. Bartel et al., Z. Phys. C33 (1986) 23; JADE Coll., S. Bethke et al., Phys. Lett. B213 (1988) 235.Google Scholar
  19. 19.
    P.V. Chliapnikov, V.A Uvarov, F. Bianchi, Phys. Lett. B300 (1993) 183.CrossRefGoogle Scholar
  20. 20.
    S. Mart’? Ph. D. Thesis, “Estudi de la dependència energética de les diferències entre jets de quarks i de gluons utilitzant el detector DELPHI de LEP”. Universitat de València, IFIC/95-59.Google Scholar
  21. 21.
    O. Klapp, Diplomarbeit “Quark- und Gluonjets aus Z-Zerfallen — Vergleichende Studien des Jetendzustandes und der Substruktur”. WU D 95-15. University of Wuppertal.Google Scholar
  22. 22.
    T. Sjöstrand, Comp. Phys. Comm. 39 (1986) 346; T. Sjöstrand, M. Bengtsson, Comp. Phys. Comm. 43 (1987) 367.CrossRefGoogle Scholar
  23. 23.
    DELSIM user’s guide, DELPHI 89-15 PROG 130, CERN, February 1989; DELSIM Reference Manual, DELPHI 89-68 PROG 143, CERN, September 1989.Google Scholar
  24. 24.
    DELPHI Coll., P. Aarnio et al., Phys. Lett. B341 (1994) 109.Google Scholar
  25. 25.
    ALEPH Coll., D. Buskulic et al., Phys. Lett. B313 (1993) 535.CrossRefGoogle Scholar
  26. 26.
    G.V. Borisov, DELPHI Internal Note, DELPHI 94-27 PHYS 361 (1994); G.V. Borisov, Lifetime Tag of Events with B-hadrons with the DELPHI detector, preprint IHEP (Protvino), 94-98 (1994); DELPHI Coll., P. Abreu et al., Z. Phys. C65 (1995) 555.Google Scholar
  27. 27.
    See for example A.S. Schwarz, Phys. Rep. 238 (1994) 1, and references therein.CrossRefGoogle Scholar
  28. 28.
    F. Bianchi, P.V. Chliapnikov, L. Gerdyukov, A. Giovannini, “A study of the ratio of quark and gluon jet mean charged particle multiplicity at LEP by the correlation method”, DELPHI 95-40 PHYS 483.Google Scholar
  29. 29.
    DELPHI Coll., P. Abreu et al., Phys. Lett. B347 (1995) 447.CrossRefGoogle Scholar
  30. 30.
    OPAL Coll., R. Akers et al., Phys. Lett. B352 (1995) 176.CrossRefGoogle Scholar
  31. 31.
    Z. Fodor, Phys. Lett. B263 (1991) 305.CrossRefGoogle Scholar
  32. 32.
    AMY Coll., Y.K. Li et al., Phys. Rev. D41 (1990) 2675.Google Scholar
  33. 33.
    TASSO Coll., W. Braunschweig et al., Z. Phys. C47 (1990) 187.Google Scholar
  34. 34.
    DELPHI Coll., P. Abreu et al., Phys. Lett. B311 (1993) 408; ALEPH Coll., D. Buskulic et al., Phys. Lett. B357 (1995) 487.CrossRefGoogle Scholar
  35. 35.
    B.R. Webber, Phys. Lett. B143 (1984) 501 and references therein.CrossRefGoogle Scholar
  36. 36.
    P.V. Chliapnikov, V.A. Uvarov, Phys. Lett. B251 (1990) 192 and references therein.CrossRefGoogle Scholar
  37. 37.
    A. Ballestrero, E. Maina and S. Moretti, Phys. Lett. B294 (1992) 425.CrossRefGoogle Scholar
  38. 38.
    M. Bilenky, G. Rodrigo, A. Santamaria, Nucl. Phys. B439 (1995) 505.CrossRefGoogle Scholar

Copyright information

© Springer-Verlag 1996

Authors and Affiliations

  • DELPHI Collaboration

There are no affiliations available

Personalised recommendations