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Leptoquarks

The theory of leptoquarks used by this generator starts from an effective lagrangian with the most general dimensionless tex2html_wrap_inline1064 invariant couplings of scalar and vector leptoquarks satisfying baryon and lepton number conservation [2]. From the effective lagrangian one obtains the various partial leptoquark decay widths, tex2html_wrap_inline1066 . For the scalar (S) and vector (V) leptoquarks we have

equation108

where tex2html_wrap_inline1068 denote the leptoquark couplings to a particular final state and tex2html_wrap_inline1070 is the leptoquark mass. The total widths are obtained by summing over all possible final states.

In the limit of very narrow width ( tex2html_wrap_inline1072 ) leptoquarks, the cross-section can be approximated (narrow width approximation) by

equation123

where the parton density q is evaluated at the resonance peak tex2html_wrap_inline1076 and QCD scale tex2html_wrap_inline1078 . For some leptoquarks the parton density is for anti-quarks, tex2html_wrap_inline1080 . In addition to integrating the full cross-section, LQUARK\ calculates the cross-section using two different narrow width approximations for comparison. The above formula is obtained by using a delta-function approximation to the Briet-Wigner resonance. The total cross-section is also estimated by assuming the parton densities change very little within the resonance region.

Adapting the notation of reference 9 gif and using the calculated amplitudes in reference 2, the possible leptoquark reactions proceeding from an electron beam are as follows.

  1. tex2html_wrap_inline1086 ,
  2. tex2html_wrap_inline1088 ,
  3. tex2html_wrap_inline1090 ,
  4. tex2html_wrap_inline1092 ,
  5. tex2html_wrap_inline1094 ,
  6. tex2html_wrap_inline1096 ,
  7. tex2html_wrap_inline1098 ,
  8. tex2html_wrap_inline1100 ,
  9. tex2html_wrap_inline1102 ,
  10. tex2html_wrap_inline1104 ,
  11. tex2html_wrap_inline1106 ,
  12. tex2html_wrap_inline1108 ,
  13. tex2html_wrap_inline1110 or
  14. tex2html_wrap_inline1112 ,

where q is either a u- or d-type quark. An equivalent set of processes have also been coded for a positron beam. Whereas processes 1-5 and 11-12 are mainly produced in tex2html_wrap_inline1114 collisions, processes 6-10 and 13-14 are primarily created in the tex2html_wrap_inline1116 reactions. Table 1 gives the quantum numbers, couplings, production and decay channels for all leptoquarks.

  table179
Table 1:   Quantum numbers (Q is electric charge, T is weak isospin and tex2html_wrap_inline1002 is third component of isospin), coupling constants, and production and decay channels for leptoquarks.


next up previous
Next: Leptogluons Up: Physics Processes Previous: Physics Processes

Douglas M. Gingrich
Fri Mar 29 09:41:51 MST 1996