Abstract submitted to the
         International Europhysics Conference on High Energy Physics
                  July 12 - 18, 2001, Budapest, Hungary
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             Measurements of jet substructure in neutral current deep
             inelastic scattering and determination of alpha_s at HERA

                    
                               ZEUS Collaboration



                                    Abstract


          The substructure of jets has been measured in neutral current
          interactions at Q^2 > 125 GeV^2 with the ZEUS detector at HERA
          using an integrated luminosity of 42.7 pb^{-1}. Jets have been 
          identified in the laboratory frame using the longitudinally 
          invariant k_T-cluster algorithm. The substructure of jets has 
          been studied in terms of the jet shape and subjet multiplicity. 
          The subjet multiplicity is defined as the number of clusters 
          resolved in a jet by reapplying the jet algorithm at a smaller 
          resolution scale. Measurements of the integrated jet shape and
          mean subjet multiplicity for jets with transverse energies
          E_T^jet > 14 GeV are presented. The jets are observed to become
          narrower and the mean subjet multiplicity decreases as E_T^jet
          increases. Next-to-leading-order QCD calculations give a good
          description of the measurements and are used to make a 
          determination of alpha_s.