Quasi-elastic Charm Production In Neutrino-nucleon Scattering

A study of quasi elastic charm production in charged current neutrino-nucleon scattering is presented. A sample of about 1.3 million interactions recorded with the NOMAD detector in the CERN SPS wide band neutrino beam has been searched for quasi elastically produced charmed baryons (<math> <f> <g>L</g>⁺<inf>c</inf>,<g>S</g><inf>c</inf></f> </math> and <math> <f> <g>S</g>^*<inf>c<rm></rm></inf></f> </math>). The search has been performed in two exclusive decay channels of the <math> <f> <g>L</g>⁺<inf>c</inf>,</f> </math> both including a <math> <f> <g>L</g></f> </math>. Also, the semi-inclusive decay channels <math> <f> <g>L</g>⁺<inf>c</inf>,<g>S</g><inf>c</inf>,<g>S</g>^*<inf>c</inf>&rarr;<g>L</g>+X</f> </math> have been studied. Kinematic selection criteria have been chosen in order to obtain samples enriched with quasi elastic charm events. Signal efficiencies and background expectations have been estimated by Monte Carlo simulations. The observed number of events in each searched channel has been found to agree with the background expectation from charged and neutral current reactions and an upper limit for the cross section has been derived. For the quasi elastic charm production cross section averaged over the neutrino energy spectrum (&lang;<italic>E_&nu;</italic>&rang;) = 24.3 GeV) the upper limit has been found to be &lang;&sigma;_QEC&rang; &lt; 3.58 x 10<super> &minus;40</super> cm<super>2</super> or relative to the total charged current cross section &lang;&sigma;_QEC&rang;/&lang;&sigma;_cc&rang; &lt; 0.22% at 95% confidence level. Assuming an energy independent cross section for neutrino energies above 15 GeV, an upper limit of &sigma;_QEC &lt; 4.0 &times; 10<super>&minus;40</super> cm<super>2</super> (95% C. L.) has been found for the absolute cross section.