Study of diquark fragmentation intoΛandY*+inνnand

Abstract

We apply a new method to determine the probability of the uu diquark from vp interactions fragmenting as independent quarks. In particular, by assuming that all 12's which do not come from Y*', N*', or charmed baryons must come from independent fragmentation, we show this probability to be about 50%. We also provide information from v n interactions on the fragmentation of ud diquarks into A's, and from this determine the probability of capturing a strange quark from the sea in the target region to be 7 , = 0.051 k0.013, about half the value found in the current region, y , =0.12 k0.02. Overall A production rates in v n and v p reactions are (7.0 +0.8)% and (7.0k 1.2)%, respectively, when cuts of W > 4 GeV and x~ > 0.2 are made on the data.In charged-current neutrino-nucleon interactions the neutrino interacts primarily with the d valence quark. Thus the recoiling diquark system in v p interactions is uu and in v n interactions it is ud. Models of diquark hadronization have been the subject of several theoretical papers.'-' In these models two basic processes of fragmentation are considered. In the first the diquark system fragments coherently, becoming part of a baryon. In the second the quarks fragment independently, a baryon being formed further down the hadronization chain. A parameter of interest is the relative frequency of these two processes.A measurement of this relative frequency may shed light on questions of nucleon structure, in particular, whether the diquark exists as a basic subunit of the n~c l e o n .~, 'Recent papers using diquark-quark models have achieved some success in explaining SU(6) violations in quasi-two-body reactions,' the negative charge radius of the n e~t r o n ,~ baryon mass spectra,'' and deep-inelastic structure functions." They suggest the existence within the nucleon of a tightly bound ud diquark with I = 0, S = 0, but not the existence of a I = 1, S = 1 state (uu, dd, or u d ) .If this were the case one might expect a more closely correlated, more coherently fragmenting, diquark in the v n case than in the vp, for in the latter the core is always broken up. This makes a comparison of diquark fragmentation in the two cases interesting.In the models of Sukhatme, Lassila, and 0rava3 and Bartl, Fraas, and ~a j e r o t t o ,~ distributions in x~. in the target region are calculated assuming a fixed probability, the same for ud and uu, for independent fragmentation. Comparisons are made with v p and v p data, and although the qualitative trend of the x~ distributions is in agreement, limitations on both the data and the inodels make it difficult to determine well the fraction of independent fragmentation.A different type of experiment was carried out at the CERN ISR by Hanna et a1.I2 Assuming all pp interactions are quark-quark scatterings, their data suggested predominantly coherent fragmentation for both diquarks. It has been pointed however, that gluon interactions should account for -40% of the events; hence the interpretation is unclear. In this work we use a model-independen...

Anatomy of mixing-induced CP asymmetries in left–right symmetric models with spontaneous CP violation

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