Spin effects in inclusive strange particle production

[摘要] The origin of spin effects in inclusive particle production at high energies is still a puzzle. Various experiments since 1976, when large values of polarization were observed in inclusive $Lambda$ production (BUN76), have yielded measurements for the polarization P, of the baryon octet members, analyzing power A, for $Lambda$, $Sigmasp{0}$, the pions and K$sb{s}$ and depolarization parameter D for $Lambda$ production. In an ongoing effort to understand the dynamics of the phenomenon we have carried out an experiment to measure P, A and D parameters for inclusively produced $Sigmasp{0}$'s. We were also able to measure A for K$sb{s}$ production which is in good agreement with an earlier measurement (BON88). We find that the polarization for $Sigmasp{0}$'s is 23.0 $pm$ 13.0% also in good agreement with an earlier measurement of 28.0 $pm$ 13.0% (DUK87). The analyzing power and depolarization are A = 1.8 $pm$ 5.5% and D = 26.0 $pm$ 16.0% averaged over all the data with x$sb{m F} >$ 0.2.Comparing the results with a phenomenological model we find that the A and D values differ considerably from the predictions. This model is based on ideas from parton fragmentation-recombination models and uses SU(6) symmetry for the wavefunctions. The transition amplitudes are parameterized by parameters $epsilon, epsilonspprime, delta$, and $deltaspprime$ in such a way that fast quarks preferentially recombine with spin up and slow quarks with spin down. We have extended this model by allowing partial transfer of common valence quarks between the beam particle and the final state. Thus, whereas in the original version p $o Sigmasp{0}$ could proceed only by (ud) diquark transfer now it is enhanced by u and d single quark transfer.Another extension to the model is the inclusion of finite probability of transversity spin flip (XSF) during recombination. By fitting the ratio of the production cross sections for $Lambda$'s and $Sigmasp{0}$'s we obtain a single XSF probability of p = 0.34%. With these modifications the predictions for A and D in $Sigmasp{0}$ production are 5.6% and 33% respectively in excellent agreement with the experimental values. With the inclusion of XSF, the analyzing power for p $o pisp{+}$ and p $o pisp{-}$ also come into agreement.

[发布机构] Rice University

[效力级别] physics