a Search for Lambda

An extensive analysis was performed on 8.0 pb ^{-1} of dimuon data produced in pi- A collisions at 515 GeV/c to search for Lambda_{rm b} events in the decay channel Lambda_{b}to J/Psi Lambda^0, with rm J/ Psitomu^{+}mu^ - and Lambda^0to p pi^- (and for the conjugate reactions). The muon tracks rm J/Psi decays were refitted with the mass constraint of two-body decay and with the constraint that both muon tracks intersect at a common point. The Lambda ^0 s were identified by their characteristic decay, giving the large fraction of their momenta to the protons. Lambda^0 s were reconstructed in three regions of the E672/E706 spectrometer, in the SSD/target region, in the region between the SSDs and the dipole magnet, and inside the dipole magnet using an iterating algorithm. Several cuts were applied to the Lambda^0 (and | Lambda^0) to make a clean Lambda^0 (and |Lambda ^0) data sample. Among the cuts there was K^0_{rm s} mass cut, in which if the Lambda^0 (or |Lambda^0) had the mass of the K^0_{rm s} under the hypothesis of both tracks being pi^+pi^-, the Lambda^0 (or | Lambda^0) candidates were rejected. These give a clean Lambda^0 (and |Lambda^0) data sample of 575 +/- 35 Lambda ^0 (and |Lambda^0) candidates. To search for the Lambda _{b} to J/Psi Lambda ^0 (and charge conjugate reaction), J/ Psi s that passed the muon refit were combined with Lambda^0 s (or |Lambda^0s) when they existed in the same event. The results show 2 events in the Lambda_{rm b} mass region. Using the E672 measurement of the bb cross-section, and considering the 2 Lambda_{b} event candidates as signal with zero background, an upper limit to rm F(Lambda_{b}) * Br(Lambda _{b}to J/Psi Lambda ^0) was found to be less than 6.2 times10^{-2} at 90% C.L. An upper limit was also calculate without using a K ^0_{rm s} mass cut for the Lambda^0 s (and |Lambda^0 s), and then, requiring that the J/Psi s originate from secondary vertices, giving F(Lambda_ {b}) * Br(Lambda_{b}to J/Psi Lambda^0)< 3.1times10 ^{-2} at 90% C.L and rm F(Lambda_{b}) * Br(Lambda _{b}to J/PsiLambda^0) < 3.2times10^{-2} at 90% C.L, respectively.