A Search for Lambda sub-b in pi^- - A Collisions at 515 GeV/c

TL;DR

This paper reports a search for Lambda_b baryons in pi- - A collisions at 515 GeV/c, analyzing dimuon data to set upper limits on the production and decay rate of Lambda_b particles.

Contribution

It provides the first experimental upper limits on Lambda_b production cross-section times branching ratio in pi- - A collisions at this energy.

Findings

Detected 2 candidate events in the Lambda_b mass region.

Set upper limits on F(Lambda_b) * Br(Lambda_b --> J/psi Lambda^0) at 90% confidence level.

Used data from Fermilab fixed target experiments E672 and E706.

Abstract

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_b events in the decay channel Lambda_b --> J/psi Lambda^0, with J/psi --> mu^+ mu^- and Lambda^0 --> p pi^- (and for the conjugate reactions). The data was collected by the Fermilab fixed target experiments E672 and E706. Several cuts were applied to the Lambda^0 (and anti-Lambda^0) to make a clean Lambda^0 (and anti-Lambda^0) data sample. Among the cuts there was a K^0_s mass cut, in which if the Lambda^0 --> p pi^- (or conjugate reaction) had the mass of the K^0_s under the hypothesis of both tracks being pi^+ pi^-, the Lambda^0 (or anti-Lambda^0) candidates were rejected. The results show 2 events in the Lambda_b mass region. Using the E672/E706 measurement of the bb_bar cross-section, and considering the 2 Lambda_b event candidates as signal with zero background, an upper limit to F(Lambda_b) * Br(Lambda_b --> J/psi Lambda^0) was found to be less than 6.2x10^-2 at 90 % C. L. An upper limit was also calculate without using the K^0_s mass cut for the Lambda^0 s (and anti-Lambda^0 s), and again, requiring that the J/psi s originate from secondary vertices, giving that F(Lambda_b) * Br(Lambda_b --> J/psi Lambda^0) < 3.1x10^-2 at 90 % C. L. and F(Lambda_b) * Br(Lambda_b --> J/psi Lambda^0) < 3.2x10$^-2 at 90 % C.L., respectively.