Improved Measurement of the Form Factors and First Search for CP Violation in the Decay of Lambda_c^+ to Lambda e^+ nu_e

Abstract

Using the CLEO detector at the Cornell Electron Storage Ring we have studied the angular distributions in the decay Lambda_c^+ to Lambda e+ nu_e. By performing a four-dimensional maximum likelihood fit, we extract the form factor ratio, R = f_2/f_1, and the pole mass, which determines the shape of the form factors, M_{pole}. They are found to be -0.31 +/- 0.05_{stat} +/- 0.04_{syst}$ and (2.13 +/- 0.07_{stat} +/- 0.10_{syst}) GeV/c^2, respectively. These results correspond to the following value of the decay asymmetry parameter: alpha_{Lambda_c} = -0.85 +/- {0.03}_{stat} +/- 0.02_{sys}, for <q^2> = 0.67 (GeV/c^2)^2. We search for CP violation in the angular distributions of the decay and find no evidence for CP violation, obtaining anasymmetry ratio; A_{Lambda_{c}} = (alpha_{Lambda_c} + alpha_{\bar{Lambda}_c}) / (alpha_{Lambda_c} - alpha_{\bar{Lambda}_c}) = 0.01 +/- 0.03_{stat} +/- 0.01_{sys} +/- 0.02_{A_{Lambda}}, where the third error is from the uncertainty in the world average of the CP violating parameter, A_{Lambda}, for Lambda decay to p pi^-. All results presented in this paper are preliminary.