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

TL;DR

This study measures the form factors of Lambda_c^+ decay to Lambda e^+ nu_e and searches for CP violation, finding no evidence of CP violation and providing precise form factor ratios and decay asymmetry parameters.

Contribution

The paper presents the first measurement of the form factor ratio and pole mass in Lambda_c^+ decay, along with a CP violation search using a four-dimensional likelihood fit.

Findings

Form factor ratio R = -0.31 +/- 0.05 (stat) +/- 0.04 (syst)

Pole mass M_{pole} = 2.13 +/- 0.07 (stat) +/- 0.10 (syst) GeV/c^2

No evidence of CP violation, asymmetry ratio A_{Lambda_c} = 0.01 +/- 0.03 (stat) +/- 0.01 (syst)

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.