; Lu, Cai-Dian] Inst High Energy Phys, Beijing 100049, Peoples R China
; [Wang, Yu-Ming
; Lu, Cai-Dian] CAS, Sci Facil, Ctr Theoret Phys, Beijing 100049, Peoples R China
; [Aslam, M. Jamil] Quaid I Azam Univ, Natl Ctr Phys, Islamabad, Pakistan
; [Aslam, M. Jamil] Natl Univ Sci & Technol, Ctr Adv Math & Phys, Rawalpindi, Pakistan
The exclusive weak decay of Lambda(b) -> Lambda gamma and Lambda(b) -> Lambda l(+)l(-) are investigated in the Appelquist-Cheng- Dobrescu model, which is an extension of the standard model in the presence of universal extra dimensions. Employing the transition form factors obtained in the light-cone sum rules, we analyze how the invariant-mass distribution, the forward-backward asymmetry and the polarization asymmetry of the Lambda baryon of these decay modes can be used to constrain the only additional free parameter with respect to the standard model, namely, the radius, R, of the extra dimension. Our results indicate that the Kaluza-Klein modes can lead to approximately 25% suppression of the branching ratio of Lambda(b) -> Lambda gamma; however, their contributions can bring about 10% enhancement to the decay rate of Lambda(b) -> Lambda l(+)l(-). It is shown that in the present scenario the zero position of the forward-backward asymmetry of Lambda(b) -> Lambda mu(+)mu(-) sensitive to the compactification parameter R, while the measurement of polarizations of Lambda baryon in the Lambda(b) decays are not a useful tool to provide any valuable information for the universal extra-dimension model.