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摘要
In Bc-</mml:msubsup> -> J/psi(-> mu (+)mu (-))tau (-)nu <overbar></mml:mover>tau decay, the three-momentum p tau- cannot be determined accurately due to the decay products of tau (-) inevitably include an undetected nu (tau). As a consequence, the angular distribution of this decay cannot be measured. In this work, we construct a measurable angular distribution by considering the subsequent decay tau (-) -> pi (-)nu (tau). The full cascade decay is Bc-</mml:msubsup> -> J/psi(-> mu (+)mu (-))tau (-)(-> pi (-)nu (tau))nu <overbar></mml:mover>tau, in which the three-momenta p mu+,p mu-, and p pi- can be measured. The five-fold differential angular distribution containing all Lorentz structures of the new physics (NP) effective operators can be written in terms of twelve angular observables I-i(q(2), E-pi). Integrating over the energy of pion E-pi, we construct twelve normalized angular observables I</mml:mover>i(q(2)) and two lepton-flavor-universality ratios R<mml:mfenced close=")" open="(">PL,TJ/psi</mml:mfenced>(q(2)). Based on the B-c -> J/psi form factors calculated by the latest lattice QCD and sum rule, we predict the q(2) distribution of all <mml:msub>I</mml:mover>i and R<mml:mfenced close=")" open="(">PL,TJ/psi</mml:mfenced> both within the Standard Model and in eight NP benchmark points. We find that the benchmark BP2 (corresponding to the hypothesis of tensor operator) has the greatest effect on all I-i and R<mml:mfenced close=")" open="(">PL,TJ<mml:mo>/psi</mml:mfenced>, except <mml:msub><mml:mover accent="true">I<mml:mo stretchy="true"></mml:mover>5. The ratios R<mml:mfenced close=")" open="(">PL<mml:mo>,TJ<mml:mo>/psi</mml:mfenced> are more sensitive to the NP with pseudo-scalar operators than the I-i. Finally, we discuss the symmetries in the angular observables and present a model-independent method to determine the existence of tensor operators.
