Scrutinizing new physics in semi-leptonic <i>B</i> <sub> <i>c</i> </sub> → <i>J</i> / <i>ψτν</i> decay
Ru-Ying Tang, Zhuo-Ran Huang, Cai-Dian Lü, Ruilin Zhu
Abstract
Abstract We perform a global analysis of the b → cτν data using the recent lattice results on the B c → J / ψ vector and axial-vector form factors. To explore the effects from the tensor operator of new physics beyond the Standard Model, we determine the tensor form factors by using the non-relativistic QCD (NRQCD) relations between tensor and (axial-)vector form factors. Based on the lattice + NRQCD form factors, we fit the Wilson coefficients and the new physics couplings in R 2 , S 1 and U 1 leptoquark models by including the recently measured R (Λ c ) and imposing the relaxed constraint <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mi mathvariant="script">B</mml:mi> <mml:mrow> <mml:mo stretchy="false">(</mml:mo> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>B</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>c</mml:mi> </mml:mrow> </mml:msub> <mml:mo>→</mml:mo> <mml:mi>J</mml:mi> <mml:mo>/</mml:mo> <mml:mi>ψ</mml:mi> </mml:mrow> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> <mml:mo><</mml:mo> <mml:mn>30</mml:mn> <mml:mi>%</mml:mi> </mml:math> in light of the recent studies on LEP1 data and B c lifetime. We give predictions for the experimental observables including R ( J / ψ ), P τ ( J / ψ ), F L ( J / ψ ) and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi mathvariant="script">A</mml:mi> </mml:mrow> <mml:mrow> <mml:mtext>FB</mml:mtext> </mml:mrow> </mml:msub> <mml:mrow> <mml:mo stretchy="false">(</mml:mo> <mml:mrow> <mml:mi>J</mml:mi> <mml:mo>/</mml:mo> <mml:mi>ψ</mml:mi> </mml:mrow> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> </mml:math> as well as their q 2 distribution in new physics scenarios/models. Our results suggest that the longitudinal τ polarization fraction P τ ( J / ψ ) and the forward–backward asymmetry <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi mathvariant="script">A</mml:mi> </mml:mrow> <mml:mrow> <mml:mtext>FB</mml:mtext> </mml:mrow> </mml:msub> <mml:mrow> <mml:mo stretchy="false">(</mml:mo> <mml:mrow> <mml:mi>J</mml:mi> <mml:mo>/</mml:mo> <mml:mi>ψ</mml:mi> </mml:mrow> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> </mml:math> are useful for testing the R 2 leptoquark model.