Abstract
We study the rare Lambda _brightarrow Lambda mu ^+mu ^- decay in the Standard Model and beyond. Beyond the Standard Model we include new vector and axial-vector operators, scalar and pseudo-scalar operators, and tensor operators in the effective Hamiltonian. Working in the helicity basis and using appropriate parametrization of the Lambda _b rightarrow Lambda hadronic matrix elements, we give expressions of hadronic and leptonic helicity amplitudes and derive expression of double differential branching ratio with respect to dilepton invariant mass squared and cosine of lepton angle. Appropriately integrating the differential branching ratio over the lepton angle, we obtain the longitudinal polarization fraction and the leptonic forward-backward asymmetry and sequentially study the observables in the presence of the new couplings. To analyze the implications of the new vector and axial-vector couplings, we follow the current global fits to brightarrow smu ^+mu ^- data. While the impacts of scalar couplings can be significant, exclusive bar{B}rightarrow X_smu ^+mu ^- data imply stringent constraints on the tensor couplings and hence the effects on Lambda _brightarrow Lambda mu ^+mu ^- are negligible.
Highlights
Which deviate from the Standard Model (SM) predictions [17,18] by about 2– 3σ with a combined deviation of ≈ 4σ
At large recoil, which correspond to low q2, the form factors are taken from recent calculations in the light cone sum-rules [42] and at low recoil, which correspond to large q2, we use results from the calculations in lattice QCD [36]
In this paper we have investigated the effects of New Physics (NP) couplings on the b → sμ+μ− mediated rare decay b → μ+μ−
Summary
Which deviate from the SM predictions [17,18] by about 2– 3σ with a combined deviation of ≈ 4σ. Data on baryonic modes are rather limited and only recently LHCb has reported a measurement of several b → μ+μ− observables where the branching ratio is found to be lower than the SM prediction at low q2 and higher at large q2 [22]. One of the challenging aspect of b → + − decay is to estimate the hadronic b → form factors Recent progress in this respect includes the lattice QCD results at low and intermediate. At large recoil, which correspond to low q2, the form factors are taken from recent calculations in the light cone sum-rules [42] and at low recoil, which correspond to large q2, we use results from the calculations in lattice QCD [36]. The paper is supplemented with a number of appendixes which contain the details of the calculations
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