B→D*τν¯τsensitivity to new physics

Abstract

B physics has played a prominent role in investigations of new physics effects at low-energies. Presently, the largest discrepancy between a standard model prediction and experimental measurements appears in the branching ratio of the charged current mediated B ! " decay, where the large mass lifts the helicity suppression arising in leptonic B decays. Less significant systematic deviations are also observed in the semileptonic B ! D ðÃÞ " rates. Because of the rich spin structure of the final state, the decay mode B ! D à " offers a number of tests of such possible standard model deviations. We investigate the most general set of lowest dimensional effective operators leading to helicity suppressed modifications of b ! c (semi)leptonic transitions. We explore such contributions to the B ! D à " decay amplitudes by determining the differential decay rate, longitudinal D à polarization fraction, D à À opening angle asymmetry and the helicity asymmetry. We identify the size of possible new physics contributions to these observables constrained by the present B ! D ðÃÞ " rate measurements and find significant modifications are still possible in all of them. In particular, the opening angle asymmetry can be shifted by almost 30%, relative to the standard model prediction, while the helicity asymmetry can still deviate by as much as 80%.

Status of B to D(*) τ ν decays in two-Higgs-doublet models

“…The BaBar collaboration measured the ratios [2] R(D ( * ) ) = Γ(B → D ( * ) τ −ν τ ) Γ(B → D ( * ) −ν ) , (1.1) where is either e or µ, finding R(D) = 0.440 ± 0.058 ± 0.042 and R(D * ) = 0.332 ± 0.024 ± 0.018. These results show a 2.0σ and 2.7σ excess with respect to the standard model (SM) predictions respectively [3,4]. Subsequent theoretical works have found a better agreement between the SM and the experimental value for R(D) by revisiting the treatment of the hadronic matrix elements.…”

“…[4,10,[15][16][17][18]. These observables can be useful to disentangle different kinds of new physics in b → cτν transitions and more importantly to our discussion, they can be used to test for charged scalar contributions independently of the flavour structure of its fermionic couplings.…”

New physics in the kinematic distributions of B¯→D(*)τ−(→

“…As for the BD * process, the axial, vector and pseudoscalar form factors are described in terms of a HQET form factor, h A1 (w), and the ratios R i (w) [9,16]: …”

“…Those for V1(1), M0, a (0) i and their correlations are obtained from [13], hA 1 (1) from [45] and R0(1) from ref. [16]. (30) R0(1) = 1.14(10) a…”

“…The discrepancy between experiment and the SM is at the level of 4σ, and it can be explained with new physics (NP) [11,[15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33]. These analyses of the data are most fruitful when casted model-independently in an effective field theoretical framework.…”