Parity doubling as a tool for right-handed current searches

Abstract

The V-A structure of the weak interactions leads to definite amplitude hierarchies in exclusive heavy-to-light decays mediated by b → (d, s)γ and b → (d, s) ¯ . However, the extraction of right-handed currents beyond the Standard Model is contaminated by V-A long-distance contributions leaking into right-handed amplitudes. We propose that these quantum-number changing long-distance contributions can be controlled by considering the almost parity-degenerate vector meson final states by exploiting the opposite relative sign of left-versus right-handed amplitudes. For example, measuring the time-dependent rates of a pair of vector V (J P = 1 − ) and axial A(1 + ) mesons in B → (V, A)γ, up to an order of magnitude is gained on the theory uncertainty prediction, controlled by long-distance ratios to the righthanded amplitude. This renders these decays clean probes to null tests, from the theory side. referred to as short-distance (SD) contributions hereafter, obey exact algebraic relations, leading to accidental control in the SD part. However, sizeable tree-level four-quark operators with charm and up quarks, H eff ∼d L γ µ UŪ L γ µ b (U = u, c), induce genuine long-distance (LD) effects, which are more difficult to control. It was argued, based on studying the inclusivē B → X s γ decay, that such contaminations could be rather significant [12], whereas actual computations show smaller effects in exclusive channels [13][14][15][16][17].In this article, we show that these LD effects can be controlled by a symmetry that in turn also explains the smallness found in the concrete computation [13] quoted just above. The symmetry in question is the chiral restoration limit. The crucial point is that decays of opposite parity, such asB → ρ(1 −− )γ versusB → a 1 (1 ++ )γ, are opposite in sign in the righthanded amplitude between the exact SD and LD contributions (originating from the sizeable V-A part). 1 While decays of axial mesons have received some attention as complementary probes for RHC (e.g. [21-23]), we advocate that the combination of the two decay channels allows for a cleaner extraction of the relevant observables controlled by ratios of vector to axial LD amplitudes. In light-cone approaches, this necessitates axial vector meson distribution amplitudes (DAs) [24], whose symmetry relations with vector meson DAs can be studied rather systematically [25]. For a simplified discussion of the main ideas of this paper we refer the reader to [26].The paper is organised as follows. In section 2 it is shown, using the path integral, that the fraction of LD-over SD-RHC flips sign for parity doublers. In section 3, the parity doublers are listed (section 3.1), followed by a discussion of the sources of correction to the symmetry limit in section 3.2. Applications to the time-dependent rates ofB → (V, A)γ, a detailed breakdown ofB s → φ(f 1 )γ, and remarks on B → (V, A) ¯ are presented in sections 4.1, 4.2 and 4.3 respectively. The paper ends with conclusions in section 5, including comments on the experimental feasibility of...

Radiative decays of heavy-light mesons and the $$ {f}_{H,{H}^{\ast },{H}_1}^{(T)} $$ decay constants

“…The correlation functions for the {f B 1 , f T B 1 } decay constants follow with rules for the insertion of the γ 5 into the currents cf. (B.10) and B * → B 1 in (4.1) following the ideas in [34].…”

QCD and High Energy Interactions: Moriond 2018 Theory Summary

“…Roman Zwicky explained that the contamination of right-handed currents in B → V γ (or B → V l l) decays due to long-distance effects can be controlled by considering in addition the corresponding decay B → Aγ (l l), where V /A are vector/axial vector mesons, exploiting the opposite relative sign of left-versus right-handed amplitudes 56,57 . Giancarlo D'Ambrosio gave us a broad overview on recent developments in Kaon physics 58 , also listing models which address the / anomaly and discussing the interplay with B-anomalies.…”