Reconciling anomalous measurements in $B_s-\bar{B}_s$ mixing: the role of CPT-conserving and CPT-violating new physics

TL;DR

This paper investigates anomalies in $B_s$ mixing and decay, demonstrating that new physics with both dispersive and absorptive contributions, including CPT violation, is needed to explain observations, implying potential large branching ratios for certain decays.

Contribution

It provides a model-independent analysis showing the necessity of absorptive new physics contributions and extends the formalism to include CPT violation effects.

Findings

Absorptive new physics contributions are strongly favored over models without them.

CPT violation alone marginally helps in explaining anomalies.

Large branching fractions for $B_s o au^+ au^-$ are implied by the results.

Abstract

Recently observed anomalies in the $B_s \to J/\psi \phi$ decay and the like-sign dimuon asymmetry $A^b_{sl}$ hint at possible new physics (NP) in the $\bsbsbar$ mixing. We parameterize the NP with four model-independent quantities: the magnitudes and phases of the dispersive part $M_{12}$ and the absorptive part $\Gamma_{12}$ of the NP contribution to the effective Hamiltonian. We constrain these parameters using the four observables $\Delta M_s$, $\Delta\Gamma_s$, the mixing phase $\beta_s^{J/\psi\phi}$, and $A^b_{sl}$. Our quantitative fit indicates that the NP should contribute a significant dispersive as well as absorptive part. In fact, models that do not contribute a new absorptive part are disfavored at more than 99% confidence level. We extend this formalism to include CPT violation, and show that CPT violation by itself, or even in presence of CPT-conserving new physics without an absorptive part, helps only marginally in the simultaneous resolution of these anomalies. The NP absorptive contribution to $\bsbsbar$ mixing therefore seems to be essential, and would imply a large branching fraction for channels like $B_s \to \tau^+ \tau^-$.