New strategies for New Physics search in B -> K* nu anti-nu, B -> K nu anti-nu and B -> X(s) nu anti-nu decays

TL;DR

The paper addresses the NP sensitivity of b→sνν̄ decays by delivering updated SM predictions for B→K*νν̄, B→Kνν̄, and B→X_sνν̄ and introducing an ε‑η framework to parametrize potential right-handed down-quark couplings. It systematically explores NP scenarios (modified Z/Z′ penguins, LHT, RS, MSSM) and shows that MSSM with specific chargino-induced Z penguin contributions can yield noticeable deviations, while other models often predict small effects. The analysis also considers exotic possibilities like invisible scalars, detailing how they would distort spectra and complicate ε‑η extraction, thereby offering robust, multi-channel tests when combined with kaon decays and b→sℓℓ data. Overall, the work provides a comprehensive, testable blueprint for probing NP in b→sνν̄ transitions and clarifies how these modes complement other flavor observables.

Abstract

The rare decay B -> K* nu anti-nu allows a transparent study of Z penguin and other electroweak penguin effects in New Physics (NP) scenarios in the absence of dipole operator contributions and Higgs (scalar) penguin contributions that are often more important than Z contributions in B -> K* l+l- and B(s) -> l+l- decays. We present a new analysis of B -> K* nu anti-nu with improved form factors and of the decays B -> K nu anti-nu and B -> X(s) nu anti-nu in the SM and in a number of NP scenarios like the general MSSM, general scenarios with modified Z/Z' penguins and in a singlet scalar extension of the SM. We also summarize the results in the Littlest Higgs model with T-parity and a Randall-Sundrum (RS) model with custodial protection of left-handed Z-di-dj couplings. Our SM prediction BR(B -> K* nu anti-nu)=(6.8^+1.0_-1.1) x 10^-6 turns out to be significantly lower than the ones present in the literature. Our improved calculation BR(B -> X(s) nu anti-nu)=(2.7+-0.2) x 10^-5 in the SM avoids the normalization to the BR(B -> X(c) e anti-nu(e)) and, with less than 10% total uncertainty, is the most accurate to date. The results for the SM and NP scenarios can be transparently summarized in a (epsilon,eta) plane with a non-vanishing eta signalling the presence of new right-handed down-quark flavour violating couplings which can be ideally probed by the decays in question. Measuring the three branching ratios and one additional polarization observable in B -> K* nu anti-nu allows to overconstrain the resulting point in the (epsilon,eta) plane with (epsilon,eta)=(1,0) corresponding to the SM. The correlations of these three channels with the rare decays K+ -> pi+ nu anti-nu, KL -> pi0 nu anti-nu, B -> X(s) l+ l- and B(s) -> mu+ mu- offer powerful tests of New Physics with new right-handed couplings and non-MFV interactions.

Figures (14)

• Figure 1: Dependence of the four $b\to s\nu\bar{\nu}$ observables on the normalized neutrino invariant masses squared $s_{b,B}$ within the SM. The error bands reflect the theoretical uncertainties. In the lower plots, the black dashed lines and dotted red lines are the results based on the form factor sets $B$ and $C$, respectively. See the text for more details.
• Figure 2: Existing experimental constraints on $\epsilon$ and $\eta$. Dashed line: constraint from $\text{BR}(B \to K^* \nu\bar{\nu})$, solid line: constraint from $\text{BR}(B \to K \nu\bar{\nu})$, dotted line: constraint from $\text{BR}(B \to X_s \nu\bar{\nu})$. The shaded area is ruled out experimentally at the 90% confidence level. The blue circle represents the SM point.
• Figure 3: Hypothetical constraints on the $\epsilon$-$\eta$-plane, assuming all four observables have been measured with infinite precision. The error bands reflect the theoretical uncertainty as described in section \ref{['sec:SM']}. The green band (dashed line) represents $\text{BR}(B \to K^* \nu\bar{\nu})$, the black band (solid line) $\text{BR}(B \to K \nu\bar{\nu})$, the red band (dotted line) $\text{BR}(B \to X_s \nu\bar{\nu})$ and the orange band (dot-dashed line) $\langle F_L \rangle$. Left: SM values for the Wilson coefficients, right: assuming $C^\nu_L=0.5(C^\nu_L)^\text{SM}$ and $C^\nu_R=0.2(C^\nu_L)^\text{SM}$. The blue circle represents the SM point.
• Figure 4: Left: $F_L(s_B)$ for different values of $\eta$, from top to bottom: $\eta=0.5, 0, -0.2, -0.4, -0.45$. Right: Dependence of the $s_B$-integrated $\langle F_L \rangle$ on $\eta$.
• Figure 5: Constraints on the real and imaginary parts of $Z_L^\text{NP}$ coming from $\Delta M_s$ (blue, assuming 30% theory uncertainty), $\text{BR}(B\to X_s\ell^+\ell^-)$ (red) and $\text{BR}(B_s\to\mu^+\mu^-)$ (black) assuming $Z_R=0$. The green lines correspond to values of the $B_s$ mixing phase $\phi_{B_s}=-11^\circ$, $-19^\circ$ and $-27^\circ$, respectively Bona:2008jn.