Light gauge boson interpretation for $(g-2)_μ$ and the $K_L \rightarrow π^0 + \text{(invisible)}$ anomaly at the J-PARC KOTO experiment

在KOTO实验中探测长寿命轴子

Probing long-lived axions at the KOTO experiment

本文评估KOTO及KOTO Step-2对长寿命重QCD轴子/类轴子粒子的探测灵敏度，并通过ALPINIST公开代码提供仿真与数据集支持。

The Light Sgoldstino Phenomenology: Explanations for the Muon $(g-2)$ Deviation and KOTO Anomaly

In this work, we study the long-standing experimental anomaly in muon $(g-2)$ and also recent anomalous excess in $K_L\to π^0+ν\barν$ at the J-PARC KOTO experiment with sgoldstino. After supersymmetry breaking, the interactions between quarks and sgoldstino ($s$) make the decays $K\to π+s$ sizable through loop diagrams, which affects the measurements of decays $K\to π+\mathrm{invisible}$. Furthermore, the couplings between photons and sgoldstino contribute to $Δa_μ$ as well as the bino-slepton contribution. With satisfying all known experimental constraints such as from NA62, E949, E137, Orsay…

Constraints on long-lived light scalars with flavor-changing couplings and the KOTO anomaly

Recently, the KOTO experiment at J-PARC has observed three anomalous events in the flavor-changing rare decay $K_L \to π^0 ν\barν$, which indicates that the corresponding branching ratio is almost two orders of magnitude larger than the Standard Model (SM) prediction. Taking this intriguing result at face value, we explore model implications of its viable explanation by a long-lived light SM-singlet scalar ($S$) emission, i.e. $K_L \to π^0 S$, with $S$ decaying outside the KOTO detector. We derive constraints on the parameter space of such a light scalar in the context of three simple models: …

Loophole in $K \to πν\barν$ Search \ \& $K_L \to π^0 ν\barν$ Beyond Grossman--Nir Bound

The Grossman-Nir bound concept is robust, but the common perception of $K_L \to π^0ν\barν< 1.4 \times 10^{-9}$ may be circumvented. Because of the blinding $K\pi2$(3) decay, $K^+$ decay experiments such as E787/E949 and the currently running NA62 kinematically exclude the "blinding zone". This offers an opportunity for the currently running KOTO experiment. With no kinematic control, if the KOTO experiment is able to veto all true background, it may discover $K_L \to π^0 + X^0$, where $X^0$ is an invisible "dark" boson with mass $m_{X^0} \sim m_{π^0}$. This could happen with 2015 data at hand,…

Three Exceptions to the Grossman-Nir Bound

We show that the Grossman-Nir (GN) bound, $\text{Br}(K_L\to π^0ν\barν)\leq 4.3 \, \text{Br}(K^+\to π^+ν\barν)$, can be violated in the presence of light new physics with flavor violating couplings. We construct three sample models in which the GN bound can be violated by orders of magnitude, while satisfying all other experimental bounds. In the three models the enhanced branching ratio $\text{Br}(K_L\to π^0+{\rm inv})$ is due to $K_L\to π^0ϕ_1$, $K_L\to π^0ϕ_1ϕ_1$, $K_L\to π^0ψ_1\bar ψ_1$ transitions, respectively, where $ϕ_1 (ψ_1)$ is a light scalar (fermion) that escapes the detector. In th…

$(g-2)_μ$ Versus $K \to π+E_{miss}$ Induced by the $(B-L)_{23}$ Boson

To address the long-standing $(g-2)_μ$ anomaly via a light boson, in Ref. [1] we proposed to extend the standard model (SM) by the local $(B-L)_{23}$, under which only the second and third generations of fermions are charged. It predicts an invisible $Z'$ with mass ${\cal O}(100)$ MeV, and moreover it has flavor-changing neutral current (FCNC) couplings to the up-type quarks at tree level. Such a $Z'$, via $K_L \to π^0 + Z'(\to ν\barν)$ at loop level, may be a natural candidate to account for the recent KOTO anomaly. In this article, we investigate this possibility, to find that $Z'$ can readi…