Search for Invisible Decays of a Light Scalar in Radiative Transitions Upsilon(3S) -> gamma A0

TL;DR

This study searches for a light CP-odd Higgs $A^{0}$ in NMSSM via the radiative decay $\u0003S\rightarrow\gamma A^{0}$ with $A^{0}$ decaying invisibly to neutralinos, using a missing-mass technique on $\sim$1.2×10^8 $\u0003S$ decays collected by BABAR. The analysis employs separate high- and low-photon-energy regions, with unbinned extended maximum-likelihood fits to the missing-mass squared $m_X^2$ and Crystal Ball PDFs to extract potential signals while modeling dominant QED and ISR backgrounds. No significant excess is observed, and 90% C.L. upper limits on the product branching fraction $\mathcal{B}(\u0003S\rightarrow\gamma A^{0})\times\mathcal{B}(A^{0}\rightarrow\text{invisible})$ are set across $0<m_{A^{0}}\le7.8$ GeV, spanning $(0.7-31)\times10^{-6}$, with the results being preliminary. The findings constrain NMSSM scenarios with light $A^{0}$ and invisible decays and demonstrate the efficacy of single-photon missing-mass analyses at $e^{+}e^{-}$ colliders.

Abstract

We search for a light scalar particle produced in single-photon decays of the Upsilon(3S) resonance through the process Upsilon(3S) -> gamma A0, A0 -> invisible. Such an object appears in Next-to-Minimal Supersymmetric extensions of the Standard Model, where a light CP-odd Higgs boson naturally couples strongly to b-quarks. If, in addition, there exists a light, stable neutralino, decays of A0 could be preferentially to an invisible final state. We search for events with a single high-energy photon and a large missing mass, consistent with a 2-body decay of Upsilon(3S). We find no evidence for such processes in a sample of 122*10^6 Upsilon(3S) decays collected by the BABAR collaboration at the PEP-II B-factory, and set 90% C.L. upper limits on the branching fraction B(Upsilon(3S) -> gamma A0)*B(A0 -> invisible) at (0.7-31)*10^{-6} in the mass range m(A0)<=7.8 GeV. The results are preliminary.

Figures (5)

• Figure 1: Sample fit to the high-energy dataset ($122\times10^6$$焇{(3S)}$ decays). The bottom plot shows the data (solid points) overlaid by the full PDF curve (solid blue line), signal contribution with $m_{A^{0}}\xspace=5.2$ GeV (solid red line), $e^+e^-\rightarrow\xspace\gamma\gamma$ contribution (dot-dashed green line), and continuum background PDF (black dashed line). The top plot shows the pulls $p=(\mathrm{data}-\mathrm{fit})/\sigma(\mathrm{data})$ with unit error bars.
• Figure 2: Signal yields $N_\mathrm{sig}$ as a function of assumed mass ${\rm \,m}\xspace_{{A^{0}}\xspace}$ in the high-energy dataset. Blue error bars are statistical only, and the red error bars include the systematic contributions. Since the spacing between the points is smaller than the experimental resolution, the neighboring points are highly correlated.
• Figure 3: Sample fit to the low-energy dataset ($83\times10^6$$焇{(3S)}$ decays). The bottom plot shows the data (solid points) overlaid by the full PDF curve (solid blue line), signal contribution with $m_{A^{0}}\xspace=7.275$ GeV (solid red line), $e^+e^-\rightarrow\xspace\gamma\gamma$ contribution (dot-dashed green line), and continuum background PDF (black dashed line). The top plot shows the pulls $p=(\mathrm{data}-\mathrm{fit})/\sigma(\mathrm{data})$ with unit error bars.
• Figure 4: Signal yields $N_\mathrm{sig}$ as a function of assumed mass ${\rm \,m}\xspace_{{A^{0}}\xspace}$ in the "LowE" region. Blue error bars are statistical only, and the red error bars include the systematic contributions. Since the spacing between the points is smaller than the experimental resolution, the neighboring points are highly correlated.
• Figure 5: 90% C.L. upper limits on the branching fraction $\mathcal{B}(焇{(3S)}\xspace\rightarrow\xspace\gamma{A^{0}}\xspace)\times\mathcal{B}({A^{0}}\xspace\rightarrow\xspace\mathrm{invisible})$. The dashed blue line shows the statistical uncertainties only, the solid red line includes the systematic uncertainties.