Search for a Narrow Resonance in e+e- to Four Lepton Final States

TL;DR

<3-5 sentence high-level summary> BaBar conducts a search for a narrow W' resonance in exclusive e+e− → W'W' → (l+l−)(l′+l′−) events using 536 fb−1, targeting GeV-scale hidden sectors with kinetic mixing. The analysis uses a cut-and-count strategy in bins of the average dilepton mass m̄, leveraging Δm sidebands to estimate backgrounds and a profile-likelihood approach to set 90% CL upper limits on cross sections for e+e− → W'W' → l+l−l′+l′− across 0.24–5.3 GeV W' masses. No signal is observed, and the resulting cross-section limits (combined 25–60 ab) are interpreted as constraints on the SM–dark sector mixing parameter ε and the dark coupling αD in non-Abelian Higgsed scenarios, disfavoring much of the preferred parameter space for higher A′ masses. These results demonstrate BaBar’s sensitivity to low-mass hidden sectors via four-lepton final states and provide important benchmarks for future searches at B-factories and low-energy colliders.

Abstract

Motivated by recent models proposing a hidden sector with $\sim$GeV scale force carriers, we present a search for a narrow dilepton resonance in 4 lepton final states using $536fb^{-1}$ collected by the BaBar detector. We search for the reaction, $e^+e^-\to W^\prime W^\prime\to(l^+l^-)(l^{\prime+}l^{\prime-})$, where the leptons carry the full 4-momentum and the two dilepton pair invariant masses are equal. We do not observe a significant signal and we set 90% upper limits of $σ(e^+e^-\to W^\prime W^\prime\to(e^+e^-)(e^+e^-))<(15-70) ab$, $σ(e^+e^-\to W^\prime W^\prime\to(e^+e^-)(μ^+μ^-))<(15-40) ab$, and $σ(e^+e^-\to W^\prime W^\prime\to(μ^+μ^-)(μ^+μ^-))<(11-17) ab$ in the $W^\prime$ mass range between 0.24 and 5.3GeV. Under the assumption that the $W^\prime$ coupling to electrons and muons is the same, we obtain a combined upper limit of $σ(e^+e^-\to W^\prime W^\prime\to(l^+l^-)(l^{\prime+}l^{\prime-}))<(25-60) ab$. Using these limits, we constrain the product of the SM-dark sector mixing and the dark coupling constant in the case of a non-Abelian Higgsed dark sector.

Figures (15)

• Figure 1: The dilepton invariant mass distributions from data for (left to right) $e^+e^-e^+e^-$, $e^+e^-\mu^+\mu^-$, and $\mu^+\mu^-\mu^+\mu^-$ after all other cuts. The solid lines denotes $m_1=m_2$.
• Figure 2: The transformed mass distributions,$\Delta m$ vs $\overline{m}$, from data for (left to right) $e^+e^-e^+e^-$, $e^+e^-\mu^+\mu^-$, and $\mu^+\mu^-\mu^+\mu^-$ after all other cuts. The solid lines denotes the $\Delta m$ cut value.
• Figure 3: The signal efficiency versus $W^\prime$ mass for (left to right) $W^\prime W^\prime\rightarrow\xspace e^+e^-e^+e^-$, $W^\prime W^\prime\rightarrow\xspace e^+e^-\mu^+\mu^-$, and $W^\prime W^\prime\rightarrow\xspace\mu^+\mu^-\mu^+\mu^-$ after all cuts.
• Figure 4: The $\Delta m$ distributions for four different $W^\prime$ mass values (left to right) $W^\prime W^\prime\rightarrow\xspace e^+e^-e^+e^-$, $W^\prime W^\prime\rightarrow\xspace e^+e^-\mu^+\mu^-$, and $W^\prime W^\prime\rightarrow\xspace\mu^+\mu^-\mu^+\mu^-$ after all cuts.
• Figure 5: The values of the cut on $\Delta m$ keeping 90% of signal events as a function of $W^\prime$ mass for (left to right) $W^\prime W^\prime\rightarrow\xspace e^+e^-e^+e^-$, $W^\prime W^\prime\rightarrow\xspace e^+e^-\mu^+\mu^-$, and $W^\prime W^\prime\rightarrow\xspace\mu^+\mu^-\mu^+\mu^-$. The line is a fit to a fourth order polynomial. This cut defines our signal and background region.