Detecting light leptophilic gauge boson at BESIII detector

TL;DR

The paper investigates a GeV-scale, leptophilic U-boson arising from a U(1)_{L_i-L_j} gauge symmetry as a mediator between leptons and dark matter. It analyzes the DM sector, showing that a TeV-scale χ with g_χ ~ O(0.1) can yield the correct relic density, with Sommerfeld enhancement boosting present-day annihilations by up to ~O(10^2). The authors study the prospects of detecting the U-boson at BESIII via e^+e^- -> U γ, considering both invisible (U -> ν ν̄) and visible (U -> l^+ l^-) decay modes, using realistic detector resolutions and selection cuts. They find that BESIII can probe g_l down to ~O(10^-4–10^-5) for the invisible channel and ~O(10^-3–10^-4) for the visible channels in the m_U range ~0.5–3 GeV, with the invisible mode offering superior sensitivity, and suggest scanning √s between 2–5 GeV could further enhance reach. Overall, the work demonstrates BESIII’s potential to test a well-motivated leptophilic U-boson scenario linked to DM phenomenology and PAMELA/ATIC observations.

Abstract

The $ O(GeV)$ extra $ U(1)$ gauge boson named U-boson, has been proposed to mediate the interaction among leptons and dark matter (DM), in order to account for the observations by PAMELA and ATIC. In such kind of models, the extra U(1) gauge group can be chosen as $U(1)_{L_i-L_j}$ with $L_i$ the $i-$th generation lepton number. This anomaly-free model provides appropriate dark matter relic density and boost factor required by experiments. In this work the observability of such kind of U-boson at BESIII detector is investigated through the processes $ e^ + e^ - \to Uγ$, followed by $U\to e^+e^-$, $U\to μ^+μ^-$ and $U\to ν\overlineν$. In the invisible channel where U-boson decays into neutrinos, BESIII can measure the coupling of the extra $ U(1)$ down to $ O(10^{- 4}) \sim O(10^{- 5})$ because of the low Standard Model backgrounds. In the visible channel where U-boson decays into charged lepton pair, BESIII can only measure the coupling down to $ O(10^{- 3}) \sim O(10^{- 4})$ due to the large irreducible QED backgrounds.

Figures (10)

• Figure 1: The ellipses indicate the region of the $m_\chi,g_\chi$ plane which satisfied the relic density $0.085<\Omega h^2<0.119$, with $m_U = 0.5GeV$. Solid lines denote for fermion DM and dash lines denote for scalar DM.
• Figure 2: The Sommerfeld enhancement factor S as a function of DM mass. Here we choose $m_U=0.5GeV$ and $g_\chi=0.55$ ($\alpha = 2.41 \times 10^{ - 2}$ ). Four curves denote different DM velocity $\beta$ as $10^{-2}$, $10^{-3}$,$10^{-4}$, $10^{-5}$ from bottom to top.
• Figure 3: Same with Fig.\ref{['sommerm1']}, but for the averaged Sommerfeld enhancement factor $\bar{S}$ as a function of DM mass. Four curves denote different DM velocity dispersion $\sigma _v$ as $10^{-2}$, $10^{-3}$,$10^{-4}$, $10^{-5}$ from bottom to top.
• Figure 4: The averaged Sommerfeld enhancement factor $\left\langle S \right\rangle$ as a function of DM velocity dispersions $\sigma _v$. Here we choose $m_\chi=1TeV$ and $g_\chi=0.55$ ($\alpha = 2.41 \times 10^{ - 2}$ ). Five curves denote different U-boson mass as $10 GeV$, $5GeV$, $0.5GeV$, $0.1GeV$, $1GeV$, from bottom to top.
• Figure 5: Photon energy distribution of SM background for $e^ + e^ - \to \nu\bar{\nu}\gamma$ with $\left| {\cos \theta _\gamma } \right| < 0.9$.