Search for Neutral, Long-Lived Particles Decaying into Two Muons in $p\overline{p}$ Collisions at $\sqrt{s}=1.96\mathrm{TeV}$

We present a search for a neutral particle, pair produced in $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$, which decays into two muons and lives long enough to travel at least 5 cm before decaying. The analysis uses $\approx 380{\mathrm{pb}}^{-1}$ of data recorded with the D0 detector. The background is estimated to be about one event. No candidates are observed, and limits are set on the pair-production cross section times branching fraction into dimuons $+$ $X$ for such particles. For a mass of 10 GeV and lifetime of $4\times {10}^{-11}\mathrm{s}$, we exclude values greater than 0.14 pb (95% C.L.). These results are used to limit the interpretation of NuTeV’s excess of dimuon events.

Figure 1

Feynman diagrams for pair production (left) and decay (right) of a neutral particle; in this case neutralinos with $R$-parity violation.

Figure 2

Distribution of the vertex radius for events where one muon passes the DCA criteria and the second fails it (top), and where both muons pass the DCA criteria (bottom).

Figure 3

Limit on cross section × branching fraction for the pair production of neutral, long-lived particles as a function of lifetime. The dark gray area and above represents the D0 99% C.L. for the 5 GeV mass point. The solid line shows the D0 95% C.L. The light gray region represents the NuTeV 99% C.L. exclusion [4] converted to a $p\overline{p}$ cross section at $\sqrt{s}=1960\mathrm{GeV}$. The white region represents a 99% C.L. preferred region given the three events from NuTeV.

Figure 4

Limits on $N_{\mathrm{LL}}^0$ pair production as a function of its mass. The limit is for a lifetime of $4\times {10}^{-11}\mathrm{s}$.