Searching for exotic $B$-meson decays enabled by the CMS L1 track trigger

The CMS phase II track trigger may allow for a displaced dimuon vertex trigger with qualitatively lower $p_T$ thresholds than existing dimuon triggers. With this technique, we show that the CMS reach for exotic $B$-meson decays involving a displaced dimuon resonance, such as a light, Higgs-mixed scalar, can be competitive with that of LHCb and Belle II.

Figure 1

Background component from $B$-meson decays for the cuts specified in Table 2. (See Sec. 4 for details.)

Figure 2

Left: isolation variable $\delta$ for two signal benchmarks. The rightmost bin is an overflow bin, containing all events with $\delta >0.5$. The isolation efficiencies for the $m_{\varphi }=0.5\mathrm{GeV}$ and $m_{\varphi }=2\mathrm{GeV}$ benchmarks are 0.68 and 0.66, respectively. Right: truth level $\mathrm{\Delta }R$ between $\varphi$ and its sister meson. The vertical dashed line indicates the isolation cone of $\mathrm{\Delta }R=0.25$.

Figure 3

Distribution of a signal benchmark (left) and background (right) for the $L_{xy}/d_{\varphi }$ and $\sum p_{T_{\mu }}$ variables, after imposing the baseline cuts and isolation requirements ($I_b$ in Table 2). The red box indicates the signal region.

Figure 4

Projected reach in the model independent parametrization, for the cuts in Table 2. Left: $m_{\varphi }=0.5\mathrm{GeV}$; Right: $m_{\varphi }=2\mathrm{GeV}$. Shaded region and dashed line represent the existing LHCb limits [18] and an optimistic extrapolation of the LHCb reach. (See text.)

Figure 5

Projected reach in terms of the mass ($m_{\varphi }$) and mixing angle ($s_{\theta }$) of a light scalar mixing with the SM Higgs. Shaded regions represent the existing LHCb [18] and LSND [39] limits. The dashed gray contours indicate the proper lifetime of $\varphi$ [17]. We also show projections for Belle II [40] and the FASER upgrade [41].