Study of High Momentum ${\eta }^{\prime }$ Production in $B\to {\eta }^{\prime }{X}_s$

We measure the branching fraction for the charmless semi-inclusive process $B\to {\eta }^{\prime }{X}_s$, where the ${\eta }^{\prime }$ meson has a momentum in the range 2.0 to $2.7\mathrm{G}\mathrm{e}\mathrm{V}/c$ in the ${\rm Y}(4S)$ center-of-mass frame and $X_s$ represents a system comprising a kaon and zero to four pions. We find $\mathcal{B}(B\to {\eta }^{\prime }{X}_s)=[3.9\pm 0.8\mathrm{(}\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t}\mathrm{)}\pm 0.5\mathrm{(}\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t}\mathrm{)}\pm 0.8\mathrm{(}\mathrm{\text{model}}\mathrm{)}]\times {10}^{-4}$. We also obtain the $X_s$ mass spectrum and find that it fits models predicting high masses.

Figure 1

Lowest order diagrams for (a)–(c) $B\to {\eta }^{\prime }{X}_s$ and (d) the color-suppressed background ${\overline{B}}^0\to {\eta }^{\prime }{D}^{(*)0}$.

Figure 2

Fits to the $\eta \pi \pi$ invariant mass for on-resonance (a),(c) and off-resonance (b),(d) data samples, for the modes (a),(b) $K^{\pm }$ and (c),(d) $K_S^0$.

Figure 3

Continuum-subtracted $Kn\pi$ invariant-mass distributions for (a) all $B$ modes and (b) $B^0$ modes, including combinatorial background. Solid and dashed histograms represent expected backgrounds from ${\overline{B}}^0\to {\eta }^{\prime }{D}^0$ and ${\overline{B}}^0\to {\eta }^{\prime }{D}^{*0}$, respectively.

Figure 4

Variation of the efficiency averaged over charged and neutral kaons with $m(X_s)$. The filled circles indicate the efficiency for nonresonant $X_s$ simulation. The other symbols denote the values for the resonances.

Figure 5

Branching fractions as a function of $m(X_s)$. Both (a) and (b) show the same data, though the efficiency used in (a) is derived from the nonresonant model, while the efficiency in (b) comes from the model with a combination of resonances. The errors include bin-to-bin systematics; an additional systematic error of $\sim 8\%$ (not shown) is common to all points. (a) The open histogram represents the expectation from nonresonant $m(X_s)$ simulation. (b) The open histogram represents the expectation from a mixture of resonant modes with equal proportions. The hatched histogram results if some heavy resonances are enhanced.