Measurement of Branching Fractions and Mass Spectra of $B\to K\pi \pi \gamma$

We present a measurement of the partial branching fractions and mass spectra of the exclusive radiative penguin processes $B\to K\pi \pi \gamma$ in the range $m_{K\pi \pi }<1.8\mathrm{GeV}/c^2$. We reconstruct four final states: $K^{+}{\pi }^{-}{\pi }^{+}\gamma$, $K^{+}{\pi }^{-}{\pi }^0\gamma$, $K_S^0{\pi }^{-}{\pi }^{+}\gamma$, and $K_S^0{\pi }^{+}{\pi }^0\gamma$, where $K_S^0\to {\pi }^{+}{\pi }^{-}$. Using $232\times {10}^6$ $e^{+}{e}^{-}\to B\overline{B}$ events recorded by the BABAR experiment at the SLAC PEP-II asymmetric-energy storage ring, we measure the branching fractions $\mathcal{B}(B^{+}\to K^{+}{\pi }^{-}{\pi }^{+}\gamma )=[2.95\pm 0.13(\mathrm{stat})\pm 0.20(\mathrm{syst})]\times {10}^{-5}$, $\mathcal{B}(B^0\to K^{+}{\pi }^{-}{\pi }^0\gamma )=[4.07\pm 0.22(\mathrm{stat})\pm 0.31(\mathrm{syst})]\times {10}^{-5}$, $\mathcal{B}(B^0\to K^0{\pi }^{+}{\pi }^{-}\gamma )=[1.85\pm 0.21(\mathrm{stat})\pm 0.12(\mathrm{syst})]\times {10}^{-5}$, and $\mathcal{B}(B^{+}\to K^0{\pi }^{+}{\pi }^0\gamma )=[4.56\pm 0.42(\mathrm{stat})\pm 0.31(\mathrm{syst})]\times {10}^{-5}$.

Figure 1

Distributions of $m_{\mathrm{ES}}$ (points). Projected $m_{\mathrm{ES}}$ distributions from the fit are shown as cumulative curves: continuum and generic $B\overline{B}$ component (dashed line), $b\to s\gamma$ component (dotted line, includes cross feed), and signal (solid line). The small oscillation in the dotted and solid curves is due to the use of binned distributions to model the $b\to s\gamma$ component.

Figure 2

Background-subtracted $m_{K\pi \pi }$ spectra. The branching fraction in each bin is computed from the weighted event yield. Error bars show statistical uncertainties; the systematic uncertainties due to $b\to s\gamma$ model assumptions are small.