# Measurement of the $B^0\to X_{u}^- \ell^+ {\nu_\ell}$ decays near the kinematic endpoint of the lepton spectrum and search for violation of isospin symmetry

Abstract : We present the first measurement of the $B^0\to X_{u}^- \ell^+ {\nu_\ell}$ partial branching fraction in the end-point region of the lepton momentum spectrum, above the threshold for $B\to X_c\ell {\nu_\ell}$ decays. The analysis is based on a sample of 383 million $\Upsilon(4S)$ decays into $B{\bar B}$ pairs collected with the {\sc BaBar} detector at the PEP-II $e^+e^-$ storage rings. We select $B^0{\bar B}^0$ events by partially reconstructing one $\B$ meson via the ${\bar B}^0\to D^{*+} \ell^- \bar{\nu}_\ell$ decays then select $B^0\to X_{u}^- \ell^+ {\nu_\ell}$ decays identifying a second high momentum lepton. In the momentum interval ranging from 2.3 to 2.6 GeV/c we measure the partial branching fraction $\Delta{\cal B}(B^0\to X_u\ell\nu)=(1.30\pm0.21_{stat}\pm0.07_{syst})\times 10^{-4}$ where the first error is statistical and the second is systematic. By comparing this measurement with the one obtained from untagged B decays we obtain $R^{+/0}=\Delta{\cal B}(B^0\to X_u\ell\nu)/\Delta{\cal B}(B^+\to X_u\ell\nu)= 1.18 \pm 0.35_{stat} \pm 0.17_{syst}$. Using this measurement we extract a limit on the contributions from processes breaking isospin symmetry in charmless semileptonic B decays.
Document type :
Preprints, Working Papers, ...

http://hal.in2p3.fr/in2p3-00167014
Contributor : Dominique Girod <>
Submitted on : Tuesday, August 14, 2007 - 9:41:37 AM
Last modification on : Saturday, November 28, 2020 - 12:58:03 PM

### Identifiers

• HAL Id : in2p3-00167014, version 1
• ARXIV : 0708.1753

### Citation

B. Aubert, M. Bona, D. Boutigny, Y. Karyotakis, J.P. Lees, et al.. Measurement of the $B^0\to X_{u}^- \ell^+ {\nu_\ell}$ decays near the kinematic endpoint of the lepton spectrum and search for violation of isospin symmetry. 2007. ⟨in2p3-00167014⟩

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