Measurement of B-> pi pi l nu with Full Hadronic Reconstruction at Belle

by Cesar Augusto Beleno de la Barrera
Doctoral thesis
Date of Examination:2018-10-01
Date of issue:2018-12-03
Advisor:Prof. Dr. Ariane Frey
Referee:Prof. Dr. Ariane Frey
Referee:Prof. Dr. Jochen Dingfelder
Persistent Address: http://dx.doi.org/10.53846/goediss-7172

 

 

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Abstract

English

This thesis presents an analysis of the exclusive $B\to\pi^{+}\pi^{-}\ell\nu_{\ell}$ decay, where $\ell$ represents an electron or a muon. The analysis uses the complete $\Upsilon(4S)$ data sample collected by the Belle detector, corresponding to 711 fb$^{-1}$. The events are selected by fully reconstructing one $B$ meson into hadronic decay modes, consequently the properties of the other $B$ meson, ''the signal $B$´´, can be inferred via conservation laws. The branching ratio is extracted by using an extended binned maximum likelihood method and measured to be ${{\cal B}(B^{+}\to \pi^{+}\pi^{-}\ell^{+}\nu_{\ell})= (2.24 \pm 0.19_{\mathrm{stat}} \pm 0.13_{\mathrm{syst}} )\times 10^{-4}}$. This result is the first reported measurement of this decay. The dominant resonance in the dipion mass spectrum is the $\rho^{0}$ meson, observed with a branching ratio of ${\cal B}(B^{+}\to \rho^{0} \ell^{+}\nu_{\ell})= (1.71 \pm 0.16_{\mathrm{stat}} \pm 0.10_{\mathrm{syst}})\times10^{-4}$. From this result, the magnitude of the CKM matrix element $V_{ub}$ is obtained as $|V_{ub}|=(3.56\pm0.17\pm 0.10\; {}^{+0.38}_{-0.25})\times 10^{-3}$, in agreement with the most precise measurement of this value from global fits to the $B\to\pi\ell\nu_{\ell}$ channel. Another resonance is reported with a product of branching ratios, ${\cal B}(B^{+}\to f_{2}(1270)\ell^{+}\nu)\times {\cal B}(f_{2}(1270)\to \pi^{+}\pi^{-})=(1.8 \pm 0.9_{\mathrm{stat}} {}^{+0.2}_{-0.1}{}_{\mathrm{syst}})\times 10^{-5}$, with a $2.2\sigma$ statistical significance without taking into account systematic uncertainties.
Keywords: Semileptonic B decays, CKM matrix, Vub, resonances, branching ratios, charmless, rho0 meson, hadronic tag, full reconstruction
 
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