Determination of the CKM matrix element |Vcb| from exclusive B0 → D*lν decays with the Belle experiment

© 2018 Dr. Eiasha WaheedThe magnitude of of the CKM matrix element |Vcb| is determined based on the exclusive semileptonic B0 → D*lν decay with data from the Belle experiment at KEKB. Two different parameterisations of the hadronic transition form factors are used in the extraction of the form factor parameters and F (1)|Vcb|ηEW . We find that the commonly used model dependent Caprini-Lellouch-Neubert form factor parameterisation yielded |Vcb| results 10% lower than the model independent Boyd-Grinstein-Lebed approach. The latter are in good agreement with the inclusive approach for the determination of |Vcb|, suggesting the long standing inclusive- exclusive tension may be solved. The branching fraction of B0 → D*lν decays and the lepton universality ratio B(B0 → D*eν)/B(B0 → D*μν) are also measured. Results compatible with the world average for the former, and with the SM for the latter are found. This thesis presents the most precise measurements of B0 → D*lν and exclusive |Vcb| ever performed

Measurement of the branching fractions for Cabibbo-suppressed decays D+→K+K−π+π0D^{+}\to K^{+} K^{-}\pi^{+}\pi^{0} and D(s)+→K+π−π+π0D_{(s)}^{+}\to K^{+}\pi^{-}\pi^{+}\pi^{0} at Belle

International audienceWe present measurements of the branching fractions for the singly Cabibbo-suppressed decays $D^+\to K^{+}K^{-}\pi^{+}\pi^{0}$ and $D_s^{+}\to K^{+}\pi^{-}\pi^{+}\pi^{0}$, and the doubly Cabibbo-suppressed decay $D^{+}\to K^{+}\pi^{-}\pi^{+}\pi^{0}$, based on 980 ${\rm fb}^{-1}$ of data recorded by the Belle experiment at the KEKB $e^{+}e^{-}$ collider. We measure these modes relative to the Cabibbo-favored modes $D^{+}\to K^{-}\pi^{+}\pi^{+}\pi^{0}$ and $D_s^{+}\to K^{+}K^{-}\pi^{+}\pi^{0}$. Our results for the ratios of branching fractions are $B(D^{+}\to K^{+}K^{-}\pi^{+}\pi^{0})/B(D^{+}\to K^{-}\pi^{+}\pi^{+}\pi^{0}) = (11.32 \pm 0.13 \pm 0.26)\%$, $B(D^{+}\to K^{+}\pi^{-}\pi^{+}\pi^{0})/B(D^{+}\to K^{-}\pi^{+}\pi^{+}\pi^{0}) = (1.68 \pm 0.11\pm 0.03)\%$, and $B(D_s^{+}\to K^{+}\pi^{-}\pi^{+}\pi^{0})/B(D_s^{+}\to K^{+}K^{-}\pi^{+}\pi^{0}) = (17.13 \pm 0.62 \pm 0.51)\%$, where the uncertainties are statistical and systematic, respectively. The second value corresponds to $(5.83\pm 0.42)\times\tan^4\theta_C$, where $\theta_C$ is the Cabibbo angle; this value is larger than other measured ratios of branching fractions for a doubly Cabibbo-suppressed charm decay to a Cabibbo-favored decay. Multiplying these results by world average values for $B(D^{+}\to K^{-}\pi^{+}\pi^{+}\pi^{0})$ and $B(D_s^{+}\to K^{+}K^{-}\pi^{+}\pi^{0})$ yields $B(D^{+}\to K^{+}K^{-}\pi^{+}\pi^{0})= (7.08\pm 0.08\pm 0.16\pm 0.20)\times10^{-3}$, $B(D^{+}\to K^{+}\pi^{-}\pi^{+}\pi^{0})= (1.05\pm 0.07\pm 0.02\pm 0.03)\times10^{-3}$, and $B(D_s^{+}\to K^{+}\pi^{-}\pi^{+}\pi^{0}) = (9.44\pm 0.34\pm 0.28\pm 0.32)\times10^{-3}$, where the third uncertainty is due to the branching fraction of the normalization mode. The first two results are consistent with, but more precise than, the current world averages. The last result is the first measurement of this branching fraction

Measurement of the B+/B0B^+/B^0 production ratio in e+e−e^+e^- collisions at the Υ(4S)\Upsilon(4S) resonance using B→J/ψ(ℓℓ)KB \rightarrow J/\psi(\ell\ell) K decays at Belle

We measure the ratio of branching fractions for the $\Upsilon (4S)$ decays to $B^+B^-$ and $B^0\bar{B}{}^0$ using $B^+ \rightarrow J/\psi(\ell\ell) K^+$ and $B^0 \rightarrow J/\psi(\ell\ell) K^0$ samples, where $J/\psi(\ell\ell)$ stands for $J/\psi \to \ell^+\ell^-$ ($\ell = e$ or $\mu$), with $711$ fb$^{-1}$ of data collected at the $\Upsilon(4S)$ resonance with the Belle detector. We find the decay rate ratio of $\Upsilon(4S) \rightarrow B^+B^-$ over $\Upsilon(4S) \rightarrow B^0\bar{B}{}^0$ to be $1.065\pm0.012\pm 0.019 \pm 0.047$, which is the most precise measurement to date. The first and second uncertainties are statistical and systematic, respectively, and the third uncertainty is systematic due to the assumption of isospin symmetry in $B \to J/\psi(\ell\ell) K$