arXiv subjects

M. Novoa-Brunet

Publications and source records attributed to M. Novoa-Brunet.

3 recordsLinked to original sources

arXiv2022

Relations among $B_c \to J/ψ, η_c$ form factors

We analyze the form factors parametrizing the $B_c \to J/ψ, η_c$ matrix elements of the operators in a generalized low-energy $b \to c$ semileptonic Hamiltonian. We consider an expansion in nonrelativistic QCD, classifying the heavy quark spin symmetry breaking terms and expressing the form factors in terms of universal functions in a selected kinematical range. Using as an input the lattice QCD results for the $B_c \to J/ψ$ matrix element of the SM operator, we obtain information on other form factors. The extrapolation to the full kinematical range is also presented.

hep-ph↗

arXiv2022

Semileptonic $B_c$ decays to $P-$wave charmonium and the nature of $χ_{c1}(3872)$

The hadronic form factors of $B_c$ semileptonic decays to the $P-$wave charmonium 4-plet can be expressed near the zero-recoil point in terms of universal functions, performing a systematic expansion in QCD in the relative velocity of the heavy quarks and in $1/m_Q$. Such functions are independent of the member of the multiplet involved in the transitions. We present the results of an NLO calculation up to $O(1/m_Q^2)$ classifying the universal functions at this order. We work out a set of relations among the form factors of the same mode and of different modes, which should be reproduced by explicit calculations, reducing the hadronic uncertainty affecting such channels. The approach is also helpful to investigate the debated nature of $χ_{c1}(3872)$, studying the production in $B_c$ semileptonic decays and comparing it to the modes involving the other $2P$ charmonia.

hep-ph↗

arXiv2021

Anatomy of a new anomaly in non-leptonic B decays

We discuss the anatomy of the $L_{VV}$ observable designed as a ratio of the longitudinal components of $B_s \to VV$ versus $B_d \to VV$ decays. We focus on the particular case of $B_{d,s} \to K^{*0} {\bar K^{*0}}$ where we find for the SM prediction $L_{K^* \bar{K}^*}=19.5^{+9.3}_{-6.8}$ implying a 2.6$σ$ tension with respect to data. The interpretation of this tension in a model independent way identifies two Wilson coefficients ${\cal C}_{4}$ and ${\cal C}_{8g}$ as possible sources. The example of one simplified model including a Kaluza-Klein (KK) gluon is discussed. This KK gluon embedded inside a composite/extra dimensional model combined with a $Z^\prime$ can explain also the $b\to s\ell\ell$ anomalies albeit with a significant amount of fine-tuning.

hep-ph↗