Home > Books, Theses & Reports > Theses > Phenomenological analysis and sensibility in Belle II of the $D_s^+ \to \pi^+ \mu^+\mu^-$ decay. |

Thesis | BELLE2-PTHESIS-2023-013 |

Marxil Sanchez Garcia ; Genaro Toledo Sanchez ; Ivan Heredia De La Cruz

2023

Universidad Nacional Autonoma de Mexico
Mexico City

**Abstract: **In this work we present a theoretical study and an experimental analysis of the $D_s^+ \to \pi^+ \mu^+\mu^-$ process in the Belle II experiment environment. This kind of process is interesting since it is used as reference in the search of suppressed or forbidden processes of the form $D_s^+ \to P^+ l^+ l^-$. In the theoretical part we explore the role of the parameters involved in the resonant region. We pay particular attention in the relative phase between the $\rho$ and the $\phi$ mesons ($\delta_{\rho\phi}$). We show that this parameter can be bound using LHCb data, and get $\delta_{\rho\phi}= (0.44 \pm 0.24)\pi$. We compute the invariant mass distribution of the lepton pair at a given angle and the corresponding forward-backward asymmetry, to show that this observable is insensitive to the phase. Background, short distance and non-standard contributions are also computed and compared for such observable. In the experimental side, we consider Monte Carlo simulation data in the Belle II environment, to determine the possibility to improve the upper bound for the branching ratio of the process. The analysis was performed considering the reconstruction and optimization of the process in the Belle II environment, we found that the reconstruction efficiency after optimization was 8.946%. The analysis considered 100 fb$^{-1}$ background samples. We show the procedure to reduce the noise considering several cuts. Finally, using the CL method we obtained an upper limit to the branching ratio of $Br(D_s^+ \to \pi^+ \mu^+\mu^-)< 7.618\times 10^{-5}$ in the invariant mass window of $m_{D_s} [1, 2.8]$ GeV.

**Note: **Presented on 02 02 2023 **Note: **PhD

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Record created 2023-06-22, last modified 2023-06-22