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title: EWP abstracts for summer 2021 Summer

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# EWP abstracts for summer 2021 Summer
## (Combined Abstract) Results and Prospects of Radiative and Electroweak Penguin Decays at Belle (II) 
In the recent years, several measurements of $B$-decays with flavor changing neutral currents, i.e. $b\to s$ transitions hint at deviations from the Standard Model (SM) predictions. These decays are forbidden at tree-level in the SM and can only proceed via suppressed loop level or box diagrams. Rare decays of $B$ mesons are an ideal probe to search for phenomena beyond the SM, since contributions from new particles can affect the decays on the same level as SM particles.
The Belle II experiment is a substantial upgrade of the Belle detector and operates at the SuperKEKB energy-asymmetric $e^+ e^-$ collider. Radiative $b\to s \gamma$ decays is already been observed and inclusive photon spectra is also obtained with only a small dataset of Belle II. Early measurements related to the electro-weak penguin $b\to s \ell\ell$ and $b\to s \nu\bar\nu$ decays has also been performed. We will discuss the results obtained with the current dataset along with the prospects for the searches of these radiative and electroweak penguin decays with the expected $50~ab^{-1}$ full dataset  of Belle II.

## 1. Search for rare electroweak decay $B^{+} \to K^{+}νν$ in early Belle II dataset.
In the recent years, several measurements of $B$-decays with flavor changing neutral currents (FCNC), i.e. $b\to s \ell \ell$ transitions, hint at deviations from the Standard Model (SM) predictions.
A search for the flavor-changing neutral current decay $B^{+}→K^{+}\nu\bar{\nu}$ is performed with data  sample  corresponding  to  $63~fb^{−1}$ collected  at the Υ(4S) resonance by the Belle II experiment. A novel measurement method is developed, which exploits topological properties of the decay that differ from both generic B-meson decays and light-quark pair-production. This inclusive tagging approach has the benefit of a higher signal efficiency compared to previous searches for this rare decay. As no significant signal is observed, an upper limit on the branching fraction of $B^{+}→K^{+}\nu\bar{\nu}$ = $4.1 \times 10^{−5}$ is set at the 90% confidence level. We will talk about this novel analysis technique and the result.

## 2. Search for rare electroweak decay $B \to K^{(*)}\ell\ell$ in early Belle II dataset.
In the recent years, several measurements of $B$-decays with flavor changing neutral currents (FCNC), i.e. $b\to s \ell \ell$ transitions, hint at deviations from the Standard Model (SM) predictions. 
With early Belle II dataset, we performed measumerments related to the control sample $B \to K^{(*)}J/\psi(\to\ell\ell)$ as well as $B \to K^{(*)}\ell\ell$.  We will also discuss about the prospects of these electroweak penguin decays with the expected $50~ab^{-1}$ dataset  of Belle II.

## 3. Search for rare radiative decay with transition $b \to s\gamma$ in early Belle II dataset.
We report on the search for radiative $b\to s \gamma$ decays with early Belle-II dataset. We will discuss the results obtained with the current dataset along with the prospects for the searches with the expected $50~ab^{-1}$ full dataset  of Belle II.

## 4. Measurement of the inclusive decays $B \to X J/\psi$ 
We report the first measurements of the individual branching fractions $\mathcal{B}(B^+ \to X^+ J/\psi$) and $\mathcal{B}(B^0 \to X^0 J/\psi$). The analysis employs hadronic tagging and utilizes recorded Belle II data. In addition, the employment of hadronic tagging allows for a novel determination of the distributions of the mass of the X system, the helicity angle for the decay and the momentum magnitudes of the $J/\psi$ and $X$ in the $B$ rest frame. The measured distributions are unfolded for detector resolution and acceptance effects. These fully inclusive measurements of $B \to X J/\psi$ decays represent an important benchmark towards a future fully inclusive analysis of $b \to s\ell\ell$ decays with tag-side reconstruction.