arXiv subjects

T. Ferber

Publications and source records attributed to T. Ferber.

At least 19 recordsLinked to original sources

arXiv2026

Commissioning and Low Latency Operation of the Graph Neural Network Electromagnetic Calorimeter Trigger at the Belle II Experiment

We present the commissioning and operation of the Graph Neural Network Electromagnetic Calorimeter Trigger Module (GNN-ETM) of the Belle II experiment at the SuperKEKB collider. The GNN-ETM processes calorimeter trigger cells as graph nodes to perform clustering and feature extraction. We fully integrate the system with the successive stages of the first-level trigger, develop slow-control drivers, and add online monitoring capabilities. We optimise the existing FPGA-based architecture through hardware-algorithm co-design, achieving an overall system latency of 1.053 us. Our hardware implementation is validated through register-transfer-level simulations, achieving bit-accurate agreement with the offline reference model. Online monitoring enables the measurement of instantaneous trigger rates, providing a quantitative basis for trigger-level performance studies. In summary, we report on the GNN-ETM as a fully operational, low-latency trigger module with online control and monitoring capabilities, compatible with the latency requirements of the Belle II first-level trigger system.

hep-ex↗

arXiv2026

Search for $\Xi^0p$, $\Omega^- p$, and $\Omega^- n$ dibaryons in $\Upsilon(1S)$ and $\Upsilon(2S)$ decays at Belle

We search for $\Xi^0p$, $\Omega^-p$, and $\Omega^-n$ dibaryon states in $\Upsilon(1S)$ and $\Upsilon(2S)$ decays, probing mass regions near the corresponding baryon-pair thresholds. Multistrange baryon-baryon interactions are relevant to neutron-star matter but remain largely unconstrained. Experimental and theoretical studies supporting attractive $\Xi N$ and $\Omega N$ interactions, where $N$ denotes a nucleon, motivate searches for weakly bound states. We use samples of $102$ million $\Upsilon(1S)$ and $158$ million $\Upsilon(2S)$ decays collected with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. No significant signals are observed, and the first $90$% confidence-level upper limits are set on the branching fractions of $\Upsilon(1S)$ and $\Upsilon(2S)$ decays to $\Xi^0p$, $\Omega^-p$, and $\Omega^-n$ dibaryon states, at the level of $O(10^{-7})$-$O(10^{-6})$, depending on the channel and the assumed mass difference from the corresponding baryon-pair threshold.

hep-ex↗

arXiv2026

Real-time graph neural networks on FPGAs for the Belle II electromagnetic calorimeter

We present the development and evaluation of a real-time Graph Neural Network-based trigger module for the electromagnetic calorimeter of the Belle~II experiment at the SuperKEKB collider. The algorithm processes calorimeter trigger cells as graph nodes to perform clustering, feature extraction, and per-cluster signal classification with deterministic latency. The model predicts cluster positions and energies and provides a signal classification score, enabling a more flexible clustering strategy than the baseline trigger algorithm. Implemented on an FPGA and integrated into the Belle~II trigger readout infrastructure for synchronous operation, the system sustains the MHz trigger throughput with an end-to-end latency of $3.168\,\mu$s. The performance is evaluated on simulated events and collision data. The energy resolution is comparable to the baseline trigger, while the position resolution for high-energy clusters improves by up to 18% in the central detector region. Cluster purity increases by up to 20% at low energies for isolated clusters, and cluster efficiency improves by up to 20% for overlapping clusters. The signal classifier enables additional background suppression at fixed signal retention. These results demonstrate a first step towards GNN-based real-time reconstruction on FPGAs in a collider trigger. While the end-to-end latency exceeds the trigger decision budget, the system already sustains full operational conditions with 100% uptime.

physics.ins-det↗

arXiv2025

Measurements of the mass difference $m(B^0)-m(B^+)$ and the energy dependence of the cross-section ratio $\sigma(e^+e^-\to B^0\bar{B}^0) / \sigma(e^+e^-\to B^+B^-)$ at Belle and Belle II

Using data samples collected by the Belle and Belle II experiments at the $\Upsilon(4S)$ resonance with integrated luminosities of 571 fb$^{-1}$ and 365 fb$^{-1}$, respectively, we measure the pseudoscalar $B$-meson mass difference to be $m(B^0)-m(B^+) = (0.495\pm0.024\pm0.005)$ MeV/c$^2$. The results are based on a simultaneous fit to the variable $\tilde{M}_{bc}$, which is related to the $B$ momentum, for $B^0$ and $B^+$ candidates; and to the energy dependence of ${\cal R}=\sigma(e^+e^-\to B^0\bar{B}^0) / \sigma(e^+e^-\to B^+B^-)$, which is measured using changes in the average center-of-mass energy over the data taking periods. The phase-space hypothesis ${\cal R}=(p_{B^0}/p_{B^+})^3$, upon which previous measurements rely, is strongly disfavored by our fit; the measured mass-difference value for the phase-space hypothesis also differs significantly from our measurement. We constrain ${\cal R}$ in a broader energy range than covered by the direct measurement and extract the energy dependence of ${\cal R}$ in the range from the $B\bar{B}$ threshold up to 10.59 GeV. We interpret the results using a phenomenological model and constrain the parameters of the $B\bar{B}$ potential in the isovector channel.

hep-ex↗

arXiv2025

Observation of the radiative decay $D_s (2317)^+ \to D_s^* \gamma$

We observe the radiative decay $D^{*}_{s0}(2317)^{+} \to D_{s}^{*+} \gamma$ for the first time, with a significance exceeding $10$ standard deviations. The signal is found in the continuum $e^+ e^- \to c\bar{c}$ process with the combined data samples of 980.4~$\rm fb^{-1}$ and 427.9~$\rm fb^{-1}$ collected by the Belle and Belle~II detectors operating at the KEKB and SuperKEKB asymmetric-energy $e^+e^-$ colliders, respectively. The branching fraction ratio ${\cal B}(D^{*}_{s0}(2317)^{+} \to D_{s}^{*+} \gamma)/{\cal B}(D^{*}_{s0}(2317)^{+} \to D_{s}^{+} \pi^{0})$ is measured to be $[7.13 \pm 0.70({\rm stat.}) \pm 0.23({\rm syst.})]\%$. This result provides significant new experimental input for the determination of the quark structure of the $D^{*}_{s0}(2317)^{+}$, which remains unknown.

hep-ex↗

arXiv2025

Improved measurement of Born cross sections for $\chi_{bJ}\,\omega$ and $\chi_{bJ}\,(\pi^+\pi^-\pi^0)_{\rm non-\omega}$ ($J$ = 0, 1, 2) at Belle and Belle II

We study the processes $\chi_{bJ}\,\omega$ and $\chi_{bJ}\,(\pi^+\pi^-\pi^0)_{\rm non-\omega}$ ($J$ = 0, 1, 2) at center-of-mass energies $\sqrt{s}$ from 10.73 to 11.02 GeV using a $142.5\,\mathrm{fb}^{-1}$ data sample collected with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider; and at $\sqrt{s}\sim10.75$ GeV using a $19.8\,\mathrm{fb}^{-1}$ sample collected with Belle II at SuperKEKB. We find that the $\Upsilon(10753)$ state decays into $\chi_{bJ}\,\omega$ but not into $\chi_{bJ}\,(\pi^+\pi^-\pi^0)_{\rm non-\omega}$, while the $\Upsilon(10860)$ state, in contrast, decays into $\chi_{bJ}\,(\pi^+\pi^-\pi^0)_{\rm non-\omega}$ but not into $\chi_{bJ}\,\omega$. The mass and width of the $\Upsilon(10753)$ state are measured to be $(10756.1\pm3.4({\rm stat.})\pm2.7({\rm syst.}))$ MeV/$c^2$ and $(32.2\pm11.3({\rm stat.})\pm14.9({\rm syst.}))$ MeV. The products of the partial width to $e^+e^-$ and branching fractions for $\Upsilon(10753)\to\chi_{b1}\,\omega$ and $\Upsilon(10753)\to\chi_{b2}\,\omega$ are ($1.57\pm0.27({\rm stat.})\pm 0.22({\rm syst.})$) eV and ($1.39\pm0.41({\rm stat.})\pm 0.33({\rm syst.})$) eV.

hep-ex↗

arXiv2025

Measurement of the $CP$ asymmetry in $D^0\to\pi^+\pi^-\pi^0$ decays at Belle II

We measure the time- and phase-space-integrated $CP$ asymmetry $A_{CP}$ in $D^0\to\pi^+\pi^-\pi^0$ decays reconstructed in $e^+e^-\to c\bar c$ events collected by the Belle II experiment from 2019 to 2022. This sample corresponds to an integrated luminosity of 428 fb$^{-1}$. We require $D^0$ mesons to be produced in $D^{*+}\to D^0\pi^+$ decays to determine their flavor at production. Control samples of $D^0\to K^-\pi^+$ decays are used to correct for reconstruction-induced asymmetries. The result, $A_{CP}(D^0\to\pi^+\pi^-\pi^0)=(0.29\pm0.27\pm0.13)\%$, where the first uncertainty is statistical and the second systematic, is the most precise result to date and is consistent with $CP$ conservation.

hep-ex↗

arXiv2025

First measurements of the branching fractions for the decay modes $\Xi_c^{0} \to \Lambda \eta$ and $\Xi_c^0 \to \Lambda \eta'$ and search for the decay $\Xi_c^{0} \to \Lambda \pi^0$ using Belle and Belle II data

Using data samples of 988.4 fb$^{-1}$ and 427.9 fb$^{-1}$ collected with the Belle and Belle II detectors, we present a study of the singly Cabibbo-suppressed decays $\Xi_c^{0} \to \Lambda \eta$, $\Lambda \eta'$, and $\Lambda \pi^0$. We observe the decay $\Xi_c^0 \to \Lambda \eta$ and find evidence for the decay $\Xi_c^0 \to \Lambda \eta'$, with corresponding branching ratios determined to be ${\mathcal{B}(\Xi_c^0 \to \Lambda \eta)}/{\mathcal{B}(\Xi_c^0 \to \Xi^- \pi^+)}= (4.16 \pm 0.91 \pm {0.23})\%$ and ${\mathcal{B}(\Xi_c^0 \to \Lambda \eta')}/{\mathcal{B}(\Xi_c^0 \to \Xi^- \pi^+)}= (2.48 \pm 0.82 \pm {0.12})\%$, respectively. We find no significant signal in the $\Xi_c^0 \to \Lambda \pi^0$ decay mode and set an upper limit at the 90% credibility level of ${\mathcal{B}(\Xi_c^0 \to \Lambda \pi^0)}/{\mathcal{B}(\Xi_c^0 \to \Xi^- \pi^+)}< {3.5\%}$. Multiplying these ratios by the world-average branching fraction of the normalization channel, $\mathcal{B}(\Xi_c^0 \to \Xi^- \pi^+)=(1.43 \pm 0.27)\%$, we obtain the absolute branching fractions of $\mathcal{B}(\Xi_c^0 \to \Lambda \eta)= (5.95 \pm 1.30 \pm {0.32} \pm 1.13) \times 10^{-4}$, $\mathcal{B}(\Xi_c^0 \to \Lambda \eta')= (3.55 \pm 1.17 \pm {0.17} \pm 0.68) \times 10^{-4}$, and an upper limit at the 90% credibility level on the absolute branching fraction of $\mathcal{B}(\Xi_c^0 \to \Lambda \pi^0)< {5.2} \times 10^{-4}$. The quoted first and second uncertainties are statistical and systematic, respectively, while the third uncertainties arise from the branching fraction of the normalization mode. These results are consistent with most theoretical predictions and further the understanding of the underlying decay mechanisms.

hep-ex↗

arXiv2025

Development of Deep Neural Network First-Level Hardware Track Trigger for the Belle II Experiment

The Belle II experiment at the SuperKEKB accelerator is designed to explore physics beyond the Standard Model with unprecedented luminosity. As the beam intensity increased, the experiment faced significant challenges due to higher beam-induced background, leading to a high trigger rate and placing limitations on further luminosity increases. To address this problem, we developed trigger logic for tracking using deep neural network (DNN) technology on an FPGA for the Belle II hardware trigger system, employing high-level synthesis techniques. By leveraging drift time and hit pattern information from the Central Drift Chamber and incorporating a simplified self-attention architecture, the DNN track trigger significantly improves track reconstruction performance at the hardware level. Compared to the existing neural track trigger, our implementation reduces the total track trigger rate by 37% while improving average efficiency for the signal tracks from 96% to 98% for charged tracks with transverse momentum > 0.3 GeV. This upgrade ensures the long-term viability of the Belle II data acquisition system as luminosity continues to increase.

physics.ins-det↗

arXiv2025

Measurement of time-dependent $CP$ asymmetries in $B^0 \to K_{\rm S}^0 \: \pi^{+} \pi^{-} \gamma$ decays at Belle and Belle II

We present a measurement of the time-dependent $CP$ asymmetry in $B^0 \to K_{\rm S}^0 \: \pi^{+} \pi^{-} \gamma$ decays using a data set of 365 fb$^{-1}$ recorded by the Belle II experiment and the final data set of 711 fb$^{-1}$ recorded by the Belle experiment at the ${\rm \Upsilon(4S)}$ resonance. The direct and mixing-induced time-dependent $CP$ violation parameters $C$ and $S$ are determined along with two additional quantities, $S^{+}$ and $S^{-}$, defined in the two halves of the $m^2(K_{\rm S}^0 \pi^{+})-m^2(K_{\rm S}^0 \pi^{-})$ plane. The measured values are $C = -0.17 \pm 0.09 \pm 0.04$, $S = -0.29 \pm 0.11 \pm 0.05$, $S^{+} = -0.57 \pm 0.23 \pm 0.10$ and $S^{-} = 0.31 \pm 0.24 \pm 0.05$, where the first uncertainty is statistical and the second systematic.

hep-ex↗

arXiv2025

Search for $CP$ violation in $\Xi_c^+\to\Sigma^+h^+h^-$ and $\Lambda_c^+\to ph^+h^-$ at Belle II

We report decay-rate $CP$ asymmetries of the singly-Cabibbo-suppressed decays $\Xi_c^+\to\Sigma^+h^+h^-$ and $\Lambda_c^+\to ph^+h^-$, with $h=K,\pi$, measured using 428 fb$^{-1}$ of $e^+e^-$ collisions collected by the Belle II experiment at the SuperKEKB collider. The results, \begin{equation} A_{CP}(\Xi_c^+\to\Sigma^+K^+K^-) = (3.7\pm6.6\pm0.6)\%, \end{equation} \begin{equation} A_{CP}(\Xi_c^+\to\Sigma^+\pi^+\pi^-) = (9.5\pm6.8\pm0.5)\%, \end{equation} \begin{equation} A_{CP}(\Lambda_c^+\to pK^+K^-) = (3.9\pm1.7\pm0.7)\%, \end{equation} \begin{equation} A_{CP}(\Lambda_c^+\to p\pi^+\pi^-) = (0.3\pm1.0\pm0.2)\%, \end{equation} where the first uncertainties are statistical and the second systematic, agree with $CP$ symmetry. From these results we derive the sums \begin{equation} A_{CP}(\Xi_c^+\to\Sigma^+\pi^+\pi^-) \, + \, A_{CP}(\Lambda_c^+\to pK^+K^-) = (13.4 \pm 7.0\pm 0.9)\%, \end{equation} \begin{equation} A_{CP}(\Xi_c^+\to\Sigma^+K^+K^-) \, + \, A_{CP}(\Lambda_c^+\to p\pi^+\pi^-) = (\phantom{0}4.0 \pm 6.6\pm 0.7)\%, \end{equation} which are consistent with the $U$-spin symmetry prediction of zero. These are the first measurements of $CP$ asymmetries for individual hadronic three-body charmed-baryon decays.

hep-ex↗

arXiv2025

Search for $e^+ e^- \to \gamma\chi_{bJ}$ ($J$ = 0, 1, 2) near $\sqrt{s} = 10.746$ GeV at Belle II

We search for the $e^+ e^- \to \gamma \chi_{bJ}$ ($J$ = 0, 1, 2) processes at center-of-mass energies $\sqrt{s}$ = 10.653, 10.701, 10.746, and 10.804 GeV. These data were collected with the Belle II detector at the SuperKEKB collider and correspond to 3.5, 1.6, 9.8, and 4.7 fb$^{-1}$ of integrated luminosity, respectively. We set upper limits at the 90\% confidence level on the Born cross sections for $e^+ e^- \to \gamma \chi_{bJ}$ at each center-of-mass energy $\sqrt{s}$ near 10.746 GeV. The upper limits at 90\% confidence level on the Born cross sections for $e^+ e^- \to \gamma \chi_{b1}$ are significantly smaller than the corresponding measured values for $e^+e^-\to\omega\chi_{b1}$ and $e^+e^-\to\pi^+\pi^-\Upsilon(2S)$ at $\sqrt{s}$ = 10.746 GeV.

hep-ex↗

arXiv2025

Model-agnostic likelihood for the reinterpretation of the $B^+\to K^+\nu\bar{\nu}$ measurement at Belle II

We recently measured the branching fraction of the $B^{+}\rightarrow K^{+}\nu\bar{\nu}$ decay using 362fb$^{-1}$ of on-resonance $e^+e^-$ collision data under the assumption of Standard Model kinematics, providing the first evidence for this decay. To facilitate future reinterpretations and maximize the scientific impact of this measurement, we publicly release the full analysis likelihood along with all necessary material required for reinterpretation under arbitrary theoretical models sensitive to this measurement. In this work, we demonstrate how the measurement can be reinterpreted within the framework of the Weak Effective Theory. Using a kinematic reweighting technique in combination with the published likelihood, we derive marginal posterior distributions for the Wilson coefficients, construct credible intervals, and assess the goodness of fit to the Belle II data. For the Weak Effective Theory Wilson coefficients, the posterior mode of the magnitudes $|C_\mathrm{VL}+C_\mathrm{VR}|$, $|C_\mathrm{SL}+C_\mathrm{SR}|$, and $|C_\mathrm{TL}|$ corresponds to the point ${(11.3, 0.0, 8.2)}$. The respective 95\% credible intervals are $[1.9, 16.2]$, $[0.0, 15.4]$, and $[0.0, 11.2]$.

hep-ex↗

arXiv2025

Observation of the decays $B^{+} \to \Sigma_{c}(2455)^{++} \overline{\Xi}_{c}^{-}$ and $B^{0} \to \Sigma_{c}(2455)^{0} \overline{\Xi}_{c}^{0}$

We report the first observation of the two-body baryonic decays $B^{+} \to \Sigma_{c}(2455)^{++} \overline{\Xi}_{c}^{-}$ and $B^{0} \to \Sigma_{c}(2455)^{0} \overline{\Xi}_{c}^{0}$ with significances of $7.3\,\sigma$ and $6.2\,\sigma$, respectively, including statistical and systematic uncertainties. The branching fractions are measured to be $\mathcal{B}(B^{+} \to \Sigma_{c}(2455)^{++} \overline{\Xi}_{c}^{-}) = (5.74 \pm 1.11 \pm 0.42_{-1.53}^{+2.47}) \times 10^{-4}$ and $\mathcal{B}(B^{0} \to \Sigma_{c}(2455)^{0} \overline{\Xi}_{c}^{0}) = (4.83 \pm 1.12 \pm 0.37_{-0.60}^{+0.72}) \times 10^{-4}$. The first and second uncertainties are statistical and systematic, respectively, while the third ones arise from the absolute branching fractions of $\overline{\Xi}_{c}^{-}$ or $\overline{\Xi}_{c}^{0}$ decays. The data samples used for this analysis have integrated luminosities of 711~$\mathrm{fb}^{-1}$ and 365~$\mathrm{fb}^{-1}$, and were collected at the $\Upsilon(4S)$ resonance by the Belle and Belle~II detectors operating at the KEKB and SuperKEKB asymmetric-energy $e^{+}e^{-}$ colliders, respectively.

hep-ex↗

arXiv2025

Search for an Axion-Like Particle in $B\rightarrow K^{(*)} a (\rightarrow\gamma\gamma)$ Decays at Belle

We report a search for an axion-like particle $a$ in $B\rightarrow K^{(*)} a (\rightarrow\gamma\gamma)$ decays using data collected with the Belle detector at the KEKB asymmetric energy electron-positron collider. The search is based on a $711 \mathrm{fb^{-1}}$ data sample collected at the $\Upsilon 4S$ resonance energy, corresponding to a sample of $772\times10^6$ $\Upsilon 4S$ events. In this study, we search for the decay of the axion-like particle into a pair of photons, $a \rightarrow \gamma\gamma$. We scan the two-photon invariant mass in the range $0.16\ \mathrm{GeV/}c^2-4.50\ \mathrm{GeV}/c^2$ for the $K$ modes and $0.16\ \mathrm{GeV/}c^2-4.20\ \mathrm{GeV}/c^2$ for the $K^{*}$ modes. No significant signal is observed in any of the modes, and 90\% confidence level upper limits are established on the coupling to the $W$ boson, $g_aW$, as a function of $a$ mass. The limits range from $3 \times 10^{-6} \mathrm{GeV}^{-1}$ to $3 \times 10^{-5} \mathrm{GeV}^{-1}$, improving the current constraints on $g_aW$ by a factor of two over the most stringent previous experimental results.

hep-ex↗

arXiv2025

Determination of $|V_{cb}|$ using $B\to D\ell\nu_\ell$ Decays at Belle II

We present a determination of the Cabibbo-Kobayashi-Maskawa matrix element $|V_{cb}|$ from the decay $B\to D\ell\nu_\ell$ using a $365~\mathrm{fb}^{-1}$ $e^+e^-\to\Upsilon(4S)\to B\bar B$ data sample recorded by the Belle II experiment at the SuperKEKB collider. The semileptonic decay of one $B$ meson is reconstructed in the modes $B^0\to D^-(\to K^+\pi^-\pi^-)\ell^+\nu_\ell$ and $B^+\to \bar D^0(\to K^+\pi^-)\ell^+\nu_\ell$, where $\ell$ denotes either an electron or a muon. Charge conjugation is implied. The second $B$ meson in the $\Upsilon(4S)$ event is not reconstructed explicitly. Using an inclusive reconstruction of the unobserved neutrino momentum, we determine the recoil variable $w=v_B\cdot v_D$, where $v_B$ and $v_D$ are the 4-velocities of the $B$ and $D$ mesons. We measure the total decay branching fractions to be $\mathcal{B}(B^0\to D^-\ell^+\nu_\ell)=(2.06 \pm 0.05\,(\mathrm{stat.}) \pm 0.10\,(\mathrm{sys.}))\%$ and $\mathcal{B}(B^+\to\bar D^0\ell^+\nu_\ell)=(2.31 \pm 0.04\,(\mathrm{stat.}) \pm 0.09\,(\mathrm{sys.}))\%$. We probe lepton flavor universality by measuring $\mathcal{B}(B\to De\nu_e)/\mathcal{B}(B\to D\mu\nu_\mu)=1.020 \pm 0.020\,(\mathrm{stat.})\pm 0.022\,(\mathrm{sys.})$. Fitting the partial decay branching fraction as a function of $w$ and using the average of lattice QCD calculations of the $B\to D$ form factor, we obtain $ |V_{cb}|=(39.2\pm 0.4\,(\mathrm{stat.}) \pm 0.6\,(\mathrm{sys.}) \pm 0.5\,(\mathrm{th.})) \times 10^{-3}$.

hep-ex↗

arXiv2025

Measurement of the CP asymmetry in $D^+ \to \pi^+ \pi^0$ decays at Belle II

We measure the CP asymmetry in $D^+ \to \pi^+ \pi^0$ decays reconstructed in $e^+ e^-$ collisions at the Belle II experiment using a data set corresponding to an integrated luminosity of 428 fb$^{-1}$. A control sample of $D^+ \to \pi^+ K_{S}$ decays is used to correct for detection and production asymmetries. The result, $A_{CP}(D^+ \to \pi^+\pi^0) =(-1.8 \pm 0.9 \pm 0.1)\%$, where the first uncertainty is statistical and the second systematic, is the most precise determination to date. It agrees with the prediction of CP symmetry from the standard model, and with results of previous measurements.

hep-ex↗

arXiv2025

Charged-hadron identification at Belle II

The Belle II experiment's ability to identify particles critically affects the sensitivity of its measurements. We describe Belle II's algorithms for identifying charged particles and evaluate their performance in separating pions, kaons, and protons using 426 fb$^{-1}$ of data collected at the energy-asymmetric $e^+e^-$ collider SuperKEKB in 2019--2022 at center-of-mass energies at and near the mass of the $\Upsilon(4S)$.

hep-ex↗