arXiv subjects

G. Finocchiaro

Publications and source records attributed to G. Finocchiaro.

At least 37 records · Page 2Linked to original sources

arXiv2025

Model-independent measurement of $D^0$-$\overline{D}{}^0$ mixing parameters in $D^0\rightarrow K^0_{S}π^+π^-$ decays at Belle and Belle II

We perform a model-independent measurement of the $D^0$-$\overline{D}{}^0$ mixing parameters using samples of $e^+e^-$-collision data collected by the Belle and Belle II experiments that have integrated luminosities of $951\ \text{fb}^{-1}$ and $408\ \text{fb}^{-1}$, respectively. Approximately $2.05\times10^6$ neutral $D$ mesons are reconstructed in the $D^0\rightarrow K^0_{S}π^+π^-$ channel, with the neutral $D$ flavor tagged by the charge of the pion in the $D^{*+}\rightarrow D^0π^+$ decay. Assuming charge-parity symmetry, the mixing parameters are measured to be $ x = (4.0\pm1.7\pm0.4)\times 10^{-3} $ and $ y = (2.9\pm1.4\pm0.3)\times 10^{-3}$, where the first uncertainties are statistical and the second systematic. The results are consistent with previous determinations.

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arXiv2025

Measurement of the branching fraction, polarization, and time-dependent $CP$ asymmetry in $B^0 \to ρ^+ρ^-$ decays and constraint on the CKM angle $ϕ_2$

We present a measurement of the branching fraction and fraction of longitudinal polarization of $B^0 \to ρ^+ ρ^-$ decays, which have two $π^0$'s in the final state. We also measure time-dependent {\it CP} violation parameters for decays into longitudinally polarized $ρ^+ ρ^-$ pairs. This analysis is based on a data sample containing $(387\pm6) \times 10^6$ $Υ(4S)$ mesons collected with the Belle~II detector at the SuperKEKB asymmetric-energy $e^+e^-$ collider in 2019-2022. We obtain $\mathcal{B}(B^0\toρ^+ρ^-) = (2.89 ^{+0.23}_{-0.22} {}^{+0.29}_{-0.27}) \times 10^{-5}, f_{L} = 0.921 ^{+0.024}_{-0.025} {}^{+0.017}_{-0.015}$, \mbox{$S = -0.26\pm0.19\pm0.08$}, and $C = -0.02\pm0.12^{+0.06}_{-0.05}$, where the first uncertainties are statistical and the second are systematic. We use these results to perform an isospin analysis to constrain the CKM angle $ϕ_2$ and obtain two solutions; the result consistent with other Standard Model constraints is $ϕ_2 = (92.6^{+4.5}_{-4.7})^\circ$.

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arXiv2025

Search for lepton-flavor-violating $τ^- \to \ell^- K_s^0$ decays at Belle and Belle II

We present the results of a search for charged-lepton-flavor violating decays $τ^{-} \rightarrow \ell^{-}K_{S}^{0}$, where $\ell^{-}$ is either an electron or a muon. We combine $e^+e^-$ data samples recorded by the Belle II experiment at the SuperKEKB collider (428 fb$^{-1}$) with samples recorded by the Belle experiment at the KEKB collider (980 fb$^{-1}$) to obtain a sample of 1.3 billion $e^+e^-\toτ^+τ^-$ events. We observe 0 and 1 events and set $90\%$ confidence level upper limits of $0.8 \times 10^{-8}$ and $1.2 \times 10^{-8}$ on the branching fractions of the decay modes $τ^{-} \rightarrow e^{-}K_{S}^{0}$ and $τ^{-} \rightarrow μ^{-}K_{S}^{0}$, respectively. These are the most stringent upper limits to date.

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arXiv2025

Observation of the decay $B^0 \to J/ψω$ at Belle II

We measure the branching fraction of the decay $B^0 \to J/ψω$ using data collected with the Belle II detector at the SuperKEKB collider. The data contain $(387 \pm 6) \times 10^6$ $B\overline{B}$ meson pairs produced in energy-asymmetric $e^+e^-$ collisions at the $Υ(4S)$ resonance. The measured branching fraction $\mathcal{B}(B^0 \to J/ψω) = \left( 2.16 \pm 0.30 \pm 0.14 \right) \times 10^{-5}$, where the first uncertainty is statistical and the second is systematic, is more precise than previous results and constitutes the first observation of the decay with a significance of $6.5$ standard deviations.

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arXiv2025

Search for $C\!P$ violation in $D^+_{(s)}\to{}K_{S}^{0}K^{-}π^{+}π^{+}$ decays using triple and quadruple products

We perform the first search for $C\!P$ violation in ${D_{(s)}^{+}\to{}K_{S}^{0}K^{-}π^{+}π^{+}}$ decays. We use a combined data set from the Belle and Belle II experiments, which study $e^+e^-$ collisions at center-of-mass energies at or near the $Υ(4S)$ resonance. We use 980 fb$^{-1}$ of data from Belle and 428 fb$^{-1}$ of data from Belle~II. We measure six $C\!P$-violating asymmetries that are based on triple products and quadruple products of the momenta of final-state particles, and also the particles' helicity angles. We obtain a precision at the level of 0.5% for $D^+\to{}K_{S}^{0}K^{-}π^{+}π^{+}$ decays, and better than 0.3% for $D^+_{s}\to{}K_{S}^{0}K^{-}π^{+}π^{+}$ decays. No evidence of $C\!P$ violation is found. Our results for the triple-product asymmetries are the most precise to date for singly-Cabibbo-suppressed $D^+$ decays. Our results for the other asymmetries are the first such measurements performed for charm decays.

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arXiv2025

Measurement of $B^+\toτ^+ν_τ$ branching fraction with a hadronic tagging method at Belle II

We present a measurement of the branching fraction of $B^+\toτ^+ν_τ$ decays using $(387\pm6)\times 10^6$ $Υ(4S)$ collected between 2019 and 2022 with the Belle II detector at the SuperKEKB $e^+e^-$ collider. We reconstruct the accompanying $B^-$ meson using the hadronic tagging method, while $B^+\toτ^+ν_τ$ candidates are identified in the recoil. We find evidence for $B^+\toτ^+ν_τ$ decays at 3.0 standard deviations, including systematic uncertainties. The measured branching fraction is $\mathcal{B}(B^+\toτ^+ν_τ) = [1.24 \pm 0.41 (\text{stat.}) \pm 0.19 (\text{syst.})] \times 10^{-4}$.

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arXiv2025

Design and Commissioning of Readout Electronics for a $K_L^0$ and $μ$ Detector at the Belle II Experiment

The K-long and muon detector (KLM) constitutes the outer-most volume of the Belle II spectrometer at the interaction region of the SuperKEKB collider in Tsukuba, Japan. The KLM detector was partially upgraded since the Belle experiment by replacing many of its resistive-plate chambers with scintillators containing wavelength-shifting fibers and instrumenting it with silicon photomultipliers. We describe the readout electronics, firmware, and software created to control and acquire data from the scintillators and resistive-plate chambers.

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arXiv2025

Observation of time-dependent $CP$ violation and measurement of the branching fraction of $B^0 \to J/ψπ^0$ decays

We present a measurement of the branching fraction and time-dependent charge-parity ($CP$) decay-rate asymmetries in $B^0 \to J/ψπ^0$ decays. The data sample was collected with the Belle~II detector at the SuperKEKB asymmetric $e^+e^-$ collider in 2019-2022 and contains $(387\pm 6)\times 10^6$ $B\overline{B}$ meson pairs from $Υ(4S)$ decays. We reconstruct $392\pm 24$ signal decays and fit the $CP$ parameters from the distribution of the proper-decay-time difference of the two $B$ mesons. We measure the branching fraction to be $B(B^0 \to J/ψπ^0)=(2.00 \pm 0.12 \pm 0.09)\times 10^{-5}$ and the direct and mixing-induced $CP$ asymmetries to be $C_{CP}=0.13 \pm 0.12 \pm 0.03$ and $S_{CP}=-0.88 \pm 0.17 \pm 0.03$, respectively, where the first uncertainties are statistical and the second are systematic. We observe mixing-induced $CP$ violation with a significance of $5.0$ standard deviations for the first time in this mode.

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arXiv2024

Observations of the singly Cabibbo-suppressed decays $Ξ_c^{+} \to pK_{S}^{0}$, $Ξ_c^+ \to Λπ^+$, and $Ξ_c^+ \to Σ^{0} π^+$ at Belle and Belle II

Using data samples of 983.0~$\rm fb^{-1}$ and 427.9~$\rm fb^{-1}$ accumulated with the Belle and Belle~II detectors operating at the KEKB and SuperKEKB asymmetric-energy $e^+e^-$ colliders, singly Cabibbo-suppressed decays $Ξ_c^{+} \to pK_{S}^{0}$, $Ξ_c^+ \to Λπ^+$, and $Ξ_c^+ \to Σ^{0} π^+$ are observed for the first time. The ratios of branching fractions of $Ξ_{c}^{+}\to p K_{S}^{0}$, $Ξ_{c}^{+}\to Λπ^{+}$, and $Ξ_{c}^{+}\to Σ^{0} π^{+}$ relative to that of $Ξ_c^+ \to Ξ^- π^{+} π^{+}$ are measured to be \begin{equation} \frac{{\cal B}(Ξ_c^+ \to pK_S^0)}{{\cal B}(Ξ_c^{+} \to Ξ^{-} π^+ π^+)} = (2.47 \pm 0.16 \pm 0.07)\% \notag, \end{equation} \begin{equation} \frac{{\cal B}(Ξ_c^+ \to Λπ^+)}{{\cal B}(Ξ_c^{+} \to Ξ^{-} π^+ π^+)} = (1.56 \pm 0.14 \pm 0.09)\% \notag, \end{equation} \begin{equation} \frac{{\cal B}(Ξ_c^+ \to Σ^0 π^+)}{{\cal B}(Ξ_c^{+} \to Ξ^{-} π^+ π^+)} = (4.13 \pm 0.26 \pm 0.22)\% \notag. \end{equation} Multiplying these values by the branching fraction of the normalization channel, ${\cal B}(Ξ_c^{+} \to Ξ^{-} π^+π^+) = (2.9 \pm 1.3)\%$, the absolute branching fractions are determined to be \begin{equation} {\cal B}(Ξ_c^{+} \to p K_{S}^{0}) = (7.16 \pm 0.46 \pm 0.20 \pm 3.21) \times 10^{-4} \notag, \end{equation} \begin{equation} {\cal B}(Ξ_c^{+} \to Λπ^+) = (4.52 \pm 0.41 \pm 0.26 \pm 2.03) \times 10^{-4} \notag, \end{equation} \begin{equation} {\cal B}(Ξ_c^{+} \to Σ^0 π^+) = (1.20 \pm 0.08 \pm 0.07 \pm 0.54) \times 10^{-3} \notag. \end{equation} The first and second uncertainties above are statistical and systematic, respectively, while the third ones arise from the uncertainty in ${\cal B}(Ξ_c^{+} \to Ξ^{-} π^{+} π^{+})$.

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arXiv2024

Measurement of the $e^+e^- \to π^+π^-π^0$ cross section in the energy range 0.62-3.50 GeV at Belle II

We report a measurement of the $e^+e^- \to π^+π^-π^0$ cross section in the energy range from 0.62 to 3.50 GeV using an initial-state radiation technique. We use an $e^+e^-$ data sample corresponding to 191 $\text{fb}^{-1}$ of integrated luminosity, collected at a center-of-mass energy at or near the $Υ{(4S)}$ resonance with the Belle II detector at the SuperKEKB collider. Signal yields are extracted by fitting the two-photon mass distribution in $e^+e^- \to π^+π^-π^0γ$ events, which involve a $π^0 \to γγ$ decay and an energetic photon radiated from the initial state. Signal efficiency corrections with an accuracy of 1.6% are obtained from several control data samples. The uncertainty on the cross section at the $ω$ and $ϕ$ resonances is dominated by the systematic uncertainty of 2.2%. The resulting cross sections in the 0.62-1.80 GeV energy range yield $ a_μ^{3π} = [48.91 \pm 0.23~(\mathrm{stat}) \pm 1.07~(\mathrm{syst})] \times 10^{-10} $ for the leading-order hadronic vacuum polarization contribution to the muon anomalous magnetic moment. This result differs by $2.5$ standard deviations from the most precise current determination.

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arXiv2024

Measurement of $CP$ asymmetries in $B^0\toη'K^0_s$ decays at Belle II

We describe a measurement of charge-parity ($CP$) violation asymmetries in $B^0\toη'K^0_S$ decays using Belle II data. We consider $η'\toη(\toγγ)π^+π^-$ and $η'\toρ(\toπ^+π^-)γ$ decays. The data were collected at the SuperKEKB asymmetric-energy $e^+e^-$ collider between the years 2019 and 2022, and contain $(387\pm 6) \times 10^6$ bottom-antibottom meson pairs. We reconstruct $829\pm35$ signal decays and extract the $CP$ violating parameters from a fit to the distribution of the proper-decay-time difference between the two $B$ mesons. The measured direct and mixing-induced $CP$ asymmetries are $\text{C}_{η'K^0_S} = -0.19 \pm 0.08 \pm 0.03 $ and $\text{S}_{η'K^0_S} = +0.67 \pm 0.10 \pm 0.04 $, respectively, where the first uncertainties are statistical and the second are systematic. These results are in agreement with current world averages and standard model predictions.

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arXiv2024

Measurement of the integrated luminosity of data samples collected during 2019-2022 by the Belle II experiment

A series of data samples was collected with the Belle~II detector at the SuperKEKB collider from March 2019 to June 2022. We determine the integrated luminosities of these data samples using three distinct methodologies involving Bhabha ($e^+e^- \to e^+e^-(nγ)$), digamma ($e^+e^- \to γγ(nγ)$), and dimuon ($e^+e^- \to μ^+ μ^- (nγ)$) events. The total integrated luminosity obtained with Bhabha, digamma, and dimuon events is ({426.88} $\pm$ 0.03 $\pm$ {2.61})~fb$^{-1}$, ({429.28} $\pm$ 0.03 $\pm$ {2.62})~fb$^{-1}$, and ({423.99} $\pm$ 0.04 $\pm$ {3.83})~fb$^{-1}$, where the first uncertainties are statistical and the second are systematic. The resulting total integrated luminosity obtained from the combination of the three methods is ({427.87 $\pm$ 2.01})~fb$^{-1}$.

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arXiv2024

Search for Rare $b \to d\ell^+\ell^-$ Transitions at Belle

We present the results of a search for the $b \to d\ell^+\ell^-$ flavor-changing neutral-current rare decays $B^{+, 0} \to (η, ω, π^{+,0}, ρ^{+, 0}) e^+e^-$ and $B^{+, 0} \to (η, ω, π^{0}, ρ^{+}) μ^+μ^-$ using a $711$ fb$^{-1}$ data sample that contains $772 \times 10^{6}$ $B\overline{B}$ events. The data were collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. We find no evidence for signal and set upper limits on branching fractions at the $90\%$ confidence level in the range $(3.8 - 47) \times 10^{-8}$ depending on the decay channel. The obtained limits are the world's best results. This is the first search for the channels $B^{+, 0} \to (ω, ρ^{+,0}) e^+e^-$ and $B^{+, 0} \to (ω, ρ^{+})μ^+μ^-$.

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arXiv2024

Determination of the CKM angle $ϕ_{3}$ from a combination of Belle and Belle II results

We report a determination of the CKM angle $ϕ_{3}$, also known as $γ$, from a combination of measurements using samples of up to 711~fb$^{-1}$ from the Belle experiment and up to 362~fb$^{-1}$ from the Belle II experiment. We combine results from analyses of $B^+\to DK^+, B^+\to Dπ^+$, and $B^+ \to D^{*}K^+$ decays, where $D$ is an admixture of $D^0$ and $\overline{D}{}^{0}$ mesons, in a likelihood fit to obtain $ϕ_{3} = (78.6^{+7.2}_{-7.3})^{\circ}$. We also briefly discuss the interpretation of this result.

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arXiv2024

New graph-neural-network flavor tagger for Belle II and measurement of $\sin2ϕ_1$ in $B^0 \to J/ψK^0_\text{S}$ decays

We present GFlaT, a new algorithm that uses a graph-neural-network to determine the flavor of neutral $B$ mesons produced in $Υ(4S)$ decays. It improves previous algorithms by using the information from all charged final-state particles and the relations between them. We evaluate its performance using $B$ decays to flavor-specific hadronic final states reconstructed in a 362 $\text{fb}^{-1}$ sample of electron-positron collisions collected at the $Υ(4S)$ resonance with the Belle II detector at the SuperKEKB collider. We achieve an effective tagging efficiency of $(37.40 \pm 0.43 \pm 0.36) \%$, where the first uncertainty is statistical and the second systematic, which is $18\%$ better than the previous Belle II algorithm. Demonstrating the algorithm, we use $B^{0}\to J/ψK^0_\text{S}$ decays to measure the mixing-induced and direct $CP$ violation parameters, $S = (0.724 \pm 0.035 \pm 0.009)$ and $C = (-0.035 \pm 0.026 \pm 0.029)$.

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arXiv2024

Measurement of branching fractions, CP asymmetry, and isospin asymmetry for $\boldsymbol{B\rightarrowργ}$ decays using Belle and Belle II data

We present measurements of $B^{+}\rightarrowρ^{+}γ$ and $B^{0}\rightarrowρ^{0}γ$ decays using a combined data sample of $772 \times 10^6$ $B\overline{B}$ pairs collected by the Belle experiment and $387\times 10^6$ $B\overline{B}$ pairs collected by the Belle II experiment in $e^{+}e^{-}$ collisions at the $Υ(4S)$ resonance. After an optimized selection, a simultaneous fit to the Belle and Belle II data sets yields $114\pm 12$ $B^{+}\rightarrowρ^{+}γ$ and $99\pm 12$ $B^{0}\rightarrowρ^{0}γ$ decays. The measured branching fractions are $(13.1^{+2.0 +1.3}_{-1.9 -1.2})\times 10^{-7}$ and $(7.5\pm 1.3^{+1.0}_{-0.8})\times 10^{-7}$ for $B^{+}\rightarrowρ^{+}γ$ and $B^{0}\rightarrowρ^{0}γ$ decays, respectively, where the first uncertainty is statistical and the second is systematic. We also measure the isospin asymmetry $A_{\rm I}(B\rightarrowργ)=(10.9^{+11.2 +7.8}_{-11.7 -7.3})\%$ and the direct CP asymmetry $A_{CP}(B^{+}\rightarrowρ^{+}γ)=(-8.2\pm 15.2^{+1.6}_{-1.2})\%$.

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arXiv2024

Search for the baryon number and lepton number violating decays $τ^-\to Λπ^-$ and $τ^-\to \barΛπ^-$ at Belle II

We present a search for the baryon number $B$ and lepton number $L$ violating decays $τ^- \rightarrow Λπ^-$ and $τ^- \rightarrow \barΛ π^-$ produced from the $e^+e^-\to τ^+τ^-$ process, using a 364 fb$^{-1}$ data sample collected by the Belle~II experiment at the SuperKEKB collider. No evidence of signal is found in either decay mode, which have $|Δ(B-L)|$ equal to $2$ and $0$, respectively. Upper limits at 90\% credibility level on the branching fractions of $τ^- \rightarrow Λπ^-$ and $τ^- \rightarrow \barΛπ^-$ are determined to be $4.7 \times 10^{-8}$ and $4.3 \times 10^{-8}$, respectively.

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arXiv2024

The Belle II Detector Upgrades Framework Conceptual Design Report

We describe the planned near-term and potential longer-term upgrades of the Belle II detector at the SuperKEKB electron-positron collider operating at the KEK laboratory in Tsukuba, Japan. These upgrades will allow increasingly sensitive searches for possible new physics beyond the Standard Model in flavor, tau, electroweak and dark sector physics that are both complementary to and competitive with the LHC and other experiments.

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