arXiv subjects

F. Bianchi

Publications and source records attributed to F. Bianchi.

At least 577 records · Page 32Linked to original sources

arXiv2022

Determination of $|V_{cb}|$ from $B\to D\ellν$ decays using 2019-2021 Belle II data

We present a determination of the magnitude of the Cabibbo-Kobayashi-Maskawa (CKM) matrix element $V_{cb}$ using $B\to D\ellν$ decays. The result is based on $e^+e^-\toΥ(4S)$ data recorded by the Belle II detector corresponding to 189.2/fb of integrated luminosity. The semileptonic decays $B^0\to D^-(\to K^+π^-π^-)\ell^+ν_\ell$ and $B^+\to\bar D^0(\to K^+π^-)\ell^+ν_\ell$ are reconstructed, where $\ell$ is either electron or a muon. The second $B$ meson in the $Υ(4S)$ event is not explicitly reconstructed. Using the diamond-frame method, we determine the $B$ meson four-momentum and thus the hadronic recoil. We extract the partial decay rates as functions of $w$ and perform a fit to the decay form-factor and the CKM parameter $|V_{cb}|$ using the BGL parameterization of the form factor and lattice QCD input from the FNAL/MILC and HPQCD collaborations. We obtain $η_{EW}|V_{cb}|=(38.53\pm 1.15)\times 10^{-3}$, where $η_{EW}$ is an electroweak correction, and the error accounts for theoretical and experimental sources of uncertainty.

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arXiv2022

Measurement of the photon-energy spectrum in inclusive $B\rightarrow X_{s}γ$ decays identified using hadronic decays of the recoil $B$ meson in 2019-2021 Belle II data

We measure the photon-energy spectrum in radiative bottom-meson ($B$) decays into inclusive final states involving a strange hadron and a photon. We use SuperKEKB electron-positron collisions corresponding to $189~\mathrm{fb}^{-1}$ of integrated luminosity collected at the $Υ(4S)$ resonance by the Belle II experiment. The partner $B$ candidates are fully reconstructed using a large number of hadronic channels. The $B \rightarrow X_s γ$ partial branching fractions are measured as a function of photon energy in the signal $B$ meson rest frame in eight bins above $1.8~\mathrm{GeV}$. The background-subtracted signal yield for this photon energy region is $343 \pm 122$ events. Integrated branching fractions for three photon energy thresholds of $1.8~\mathrm{GeV}$, $2.0~\mathrm{GeV}$, and $2.1~\mathrm{GeV}$ are also reported, and found to be in agreement with world averages.

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arXiv2022

Measurement of the absolute branching fraction of the singly Cabibbo suppressed decay $Λ^{+}_{c}\to pη^{\prime}$

The singly Cabibbo suppressed decay $Λ^{+}_{c}\to pη^{\prime}$ is measured using 4.5 $\mathrm{fb}^{-1}$ of $e^+e^-$ collision data collected at center-of-mass energies between 4.600 and 4.699 GeV with the BESIII detector at BEPCII. Evidence for $Λ^{+}_{c}\to pη^{\prime}$ with a statistical significance of $3.6σ$ is reported with a double-tag approach. The $Λ^{+}_{c}\to pη^{\prime}$ absolute branching fraction is determined to be $(5.62^{+2.46}_{-2.04} \pm 0.26)\times 10^{-4}$, where the first and second uncertainties are statistical and systematic, respectively. Our result is consistent with the branching fraction obtained by the Belle collaboration within the uncertainty of $1σ$.

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arXiv2022

Amplitude analysis and branching fraction measurement of the decay \boldmath $D_{s}^{+} \to K^+π^{+}π^{-}π^{0}$

The singly Cabibbo-suppressed decay $D_{s}^{+} \to K^+π^{+}π^{-}π^{0}$ is observed, using a data set corresponding to an integrated luminosity of 6.32 $\rm fb^{-1}$ recorded by the BESIII detector at the centre-of-mass energies between 4.178 and 4.226 GeV. The first amplitude analysis of $D_{s}^{+} \to K^+π^{+}π^{-}π^{0}$ reveals the sub-structures in this decay and determines the fractions and relative phases of different intermediate processes. The dominant intermediate process is $D_s^+ \to K^{*0}ρ^+$, with a fit fraction of $(40.5\pm2.8_{\rm{stat.}}\pm1.5_{\rm{syst.}})\%$. With the detection efficiency based on our amplitude analysis, the absolute branching fraction for $D_{s}^{+} \to K^+π^{+}π^{-}π^{0}$ is measured to be $(9.75\pm0.54_{\rm{stat.}}\pm0.17_{\rm{syst.}})\times 10^{-3}$.

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arXiv2022

Measurement of decay-time dependent $CP$ violation in $B^0 \rightarrow K^0_S K^0_S K^0_S$ using 2019--2021 Belle II data

We report a measurement of decay-time dependent $CP$-violating parameters in $B^0 \rightarrow K^0_S K^0_S K^0_S$ decays. We use $(198.0 \pm 3.0) \times 10^6\ B\overline{B}$ pairs collected at the $Υ(4S)$ resonance with the Belle II detector at the SuperKEKB asymmetric-energy $e^+e^-$ collider. The observed mixing-induced and direct $CP$ violation parameters are $\mathcal{S} = -1.86\ _{-0.46}^{+0.91}~{\rm (stat)} \pm 0.09~{\rm (syst)}$ and $\mathcal{A} = -0.22\ _{-0.27}^{+0.30}~{\rm (stat)} \pm 0.04~{\rm (syst)}$, respectively.

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arXiv2022

Measurement of the $e^+e^-\toπ^+π^-J/ψ$ cross section in the vicinity of 3.872 GeV

We report a measurement of the cross section for the process $e^+e^-\toπ^+π^-J/ψ$ around the $X(3872)$ mass in search for the direct formation of $e^+e^-\to X(3872)$ through the two-photon fusion process. No enhancement of the cross section is observed at the $X(3872)$ peak and an upper limit on the product of electronic width and branching fraction of $X(3872)\toπ^+π^-J/ψ$ is determined to be $Γ_{ee}\times\mathcal{B}(X(3872)\toπ^+π^-J/ψ)<7.5\times10^{-3}\,\text{eV}$ at $90\,\%$ confidence level under an assumption of total width of $1.19\pm0.21$ MeV. This is an improvement of a factor of about $17$ compared to the previous limit. Furthermore, using the latest result of $\mathcal{B}(X(3872)\toπ^+π^-J/ψ)$, an upper limit on the electronic width $Γ_{ee}$ of $X(3872)$ is obtained to be $<0.32\,\text{eV}$ at the $90\,\%$ confidence level.

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arXiv2022

Precise Measurements of Decay Parameters and $CP$ Asymmetry with Entangled $Λ-\barΛ$ Pairs

Based on 10 billion $J/ψ$ events collected at the BESIII experiment, a search for $CP$ violation in $Λ$ decay is performed in the difference between $CP$-odd decay parameters $α_{-}$ for $Λ\rightarrow pπ^-$ and $α_{+}$ for $\barΛ\rightarrow \bar{p}π^+$ by using the process $e^+e^- \to J/ψ\rightarrow Λ\barΛ$. With a five-dimensional fit to the full angular distributions of the daughter baryon, the most precise values for the decay parameters are determined to be $α_{-} = 0.7519 \pm 0.0036 \pm 0.0024$ and $α_{+} = -0.7559 \pm 0.0036 \pm 0.0030$, respectively. The $Λ$ and $\barΛ$ averaged value of the decay parameter is extracted to be $α_{\rm{avg}} = 0.7542 \pm 0.0010 \pm 0.0024$ with unprecedented accuracy. The $CP$ asymmetry $A_{CP}=(α_{-}+α_{+})/(α_{-}-α_{+})$ is determined to be $-0.0025 \pm 0.0046 \pm 0.0012$, which is one of the most precise measurements in the baryon sector. The reported results for the decay parameter will play an important role in the studies of the polarizations and $CP$ violations for the strange, charmed and beauty baryons.

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arXiv2022

Improved measurement of the strong-phase difference $δ_D^{Kπ}$ in quantum-correlated $D\bar{D}$ decays

The decay $D\to K^-π^+$ is studied in a sample of quantum-correlated $D\bar{D}$ pairs, based on a data set corresponding to an integrated luminosity of 2.93\,fb$^{-1}$ collected at the $ψ(3770)$ resonance by the BESIII experiment. The asymmetry between $C\!P$-odd and $C\!P$-even eigenstate decays into $K^-π^+$ is determined to be ${\cal A}_{Kπ} = 0.132 \pm 0.011 \pm 0.007$, where the first uncertainty is statistical and the second is systematic. This measurement is an update of an earlier study exploiting additional tagging modes, including several decay modes involving a $K^0_L$ meson. The branching fractions of the $K^0_L$ modes are determined as input to the analysis in a manner that is independent of any strong phase uncertainty. Using the predominantly $C\!P$-even tag $D\to π^+π^-π^0$ and the ensemble of $C\!P$-odd eigenstate tags, the observable ${\cal A}_{Kπ}^{πππ^0}$ is measured to be $0.130 \pm 0.012 \pm 0.008$. The two asymmetries are sensitive to $r_D^{Kπ} \cos δ_D^{Kπ}$, where $r_D^{Kπ}$ and $δ_D^{Kπ}$ are the ratio of amplitudes and phase difference, respectively, between the doubly Cabibbo-suppressed and Cabibbo-favoured decays. In addition, events containing $D \to K^-π^+$ tagged by $D \to K^0_{S,L} π^+π^-$ are studied in bins of phase space of the three-body decays. This analysis has sensitivity to both $r_D^{Kπ} \cos δ_D^{Kπ}$ and $r_D^{Kπ} \sin δ_D^{Kπ}$. A fit to ${\cal A}_{Kπ}$, ${\cal A}_{Kπ}^{πππ^0}$ and the phase-space distribution of the $D \to K^0_{S,L} π^+π^-$ tags yields $δ_D^{Kπ}= \left( 187.6 {^{+8.9}_{-9.7}}{^{+5.4}_{-6.4}} \right)$ degrees, where external constraints are applied for $r_D^{Kπ}$ and other relevant parameters. This is the most precise measurement of $δ_D^{Kπ}$ in quantum-correlated $D\bar{D}$ decays.

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arXiv2022

Study of Exclusive $B \to πe^+ ν_e$ Decays with Hadronic Full-event-interpretation Tagging in 189.3 fb$^{-1}$ of Belle II Data

We present a reconstruction of the semileptonic decays $B^0 \to π^- e^+ ν_e$ and $B^+ \to π^0 e^+ ν_e$ in a sample corresponding to 189.3 fb$^{-1}$ of Belle II data, using events where the partner $B$-meson is reconstructed from a large variety of hadronic channels via a tagging algorithm known as the full-event-interpretation. We determine the partial branching fractions in three bins of the squared momentum transfer to the leptonic system using fits to the distribution of the square of the missing mass. The partial branching fractions are summed to determine $\mathcal{B}(B^0 \to π^- e^+ ν_e)$ = (1.43 $\pm$ 0.27(stat) $\pm$ 0.07(syst)) $\times 10^{-4}$ and $\mathcal{B}(B^+ \to π^0 e^+ ν_e)$ = (8.33 $\pm$ 1.67(stat) $\pm$ 0.55(syst)) $\times 10^{-5}$. We extract a first Belle II measurement of the magnitude of the Cabibbo-Kobayashi-Maskawa matrix element $|V_{\mathrm{ub}}|$, with $|V_{\mathrm{ub}}|$ = (3.88 $\pm$ 0.45) $\times 10^{-3}$.

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arXiv2022

Measurement of the branching fraction for the decay $B \to K^{\ast}(892)\ell^+\ell^-$ at Belle II

We report a measurement of the branching fraction of $B \to K^{\ast}(892)\ell^+\ell^-$ decays, where $\ell^+\ell^- = μ^+μ^-$ or $e^+e^-$, using electron-positron collisions recorded at an energy at or near the $Υ(4S)$ mass and corresponding to an integrated luminosity of $189$ fb$^{-1}$. The data was collected during 2019--2021 by the Belle II experiment at the SuperKEKB $e^{+}e^{-}$ asymmetric-energy collider. We reconstruct $K^{\ast}(892)$ candidates in the $K^+π^-$, $K_{S}^{0}π^+$, and $K^+π^0$ final states. The signal yields with statistical uncertainties are $22\pm 6$, $18 \pm 6$, and $38 \pm 9$ for the decays $B \to K^{\ast}(892)μ^+μ^-$, $B \to K^{\ast}(892)e^+e^-$, and $B \to K^{\ast}(892)\ell^+\ell^-$, respectively. We measure the branching fractions of these decays for the entire range of the dilepton mass, excluding the very low mass region to suppress the $B \to K^{\ast}(892)γ(\to e^+e^-)$ background and regions compatible with decays of charmonium resonances, to be \begin{equation} {\cal B}(B \to K^{\ast}(892)μ^+μ^-) = (1.19 \pm 0.31 ^{+0.08}_{-0.07}) \times 10^{-6}, {\cal B}(B \to K^{\ast}(892)e^+e^-) = (1.42 \pm 0.48 \pm 0.09)\times 10^{-6}, {\cal B}(B \to K^{\ast}(892)\ell^+\ell^-) = (1.25 \pm 0.30 ^{+0.08}_{-0.07}) \times 10^{-6}, \end{equation} where the first and second uncertainties are statistical and systematic, respectively. These results, limited by sample size, are the first measurements of $B \to K^{\ast}(892)\ell^+\ell^-$ branching fractions from the Belle II experiment.

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arXiv2022

Measurement of the branching fractions and $CP$ asymmetries of $B^+ \rightarrow π^+ π^0$ and $B^+ \rightarrow K^+ π^0$ decays in 2019-2021 Belle II data

We determine the branching fractions ${\mathcal{B}}$ and $CP$ asymmetries ${\mathcal{A}_{\it CP}}$ of the decays $B^+ \rightarrow π^+ π^0$ and $B^+ \rightarrow K^+ π^0$. The results are based on a data set containing 198 million bottom-antibottom meson pairs corresponding to an integrated luminosity of $190\;\text{fb}^{-1}$ recorded by the Belle II detector in energy-asymmetric electron-positron collisions at the $Υ(4S)$ resonance. We measure ${\mathcal{B}(B^+ \rightarrow π^+ π^0) = (6.12 \pm 0.53 \pm 0.53)\times 10^{-6}}$, ${\mathcal{B}(B^+ \rightarrow K^+ π^0) = (14.30 \pm 0.69 \pm 0.79)\times 10^{-6}}$, ${\mathcal{A}_{\it CP}(B^+ \rightarrow π^+ π^0) = -0.085 \pm 0.085 \pm 0.019}$, and ${\mathcal{A}_{\it CP}(B^+ \rightarrow K^+ π^0) = 0.014 \pm 0.047 \pm 0.010}$, where the first uncertainties are statistical and the second are systematic. These results improve a previous Belle II measurement and agree with the world averages.

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arXiv2022

Observation of resonance structures in $e^+e^-\to π^+π^-ψ_2(3823)$ and mass measurement of $ψ_2(3823)$

Using a data sample corresponding to an integrated luminosity of 11.3 $\rm fb^{-1}$ collected at center-of-mass energies from $4.23$ to $4.70$ GeV with the BESIII detector, we measure the product of the $e^+e^-\to π^+π^-ψ_2(3823)$ cross section and the branching fraction $\mathcal{B}[ψ_2(3823)\to γχ_{c1}]$. For the first time, resonance structure is observed in the cross section line shape of $e^+e^-\to π^+π^-ψ_2(3823)$ with significances exceeding $5σ$. A fit to data with two coherent Breit-Wigner resonances modeling the $\sqrt{s}$-dependent cross section yields $M(R_1)=4406.9\pm 17.2\pm 4.5$ MeV/$c^2$, $Γ(R_1)=128.1\pm 37.2\pm 2.3$ MeV, and $M(R_2)=4647.9\pm 8.6\pm 0.8$ MeV/$c^2$, $Γ(R_2)=33.1\pm 18.6\pm 4.1$ MeV. Though weakly disfavored by the data, a single resonance with $M(R)=4417.5\pm26.2\pm3.5$ MeV/$c^2$, $Γ(R)=245\pm48\pm13$ MeV is also possible to interpret data. This observation deepens our understanding of the nature of the vector charmoniumlike states. The mass of the $ψ_2(3823)$ state is measured as $(3823.12\pm 0.43\pm 0.13)$ MeV/$c^2$, which is the most precise measurement to date.

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arXiv2022

Observation of the doubly Cabibbo-Suppressed decays $D^+\to K^+π^0π^0$ and $D^+\to K^+π^0η$

By analyzing $e^+e^-$ annihilation data corresponding to an integrated luminosity of $2.93\,\rm fb^{-1}$ collected at the center-of-mass energy of 3.773\,GeV with the BESIII detector, we report the first observations of the doubly Cabibbo-suppressed decays $D^+\to K^+π^0π^0$ and $D^+\to K^+π^0η$. The branching fractions of $D^+\to K^+π^0π^0$ and $D^+\to K^+π^0η$ are measured to be $(2.1 \pm 0.4_{\rm stat} \pm 0.1_{\rm syst})\times 10^{-4}$ and $(2.1 \pm 0.5_{\rm stat} \pm 0.1_{\rm syst})\times 10^{-4}$ with statistical significances of 8.8$σ$ and 5.5$σ$, respectively. In addition, we search for the subprocesses $D^+\to K^{*}(892)^{+}π^0$ and $D^+\to K^{*}(892)^{+}η$ with $K^{*}(892)^+\to K^+π^0$. The branching fraction of $D^+\to K^{*}(892)^{+}η$ is determined to be $({4.4^{+1.8}_{-1.5}}_{\rm stat}\pm0.2_{\rm syst})\times10^{-4}$, with a statistical significance of 3.2$σ$. No significant signal for $D^+\to K^{*}(892)^{+}π^0$ is found and we set an upper limit on the branching fraction of this decay at the 90\% confidence level to be $5.4\times10^{-4}$.

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arXiv2022

Observation of $η_c(2S) \to 3(π^+π^-)$ and measurements of $χ_{cJ} \to 3(π^+π^-)$ in $ψ(3686)$ radiative transitions

The hadronic decay $η_c(2S) \to 3(π^+π^-)$ is observed with a statistical significance of 9.3 standard deviations using $(448.1\pm2.9)\times10^6$ $ψ(3686)$ events collected by the BESIII detector at the BEPCII collider. The measured mass and width of $η_c(2S)$ are $(3643.4 \pm 2.3 (\rm stat.) \pm 4.4 (\rm syst.))$ MeV/$c^2$ and $(19.8 \pm 3.9 (\rm stat.) \pm 3.1 (\rm syst.))$ MeV, respectively, which are consistent with the world average values within two standard deviations. The product branching fraction $\mathcal{B}[ψ(3686)\to γη_c(2S)]\times\mathcal{B}[η_c(2S)\to3(π^+π^-)]$ is measured to be $(9.2 \pm 1.0 (\rm stat.) \pm 0.9 (\rm syst.))\times10^{-6}$. Using $\mathcal{B}[ψ(3686)\to γη_c(2S)]=(7.0^{+3.4}_{-2.5})\times10^{-4}$, we obtain $\mathcal{B}[η_c(2S) \to 3(π^+π^-)] = (1.31 \pm 0.15 (\rm stat.) \pm 0.13 (\rm syst.)(^{+0.64}_{-0.47}) (\rm extr))\times10^{-2}$, where the third uncertainty is from $\mathcal{B}[ψ(3686) \to γη_c(2S)]$. We also measure the $χ_{cJ} \to 3(π^+π^-)$ ($J=0, 1, 2$) decays via $ψ(3686) \to γχ_{cJ}$ transitions. The branching fractions are $\mathcal{B}[χ_{c0} \to 3(π^+π^-)] = (2.080\pm0.006 (\rm stat.)\pm0.068 (\rm syst.))\times10^{-2}$, $\mathcal{B}[χ_{c1} \to 3(π^+π^-)] = (1.092\pm0.004 (\rm stat.)\pm0.035 (\rm syst.))\times10^{-2}$, and $\mathcal{B}[χ_{c2} \to 3(π^+π^-)] = (1.565\pm0.005 (\rm stat.)\pm0.048 (\rm syst.))\times10^{-2}$.

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arXiv2022

Measurement of the $C\!P$-even fraction of $D^{0}\toπ^{+}π^{-}π^{+}π^{-}$

A measurement of the $C\!P$-even fraction of the decay $D^{0}\toπ^{+}π^{-}π^{+}π^{-}$ is performed with a quantum-correlated $ψ(3770)\to D\bar{D}$ data sample collected by the BESIII experiment, corresponding to an integrated luminosity of 2.93 $\textrm{fb}^{-1}$. Using a combination of $C\!P$ eigenstates, $D \to π^+π^-π^0$ and $D \to K_{S,L}^0π^{+}π^{-}$ as tagging modes, the $C\!P$-even fraction is measured to be $F_{+}^{4π} = 0.735 \pm 0.015 \pm 0.005$, where the first uncertainty is statistical and the second is systematic. This is the most precise determination of this quantity to date. It provides valuable model-independent input for the measurement of the CKM angle $γ$ with $B^\pm\to D K^\pm$ decays, and for time-dependent studies of $C\!P$ violation and mixing in the $D^{0}$-$\bar{D}^{0}$ system.

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arXiv2022

Amplitude analysis and branching fraction measurement of the decay $D_{s}^{+} \to K^+π^+π^-$

Using $6.32$ fb$^{-1}$ of $e^{+}e^{-}$ collision data collected at the center-of-mass energies between 4.178 and 4.226 GeV with the BESIII detector, we perform an amplitude analysis of the decay $D^+_s \to K^+π^+π^-$ and determine the amplitudes of the various intermediate states. The absolute branching fraction of $D^+_s\to K^+π^+π^-$ is measured to be ($6.11\pm0.18_{\rm stat.}\pm0.11_{\rm syst.})\times 10^{-3}$. The branching fractions of the dominant intermediate processes $D_{s}^{+} \to K^+ρ^0, ρ^0 \to π^+π^-$ and $D_{s}^{+} \to K^*(892)^0π^+, K^*(892)^0 \to K^+π^-$ are determined to be $(1.96\pm0.19_{\rm stat.}\pm0.23_{\rm syst.})\times 10^{-3}$ and $(1.85\pm0.12_{\rm stat.}\pm0.13_{\rm syst.})\times 10^{-3}$, respectively. The intermediate resonances $f_0(500)$, $f_0(980)$, and $f_0(1370)$ are observed for the first time in this channel.

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arXiv2022

Study of the resonance structures in $e^{+}e^{-} \rightarrow π^{+}π^{-}J/ψ$ process

Using about 23 $\mathrm{fb^{-1}}$ of data collected with the BESIII detector operating at the BEPCII storage ring, a precise measurement of the $e^{+}e^{-} \rightarrow π^{+}π^{-}J/ψ$ Born cross section is performed at center-of-mass energies from 3.7730 to 4.7008 GeV. Two structures, identified as the $Y(4220)$ and the $Y(4320)$ states, are observed in the energy-dependent cross section with a significance larger than $10σ$. The masses and widths of the two structures are determined to be ($M, Γ$) = ($4221.4\pm1.5\pm2.0$ MeV/$c^{2}$, $41.8\pm2.9\pm2.7$ MeV) and ($M, Γ$) = ($4298\pm12\pm26$ MeV/$c^{2}$, $127\pm17\pm10$ MeV), respectively. A small enhancement around 4.5 GeV with a significance about $3σ$, compatible with the $ψ(4415)$, might also indicate the presence of an additional resonance in the spectrum. The inclusion of this additional contribution in the fit to the cross section affects the resonance parameters of the $Y(4320)$ state.

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arXiv2022

Measurement of Branching Fraction and Longitudinal Polarization in $B^0 \to ρ^+ ρ^-$ Decays at Belle II

We present a measurement of the branching fraction and longitudinal polarization of $B^0 \to ρ^+ ρ^-$ decays. SuperKEKB electron-positron collision data corresponding to 189~fb$^{-1}$ of integrated luminosity and containing $198 \times 10^6 B\bar{B}$ pairs collected with the Belle II detector are used. We obtain \begin{eqnarray*} \mathcal{B}(B^0\toρ^+ρ^-) &=& [2.67\pm0.28\,(\mathrm{stat})\,\pm0.28\,(\mathrm{syst})] \times 10^{-5}, \end{eqnarray*} \begin{eqnarray*} f_L &=& 0.956\pm0.035\,(\mathrm{stat})\,\pm 0.033\,(\mathrm{syst}), \end{eqnarray*} These results are consistent with previous measurements and can be used to constrain penguin pollution and to extract the quark-mixing angle $ϕ_2$.

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