arXiv subjects

M. Destefanis

Publications and source records attributed to M. Destefanis.

At least 505 records · Page 28Linked to original sources

arXiv2023

Measurement of the branching fraction and $\it CP$ asymmetry of $B^{0} \rightarrow π^{0} π^{0}$ decays using $198 \times 10^6$ $B\overline{B}$ pairs in Belle II data

We report measurements of the branching fraction and $\it CP$ asymmetry in $B^{0} \to π^{0} π^{0}$ decays reconstructed at Belle II in an electron-positron collision sample containing $198 \times 10^{6}$ $B\overline{B}$ pairs. We measure a branching fraction $\mathcal{B}(\Bpipi) = (1.38 \pm 0.27 \pm 0.22) \times 10^{-6}$ and a $\it CP$ asymmetry $\Acp(\Bpipi) = 0.14 \pm 0.46 \pm 0.07$, where the first uncertainty is statistical and the second is systematic.

hep-ex↗

arXiv2023

A test of light-lepton universality in the rates of inclusive semileptonic $B$-meson decays at Belle II

We present the first measurement of the ratio of branching fractions of inclusive semileptonic $B$-meson decays, $R(X_{e/μ}) = \mathcal{B}(B\to X \, e \, ν) / \mathcal{B}(B\to X \, μ\, ν)$, a precision test of electron-muon universality, using data corresponding to $189\,\mathrm{fb}^{-1}$ from electron-positron collisions collected with the Belle II detector. In events where the partner $B$ meson is fully reconstructed, we use fits to the lepton momentum spectra above $1.3\,\mathrm{GeV}/c$ to obtain $R(X_{e/μ}) = 1.007 \pm 0.009~(\mathrm{stat}) \pm 0.019~(\mathrm{syst})$, which is the most precise lepton-universality test of its kind and agrees with the standard-model expectation.

hep-ex↗

arXiv2023

Determination of spin and parity of $D^{*}_{(s)}$ mesons

The spin and parity of the charmed mesons $D_{s}^{*+}$, $D^{*0}$ and $D^{*+}$ are determined for the first time to be $J^P=1^{-}$ with significances greater than 10$σ$ over other hypotheses of $2^{+}$ and $3^{-}$, using an $e^+e^-$ collision data sample with an integrated luminosity of 3.19 fb$^{-1}$ collected by the BESIII detector at a center-of-mass energy of 4.178 GeV. Different spin-parity hypotheses for $D_{s}^{*+}$, $D^{*0}$, and $D^{*+}$ mesons are tested via a helicity amplitude analysis of the processes $e^+e^-\to D^{*+}_{s}D^{-}_{s}$, $D^{*0}D^{0}$ and $D^{*+}D^{-}$, with $D^{*+}_{s}\to D^{+}_{s} γ$, $D^{*0}\to D^{0}π^{0}$, and $D^{*+}\to D^{+}π^{0}$. The results confirm the quark model predictions.

hep-ex↗

arXiv2023

Precision Measurement of the Decay $Σ^{+} \rightarrow pγ$ in the Process $J/ψ\rightarrow Σ^{+}\barΣ^{-}$

Using $(10\:087\pm44)\times10^{6}$ $J/ψ$ events collected with the BESIII detector, the radiative hyperon decay $Σ\rightarrow pγ$ is studied at an electron-positron collider experiment for the first time. The absolute branching fraction is measured to be $\left(0.996 \pm 0.021_{\rm stat.}\pm 0.018_{\rm syst.}\right)\times 10^{-3}$, which is lower than its world average value by $4.2$ standard deviations. Its decay asymmetry parameter is determined to be $-0.652 \pm 0.056_{\rm stat.}\pm 0.020_{\rm syst.}$. The branching fraction and decay asymmetry parameter are the most precise to date, and the accuracies are improved by $78\%$ and $34\%$, respectively.

hep-ex↗

arXiv2023

Precision measurement of the matrix elements for $η\toπ^+π^-π^0$ and $η\toπ^0π^0π^0$ decays

A precision measurement of the matrix elements for $η\toπ^+π^-π^0$ and $η\toπ^0π^0π^0$ decays is performed using a sample of $(10087\pm44)\times10^6$ $J/ψ$ decays collected with the BESIII detector. The decay $J/ψ\to γη$ is used to select clean samples of 631,686 $η\toπ^+π^-π^0$ decays and 272,322 $η\toπ^0π^0π^0$ decays. The matrix elements for both channels are in reasonable agreement with previous measurements. The non-zero $gX^2Y$ term for the decay mode $η\toπ^+π^-π^0$ is confirmed, as reported by the KLOE Collaboration, while the other higher-order terms are found to be insignificant. Dalitz plot asymmetries in the $η\toπ^+π^-π^0$ decay are also explored and are found to be consistent with charge conjugation invariance. In addition, a cusp effect is investigated in the $η\toπ^0π^0π^0$ decay, and no obvious structure around the $π^+π^-$ mass threshold is observed.

hep-ex↗

arXiv2023

Search for baryon and lepton number violating decays of $Ξ^{0}$ hyperons

Using $(1.0087\pm0.0044)\times10^{10}$ $J/ψ$ events collected by the BESIII detector at the BEPCII collider, we report the first search for the baryon and lepton number violating decays $Ξ^{0} \rightarrow K^{-} e^{+}$ with $Δ(B-L)=0$ and $Ξ^{0} \rightarrow K^{+} e^{-}$ with $|Δ(B-L)|=2$, where $B$ ($L$) is the baryon (lepton) number. While no signal is observed, the upper limits on the branching fractions of these two decays are set to $\mathcal B(Ξ^{0} \rightarrow K^{-} e^{+})<3.6\times10^{-6}$ and $\mathcal B(Ξ^{0} \rightarrow K^{+} e^{-})<1.9\times10^{-6}$ at the 90\% confidence level, respectively. These results offer a direct probe of baryon number violating interactions involving a strange quark.

hep-ex↗

arXiv2023

Determination of the $C\!P$-even fraction of $D^0\rightarrow K_S^0π^+π^-π^0$

Quantum-correlated $D\bar{D}$ pairs collected by the BESIII experiment at the $ψ(3770)$ resonance, corresponding to an integrated luminosity of 2.93 fb$^{-1}$, are used to study the $D^0 \rightarrow K^{0}_Sπ^{+} π^{-} π^{0}$ decay mode. The $C\!P$-even fraction of $D^0 \rightarrow K^{0}_Sπ^{+} π^{-} π^{0}$ decays is determined to be $0.235\pm 0.010\pm 0.002$, where the first uncertainty is statistical and the second is systematic.

hep-ex↗

arXiv2023

Search for Lepton-Flavor-Violating $τ$ Decays to a Lepton and an Invisible Boson at Belle II

We search for lepton-flavor-violating $τ^-\to e^-α$ and $τ^-\toμ^-α$ decays, where $α$ is an invisible spin-0 boson. The search uses electron-positron collisions at $10.58$ GeV center-of-mass energy with an integrated luminosity of $62.8$ fb$^{-1}$, produced by the SuperKEKB collider and collected with the Belle II detector. We search for an excess in the lepton-energy spectrum of the known $τ^-\to e^-\barν_e ν_τ$ and $τ^-\to μ^-\barν_μν_τ$ decays. We report 95\% confidence-level upper limits on the branching-fraction ratio ${\mathcal B}(τ^-\to e^- α) / {\mathcal B}(τ^- \to e^- \barν_e ν_τ)$ in the range $(1.1-9.7) \times 10^{-3}$ and on ${\mathcal B}(τ^-\to μ^- α) / {\mathcal B}(τ^- \to μ^- \barν_μν_τ)$ in the range $(0.7-12.2) \times 10^{-3}$ for $α$ masses between 0 and 1.6 GeV/c$^2$. These results provide the most stringent bounds on invisible boson production from $τ$ decays.

hep-ex↗

arXiv2023

Test of $C\!P$ Symmetry in Hyperon to Neutron Decays

The quantum entangled $J/ψ\to Σ^{+}\barΣ^{-}$ pairs from $(1.0087\pm0.0044)\times10^{10}$ $J/ψ$ events taken by the BESIII detector are used to study the non-leptonic two-body weak decays $Σ^{+} \to n π^{+}$ and $\barΣ^{-} \to \bar{n} π^{-}$. The $C\!P$-odd weak decay parameters of the decays $Σ^{+} \to n π^{+}$ ($α_{+}$) and $\barΣ^{-} \to \bar{n} π^{-}$ ($\barα_{-}$) are determined to be $-0.0565\pm0.0047_{\rm stat}\pm0.0022_{\rm syst}$ and $0.0481\pm0.0031_{\rm stat}\pm0.0019_{\rm syst}$, respectively. The decay parameter $\barα_{-}$ is measured for the first time, and the accuracy of $α_{+}$ is improved by a factor of four compared to the previous results. The simultaneously determined decay parameters allow the first precision $C\!P$ symmetry test for any hyperon decay with a neutron in the final state with the measurement of $A_{C\!P}=(α_{+}+\barα_{-})/(α_{+}-\barα_{-})=-0.080\pm0.052_{\rm stat}\pm0.028_{\rm syst}$. Assuming $C\!P$ conservation, the average decay parameter is determined as $\left< α_{+}\right>=(α_{+}- \barα_{-})/2 = -0.0506\pm0.0026_{\rm stat}\pm0.0019_{\rm syst}$, while the ratios $α_{+}/α_{0}$ and $\barα_{-}/\barα_{0}$ are $-0.0490\pm0.0032_{\rm stat}\pm0.0021_{\rm syst}$ and $-0.0571\pm0.0053_{\rm stat}\pm0.0032_{\rm syst}$, where $α_{0}$ and $\barα_{0}$ are the decay parameters of the decays $Σ^{+} \to p π^{0}$ and $\barΣ^{-} \to \bar{p} π^{0}$, respectively.

hep-ex↗

arXiv2023

Measurement of $e^+ e^- \rightarrow ϕη^{\prime}$ cross sections at center-of-mass energies between 3.508 and 4.600 GeV

We present a measurement of the dressed cross sections for $e^+ e^- \rightarrow ϕη^{\prime}$ at different center-of-mass energies between 3.508 and 4.600 GeV based on 15.1 fb$^{-1}$ of $e^+ e^-$ annihilation data collected with the BESIII detector operating at the BEPCII collider. In addition, a search for the decay $Y(4230) \to ϕη^{\prime}$ is performed. No clear signal is observed and the corresponding upper limit is provided.

hep-ex↗

arXiv2023

First Experimental Study of the Purely Leptonic Decay $D_s^{*+}\to e^+ν_e$

Using $7.33~\mathrm{fb}^{-1}$ of $e^+e^-$ collision data taken with the BESIII detector at the BEPCII collider, we report the first experimental study of the purely leptonic decay $D_s^{*+}\to e^+ν_e$. A signal for the decay $D_s^{*+}\to e^+ν_e$ is observed with a statistical significance of $2.9σ$. The branching fraction of ${D_s^{*+}\to e^+ν_e}$ is measured to be $(2.1{^{+1.2}_{-0.9}}_{\rm stat.}\pm0.2_{\rm syst.})\times 10^{-5}$, corresponding to an upper limit of $4.0\times10^{-5}$ at the 90\% confidence level. Taking the total width of the $D_s^{*+}$~(($0.070\pm0.028$) keV) predicted by lattice quantum chromodynamics as input, the decay constant of the $D^{*+}_s$ is determined to be $f_{D_s^{*+}}=(213.6{^{+61.0}_{-45.8}}_{\rm stat.}\pm43.9_{\rm syst.})$ MeV, corresponding to an upper limit of 353.8 MeV at the 90\% confidence level.

hep-ex↗

arXiv2023

Measurement of Branching Fractions of Singly Cabibbo-suppressed Decays $Λ_c^+ \rightarrow Σ^{0} K^+$ and $Σ^{+} K_{S}^0$

Based on a sample of 4.4 $\mathrm{fb}^{-1}$ of $e^{+}e^{-}$ annihilation data collected in the energy region between 4.6 GeV and 4.7 GeV with the BESIII detector at BEPCII, two singly Cabibbo-suppressed decays $Λ_c^+ \rightarrow Σ^0 K^+$ and $Λ_{c}^{+} \rightarrow Σ^+ K_{S}^0$ are studied. The ratio of the branching fraction $\mathcal{B}(Λ_c^+ \rightarrow Σ^0 K^+)$ relative to $\mathcal{B}(Λ_c^+ \rightarrow Σ^0 π^+)$ is measured to be $0.0361 \pm 0.0073(\mathrm{stat.}) \pm 0.0005(\mathrm{syst.})$, and the ratio of $\mathcal{B}(Λ_c^+ \rightarrow Σ^+ K_{S}^0)$ relative to $\mathcal{B}(Λ_{c}^{+} \rightarrow Σ^+ π^+ π^-)$ is measured to be $0.0106 \pm 0.0031(\mathrm{stat.}) \pm 0.0004(\mathrm{syst.})$. After taking the world-average branching fractions of the reference decay channels, the branching fractions $\mathcal{B}(Λ_c^+ \rightarrow Σ^0 K^+)$ and $\mathcal{B}(Λ_{c}^{+} \rightarrow Σ^+ K_{S}^0)$ are determined to be $(4.7\pm 0.9(\mathrm{stat.})\pm 0.1(\mathrm{syst.}) \pm 0.3(\mathrm{ref.}))\times10^{-4}$ and $(4.8\pm 1.4(\mathrm{stat.})\pm 0.2(\mathrm{syst.}) \pm 0.3(\mathrm{ref.}))\times10^{-4}$, respectively. The branching fraction of the $Λ_{c}^{+} \rightarrow Σ^+ K_{S}^0$ decay is measured for the first time.

hep-ex↗

arXiv2023

Observation of the decay $χ_{cJ} \to Ω^- \barΩ^+$

Using an $e^+e^-$ collision data sample of $(27.08 \pm 0.14) \times 10^{8}$ $ψ(3686)$ events collected by the BESIII detector, we report the first observation of $χ_{cJ} \to Ω^- \barΩ^+$ ($J=0,\,1,\,2$) decays with significances of $5.6σ$, $6.4σ$, and $18σ$, respectively, where the $χ_{cJ}$ mesons are produced in the radiative $ψ(3686)$ decays. The branching fractions are determined to be $\mathcal{B}(χ_{c0} \to Ω^- \barΩ^+) = (3.51 \pm 0.54 \pm 0.29) \times 10^{-5}$, $\mathcal{B}(χ_{c1} \to Ω^- \barΩ^+) = (1.49 \pm 0.23 \pm 0.10) \times 10^{-5}$, and $\mathcal{B}(χ_{c2} \to Ω^- \barΩ^+) = (4.52 \pm 0.24 \pm 0.18) \times 10^{-5}$, where the first and second uncertainties are statistical and systematic, respectively.

hep-ex↗

arXiv2023

Evidence for $η_c$(2S)$\to\pipieta$ decay

The decay $η_c(2S)\to\pipieta$ is searched for through the radiative transition $ψ(3686) \toγη_c(2S)$ using 448 million $ψ$(3686) events accumulated at the BESIII detector. The first evidence of $η_c(2S)\toπ^+π^-η$ is found with a statistical significance of 3.5$σ$. The product of the branching fractions of $ψ(3686)\toγη_c(2S)$ and $η_c(2S)\to\pipieta$ is measured to be $Br(ψ(3686)\toγη_c(2S))\times Br(η_c(2S)\to\pipieta)=(2.97\pm0.81\pm0.26)\times10^{-6}$, where the first uncertainty is statistical and the second one is systematic. The branching fraction of the decay $η_c(2S)\to\pipieta$ is determined to be $Br(η_c(2S)\to\pipieta)=(42.4\pm11.6\pm3.8\pm30.3)\times10^{-4}$, where the third uncertainty is transferred from the uncertainty of the branching fraction of $ψ(3686)\toγη_c(2S)$.

hep-ex↗

arXiv2023

Cross section measurements of $e^+e^- \to ΦK^+ K^-$ and $e^+ e^- \to ΦK_S^0 K_S^0$ at center-of-mass energies between 3.7730 GeV and 4.7008 GeV

Based on 22.7 fb$^{-1}$ of $e^+e^-$ annihilation data collected at 33 different center-of-mass energies between 3.7730 GeV and 4.7008 GeV with the BESIII detector at the BEPCII collider, Born cross sections of the two processes $e^+e^-\to ϕK^+ K^-$ and $e^+ e^- \to ϕK_{S}^{0} K_{S}^{0}$ are measured for the first time. No indication of resonant production through an intermediate vector state $V$ is observed, and the upper limits on the product of the electronic width $Γ_{e^+e^-}$ and the branching fraction $Br(V\rightarrow ϕK \bar{K})$ of the processes $e^+e^- \to V \to ϕK^+ K^-$ and $e^+e^- \to V \to ϕK_S^0K_S^0$ at the $90\%$ confidence level are obtained for a large parameter space in resonance masses and widths. For the current world average mass and width of the $ψ(4230)$ of $m=4.2187$ GeV$/c^2$ and $Γ=44$ MeV, we set upper limits on the $ϕK^+ K^-$ and $ϕK_S^0K_S^0$ final states of 1.75 eV and 0.47 eV at the $90\%$ confidence level, respectively.

hep-ex↗

arXiv2023

Observation of a New $X(3872)$ Production Process $e^+e^-\toωX(3872)$

Using $4.7~\rm fb^{-1}$ of $e^+e^-$ collision data at center-of-mass energies from 4.661 to 4.951 GeV collected by the BESIII detector at the BEPCII collider, we observe the $X(3872)$ production process $e^{+}e^{-}\toωX(3872)$ for the first time. The significance is $7.8σ$, including both the statistical and systematic uncertainties. The $e^+e^-\toωX(3872)$ Born cross section and the corresponding upper limit at 90\% confidence level at each energy point are reported. The line shape of the cross section indicates that the $ωX(3872)$ signals may be from the decays of some non-trivial structures.

hep-ex↗

arXiv2023

Novel method for the identification of the production flavor of neutral charmed mesons

We propose a new algorithm for the identification of the production flavor of neutral $D$ mesons in the Belle II experiment. The algorithm exploits the correlation between the flavor of a reconstructed neutral $D$ meson (signal $D$ meson) and the electric charges of particles reconstructed in the rest of the $e^+e^-\to c \bar{c}$ event. These include those originating from the decay of the other charm hadron produced in the event, as well as those possibly produced in association with the signal $D$ meson. We develop the algorithm using simulation and calibrate it in data using decay modes that identify the flavor of the decaying neutral $D$ meson. We use a data sample of $e^+e^-$ collisions, corresponding to $362\,\mathrm{fb}^{-1}$ of integrated luminosity, collected by Belle II at center-of-mass energies near the $Υ(4S)$ mass. The effective tagging efficiency in data is $(47.91 \pm 0.07 \mathrm{(stat)} \pm 0.51 \mathrm{(syst)})\%$, independent of the neutral-$D$-meson decay mode. This charm flavor tagger will approximately double the effective sample size of many $CP$-violation and charm-mixing measurements that so far have exclusively relied on neutral $D$ mesons originating from $D^{*\pm}$ decays. While developed for Belle II, the basic principles underlying the charm flavor tagger can be used in other experiments, including those at hadron colliders.

hep-ex↗

arXiv2023

Search for an axion-like particle in radiative $J/ψ$ decays

We search for an axion-like particle (ALP) $a$ through the process $ψ(3686)\rightarrowπ^+π^-J/ψ$, $J/ψ\rightarrowγa$, $a\rightarrowγγ$ in a data sample of $(2.71\pm0.01)\times10^9$ $ψ(3686)$ events collected by the BESIII detector. No significant ALP signal is observed over the expected background, and the upper limits on the branching fraction of the decay $J/ψ\rightarrowγa$ and the ALP-photon coupling constant $g_{aγγ}$ are set at 95% confidence level in the mass range of $0.165\leq m_a\leq2.84\,\mbox{GeV}/c^2$. The limits on $B(J/ψ\rightarrowγa)$ range from $8.3\times10^{-8}$ to $1.8\times10^{-6}$ over the search region, and the constraints on the ALP-photon coupling are the most stringent to date for $0.165\leq m_a\leq1.468\,\mbox{GeV}/c^2$.

hep-ex↗