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M. Dorigo

Publications and source records attributed to M. Dorigo.

At least 91 records · Page 5Linked to original sources
arXiv2023

Tests of light-lepton universality in angular asymmetries of $B^0 \to D^{*-} \ell ν$ decays

We present the first comprehensive tests of light-lepton universality in the angular distributions of semileptonic $B^0$-meson decays to charged spin-1 charmed mesons. We measure five angular-asymmetry observables as functions of the decay recoil that are sensitive to lepton-universality-violating contributions. We use events where one neutral $B$ is fully reconstructed in $Υ\left(4S\right)\to{}B \overline{B}$ decays in data corresponding to $189~\mathrm{fb}^{-1}$ integrated luminosity from electron-positron collisions collected with the Belle II detector. We find no significant deviation from the standard model expectations.

hep-ex↗
arXiv2023

Measurement of $CP$ asymmetries in $B^0\to ϕK^0_S$ decays with Belle II

We present a measurement of time-dependent rate asymmetries in $B^0\to ϕK^0_S$ decays to search for non-standard-model physics in $b\to q \overline{q}s$ transitions. The data sample is collected with the Belle II detector at the SuperKEKB asymmetric-energy $e^{+}e^{-}$ collider in 2019-2022 and contains $(387\pm 6)\times 10^6$ bottom-antibottom mesons from $Υ(4S)$ resonance decays. We reconstruct $162\pm17$ signal events and extract the charge-parity ($CP$) violating parameters from a fit to the distribution of the proper-decay-time difference of the two $B$ mesons. The measured direct and mixing-induced $CP$ asymmetries are $A=0.31\pm0.20\pm0.05$ and $S=0.54\pm0.26^{+0.06}_{-0.08}$, respectively, where the first uncertainties are statistical and the second are systematic. The results are compatible with the $CP$ asymmetries observed in $b\to c\overline{c} s$ transitions.

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arXiv2023

Measurement of $C\!P$ asymmetries and branching-fraction ratios for $B^\pm \to DK^\pm$ and $Dπ^\pm$ with $D\to K^0_{\rm S} K^\pmπ^\mp$ using Belle and Belle II data

We measure $C\!P$ asymmetries and branching-fraction ratios for $B^\pm \to DK^\pm$ and $Dπ^\pm$ decays with $D\to K^0_{\rm S} K^\pmπ^\mp$, where $D$ is a superposition of $D^0$ and $\bar{D}^0$. We use the full data set of the Belle experiment, containing $772\times 10^6~B\bar{B}$ pairs, and data from the Belle~II experiment, containing $387\times 10^6~B\bar{B}$ pairs, both collected in electron-positron collisions at the $Υ(4S)$ resonance. Our results provide model-independent information on the unitarity triangle angle $ϕ_3$.

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arXiv2023

Search for a $τ^+τ^-$ resonance in $e^{+}e^{-}\rightarrow μ^{+}μ^{-} τ^+τ^-$ events with the Belle II experiment

We report the first search for a non-standard-model resonance decaying into $τ$ pairs in $e^{+}e^{-}\rightarrow μ^{+}μ^{-} τ^+τ^-$ events in the 3.6-10 GeV/$c^{2}$ mass range. We use a 62.8 fb$^{-1}$ sample of $e^+e^-$ collisions collected at a center-of-mass energy of 10.58 GeV by the Belle II experiment at the SuperKEKB collider. The analysis probes three different models predicting a spin-1 particle coupling only to the heavier lepton families, a Higgs-like spin-0 particle that couples preferentially to charged leptons (leptophilic scalar), and an axion-like particle, respectively. We observe no evidence for a signal and set exclusion limits at 90% confidence level on the product of cross section and branching fraction into $τ$ pairs, ranging from 0.7 fb to 24 fb, and on the couplings of these processes. We obtain world-leading constraints on the couplings for the leptophilic scalar model for masses above 6.5 GeV/$c^2$ and for the axion-like particle model over the entire mass range.

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arXiv2023

Measurement of branching-fraction ratios and $CP$ asymmetries in $B^{\pm} \to D_{CP\pm}K^{\pm}$ decays at Belle and Belle II

We report results from a study of $B^\pm \rightarrow DK^\pm$ decays followed by $D$ decaying to $CP$~eigenstates, where $D$ indicates a $D^0$ or $\bar{D}^{0}$ meson. These decays are sensitive to the Cabibbo-Kobayashi-Maskawa unitarity-triangle angle $ϕ_{3}$. The results are based on a combined analysis of the final data set of $772 \times 10^6~B\bar{B}$ pairs collected by the Belle experiment and a data set of $198 \times 10^6~B\bar{B}$ pairs collected by the Belle~II experiment, both in electron-positron collisions at the $Υ(4S)$ resonance. We measure the $CP$ asymmetries to be $\mathcal{ A}_{CP +} =~(+12.5 \pm 5.8 \pm 1.4)\% $ and $\mathcal{ A}_{CP -} =~(-16.7 \pm 5.7 \pm 0.6)\%$, and the ratios of branching fractions to be $\mathcal{ R}_{CP+}=~1.164 \pm 0.081 \pm 0.036 $ and $\mathcal{ R}_{CP-} =~1.151 \pm 0.074 \pm 0.019$. The first contribution to the uncertainties is statistical, and the second is systematic. The asymmetries $\mathcal{A}_{CP +}$ and $\mathcal{A}_{CP -}$ have similar magnitudes and opposite signs; their difference corresponds to 3.5~standard deviations. From these values we calculate 68.3\% confidence intervals of ($8.5^{\circ}<ϕ_{3}<16.5^{\circ}$) or ($84.5^{\circ}<ϕ_{3}<95.5^{\circ}$) or ($163.3^{\circ}<ϕ_{3}<171.5^{\circ}$) and $0.321<r_{B}<0.465$.

hep-ex↗
arXiv2023

Search for an invisible $Z^\prime$ in a final state with two muons and missing energy at Belle II

The $L_μ-L_τ$ extension of the standard model predicts the existence of a lepton-flavor-universality-violating $Z^{\prime}$ boson that couples only to the heavier lepton families. We search for such a $Z^\prime$ through its invisible decay in the process $e^+ e^- \to μ^+ μ^- Z^{\prime}$. We use a sample of electron-positron collisions at a center-of-mass energy of 10.58GeV collected by the Belle II experiment in 2019-2020, corresponding to an integrated luminosity of 79.7fb$^{-1}$. We find no excess over the expected standard-model background. We set 90$\%$-confidence-level upper limits on the cross section for this process as well as on the coupling of the model, which ranges from $3 \times 10^{-3}$ at low $Z^{\prime}$ masses to 1 at $Z^{\prime}$ masses of 8$GeV/c^{2}$.

hep-ex↗
arXiv2023

Search for a dark photon and an invisible dark Higgs boson in $μ^+μ^-$ and missing energy final states with the Belle II experiment

The dark photon $A^\prime$ and the dark Higgs boson $h^\prime$ are hypothetical particles predicted in many dark sector models. We search for the simultaneous production of $A^\prime$ and $h^\prime$ in the dark Higgsstrahlung process $e^{+}e^{-}\rightarrow A^\prime \, h^\prime$ with $A^\prime \rightarrow μ^+μ^-$ and $ h^\prime$ invisible in electron-positron collisions at a center-of-mass energy of 10.58 GeV collected by the Belle II experiment in 2019. With an integrated luminosity of 8.34 fb$^{-1}$, we observe no evidence for signal. We obtain exclusion limits at 90% Bayesian credibility in the range of 1.7--5.0 fb on the cross section and in the range of $1.7 \times10^{-8}$--$200 \times10^{-8}$ on the effective coupling $\varepsilon^2 \times α_D$ for the $A^\prime$ mass in the range of 4.0 GeV/$c^2$ $< M_{A^\prime}< 9.7$ GeV/$c^2$ and for the $h^\prime$ mass $M_{h^\prime} < M_{A^\prime}$, where $\varepsilon$ is the mixing strength between the standard model and the dark photon and $α_D$ is the coupling of the dark photon to the dark Higgs boson. Our limits are the first in this mass range.

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arXiv2023

Measurement of the $τ$-lepton mass with the Belle~II experiment

We present a measurement of the $τ$-lepton mass using a sample of about 175 million $e^+e^- \to τ^+τ^-$ events collected with the Belle II detector at the SuperKEKB $e^+e^-$ collider at a center-of-mass energy of $10.579\,\mathrm{Ge\kern -0.1em V}$. This sample corresponds to an integrated luminosity of $190\,\mathrm{fb^{-1}}$. We use the kinematic edge of the $τ$ pseudomass distribution in the decay ${τ^-\toπ^-π^+π^-ν_τ}$ and measure the $τ$ mass to be $1777.09 \pm 0.08 \pm 0.11 \,\mathrm{Me\kern -0.1em V\!/c^2}$, where the first uncertainty is statistical and the second systematic. This result is the most precise to date.

hep-ex↗
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.

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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.

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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

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.

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arXiv2023

Measurement of the $Ω_c^0$ lifetime at Belle II

We report on a measurement of the $Ω_c^0$ lifetime using $Ω_c^0 \to Ω^-π^+$ decays reconstructed in $e^+e^-\to c\bar{c}$ data collected by the Belle II experiment and corresponding to $207~{\rm fb^{-1}}$ of integrated luminosity. The result, $\rmτ(Ω_c^0)=243\pm48( stat)\pm11(syst)~fs$, agrees with recent measurements indicating that the $Ω_c^0$ is not the shortest-lived weakly decaying charmed baryon.

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arXiv2023

Measurement of the $B^0$ lifetime and flavor-oscillation frequency using hadronic decays reconstructed in 2019-2021 Belle II data

We measure the $B^0$ lifetime and flavor-oscillation frequency using $B^0\to D^{(*)-}π^+$ decays collected by the Belle II experiment in asymmetric-energy $e^+e^-$ collisions produced by the SuperKEKB collider operating at the $Υ(4S)$ resonance. We fit the decay-time distribution of signal decays, where the initial flavor is determined by identifying the flavor of the other $B$ meson in the event. The results, based on $33000$ signal decays reconstructed in a data sample corresponding to ${190}\text{fb}^{-1}$, are $τ_{B^0} = {1.499}\pm{0.013}\pm{0.008}\;\text{ps}$, $Δm_d = {0.516}\pm{0.008}\pm{0.005}\;\text{ps}^{-1}$, where the first uncertainties are statistical and the second are systematic. These results are consistent with the world-average values.

hep-ex↗
arXiv2023

Observation of $e^+e^-\toωχ_{bJ}(1P)$ and search for $X_b \to ωΥ(1S)$ at $\sqrt{s}$ near 10.75 GeV

We study the processes $e^+e^-\toωχ_{bJ}(1P)$ ($J$ = 0, 1, or 2) using samples at center-of-mass energies $\sqrt{s}$ = 10.701, 10.745, and 10.805 GeV, corresponding to 1.6, 9.8, and 4.7 fb$^{-1}$ of integrated luminosity, respectively. These data were collected with the Belle II detector during special operations of the SuperKEKB collider above the $Υ(4S)$ resonance. We report the first observation of $ωχ_{bJ}(1P)$ signals at $\sqrt{s}$ = 10.745 GeV. By combining Belle II data with Belle results at $\sqrt{s}$ = 10.867 GeV, we find energy dependencies of the Born cross sections for $e^+e^-\to ωχ_{b1,b2}(1P)$ to be consistent with the shape of the $Υ(10753)$ state. These data indicate that the internal structures of the $Υ(10753)$ and $Υ(10860)$ states may differ. Including data at $\sqrt{s}$ = 10.653 GeV, we also search for the bottomonium equivalent of the $X(3872)$ state decaying into $ωΥ(1S)$. No significant signal is observed for masses between 10.45 and 10.65 GeV/$c^2$.

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arXiv2022

FPGA-based real-time data processing for accelerating reconstruction at LHCb

In Run-3, beginning in 2022, the LHCb software trigger will start reconstructing events at the LHC average crossing rate of 30 MHz. Within the upgraded DAQ system, LHCb established a testbed for new heterogeneous computing solutions for real-time event reconstruction, in view of future runs at even higher luminosities. One such solution is a highly-parallelized custom tracking processor ("Artificial Retina"), implemented in state of the art FPGA devices connected by fast serial links. We describe the status of a realistic prototype for the reconstruction of pixel tracking detectors that will run on real data during Run-3.

physics.ins-det↗
arXiv2022

A Comparison of CPU and GPU implementations for the LHCb Experiment Run 3 Trigger

The LHCb experiment at CERN is undergoing an upgrade in preparation for the Run 3 data taking period of the LHC. As part of this upgrade the trigger is moving to a fully software implementation operating at the LHC bunch crossing rate. We present an evaluation of a CPU-based and a GPU-based implementation of the first stage of the High Level Trigger. After a detailed comparison both options are found to be viable. This document summarizes the performance and implementation details of these options, the outcome of which has led to the choice of the GPU-based implementation as the baseline.

physics.ins-det↗
arXiv2021

Combined analysis of Belle and Belle II data to determine the CKM angle $ ϕ_{3} $ using $B^+ \to D(K_{S}^0 h^- h^+) h^+$ decays

We present a measurement of the Cabibbo-Kobayashi-Maskawa unitarity triangle angle $ ϕ_{3} $ (also known as~$γ$) using a model-independent Dalitz plot analysis of \linebreak $B^+\to D\left(K_{S}^{0}h^{+}h^{-}\right)h^+$, where $D$ is either a $D^0$ or $\bar{D}{}^0$ meson and $h$ is either a $π$ or $K$. This is the first measurement that simultaneously uses Belle and Belle~II data, combining samples corresponding to integrated luminosities of \SI{711}{fb^{-1}} and \SI{128}{fb^{-1}}, respectively. All data were accumulated from energy-asymmetric $e^+e^-$ collisions at a centre-of-mass energy corresponding to the mass of the $Υ(4S)$ resonance. We measure $ϕ_3 = \left(78.4 \pm 11.4 \pm 0.5 \pm 1.0 \right)^{\circ}$, where the first uncertainty is statistical, the second is the experimental systematic uncertainty and the third is from the uncertainties on external measurements of the $D$-decay strong-phase parameters.

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