arXiv subjects

A. Aloisio

Publications and source records attributed to A. Aloisio.

At least 145 records · Page 8Linked to original sources

arXiv2021

Study of $B\to D^{(*)}h$ decays using $62.8~\mathrm{fb}^{-1}$ of Belle II data

We report measurements related to hadronic $B$ decays to final states that contain charm mesons. The analyses are performed on a $62.8~\mathrm{fb}^{-1}$ data set collected by the Belle II experiment at a center-of-mass energy corresponding to the mass of the $Υ(4S)$ resonance. The measurements reported are for the decay modes $B^-\to D^0 h^-$, $B^{-}\to D^{*0}h^-$, $\bar{B}^{0}\to D^{+} h^{-}$ and $\bar{B}^{0}\to D^{*+} h^{-}$, where $h=π$ or $K$. These modes are either signal or control channels for measurements related to the unitarity triangle angle $γ$ in direct or time-dependent $CP$-violation measurements. The reported observables are the ratios between the $B\to D^{(*)}K$ and $B\to D^{(*)}π$ decay rates, which are found to be in agreement with previous measurements.

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arXiv2021

$τ$ lepton mass measurement at Belle II

The reconstruction of tau-pair production, $e^{+}e^{-} \to τ^{+}τ^{-}$, from the subsequent 3-prong ($τ^{+} \rightarrow π^{+} π^{-} π^{+} \barν_τ$) and 1-prong ($τ^{-} \to \ell^{-} \barν_{\ell} ν_τ$, $τ^{-} \to h^{-} ν_τ$ or $τ^{-} \to π^{-} π^0 ν_τ$) decays, is presented using 8.8 fb$^{-1}$ of $e^{+}e^{-}$ collision data of Belle II at the center-of-mass energy $\sqrt{s} = m_{Υ(4S)}$. The pseudomass technique developed by the ARGUS experiment is used to measure the $τ$-lepton mass $m_τ$ in the 3-prong $τ^{+} \to π^{+} π^{-} π^{+} \barν_τ $ decay, resulting in $m_τ = 1777.28 \pm 0.75~{\rm (stat.)} \pm 0.33 ~{\rm (sys.)}~{\rm{MeV}/\rm{c}^2}$.

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arXiv2020

Search for Axion-Like Particles produced in $e^+e^-$ collisions at Belle II

We present a search for the direct production of a light pseudoscalar $a$ decaying into two photons with the Belle II detector at the SuperKEKB collider. We search for the process ${e^+e^-\toγa, a \toγγ}$ in the mass range ${0.2} \,< m_a < {9.7}\,{\text{GeV/$c$}^2}$ using data corresponding to an integrated luminosity of $(445\pm 3)\,\text{pb}^{-1}$. Light pseudoscalars interacting predominantly with standard model gauge bosons (so-called axion-like particles or ALPs) are frequently postulated in extensions of the standard model. We find no evidence for ALPs and set 95% confidence level upper limits on the coupling strength $g_{aγγ}$ of ALPs to photons at the level of $10^{-3}\,{\text{GeV}^{-1}}$. The limits are the most restrictive to date for $0.2\,<\,m_a\,<\,1\,{\text{GeV/$c$}^2}$.

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arXiv2020

Measurements of branching fractions and CP-violating charge asymmetries in charmless $B$ decays reconstructed in 2019--2020 Belle~II data

We report on first measurements of branching fractions~($\mathcal{B}$) and CP-violating charge asymmetries~($\mathcal{A}$) in charmless $B$ decays at Belle~II. We use a sample of electron-positron collisions collected in 2019 and 2020 at the $Υ(4S)$ resonance and corresponding to $34.6$\,fb$^{-1}$ of integrated luminosity. We use simulation to determine optimized event selections. The $ΔE$ distributions of the resulting samples, restricted in $M_{\rm bc}$, are fit to determine signal yields. Signal yields are corrected for efficiencies determined from simulation and control data samples to obtain branching fractions and CP-violating asymmetries for flavour-specific channels. These are the first measurements in charmless decays reported by Belle~II. Results are compatible with known determinations and show detector performance comparable with the best Belle results offering a reliable basis to assess projections for future reach.

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arXiv2020

Measurement of the semileptonic $\bar{B}^0 \to D^{*+} \ell^{-} ν_{\ell}$ branching fraction with fully reconstructed $B$ meson decays and 34.6 fb$^{-1}$of Belle II data

We present a first measurement of the $\bar{B^{0}} \rightarrow D^{*+} \ell^{-} ν_{\ell}$ branching fraction using fully reconstructed $B$ meson decays employing the Full Event Interpretation algorithm. Collision events corresponding to an integrated luminosity of \lumi are analyzed, which were recorded by the Belle~II detector operated at the SuperKEKB accelerator complex. We measure$\cal{B}(\bar{B^{0}} \rightarrow D^{*+} \ell^{-} ν_{\ell}) =4.51 \pm 0.41_{stat}\pm0.27_{syst} \pm0.45_{π_s}$, with the first and second error denoting the statistical and systematic uncertainty, respectively, and the third dominant uncertainty is from the slow pion reconstruction efficiency.

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arXiv2020

Measurement of Hadronic Mass Moments $\langle M_X^n \rangle $ in $B \rightarrow X_c \ell ν$ Decays at Belle II

We present measurements of the first six hadronic mass moments in semileptonic $B \rightarrow X_c \ell ν$ decays. The hadronic mass moments, together with other observables of inclusive $B$ decays, can be used to determine the CKM matrix element $|{V_{cb}}|$ and mass of the $b$-quark $m_b$ in the context of Heavy Quark Expansions of QCD. The Belle~II data recorded at the $Υ(4S)$ resonance in 2019 and 2020 (March-July), corresponding to an integrated luminosity of $34.6\;\mathrm{fb}^{-1}$, is used for this measurement. The decay $Υ(4S) \rightarrow B \overline{B}$ is reconstructed by applying the hadronic tagging algorithm provided by the Full Event Interpretation to fully reconstruct one $B$ meson. The second $B$ meson is reconstructed inclusively by selecting a high-momentum lepton. The $X_c$ system is identified by the remaining reconstructed tracks and clusters in the electromagnetic calorimeter. We report preliminary results for the hadronic mass moments $\langle M_X^n \rangle $ with $n=1,\dots,6$, measured as a function of a lower cut on the lepton momentum in the signal $B$ rest frame.

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arXiv2020

Exclusive $B^0 \to π^- \ell^+ ν_\ell$ Decays with Hadronic Full Event Interpretation Tagging in 34.6 fb$^{-1}$ of Belle II Data

We present the results of the re-discovery of the decay $B^0 \to π^- \ell^+ ν_\ell$ in 34.6 fb$^{-1}$ of Belle II data using hadronic $B$-tagging via the Full Event Interpretation algorithm. We observe 21 signal events on a background of 155 in a fit to the distribution of the square of the missing mass, $M_{\mathrm{miss}}^2$, with a significance of 5.69$σ$, and determine a total branching fraction of (1.58 $\pm$ 0.43$_{\mathrm{stat}}$ $\pm$ 0.07$_{\mathrm{sys}}$) $\times 10^{-4}$.

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arXiv2020

Studies of the semileptonic $\bar B^0\to D^{*+}\ell^-\barν_\ell$ and $B^-\to D^{0}\ell^-\barν_\ell$ decay processes with 34.6 fb$^{-1}$ of Belle II data

We report measurements of the $\bar{B}^0 \to D^{*+} \ell^{-} \barν_l$ and $B^- \to D^{0} \ell^{-} \barν_l$ processes using 34.6 fb$^{-1}$ of collision events recorded by the Belle II experiment at the SuperKEKB asymmetric-energy $e^+ e^-$ collider. For the $B^-\to D^{0}\ell^-\barν_\ell$ channel, we present first studies that isolate this decay from other semileptonic processes and backgrounds. We report a measurement of the $\bar{B}^0 \to D^{*+} \ell^{-} \barν_l$ branching fraction and obtain ${\cal B}(\bar{B}^0 \to D^{*+} \ell^{-} \barν_l) = \left(4.60 \pm 0.05_{\mathrm{stat}}\pm0.17_{\mathrm{syst}} \pm 0.45_{π_s}\right) \%$, in agreement with the world average. Here, the uncertainties are statistical, systematic, and related to slow pion reconstruction, respectively. The systematic uncertainties are limited by the statistics of auxiliary measurements and will improve in the future. We also report differential branching fractions in five bins of the hadronic recoil parameter $w$ for $\bar{B}^0 \to D^{*+} \ell^{-} \barν_l$, unfolded to account for resolution and efficiency effects.

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arXiv2020

A calibration of the Belle II hadronic tag-side reconstruction algorithm with $B \rightarrow X\ell ν$ decays

Tag-side reconstruction is an important method for reconstructing $B$ meson decays with missing energy. The Belle II tag-side reconstruction algorithm, Full Event Interpretation, relies on a hierarchical reconstruction of $B$ meson decays with multivariate classification employed at each stage of reconstruction. Given the large numbers of classifiers employed and decay chains reconstructed, the performance of the algorithm on data and simulation differs significantly. Here, calibration factors are derived for hadronic tag-side $B$ decays by measuring a signal side decay, $B \rightarrow X\ell ν$, in $34.6$ fb$^{-1}$ of Belle II data. For a very loose selection on the tag-side $B$ multivariate classifier, the calibration factors are $0.65 \pm 0.02$ and $0.83 \pm 0.03$ for tag-side $B^{+}$ and $B^{0}$ mesons, respectively.

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arXiv2020

Rediscovery of $B \to ϕK^{()}$ decays and measurement of the longitudinal polarization fraction $f_L$ in $B \to ϕK^{}$ decays using the Summer 2020 Belle II dataset

We utilize a sample of 34.6 fb$^{-1}$, collected by the Belle II experiment at the SuperKEKB asymmetric energy $e^+e^-$ collider, to search for the $B^+ \to ϕK^+$, $B^+ \to ϕK^{*+}$, $B^0 \to ϕK^0_S$, and $B^0 \to ϕK^{*0}$ decays. Charmless hadronic $B$ decays represent an important part of the Belle II physics program, and are an ideal benchmark to test the detector capabilities in terms of tracking efficiency, charged particle identification, vertexing, and advanced analysis techniques. Each channel is observed with a significance that exceeds 5 standard deviations, and we obtain measurements of their branching ratios that are in good agreement with the world averages. For the $B \to ϕK^*$ modes, we also perform a measurement of the longitudinal polarization fraction $f_L$.

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arXiv2020

First flavor tagging calibration using 2019 Belle II data

We report on the first calibration of the standard Belle II $B$-flavor tagger using the full data set collected at the $Υ(4{\rm S})$ resonance in 2019 with the Belle II detector at the SuperKEKB collider, corresponding to 8.7 fb$^{-1}$ of integrated luminosity. The calibration is performed by reconstructing various hadronic charmed $B$-meson decays with flavor-specific final states. We use simulation to optimize our event selection criteria and to train the flavor tagging algorithm. We determine the tagging efficiency and the fraction of wrongly identified tag-side $B$~candidates from a measurement of the time-integrated $B^0-\overline{B}^0$ mixing probability. The total effective efficiency is measured to be $\varepsilon_{\rm eff} = \big(33.8 \pm 3.6(\text{stat}) \pm 1.6(\text{sys})\big)\%$, which is in good agreement with the predictions from simulation and comparable with the best one obtained by the Belle experiment. The results show a good understanding of the detector performance and offer a basis for future calibrations.

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arXiv2020

Measurement of the branching fraction ${\cal B}(\bar B^0\to D^{*+}\ell^-\barν_\ell)$ with early Belle II data

We measure the branching fractions for the decays $\bar{B}^0 \to D^{*+} e^{-} \barν_e$ and $\bar{B}^0 \to D^{*+} μ^{-} \barν_μ$ using $8.70 \pm 0.09~{\rm fb}^{-1}$ of data collected by the Belle II experiment at the SuperKEKB asymmetric-energy $e^+ e^-$ collider. Candidate signal decays are reconstructed with the subsequent decays $D^{*+}\to D^0 π^+$ and $D^0\to K^-π^+$. We obtain the results ${\cal B}(\bar{B}^0 \to D^{*+} e^{-} \barν_e)$ = $(4.55\pm0.14(\mathrm{stat})\pm0.35 (\mathrm{syst})) \%$ and ${\cal B}(\bar{B}^0 \to D^{*+} μ^{-} \barν_μ)$ = $(4.84\pm 0.13(\mathrm{stat})\pm0.37(\mathrm{syst})) \%$, in agreement with the world averages. The measurements serve to validate the full chain of detector operation and calibration, data collection and processing, and production of physics results in the case of semileptonic $B$-meson decays.

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arXiv2020

Charmless $B$ decay reconstruction in 2019 Belle II data

We report on the reconstruction of various charmless $B$ decays from electron-positron collisions at the energy corresponding to the $Υ(4S)$ resonance collected with the Belle II detector at the SuperKEKB collider. We use simulation to devise optimized event selections and apply them to the full data set collected in 2019, corresponding to 8.7\,fb$^{-1}$ of integrated luminosity. We fit the difference between half of the collision energy and the $B$ candidate energy (in the $Υ(4S)$ frame) for events restricted to a signal-rich range in beam-energy-constrained mass to search for charmless signals. Signal yields of approximately 80, 15, 20, 30, 90, and 160 decays are reconstructed for the channels $B^0 \to K^+π^-$, $B^0 \to π^+π^-$, $B^+ \to K^0_S(\to π^+π^-)π^+$, $B^+ \to K^+π^0(\to γγ)$, $B^+ \to K^+K^-K^+$, and $B^+ \to K^+π^-π^+$, respectively. Yields and background contaminations are compatible with those expected from simulation and comparable with those obtained by the Belle experiment. The results show a good understanding of the detector performance and offer a reliable basis to assess projections for future reach.

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arXiv2020

Measurement of the $B^0$ lifetime using fully reconstructed hadronic decays in the 2019 Belle II dataset

This document presents the measurement of $B^0$ meson lifetimes using the 2019 Belle II dataset that corresponds to an integrated luminosity of $8.7 \pm 0.2$ fb$^{-1}$. Each candidate is fully reconstructed with hadronic decay final states on the signal side, while the rest-of-event technique allows to infer the decay vertex position on the other (tag) side. $B^0$ lifetime is extracted from an unbinned maximum likelihood fit to the distribution of the difference between the signal side $B^0$ candidate and the tag side decay times. The measured lifetime is $τ_{B^0} = 1.48 \pm 0.28 \pm 0.06 $ ps, where the first uncertainty is statistical and the second is systematic.

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arXiv2020

Search for an invisibly decaying $Z^{\prime}$ boson at Belle II in $e^+ e^- \to μ^+ μ^- (e^{\pm} μ^{\mp})$ plus missing energy final states

Theories beyond the standard model often predict the existence of an additional neutral boson, the $Z^{\prime}$. Using data collected by the Belle II experiment during 2018 at the SuperKEKB collider, we perform the first searches for the invisible decay of a $Z^{\prime}$ in the process $e^+ e^- \to μ^+ μ^- Z^{\prime}$ and of a lepton-flavor-violating $Z^{\prime}$ in $e^+ e^- \to e^{\pm} μ^{\mp} Z^{\prime}$. We do not find any excess of events and set 90\% credibility level upper limits on the cross sections of these processes. We translate the former, in the framework of an $L_μ-L_τ$ theory, into upper limits on the $Z^{\prime}$ coupling constant at the level of $5 \times 10^{-2}$ -- $1$ $M_{Z^\prime}\leq 6$ GeV/$c^2$.

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arXiv2019

Measurement of the integrated luminosity of the Phase 2 data of the Belle II experiment

From April to July 2018, a data sample at the peak energy of the $Υ(4S)$ resonance was collected with the Belle~II detector at the SuperKEKB electron-positron collider. This is the first data sample of the Belle~II experiment. Using Bhabha and digamma events, we measure the integrated luminosity of the data sample to be ($496.3 \pm 0.3 \pm 3.0$)~pb$^{-1}$, where the first uncertainty is statistical and the second is systematic. This work provides a basis for future luminosity measurements at Belle~II.

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arXiv2018

The Monitoring System of the End-Cap Calorimeter in the Belle II experiment

The Belle II experiment is presently in phase-2 operation at the SuperKEKB electron-positron collider in KEK (Tsukuba, Japan). The detector is an upgrade of the Belle experiment at the KEKB collider and it is optimized for the study of rare B decays, being also sensitive to signals of New Physics beyond the Standard Model. The Electromagnetic Calorimeter (ECL) is based on CsI(Tl) scintillation crystals. It splits in a barrel and two annular end-cap regions, these latter named Forward and Backward, according to the asymmetric design of the collider. CsI(Tl) crystals deliver a high light output at an affordable cost, however their yield changes with temperature and can be permanently damaged by humidity, due to the strong chemical affinity for moisture. Each ECL region is then equipped with thermistors and humidity probes to monitor environmental data. While sensors and cabling have been inherited from the original Belle design, the ECL monitoring system has been fully redesigned. In this paper, we present hardware and software architecture deployed for the 2112 CsI(Tl) crystals arranged in the Forward and Backward end-caps. Single-Board Computers (SBCs) have been designed ad-hoc for embedded applications. For sensor read-out, a data-acquisition system based on 24-bit ADCs with local processing capability has been realized and interfaced with the SBCs. EPICS applications send data across the Local Area Network for remote control and display.

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arXiv2018

The Phase-1 Upgrade for the Level-1 Muon Barrel Trigger of the ATLAS Experiment at LHC

The Level-1 Muon Barrel Trigger of the ATLAS Experiment at LHC makes use of Resistive Plate Chamber (RPC) detectors. The on-detector trigger electronics modules are able to identify muons with predefined transverse momentum values (pT) by executing a coincidence logic on signals coming from the various detector layers. Then, on-detector trigger boards transfer trigger data to the off-detector electronics. A complex trigger system processes the incoming data by combining trigger information from the Barrel and the End-cap regions, and by providing the combined muon candidate to the Central Trigger Processor (CTP). For almost a decade, the Level-1 Trigger system has been operating very well, despite the challenging requirements on trigger efficiency and performance, and the continuously increasing LHC luminosity. In order to cope with these constraints, various upgrades for the full trigger system were already deployed, and others have been designed to be installed in the next years. Most of the upgrades to the trigger system rely on state-of-the-art technologies, thus allowing to increase the processing power and data transfer bandwidth, and to design more complex trigger menus. As a consequence, more trigger candidates might be selected by the system, thus supporting new physics studies or topological selections. In this work, we discuss the design of the first prototype of the new Barrel Interface Board, designed around a Xilinx FPGA, which will be used to transfer RPC trigger data to the CTP system. The main requirement for the board is to support the optical transmission of the trigger data with fixed latency and to allow the implementation of new trigger algorithms. We describe the hardware implementation and the results of the first functional and integration tests.

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