arXiv subjects

F. Ameli

Publications and source records attributed to F. Ameli.

At least 55 records · Page 3Linked to original sources

arXiv2022

Measurement of the branching fraction of the $B^0 \to K_S^0 π^0 γ$ decay using 190 fb$^{-1}$ of Belle II data

We report the measurement of the branching fraction of the $B^0 \to K_S^0 π^0 γ$ decay in $e^+ e^- \to Υ(4S) \to B \overline{B}$ data recorded by the Belle II experiment at the SuperKEKB asymmetric-energy collider and corresponding to 190 fb$^{-1}$ of integrated luminosity. The signal yield is measured to be $121\pm 29\,\hbox{(stat.)}$, leading to the branching fraction ${\cal B}\left(B^0 \to K_S^0 π^0 γ\right) = \left(7.3 \pm 1.8\,\hbox{(stat.)} \pm 1.0\,\hbox{(syst.)} \right)\times 10^{-6}$, which agrees with the known value.

hep-ex↗

arXiv2022

First decay-time-dependent analysis of $B^{0} \to K_{S}^{0} π^{0}$ at Belle II

We report measurements of the branching fraction ($\mathcal{B}$) and direct $CP$-violating asymmetry ($A_{CP}$) of the charmless decay $B^{0} \to K^0 π^0$ at Belle II. A sample of $e^{+} e^{-}$ collisions, corresponding to $189.8 fb^{-1}$ of integrated luminosity, recorded at the $Υ(4S)$ resonance is used for the first decay-time-dependent analysis of these decays within the experiment. We reconstruct about 135 signal candidates, and measure $\mathcal{B}(B^{0} \to K^{0} π^{0})= [11.0 \pm 1.2 (stat) \pm 1.0 (syst)] \times 10^{-6}$ and $A_{CP} (B^{0} \to K^{0} π^{0})= -0.41_{-0.32}^{+0.30} (stat) \pm 0.09 (syst)$.

hep-ex↗

arXiv2021

Implementation and first results of the KM3NeT real-time core-collapse supernova neutrino search

The KM3NeT research infrastructure is under construction in the Mediterranean Sea. KM3NeT will study atmospheric and astrophysical neutrinos with two multi-purpose neutrino detectors, ARCA and ORCA, primarily aimed at GeV-PeV neutrinos. Thanks to the multi-photomultiplier tube design of the digital optical modules, KM3NeT is capable of detecting the neutrino burst from a Galactic or near-Galactic core-collapse supernova. This potential is already exploitable with the first detection units deployed in the sea. This paper describes the real-time implementation of the supernova neutrino search, operating on the two KM3NeT detectors since the first months of 2019. A quasi-online astronomy analysis is introduced to study the time profile of the detected neutrinos for especially significant events. The mechanism of generation and distribution of alerts, as well as the integration into the SNEWS and SNEWS 2.0 global alert systems are described. The approach for the follow-up of external alerts with a search for a neutrino excess in the archival data is defined. Finally, an overview of the current detector capabilities and a report after the first two years of operation are given.

astro-ph.HE↗

arXiv2021

Determining the Neutrino Mass Ordering and Oscillation Parameters with KM3NeT/ORCA

The next generation of water Cherenkov neutrino telescopes in the Mediterranean Sea are under construction offshore France (KM3NeT/ORCA) and Sicily (KM3NeT/ARCA). The KM3NeT/ORCA detector features an energy detection threshold which allows to collect atmospheric neutrinos to study flavour oscillation. This paper reports the KM3NeT/ORCA sensitivity to this phenomenon. The event reconstruction, selection and classification are described. The sensitivity to determine the neutrino mass ordering was evaluated and found to be 4.4 $σ$ if the true ordering is normal and 2.3 $σ$ if inverted, after three years of data taking. The precision to measure $Δm^2_{32}$ and $θ_{23}$ were also estimated and found to be $85\cdot10^{-6}$ eV$^2$ and $(^{+1.9}_{-3.1})^{\circ}$ for normal neutrino mass ordering and, $75\cdot10^{-6}$ eV$^2$ and $(^{+2.0}_{-7.0})^{\circ}$ for inverted ordering. Finally, a unitarity test of the leptonic mixing matrix by measuring the rate of tau neutrinos is described. Three years of data taking were found to be sufficient to exclude $ν_τ$ and $\barν_τ$ event rate variations larger than 20% at $3σ$ level.

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arXiv2021

Sensitivity to light sterile neutrino mixing parameters with KM3NeT/ORCA

KM3NeT/ORCA is a next-generation neutrino telescope optimised for atmospheric neutrino oscillations studies. In this paper, the sensitivity of ORCA to the presence of a light sterile neutrino in a 3+1 model is presented. After three years of data taking, ORCA will be able to probe the active-sterile mixing angles $θ_{14}$, $θ_{24}$, $θ_{34}$ and the effective angle $θ_{μe}$, over a broad range of mass squared difference $Δm^2_{41} \sim [10^{-5}, 10]$ $\rm{eV}^2$, allowing to test the eV-mass sterile neutrino hypothesis as the origin of short baseline anomalies, as well as probing the hypothesis of a very light sterile neutrino, not yet constrained by cosmology. ORCA will be able to explore a relevant fraction of the parameter space not yet reached by present measurements.

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arXiv2021

Exclusive $B \to X_u \ell ν_\ell$ Decays with Hadronic Full-event-interpretation Tagging in 62.8 fb$^{-1}$ of Belle II Data

We present a reconstruction in early data of the semileptonic decay $B^+ \to π^0 \ell^+ ν_\ell$, and first results of a reconstruction of the decays $B^+ \to ρ^0 \ell^+ ν_\ell$ and $B^0 \to ρ^- \ell^+ ν_\ell$ in a sample corresponding to 62.8 fb$^{-1}$ of Belle II data using hadronic $B$-tagging via the full-event-interpretation algorithm. We determine the total branching fractions via fits to the distribution of the square of the missing mass, and find $\mathcal{B}(B^+ \to π^0 \ell^+ ν_\ell)$ = (8.29 $\pm$ 1.99(stat) $\pm$ 0.46(syst)) $\times 10^{-5}$. We obtain $95\%$ CL upper limits on the branching fractions with $\mathcal{B}(B^0 \to ρ^- \ell^+ ν_\ell) < 3.37 \times 10^{-4}$ and $\mathcal{B}(B^+ \to ρ^0 \ell^+ ν_\ell) < 19.7 \times 10^{-5}$. We also obtain an updated branching fraction for the $B^0 \to π^- \ell^+ ν_\ell$ decay, $\mathcal{B}(B^0 \to π^- \ell^+ ν_\ell)$ = (1.47 $\pm$ 0.29(stat) $\pm$ 0.05(syst)) $\times 10^{-4}$, based on the sum of the partial branching fractions in three bins of the squared momentum transfer to the leptonic system.

hep-ex↗

arXiv2021

Nanobeacon: A time calibration device for the KM3NeT neutrino telescope

The KM3NeT Collaboration is currently constructing a multi-site high-energy neutrino telescope in the Mediterranean Sea consisting of matrices of pressure-resistant glass spheres, each holding a set of 31 small-area photomultipliers. The main goals of the telescope are the observation of neutrino sources in the Universe and the measurement of the neutrino oscillation parameters with atmospheric neutrinos. Both extraterrestrial and atmospheric neutrinos are detected through the Cherenkov light induced in seawater by charged particles produced in neutrino interactions in the surrounding medium. A relative time synchronization between photomultipliers of the order of 1 ns is needed to guarantee the required angular resolution of the detector. Due to the large detector volumes to be instrumented by KM3NeT, a cost reduction of the different systems is a priority. To this end, the inexpensive Nanobeacon has been designed and developed by the KM3NeT Collaboration to be used for detector time-calibration studies. At present, more than 600 Nanobeacons have been already produced. The characterization of the optical pulse and the wavelength emission profile of the devices are critical for the time calibration. In this paper, the main features of the Nanobeacon design, production and operation, together with the main properties of the light pulse generated are described.

astro-ph.IM↗

arXiv2021

Science Requirements and Detector Concepts for the Electron-Ion Collider: EIC Yellow Report

This report describes the physics case, the resulting detector requirements, and the evolving detector concepts for the experimental program at the Electron-Ion Collider (EIC). The EIC will be a powerful new high-luminosity facility in the United States with the capability to collide high-energy electron beams with high-energy proton and ion beams, providing access to those regions in the nucleon and nuclei where their structure is dominated by gluons. Moreover, polarized beams in the EIC will give unprecedented access to the spatial and spin structure of the proton, neutron, and light ions. The studies leading to this document were commissioned and organized by the EIC User Group with the objective of advancing the state and detail of the physics program and developing detector concepts that meet the emerging requirements in preparation for the realization of the EIC. The effort aims to provide the basis for further development of concepts for experimental equipment best suited for the science needs, including the importance of two complementary detectors and interaction regions. This report consists of three volumes. Volume I is an executive summary of our findings and developed concepts. In Volume II we describe studies of a wide range of physics measurements and the emerging requirements on detector acceptance and performance. Volume III discusses general-purpose detector concepts and the underlying technologies to meet the physics requirements. These considerations will form the basis for a world-class experimental program that aims to increase our understanding of the fundamental structure of all visible matter

physics.ins-det↗

arXiv2021

Measurements of the branching fractions for $B \to K^{*}γ$ decays at Belle II

This paper reports a study of $B \to K^{*}γ$ decays using $62.8\pm 0.6$ fb$^{-1}$ of data collected during 2019--2020 by the Belle II experiment at the SuperKEKB $e^{+}e^{-}$ asymmetric-energy collider, corresponding to $(68.2 \pm 0.8) \times 10^6$ $B\overline{B}$ events. We find $454 \pm 28$, $50 \pm 10$, $169 \pm 18$, and $160 \pm 17$ signal events in the decay modes $B^{0} \to K^{*0}[K^{+}π^{-}]γ$, $B^{0} \to K^{*0}[K^0_{\rm S}π^{0}]γ$, $B^{+} \to K^{*+}[K^{+}π^{0}]γ$, and $B^{+} \to K^{*+}[K^{+}π^{0}]γ$, respectively. The uncertainties quoted for the signal yield are statistical only. We report the branching fractions of these decays: $$\mathcal{B} [B^{0} \to K^{*0}[K^{+}π^{-}]γ] = (4.5 \pm 0.3 \pm 0.2) \times 10^{-5}, $$ $$\mathcal{B} [B^{0} \to K^{*0}[K^0_{\rm S}π^{0}]γ] = (4.4 \pm 0.9 \pm 0.6) \times 10^{-5},$$ $$\mathcal{B} [B^{+} \to K^{*+}[K^{+}π^{0}]γ] = (5.0 \pm 0.5 \pm 0.4)\times 10^{-5},\text{ and}$$ $$\mathcal{B} [B^{+} \to K^{*+}[K^0_{\rm S}π^{+}]γ] = (5.4 \pm 0.6 \pm 0.4) \times 10^{-5},$$ where the first uncertainty is statistical, and the second is systematic. The results are consistent with world-average values.

hep-ex↗

arXiv2021

Measurement of the branching fraction for $B^{0} \rightarrow π^{0} π^{0}$ decays reconstructed in 2019-2020 Belle II data

We report the first reconstruction of the $B^{0} \to π^{0} π^{0}$ decay mode at Belle II using samples of 2019 and 2020 data that correspond to 62.8 fb$^{-1}$ of integrated luminosity. We find $14.0^{+6.8}_{-5.6}$ signal decays, corresponding to a significance of 3.4 standard deviations and determine a branching ratio of $\mathcal{B}(B^{0} \rightarrow π^{0} π^{0}) = [0.98^{+0.48}_{-0.39} \pm 0.27] \times 10^{-6}$. The results agree with previous determinations and contribute important information to an early assessment of detector performance and Belle II's potential for future determinations of $α/ϕ_2$ using $B \rightarrow ππ$ modes.

hep-ex↗

arXiv2021

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

We report on measurements of branching fractions ($\mathcal{B}$) and CP-violating charge asymmetries ($\mathcal{A}_{\rm CP}$) of multibody charmless $B$ decays reconstructed by the Belle II experiment at the SuperKEKB electron-positron collider. We use a sample of collisions collected in 2019 and 2020 at the $Υ(4S)$ resonance and corresponding to $62.8$ fb$^{-1}$ of integrated luminosity. We use simulation to determine optimized event selections. The $ΔE$ and $M_{\rm bc}$ distributions of the resulting samples are fit to determine signal yields of approximately 690, 840, and 380 decays for the channels $B^+ \to K^+K^-K^+$, $B^+ \to K^+π^-π^+$, and $B^0 \to K^+π^-π^0$, respectively. These yields are corrected for efficiencies determined from simulation and control data samples to obtain $\mathcal{B}(B^+ \to K^+K^-K^+) = [35.8 \pm 1.6(\rm stat) \pm 1.4 (\rm syst)]\times 10^{-6}$, $\mathcal{B}(B^+ \to K^+π^-π^+) = [67.0 \pm 3.3 (\rm stat)\pm 2.3 (\rm syst)]\times 10^{-6}$, $\mathcal{B}(B^0 \to K^+π^-π^0) = [38.1 \pm 3.5 (\rm stat)\pm 3.9 (\rm syst)]\times 10^{-6}$, $\mathcal{A}_{\rm CP}(B^+ \to K^+K^-K^+) = -0.103 \pm 0.042(\rm stat) \pm 0.020 (\rm syst)$, $\mathcal{A}_{\rm CP}(B^+ \to K^+π^-π^+) = -0.010 \pm 0.050 (\rm stat)\pm 0.021(\rm syst)$, and $\mathcal{A}_{\rm CP}(B^0 \to K^+π^-π^0) = 0.207 \pm 0.088 (\rm stat)\pm 0.011(\rm syst)$. Results are consistent with previous measurements and demonstrate detector performance comparable with the best Belle results.

hep-ex↗

arXiv2021

Angular analysis of $B^+ \to ρ^+ρ^0$ decays reconstructed in 2019-2020 Belle II data

We report on the first Belle II measurement of the branching fraction ($\mathcal{B}$) and longitudinal polarization fraction ($f_L$) of $B^+\to ρ^+ρ^0$ decays. We reconstruct $B^+\to ρ^+(\to π^+π^0(\to γγ))ρ^0(\to π^+π^-)$ decays in a sample of SuperKEKB electron-positron collisions collected by the Belle II experiment in 2019 and 2020 at the $Υ$(4S) resonance and corresponding to $62.8$ fb$^{-1}$ of integrated luminosity. We fit the distributions of the difference between expected and observed $B$ candidate energy, continuum-suppression variable, dipion masses, and angular distributions of the resulting samples, to determine a signal yield of $104\pm16$ events. The signal yields are corrected for efficiencies determined from simulation and control data samples to obtain $\mathcal{B}(B^+ \to ρ^+ρ^0) = [20.6 \pm 3.2(\rm stat) \pm 4.0(\rm syst)]\times 10^{-6}$, and $f_L(B^+ \to ρ^+ρ^0) = 0.936 ^{+0.049}_{-0.041}(\rm stat)\pm 0.021(\rm syst)$. This first Belle II $B^+ \to ρ^+ρ^0$ angular analysis yields results compatible with previous determinations, and indicates Belle II performance superior to early Belle results.

hep-ex↗

arXiv2021

Combined sensitivity of JUNO and KM3NeT/ORCA to the neutrino mass ordering

This article presents the potential of a combined analysis of the JUNO and KM3NeT/ORCA experiments to determine the neutrino mass ordering. This combination is particularly interesting as it significantly boosts the potential of either detector, beyond simply adding their neutrino mass ordering sensitivities, by removing a degeneracy in the determination of $Δm_{31}^2$ between the two experiments when assuming the wrong ordering. The study is based on the latest projected performances for JUNO, and on simulation tools using a full Monte Carlo approach to the KM3NeT/ORCA response with a careful assessment of its energy systematics. From this analysis, a $5σ$ determination of the neutrino mass ordering is expected after 6 years of joint data taking for any value of the oscillation parameters. This sensitivity would be achieved after only 2 years of joint data taking assuming the current global best-fit values for those parameters for normal ordering.

hep-ex↗

arXiv2021

Supernova Model Discrimination with Hyper-Kamiokande

Core-collapse supernovae are among the most magnificent events in the observable universe. They produce many of the chemical elements necessary for life to exist and their remnants -- neutron stars and black holes -- are interesting astrophysical objects in their own right. However, despite millennia of observations and almost a century of astrophysical study, the explosion mechanism of core-collapse supernovae is not yet well understood. Hyper-Kamiokande is a next-generation neutrino detector that will be able to observe the neutrino flux from the next galactic core-collapse supernova in unprecedented detail. We focus on the first 500 ms of the neutrino burst, corresponding to the accretion phase, and use a newly-developed, high-precision supernova event generator to simulate Hyper-Kamiokande's response to five different supernova models. We show that Hyper-Kamiokande will be able to distinguish between these models with high accuracy for a supernova at a distance of up to 100 kpc. Once the next galactic supernova happens, this ability will be a powerful tool for guiding simulations towards a precise reproduction of the explosion mechanism observed in nature.

astro-ph.IM↗

arXiv2021

Rediscovery of $B^0\to J\mskip 1mu / ψ\mskip 2mu K^0_{\scriptscriptstyle L}$ at Belle II

We present preliminary results on the reconstruction of the $B^0\to J\mskip 1mu / ψ\mskip 2mu K^0_{\scriptscriptstyle L}$ decay, where $J\mskip 1mu / ψ\mskip 2mu\toμ^+μ^-$ or $e^+e^-$. Using a dataset corresponding to a luminosity of $62.8\pm0.6\mbox{fb}^{-1}$ collected by the Belle II experiment at the SuperKEKB asymmetric energy $e^+e^-$ collider, we measure a total of $267\pm21$ candidates with $J\mskip 1mu / ψ\mskip 2mu\toμ^+μ^-$ and $226\pm20$ with with $J\mskip 1mu / ψ\mskip 2mu\to e^+e^-$. The quoted errors are statistical only.

hep-ex↗

arXiv2021

Measurements of branching fractions and direct CP asymmetries in $B^{0}\to K^{+} π^{-}$, $B^+ \to K_{\rm S}^0π^+$ and $B^0 \to π^+π^-$ using 2019 and 2020 data

We report updated measurements of branching fractions ($\mathcal{B}$) and CP-violating charge asymmetries ($\mathcal{A_{\rm CP}}$) for charmless $B$ decays at Belle II, which operates on or near the $Υ$(4S) resonance at the SuperKEKB asymmetric energy $e^{+}e^{-}$ collider. We use samples of 2019 and 2020 data corresponding to 62.8 fb$^{-1}$ of integrated luminosity. The samples are analysed using two-dimensional fits in $ΔE$ and $M_{\it bc}$ to determine signal yields of approximately 568, 103, and 115 decays for the channels $B^0 \to K^+π^-$, $B^+ \to K_{\rm S}^0π^+$, and $B^0 \to π^+π^-$, respectively. 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. The results are compatible with known determinations and contribute important information to an early assessment of Belle II detector performance.

hep-ex↗

arXiv2021

Measurement of the time-integrated mixing probability $χ_d$ with a semileptonic double-tagging strategy and $34.6 {\rm fb}^{-1}$ of Belle II collision data

We present the first measurement of the time-integrated mixing probability $χ_d$ using Belle II data collected at a center-of-mass (CM) energy of 10.58 GeV, corresponding to the mass of the $Υ$(4S) resonance, with an integrated luminosity of $34.6 {\rm fb}^{-1}$ at the SuperKEKB $e^+ e^-$ collider. We reconstruct pairs of B mesons both of which decay to semileptonic final states. Using a novel methodology, we measure $χ_d = 0.187 \pm 0.010 \text{ (stat.)} \pm 0.019 \text{ (syst.)}$, which is compatible with existing indirect and direct determinations.

hep-ex↗

arXiv2021

Measurement of the branching fractions of $B\toη' K$ decays using 2019/2020 Belle II data

This note describes the rediscovery of $B\toη' K$ decays in Belle II data, both in the charged and neutral final state: $B_0\toη' K_S$ and $B^\pm\toη' K^\pm$. The $η'$ is searched for in two decay modes: $η'\toηπ^+π^-$ with $η\toγγ$, and $η'\toργ$. The analysis uses data collected in 2019 and 2020 at the SuperKEKB asymmetric $e^+e^-$ collider, with an integrated luminosity of $62.8~fb^{-1}$, corresponding to $68.2$ million of $B\bar{B}$ pairs produced. The signal yield is obtained via an unbinned maximum likelihood fit to signal sensitive variables, obtaining branching ratios: $$\mathcal{B}\left(B^\pm\toη'K^\pm\right) = \left(63.4~^{+3.4}_{-3.3}\,(stat)\,\pm3.2\,(syst)\,\right) \times10^{-6} $$ $$\mathcal{B}\left(B_0\toη'K_S\right) = \left(59.9~^{+5.8}_{-5.5}\,(stat)\,\pm2.9\,(syst)\,\right) \times10^{-6} $$ which are consistent with world average.

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