Advanced search in
Research products
arrow_drop_down
Searching FieldsTerms
Project
arrow_drop_down
is
arrow_drop_down
[FLAVOUR] Towards the Construction of the Fundamental Theory of Flavour (267104)
Include:
The following results are related to Canada. Are you interested to view more results? Visit OpenAIRE - Explore.
12 Research products, page 1 of 2

  • Canada
  • Publications

10
arrow_drop_down
Date (most recent)
arrow_drop_down
  • Open Access
    Authors: 
    Belle II collaboration; Abudinén, F.; Adachi, I.; Adak, R.; Adamczyk, K.; Ahlburg, P.; Ahn, J. K.; Aihara, H.; Akopov, N.; Aloisio, A.; +190 more
    Country: France
    Project: EC | FLAVOUR (267104), EC | NIOBE (700525), NSF | RUI: Studies of Heavy Qua... (1807007), NSERC , EC | JENNIFER2 (822070), EC | InterLeptons (947006), FWF | Searches for Dark Matter ... (P 31361), EC | NEPAL (819127), NSF | Experimental Nuclear Phys... (1913789), EC | EFTSTRONG (622527),...

    We report on the first Belle II measurement of the branching fraction ($\mathcal{B}$) and longitudinal polarization fraction ($f_L$) of $B^+\to \rho^+\rho^0$ decays. We reconstruct $B^+\to \rho^+(\to \pi^+\pi^0(\to \gamma\gamma))\rho^0(\to \pi^+\pi^-)$ decays in a sample of SuperKEKB electron-positron collisions collected by the Belle II experiment in 2019 and 2020 at the $\Upsilon$(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 $\mathcal{B}(B^+ \to \rho^+\rho^0) = [20.6 \pm 3.2(\rm stat) \pm 4.0(\rm syst)]\times 10^{-6}$, and $f_L(B^+ \to \rho^+\rho^0) = 0.936 ^{+0.049}_{-0.041}(\rm stat)\pm 0.021(\rm syst)$. This first Belle II $B^+ \to \rho^+\rho^0$ angular analysis yields results compatible with previous determinations, and indicates Belle II performance superior to early Belle results.

  • Open Access
    Authors: 
    Belle II collaboration; Abudinén, F.; Adachi, I.; Adak, R.; Adamczyk, K.; Ahlburg, P.; Ahn, J. K.; Aihara, H.; Akopov, N.; Aloisio, A.; +190 more
    Country: France
    Project: NSF | Experimental Nuclear Phys... (1913789), EC | NEPAL (819127), EC | FAIME (884719), FWF | Searches for Dark Matter ... (P 31361), EC | JENNIFER2 (822070), EC | EFTSTRONG (622527), EC | FLAVOUR (267104), EC | NIOBE (700525), NSF | RUI: Studies of Heavy Qua... (1807007), NSERC ,...

    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 $\Upsilon(4S)$ resonance and corresponding to $62.8$ fb$^{-1}$ of integrated luminosity. We use simulation to determine optimized event selections. The $\Delta E$ 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 $B^+ \to K^+K^-K^+$, $B^+ \to K^+\pi^-\pi^+$, and $B^0 \to K^+\pi^-\pi^0$, respectively. These yields are corrected for efficiencies determined from simulation and control data samples to obtain $\mathcal{B}(B^+ \to K^+K^-K^+) = [35.8 \pm 1.6(\rm stat) \pm 1.4 (\rm syst)]\times 10^{-6}$, $\mathcal{B}(B^+ \to K^+\pi^-\pi^+) = [67.0 \pm 3.3 (\rm stat)\pm 2.3 (\rm syst)]\times 10^{-6}$, $\mathcal{B}(B^0 \to K^+\pi^-\pi^0) = [38.1 \pm 3.5 (\rm stat)\pm 3.9 (\rm syst)]\times 10^{-6}$, $\mathcal{A}_{\rm CP}(B^+ \to K^+K^-K^+) = -0.103 \pm 0.042(\rm stat) \pm 0.020 (\rm syst)$, $\mathcal{A}_{\rm CP}(B^+ \to K^+\pi^-\pi^+) = -0.010 \pm 0.050 (\rm stat)\pm 0.021(\rm syst)$, and $\mathcal{A}_{\rm CP}(B^0 \to K^+\pi^-\pi^0) = 0.207 \pm 0.088 (\rm stat)\pm 0.011(\rm syst)$. Results are consistent with previous measurements and demonstrate detector performance comparable with the best Belle results.

  • Open Access
    Authors: 
    Belle II Collaboration; Abudinén, F.; Adachi, I.; Adak, R.; Adamczyk, K.; Ahlburg, P.; Ahn, J. K.; Aihara, H.; Akopov, N.; Aloisio, A.; +190 more
    Country: France
    Project: NSERC , EC | JENNIFER2 (822070), EC | NEPAL (819127), EC | InterLeptons (947006), EC | FLAVOUR (267104), EC | NIOBE (700525), NSF | RUI: Studies of Heavy Qua... (1807007), NSF | Experimental Nuclear Phys... (1913789), FWF | Searches for Dark Matter ... (P 31361), EC | FAIME (884719),...

    We report the first reconstruction of the $B^{0} \to \pi^{0} \pi^{0}$ 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 $\mathcal{B}(B^{0} \rightarrow \pi^{0} \pi^{0}) = [0.98^{+0.48}_{-0.39} \pm 0.27] \times 10^{-6}$. 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 $\alpha/\phi_2$ using $B \rightarrow \pi \pi$ modes. Comment: 19 pages, 4 figures. Supporting material for Moriond 2021 conference

  • Open Access English
    Authors: 
    Belle II Collaboration; Abudinén, F.; Adachi, I.; Adak, R.; Adamczyk, K.; Ahlburg, P.; Ahn, J. K.; Aihara, H.; Akopov, N.; Aloisio, A.; +190 more
    Project: EC | JENNIFER2 (822070), NSF | Experimental Nuclear Phys... (1913789), FWF | Searches for Dark Matter ... (P 31361), EC | FAIME (884719), EC | NEPAL (819127), EC | FLAVOUR (267104), EC | NIOBE (700525), NSF | RUI: Studies of Heavy Qua... (1807007), NSERC , EC | InterLeptons (947006),...

    We present preliminary results on the reconstruction of the $B^0\to J\mskip 1mu / \psi\mskip 2mu K^0_{\scriptscriptstyle L}$ decay, where $J\mskip 1mu / \psi\mskip 2mu\to\mu^+\mu^-$ 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 $J\mskip 1mu / \psi\mskip 2mu\to\mu^+\mu^-$ and $226\pm20$ with with $J\mskip 1mu / \psi\mskip 2mu\to e^+e^-$. The quoted errors are statistical only. Comment: 15 pages, 4 figures

  • Open Access English
    Authors: 
    Belle II Collaboration; Abudinén, F.; Adachi, I.; Adak, R.; Adamczyk, K.; Ahlburg, P.; Ahn, J. K.; Aihara, H.; Akopov, N.; Aloisio, A.; +190 more
    Publisher: HAL CCSD
    Country: France
    Project: EC | JENNIFER2 (822070), EC | NEPAL (819127), NSF | Experimental Nuclear Phys... (1913789), FWF | Searches for Dark Matter ... (P 31361), NSERC , EC | FAIME (884719), EC | InterLeptons (947006), EC | EFTSTRONG (622527), EC | FLAVOUR (267104), EC | NIOBE (700525),...

    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 $\Upsilon$(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 $\Delta E$ and $M_{\it bc}$ to determine signal yields of approximately 568, 103, and 115 decays for the channels $B^0 \to K^+\pi^-$, $B^+ \to K_{\rm S}^0\pi^+$, and $B^0 \to \pi^+\pi^-$, 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. Comment: 23 pages, 8 figures. Supporting material for Spring 2021 conferences

  • Open Access English
    Authors: 
    Belle II Collaboration; Abudinén, F.; Adachi, I.; Adak, R.; Adamczyk, K.; Ahlburg, P.; Ahn, J. K.; Aihara, H.; Akopov, N.; Aloisio, A.; +190 more
    Country: France
    Project: EC | JENNIFER2 (822070), EC | FLAVOUR (267104), EC | NIOBE (700525), NSF | RUI: Studies of Heavy Qua... (1807007), EC | FAIME (884719), NSERC , FWF | Searches for Dark Matter ... (P 31361), NSF | Experimental Nuclear Phys... (1913789), EC | InterLeptons (947006), EC | EFTSTRONG (622527),...

    We report on the first measurement of the direct $CP$-violating asymmetry ($\mathcal{A}$) in the charmless decay $B^0 \to K^0\pi^0$ at Belle II and an updated measurement of its branching fraction ($\mathcal{B}$). We use a sample of electron-positron collisions collected in 2019 and 2020 at the $\Upsilon(4S)$ resonance and corresponding to $62.8$ $\text{fb}^{-1}$ of integrated luminosity. We reconstruct and select about $50$ $B^0 \to K_S^0 \pi^0$ candidates, and we measure $\mathcal{A}_{{K^0\pi^0}} = -0.40_{-0.44}^{+0.46} (\text{stat}) \pm 0.04 (\text{syst})$ and $\mathcal{B}(B^0 \to K^0 \pi^0) = [8.5_{-1.6}^{+1.7} (\text{stat}) \pm 1.2 (\text{syst})] \times 10^{-6}$. This is the first measurement of $CP$ violation in $B^0 \to K^0\pi^0$ decays reported by Belle II. The results agree with previous determinations and show a detector performance comparable with the best Belle results. Comment: 19 pages, 5 figures. Supporting material for Winter 2021 conferences

  • Open Access English
    Authors: 
    Belle II Collaboration; Abudinén, F.; Adachi, I.; Adamczyk, K.; Ahlburg, P.; Aihara, H.; Akopov, N.; Aloisio, A.; Ky, N. Anh; Asner, D. M.; +190 more
    Project: EC | FLAVOUR (267104), EC | NIOBE (700525), NSF | RUI: Studies of Heavy Qua... (1807007), NSERC , NSF | Experimental Nuclear Phys... (1913789), EC | FAIME (884719), EC | InterLeptons (947006), EC | EFTSTRONG (622527), EC | NEPAL (819127), FWF | Searches for Dark Matter ... (P 31361),...

    A search for the flavor-changing neutral-current decay $B^{+}\to K^{+}\nu\bar{\nu}$ is performed at the Belle II experiment at the SuperKEKB asymmetric energy electron-positron collider. The results are based on a data sample corresponding to an integrated luminosity of $63\,\mbox{fb}^{-1}$ collected at the $\Upsilon{(4S)}$ resonance and a sample of $9\,\mbox{fb}^{-1}$ collected at an energy $60\mathrm{\,Me\kern -0.1em V}$ below the resonance. A novel measurement method is employed, which exploits topological properties of the $B^{+}\to K^{+}\nu\bar{\nu}$ decay that differ from both generic bottom-meson decays and light-quark pair production. This inclusive tagging approach offers a higher signal efficiency compared to previous searches. No significant signal is observed. An upper limit on the branching fraction of $B^{+}\to K^{+}\nu\bar{\nu}$ of $4.1 \times 10^{-5}$ is set at the 90% confidence level. Comment: 10 pages, 3 figures + supplemental material

  • Publication . Article . Conference object . Preprint . 2021
    Open Access
    Authors: 
    Belle II Collaboration; Abudinen, F.; Adachi, I.; Adak, R.; Adamczyk, K.; Ahlburg, P.; Ahn, J. K.; Aihara, H.; Akopov, N.; Aloisio, A.; +190 more
    Country: France
    Project: EC | JENNIFER2 (822070), EC | NEPAL (819127), FWF | Searches for Dark Matter ... (P 31361), NSERC , EC | InterLeptons (947006), EC | FLAVOUR (267104), EC | NIOBE (700525), NSF | RUI: Studies of Heavy Qua... (1807007), NSF | Experimental Nuclear Phys... (1913789), EC | FAIME (884719),...

    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 $\Upsilon(4S)$ 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 $h=\pi$ or $K$. These modes are either signal or control channels for measurements related to the unitarity triangle angle $\gamma$ in direct or time-dependent $CP$-violation measurements. The reported observables are the ratios between the $B\to D^{(*)}K$ and $B\to D^{(*)}\pi$ decay rates, which are found to be in agreement with previous measurements. Comment: 19 pages, 5 figures, Moriond QCD

  • Open Access English
    Authors: 
    Adachi, I.; Ahlburg, P.; Aihara, H.; Akopov, N.; Aloisio, A.; Anh Ky, N.; Asner, D. M.; Atmacan, H.; Aushev, T.; Aushev, V.; +190 more
    Publisher: APS
    Project: EC | EFTSTRONG (622527), FWF | Searches for Dark Matter ... (P 31361), NSF | Experimental Nuclear Phys... (1913789), EC | FLAVOUR (267104), EC | NIOBE (700525), NSF | RUI: Studies of Heavy Qua... (1807007), EC | NewAve (638528), NSERC , EC | JENNIFER (644294)

    Theories beyond the standard model often predict the existence of an additional neutral boson, the Z′. 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′ in the process e+e−→μ+μ−Z′ and of a lepton-flavor-violating Z′ in e+e−→e±μ∓Z′. 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 Lμ−Lτ theory, into upper limits on the Z′ coupling constant at the level of 5×10−2−1 for MZ′≤6 GeV/c2.

  • Open Access English
    Authors: 
    Belle II Collaboration; Adachi, I.; Ahlburg, P.; Aihara, H.; Akopov, N.; Aloisio, A.; Ky, N. Anh; Asner, D. M.; Atmacan, H.; Aushev, T.; +190 more
    Publisher: HAL CCSD
    Countries: France, Germany
    Project: NSF | Experimental Nuclear Phys... (1913789), FWF | Searches for Dark Matter ... (P 31361), EC | NewAve (638528), EC | JENNIFER (644294), NSERC , EC | FLAVOUR (267104), EC | NIOBE (700525), NSF | RUI: Studies of Heavy Qua... (1807007)

    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 $e^+ e^- \to \mu^+ \mu^- Z^{\prime}$ and of a lepton-flavor-violating $Z^{\prime}$ in $e^+ e^- \to e^{\pm} \mu^{\mp} Z^{\prime}$. 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 $L_{\mu}-L_{\tau}$ 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/$c^2$. Comment: 9 pages, 5 figures + supplemental materials. Accepted for publication in Physical Review Letters

Advanced search in
Research products
arrow_drop_down
Searching FieldsTerms
Project
arrow_drop_down
is
arrow_drop_down
[FLAVOUR] Towards the Construction of the Fundamental Theory of Flavour (267104)
Include:
The following results are related to Canada. Are you interested to view more results? Visit OpenAIRE - Explore.
12 Research products, page 1 of 2
  • Open Access
    Authors: 
    Belle II collaboration; Abudinén, F.; Adachi, I.; Adak, R.; Adamczyk, K.; Ahlburg, P.; Ahn, J. K.; Aihara, H.; Akopov, N.; Aloisio, A.; +190 more
    Country: France
    Project: EC | FLAVOUR (267104), EC | NIOBE (700525), NSF | RUI: Studies of Heavy Qua... (1807007), NSERC , EC | JENNIFER2 (822070), EC | InterLeptons (947006), FWF | Searches for Dark Matter ... (P 31361), EC | NEPAL (819127), NSF | Experimental Nuclear Phys... (1913789), EC | EFTSTRONG (622527),...

    We report on the first Belle II measurement of the branching fraction ($\mathcal{B}$) and longitudinal polarization fraction ($f_L$) of $B^+\to \rho^+\rho^0$ decays. We reconstruct $B^+\to \rho^+(\to \pi^+\pi^0(\to \gamma\gamma))\rho^0(\to \pi^+\pi^-)$ decays in a sample of SuperKEKB electron-positron collisions collected by the Belle II experiment in 2019 and 2020 at the $\Upsilon$(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 $\mathcal{B}(B^+ \to \rho^+\rho^0) = [20.6 \pm 3.2(\rm stat) \pm 4.0(\rm syst)]\times 10^{-6}$, and $f_L(B^+ \to \rho^+\rho^0) = 0.936 ^{+0.049}_{-0.041}(\rm stat)\pm 0.021(\rm syst)$. This first Belle II $B^+ \to \rho^+\rho^0$ angular analysis yields results compatible with previous determinations, and indicates Belle II performance superior to early Belle results.

  • Open Access
    Authors: 
    Belle II collaboration; Abudinén, F.; Adachi, I.; Adak, R.; Adamczyk, K.; Ahlburg, P.; Ahn, J. K.; Aihara, H.; Akopov, N.; Aloisio, A.; +190 more
    Country: France
    Project: NSF | Experimental Nuclear Phys... (1913789), EC | NEPAL (819127), EC | FAIME (884719), FWF | Searches for Dark Matter ... (P 31361), EC | JENNIFER2 (822070), EC | EFTSTRONG (622527), EC | FLAVOUR (267104), EC | NIOBE (700525), NSF | RUI: Studies of Heavy Qua... (1807007), NSERC ,...

    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 $\Upsilon(4S)$ resonance and corresponding to $62.8$ fb$^{-1}$ of integrated luminosity. We use simulation to determine optimized event selections. The $\Delta E$ 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 $B^+ \to K^+K^-K^+$, $B^+ \to K^+\pi^-\pi^+$, and $B^0 \to K^+\pi^-\pi^0$, respectively. These yields are corrected for efficiencies determined from simulation and control data samples to obtain $\mathcal{B}(B^+ \to K^+K^-K^+) = [35.8 \pm 1.6(\rm stat) \pm 1.4 (\rm syst)]\times 10^{-6}$, $\mathcal{B}(B^+ \to K^+\pi^-\pi^+) = [67.0 \pm 3.3 (\rm stat)\pm 2.3 (\rm syst)]\times 10^{-6}$, $\mathcal{B}(B^0 \to K^+\pi^-\pi^0) = [38.1 \pm 3.5 (\rm stat)\pm 3.9 (\rm syst)]\times 10^{-6}$, $\mathcal{A}_{\rm CP}(B^+ \to K^+K^-K^+) = -0.103 \pm 0.042(\rm stat) \pm 0.020 (\rm syst)$, $\mathcal{A}_{\rm CP}(B^+ \to K^+\pi^-\pi^+) = -0.010 \pm 0.050 (\rm stat)\pm 0.021(\rm syst)$, and $\mathcal{A}_{\rm CP}(B^0 \to K^+\pi^-\pi^0) = 0.207 \pm 0.088 (\rm stat)\pm 0.011(\rm syst)$. Results are consistent with previous measurements and demonstrate detector performance comparable with the best Belle results.

  • Open Access
    Authors: 
    Belle II Collaboration; Abudinén, F.; Adachi, I.; Adak, R.; Adamczyk, K.; Ahlburg, P.; Ahn, J. K.; Aihara, H.; Akopov, N.; Aloisio, A.; +190 more
    Country: France
    Project: NSERC , EC | JENNIFER2 (822070), EC | NEPAL (819127), EC | InterLeptons (947006), EC | FLAVOUR (267104), EC | NIOBE (700525), NSF | RUI: Studies of Heavy Qua... (1807007), NSF | Experimental Nuclear Phys... (1913789), FWF | Searches for Dark Matter ... (P 31361), EC | FAIME (884719),...

    We report the first reconstruction of the $B^{0} \to \pi^{0} \pi^{0}$ 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 $\mathcal{B}(B^{0} \rightarrow \pi^{0} \pi^{0}) = [0.98^{+0.48}_{-0.39} \pm 0.27] \times 10^{-6}$. 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 $\alpha/\phi_2$ using $B \rightarrow \pi \pi$ modes. Comment: 19 pages, 4 figures. Supporting material for Moriond 2021 conference

  • Open Access English
    Authors: 
    Belle II Collaboration; Abudinén, F.; Adachi, I.; Adak, R.; Adamczyk, K.; Ahlburg, P.; Ahn, J. K.; Aihara, H.; Akopov, N.; Aloisio, A.; +190 more
    Project: EC | JENNIFER2 (822070), NSF | Experimental Nuclear Phys... (1913789), FWF | Searches for Dark Matter ... (P 31361), EC | FAIME (884719), EC | NEPAL (819127), EC | FLAVOUR (267104), EC | NIOBE (700525), NSF | RUI: Studies of Heavy Qua... (1807007), NSERC , EC | InterLeptons (947006),...

    We present preliminary results on the reconstruction of the $B^0\to J\mskip 1mu / \psi\mskip 2mu K^0_{\scriptscriptstyle L}$ decay, where $J\mskip 1mu / \psi\mskip 2mu\to\mu^+\mu^-$ 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 $J\mskip 1mu / \psi\mskip 2mu\to\mu^+\mu^-$ and $226\pm20$ with with $J\mskip 1mu / \psi\mskip 2mu\to e^+e^-$. The quoted errors are statistical only. Comment: 15 pages, 4 figures

  • Open Access English
    Authors: 
    Belle II Collaboration; Abudinén, F.; Adachi, I.; Adak, R.; Adamczyk, K.; Ahlburg, P.; Ahn, J. K.; Aihara, H.; Akopov, N.; Aloisio, A.; +190 more
    Publisher: HAL CCSD
    Country: France
    Project: EC | JENNIFER2 (822070), EC | NEPAL (819127), NSF | Experimental Nuclear Phys... (1913789), FWF | Searches for Dark Matter ... (P 31361), NSERC , EC | FAIME (884719), EC | InterLeptons (947006), EC | EFTSTRONG (622527), EC | FLAVOUR (267104), EC | NIOBE (700525),...

    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 $\Upsilon$(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 $\Delta E$ and $M_{\it bc}$ to determine signal yields of approximately 568, 103, and 115 decays for the channels $B^0 \to K^+\pi^-$, $B^+ \to K_{\rm S}^0\pi^+$, and $B^0 \to \pi^+\pi^-$, 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. Comment: 23 pages, 8 figures. Supporting material for Spring 2021 conferences

  • Open Access English
    Authors: 
    Belle II Collaboration; Abudinén, F.; Adachi, I.; Adak, R.; Adamczyk, K.; Ahlburg, P.; Ahn, J. K.; Aihara, H.; Akopov, N.; Aloisio, A.; +190 more
    Country: France
    Project: EC | JENNIFER2 (822070), EC | FLAVOUR (267104), EC | NIOBE (700525), NSF | RUI: Studies of Heavy Qua... (1807007), EC | FAIME (884719), NSERC , FWF | Searches for Dark Matter ... (P 31361), NSF | Experimental Nuclear Phys... (1913789), EC | InterLeptons (947006), EC | EFTSTRONG (622527),...

    We report on the first measurement of the direct $CP$-violating asymmetry ($\mathcal{A}$) in the charmless decay $B^0 \to K^0\pi^0$ at Belle II and an updated measurement of its branching fraction ($\mathcal{B}$). We use a sample of electron-positron collisions collected in 2019 and 2020 at the $\Upsilon(4S)$ resonance and corresponding to $62.8$ $\text{fb}^{-1}$ of integrated luminosity. We reconstruct and select about $50$ $B^0 \to K_S^0 \pi^0$ candidates, and we measure $\mathcal{A}_{{K^0\pi^0}} = -0.40_{-0.44}^{+0.46} (\text{stat}) \pm 0.04 (\text{syst})$ and $\mathcal{B}(B^0 \to K^0 \pi^0) = [8.5_{-1.6}^{+1.7} (\text{stat}) \pm 1.2 (\text{syst})] \times 10^{-6}$. This is the first measurement of $CP$ violation in $B^0 \to K^0\pi^0$ decays reported by Belle II. The results agree with previous determinations and show a detector performance comparable with the best Belle results. Comment: 19 pages, 5 figures. Supporting material for Winter 2021 conferences

  • Open Access English
    Authors: 
    Belle II Collaboration; Abudinén, F.; Adachi, I.; Adamczyk, K.; Ahlburg, P.; Aihara, H.; Akopov, N.; Aloisio, A.; Ky, N. Anh; Asner, D. M.; +190 more
    Project: EC | FLAVOUR (267104), EC | NIOBE (700525), NSF | RUI: Studies of Heavy Qua... (1807007), NSERC , NSF | Experimental Nuclear Phys... (1913789), EC | FAIME (884719), EC | InterLeptons (947006), EC | EFTSTRONG (622527), EC | NEPAL (819127), FWF | Searches for Dark Matter ... (P 31361),...

    A search for the flavor-changing neutral-current decay $B^{+}\to K^{+}\nu\bar{\nu}$ is performed at the Belle II experiment at the SuperKEKB asymmetric energy electron-positron collider. The results are based on a data sample corresponding to an integrated luminosity of $63\,\mbox{fb}^{-1}$ collected at the $\Upsilon{(4S)}$ resonance and a sample of $9\,\mbox{fb}^{-1}$ collected at an energy $60\mathrm{\,Me\kern -0.1em V}$ below the resonance. A novel measurement method is employed, which exploits topological properties of the $B^{+}\to K^{+}\nu\bar{\nu}$ decay that differ from both generic bottom-meson decays and light-quark pair production. This inclusive tagging approach offers a higher signal efficiency compared to previous searches. No significant signal is observed. An upper limit on the branching fraction of $B^{+}\to K^{+}\nu\bar{\nu}$ of $4.1 \times 10^{-5}$ is set at the 90% confidence level. Comment: 10 pages, 3 figures + supplemental material

  • Publication . Article . Conference object . Preprint . 2021
    Open Access
    Authors: 
    Belle II Collaboration; Abudinen, F.; Adachi, I.; Adak, R.; Adamczyk, K.; Ahlburg, P.; Ahn, J. K.; Aihara, H.; Akopov, N.; Aloisio, A.; +190 more
    Country: France
    Project: EC | JENNIFER2 (822070), EC | NEPAL (819127), FWF | Searches for Dark Matter ... (P 31361), NSERC , EC | InterLeptons (947006), EC | FLAVOUR (267104), EC | NIOBE (700525), NSF | RUI: Studies of Heavy Qua... (1807007), NSF | Experimental Nuclear Phys... (1913789), EC | FAIME (884719),...

    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 $\Upsilon(4S)$ 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 $h=\pi$ or $K$. These modes are either signal or control channels for measurements related to the unitarity triangle angle $\gamma$ in direct or time-dependent $CP$-violation measurements. The reported observables are the ratios between the $B\to D^{(*)}K$ and $B\to D^{(*)}\pi$ decay rates, which are found to be in agreement with previous measurements. Comment: 19 pages, 5 figures, Moriond QCD

  • Open Access English
    Authors: 
    Adachi, I.; Ahlburg, P.; Aihara, H.; Akopov, N.; Aloisio, A.; Anh Ky, N.; Asner, D. M.; Atmacan, H.; Aushev, T.; Aushev, V.; +190 more
    Publisher: APS
    Project: EC | EFTSTRONG (622527), FWF | Searches for Dark Matter ... (P 31361), NSF | Experimental Nuclear Phys... (1913789), EC | FLAVOUR (267104), EC | NIOBE (700525), NSF | RUI: Studies of Heavy Qua... (1807007), EC | NewAve (638528), NSERC , EC | JENNIFER (644294)

    Theories beyond the standard model often predict the existence of an additional neutral boson, the Z′. 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′ in the process e+e−→μ+μ−Z′ and of a lepton-flavor-violating Z′ in e+e−→e±μ∓Z′. 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 Lμ−Lτ theory, into upper limits on the Z′ coupling constant at the level of 5×10−2−1 for MZ′≤6 GeV/c2.

  • Open Access English
    Authors: 
    Belle II Collaboration; Adachi, I.; Ahlburg, P.; Aihara, H.; Akopov, N.; Aloisio, A.; Ky, N. Anh; Asner, D. M.; Atmacan, H.; Aushev, T.; +190 more
    Publisher: HAL CCSD
    Countries: France, Germany
    Project: NSF | Experimental Nuclear Phys... (1913789), FWF | Searches for Dark Matter ... (P 31361), EC | NewAve (638528), EC | JENNIFER (644294), NSERC , EC | FLAVOUR (267104), EC | NIOBE (700525), NSF | RUI: Studies of Heavy Qua... (1807007)

    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 $e^+ e^- \to \mu^+ \mu^- Z^{\prime}$ and of a lepton-flavor-violating $Z^{\prime}$ in $e^+ e^- \to e^{\pm} \mu^{\mp} Z^{\prime}$. 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 $L_{\mu}-L_{\tau}$ 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/$c^2$. Comment: 9 pages, 5 figures + supplemental materials. Accepted for publication in Physical Review Letters