arXiv subjects

D. N. Brown

Publications and source records attributed to D. N. Brown.

At least 37 records · Page 2Linked to original sources

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 $A_{CP} (B^{0} \to K^{0} π^{0})= -0.41_{-0.32}^{+0.30} (stat) \pm 0.09 (syst)$.

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arXiv2022

Detector and Beamline Simulation for Next-Generation High Energy Physics Experiments

The success of high energy physics programs relies heavily on accurate detector simulations and beam interaction modeling. The increasingly complex detector geometries and beam dynamics require sophisticated techniques in order to meet the demands of current and future experiments. Common software tools used today are unable to fully utilize modern computational resources, while data-recording rates are often orders of magnitude larger than what can be produced via simulation. In this paper, we describe the state, current and future needs of high energy physics detector and beamline simulations and related challenges, and we propose a number of possible ways to address them.

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arXiv2022

Mu2e-II: Muon to electron conversion with PIP-II

An observation of Charged Lepton Flavor Violation (CLFV) would be unambiguous evidence for physics beyond the Standard Model. The Mu2e and COMET experiments, under construction, are designed to push the sensitivity to CLFV in the mu to e conversion process to unprecedented levels. Whether conversion is observed or not, there is a strong case to be made for further improving sensitivity, or for examining the process on additional target materials. Mu2e-II is a proposed upgrade to Mu2e, with at least an additional order of magnitude in sensitivity to the conversion rate over Mu2e. The approach and challenges for this proposal are summarized. Mu2e-II may be regarded as the next logical step in a continued high-intensity muon program at FNAL.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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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arXiv2021

Measurements of branching fractions and direct ${\it CP}$-violating asymmetries in $B^+ \to K^+ π^0~\mbox{and}~π^+ π^0$ decays using 2019 and 2020 Belle II data

We report measurements of branching fractions ($\mathcal B$) and direct ${\it CP}$-violating asymmetries ($\mathcal A_{\it CP}$) for the decays $B^+\to K^+π^0$ and $B^+ \to π^+π^0$ reconstructed with the Belle II detector in a sample of asymmetric-energy electron-positron collisions at the $Υ(4S)$ resonance corresponding to 62.8 $\text{fb}^{-1}$ of integrated luminosity. The results are $\mathcal{B}(B^+ \to K^+π^0) = [11.9 ^{+1.1}_{-1.0} (\rm stat)\pm 1.6(\rm syst)]\times 10^{-6}$, $\mathcal{B}(B^+ \to π^+π^0) = [5.5 ^{+1.0}_{-0.9} (\rm stat)\pm 0.7(\rm syst)]\times 10^{-6}$, $\mathcal A_{\it CP}(B^+ \to K^+π^0) = -0.09 \pm 0.09 (\rm stat)\pm 0.03(\rm syst)$, and $\mathcal A_{\it CP}(B^+ \to π^+π^0) = -0.04 \pm 0.17 (\rm stat)\pm 0.06(\rm syst)$. The results are consistent with previous measurements and show a detector performance comparable with early Belle performance.

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arXiv2021

First search for direct $CP$-violating asymmetry in $B^0 \to K^0 π^0$ decays at Belle II

We report on the first measurement of the direct $CP$-violating asymmetry ($\mathcal{A}$) in the charmless decay $B^0 \to K^0π^0$ 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 $Υ(4S)$ resonance and corresponding to $62.8$ $\text{fb}^{-1}$ of integrated luminosity. We reconstruct and select about $50$ $B^0 \to K_S^0 π^0$ candidates, and we measure $\mathcal{A}_{K^0π^0} = -0.40_{-0.44}^{+0.46} (\text{stat}) \pm 0.04 (\text{syst})$ and $\mathcal{B}(B^0 \to K^0 π^0) = [8.5_{-1.6}^{+1.7} (\text{stat}) \pm 1.2 (\text{syst})] \times 10^{-6}$. This is the first measurement of $CP$ violation in $B^0 \to K^0π^0$ decays reported by Belle II. The results agree with previous determinations and show a detector performance comparable with the best Belle results.

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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

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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