arXiv subjects

A. Bondar

Publications and source records attributed to A. Bondar.

At least 253 records · Page 14Linked to original sources

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.

hep-ex↗

arXiv2020

The well correlated DIBs at $λλ$ 6196, 6614 Å and their possible companions

Considered here is the interrelation between five diffuse interstellar bands (DIBs): $λλ$ 5545, 6113, 6196, 6445 and 6614 Å. Two DIBs ($λ$ 6196 and $λ$ 6614 Å) have already been known as well correlated with each other; their relation with three other, weaker bands, was investigated for the first time. To accomplish this task high-resolution spectra ($λ/Δλ$ $\approx$ 100,000) with high signal-to-noise ratio (S/N) of 54 hot O -- B stars with reddening 0.12 -- 1.45 mag were used. Analysis of measured equivalent widths has allowed to establish linear dependencies and evaluate linear correlation coefficients as high as 0.968 -- 0.988 between the intensities of these five DIBs. Such a degree of correlation may indicate their common origin. Several spacings in wavenumbers found between these DIBs correspond to the energies of vibrational transitions in some PAHs resulting in IR emissions at $λλ$ 16.4, 11.3, 7.7, 6.2 and 3.3 $μ$m.

astro-ph.GA↗

arXiv2020

Observation of the semileptonic decay $B^{+}\to p\overline{p}μ^{+}ν_μ$

The Cabibbo-suppressed semileptonic decay $B^{+}\to p\overline{p}μ^{+}ν_μ$ is observed for the first time using a sample of $pp$ collisions corresponding to an integrated luminosity of 1.0, 2.0 and 1.7fb$^{-1}$ at centre-of-mass energies of 7, 8 and 13TeV, respectively. The differential branching fraction is measured as a function of the $p\overline{p}$ invariant mass using the decay mode $B^{+}\to J/ψK^{+}$ for normalisation. The total branching fraction is measured to be \begin{align*} \mathcal{B}(B^{+}\to p\overline{p}μ^{+}ν_μ) = (5.27 ^{+0.23}_{-0.24} \pm 0.21 \pm 0.15)\times 10^{-6}, \end{align*} where the first uncertainty is statistical, the second systematic and the third is from the uncertainty on the branching fraction of the normalisation channel.

hep-ex↗

arXiv2020

Search for the rare decays $B^0_s\to e^+e^-$ and $B^0\to e^+e^-$

A search for the decays $B^0_s\to e^+e^-$ and $B^0\to e^+e^-$ is performed using data collected with the LHCb experiment in proton-proton collisions at center-of-mass energies of $7$, $8$ and $13\,\text{TeV}$, corresponding to integrated luminosities of $1$, $2$ and $2\,\text{fb}^{-1}$, respectively. No signal is observed. Assuming no contribution from $B^0\to e^+e^-$ decays, an upper limit of $\mathcal{B}(B^0_s\to e^+e^-)<9.4\,(11.2)\times10^{-9}$ is obtained at $90\,(95)\,\%$ confidence level. If no $B^0_s\to e^+e^-$ contribution is assumed, a limit of $\mathcal{B}(B^0\to e^+e^-)<2.5\,(3.0)\times10^{-9}$ is determined at $90\,(95)\,\%$ confidence level. These upper limits are more than one order of magnitude lower than the previous values.

hep-ex↗

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.

hep-ex↗

arXiv2020

Test of lepton universality with $Λ^{0}_{b} \to p K^- \ell^+ \ell^-$ decays

The ratio of branching fractions of the decays $Λ^{0}_{b}\to pK^{-}e^{+}e^{-}$ and $Λ^{0}_{b}\to pK^{-}μ^{+}μ^{-}$, $R^{-1}_{pK}$, is measured for the first time using proton-proton collision data corresponding to an integrated luminosity of 4.7 $fb^{-1}$ recorded with the LHCb experiment at center-of-mass energies of 7, 8 and 13 TeV. In the dilepton mass-squared range $0.1 < q^{2} < 6.0$ $GeV^{2}/c^{4}$ and the $pK^{-}$ mass range $m(pK^{-}) < 2600$ $MeV/c^{2}$, the ratio of branching fractions is measured to be $R^{-1}_{pK} = 1.17 ^{+0.18}_{-0.16} \pm 0.07$, where the first uncertainty is statistical and the second systematic. This is the first test of lepton universality with b baryons and the first observation of the decay $Λ^{0}_{b}\to pK^{-}e^{+}e^{-}$.

hep-ex↗

arXiv2020

Observation of unusual slow components in electroluminescence signal of two-phase argon detector

Proportional electroluminescence (EL) in noble gases is used in two-phase detectors for dark matter search to record ionization signals in the gas phase induced by particle scattering in the liquid phase (S2 signals). In this work, the EL pulse-shapes in a two-phase argon detector have for the first time been studied systematically in a wide range of reduced electric field, varying from 3 to 9 Td. The pulse-shapes were studied at different readout configurations and spectral ranges: using cryogenic PMTs and SiPMs, with and without a wavelength shifter (WLS), in the VUV and visible range. We observed the fast component and two unusual slow components, with time constants of about 5 $μ$s and 40 $μ$s. The unusual characteristic property of slow components was that their contribution and time constants increased with electric field.

physics.ins-det↗

arXiv2020

Observation of primary scintillations in the visible range in liquid argon doped with methane

Neutron veto detector based on liquid scintillator containing hydrogen atoms is an integral part of any underground experiment for dark matter search. So far, a flammable mixture of liquid hydrocarbons was used as a liquid scintillator in such detectors. A safe alternative might be a liquid scintillator based on liquid argon doped with methane. In this work, we have studied the primary scintillations in pure liquid argon and its mixtures with methane, the CH4 content varying from 100 ppm to 5%. The primary scintillations have for the first time been observed in liquid argon doped with methane, in the visible and near infrared range, and their relative light yields have been measured as a function of the CH4 content.

physics.ins-det↗

arXiv2020

Measurement of $|V_{cb}|$ with $B_s^0 \to D_s^{(*)-} μ^+ ν_μ$ decays

The element $|V_{cb}|$ of the Cabibbo-Kobayashi-Maskawa matrix is measured using semileptonic $B_s^0$ decays produced in proton-proton collision data collected with the LHCb detector at center-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of 3 fb$^{-1}$. Rates of $B_s^0 \to D_s^{-} μ^+ ν_μ$ and $B_s^0 \to D_s^{*-} μ^+ ν_μ$ decays are analyzed using hadronic form-factor parametrizations derived either by Caprini, Lellouch and Neubert (CLN) or by Boyd, Grinstein and Lebed (BGL). The measured values of $|V_{cb}|$ are ${(41.4 \pm 0.6 \pm 0.9 \pm 1.2)\times 10^{-3}}$ and ${(42.3 \pm 0.8 \pm 0.9 \pm 1.2)\times 10^{-3}}$ in the CLN and BGL parametrization, respectively. The first uncertainty is statistical, the second systematic, and the third is due to the external inputs used in the measurement. These results are in agreement with those obtained from decays of $B^+$ and $B^0$ mesons. They are the first determinations of $|V_{cb}|$ at a hadron-collider experiment and the first using $B_s^0$ meson decays.

hep-ex↗

arXiv2020

Measurement of $CP$ violation in $B^0\to D^{*\pm} D^{\mp}$ decays

The decay-time-dependent $CP$ asymmetry in $B^0 \to D^{*\pm}D^{\mp}$ decays is measured using a data set corresponding to an integrated luminosity of $9$fb$^{-1}$ recorded by the LHCb detector in proton-proton collisions at centre-of-mass energies of 7, 8 and 13 TeV. The $CP$ parameters are measured as $ S_{D^*D} = -0.861 \pm 0.077\,\text{(stat)} \pm 0.019 \,\text{(syst)}\,, $ $ ΔS_{D^*D} = 0.019 \pm 0.075 \,\text{(stat)} \pm 0.012 \,\text{(syst)} \,, $ $ C_{D^*D} = -0.059 \pm 0.092 \,\text{(stat)} \pm 0.020 \,\text{(syst)} \,, $ $ ΔC_{D^*D} = -0.031 \pm 0.092 \,\text{(stat)} \pm 0.016 \,\text{(syst)} \,, $ $ {\cal A}_{D^*D} = 0.008 \pm 0.014 \,\text{(stat)} \pm 0.006 \,\text{(syst)}\,. $ The analysis provides the most precise single measurement of $CP$ violation in this decay channel to date. All parameters are consistent with their current world average values.

hep-ex↗

arXiv2020

Measurement of $f_s / f_u$ variation with proton-proton collision energy and $B$-meson kinematics

The ratio of the $\mathrm{B}^0_\mathrm{s}$ and $\mathrm{B}^+$ fragmentation fractions $f_\mathrm{s}$ and $f_u$ is studied with $B^0_\mathrm{s}\to\mathrm{J}/ψϕ$ and $B^+\to\mathrm{J}/ψK^+$ decays using data collected by the LHCb experiment in proton-proton collisions at 7, 8 and 13$\text{ TeV}$ center-of-mass energies. The analysis is performed in bins of $\mathrm{B}$-meson momentum, longitudinal momentum, transverse momentum, pseudorapidity and rapidity. The fragmentation-fraction ratio $f_\mathrm{s} / f_u$ is observed to depend on the $\mathrm{B}$-meson transverse momentum with a significance of $6.0\,σ$. This dependency is driven by the 13$\text{ TeV}$ sample ($8.7\,σ$) while the results for the other collision energies are not significant when considered separately. Furthermore the results show a $4.8\,σ$ evidence for an increase of $f_\mathrm{s} / f_u$ as a function of collision energy.

hep-ex↗

arXiv2020

Updated measurement of time-dependent $CP$-violating observables in $B^{0}_{s}\to J/ψK^+ K^-$ decays

The decay-time-dependent $CP$ asymmetry in $B^{0}_{s}\to J/ψK^{+} K^{-}$ decays is measured using proton-proton collision data, corresponding to an integrated luminosity of $1.9\,\mathrm{fb^{-1}}$, collected with the LHCb detector at a centre-of-mass energy of $13\,\mathrm{TeV}$ in 2015 and 2016. Using a sample of approximately 117\,000 signal decays with an invariant $K^{+} K^{-}$ mass in the vicinity of the $ϕ(1020)$ resonance, the $CP$-violating phase $ϕ_s$ is measured, along with the difference in decay widths of the light and heavy mass eigenstates of the $B^{0}_{s}$-$\bar{B}^{0}_{s}$ system, $ΔΓ_s$. The difference of the average $B^{0}_{s}$ and $B^{0}$ meson decay widths, $Γ_s-Γ_d$, is determined using in addition a sample of $B^{0} \to J/ψK^{+} π^{-}$ decays. The values obtained are $ϕ_s = -0.083\pm0.041\pm0.006\,\mathrm{rad}$, $ΔΓ_s = 0.077 \pm 0.008 \pm 0.003\, \mathrm{ps^{-1}}$ and $Γ_s-Γ_d = -0.0041 \pm 0.0024 \pm 0.0015\,\mathrm{ps^{-1}}$, where the first uncertainty is statistical and the second systematic. These are the most precise single measurements of these quantities to date and are consistent with expectations based on the Standard Model and with a previous LHCb analysis of this decay using data recorded at centre-of-mass energies 7 and 8 TeV. Finally, the results are combined with recent results from $B^{0}_{s}\to J/ψπ^{+} π^{-}$ decays obtained using the same dataset as this analysis, and with previous independent LHCb results.

hep-ex↗

arXiv2020

Isospin amplitudes in $Λ_b^0\to J/ψΛ(Σ^0)$ and $Ξ_b^0\to J/ψΞ^0(Λ)$ decays

Ratios of isospin amplitudes in hadron decays are a useful probe of the interplay between weak and strong interactions, and allow searches for physics beyond the Standard Model. We present the first results on isospin amplitudes in $b$-baryon decays, using data corresponding to an integrated luminosity of 8.5 fb$^{-1}$, collected with the LHCb detector in $pp$ collisions at center of mass energies of 7, 8 and 13 TeV. The isospin amplitude ratio $|A_1(Λ_b^0\to J/ψΣ^0)/A_0(Λ_b^0\to J/ψΛ)|$, where the subscript on $A$ indicates the final-state isospin, is measured to be less than 1/21.8 at 95\% confidence level. The Cabibbo suppressed $Ξ_b^0\to J/ψΛ$ decay is observed for the first time, allowing for the measurement $|A_0(Ξ_b^0\to J/ψΛ)/A_{1/2}(Ξ_b^0\to J/ψΞ^0)| =0.37 \pm 0.06\pm 0.02$, where the uncertainties are statistical and systematic, respectively.

hep-ex↗

arXiv2020

Measurement of the weak mixing angle at a Super Charm-Tau factory with data-driven monitoring of the average electron beam polarization

A method for measuring the average longitudinal polarization of the electron beam at an electron-positron collider operating near the $J/ψ$ resonance is proposed. The method utilizes the differential cross-section of $J/ψ\to [Λ\to pπ^-][\barΛ\to\bar{p}π^+]$ decay. It can be used to measure the average longitudinal polarization of electrons with the statistical precision better than $10^{-3}$ at a Super Charm-Tau factory operating at the luminosity of $10^{35}~\mathrm{cm}{}^{-2}\mathrm{s}{}^{-1}$. The method is discussed in the context of the weak mixing angle measurement in the same experiment.

hep-ph↗

arXiv2020

Search for the lepton flavour violating decay $B^+ \rightarrow K^+ μ^- τ^+$ using $B_{s2}^{*0}$ decays

A search is presented for the lepton flavour violating decay $B^+ \rightarrow K^+ μ^- τ^+$ using a sample of proton--proton collisions at centre-of-mass energies of 7, 8, and 13 TeV, collected with the LHCb detector and corresponding to a total integrated luminosity of 9 fb${}^{-1}$. The $τ$ leptons are selected inclusively, primarily via decays with a single charged particle. The four-momentum of the $τ$ lepton is determined by using $B^+$ mesons from $B_{s2}^{*0} \rightarrow B^+ K^-$ decays. No significant excess is observed, and an upper limit is set on the branching fraction $B(B^+ \rightarrow K^+ μ^- τ^+) < 3.9 \times 10^{-5}$ at 90% confidence level. The obtained limit is comparable to the world-best limit.

hep-ex↗

arXiv2020

Measurement of the $η_c(1S)$ production cross-section in $pp$ collisions at $\sqrt{s} = 13$ TeV

Using a data sample corresponding to an integrated luminosity of $2.0\,fb^{-1}$, collected by the LHCb experiment, the production of the $η_c(1S)$ state in proton-proton collisions at a centre-of-mass energy of $\sqrt{s}=13 \text{ TeV}$ is studied in the rapidity range ${2.0 < y < 4.5}$ and in the transverse momentum range ${6.5 < p_{T} < 14.0\text{ GeV}}$. The cross-section for prompt production of $η_c(1S)$ mesons relative to that of the $J/ψ$ meson is measured using the ${p\bar{p}}$ decay mode and is found to be ${σ_{η_c(1S)}/σ_{J/ψ} = 1.69 \pm 0.15 \pm 0.10 \pm 0.18}$. The quoted uncertainties are, in order, statistical, systematic and due to uncertainties on the branching fractions of the ${J/ψ\to p \bar{p}}$ and ${η_c\to p \bar{p}}$ decays. The prompt $η_c(1S)$ production cross-section is determined to be ${σ_{η_c(1S)} = 1.26 \pm 0.11\pm 0.08 \pm 0.14 \,μb}$, where the last uncertainty includes that on the ${J/ψ}$ meson cross-section. The ratio of the branching fractions of $b$-hadron decays to the $η_c(1S)$ and ${J/ψ}$ states is measured to be ${\mathcal{B}_{b\toη_c X}/\mathcal{B}_{b\to J/ψX} = 0.48 \pm 0.03 \pm 0.03 \pm 0.05}$, where the last uncertainty is due to those on the branching fractions of the ${J/ψ\to p \bar{p}}$ and ${η_c\to p \bar{p}}$ decays. The difference between the ${J/ψ}$ and $η_c(1S)$ masses is also determined to be ${113.0 \pm 0.7 \pm 0.1\text{ MeV}}$, which is the most precise single measurement of this quantity to date.

hep-ex↗

arXiv2020

Survey of very broad Diffuse Interstellar Bands

This paper considers a very special set of a few interstellar features --- broad diffuse interstellar bands (DIBs) at 4430, 4882, 5450, 5779 and 6175 ÅÅ. The set is small, and measurements of equivalent widths of these DIBs are challenging because of severe stellar, interstellar, and sometimes, also telluric contaminations inside their broad profiles. Nevertheless, we demonstrate that they do correlate pretty tightly (DIBs 4882 and 5450 to a lesser extent though) with other narrower diffuse bands, as well as with the color excess E(B$-$V). The studied broad DIBs correlate well with both interstellar molecule CH and interstellar K{\sc i}, i.e. it is hardly possible to verify whether the environments, facilitating the formation of very broad DIB carriers, are dominated by either molecular or atomic gas as both these species likely occupy the same volume.

astro-ph.GA↗

arXiv2020

First observation of excited $Ω_b^-$ states

We report four narrow peaks in the $Ξ_b^0K^-$ mass spectrum obtained using $pp$ collisions at center-of-mass energies of 7, 8 and 13 TeV, corresponding to a total integrated luminosity of 9 fb$^{-1}$ recorded by the LHCb experiment. Referring to these states by their mass, the mass values are \begin{align*} m(Ω_b(6316)^-) &= 6315.64\pm0.31\pm0.07\pm0.50 {\rm MeV}, \\ m(Ω_b(6330)^-) &= 6330.30\pm0.28\pm0.07\pm0.50 {\rm MeV}, \\ m(Ω_b(6340)^-) &= 6339.71\pm0.26\pm0.05\pm0.50 {\rm MeV}, \\ m(Ω_b(6350)^-) &= 6349.88\pm0.35\pm0.05\pm0.50 {\rm MeV}, \end{align*}where the uncertainties are statistical, systematic and the last is due to the knowledge of the $Ξ_b^0$ mass. The natural widths of the three lower mass states are consistent with zero, and the 90% confidence-level upper limits are determined to be ${Γ(Ω_b(6316)^-)<2.8}$ MeV, ${Γ(Ω_b(6330)^-)<3.1}$ MeV and ${Γ(Ω_b(6340)^-)<1.5}$ MeV. The natural width of the $Ω_b(6350)^-$ peak is $1.4^{+1.0}_{-0.8}\pm0.1$ MeV, which is 2.5$σ$ from zero and corresponds to an upper limit of 2.8 MeV. The peaks have local significances ranging from 3.6$σ$ to 7.2$σ$. After accounting for the look-elsewhere effect, the significances of the $Ω_b(6316)^-$ and $Ω_b(6330)^-$ peaks are reduced to 2.1$σ$ and 2.6$σ$ respectively, while the two higher mass peaks exceed 5$σ$. The observed peaks are consistent with expectations for excited $Ω_b^-$ resonances.

hep-ex↗