arXiv subjects

A. Bondar

Publications and source records attributed to A. Bondar.

At least 397 records · Page 22Linked to original sources

arXiv2018

Measurement of the ratio of branching fractions $\mathcal{B}(B_c^+\,\to\,J/ψτ^+ν_τ)$/$\mathcal{B}(B_c^+\,\to\,J/ψμ^+ν_μ)$

A measurement is reported of the ratio of branching fractions $\mathcal{R}(J/ψ)=\mathcal{B}(B_c^+\,\to\,J/ψτ^+ν_τ)/\mathcal{B}(B_c^+\,\to\,J/ψμ^+ν_μ)$, where the $τ^+$ lepton is identified in the decay mode $τ^+\,\to\,μ^+ν_μ\overlineν_τ$. This analysis uses a sample of proton-proton collision data corresponding to 3.0$\mathrm{\,fb}^{-1}$ of integrated luminosity recorded with the LHCb experiment at center-of-mass energies $7\,\mathrm{TeV}$ and $8\,\mathrm{TeV}$. A signal is found for the decay $B_c^+\,\to\,J/ψτ^+ν_τ$ at a significance of 3 standard deviations, corrected for systematic uncertainty, and the ratio of the branching fractions is measured to be $\mathcal{R}(J/ψ) = 0.71 \pm 0.17 \mathrm{\,(stat)} \pm 0.18\mathrm{\,(syst)}$. This result lies within 2 standard deviations above the range of existing predictions in the Standard Model.

hep-ex↗

arXiv2018

Observation of $Υ(4S)\to η' Υ(1S)$

We report the first observation of the hadronic transition $Υ(4S)\toη'Υ(1S)$, using 496 fb$^{-1}$ data collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^{+}e^{-}$ collider. We reconstruct the $η'$ meson through its decays to $ρ^0γ$ and to $π^+π^-η$, with $η\toγγ$. We measure: ${\cal B}(Υ(4S)\toη'Υ(1S))=(3.43\pm 0.88 {\rm(stat.)} \pm 0.21 {\rm(syst.)})\times10^{-5}$, with a significance of 5.7$σ$.

hep-ex↗

arXiv2018

A method for model-independent measurement of the CKM angle $β$ via time-dependent analysis of the $B^0\to Dπ^+π^-$, $D\to K_S^0π^+π^-$ decays

A new method for model-independent measurement of the CKM angle $β$ is proposed, that employs time-dependent analysis of flavour-tagged $B^0\to Dπ^+π^-$ decays with $D$ meson decays into CP-specific and~$K_S^0π^+π^-$ final states. This method can be used to measure the angle $β$ with future data from the Belle II and LHCb experiments with the precision level of one degree.

hep-ph↗

arXiv2018

Measurement of $CP$ asymmetry in $B_s^0 \to D_s^{\mp} K^{\pm}$ decays

We report the measurements of the $CP$-violating parameters in $B_s^0 \to D_s^{\mp} K^{\pm}$ decays observed in $pp$ collisions, using a data set corresponding to an integrated luminosity of $3.0\,\text{fb}^{-1}$ recorded with the LHCb detector. We measure $C_f = 0.73 \pm 0.14 \pm 0.05$, $A^{ΔΓ}_f = 0.39 \pm 0.28 \pm 0.15$, $A^{ΔΓ}_{\overline{f}} = 0.31 \pm 0.28 \pm 0.15$, $S_f = -0.52 \pm 0.20 \pm 0.07$, $S_{\overline{f}} = -0.49 \pm 0.20 \pm 0.07$, where the uncertainties are statistical and systematic, respectively. These parameters are used together with the world-average value of the $B_s^0$ mixing phase, $-2β_s$, to obtain a measurement of the CKM angle $γ$ from $B_s^0 \to D_s^{\mp} K^{\pm}$ decays, yielding $γ= (128\,_{-22}^{+17})^\circ$ modulo $180^\circ$, where the uncertainty contains both statistical and systematic contributions. This corresponds to $3.8\,σ$ evidence for $CP$ violation in the interference between decay and decay after mixing.

hep-ex↗

arXiv2018

Measurement of the shape of the $Λ_b^0\toΛ_c^+ μ^- \overlineν$ differential decay rate

A measurement of the shape of the differential decay rate and the associated Isgur-Wise function for the decay $Λ_b^0\toΛ_c^+μ^-\overlineν$ is reported, using data corresponding to $3 fb^{-1}$ collected with the LHCb detector in proton-proton collisions. The $Λ_c^+μ^-\overlineν$(+ anything) final states are reconstructed through the detection of a muon and a $Λ_c^+$ baryon decaying into $pK^-π^+$, and the decays $Λ_b^0\toΛ_c^+π^+π^-μ^-\overlineν$ are used to determine contributions from $Λ_b^0\to Λ_c^{\star+}μ^-\barν$ decays. The measured dependence of the differential decay rate upon the squared four-momentum transfer between the heavy baryons, $q^2$, is compared with expectations from heavy-quark effective theory and from unquenched lattice QCD predictions.

hep-ex↗

arXiv2018

Inclusive study of bottomonium production in association with an $η$ meson in $e^+e^-$ annihilations near $Υ(5S)$

We study bottomonium production in association with an $η$ meson in $e^+e^-$ annihilations near the $Υ(5S)$, at a center of mass energy of $\sqrt{s}=10.866\,$GeV. The results are based on the $121.4\,$fb$^{-1}$ data sample collected by the Belle experiment at the asymmetric energy KEKB collider. Only the $η$ meson is reconstructed and the missing-mass spectrum of $η$ candidates is investigated. We observe the $e^+e^-\toηΥ_J(1D)$ process and find evidence for the $e^+e^-\toηΥ(2S)$ process, while no significant signals of $Υ(1S)$, $h_b(1P)$, nor $h_b(2P)$ are found. Cross sections for the studied processes are reported.

hep-ex↗

arXiv2018

Updated determination of $D^0$-$\overline{D}{}^0$ mixing and CP violation parameters with $D^0\to K^+π^-$ decays

We report measurements of charm-mixing parameters based on the decay-time-dependent ratio of $D^0\to K^+π^-$ to $D^0\to K^-π^+$ rates. The analysis uses a data sample of proton-proton collisions corresponding to an integrated luminosity of $5.0$ fb$^{-1}$ recorded by the LHCb experiment from 2011 through 2016. Assuming charge-parity (CP) symmetry, the mixing parameters are determined to be $x'^2=(3.9 \pm 2.7) \times10^{-5}$, $y'=(5.28 \pm 0.52) \times 10^{-3}$, and $R_D=(3.454 \pm 0.031)\times10^{-3}$. Without this assumption, the measurement is performed separately for $D^0$ and $\overline{D}{}^0$ mesons, yielding a direct CP-violating asymmetry $A_D =(-0.1\pm9.1)\times10^{-3}$, and magnitude of the ratio of mixing parameters $1.00< |q/p| <1.35$ at the $68.3\%$ confidence level. All results include statistical and systematic uncertainties and improve significantly upon previous single-measurement determinations. No evidence for CP violation in charm mixing is observed.

hep-ex↗

arXiv2018

Measurement of branching fractions of charmless four-body $Λ_b^0$ and $Ξ_b^0$ decays

A search for charmless four-body decays of $Λ_{b}^{0}$ and $Ξ_{b}^{0}$ baryons with a proton and three charged mesons (either kaons or pions) in the final state is performed. The data sample used was recorded in 2011 and 2012 with the LHCb experiment and corresponds to an integrated luminosity of 3 fb$^{-1}$. Six decay modes are observed, among which $Λ_{b}^{0} \to pK^{-}π^{+}π^{-}$, $Λ_{b}^{0} \to pK^{-}K^{+}K^{-}$, $Ξ_{b}^{0} \to pK^{-}π^{+}π^{-}$ and $Ξ_{b}^{0} \to pK^{-} π^{+}K^{-}$ are established for the first time. Their branching fractions (including the ratio of hadronisation fractions in the case of the $Ξ_{b}^{0}$ baryon) are determined relative to the $Λ_{b}^{0} \to Λ_{c}^{+}π^{-}$ decay.

hep-ex↗

arXiv2018

Search for $C$ violation in the decay $η\rightarrowπ^0+e^++e^-$ with WASA-at-COSY

We report on the investigation of the rare decay $η\rightarrowπ^0+\text{e}^++\text{e}^-$ which is of interest to study both $C$ violation in the electromagnetic interaction and to search for contributions from physics beyond the Standard Model, since the allowed decay via a two-photon intermediate state is strongly suppressed. The experiment has been performed using the WASA-at-COSY installation, located at the COSY accelerator of the Forschungszentrum Jülich, Germany. In total $3\times10^7$ events of the reaction $\text{p}+\text{d}\rightarrow{^3\text{He}}+η$ have been recorded at an excess energy of $Q = 59.8\,\textrm{MeV}$. Based on this data set the $C$ parity violating decay $η\rightarrowπ^0+γ^*\rightarrowπ^0+\textrm{e}^++\textrm{e}^-$ via a single-photon intermediate state has been searched for, resulting in new upper limits of $Γ\left(η\rightarrowπ^0+\textrm{e}^++\textrm{e}^-\right)/ Γ\left(η\rightarrowπ^++π^-+π^0\right) < 3.28\times10^{-5}$ and $Γ\left(η\rightarrowπ^0+\textrm{e}^++\textrm{e}^-\right)/ Γ\left(η\rightarrow\textrm{all}\right) < 7.5\times10^{-6}\ (\textrm{CL} = 90\,\%)$, respectively.

hep-ex↗

arXiv2018

Search for excited $B_c^+$ states

A search is performed in the invariant mass spectrum of the $B_c^{+}π^{+}π^{-}$ system for the excited $B_c^{+}$ states $B_c(2^{1}S_{0})^+$ and $B_c(2^{3}S_{1})^+$ using a data sample of $pp$ collisions collected by the LHCb experiment at the centre-of-mass energy of $\sqrt{s} = 8 \,{\mathrm{TeV}}$, corresponding to an integrated luminosity of $2 \,{\mathrm{fb^{-1}}}$. No evidence is seen for either state. Upper limits on the ratios of the production cross-sections of the $B_c(2^{1}S_{0})^+$ and $B_c(2^{3}S_{1})^+$ states times the branching fractions of ${B_c(2^{1}S_{0})^+} \to {B_c^{+}π^{+}π^{-}}$ and ${B_c(2^{3}S_{1})^+} \to {B_c^{*+}π^{+}π^{-}}$ over the production cross-section of the $B_c^{+}$ state are given as a function of their masses. They are found to be between 0.02 and 0.14 at $95\%$ confidence level for $B_c(2^{1}S_{0})^+$ and $B_c(2^{3}S_{1})^+$ in the mass ranges $[6830, 6890] \,{\mathrm{MeV}}/c^{2}$ and $[6795,6890] \,{\mathrm{MeV}}/c^{2}$, respectively.

hep-ex↗

arXiv2018

Search for dark photons produced in 13 TeV $pp$ collisions

Searches are performed for both prompt-like and long-lived dark photons, $A^{\prime}$, produced in proton-proton collisions at a center-of-mass energy of 13 TeV, using $A^{\prime}\toμ^+μ^-$ decays and a data sample corresponding to an integrated luminosity of 1.6 fb$^{-1}$ collected with the LHCb detector. The prompt-like $A^{\prime}$ search covers the mass range from near the dimuon threshold up to 70 GeV, while the long-lived $A^{\prime}$ search is restricted to the low-mass region $214<m(A^{\prime})<350$ MeV. No evidence for a signal is found, and 90% confidence level exclusion limits are placed on the $γ$-$A^{\prime}$ kinetic-mixing strength. The constraints placed on prompt-like dark photons are the most stringent to date for the mass range $10.6 < m(A^{\prime}) < 70$ GeV, and are comparable to the best existing limits for $m(A^{\prime}) < 0.5$ GeV. The search for long-lived dark photons is the first to achieve sensitivity using a displaced-vertex signature.

hep-ex↗

arXiv2018

First observation of forward $Z \rightarrow b \bar{b}$ production in $pp$ collisions at $\sqrt{s}=8$ TeV

The decay $Z \rightarrow b \bar{b}$ is reconstructed in $pp$ collision data, corresponding to 2 fb$^{-1}$ of integrated luminosity, collected by the LHCb experiment at a centre-of-mass energy of $\sqrt{s}=8$ TeV. The product of the $Z$ production cross-section and the $Z \rightarrow b \bar{b}$ branching fraction is measured for candidates in the fiducial region defined by two particle-level $b$-quark jets with pseudorapidities in the range $2.2 < η< 4.2$, with transverse momenta $p_{T}>20$ GeV and dijet invariant mass in the range $45 < m_{jj} < 165$ GeV. From a signal yield of $5462 \pm 763$ $Z \rightarrow b \bar{b}$ events, where the uncertainty is statistical, a production cross-section times branching fraction of $332 \pm 46 \pm 59$ pb is obtained, where the first uncertainty is statistical and the second systematic. The measured significance of the signal yield is 6.0 standard deviations. This measurement represents the first observation of the $Z \rightarrow b \bar{b}$ production in the forward region of $pp$ collisions.

hep-ex↗

arXiv2018

First observation of $B^{+} \to D_s^{+}K^{+}K^{-}$ decays and a search for $B^{+} \to D_s^{+}ϕ$ decays

A search for $B^{+} \to D_s^{+}K^{+}K^{-}$ decays is performed using $pp$ collision data corresponding to an integrated luminosity of 4.8 fb$^{-1}$, collected at centre-of-mass energies of 7, 8 and 13$\,$TeV with the LHCb experiment. A significant signal is observed for the first time and the branching fraction is determined to be \begin{equation*} \mathcal{B}(B^{+} \to D_s^{+}K^{+}K^{-} ) = (7.1 \pm 0.5 \pm 0.6 \pm 0.7) \times 10^{-6}, \end{equation*} where the first uncertainty is statistical, the second systematic and the third due to the uncertainty on the branching fraction of the normalisation mode $B^{+} \to D_s^{+} \overline{\kern -0.2em D}^{0}$. A search is also performed for the pure annihilation decay $B^{+} \to D_s^{+}ϕ$. No significant signal is observed and a limit of \begin{equation*} \mathcal{B}(B^{+} \to D_s^{+}ϕ) < 4.9 \times 10^{-7}~(4.2 \times 10^{-7}) \end{equation*} is set on the branching fraction at 95$\%$ (90$\%$) confidence level.

hep-ex↗

arXiv2018

A search for weakly decaying b-flavored pentaquarks

Investigations of the existence of pentaquark states containing a single $b$ (anti)quark decaying weakly into four specific final states J/$ψK^+π^- p$, J/$ψK^- π^- p$, J/$ψK^- π^+ p$, and $J/ψϕ(1020) p$ are reported. The data sample corresponds to an integrated luminosity of 3.0/fb in 7 and 8 TeV pp collisions acquired with the LHCb detector. Signals are not observed and upper limits are set on the product of the production cross section times branching fraction with respect to that of the $Λ_b$.

hep-ex↗

arXiv2018

Total and differential cross sections of $η$-production in proton-deuteron fusion for excess energies between $Q_η=13\;\text{MeV}$ and $Q_η=81\;\text{MeV}$

New data on both total and differential cross sections of the production of $η$ mesons in proton-deuteron fusion to ${}^3\text{He}\,η$ in the excess energy region $13.6\;\text{MeV}\leq Q_η\leq 80.9\;\text{MeV}$ are presented. These data have been obtained with the WASA-at-COSY detector setup located at the Forschungszentrum Jülich, using a proton beam at 15 different beam momenta between $p_p = 1.60\;\text{GeV}/c$ and $p_p = 1.74\;\text{GeV}/c$. While significant structure of the total cross section is observed in the energy region $20\;\text{MeV}\lesssim Q_η\lesssim 60\;\text{MeV}$, a previously reported sharp variation around $Q_η\approx 50\;\text{MeV}$ cannot be confirmed. Angular distributions show the typical forward-peaking that was reported elsewhere. For the first time, it is possible to study the development of these angular distributions with rising excess energy over a large interval.

nucl-ex↗

arXiv2018

Measurement of Branching Fractions of Hadronic Decays of the $Ω_c^0$ Baryon

Using a data sample of 980 ${\rm fb}^{-1}$ of $e^+e^-$ annihilation data taken with the Belle detector operating at the KEKB asymmetric-energy $e^+e^-$ collider, we report the results of a study of the decays of the $Ω_c^0$ charmed baryon into hadronic final states. We report the most precise measurements to date of the relative branching fractions of the $Ω_c^0$ into $Ω^-π^+π^0$, $Ω^-π^+π^-π^+$, $Ξ^-K^-π^+π^+$, and $Ξ^0K^-π^+$, as well as the first measurements of the branching fractions of the $Ω_c^0$ into $Ξ^-\bar{K}^0π^+$, $Ξ^0\bar{K}^0$, and $Λ\bar{K}^0\bar{K}^0$, all with respect to the $Ω^-π^+$ decay. In addition, we investigate the resonant substructure of these modes. Finally, we present a limit on the branching fraction for the decay $Ω_c^0\toΣ^+K^-K^-π^+$.

hep-ex↗

arXiv2018

Measurement of $CP$ violation in $B^0\rightarrow J/ψK^0_\mathrm{S}$ and $B^0\rightarrowψ(2S) K^0_\mathrm{S}$ decays

A measurement is presented of decay-time-dependent $CP$ violation in the decays $B^0\rightarrow J/ψK^0_\mathrm{S}$ and $B^0\rightarrowψ(2S) K^0_\mathrm{S}$, where the $J/ψ$ is reconstructed from two electrons and the $ψ(2S)$ from two muons. The analysis uses a sample of $pp$ collision data recorded with the LHCb experiment at centre-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of 3 $\mathrm{fb}^{-1}$. The $CP$-violation observables are measured to be \begin{equation*} \begin{aligned} C\left(B^0\rightarrow J/ψK^0_\mathrm{S}\right)&=\phantom{+}\,0.12\,\pm\,0.07\pm\,0.02\,, S\left(B^0\rightarrow J/ψK^0_\mathrm{S}\right)&=\phantom{+}\,0.83\,\pm\,0.08\pm\,0.01\,, C\left(B^0\rightarrowψ(2S) K^0_\mathrm{S}\right)&=-\,0.05\,\pm\,0.10\pm\,0.01\,, S\left(B^0\rightarrowψ(2S) K^0_\mathrm{S}\right)&=\phantom{+}\,0.84\,\pm\,0.10\pm\,0.01\,, \end{aligned} \end{equation*} where $C$ describes $CP$ violation in the direct decay, and $S$ describes $CP$ violation in the interference between the amplitudes for the direct decay and for the decay after $B^0$-$\overline{B}^0$ oscillation. The first uncertainties are statistical and the second are systematic. The two sets of results are compatible with the previous LHCb measurement using $B^0\rightarrow J/ψK^0_\mathrm{S}$ decays, where the $J/ψ$ meson was reconstructed from two muons. The averages of all three sets of LHCb results are \begin{equation*} \begin{aligned} C\left(B^0\rightarrow[c\bar{c}]K^0_\mathrm{S}\right)&=-0.017 \pm 0.029\,, S\left(B^0\rightarrow[c\bar{c}]K^0_\mathrm{S}\right)&=\phantom{+}0.760 \pm 0.034\,, \end{aligned} \end{equation*} under the assumption that higher-order contributions to the decay amplitudes are negligible. The uncertainties include statistical and systematic contributions.

hep-ex↗

arXiv2018

Measurement of the $τ$ lepton polarization and $R(D^)$ in the decay $\bar{B} \rightarrow D^ τ^- \barν_τ$ with one-prong hadronic $τ$ decays at Belle

With the full data sample of $772 \times 10^6$ $B{\bar B}$ pairs recorded by the Belle detector at the KEKB electron-positron collider, the decay $\bar{B} \rightarrow D^* τ^- \barν_τ$ is studied with the hadronic $τ$ decays $τ^- \rightarrow π^- ν_τ$ and $τ^- \rightarrow ρ^- ν_τ$. The $τ$ polarization $P_τ(D^*)$ in two-body hadronic $τ$ decays is measured, as well as the ratio of the branching fractions $R(D^{*}) = \mathcal{B}(\bar {B} \rightarrow D^* τ^- \barν_τ) / \mathcal{B}(\bar{B} \rightarrow D^* \ell^- \barν_\ell)$, where $\ell^-$ denotes an electron or a muon. Our results, $P_τ(D^*) = -0.38 \pm 0.51 {\rm (stat)} ^{+0.21}_{-0.16} {\rm (syst)}$ and $R(D^*) = 0.270 \pm 0.035{\rm (stat)} ^{+0.028}_{-0.025}{\rm (syst)}$, are consistent with the theoretical predictions of the Standard Model. The polarization values of $P_τ(D^*) > +0.5$ are excluded at the 90\% confidence level.

hep-ex↗