arXiv subjects

N. Beliy

Publications and source records attributed to N. Beliy.

At least 19 recordsLinked to original sources

arXiv2021

Constraints on the $K^0_{\mathrm{S}}\rightarrowμ^{+}μ^{-}$ branching fraction

A search for the decay $K^0_{\mathrm{S}}\rightarrowμ^{+}μ^{-}$ is performed using proton-proton collision data, corresponding to an integrated luminosity of $5.6\,\text{fb}^{-1}$ and collected with the LHCb experiment during 2016, 2017 and 2018 at a center-of-mass energy of $13\,\mathrm{TeV}$. The observed signal yield is consistent with zero, yielding an upper limit of ${\cal B}(K^0_{\mathrm{S}}\rightarrowμ^{+}μ^{-}) < 2.2 \times 10^{-10}$ at 90% CL. The limit reduces to ${\cal B}(K^0_{\mathrm{S}}\rightarrowμ^{+}μ^{-}) < 2.1 \times 10^{-10}$ at 90% CL once combined with the result from data taken in 2011 and 2012.

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arXiv2020

Search for $CP$ violation in $Ξ_c^+\rightarrow pK^-π^+$ decays using model-independent techniques

A first search for $CP$ violation in the Cabibbo-suppressed $Ξ_c^+\rightarrow pK^-π^+$ decay is performed using both a binned and an unbinned model-independent technique in the Dalitz plot. The studies are based on a sample of proton-proton collision data, corresponding to an integrated luminosity of $3.0~{\rm fb^{-1}}$, and collected by the LHCb experiment at centre-of-mass energies of $7$ and $8~\rm TeV$. The data are consistent with the hypothesis of no $CP$ violation.

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arXiv2020

Search for $C\!P$ violation and observation of $P$ violation in $Λ_b^0 \to p π^- π^+ π^-$ decays

A search for $C\!P$ violation in the $Λ_b^0 \to p π^- π^+ π^-$ decay is performed using LHCb data corresponding to an integrated luminosity of 6.6$\,fb^{-1}$ collected in $pp$ collisions at centre-of-mass energies of 7, 8 and 13$\,Te\kern -0.1em V$. The analysis uses both triple product asymmetries and the unbinned energy test method. The highest significances of $C\!P$ asymmetry are 2.9 standard deviations from triple product asymmetries and 3.0 standard deviations for the energy test method. Once the global $p$-value is considered, all results are consistent with no $C\!P$ violation. Parity violation is observed at a significance of $5.5$ standard deviations for the triple product asymmetry method and $5.3$ standard deviations for the energy test method.

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arXiv2020

Measurement of the branching fraction of the decay $B_s^0\to K_S^0 K_S^0$

A measurement of the branching fraction of the decay $B_s^0 \to K_S^0 K_S^0$ is performed using proton-proton collision data corresponding to an integrated luminosity of 5 $fb^{-1}$ collected by the LHCb experiment between 2011 and 2016. The branching fraction is determined to be BR($B_s^0 \to K_S^0 K_S^0$) = [8.3 $\pm$ 1.6 (stat) $\pm$ 0.9 (syst) $\pm$ 0.8 (norm) $\pm$ 0.3 ($f_s/f_d$)] $\times 10^{-6}$ , where the first uncertainty is statistical, the second is systematic, and the third and fourth are due to uncertainties on the branching fraction of the normalization mode $B^0 \to ϕK_S^0$ and the ratio of hadronization fractions $f_s/f_d$. This is the most precise measurement of this branching fraction to date. Furthermore, a measurement of the branching fraction of the decay $B^0 \to K_S^0 K_S^0$ is performed relative to that of the $B_s^0 \to K_S^0 K_S^0$ channel, and is found to be $\frac{BR(B^0 \to K_S^0 K_S^0)}{BR(B_s^0 \to K_S^0 K_S^0)}$ = [7.5 $\pm$ 3.1 (stat) $\pm$ 0.5 (syst) $\pm$ 0.3 ($f_s/f_d$)] $\times 10^{-2}$.

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arXiv2020

Measurement of psi(2S) production cross-sections in proton-proton collisions at 7 and 13 TeV

The cross-sections of $ψ(2S)$ meson production in proton-proton collisions at $\sqrt{s}=13~\mathrm{TeV}$ are measured with a data sample collected by the LHCb detector corresponding to an integrated luminosity of $275~p\mathrm{b}^{-1}$. The production cross-sections for prompt $ψ(2S)$ mesons and those for $ψ(2S)$ mesons from $b$-hadron decays ($ψ{(2S)}\mathrm{-from-}b$) are determined as functions of the transverse momentum, $p_{\mathrm{T}}$, and the rapidity, $y$, of the $ψ(2S)$ meson in the kinematic range $2<p_{\mathrm{T}}<20~\mathrm{GeV}/c$ and $2.0<y<4.5$. The production cross-sections integrated over this kinematic region are \begin{equation*} \begin{split} σ(\mbox{prompt }ψ(2S),13~\mathrm{TeV}) &= {1.430 \pm 0.005(\mathrm{stat}) \pm 0.099 (\mathrm{syst})μ\mathrm{b}},\\ σ(ψ(2S)\mathrm{-from-}b,13~\mathrm{TeV})&={0.426 \pm 0.002(\mathrm{stat}) \pm0.030 (\mathrm{syst})μ\mathrm{b}}. \end{split} \end{equation*} A new measurement of $ψ(2S)$ production cross-sections in $pp$ collisions at $\sqrt{s}=7~\mathrm{TeV}$ is also performed using data collected in 2011, corresponding to an integrated luminosity of $614~{p\mathrm{b}^{-1}}$.The integrated production cross-sections in the kinematic range $3.5<p_{\mathrm{T}}<14~\mathrm{GeV}/c$ and $2.0<y<4.5$ are \begin{equation*} \begin{split} σ(\mbox{prompt }ψ(2S),7~\mathrm{TeV}) &={0.471 \pm0.001 (\mathrm{stat}) \pm 0.025 (\mathrm{syst})μ\mathrm{b}},\\ σ(ψ(2S)\mathrm{-from-}b,7~\mathrm{TeV}) &={0.126\pm0.001 (\mathrm{stat}) \pm0.008 (\mathrm{syst})μ\mathrm{b}}. \end{split} \end{equation*} All results show reasonable agreement with theoretical calculations.

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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.

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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 $Λ^{0}_{b}\to pK^{-}e^{+}e^{-}$.

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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.

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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.

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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.

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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.

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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.

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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.

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arXiv2020

Determination of quantum numbers for several excited charmed mesons observed in $B^- \to D^{*+} π^- π^-$ decays

A four-body amplitude analysis of the $B^- \to D^{*+} π^- π^-$ decay is performed, where fractions and relative phases of the various resonances contributing to the decay are measured. Several quasi-model-independent analyses are performed aimed at searching for the presence of new states and establishing the quantum numbers of previously observed charmed meson resonances. In particular the resonance parameters and quantum numbers are determined for the $D_1(2420)$, $D_1(2430)$, $D_0(2550)$, $D^*_1(2600)$, $D_2(2740)$ and $D^*_3(2750)$ states. The mixing between the $D_1(2420)$ and $D_1(2430)$ resonances is studied and the mixing parameters are measured. The dataset corresponds to an integrated luminosity of 4.7 $fb^{-1}$, collected in proton-proton collisions at center-of-mass energies of 7, 8 and 13 TeV with the LHCb detector.

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arXiv2020

Observation of new resonances in the $Λ_{b}^0π^+π^-$ system

We report the observation of a new structure in the $Λ_b^0 π^+π^-$ spectrum using the full LHCb data set of $pp$ collisions, corresponding to an integrated luminosity of $9\,\mathrm{fb}^{-1}$, collected at $\sqrt{s}=7$, 8 and $13\,\mathrm{TeV}$. A study of the structure suggests its interpretation as a superposition of two almost degenerate narrow states. The masses and widths of these states are measured to be \begin{eqnarray*} m_{Λ_{b}\mathrm{(6146)}^0} &=&6146.17 \pm 0.33 \pm 0.22 \pm 0.16\,\mathrm{MeV} \,, m_{Λ_{b}\mathrm{(6152)}^0} &=&6152.51 \pm 0.26 \pm 0.22 \pm 0.16\,\mathrm{MeV} \,, Γ_{Λ_{b}\mathrm{(6146)}^0}&=&\phantom{615}2.9\phantom{0}\pm 1.3\phantom{0} \pm 0.3\phantom{0}\,\mathrm{MeV}\,, Γ_{Λ_{b}\mathrm{(6152)}^0} &=&\phantom{615}2.1\phantom{0}\pm 0.8\phantom{0} \pm 0.3\phantom{0}\,\mathrm{MeV}\,, \end{eqnarray*} with a mass splitting of $Δm = 6.34 \pm 0.32 \pm 0.02\,\mathrm{MeV}$, where the first uncertainty is statistical, the second systematic and the third derives from the knowledge of the mass of the $Λ_b^0$ baryon. The measured masses and widths of these new excited states suggest their possible interpretation as a doublet of $Λ_{b}\mathrm{(1D)}^0$ states.

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arXiv2020

Precision measurement of the $Ξ_{cc}^{++}$ mass

A measurement of the $Ξ_{cc}^{++}$ mass is performed using data collected by the LHCb experiment between 2016 and 2018 in $pp$ collisions at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 5.6 $\mathrm{fb}^{-1}$. The $Ξ_{cc}^{++}$ candidates are reconstructed via the decay modes $Ξ_{cc}^{++}\toΛ_c^+K^-π^+π^+$ and $Ξ_{cc}^{++}\toΞ_c^+π^+$. The result, $3621.55 \pm 0.23{\rm\,(stat)\,} \pm 0.30 {\rm\,(syst)\,}{\rm MeV}/c^2$, is the most precise measurement of the $Ξ_{cc}^{++}$ mass to date.

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arXiv2020

Measurement of $\mathitΞ_{cc}^{++}$ production in $pp$ collisions at $\sqrt{s}=13$ TeV

The production of $\mathitΞ_{cc}^{++}$ baryons in proton-proton collisions at a centre-of-mass energy of $\sqrt{s}=13$ TeV is measured in the transverse-momentum range $4<p_\mathrm{T}<15~\mathrm{GeV}$/$c$ and the rapidity range $2.0<y<4.5$. The data used in this measurement correspond to an integrated luminosity of 1.7 $\mathrm{fb}^{-1}$, recorded by the LHCb experiment during 2016. The ratio of the $\mathitΞ_{cc}^{++}$ production cross-section times the branching fraction of the $\mathit{Ξ_{cc}^{++} \to Λ_{c}^{+} K^- π^+ π^+}$ decay relative to the prompt $\mathit{Λ_c^{+}}$ production cross-section is found to be $(2.22\pm 0.27 \pm 0.29)\times 10^{-4}$, assuming the central value of the measured $\mathit{Ξ_{cc}^{++}}$ lifetime, where the first uncertainty is statistical and the second systematic.

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arXiv2020

Search for $A'\!\to\!μ^+μ^-$ decays

Searches are performed for both prompt-like and long-lived dark photons, $A'$, produced in proton-proton collisions at a center-of-mass energy of 13 TeV. These searches look for $A'\!\to\!μ^+μ^-$ decays using a data sample corresponding to an integrated luminosity of 5.5/fb collected with the LHCb detector. Neither search finds evidence for a signal, and 90% confidence-level exclusion limits are placed on the $γ$-$A'$ kinetic-mixing strength. The prompt-like $A'$ search explores the mass region from near the dimuon threshold up to 70 GeV, and places the most stringent constraints to date on dark photons with $214 < m(A') \lesssim 740$ MeV and $10.6 < m(A') \lesssim 30$ GeV. The search for long-lived $A'\!\to\!μ^+μ^-$ decays places world-leading constraints on low-mass dark photons with lifetimes $\mathcal{O}(1)$ ps.

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