arXiv subjects

I. Babuschkin

Publications and source records attributed to I. Babuschkin.

101 records · Page 6Linked to original sources

arXiv2017

Observation of $J/ψϕ$ structures consistent with exotic states from amplitude analysis of $B^+\to J/ψϕK^+$ decays

The first full amplitude analysis of $B^+\to J/ψϕK^+$ with $J/ψ\toμ^+μ^-$, $ϕ\to K^+K^-$ decays is performed with a data sample of 3 fb$^{-1}$ of $pp$ collision data collected at $\sqrt{s}=7$ and $8$ TeV with the LHCb detector. The data cannot be described by a model that contains only excited kaon states decaying into $ϕK^+$, and four $J/ψϕ$ structures are observed, each with significance over $5$ standard deviations. The quantum numbers of these structures are determined with significance of at least $4$ standard deviations. The lightest has mass consistent with, but width much larger than, previous measurements of the claimed $X(4140)$ state.

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arXiv2017

First study of the CP-violating phase and decay-width difference in $B_s^0\toψ(2S)ϕ$ decays

A time-dependent angular analysis of $B_s^0\toψ(2S)ϕ$ decays is performed using data recorded by the LHCb experiment. The data set corresponds to an integrated luminosity of 3.0\invfb collected during Run 1 of the LHC. The CP-violating phase and decay-width difference of the $B_s^0$ system are measured to be $ϕ_s = 0.23^{+0.29}_{-0.28} \pm 0.02$ rad and $ΔΓ_s = 0.066^{+0.041}_{-0.044} \pm 0.007$ ps$^{-1}$, respectively, where the first uncertainty is statistical and the second systematic. This is the first time that $ϕ_s$ and $ΔΓ_s$ have been measured in a decay containing the $ψ(2S)$ resonance.

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arXiv2017

Observation of the decay $B^0_s \to ϕπ^+π^-$ and evidence for $B^0 \to ϕπ^+π^-$

The first observation of the rare decay$B^0_s \to ϕπ^+π^-$ and evidence for $B^0 \to ϕπ^+π^-$ are reported, using $pp$ collision data recorded by the LHCb detector at centre-of-mass energies $\sqrt{s} = 7$ and 8~TeV, corresponding to an integrated luminosity of $3{\mbox{\,fb}^{-1}}$. The branching fractions in the $π^+π^-$ invariant mass range $400<m(π^+π^-)<1600{\mathrm{\,Me\kern -0.1em V\!/}c^2}$ are $[3.48\pm 0.23\pm 0.17\pm 0.35]\times 10^{-6}$ and $[1.82\pm 0.25\pm 0.41\pm 0.14]\times 10^{-7}$ for $B^0_s \to ϕπ^+π^-$ and $B^0 \to ϕπ^+π^-$ respectively, where the uncertainties are statistical, systematic and from the normalisation mode $B^0_s \to ϕϕ$. A combined analysis of the $π^+π^-$ mass spectrum and the decay angles of the final-state particles identifies the exclusive decays $B^0_s \to ϕf_0(980) $, $B_s^0 \to ϕf_2(1270) $, and $B^0_s \to ϕρ^0$ with branching fractions of $[1.12\pm 0.16^{+0.09}_{-0.08}\pm 0.11]\times 10^{-6}$, $[0.61\pm 0.13^{+0.12}_{-0.05}\pm 0.06]\times 10^{-6}$ and $[2.7\pm 0.7\pm 0.2\pm 0.2]\times 10^{-7}$, respectively.

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arXiv2017

Measurement of $CP$ violation in $B^0 \!\rightarrow D^+ D^-$ decays

The $CP$ violation observables $S$ and $C$ in the decay channel $B^0 \!\rightarrow D^+ D^-$ are determined from a sample of proton-proton collisions at center-of-mass energies of 7 and 8 TeV, collected by the LHCb experiment and corresponding to an integrated luminosity of 3 fb$^{-1}$. The observable $S$ describes $CP$ violation in the interference between mixing and the decay amplitude, and $C$ parametrizes direct $CP$ violation in the decay. The following values are obtained from a flavor-tagged, decay-time-dependent analysis: \begin{align*} S &= -0.54 \, ^{+0.17}_{-0.16} \, \text{(stat)} \pm 0.05 \, \text{(syst)}\,,\newline C &= \phantom{-}0.26 \, ^{+0.18}_{-0.17} \, \text{(stat)} \pm 0.02 \, \text{(syst)}\,. \end{align*} These values provide evidence for $CP$ violation at a significance level of 4.0 standard deviations. The phase shift due to higher-order Standard Model corrections is constrained to a small value of \begin{align*} Δϕ= -0.16\,^{+0.19}_{-0.21}\,\text{rad}\,. \end{align*}

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arXiv2016

Differential branching fraction and angular moments analysis of the decay $B^0 \to K^+ π^- μ^+ μ^-$ in the $K^*_{0,2}(1430)^0$ region

Measurements of the differential branching fraction and angular moments of the decay $B^0 \to K^+ π^- μ^+ μ^-$ in the $K^+π^-$ invariant mass range $1330<m(K^+ π^-)<1530~MeV/c^2$ are presented. Proton-proton collision data are used, corresponding to an integrated luminosity of 3 $fb^{-1}$ collected by the LHCb experiment. Differential branching fraction measurements are reported in five bins of the invariant mass squared of the dimuon system, $q^2$, between 0.1 and 8.0 $GeV^2/c^4$. For the first time, an angular analysis sensitive to the S-, P- and D-wave contributions of this rare decay is performed. The set of 40 normalised angular moments describing the decay is presented for the $q^2$ range 1.1--6.0 $GeV^2/c^4$.

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arXiv2016

Measurement of the CKM angle $γ$ from a combination of LHCb results

A combination of measurements sensitive to the CKM angle $γ$ from LHCb is performed. The inputs are from analyses of time-integrated $B^{+}\rightarrow DK^+$, $B^{0} \rightarrow D K^{*0}$, $B^{0} \rightarrow D K^+ π^-$ and $B^{+} \rightarrow D K^+π^+π^-$ tree-level decays. In addition, results from a time-dependent analysis of $B_{s}^{0} \rightarrow D_{s}^{\mp}K^{\pm}$ decays are included. The combination yields $γ= (72.2^{+6.8}_{-7.3})^\circ$, where the uncertainty includes systematic effects. The 95.5% confidence level interval is determined to be $γ\in [55.9,85.2]^\circ$. A second combination is investigated, also including measurements from $B^{+} \rightarrow D π^+$ and $B^{+} \rightarrow D π^+π^-π^+$ decays, which yields compatible results.

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arXiv2016

Study of $B_c^+$ decays to the $K^+K^-π^+$ final state and evidence for the decay $B_c^+\toχ_{c0}π^+$

A study of $B_c^+\to K^+K^-π^+$ decays is performed for the first time using data corresponding to an integrated luminosity of 3.0 $\mathrm{fb}^{-1}$ collected by the LHCb experiment in $pp$ collisions at centre-of-mass energies of $7$ and $8$ TeV. Evidence for the decay $B_c^+\toχ_{c0}(\to K^+K^-)π^+$ is reported with a significance of 4.0 standard deviations, resulting in the measurement of $\frac{σ(B_c^+)}{σ(B^+)}\times\mathcal{B}(B_c^+\toχ_{c0}π^+)$ to be $(9.8^{+3.4}_{-3.0}(\mathrm{stat})\pm 0.8(\mathrm{syst}))\times 10^{-6}$. Here $\mathcal{B}$ denotes a branching fraction while $σ(B_c^+)$ and $σ(B^+)$ are the production cross-sections for $B_c^+$ and $B^+$ mesons. An indication of $\bar b c$ weak annihilation is found for the region $m(K^-π^+)<1.834\mathrm{\,Ge\kern -0.1em V\!/}c^2$, with a significance of 2.4 standard deviations.

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arXiv2016

Measurement of forward $W\to eν$ production in $pp$ collisions at $\sqrt{s}=8\,$TeV

A measurement of the cross-section for $W \to eν$ production in $pp$ collisions is presented using data corresponding to an integrated luminosity of $2\,$fb$^{-1}$ collected by the LHCb experiment at a centre-of-mass energy of $\sqrt{s}=8\,$TeV. The electrons are required to have more than $20\,$GeV of transverse momentum and to lie between 2.00 and 4.25 in pseudorapidity. The inclusive $W$ production cross-sections, where the $W$ decays to $eν$, are measured to be \begin{equation*} σ_{W^{+} \to e^{+}ν_{e}}=1124.4\pm 2.1\pm 21.5\pm 11.2\pm 13.0\,\mathrm{pb}, \end{equation*} \begin{equation*} σ_{W^{-} \to e^{-}\barν_{e}}=\,\,\,809.0\pm 1.9\pm 18.1\pm\,\,\,7.0\pm \phantom{0}9.4\,\mathrm{pb}, \end{equation*} where the first uncertainties are statistical, the second are systematic, the third are due to the knowledge of the LHC beam energy and the fourth are due to the luminosity determination. Differential cross-sections as a function of the electron pseudorapidity are measured. The $W^{+}/W^{-}$ cross-section ratio and production charge asymmetry are also reported. Results are compared with theoretical predictions at next-to-next-to-leading order in perturbative quantum chromodynamics. Finally, in a precise test of lepton universality, the ratio of $W$ boson branching fractions is determined to be \begin{equation*} \mathcal{B}(W \to eν)/\mathcal{B}(W \to μν)=1.020\pm 0.002\pm 0.019, \end{equation*} where the first uncertainty is statistical and the second is systematic.

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arXiv2016

Amplitude analysis of $B^{-} \to D^{+} π^{-} π^{-}$ decays

The Dalitz plot analysis technique is used to study the resonant substructures of $B^{-} \to D^{+} π^{-} π^{-}$ decays in a data sample corresponding to 3.0 ${\rm fb}^{-1}$ of $pp$ collision data recorded by the LHCb experiment during 2011 and 2012. A model-independent analysis of the angular moments demonstrates the presence of resonances with spins 1, 2 and 3 at high $D^{+}π^{-}$ mass. The data are fitted with an amplitude model composed of a quasi-model-independent function to describe the $D^{+}π^{-}$ S-wave together with virtual contributions from the $D^{*}(2007)^{0}$ and $B^{*0}$ states, and components corresponding to the $D^{*}_{2}(2460)^{0}$, $D^{*}_{1}(2680)^{0}$, $D^{*}_{3}(2760)^{0}$ and $D^{*}_{2}(3000)^{0}$ resonances. The masses and widths of these resonances are determined together with the branching fractions for their production in $B^{-} \to D^{+} π^{-} π^{-}$ decays. The $D^{+}π^{-}$ S-wave has phase motion consistent with that expected due to the presence of the $D^{*}_{0}(2400)^{0}$ state. These results constitute the first observations of the $D^{*}_{3}(2760)^{0}$ and $D^{*}_{2}(3000)^{0}$ resonances.

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arXiv2016

Measurement of the forward Z boson production cross-section in pp collisions at $\sqrt{s} = 13$ TeV

A measurement of the production cross-section of Z bosons in pp collisions at $\sqrt{s} = 13$ TeV is presented using dimuon and dielectron final states in LHCb data. The cross-section is measured for leptons with pseudorapidities in the range $2.0 < η< 4.5$, transverse momenta $p_\text{T} > 20$ GeV and dilepton invariant mass in the range $60<m(\ell\ell)<120$ GeV. The integrated cross-section from averaging the two final states is \begin{equation*}σ_{\text{Z}}^{\ell\ell} = 194.3 \pm 0.9 \pm 3.3 \pm 7.6\text{ pb,}\end{equation*} where the first uncertainty is statistical, the second is due to systematic effects, and the third is due to the luminosity determination. In addition, differential cross-sections are measured as functions of the Z boson rapidity, transverse momentum and the angular variable $ϕ^*_η$.

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arXiv2016

Observation of $η_{c}(2S) \to p \bar p$ and search for $X(3872) \to p \bar p$ decays

The first observation of the decay $η_{c}(2S) \to p \bar p$ is reported using proton-proton collision data corresponding to an integrated luminosity of $3.0\rm \, fb^{-1}$ recorded by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. The $η_{c}(2S)$ resonance is produced in the decay $B^{+} \to [c\bar c] K^{+}$. The product of branching fractions normalised to that for the $J/ψ$ intermediate state, ${\cal R}_{η_{c}(2S)}$, is measured to be \begin{align*} {\cal R}_{η_{c}(2S)}\equiv\frac{{\mathcal B}(B^{+} \to η_{c}(2S) K^{+}) \times {\mathcal B}(η_{c}(2S) \to p \bar p)}{{\mathcal B}(B^{+} \to J/ψK^{+}) \times {\mathcal B}(J/ψ\to p \bar p)} =~& (1.58 \pm 0.33 \pm 0.09)\times 10^{-2}, \end{align*} where the first uncertainty is statistical and the second systematic. No signals for the decays $B^{+} \to X(3872) (\to p \bar p) K^{+}$ and $B^{+} \to ψ(3770) (\to p \bar p) K^{+}$ are seen, and the 95\% confidence level upper limits on their relative branching ratios are % found to be ${\cal R}_{X(3872)}<0.25\times10^{-2}$ and ${\cal R}_{ψ(3770))}<0.10$. In addition, the mass differences between the $η_{c}(1S)$ and the $J/ψ$ states, between the $η_{c}(2S)$ and the $ψ(2S)$ states, and the natural width of the $η_{c}(1S)$ are measured as \begin{align*} M_{J/ψ} - M_{η_{c}(1S)} =~& 110.2 \pm 0.5 \pm 0.9 \rm \, MeV, M_{ψ(2S)} -M_{η_{c}(2S)} =~ & 52.5 \pm 1.7 \pm 0.6 \rm \, MeV, Γ_{η_{c}(1S)} =~& 34.0 \pm 1.9 \pm 1.3 \rm \, MeV. \end{align*}

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