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LHCb collaboration

Publications and source records attributed to LHCb collaboration.

At least 361 records · Page 20Linked to original sources

arXiv2021

Observation of a new $Ξ_b^0$ state

Using a proton-proton collision data sample collected by the LHCb experiment, corresponding to an integrated luminosity of 8.5 fb$^{-1}$, the observation of a new excited $Ξ_b^0$ resonance decaying to the $Ξ_b^-π^+$ final state is presented. The state, referred to as $Ξ_b(6227)^0$, has a measured mass and natural width of $m(Ξ_b(6227)^0) = 6227.1^{\,+1.4}_{\,-1.5}\pm0.5$ MeV, $Γ(Ξ_b(6227)^0) = 18.6^{\,+5.0}_{\,-4.1}\pm1.4$ MeV, where the uncertainties are statistical and systematic. The production rate of the $Ξ_b(6227)^0$ state relative to that of the $Ξ_b^-$ baryon in the kinematic region $2<η<5$ and $p_{\rm T}<30$ GeV is measured to be $\frac{f_{Ξ_b(6227)^0}}{f_{Ξ_b^-}}{\mathcal{B}}(Ξ_b(6227)^0\toΞ_b^-π^+) = 0.045\pm0.008\pm0.004$, where ${\mathcal{B}}(Ξ_b(6227)^0\toΞ_b^-π^+)$ is the branching fraction of the decay, and $f_{Ξ_b(6227)^0}$ and $f_{Ξ_b^-}$ represent fragmentation fractions. Improved measurements of the mass and natural width of the previously observed $Ξ_b(6227)^-$ state, along with the mass of the $Ξ_b^-$ baryon, are also reported. Both measurements are significantly more precise than, and consistent with, previously reported values.

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arXiv2021

Measurement of branching fraction ratios for $B^+\to D^{+}D^-K^+$, $B^+\to D^{-}D^+K^+$, and $B^0\to D^{*-}D^0K^+$ decays

A measurement of four branching-fraction ratios for three-body decays of $B$ mesons involving two open-charm hadrons in the final state is presented. Run 1 and Run 2 $pp$ collision data are used, recorded by the LHCb experiment at centre-of-mass energies $7$, $8$, and $13$ TeV and corresponding to an integrated luminosity of $9$ fb$^{-1}$. The measured branching-fraction ratios are \[ \begin{eqnarray} \frac{\mathcal{B} (B^+\to D^{*+}D^-K^+)}{\mathcal{B} (B^+\to \kern 0.2em\overline{\kern -0.2em D}{}^0 D^0 K^+)} &=& 0.517 \pm 0.015 \pm 0.013 \pm 0.011 , \\ \frac{\mathcal{B} (B^+\to D^{*-}D^+K^+)}{\mathcal{B} (B^+\to \kern 0.2em\overline{\kern -0.2em D}{}^0 D^0 K^+)} &=& 0.577 \pm 0.016 \pm 0.013 \pm 0.013 , \\ \frac{\mathcal{B} (B^0\to D^{*-}D^0K^+)}{\mathcal{B} (B^0\to D^- D^0 K^+)} &=& 1.754 \pm 0.028 \pm 0.016 \pm 0.035 , \\ \frac{\mathcal{B} (B^+\to D^{*+}D^-K^+)}{\mathcal{B} (B^+\to D^{*-}D^+K^+)} &=& 0.907 \pm 0.033 \pm 0.014 ,\end{eqnarray} \] where the first of the uncertainties is statistical, the second systematic, and the third is due to the uncertainties on the $D$-meson branching fractions. These are the most accurate measurements of these ratios to date.

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arXiv2020

First observation of the decay $Λ_b^0 \to η_c(1S) p K^-$

The decay $Λ_b^0 \to η_c(1S) p K^-$ is observed for the first time using a data sample of proton-proton collisions, corresponding to an integrated luminosity of 5.5 $fb^{-1}$, collected with the LHCb experiment at a center-of-mass energy of 13 TeV. The branching fraction of the decay is measured, using the $Λ_b^0 \to J/ψp K^-$ decay as a normalization mode, to be $\mathcal{B}(Λ_b^0 \to η_c(1S) p K^-)=(1.06\pm0.16\pm0.06^{+0.22}_{-0.19})\times10^{-4}$, where the quoted uncertainties are statistical, systematic and due to external inputs, respectively. A study of the $η_c(1S) p$ mass spectrum is performed to search for the $P_c(4312)^+$ pentaquark state. No evidence is observed and an upper limit of \begin{equation*} \frac{\mathcal{B}(Λ_b^0 \to P_c(4312)^+ K^-)\times \mathcal{B}(P_c(4312)^+ \to η_c(1S) p)}{\mathcal{B}(Λ_b^0 \to η_c(1S) p K^-)} < 0.24 \end{equation*} is obtained at the 95% confidence level.

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arXiv2020

Measurement of the relative branching fractions of $B^+ \to h^+h^{\prime +}h^{\prime -}$ decays

The relative branching fractions of $B^+ \to h^+h^{\prime +}h^{\prime -}$ decays, where $h^{(\prime)}$ is a pion or kaon, are measured. The analysis is performed with a data sample, collected with the LHCb detector, corresponding to an integrated luminosity of $3.0 {\rm fb}^{-1}$ of $pp$ collisions. The results obtained improve significantly on previous measurements of these quantities, and are important for the interpretation of Dalitz plot analyses of three-body charmless hadronic decays of $B^+$ mesons.

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arXiv2020

Amplitude analysis of the $B^+\to D^+D^-K^+$ decay

Results are reported from an amplitude analysis of the $B^+\to D^+D^-K^+$ decay. The analysis is carried out using LHCb proton-proton collision data taken at $\sqrt{s}=7,8,$ and $13$ TeV, corresponding to a total integrated luminosity of 9 fb$^{-1}$. In order to obtain a good description of the data, it is found to be necessary to include new spin-0 and spin-1 resonances in the $D^-K^+$ channel with masses around 2.9 GeV$/c^2$, and a new spin-0 charmonium resonance in proximity to the spin-2 $χ_{c2}(3930)$ state. The masses and widths of these resonances are determined, as are the relative contributions of all components in the amplitude model, which additionally include the vector charmonia $ψ(3770)$, $ψ(4040)$, $ψ(4160)$ and $ψ(4415)$ states and a nonresonant component.

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arXiv2020

Model-independent study of structure in $B^+\to D^+D^-K^+$ decays

The only anticipated resonant contributions to $B^+\to D^+D^-K^+$ decays are charmonium states in the $D^+D^-$ channel. A model-independent analysis, using LHCb proton-proton collision data taken at centre-of-mass energies of $\sqrt{s}=7,8,$ and $13$ TeV, corresponding to a total integrated luminosity of 9 fb$^{-1}$, is carried out to test this hypothesis. The description of the data assuming that resonances only manifest in decays to the $D^+D^-$ pair is shown to be incomplete. This constitutes evidence for a new contribution to the decay, potentially one or more new charm-strange resonances in the $D^-K^+$ channel with masses around 2.9 GeV$/c^2$.

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arXiv2020

Strong constraints on the $b \to sγ$ photon polarisation from $B^0 \to K^{*0} e^+ e^-$ decays

An angular analysis of the $B^0 \to K^{*0} e^+ e^-$ decay is performed using a data sample corresponding to an integrated luminosity of $9~{\rm fb}^{-1}$ of $pp$ collisions collected with the LHCb experiment. The analysis is conducted in the very low dielectron mass squared ($q^2$) interval between $0.0008$ and $0.257~{\rm GeV}^2$, where the rate is dominated by the $B^0\to K^{\ast 0}γ$ transition with a virtual photon. The fraction of longitudinal polarisation of the $K^{\ast 0}$ meson, $F_{\rm L}$, is measured to be $F_{\rm L} = (4.4 \pm 2.6 \pm 1.4)\%$, where the first uncertainty is statistical and the second systematic. The $A_{\rm T}^{\rm Re}$ observable, which is related to the lepton forward-backward asymmetry, is measured to be $A_{\rm T}^{\rm Re}=-0.06 \pm 0.08 \pm 0.02$. The $A_{\rm T}^{(2)}$ and $A_{\rm T}^{\rm Im}$ transverse asymmetries, which are sensitive to the virtual photon polarisation, are found to be $A_{\rm T}^{(2)} = 0.11 \pm 0.10 \ \pm 0.02$ and $A_{\rm T}^{\rm Im} = 0.02 \pm 0.10 \pm 0.01$. The results are consistent with Standard Model predictions and provide the world's best constraint on the $b\to sγ$ photon polarisation.

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arXiv2020

Observation of enhanced double parton scattering in proton-lead collisions at $\sqrt{s_\mathrm{NN}}=8.16$ TeV

A study of prompt charm-hadron pair production in proton-lead collisions at $\sqrt{s_\mathrm{NN}}= 8.16$ TeV is performed using data corresponding to an integrated luminosity of about 30 nb${}^{-1}$, collected with the LHCb experiment. Production cross-sections for different pairs of charm hadrons are measured and kinematic correlations between the two charm hadrons are investigated. This is the first measurement of associated production of two charm hadrons in proton-lead collisions. The results confirm the predicted enhancement of double parton scattering production in proton-lead collisions compared to the single parton scattering production.

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arXiv2020

Search for the doubly heavy $\mathitΞ_{bc}^{0}$ baryon via decays to $D^0pK^-$

A search for the doubly heavy $\mathitΞ_{bc}^{0}$ baryon using its decay to the $D^0pK^-$ final state is performed using proton-proton collision data at a centre-of-mass energy of 13 TeV collected by the LHCb experiment between 2016 and 2018, corresponding to an integrated luminosity of 5.4 $\mathrm{fb}^{-1}$. No significant signal is found in the invariant mass range from 6.7 to 7.2 $\mathrm{GeV}/c^2$. Upper limits are set at $95\%$ credibility level on the ratio of the $\mathitΞ_{bc}^{0}$ production cross-section times its branching fraction to $D^0pK^-$ relative to that of the $\mathitΛ_{b}^{0} \to D^0pK^-$ decay. The limits are set as a function of the $\mathitΞ_{bc}^{0}$ mass and lifetime hypotheses, in the rapidity range from 2.0 to 4.5 and in the transverse momentum region from 5 to 25 $\mathrm{GeV}/c$. Upper limits range from $1.7\times10^{-2}$ to $3.0\times10^{-1}$ for the considered $\mathitΞ_{bc}^{0}$ mass and lifetime hypotheses.

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arXiv2020

Observation of structure in the $J/ψ$-pair mass spectrum

Using proton-proton collision data at centre-of-mass energies of $\sqrt{s} = 7$, $8$ and $13\mathrm{\,TeV}$ recorded by the LHCb experiment at the Large Hadron Collider, corresponding to an integrated luminosity of $9\mathrm{\,fb}^{-1}$, the invariant mass spectrum of $J/ψ$ pairs is studied. A narrow structure around $6.9\mathrm{\,GeV/}c^2$ matching the lineshape of a resonance and a broad structure just above twice the $J/ψ$ mass are observed. The deviation of the data from nonresonant $J/ψ$-pair production is above five standard deviations in the mass region between $6.2$ and $7.4\mathrm{\,GeV/}c^2$, covering predicted masses of states composed of four charm quarks. The mass and natural width of the narrow $X(6900)$ structure are measured assuming a Breit--Wigner lineshape.

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arXiv2020

Searches for low-mass dimuon resonances

Searches are performed for a low-mass dimuon resonance, $X$, produced in proton-proton collisions at a center-of-mass energy of 13 TeV, using a data sample corresponding to an integrated luminosity of 5.1 fb$^{-1}$ and collected with the LHCb detector. The $X$ bosons can either decay promptly or displaced from the proton-proton collision, where in both cases the requirements placed on the event and the assumptions made about the production mechanisms are kept as minimal as possible. The searches for promptly decaying $X$ bosons explore the mass range from near the dimuon threshold up to 60 GeV, with nonnegligible $X$ widths considered above 20 GeV. The searches for displaced $X \to μ^+μ^-$ decays consider masses up to 3 GeV. None of the searches finds evidence for a signal and 90% confidence-level exclusion limits are placed on the $X \to μ^+μ^-$ cross sections, each with minimal model dependence. In addition, these results are used to place world-leading constraints on GeV-scale bosons in the two-Higgs-doublet and hidden-valley scenarios.

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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

Searches for 25 rare and forbidden decays of $D^+$ and $D_s^+$ mesons

A search is performed for rare and forbidden charm decays of the form $D_{(s)}^+ \to h^\pm \ell^+ \ell^{(\prime)\mp}$, where $h^\pm$ is a pion or kaon and $\ell^{(')\pm}$ is an electron or muon. The measurements are performed using proton-proton collision data, corresponding to an integrated luminosity of $1.6\text{fb}^{-1}$, collected by the LHCb experiment in 2016. No evidence is observed for the 25 decay modes that are investigated and $90\%$ confidence level limits on the branching fractions are set between $1.4\times10^{-8}$ and $6.4\times10^{-6}$. In most cases, these results represent an improvement on existing limits by one to two orders of magnitude.

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arXiv2020

First observation of the decay $B^0 \rightarrow D^0 \overline{D}{}^0 K^+ π^-$

The first observation of the decay $B^0 \rightarrow D^0 \overline{D}{}^0 K^+ π^-$ is reported using proton-proton collision data corresponding to an integrated luminosity of 4.7 $\mathrm{fb}^{-1}$ collected by the LHCb experiment in 2011, 2012 and 2016. The measurement is performed in the full kinematically allowed range of the decay outside of the $D^{*-}$ region. The ratio of the branching fraction relative to that of the control channel $B^0 \rightarrow D^{*-} D^0 K^+$ is measured to be $\mathcal{R} = (14.2 \pm 1.1 \pm 1.0)\%$, where the first uncertainty is statistical and the second is systematic. The absolute branching fraction of $B^0 \rightarrow D^0 \overline{D}{}^0 K^+ π^-$ decays is thus determined to be $\mathcal{B}(B^0 \rightarrow D^0 \overline{D}{}^0 K^+ π^-) = (3.50 \pm 0.27 \pm 0.26 \pm 0.30) \times 10^{-4}$, where the third uncertainty is due to the branching fraction of the control channel. This decay mode is expected to provide insights to spectroscopy and the charm-loop contributions in rare semileptonic decays.

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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

First branching fraction measurement of the suppressed decay $Ξ_c^0\to π^-Λ_c^+$

The $Ξ_c^0$ baryon is unstable and usually decays into charmless final states by the $c \to s u\overline{d}$ transition. It can, however, also disintegrate into a $π^-$ meson and a $Λ_c^+$ baryon via $s$ quark decay or via $cs\to d c$ weak scattering. The interplay between the latter two processes governs the size of the branching fraction ${\cal{B}}$$(Ξ_c^0\to π^-Λ_c^+)$, first measured here to be $(0.55\pm 0.02 \pm 0.18)$%, where the first uncertainty is statistical and second systematic. This result is compatible with the larger of the theoretical predictions that connect models of hyperon decays using partially conserved axial currents and SU(3) symmetry with those involving the heavy-quark expansion and heavy-quark symmetry. In addition, the branching fraction of the normalization channel, ${\cal{B}}(Ξ_c^+\to p K^- π^+) = (1.135 \pm 0.002 \pm 0.387)$% is measured.

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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) meson production in pp collisions at sqrt(s)=7 TeV

The differential cross-section for the inclusive production of psi(2S) mesons in pp collisions at sqrt(s)=7 TeV has been measured with the LHCb detector. The data sample corresponds to an integrated luminosity of 36 pb-1. The psi(2S) mesons are reconstructed in the decay channels psi(2S) -> mu+ mu- and psi(2S) -> J/psi pi+ pi-, with the J/psi meson decaying into two muons. Results are presented both for promptly produced psi(2S) mesons and for those originating from b-hadron decays. In the kinematic range pT(psi(2S)) <= 16 GeV/c and 2 < y(psi(2S)) <= 4.5 we measure 1.44 +- 0.01 +- 0.12+0.2-0.4 mub for prompt psi(2S) production and 0.25 +- 0.01 +- 0.02 mub for psi(2S) from b-hadron decays, where the last uncertainty on the prompt cross-section is due to the unknown psi(2S) polarization. Recent QCD calculations are found to be in good agreement with our measurements. Combining the present result with the LHCb J/psi measurements we determine the inclusive branching fraction B(b -> psi(2S) X) = (2.73 +- 0.06 +- 0.16 +- 0.24) x 10^(-3), where the last uncertainty is due to the B(b -> J/psi X), B(J/psi -> mu+ mu-) and B(psi(2S) -> e+ e-) branching fraction uncertainties. All above results are corrected by an erratum included as an appendix.

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