Precision measurement of forward ZZ boson production in proton-proton collisions at s=13\sqrt{s} = 13 TeV

A precision measurement of the $Z$ boson production cross-section at $\sqrt{s} = 13$ TeV in the forward region is presented, using $pp$ collision data collected by the LHCb detector, corresponding to an integrated luminosity of 5.1 fb$^{-1}$. The production cross-section is measured using $Z\rightarrow\mu^+\mu^-$ events within the fiducial region defined as pseudorapidity $2.020$ GeV/$c$ for both muons and dimuon invariant mass $60<M_{\mu\mu}<120$ GeV/$c^2$. The integrated cross-section is determined to be \begin{equation*} \sigma(Z\rightarrow\mu^+\mu^-) = 195.3 \pm 0.2 \pm 1.5 \pm 3.9~pb, \end{equation*} where the first uncertainty is statistical, the second is systematic, and the third is due to the luminosity determination. The measured results are in agreement with theoretical predictions, including a prediction at next-to-next-to-leading order in perturbative quantum chromodynamics and a prediction with resummation

Precision measurement of forward ZZ boson production in proton-proton collisions at s=13\sqrt{s} = 13 TeV

A precision measurement of the $Z$ boson production cross-section at $\sqrt{s} = 13$ TeV in the forward region is presented, using $pp$ collision data collected by the LHCb detector, corresponding to an integrated luminosity of 5.1 fb$^{-1}$. The production cross-section is measured using $Z\rightarrow\mu^+\mu^-$ events within the fiducial region defined as pseudorapidity $2.020$ GeV/$c$ for both muons and dimuon invariant mass $60<M_{\mu\mu}<120$ GeV/$c^2$. The integrated cross-section is determined to be \begin{equation*} \sigma(Z\rightarrow\mu^+\mu^-) = 195.3 \pm 0.2 \pm 1.5 \pm 3.9~pb, \end{equation*} where the first uncertainty is statistical, the second is systematic, and the third is due to the luminosity determination. The measured results are in agreement with theoretical predictions, including a prediction at next-to-next-to-leading order in perturbative quantum chromodynamics and a prediction with resummation

Evidence for a new structure in the J/ψpJ/\psi p and J/ψpˉJ/\psi \bar{p} systems in Bs0→J/ψppˉB_s^0 \to J/\psi p \bar{p} decays

International audienceAn amplitude analysis of flavor-untagged Bs0→J/ψpp¯ decays is performed using a sample of 797±31 decays reconstructed with the LHCb detector. The data, collected in proton-proton collisions between 2011 and 2018, correspond to an integrated luminosity of 9  fb-1. Evidence for a new structure in the J/ψp and J/ψp¯ systems with a mass of 4337-4+7 -2+2  MeV and a width of 29-12+26 -14+14  MeV is found, where the first uncertainty is statistical and the second systematic, with a significance in the range of 3.1 to 3.7σ, depending on the assigned JP hypothesis

Observation of Two New Excited Ξb0\Xi_b^0 States Decaying to Λb0K−π+\Lambda^0_b K^- \pi^+

International audienceTwo narrow resonant states are observed in the Λb0K-π+ mass spectrum using a data sample of proton-proton collisions at a center-of-mass energy of 13 TeV, collected by the LHCb experiment and corresponding to an integrated luminosity of 6  fb-1. The minimal quark content of the Λb0K-π+ system indicates that these are excited Ξb0 baryons. The masses of the Ξb(6327)0 and Ξb(6333)0 states are m[Ξb(6327)0]=6327.28-0.21+0.23±0.12±0.24 and m[Ξb(6333)0]=6332.69-0.18+0.17±0.03±0.22  MeV, respectively, with a mass splitting of Δm=5.41-0.27+0.26±0.12  MeV, where the uncertainties are statistical, systematic, and due to the Λb0 mass measurement. The measured natural widths of these states are consistent with zero, with upper limits of Γ[Ξb(6327)0]&lt;2.20(2.56) and Γ[Ξb(6333)0]&lt;1.60(1.92)  MeV at a 90% (95%) credibility level. The significance of the two-peak hypothesis is larger than nine (five) Gaussian standard deviations compared to the no-peak (one-peak) hypothesis. The masses, widths, and resonant structure of the new states are in good agreement with the expectations for a doublet of 1D Ξb0 resonances

Identification of charm jets at LHCb

International audienceThe identification of charm jets is achieved at LHCb for data collected in 2015–2018 using a method based on the properties of displaced vertices reconstructed and matched with jets. The performance of this method is determined using a dijet calibration dataset recorded by the LHCb detector and selected such that the jets are unbiased in quantities used in the tagging algorithm. The charm-tagging efficiency is reported as a function of the transverse momentum of the jet. The measured efficiencies are compared to those obtained from simulation and found to be in good agreement

Search for the doubly charmed baryon Ξcc+ {\varXi}_{cc}^{+} in the Ξc+π−π+ {\varXi}_c^{+}{\pi}^{-}{\pi}^{+} final state

International audienceA search for the doubly charmed baryon ${\varXi}_{cc}^{+}$ is performed in the ${\varXi}_c^{+}{\pi}^{-}{\pi}^{+}$ invariant-mass spectrum, where the ${\varXi}_c^{+}$ baryon is reconstructed in the pK$^{−}$π$^{+}$ final state. The study uses proton-proton collision data collected with the LHCb detector at a centre- of-mass energy of 13 TeV, corresponding to a total integrated luminosity of 5.4 fb$^{−1}$. No significant signal is observed in the invariant-mass range of 3.4–3.8 GeV/c$^{2}$. Upper limits are set on the ratio of branching fractions multiplied by the production cross-section with respect to the ${\varXi}_{cc}^{++}$→ (${\varXi}_c^{+}$→ pK$^{−}$π$^{+}$)π$^{+}$ decay for different ${\varXi}_{cc}^{+}$ mass and lifetime hypotheses in the rapidity range from 2.0 to 4.5 and the transverse momentum range from 2.5 to 25 GeV/c. The results from this search are combined with a previously published search for the ${\varXi}_{cc}^{+}$→${\varLambda}_c^{+}$K$^{−}$π$^{+}$ decay mode, yielding a maximum local significance of 4.0 standard deviations around the mass of 3620 MeV/c$^{2}$, including systematic uncertainties. Taking into account the look-elsewhere effect in the 3.5–3.7 GeV/c$^{2}$ mass window, the combined global significance is 2.9 standard deviations including systematic uncertainties.[graphic not available: see fulltext

Measurement of J/ψJ/\psi production cross-sections in pppp collisions at s=5\sqrt{s}=5 TeV

International audienceThe production cross-sections of $J/\psi$ mesons in proton-proton collisions at a centre-of-mass energy of $\sqrt{s}=5$ TeV are measured using a data sample corresponding to an integrated luminosity of $9.13\pm0.18~\text{pb}^{-1}$, collected by the LHCb experiment. The cross-sections are measured differentially as a function of transverse momentum, $p_{\text{T}}$, and rapidity, $y$, and separately for $J/\psi$ mesons produced promptly and from beauty hadron decays (nonprompt). With the assumption of unpolarised $J/\psi$ mesons, the production cross-sections integrated over the kinematic range $0<p_{\text{T}}<20~\text{GeV}/c$ and $2.0<y<4.5$ are $8.154\pm0.010\pm0.283~\mu\text{b}$ for prompt $J/\psi$ mesons and $0.820\pm0.003\pm0.034~\mu\text{b}$ for nonprompt $J/\psi$ mesons, where the first uncertainties are statistical and the second systematic. These cross-sections are compared with those at $\sqrt{s}=8$ TeV and $13$ TeV, and are used to update the measurement of the nuclear modification factor in proton-lead collisions for $J/\psi$ mesons at a centre-of-mass energy per nucleon pair of $\sqrt{s_{\text{NN}}}=5$ TeV. The results are compared with theoretical predictions

Search for the radiative Ξb−→Ξ−γ\Xi_b^-\to\Xi^-\gamma decay

International audienceThe first search for the rare radiative decay ${\Xi}_b^{-}$ → Ξ$^{−}$γ is performed using data collected by the LHCb experiment in proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 5.4 fb$^{−1}$. The ${\Xi}_b^{-}$ → Ξ$^{−}$J/ψ channel is used as normalization. No ${\Xi}_b^{-}$ → Ξ$^{−}$γ signal is found and an upper limit of $\mathcal{B}$(${\Xi}_b^{-}$ → Ξ$^{−}$γ) < 1.3 × 10$^{−4}$ at 95% confidence level is obtained.[graphic not available: see fulltext

Study of Z Bosons Produced in Association with Charm in the Forward Region

International audienceEvents containing a $Z$ boson and a charm jet are studied for the first time in the forward region of proton-proton collisions. The data sample used corresponds to an integrated luminosity of $6$ $fb^{-1}$ collected at a center-of-mass energy of 13 TeV with the LHCb detector. In events with a $Z$ boson and a jet, the fraction of charm jets is determined in intervals of $Z$-boson rapidity in the range $2.0 < y(Z) < 4.5$. A sizable enhancement is observed in the forward-most $y(Z)$ interval, which could be indicative of a valence-like intrinsic-charm component in the proton wave function