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

Study of the doubly charmed tetraquark Tcc+T_{cc}^+

An exotic narrow state in the $D^0D^0\pi^+$ mass spectrum just below the $D^{*+}D^0$ mass threshold is studied using a data set corresponding to an integrated luminosity of 9 fb$^{-1}$ acquired with the LHCb detector in proton-proton collisions at centre-of-mass energies of 7, 8 and 13 TeV. The state is consistent with the ground isoscalar $T^+_{cc}$ tetraquark with a quark content of $cc\bar{u}\bar{d}$ and spin-parity quantum numbers $\mathrm{J}^{\mathrm{P}}=1^+$. Study of the $DD$ mass spectra disfavours interpretation of the resonance as the isovector state. The decay structure via intermediate off-shell $D^{*+}$ mesons is confirmed by the $D^0\pi^+$ mass distribution. The mass of the resonance and its coupling to the $D^{*}D$ system are analysed. Resonance parameters including the pole position, scattering length, effective range and compositeness are measured to reveal important information about the nature of the $T^+_{cc}$ state. In addition, an unexpected dependence of the production rate on track multiplicity is observed

Measurement of the lifetimes of promptly produced Ωc0 and Ξc0 baryons

International audienceA measurement of the lifetimes of the Ωc0 and Ξc0 baryons is reported using proton–proton collision data at a centre-of-mass energy of 13TeV, corresponding to an integrated luminosity of 5.4fb-1 collected by the LHCb experiment. The Ωc0 and Ξc0 baryons are produced directly from proton interactions and reconstructed in the pK-K-π+ final state. The Ωc0 lifetime is measured to be 276.5±13.4±4.4±0.7fs, and the Ξc0 lifetime is measured to be 148.0±2.3±2.2±0.2fs, where the first uncertainty is statistical, the second systematic, and the third due to the uncertainty on the D0 lifetime. These results confirm previous LHCb measurements based on semileptonic beauty-hadron decays, which disagree with earlier results of a four times shorter Ωc0 lifetime, and provide the single most precise measurement of the Ωc0 lifetime

Observation of the suppressed Λb0→DpK- decay with D→K+π- and measurement of its CP asymmetry

International audienceA study of Λb0 baryon decays to the DpK- final state is presented based on a proton-proton collision data sample corresponding to an integrated luminosity of 9  fb-1 collected with the LHCb detector. Two Λb0 decays are considered, Λb0→DpK- with D→K-π+ and D→K+π-, where D represents a superposition of D0 and D¯0 states. The latter process is expected to be suppressed relative to the former, and is observed for the first time. The ratio of branching fractions of the two decays is measured, and the CP asymmetry of the suppressed mode, which is sensitive to the Cabibbo-Kobayashi-Maskawa angle γ, is also reported

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

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