Search

The first observation of the singly Cabibbo-suppressed ${\mathrm{\Omega }}_c^0\to {\mathrm{\Omega }}^{-}{K}^{+}$ and ${\mathrm{\Omega }}_c^0\to {\mathrm{\Xi }}^{-}{\pi }^{+}$ decays is reported, using proton-proton collision data at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of $5.4{\mathrm{fb}}^{-1}$, collected with the LHCb detector between 2016 and 2018. The branching fraction ratios are measured to be $\frac{\mathcal{B}({\mathrm{\Omega }}_c^0\to {\mathrm{\Omega }}^{-}{K}^{+})}{\mathcal{B}({\mathrm{\Omega }}_c^0\to {\mathrm{\Omega }}^{-}{\pi }^{+})}=[6.08\pm 0.51(\mathrm{stat})\pm 0.40(\mathrm{syst})]\%,\frac{\mathcal{B}({\mathrm{\Omega }}_c^0\to {\mathrm{\Xi }}^{-}{\pi }^{+})}{\mathcal{B}({\mathrm{\Omega }}_c^0\to {\mathrm{\Omega }}^{-}{\pi }^{+})}=[15.81\pm 0.87(\mathrm{stat})\pm 0.44(\mathrm{syst})\pm 0.16(\mathrm{ext})]\%.$ In addition, using the ${\mathrm{\Omega }}_c^0\to {\mathrm{\Omega }}^{-}{\pi }^{+}$ decay channel, the ${\mathrm{\Omega }}_c^0$ baryon mass is measured to be $M({\mathrm{\Omega }}_c^0)=2695.28\pm 0.07(\mathrm{stat})\pm 0.27(\mathrm{syst})\pm 0.30(\mathrm{ext})\mathrm{MeV},$ improving the precision of the previous world average by a factor of 4.

A measurement of charm mixing and $CP$-violating parameters is reported, using $\overline{B}\to D^0(\to K_{\mathrm{S}}^0{\pi }^{+}{\pi }^{-}){\mu }^{-}{\overline{\nu }}_{\mu }X$ decays reconstructed in proton-proton collisions collected by the LHCb experiment during the years 2016 to 2018, corresponding to an integrated luminosity of $5.4{\mathrm{fb}}^{-1}$. The measured mixing and $CP$-violating parameters are $x_{CP}=[4.29\pm 1.48(\mathrm{stat})\pm 0.26(\mathrm{syst})]\times {10}^{-3}$, $y_{CP}=[12.61\pm 3.12(\mathrm{stat})\pm 0.83(\mathrm{syst})]\times {10}^{-3}$, $\mathrm{\Delta }x=[-0.77\pm 0.93(\mathrm{stat})\pm 0.28(\mathrm{syst})]\times {10}^{-3}$, $\mathrm{\Delta }y=[3.01\pm 1.92(\mathrm{stat})\pm 0.26(\mathrm{syst})]\times {10}^{-3}$. The results are complementary to and consistent with previous measurements. A combination with the recent LHCb analysis of $D^{*+}\to D^0(\to K_{\mathrm{S}}^0{\pi }^{+}{\pi }^{-}){\pi }^{+}$ decays is reported.

The first observations of $B^0\to {\overline{D}}^{*}(2007{)}^0{K}^{+}{\pi }^{-}$ and $B_s^0\to {\overline{D}}^{*}(2007{)}^0{K}^{-}{\pi }^{+}$ decays are presented, and their branching fractions relative to that of the $B^0\to {\overline{D}}^{*}(2007{)}^0{\pi }^{+}{\pi }^{-}$ decay are reported. These modes can potentially be used to investigate the spectroscopy of charm and charm-strange resonances and to determine the angle $\gamma$ of the Cabibbo-Kobayashi-Maskawa unitarity triangle. It is also important to understand them as a source of potential background in determinations of $\gamma$ from $B^{+}\to D{K}^{+}$ and $B^0\to D{K}^{+}{\pi }^{-}$ decays. The analysis is based on a sample corresponding to an integrated luminosity of $5.4{\mathrm{fb}}^{-1}$ of proton-proton collision data at 13 TeV center-of-mass energy recorded with the LHCb detector. The ${\overline{D}}^{*}(2007{)}^0$ mesons are fully reconstructed in the ${\overline{D}}^0{\pi }^0$ and ${\overline{D}}^0\gamma$ channels with the ${\overline{D}}^0\to K^{+}{\pi }^{-}$ decay. A novel weighting method is used to subtract background while simultaneously applying an event-by-event efficiency correction to account for resonant structures in the decays.

A search for the baryon- and lepton-number violating decays $B^0\to p{\mu }^{-}$ and $B_s^0\to p{\mu }^{-}$ is performed at the LHCb experiment using data collected in proton-proton collisions at $\sqrt{s}=7$, 8 and 13 TeV, corresponding to integrated luminosities of 1, 2, and $6{\mathrm{fb}}^{-1}$, respectively. No significant signal for $B^0\to p{\mu }^{-}$ and $B_s^0\to p{\mu }^{-}$ decays is found and the upper limits on the branching fractions are determined to be $\mathcal{B}(B^0\to p{\mu }^{-})<2.6(3.1)\times {10}^{-9}$ and $\mathcal{B}(B_s^0\to p{\mu }^{-})<12.1(14.0)\times {10}^{-9}$, respectively, at 90% (95%) confidence level. These are the first limits on these decays to date.

A study of prompt ${\mathrm{\Xi }}_c^{+}$ production in proton-lead collisions is performed with the LHCb experiment at a center-of-mass energy per nucleon pair of 8.16 $\text{TeV}$ in 2016 in $p\mathrm{Pb}$ and $\mathrm{Pb}p$ collisions with an estimated integrated luminosity of approximately 12.5 and 17.4 ${\text{nb}}^{-1}$, respectively. The ${\mathrm{\Xi }}_c^{+}$ production cross section, as well as the ${\mathrm{\Xi }}_c^{+}$ to ${\mathrm{\Lambda }}_c^{+}$ production cross-section ratio, are measured as a function of the transverse momentum and rapidity and compared to the latest theory predictions. The forward-backward asymmetry is also measured as a function of the ${\mathrm{\Xi }}_c^{+}$ transverse momentum. The results provide strong constraints on theoretical calculation and are a unique input for hadronization studies in different collision systems.

The LHCb Collaboration measures production of the exotic hadron ${\chi }_{c1}(3872)$ in proton-nucleus collisions for the first time. Comparison with the charmonium state $\psi (2S)$ suggests that the exotic ${\chi }_{c1}(3872)$ experiences different dynamics in the nuclear medium than conventional hadrons, and comparison with data from proton-proton collisions indicates that the presence of the nucleus may modify ${\chi }_{c1}(3872)$ production rates. This is the first measurement of the nuclear modification factor of an exotic hadron.

A study of resonant structures in $B^{+}\to D^{*+}{D}^{-}{K}^{+}$ and $B^{+}\to D^{*-}{D}^{+}{K}^{+}$ decays is performed, using proton-proton collision data at center-of-mass energies of $\sqrt{s}=7$, 8, and 13 TeV recorded by the LHCb experiment, corresponding to an integrated luminosity of $9{\mathrm{fb}}^{-1}$. A simultaneous amplitude fit is performed to the two channels with contributions from resonances decaying to $D^{*-}{D}^{+}$ and $D^{*+}{D}^{-}$ states linked by $C$ parity. This procedure allows the $C$ parities of resonances in the $D^{*\pm }{D}^{\mp }$ mass spectra to be determined. Four charmonium or charmoniumlike states are observed decaying into $D^{*\pm }{D}^{\mp }$: ${\eta }_c(3945)$, $h_c(4000)$, ${\chi }_{c1}(4010)$, and $h_c(4300)$, with quantum numbers $J^{PC}$ equal to $0^{-+}$, $1^{+-}$, $1^{++}$, and $1^{+-}$, respectively. At least three of these states have not been observed previously. In addition, the existence of the $T_{\overline{c}\overline{s}0}^{*}(2870{)}^0$ and $T_{\overline{c}\overline{s}1}^{*}(2900{)}^0$ resonances in the $D^{-}{K}^{+}$ mass spectrum, already observed in the $B^{+}\to D^{+}{D}^{-}{K}^{+}$ decay, is confirmed in a different production channel.

A study of ${\mathrm{\Lambda }}_b^0$ baryon decays to the $Dp{K}^{-}$ final state is presented based on a proton-proton collision data sample corresponding to an integrated luminosity of $9{\mathrm{fb}}^{-1}$ collected with the LHCb detector. Two ${\mathrm{\Lambda }}_b^0$ decays are considered, ${\mathrm{\Lambda }}_b^0\to Dp{K}^{-}$ with $D\to K^{-}{\pi }^{+}$ and $D\to K^{+}{\pi }^{-}$, where $D$ represents a superposition of $D^0$ and ${\overline{D}}^0$ 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 $\gamma$, is also reported.

The first observation of the doubly charmed baryon ${\mathrm{\Xi }}_{cc}^{+}$ is reported through its decay to the ${\mathrm{\Lambda }}_c^{+}{K}^{-}{\pi }^{+}$ final state, with a statistical significance exceeding seven standard deviations. The observation is made using proton-proton collision data collected in 2024 with the LHCb Run 3 detector at a center-of-mass energy of 13.6 TeV, corresponding to a total integrated luminosity of $6.9{\mathrm{fb}}^{-1}$. The ${\mathrm{\Xi }}_{cc}^{+}$ mass is measured to be $3619.97\pm 0.83\pm {0.26}_{-1.30}^{+1.90}\mathrm{MeV}/c^2$, where the first uncertainty is statistical, the second is systematic, and the third is due to the unknown ${\mathrm{\Xi }}_{cc}^{+}$ lifetime, which is assumed to lie in the range 15–160 fs with a baseline value of 45 fs. The difference between the masses of the ${\mathrm{\Xi }}_{cc}^{+}$ and ${\mathrm{\Xi }}_{cc}^{++}$ baryons is determined to be $-1.77\pm 0.84\pm {0.15}_{-1.30}^{+1.90}\mathrm{MeV}/c^2$. This is the first observation of a new particle made with the LHCb Run 3 detector.

The onset of nuclear effects in light-ion collisions is studied by measuring the ratio of $D^0$ meson production between NeNe and OO collisions at a center-of-mass energy per nucleon pair of 5.36 TeV recorded by the LHCb detector. The $D^0$ meson yields are measured differentially in transverse momentum ($p_{\mathrm{T}}$) for $0.5<p_{\mathrm{T}}<20\mathrm{GeV}$ in the rapidity ($y$) region $2.0<y<4.5$, and are normalized to the total number of recorded inelastic nucleus-nucleus collisions in each data sample. The resulting production ratio shows evidence of variation as a function of $p_{\mathrm{T}}$, which is inconsistent with predictions based on nuclear modification of nucleon structure alone. This measurement is consistent with the onset of quark-gluon plasma production with increasing nucleus size in high-energy nuclear collisions.

An amplitude analysis of the $B^{+}\to D_s^{+}{D}_s^{-}{K}^{+}$ decay is carried out to study for the first time its intermediate resonant contributions, using proton-proton collision data collected with the LHCb detector at center-of-mass energies of 7, 8, and 13 TeV. A near-threshold peaking structure, referred to as $X(3960)$, is observed in the $D_s^{+}{D}_s^{-}$ invariant-mass spectrum with significance greater than 12 standard deviations. The mass, width, and the quantum numbers of the structure are measured to be $3956\pm 5\pm 10\mathrm{MeV}$, $43\pm 13\pm 8\mathrm{MeV}$, and $J^{PC}=0^{++}$, respectively, where the first uncertainties are statistical and the second systematic. The properties of the new structure are consistent with recent theoretical predictions for a state composed of $c\overline{c}s\overline{s}$ quarks. Evidence for an additional structure is found around 4140 MeV in the $D_s^{+}{D}_s^{-}$ invariant mass, which might be caused either by a new resonance with the $0^{++}$ assignment or by a $J/\psi \varphi \leftrightarrow D_s^{+}{D}_s^{-}$ coupled-channel effect.

An amplitude analysis of flavor-untagged $B_s^0\to J/\psi p\overline{p}$ decays is performed using a sample of $797\pm 31$ decays reconstructed with the LHCb detector. The data, collected in proton-proton collisions between 2011 and 2018, correspond to an integrated luminosity of $9{\mathrm{fb}}^{-1}$. Evidence for a new structure in the $J/\psi p$ and $J/\psi \overline{p}$ systems with a mass of ${4337}_{-4}^{+7}{}_{-2}^{+2}\mathrm{MeV}$ and a width of ${29}_{-12}^{+26}{}_{-14}^{+14}\mathrm{MeV}$ is found, where the first uncertainty is statistical and the second systematic, with a significance in the range of 3.1 to $3.7\sigma$, depending on the assigned $J^P$ hypothesis.

Measurements of $CP$ asymmetries in charmless three-body decays of $B^{\pm }$ mesons are reported using proton-proton collision data collected by the LHCb detector, corresponding to an integrated luminosity of $5.9{\mathrm{fb}}^{-1}$. The previously observed $CP$ asymmetry in $B^{\pm }\to {\pi }^{\pm }{K}^{+}{K}^{-}$ decays is confirmed, and $CP$ asymmetries are observed with a significance of more than five standard deviations in the $B^{\pm }\to {\pi }^{\pm }{\pi }^{+}{\pi }^{-}$ and $B^{\pm }\to K^{\pm }{K}^{+}{K}^{-}$ decays, while the $CP$ asymmetry of $B^{\pm }\to K^{\pm }{\pi }^{+}{\pi }^{-}$ decays is confirmed to be compatible with zero. The distributions of these asymmetries are also studied as a function of the three-body phase space and suggest contributions from rescattering and resonance interference processes. An indication of the presence of the decays $B^{\pm }\to {\pi }^{\pm }{\chi }_{c0}(1P)$ in both $B^{\pm }\to {\pi }^{\pm }{\pi }^{+}{\pi }^{-}$ and $B^{\pm }\to {\pi }^{\pm }{K}^{+}{K}^{-}$ decays is observed, as is $CP$ violation involving these amplitudes.

An amplitude analysis of the $B^0\to K^{*0}{\mu }^{+}{\mu }^{-}$ decay is presented using a dataset corresponding to an integrated luminosity of $4.7{\mathrm{fb}}^{-1}$ of $pp$ collision data collected with the LHCb experiment. For the first time, the coefficients associated to short-distance physics effects, sensitive to processes beyond the standard model, are extracted directly from the data through a $q^2$-unbinned amplitude analysis, where $q^2$ is the ${\mu }^{+}{\mu }^{-}$ invariant mass squared. Long-distance contributions, which originate from nonfactorizable QCD processes, are systematically investigated, and the most accurate assessment to date of their impact on the physical observables is obtained. The pattern of measured corrections to the short-distance couplings is found to be consistent with previous analyses of $b$- to $s$-quark transitions, with the largest discrepancy from the standard model predictions found to be at the level of 1.8 standard deviations. The global significance of the observed differences in the decay is 1.4 standard deviations.

Resonant structures in the dipion mass spectrum from ${\chi }_{c1}(3872)\to {\pi }^{+}{\pi }^{-}J/\psi$ decays, produced via $B^{+}\to K^{+}{\chi }_{c1}(3872)$ decays, are analyzed using proton-proton collision data collected by the LHCb experiment, corresponding to an integrated luminosity of $9{\mathrm{fb}}^{-1}$. A sizeable contribution from the isospin conserving ${\chi }_{c1}(3872)\to \omega J/\psi$ decay is established for the first time, $(21.4\pm 2.3\pm 2.0)\%$, with a significance of more than $7.1\sigma$. The amplitude of isospin violating decay, ${\chi }_{c1}(3872)\to {\rho }^{0}J/\psi$, relative to isospin conserving decay, ${\chi }_{c1}(3872)\to \omega J/\psi$, is properly determined, and it is a factor of 6 larger than expected for a pure charmonium state.

The decay-time-dependent $CP$ asymmetry in $B_s^0\to J/\psi (\to {\mu }^{+}{\mu }^{-})K^{+}{K}^{-}$ decays is measured using proton-proton collision data, corresponding to an integrated luminosity of $6{\mathrm{fb}}^{-1}$, collected with the LHCb detector at a center-of-mass energy of 13 TeV. Using a sample of approximately 349 000 $B_s^0$ signal decays with an invariant $K^{+}{K}^{-}$ mass in the vicinity of the $\varphi (1020)$ resonance, the $CP$-violating phase ${\varphi }_s$ is measured, along with the difference in decay widths of the light and heavy mass eigenstates of the $B_s^0\text{−}{\overline{B}}_s^0$ system, $\mathrm{\Delta }{\mathrm{\Gamma }}_s$, and the difference of the average $B_s^0$ and $B^0$ meson decay widths, ${\mathrm{\Gamma }}_s-{\mathrm{\Gamma }}_d$. The values obtained are ${\varphi }_s=-0.039\pm 0.022\pm 0.006\mathrm{rad}$, $\mathrm{\Delta }{\mathrm{\Gamma }}_s=0.0845\pm 0.0044\pm 0.0024{\mathrm{ps}}^{-1}$, and ${\mathrm{\Gamma }}_s-{\mathrm{\Gamma }}_d=-0.0056_{-0.0015}^{+0.0013}\pm 0.0014{\mathrm{ps}}^{-1}$, where the first uncertainty is statistical and the second systematic. These are the most precise single measurements to date and are consistent with expectations based on the Standard Model and with the previous LHCb analyses of this decay. These results are combined with previous independent LHCb measurements. The phase ${\varphi }_s$ is also measured independently for each polarization state of the $K^{+}{K}^{-}$ system and shows no evidence for polarization dependence.

The first dedicated $Z$-boson mass measurement at the LHC with $Z\to {\mu }^{+}{\mu }^{-}$ decays is reported. The dataset uses proton-proton collisions at a center-of-mass energy of 13 TeV, recorded in 2016 by the LHCb experiment, and corresponds to an integrated luminosity of $1.7{\mathrm{fb}}^{-1}$. A template fit to the ${\mu }^{+}{\mu }^{-}$ mass distribution yields the following result for the $Z$-boson mass: $m_Z=91,185.7\pm 8.3\pm 3.9\mathrm{MeV}$, where the first uncertainty is statistical and the second systematic. This result is consistent with previous measurements and predictions from global electroweak fits.

The time-integrated $CP$ asymmetry in the Cabibbo-suppressed decay $D^0\to K^{-}{K}^{+}$ is measured using proton-proton collision data, corresponding to an integrated luminosity of $5.7{\mathrm{fb}}^{-1}$ collected at a center-of-mass energy of 13 TeV with the LHCb detector. The $D^0$ mesons are required to originate from promptly produced $D^{*+}\to D^0{\pi }^{+}$ decays, and the charge of the companion pion is used to determine the flavor of the charm meson at production. The time-integrated $CP$ asymmetry is measured to be ${\mathcal{A}}_{CP}(K^{-}{K}^{+})=[6.8\pm 5.4\pm 1.6]\times {10}^{-4}$ where the first uncertainty is statistical and the second systematic. The direct $CP$ asymmetries in $D^0\to K^{-}{K}^{+}$ and $D^0\to {\pi }^{-}{\pi }^{+}$ decays, $a_{K^{-}{K}^{+}}^d$ and $a_{{\pi }^{-}{\pi }^{+}}^d$, are derived by combining ${\mathcal{A}}_{CP}(K^{-}{K}^{+})$ with the time-integrated $CP$ asymmetry difference, $\mathrm{\Delta }{A}_{CP}={\mathcal{A}}_{CP}(K^{-}{K}^{+})-{\mathcal{A}}_{CP}({\pi }^{-}{\pi }^{+})$, and other inputs, giving $a_{K^{-}{K}^{+}}^d=(7.7\pm 5.7)\times {10}^{-4},a_{{\pi }^{-}{\pi }^{+}}^d=(23.2\pm 6.1)\times {10}^{-4},$with a correlation coefficient corresponding to $\rho =0.88$. The compatibility of these results with $CP$ symmetry is 1.4 and 3.8 standard deviations for $D^0\to K^{-}{K}^{+}$ and $D^0\to {\pi }^{-}{\pi }^{+}$ decays, respectively. This is the first evidence for direct $CP$ violation in a specific $D^0$ decay.

The $CP$ asymmetry and branching fraction of the Cabibbo-Kobayashi-Maskawa-suppressed decay $B^{+}\to J/\psi {\pi }^{+}$ are precisely measured relative to the favored decay $B^{+}\to J/\psi K^{+}$ using a sample of proton-proton collision data corresponding to an integrated luminosity of $5.4{\mathrm{fb}}^{-1}$ recorded at a center-of-mass energy of 13 TeV during 2016–2018. The results of the $CP$ asymmetry difference and branching fraction ratio are $\mathrm{\Delta }{\mathcal{A}}^{CP}\equiv {\mathcal{A}}^{CP}(B^{+}\to J/\psi {\pi }^{+})-{\mathcal{A}}^{CP}(B^{+}\to J/\psi K^{+})=(1.29\pm 0.49\pm 0.08)\times {10}^{-2}$, ${\mathcal{R}}_{\pi /K}\equiv [\mathcal{B}(B^{+}\to J/\psi {\pi }^{+})/\mathcal{B}(B^{+}\to J/\psi K^{+})]=(3.852\pm 0.022\pm 0.018)\times {10}^{-2}$, where the first uncertainties are statistical and the second are systematic. A combination with previous LHCb results based on data collected at 7 and 8 TeV in 2011 and 2012 yields $\mathrm{\Delta }{\mathcal{A}}^{CP}=(1.42\pm 0.43\pm 0.08)\times {10}^{-2}$ and ${\mathcal{R}}_{\pi /K}=(3.846\pm 0.018\pm 0.018)\times {10}^{-2}$. The combined $\mathrm{\Delta }{\mathcal{A}}^{CP}$ value deviates from zero by 3.2 standard deviations, providing the first evidence for direct $CP$ violation in the amplitudes of beauty decays to charmonium final states.

A study is presented of $B^{+}\to K_{\mathrm{S}}^0{K}^{-}{\pi }^{+}{K}^{+}$ and $B^{+}\to K_{\mathrm{S}}^0{K}^{+}{\pi }^{-}{K}^{+}$ decays based on the analysis of proton-proton collision data collected with the LHCb detector at center-of-mass energies of 7, 8 and 13 TeV, corresponding to an integrated luminosity of $9{\mathrm{fb}}^{-1}$. The $K_{\mathrm{S}}^{0}K\pi$ invariant-mass distributions of both $B^{+}$ decay modes show, in the $m(K_{\mathrm{S}}^{0}K\pi )<1.85\mathrm{GeV}$ mass region, large activity which is resolved using an amplitude analysis. A simple model, where $J^{PC}$ amplitudes are described by multiple Breit-Wigner functions with appropriate angular distributions, provides a good description of the experimental data. In this approach a complex mixture of $J^{PC}=0^{-+}$, $1^{++}$ and $1^{+-}$ amplitudes is observed that is dominated by $\eta (1405)$, $\eta (1470)$, $\eta (1760)$, $f_1(1285)$, $f_1(1420)$ and $h_1(1405)$ resonances. The $K_{\mathrm{S}}^{0}K\pi$ Dalitz plots are dominated by asymmetric crossing $K^{*}\overline{K}$ bands which are different for the two $B^{+}$ decay modes. This is due to a different interference pattern between the $1^{++}$ and $1^{+-}$ amplitudes in the two channels. Branching fractions are measured for each resonant contribution.