Search

The four decays, ${\mathrm{\Lambda }}_b^0\to {\mathrm{\Sigma }}_c^{(*)++}{D}^{(*)-}{K}^{-}$, are observed for the first time using proton-proton collision data collected with the LHCb detector at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of $6{\mathrm{fb}}^{-1}$. By considering the ${\mathrm{\Lambda }}_b^0\to {\mathrm{\Lambda }}_c^{+}{\overline{D}}^0{K}^{-}$ decay as reference channel, the following branching fraction ratios are measured to be $\frac{\mathcal{B}({\mathrm{\Lambda }}_b^0\to {\mathrm{\Sigma }}_c^{++}{D}^{-}{K}^{-})}{\mathcal{B}({\mathrm{\Lambda }}_b^0\to {\mathrm{\Lambda }}_c^{+}{\overline{D}}^0{K}^{-})}=0.282\pm 0.016\pm 0.016\pm 0.005$, $\frac{\mathcal{B}({\mathrm{\Lambda }}_b^0\to {\mathrm{\Sigma }}_c^{*++}{D}^{-}{K}^{-})}{\mathcal{B}({\mathrm{\Lambda }}_b^0\to {\mathrm{\Sigma }}_c^{++}{D}^{-}{K}^{-})}=0.460\pm 0.052\pm 0.028$, $\frac{\mathcal{B}({\mathrm{\Lambda }}_b^0\to {\mathrm{\Sigma }}_c^{++}{D}^{*-}{K}^{-})}{\mathcal{B}({\mathrm{\Lambda }}_b^0\to {\mathrm{\Sigma }}_c^{++}{D}^{-}{K}^{-})}=2.261\pm 0.202\pm 0.129\pm 0.046$, $\frac{\mathcal{B}({\mathrm{\Lambda }}_b^0\to {\mathrm{\Sigma }}_c^{*++}{D}^{*-}{K}^{-})}{\mathcal{B}({\mathrm{\Lambda }}_b^0\to {\mathrm{\Sigma }}_c^{++}{D}^{-}{K}^{-})}=0.896\pm 0.137\pm 0.066\pm 0.018$, where the first uncertainties are statistical, the second are systematic, and the third are due to uncertainties in the branching fractions of intermediate particle decays. These initial observations mark the beginning of pentaquark searches in these modes, with more datasets to become available following the LHCb upgrade.

The fraction of ${\chi }_{c1}$ and ${\chi }_{c2}$ decays in the prompt $J/\psi$ yield, $F_{{\chi }_c\to J/\psi }={\sigma }_{{\chi }_c\to J/\psi }/{\sigma }_{J/\psi }$, is measured by the LHCb detector in $p\mathrm{Pb}$ collisions at $\sqrt{s_{\mathrm{NN}}}=8.16\mathrm{TeV}$. The study covers the forward ($1.5<y^{*}<4.0$) and backward ($-5.0<y^{*}<-2.5$) rapidity regions, where $y^{*}$ is the $J/\psi$ rapidity in the nucleon-nucleon center-of-mass system. Forward and backward rapidity samples correspond to integrated luminosities of $13.6\pm 0.3$ and $20.8\pm 0.5{\mathrm{nb}}^{-1}$, respectively. The result is presented as a function of the $J/\psi$ transverse momentum $p_{\mathrm{T},J/\psi }$ in the range $1<p_{\mathrm{T},J/\psi }<20\mathrm{GeV}/c$. The $F_{{\chi }_c\to J/\psi }$ fraction at forward rapidity is compatible with the LHCb measurement performed in $pp$ collisions at $\sqrt{s}=7\mathrm{TeV}$, whereas the result at backward rapidity is $2.4\sigma$ larger than in the forward region for $1<p_{\mathrm{T},J/\psi }<3\mathrm{GeV}/c$. The increase of $F_{{\chi }_c\to J/\psi }$ at low $p_{\mathrm{T},J/\psi }$ at backward rapidity is compatible with the suppression of the $\psi (2S)$ contribution to the prompt $J/\psi$ yield. The lack of in-medium dissociation of ${\chi }_c$ states observed in this study sets an upper limit of 180 MeV on the free energy available in these $p\mathrm{Pb}$ collisions to dissociate or inhibit charmonium state formation.

A flavor-tagged time-dependent angular analysis of the decay $B_s^0\to \varphi \varphi$ is performed using $pp$ collision data collected by the LHCb experiment at the center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of $6{\mathrm{fb}}^{-1}$. The $CP$-violating phase and direct $CP$-violation parameter are measured to be ${\varphi }_s^{s\overline{s}s}=-0.042\pm 0.075\pm 0.009\mathrm{rad}$ and $|\lambda |=1.004\pm 0.030\pm 0.009$, respectively, assuming the same values for all polarization states of the $\varphi \varphi$ system. In these results, the first uncertainties are statistical and the second systematic. These parameters are also determined separately for each polarization state, showing no evidence for polarization dependence. The results are combined with previous LHCb measurements using $pp$ collisions at center-of-mass energies of 7 and 8 TeV, yielding ${\varphi }_s^{s\overline{s}s}=-0.074\pm 0.069\mathrm{rad}$ and $|\lambda |=1.009\pm 0.030$. This is the most precise study of time-dependent $CP$ violation in a penguin-dominated $B$ meson decay. The results are consistent with $CP$ symmetry and with the standard model predictions.

An amplitude analysis of $B^0\to J/\psi \varphi K_{\text{S}}^0$ decays is performed using proton-proton collision data, corresponding to an integrated luminosity of $9{\mathrm{fb}}^{-1}$, collected with the LHCb detector at center-of-mass energies of 7, 8, and 13 TeV. Evidence with a significance of 4.0 standard deviations of a structure in the $J/\psi K_{\text{S}}^0$ system, named $T_{\psi s1}^{\theta }(4000{)}^0$, is seen, with its mass and width measured to be ${3991}_{-10}^{+12}{}_{-17}^{+9}\mathrm{MeV}/{\mathrm{c}}^2$ and ${105}_{-25}^{+29}{}_{-23}^{+17}\mathrm{MeV}$, respectively, where the first uncertainty is statistical and the second systematic. The $T_{\psi s1}^{\theta }(4000{)}^0$ state is likely to be the isospin partner of the $T_{\psi s1}^{\theta }(4000{)}^{+}$ state, previously observed in the $J/\psi K^{+}$ system of the $B^{+}\to J/\psi \varphi K^{+}$ decay. When isospin symmetry for the charged and neutral $T_{\psi s1}^{\theta }(4000)$ states is assumed, the signal significance increases to 5.4 standard deviations.

A simultaneous analysis of the $B^{+}\to K^{+}{\ell }^{+}{\ell }^{-}$ and $B^0\to K^{*0}{\ell }^{+}{\ell }^{-}$ decays is performed to test muon-electron universality in two ranges of the square of the dilepton invariant mass, $q^2$. The measurement uses a sample of beauty meson decays produced in proton-proton collisions collected with the LHCb detector between 2011 and 2018, corresponding to an integrated luminosity of $9{\mathrm{fb}}^{-1}$. A sequence of multivariate selections and strict particle identification requirements produce a higher signal purity and a better statistical sensitivity per unit luminosity than previous LHCb lepton universality tests using the same decay modes. Residual backgrounds due to misidentified hadronic decays are studied using data and included in the fit model. Each of the four lepton universality measurements reported is either the first in the given $q^2$ interval or supersedes previous LHCb measurements. The results are compatible with the predictions of the Standard Model.

The first simultaneous test of muon-electron universality using $B^{+}\to K^{+}{\ell }^{+}{\ell }^{-}$ and $B^0\to K^{*0}{\ell }^{+}{\ell }^{-}$ decays is performed, in two ranges of the dilepton invariant-mass squared, $q^2$. The analysis uses beauty mesons produced in proton-proton collisions collected with the LHCb detector between 2011 and 2018, corresponding to an integrated luminosity of $9{\mathrm{fb}}^{-1}$. Each of the four lepton universality measurements reported is either the first in the given $q^2$ interval or supersedes previous LHCb measurements. The results are compatible with the predictions of the Standard Model.

A search for $CP$ violation in ${\mathrm{\Lambda }}_b^0\to p{K}^{-}$ and ${\mathrm{\Lambda }}_b^0\to p{\pi }^{-}$ decays is presented using the full Run 1 and Run 2 data samples of $pp$ collisions collected with the LHCb detector, corresponding to an integrated luminosity of $9{\mathrm{fb}}^{-1}$ at center-of-mass energies of 7, 8, and 13 TeV. For the Run 2 data sample, the $CP$-violating asymmetries are measured to be $A_{CP}^{p{K}^{-}}=(-1.4\pm 0.7\pm 0.4)\%$ and $A_{CP}^{p{\pi }^{-}}=(0.4\pm 0.9\pm 0.4)\%$, where the first uncertainty is statistical and the second is systematic. Following significant improvements in the evaluation of systematic uncertainties compared to the previous LHCb measurement, the Run 1 dataset is reanalyzed to update the corresponding results. When combining the Run 2 and updated Run 1 measurements, the final results are found to be $A_{CP}^{p{K}^{-}}=(-1.1\pm 0.7\pm 0.4)\%$ and $A_{CP}^{p{\pi }^{-}}=(0.2\pm 0.8\pm 0.4)\%$, constituting the most precise measurements of these asymmetries to date.

The first study of $J/\psi \varphi$ production in diffractive processes in proton-proton collisions is presented. The study is based on an LHCb dataset recorded at center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of $5{\mathrm{fb}}^{-1}$. The data disfavor a nonresonant $J/\psi \varphi$ production but are consistent with a resonant model including several resonant states observed previously only in $B^{+}\to J/\psi \varphi K^{+}$ decays. The ${\chi }_{c0}(4500)$ state is observed with a significance over $6\sigma$ and the ${\chi }_{c1}(4274)$ is confirmed with a significance of more than $4\sigma$.

The branching fraction ratios of ${\overline{B}}^0\to D^{+}{\tau }^{-}{\overline{\nu }}_{\tau }$ and ${\overline{B}}^0\to D^{*+}{\tau }^{-}{\overline{\nu }}_{\tau }$ decays are measured with respect to their muonic counterparts, using a data sample corresponding to an integrated luminosity of $2.0{\mathrm{fb}}^{-1}$ collected by the LHCb experiment in proton-proton collisions at $\sqrt{s}=13\mathrm{TeV}$. The reconstructed final states are formed by combining $D^{+}$ mesons with ${\tau }^{-}\to {\mu }^{-}{\overline{\nu }}_{\mu }{\nu }_{\tau }$ candidates, where the $D^{+}$ is reconstructed via the $D^{+}\to K^{-}{\pi }^{+}{\pi }^{+}$ decay. The results are $R(D^{+})=0.249\pm 0.043\pm 0.047$, $R(D^{*+})=0.402\pm 0.081\pm 0.085$, where the first uncertainties are statistical and the second systematic. The two measurements have a correlation coefficient of $-0.39$ and are compatible with the standard model.

An amplitude analysis of $B^{-}\to D^{-}{D}^0{K}_S^0$ decays is performed using proton-proton collision data, corresponding to an integrated luminosity of $9{\mathrm{fb}}^{-1}$, collected with the LHCb detector at center-of-mass energies of 7, 8, and 13 TeV. A resonant structure of spin-parity $0^{+}$ is observed in the $D^0{K}_S^0$ invariant-mass spectrum with a significance of $5.3\sigma$. The mass and width of the state, modeled with a Breit-Wigner line shape, are determined to be $2883\pm 11\pm 8\mathrm{MeV}/c^2$ and ${87}_{-47}^{+22}\pm 17\mathrm{MeV}$, respectively, where the first uncertainties are statistical and the second systematic. These properties and the quark content are consistent with those of the open-charm tetraquark candidate $T_{cs0}^{*}(2870{)}^0$ observed previously in the $D^{+}{K}^{-}$ final state of the $B^{-}\to D^{-}{D}^{+}{K}^{-}$ decay. This result confirms the existence of the $T_{cs0}^{*}(2870{)}^0$ state in a new decay mode. The $T_{cs1}^{*}(2900{)}^0$ state, reported in the $B^{-}\to D^{-}{D}^{+}{K}^{-}$ decay, is also searched for in the $D^0{K}_S^0$ invariant-mass spectrum of the $B^{-}\to D^{-}{D}^0{K}_S^0$ decay, without finding evidence for it.

A study of ${\mathrm{\Lambda }}_b^0$ and ${\mathrm{\Xi }}_b^0$ decays to $\mathrm{\Lambda }{h}^{+}{h}^{\prime -}$ ($h^{(\prime )}=\pi ,K$) is performed using $pp$ collision data collected by the LHCb experiment during LHC Runs 1–2, corresponding to an integrated luminosity of $9{\mathrm{fb}}^{-1}$. The branching fractions for these decays are measured using the ${\mathrm{\Lambda }}_b^0\to {\mathrm{\Lambda }}_c^{+}(\to \mathrm{\Lambda }{\pi }^{+}){\pi }^{-}$ decay as a control channel. The decays ${\mathrm{\Lambda }}_b^0\to \mathrm{\Lambda }{\pi }^{+}{\pi }^{-}$ and ${\mathrm{\Xi }}_b^0\to \mathrm{\Lambda }{K}^{-}{\pi }^{+}$ are observed for the first time. For decay modes with sufficient signal yields, $CP$ asymmetries are measured in the full and localized regions of the final-state phase space. Evidence is found for $CP$ violation in the ${\mathrm{\Lambda }}_b^0\to \mathrm{\Lambda }{K}^{+}{K}^{-}$ decay, interpreted as originating primarily from an asymmetric ${\mathrm{\Lambda }}_b^0\to N^{*+}{K}^{-}$ decay amplitude. The measured $CP$ asymmetries for other decays are compatible with zero.

The ${\mathrm{\Xi }}_b^{0(-)}\to {\mathrm{\Xi }}_c(3055{)}^{+(0)}(\to D^{+(0)}\mathrm{\Lambda }){\pi }^{-}$ decay chains are observed, and the spin-parity of ${\mathrm{\Xi }}_c(3055{)}^{+(0)}$ baryons is determined for the first time. The measurement is performed using proton-proton collision data at a center-of-mass energy of $\sqrt{s}=13\mathrm{TeV}$, corresponding to an integrated luminosity of $5.4{\mathrm{fb}}^{-1}$, recorded by the LHCb experiment between 2016 and 2018. The spin-parity of the ${\mathrm{\Xi }}_c(3055{)}^{+(0)}$ baryons is determined to be $3/2^{+}$ with a significance of more than $6.5\sigma$ ($3.5\sigma$) compared to all other tested hypotheses. The up-down asymmetries of the ${\mathrm{\Xi }}_b^{0(-)}\to {\mathrm{\Xi }}_c(3055{)}^{+(0)}{\pi }^{-}$ transitions are measured to be $-0.92\pm 0.10\pm 0.05$ ($-0.92\pm 0.16\pm 0.22$), consistent with maximal parity violation, where the first uncertainty is statistical and the second is systematic. These results support the hypothesis that the ${\mathrm{\Xi }}_c(3055{)}^{+(0)}$ baryons correspond to the first $D$-wave $\lambda$-mode excitation of the ${\mathrm{\Xi }}_c$ flavor triplet.

A search for time-dependent violation of the charge-parity symmetry in $D^0\to K^{+}{K}^{-}$ and $D^0\to {\pi }^{+}{\pi }^{-}$ decays is performed at the LHCb experiment using proton-proton collision data recorded from 2015 to 2018 at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of $6{\mathrm{fb}}^{-1}$. The $D^0$ meson is required to originate from a $D^{*}(2010{)}^{+}\to D^0{\pi }^{+}$ decay, such that its flavor at production is identified by the charge of the accompanying pion. The slope of the time-dependent asymmetry of the decay rates of $D^0$ and ${\overline{D}}^0$ mesons into the final states under consideration is measured to be $\mathrm{\Delta }{Y}_{K^{+}{K}^{-}}=(-2.3\pm 1.5\pm 0.3)\times {10}^{-4}$, $\mathrm{\Delta }{Y}_{{\pi }^{+}{\pi }^{-}}=(-4.0\pm 2.8\pm 0.4)\times {10}^{-4}$, where the first uncertainties are statistical and the second are systematic. These results are compatible with the conservation of the charge-parity symmetry at the level of 2 standard deviations and improve the precision by nearly a factor of 2.

Using $pp$ collision data corresponding to an integrated luminosity of $5.4{\mathrm{fb}}^{-1}$ collected with the LHCb detector at a center-of-mass energy of 13 TeV, the $B^0\to D^{-}{D}^{+}{K}^{+}{\pi }^{-}$ decay is studied. A new excited $D_s^{+}$ meson is observed decaying into the $D^{+}{K}^{+}{\pi }^{-}$ final state with large statistical significance. The pole mass and width, and the spin parity of the new state are measured with an amplitude analysis to be $m_R=2591\pm 6\pm 7\mathrm{MeV}$, ${\mathrm{\Gamma }}_R=89\pm 16\pm 12\mathrm{MeV}$, and $J^P=0^{-}$, where the first uncertainty is statistical and the second systematic. Fit fractions for all components in the amplitude analysis are also reported. The new resonance, denoted as $D_{s0}(2590{)}^{+}$, is a strong candidate to be the $D_s(2{{}^{1}S}_0{)}^{+}$ state, the radial excitation of the pseudoscalar ground-state $D_s^{+}$ meson.

A measurement of the ratios of the effective decay widths of $D^0\to {\pi }^{-}{\pi }^{+}$ and $D^0\to K^{-}{K}^{+}$ decays over that of $D^0\to K^{-}{\pi }^{+}$ decays is performed with the LHCb experiment using proton–proton collisions at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of $6{\mathrm{fb}}^{-1}$. These observables give access to the charm mixing parameters $y_{CP}^{\pi \pi }-y_{CP}^{K\pi }$ and $y_{CP}^{KK}-y_{CP}^{K\pi }$, and are measured as $y_{CP}^{\pi \pi }-y_{CP}^{K\pi }=(6.57\pm 0.53\pm 0.16)\times {10}^{-3}$, $y_{CP}^{KK}-y_{CP}^{K\pi }=(7.08\pm 0.30\pm 0.14)\times {10}^{-3}$, where the first uncertainties are statistical and the second systematic. The combination of the two measurements is $y_{CP}-y_{CP}^{K\pi }=(6.96\pm 0.26\pm 0.13)\times {10}^{-3}$, which is four times more precise than the previous world average.

The nuclear modification factor of neutral pions is measured in proton-lead collisions collected at a center-of-mass energy per nucleon of 8.16 TeV with the LHCb detector. The ${\pi }^0$ production cross section is measured differentially in transverse momentum ($p_T$) for $1.5<p_T<10.0\mathrm{GeV}$ and in center-of-mass pseudorapidity (${\eta }_{\mathrm{c}.\mathrm{m}.}$) regions $2.5<{\eta }_{\mathrm{c}.\mathrm{m}.}<3.5$ (forward) and $-4.0<{\eta }_{\mathrm{c}.\mathrm{m}.}<-3.0$ (backward) defined relative to the proton beam direction. The forward measurement shows a sizable suppression of ${\pi }^0$ production, while the backward measurement shows the first evidence of ${\pi }^0$ enhancement in proton-lead collisions at the LHC. Together, these measurements provide precise constraints on models of nuclear structure and particle production in high-energy nuclear collisions.

Two narrow resonant states are observed in the ${\mathrm{\Lambda }}_b^0{K}^{-}{\pi }^{+}$ 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 $6{\mathrm{fb}}^{-1}$. The minimal quark content of the ${\mathrm{\Lambda }}_b^0{K}^{-}{\pi }^{+}$ system indicates that these are excited ${\mathrm{\Xi }}_b^0$ baryons. The masses of the ${\mathrm{\Xi }}_b(6327{)}^0$ and ${\mathrm{\Xi }}_b(6333{)}^0$ states are $m[{\mathrm{\Xi }}_b(6327{)}^0]=6327.28_{-0.21}^{+0.23}\pm 0.12\pm 0.24$ and $m[{\mathrm{\Xi }}_b(6333{)}^0]=6332.69_{-0.18}^{+0.17}\pm 0.03\pm 0.22\mathrm{MeV}$, respectively, with a mass splitting of $\mathrm{\Delta }m=5.41_{-0.27}^{+0.26}\pm 0.12\mathrm{MeV}$, where the uncertainties are statistical, systematic, and due to the ${\mathrm{\Lambda }}_b^0$ mass measurement. The measured natural widths of these states are consistent with zero, with upper limits of $\mathrm{\Gamma }[{\mathrm{\Xi }}_b(6327{)}^0]<2.20(2.56)$ and $\mathrm{\Gamma }[{\mathrm{\Xi }}_b(6333{)}^0]<1.60(1.92)\mathrm{MeV}$ 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 $1D$ ${\mathrm{\Xi }}_b^0$ resonances.

A search for $K_{\mathrm{S}(\mathrm{L})}^0\to {\pi }^{+}{\pi }^{-}{\mu }^{+}{\mu }^{-}$ decays is performed using proton-proton collision data collected by the LHCb experiment at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of $5.4{\mathrm{fb}}^{-1}$. No $K_{\mathrm{S}(\mathrm{L})}^0\to {\pi }^{+}{\pi }^{-}{\mu }^{+}{\mu }^{-}$ signals are found and upper limits are set for the first time on the branching fractions $\mathcal{B}(K_{\mathrm{S}}^0\to {\pi }^{+}{\pi }^{-}{\mu }^{+}{\mu }^{-})<1.4\times {10}^{-9}$ and $\mathcal{B}(K_{\mathrm{L}}^0\to {\pi }^{+}{\pi }^{-}{\mu }^{+}{\mu }^{-})<6.6\times {10}^{-7}$, at the 90% confidence level.

The transverse polarization of $\mathrm{\Lambda }$ and $\overline{\mathrm{\Lambda }}$ hyperons is measured in $p\mathrm{Pb}$ collisions collected by the LHCb experiment at a nucleon-nucleon center-of-mass energy of 5.02 TeV. The polarization is averaged over hyperon transverse momentum in the range $0.15<p_{\mathrm{T}}<6.00\mathrm{GeV}/c$, and Feynman-$x$ in the ranges $0.005<x_{\mathrm{F}}<0.040$ (forward region) and $-0.10<x_{\mathrm{F}}<-0.01$ (backward region) defined relative to the proton beam direction. The transverse polarization is found to be compatible with zero for both $\mathrm{\Lambda }$ and $\overline{\mathrm{\Lambda }}$ hyperons. The results are also measured as a function of $p_{\mathrm{T}}$ and $x_{\mathrm{F}}$ with no significant dependence on these variables observed. The results are compared with previous experimental measurements at different center-of-mass energies and collision environments.

The first observation of the decay $B^0\to D^0{\overline{D}}^0{K}^{+}{\pi }^{-}$ 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 $B^0\to D^{*-}{D}^0{K}^{+}$ 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 $B^0\to D^0{\overline{D}}^0{K}^{+}{\pi }^{-}$ decays is thus determined to be $\mathcal{B}(B^0\to D^0{\overline{D}}^0{K}^{+}{\pi }^{-})=(3.50\pm 0.27\pm 0.26\pm 0.30)\times {10}^{-4}$, 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.