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 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 $K_{\mathrm{S}(\mathrm{L})}^0\to {\pi }^{+}{\pi }^{-}{\mu }^{+}{\mu }^{-}$ 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.

A sample of $pp$ collision data, corresponding to an integrated luminosity of $5.5{\mathrm{fb}}^{-1}$ and collected by the LHCb experiment during LHC Run 2, is used to measure the ratio of the lifetime of the ${\mathrm{\Xi }}_b^{-}$ baryon to that of the ${\mathrm{\Lambda }}_b^0$ baryon, $r_{\tau }\equiv {\tau }_{{\mathrm{\Xi }}_b^{-}}/{\tau }_{{\mathrm{\Lambda }}_b^0}$. The value $r_{\tau }=1.076\pm 0.013\pm 0.006$ is obtained, where the first uncertainty is statistical and the second systematic. This value is averaged with the corresponding value from Run 1 to obtain $r_{\tau }^{\mathrm{Run}1,2}=1.078\pm 0.012\pm 0.007$. Multiplying by the world-average value of the ${\mathrm{\Lambda }}_b^0$ lifetime yields ${\tau }_{{\mathrm{\Xi }}_b^{-}}^{\mathrm{Run}1,2}=1.578\pm 0.018\pm 0.010\pm 0.011\mathrm{ps}$, where the uncertainties are statistical, systematic, and due to the limited knowledge of the ${\mathrm{\Lambda }}_b^0$ lifetime. This measurement improves the precision of the current world average of the ${\mathrm{\Xi }}_b^{-}$ lifetime by about a factor of 2, and is in good agreement with the most recent theoretical predictions.

A search for the lepton-flavor violating decays $B_s^0\to \varphi {\mu }^{\pm }{\tau }^{\mp }$ is presented, using a sample of proton-proton collisions at center-of-mass energies of 7, 8, and 13 TeV, collected with the LHCb detector and corresponding to a total integrated luminosity of $9{\mathrm{fb}}^{-1}$. The $\tau$ leptons are selected using decays with three charged pions. No significant excess is observed, and an upper limit on the branching fraction is determined to be $\mathcal{B}(B_s^0\to \varphi {\mu }^{\pm }{\tau }^{\mp })<1.0\times {10}^{-5}$ at 90% confidence level.

Flow harmonic coefficients, $v_n$, which are the key to studying the hydrodynamics of the quark-gluon plasma (QGP) created in heavy-ion collisions, have been measured in various collision systems and kinematic regions and using various particle species. The study of flow harmonics in a wide pseudorapidity range is particularly valuable to understand the temperature dependence of the shear viscosity to entropy density ratio of the QGP. This paper presents the first LHCb results of the second- and the third-order flow harmonic coefficients of charged hadrons as a function of transverse momentum in the forward region, corresponding to pseudorapidities between 2.0 and 4.9, using the data collected from PbPb collisions in 2018 at a center-of-mass energy of 5.02 $\text{TeV}$. The coefficients measured using the two-particle angular correlation analysis method are smaller than the central-pseudorapidity measurements at ALICE and ATLAS from the same collision system but share similar features.

The production of prompt $D_s^{+}$ and $D^{+}$ mesons is measured by the LHCb experiment in proton-lead ($p\mathrm{Pb}$) collisions in both the forward ($1.5<y^{*}<4.0$) and backward ($-5.0<y^{*}<-2.5$) rapidity regions at a nucleon-nucleon center-of-mass energy of $\sqrt{s_{\mathrm{NN}}}=8.16\mathrm{TeV}$. The nuclear modification factors of both $D_s^{+}$ and $D^{+}$ mesons are determined as a function of transverse momentum, $p_{\mathrm{T}}$, and rapidity. In addition, the $D_s^{+}$ to $D^{+}$ cross section ratio is measured as a function of the primary charged particle multiplicity in the event. An enhanced $D_s^{+}$ to $D^{+}$ production in high-multiplicity events is observed for the whole measured $p_{\mathrm{T}}$ range, in particular at low $p_{\mathrm{T}}$ and backward rapidity, where the significance exceeds six standard deviations. This constitutes the first observation of strangeness enhancement in charm quark hadronization in high-multiplicity $p\mathrm{Pb}$ collisions. The results are also qualitatively consistent with the presence of quark coalescence as an additional charm quark hadronization mechanism in high-multiplicity proton-lead collisions.

The collinear and transverse-momentum-dependent jet fragmentation function and the radial profile for $B^{\pm }$ mesons in jets are measured. The $B^{\pm }$ mesons are reconstructed through the $J/\psi (\to {\mu }^{+}{\mu }^{-})K^{\pm }$ decay channel using proton-proton collision data collected during 2016–2018 with the LHCb detector at a center-of-mass (c.m.) energy of $\sqrt{s}=13\mathrm{TeV}$, corresponding to an integrated luminosity of $5.4{\mathrm{fb}}^{-1}$. The results complement recent measurements of jet fragmentation functions for heavy-flavor hadrons and suggest a growing contribution of gluon fragmentation to $B^{\pm }$ mesons as the jet transverse momentum increases.

A flavor-tagged time-dependent analysis of $B^0\to K_{\mathrm{S}}^0{\mu }^{+}{\mu }^{-}$ decays is performed across the full dimuon mass range excluding the $J/\psi$ and $\psi (2S)$ resonance regions. The analysis uses proton-proton collision data collected by the LHCb experiment in 2011–2018 at center-of-mass energies of 7, 8, and 13 TeV, corresponding to an integrated luminosity of $9{\mathrm{fb}}^{-1}$. The $CP$ violation parameters are determined to be $C=-0.13\pm 0.32\pm 0.04$, $S=+0.82\pm 0.29\pm 0.05$, where the first uncertainties are statistical and the second are systematic. The results are consistent with the standard model prediction. This is the first experimental study of time-dependent $CP$ violation in $b\to s{\ell }^{+}{\ell }^{-}$ processes.

An analysis of the $B^0\to K^{*0}(\to K^{+}{\pi }^{-}){\mu }^{+}{\mu }^{-}$ decay is presented using proton-proton collision data collected by the LHCb experiment, corresponding to an integrated luminosity of $8.4{\mathrm{fb}}^{-1}$. The full set of $CP$-averaged and $CP$-asymmetric angular observables is determined in bins of the invariant mass squared of the dimuon system, as well as the branching fraction relative to the $B^0\to J/\psi (\to {\mu }^{+}{\mu }^{-})K^{+}{\pi }^{-}$ decay. For the first time, the full set of observables pertaining to the $K^{+}{\pi }^{-}$ S-wave contribution to the final state are presented and consideration is given to effects arising from the mass of the muons. The extracted $CP$-asymmetry observables show no significant deviations from zero. The measurements of the $CP$-averaged observables and the branching fractions continue to exhibit the pattern of tensions with the standard model predictions that have been seen in previous analyses that use part of the dataset considered in this Letter.

The first evidence for the decay $B^{-}\to D^{**0}{\tau }^{-}{\overline{\nu }}_{\tau }$ is obtained using proton-proton collision data collected by the LHCb experiment, corresponding to an integrated luminosity of $9{\mathrm{fb}}^{-1}$, at centre-of-mass energies of 7, 8, and 13 TeV. Here, the $D^{**0}$ meson represents any of the three excited charm mesons $D_1(2420{)}^0$, $D_2^{*}(2460{)}^0$, and $D_1^{\prime }(2400{)}^0$. The $B^{-}\to D^{**0}{\tau }^{-}{\overline{\nu }}_{\tau }$ signal is measured with a significance of $3.5\sigma$, including systematic uncertainties. The combined branching fraction $\mathcal{B}(B^{-}\to D_{1,2}^{**0}{\tau }^{-}{\overline{\nu }}_{\tau })\times \mathcal{B}(D_{1,2}^{**0}\to D^{*+}{\pi }^{-})$, where $D_{1,2}^{**0}$ denotes both $D_1(2420{)}^0$ and $D_2^{*}(2460{)}^0$ contributions, is measured to be $[0.051\pm 0.013(\mathrm{stat})\pm 0.006(\mathrm{syst})\pm 0.009(\mathrm{ext})]\%$, where the last uncertainty reflects that of the branching fraction of the normalization channel $B^{-}\to D_{1,2}^{**0}{D_s^{-}}^{(*)}$. The ratio between the tauonic and muonic semileptonic $B$ decays, with the latter taken from world average values, is also determined and found to be $\mathcal{R}(D_{1,2}^{**0})=0.13\pm 0.03(\mathrm{stat})\pm 0.01(\mathrm{syst})\pm 0.02(\mathrm{ext})$.

A search for the rare decay $B^{+}\to \overline{\mathrm{\Lambda }}p{\mu }^{+}{\mu }^{-}$ is performed using proton-proton collision data recorded by the LHCb experiment at a center-of-mass energy of $\sqrt{s}=13\mathrm{TeV}$, corresponding to an integrated luminosity of $5.4{\mathrm{fb}}^{-1}$. An excess of events is found with respect to the background-only expectation, with a signal significance of 3.5 standard deviations, in the low invariant-mass region of $m(\overline{\mathrm{\Lambda }}p)<2.8\mathrm{GeV}/c^2$. The branching fraction is measured to be ${\mathcal{B}}_{\mathrm{low}}(B^{+}\to \overline{\mathrm{\Lambda }}p{\mu }^{+}{\mu }^{-})=(1.70_{-0.56}^{+0.65}(\mathrm{stat})\pm 0.17(\mathrm{syst})\pm 0.14(\mathrm{ext}))\times {10}^{-8}$, where the last uncertainty is due to external inputs on $\mathcal{B}(B^{+}\to J/\psi \overline{\mathrm{\Lambda }}p)\times \mathcal{B}(J/\psi \to {\mu }^{+}{\mu }^{-})$. With no significant signal observed in the high $m(\overline{\mathrm{\Lambda }}p)$ region above $2.8\mathrm{GeV}/c^2$, an upper limit is set to be ${\mathcal{B}}_{\mathrm{high}}(B^{+}\to \overline{\mathrm{\Lambda }}p{\mu }^{+}{\mu }^{-})<2.8(3.7)\times {10}^{-9}$ at the 90% (95%) confidence level.

The first evidence for the decay $B^{+}\to {\pi }^{+}{e}^{+}{e}^{-}$ is reported using proton-proton collision data recorded by the LHCb experiment at center-of-mass energies of 7, 8, and 13 TeV, corresponding to an integrated luminosity of $9{\mathrm{fb}}^{-1}$. A signal excess with a significance of $3.2\sigma$ is observed and the branching fraction is measured to be $\mathcal{B}(B^{+}\to {\pi }^{+}{e}^{+}{e}^{-})=({2.4}_{-0.8}^{+0.9}{}_{-0.2}^{+0.4})\times {10}^{-8}$, where the first set of uncertainties is statistical and the second is systematic. The result is consistent with the Standard Model expectation.