Search

The $B^{+}\to {D^{*}}^{-}{K}^{+}{\pi }^{+}$ decay potentially provides an excellent way to investigate charm meson spectroscopy. The decay is searched for in a sample of proton-proton collision data collected with the LHCb detector at center-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of $3{\mathrm{fb}}^{-1}$. A clear signal is observed, and the ratio of its branching fraction to that of the $B^{+}\to D^{*-}{\pi }^{+}{\pi }^{+}$ normalization channel is measured to be $\mathcal{B}(B^{+}\to D^{*-}{K}^{+}{\pi }^{+})/\mathcal{B}(B^{+}\to D^{*-}{\pi }^{+}{\pi }^{+})=(6.39\pm 0.27\pm 0.48)\times {10}^{-2},$ where the first uncertainty is statistical and the second is systematic. This is the first observation of the $B^{+}\to {D^{*}}^{-}{K}^{+}{\pi }^{+}$ decay.

The branching fraction of the decay $B_s^0\to D_s^{(*)+}{D}_s^{(*)-}$ is measured using $pp$ collision data corresponding to an integrated luminosity of $1.0{\mathrm{fb}}^{-1}$, collected using the LHCb detector at a center-of-mass energy of 7 TeV. It is found to be $\mathcal{B}(B_s^0\to D_s^{(*)+}{D}_s^{(*)-})=(3.05\pm 0.10\pm 0.20\pm 0.34)\%$, where the uncertainties are statistical, systematic, and due to the normalization channel, respectively. The branching fractions of the individual decays corresponding to the presence of one or two $D_s^{*\pm }$ are also measured. The individual branching fractions are found to be $\mathcal{B}(B_s^0\to D_s^{*\pm }{D}_s^{\mp })=(1.35\pm 0.06\pm 0.09\pm 0.15)\%$, $\mathcal{B}(B_s^0\to D_s^{*+}{D}_s^{*-})=(1.27\pm 0.08\pm 0.10\pm 0.14)\%$. All three results are the most precise determinations to date.

The decay of the narrow resonance ${\overline{B}}_{s2}^{*0}\to B^{-}{K}^{+}$ can be used to determine the $B^{-}$ momentum in partially reconstructed decays without any assumptions on the decay products of the $B^{-}$ meson. This technique is employed for the first time to distinguish contributions from $D^0$, $D^{*0}$, and higher-mass charmed states ($D^{**0}$) in semileptonic $B^{-}$ decays by using the missing-mass distribution. The measurement is performed using a data sample corresponding to an integrated luminosity of $3.0{\mathrm{fb}}^{-1}$ collected with the LHCb detector in $pp$ collisions at center-of-mass energies of 7 and 8 TeV. The resulting branching fractions relative to the inclusive $B^{-}\to D^{0}X{\mu }^{-}{\overline{\nu }}_{\mu }$ are $f_{D^0}=\mathcal{B}(B^{-}\to D^0{\mu }^{-}{\overline{\nu }}_{\mu })/\mathcal{B}(B^{-}\to D^{0}X{\mu }^{-}{\overline{\nu }}_{\mu })=0.25\pm 0.06,f_{D^{**0}}=\mathcal{B}(B^{-}\to (D^{**0}\to D^{0}X){\mu }^{-}{\overline{\nu }}_{\mu })/\mathcal{B}(B^{-}\to D^{0}X{\mu }^{-}{\overline{\nu }}_{\mu })=0.21\pm 0.07,$ with $f_{D^{*0}}=1-f_{D^0}-f_{D^{**0}}$ making up the remainder.

Investigations of the existence of pentaquark states containing a single $b$ (anti)quark decaying weakly into four specific final states $J/\psi K^{+}{\pi }^{-}p$, $J/\psi K^{-}{\pi }^{-}p$, $J/\psi K^{-}{\pi }^{+}p$, and $J/\psi \varphi (1020)p$ are reported. The data sample corresponds to an integrated luminosity of $3.0{\mathrm{fb}}^{-1}$ in 7 and 8 TeV $pp$ collisions acquired with the LHCb detector. Signals are not observed and upper limits are set on the product of the production cross section times branching fraction with respect to that of the ${\mathrm{\Lambda }}_b^0$.

Using proton-proton collision data corresponding to an integrated luminosity of $3.0{\mathrm{fb}}^{-1}$, recorded by the LHCb detector at center-of-mass energies of 7 and 8 TeV, the $B_c^{+}\to D^0{K}^{+}$ decay is observed with a statistical significance of 5.1 standard deviations. By normalizing to $B^{+}\to {\overline{D}}^0{\pi }^{+}$ decays, a measurement of the branching fraction multiplied by the production rates for $B_c^{+}$ relative to $B^{+}$ mesons in the LHCb acceptance is obtained, $R_{D^{0}K}=(f_c/f_u)\times \mathcal{B}(B_c^{+}\to D^0{K}^{+})=(9.3_{-2.5}^{+2.8}\pm 0.6)\times {10}^{-7}$, where the first uncertainty is statistical and the second is systematic. This decay is expected to proceed predominantly through weak annihilation and penguin amplitudes, and is the first $B_c^{+}$ decay of this nature to be observed.

The first observation of the rare decay $B_s^0\to \varphi {\pi }^{+}{\pi }^{-}$ and evidence for $B^0\to \varphi {\pi }^{+}{\pi }^{-}$ are reported, using $pp$ collision data recorded by the LHCb detector at center-of-mass energies $\sqrt{s}=7$ and 8 TeV, corresponding to an integrated luminosity of $3{\mathrm{fb}}^{-1}$. The branching fractions in the ${\pi }^{+}{\pi }^{-}$ invariant mass range $400<m({\pi }^{+}{\pi }^{-})<1600\mathrm{MeV}/c^2$ are $[3.48\pm 0.23\pm 0.17\pm 0.35]\times {10}^{-6}$ and $[1.82\pm 0.25\pm 0.41\pm 0.14]\times {10}^{-7}$ for $B_s^0\to \varphi {\pi }^{+}{\pi }^{-}$ and $B^0\to \varphi {\pi }^{+}{\pi }^{-}$ respectively, where the uncertainties are statistical, systematic and from the normalization mode $B_s^0\to \varphi \varphi$. A combined analysis of the ${\pi }^{+}{\pi }^{-}$ mass spectrum and the decay angles of the final-state particles identifies the exclusive decays $B_s^0\to \varphi f_0(980)$, $B_s^0\to \varphi f_2(1270)$, and $B_s^0\to \varphi {\rho }^0$ with branching fractions of $[1.12\pm 0.16_{-0.08}^{+0.09}\pm 0.11]\times {10}^{-6}$, $[0.61\pm 0.13_{-0.05}^{+0.12}\pm 0.06]\times {10}^{-6}$ and $[2.7\pm 0.7\pm 0.2\pm 0.2]\times {10}^{-7}$, respectively.

A proton-proton collision data sample, corresponding to an integrated luminosity of $3{\mathrm{fb}}^{-1}$ collected by LHCb at $\sqrt{s}=7$ and 8 TeV, is used to reconstruct $63\pm 9$ ${\mathrm{\Omega }}_b^{-}\to {\mathrm{\Omega }}_c^0{\pi }^{-}$, ${\mathrm{\Omega }}_c^0\to p{K}^{-}{K}^{-}{\pi }^{+}$ decays. Using the ${\mathrm{\Xi }}_b^{-}\to {\mathrm{\Xi }}_c^0{\pi }^{-}$, ${\mathrm{\Xi }}_c^0\to p{K}^{-}{K}^{-}{\pi }^{+}$ decay mode for calibration, the lifetime ratio and the absolute lifetime of the ${\mathrm{\Omega }}_b^{-}$ baryon are measured to be ${\tau }_{{\mathrm{\Omega }}_b^{-}}/{\tau }_{{\mathrm{\Xi }}_b^{-}}=1.11\pm 0.16\pm 0.03$, ${\tau }_{{\mathrm{\Omega }}_b^{-}}=1.78\pm 0.26\pm 0.05\pm 0.06\mathrm{ps}$, where the uncertainties are statistical, systematic and from the calibration mode (for ${\tau }_{{\mathrm{\Omega }}_b^{-}}$ only). A measurement is also made of the mass difference, $m_{{\mathrm{\Omega }}_b^{-}}-m_{{\mathrm{\Xi }}_b^{-}}$, and the corresponding ${\mathrm{\Omega }}_b^{-}$ mass, which yields $m_{{\mathrm{\Omega }}_b^{-}}-m_{{\mathrm{\Xi }}_b^{-}}=247.4\pm 3.2\pm 0.5\mathrm{MeV}/c^2$, $m_{{\mathrm{\Omega }}_b^{-}}=6045.1\pm 3.2\pm 0.5\pm 0.6\mathrm{MeV}/c^2$. These results are consistent with previous measurements.

Using $pp$ collision data corresponding to an integrated luminosity of $8.5{\mathrm{fb}}^{-1}$ recorded by the LHCb experiment at center-of-mass energies of $\sqrt{s}=7$, 8, and 13 TeV, the observation of an excited $B_c^{+}$ state in the $B_c^{+}{\pi }^{+}{\pi }^{-}$ invariant-mass spectrum is reported. The observed peak has a mass of $6841.2\pm 0.6(\mathrm{stat})\pm 0.1(\mathrm{syst})\pm 0.8(B_c^{+})\mathrm{MeV}/c^2$, where the last uncertainty is due to the limited knowledge of the $B_c^{+}$ mass. It is consistent with expectations of the $B_c^{*}(2{{}^{3}S}_1{)}^{+}$ state reconstructed without the low-energy photon from the $B_c^{*}(1{{}^{3}S}_1{)}^{+}\to B_c^{+}\gamma$ decay following $B_c^{*}(2{{}^{3}S}_1{)}^{+}\to B_c^{*}(1{{}^{3}S}_1{)}^{+}{\pi }^{+}{\pi }^{-}$. A second state is seen with a global (local) statistical significance of $2.2\sigma$ ($3.2\sigma$) and a mass of $6872.1\pm 1.3(\mathrm{stat})\pm 0.1(\mathrm{syst})\pm 0.8(B_c^{+})\mathrm{MeV}/c^2$, and is consistent with the $B_c(2{{}^{1}S}_0{)}^{+}$ state. These mass measurements are the most precise to date.

The production fractions of ${\overline{B}}_s^0$ and ${\mathrm{\Lambda }}_b^0$ hadrons, normalized to the sum of $B^{-}$ and ${\overline{B}}^0$ fractions, are measured in 13 TeV $pp$ collisions using data collected by the LHCb experiment, corresponding to an integrated luminosity of $1.67{\mathrm{fb}}^{-1}$. These ratios, averaged over the $b$ hadron transverse momenta from 4 to 25 GeV and pseudorapidity from 2 to 5, are $0.122\pm 0.006$ for ${\overline{B}}_s^0$, and $0.259\pm 0.018$ for ${\mathrm{\Lambda }}_b^0$, where the uncertainties arise from both statistical and systematic sources. The ${\mathrm{\Lambda }}_b^0$ ratio depends strongly on transverse momentum, while the ${\overline{B}}_s^0$ ratio shows a mild dependence. Neither ratio shows variations with pseudorapidity. The measurements are made using semileptonic decays to minimize theoretical uncertainties. In addition, the ratio of $D^{+}$ to $D^0$ mesons produced in the sum of ${\overline{B}}^0$ and $B^{-}$ semileptonic decays is determined as $0.359\pm 0.006\pm 0.009$, where the uncertainties are statistical and systematic.

We report measurements of the lifetimes of the ${\mathrm{\Lambda }}_c^{+}$, ${\mathrm{\Xi }}_c^{+}$ and ${\mathrm{\Xi }}_c^0$ charm baryons using proton-proton collision data at center-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of $3.0{\mathrm{fb}}^{-1}$, collected by the LHCb experiment. The charm baryons are reconstructed through the decays ${\mathrm{\Lambda }}_c^{+}\to p{K}^{-}{\pi }^{+}$, ${\mathrm{\Xi }}_c^{+}\to p{K}^{-}{\pi }^{+}$ and ${\mathrm{\Xi }}_c^0\to p{K}^{-}{K}^{-}{\pi }^{+}$, and originate from semimuonic decays of beauty baryons. The lifetimes are measured relative to that of the $D^{+}$ meson, and are determined to be ${\tau }_{{\mathrm{\Lambda }}_c^{+}}=203.5\pm 1.0\pm 1.3\pm 1.4\mathrm{fs},{\tau }_{{\mathrm{\Xi }}_c^{+}}=456.8\pm 3.5\pm 2.9\pm 3.1\mathrm{fs},{\tau }_{{\mathrm{\Xi }}_c^0}=154.5\pm 1.7\pm 1.6\pm 1.0\mathrm{fs},$ where the uncertainties are statistical, systematic, and due to the uncertainty in the $D^{+}$ lifetime. The measurements are approximately 3–4 times more precise than the current world average values. The ${\mathrm{\Lambda }}_c^{+}$ and ${\mathrm{\Xi }}_c^{+}$ lifetimes are in agreement with previous measurements; however, the ${\mathrm{\Xi }}_c^0$ baryon lifetime is approximately 3.3 standard deviations larger than the world average value.

The first observation of the $D^0\to {\pi }^{+}{\pi }^{-}{\mu }^{+}{\mu }^{-}$ and $D^0\to K^{+}{K}^{-}{\mu }^{+}{\mu }^{-}$ decays is reported using a sample of proton-proton collisions collected by LHCb at a center-of-mass energy of 8 TeV, and corresponding to $2{\mathrm{fb}}^{-1}$ of integrated luminosity. The corresponding branching fractions are measured using as normalization the decay $D^0\to K^{-}{\pi }^{+}[{\mu }^{+}{\mu }^{-}{]}_{{\rho }^0/\omega }$, where the two muons are consistent with coming from the decay of a ${\rho }^0$ or $\omega$ meson. The results are $\mathcal{B}(D^0\to {\pi }^{+}{\pi }^{-}{\mu }^{+}{\mu }^{-})=(9.64\pm 0.48\pm 0.51\pm 0.97)\times {10}^{-7}$ and $\mathcal{B}(D^0\to K^{+}{K}^{-}{\mu }^{+}{\mu }^{-})=(1.54\pm 0.27\pm 0.09\pm 0.16)\times {10}^{-7}$, where the uncertainties are statistical, systematic, and due to the limited knowledge of the normalization branching fraction. The dependence of the branching fraction on the dimuon mass is also investigated.

Asymmetries in the time-dependent rates of $D^0\to K^{+}{K}^{-}$ and $D^0\to {\pi }^{+}{\pi }^{-}$ decays are measured in a $pp$ collision data sample collected with the LHCb detector during LHC Run 1, corresponding to an integrated luminosity of $3{\mathrm{fb}}^{-1}$. The asymmetries in effective decay widths between $D^0$ and ${\overline{D}}^0$ decays, sensitive to indirect $CP$ violation, are measured to be $A_{\mathrm{\Gamma }}(K^{+}{K}^{-})=(-0.30\pm 0.32\pm 0.10)\times {10}^{-3}$ and $A_{\mathrm{\Gamma }}({\pi }^{+}{\pi }^{-})=(0.46\pm 0.58\pm 0.12)\times {10}^{-3}$, where the first uncertainty is statistical and the second systematic. These measurements show no evidence for $CP$ violation and improve on the precision of the previous best measurements by nearly a factor of two.

The first study is presented of $CP$ violation with an amplitude analysis of the Dalitz plot of $B^0\to D{K}^{+}{\pi }^{-}$ decays, with $D\to K^{+}{\pi }^{-}$, $K^{+}{K}^{-}$, and ${\pi }^{+}{\pi }^{-}$. The analysis is based on a data sample corresponding to $3.0{\mathrm{fb}}^{-1}$ of $pp$ collisions collected with the LHCb detector. No significant $CP$ violation effect is seen, and constraints are placed on the angle $\gamma$ of the unitarity triangle formed from elements of the Cabibbo-Kobayashi-Maskawa quark mixing matrix. Hadronic parameters associated with the $B^0\to D{K}^{*}(892{)}^0$ decay are determined for the first time. These measurements can be used to improve the sensitivity to $\gamma$ of existing and future studies of the $B^0\to D{K}^{*}(892{)}^0$ decay.

The $B_s^0{\pi }^{\pm }$ invariant mass distribution is investigated in order to search for possible exotic meson states. The analysis is based on a data sample recorded with the LHCb detector corresponding to $3{\mathrm{fb}}^{-1}$ of $pp$ collision data at $\sqrt{s}=7$ and 8 TeV. No significant excess is found, and upper limits are set on the production rate of the claimed $X(5568)$ state within the LHCb acceptance. Upper limits are also set as a function of the mass and width of a possible exotic meson decaying to the $B_s^0{\pi }^{\pm }$ final state. The same limits also apply to a possible exotic meson decaying through the chain $B_s^{*0}{\pi }^{\pm }$, $B_s^{*0}\to B_s^0\gamma$ where the photon is excluded from the reconstructed decays.

We report measurements of charm-mixing parameters based on the decay-time-dependent ratio of $D^0\to K^{+}{\pi }^{-}$ to $D^0\to K^{-}{\pi }^{+}$ rates. The analysis uses a data sample of proton-proton collisions corresponding to an integrated luminosity of $5.0{\mathrm{fb}}^{-1}$ recorded by the LHCb experiment from 2011 through 2016. Assuming charge-parity ($CP$) symmetry, the mixing parameters are determined to be $x^{\prime 2}=(3.9\pm 2.7)\times {10}^{-5}$, $y^{\prime }=(5.28\pm 0.52)\times {10}^{-3}$, and $R_D=(3.454\pm 0.031)\times {10}^{-3}$. Without this assumption, the measurement is performed separately for $D^0$ and ${\overline{D}}^0$ mesons, yielding a direct $CP$-violating asymmetry $A_D=(-0.1\pm 9.1)\times {10}^{-3}$, and magnitude of the ratio of mixing parameters $1.00<|q/p|<1.35$ at the 68.3% confidence level. All results include statistical and systematic uncertainties and improve significantly upon previous single-measurement determinations. No evidence for $CP$ violation in charm mixing is observed.

Searches are performed for both promptlike and long-lived dark photons, $A^{\prime }$, produced in proton-proton collisions at a center-of-mass energy of 13 TeV, using $A^{\prime }\to {\mu }^{+}{\mu }^{-}$ decays and a data sample corresponding to an integrated luminosity of $1.6{\mathrm{fb}}^{-1}$ collected with the LHCb detector. The promptlike $A^{\prime }$ search covers the mass range from near the dimuon threshold up to 70 GeV, while the long-lived $A^{\prime }$ search is restricted to the low-mass region $214<m(A^{\prime })<350\mathrm{MeV}$. No evidence for a signal is found, and 90% confidence level exclusion limits are placed on the $\gamma –A^{\prime }$ kinetic-mixing strength. The constraints placed on promptlike dark photons are the most stringent to date for the mass range $10.6<m(A^{\prime })<70\mathrm{GeV}$, and are comparable to the best existing limits for $m(A^{\prime })<0.5\mathrm{GeV}$. The search for long-lived dark photons is the first to achieve sensitivity using a displaced-vertex signature.

Results are reported from a search for the rare decays $B_s^0\to {\tau }^{\pm }{\mu }^{\mp }$ and $B^0\to {\tau }^{\pm }{\mu }^{\mp }$, where the $\tau$ lepton is reconstructed in the channel ${\tau }^{-}\to {\pi }^{-}{\pi }^{+}{\pi }^{-}{\nu }_{\tau }$. These processes are effectively forbidden in the standard model, but they can potentially occur at detectable rates in models of new physics that can induce lepton-flavor-violating decays. The search is based on a data sample corresponding to $3{\mathrm{fb}}^{-1}$ of proton-proton collisions recorded by the LHCb experiment in 2011 and 2012. The event yields observed in the signal regions for both processes are consistent with the expected standard model backgrounds. Because of the limited mass resolution arising from the undetected $\tau$ neutrino, the $B_s^0$ and $B^0$ signal regions are highly overlapping. Assuming no contribution from $B^0\to {\tau }^{\pm }{\mu }^{\mp }$, the upper limit $\mathcal{B}(B_s^0\to {\tau }^{\pm }{\mu }^{\mp })<4.2\times {10}^{-5}$ is obtained at 95% confidence level. If no contribution from $B_s^0\to {\tau }^{\pm }{\mu }^{\mp }$ is assumed, a limit of $\mathcal{B}(B^0\to {\tau }^{\pm }{\mu }^{\mp })<1.4\times {10}^{-5}$ is obtained at 95% confidence level. These results represent the first limit on $\mathcal{B}(B_s^0\to {\tau }^{\pm }{\mu }^{\mp })$ and the most stringent limit on $\mathcal{B}(B^0\to {\tau }^{\pm }{\mu }^{\mp })$.

A search for the lepton-flavor violating decays $B^{+}\to K^{+}{\mu }^{\pm }{e}^{\mp }$ is performed using a sample of proton-proton collision data, collected with the LHCb experiment at center-of-mass energies of 7 and 8 TeV and corresponding to an integrated luminosity of $3{\mathrm{fb}}^{-1}$. No significant signal is observed, and upper limits on the branching fractions are set as $\mathcal{B}(B^{+}\to K^{+}{\mu }^{-}{e}^{+})<7.0(9.5)\times {10}^{-9}$ and $\mathcal{B}(B^{+}\to K^{+}{\mu }^{+}{e}^{-})<6.4(8.8)\times {10}^{-9}$ at 90% (95)% confidence level. The results improve the current best limits on these decays by more than one order of magnitude.

The first measurement of the lifetime of the doubly charmed baryon ${\mathrm{\Xi }}_{cc}^{++}$ is presented, with the signal reconstructed in the final state ${\mathrm{\Lambda }}_c^{+}{K}^{-}{\pi }^{+}{\pi }^{+}$. The data sample used corresponds to an integrated luminosity of $1.7{\mathrm{fb}}^{-1}$, collected by the LHCb experiment in proton-proton collisions at a center-of-mass energy of 13 TeV. The ${\mathrm{\Xi }}_{cc}^{++}$ lifetime is measured to be $0.256_{-0.022}^{+0.024}(\mathrm{stat})\pm 0.014(\mathrm{syst})\mathrm{ps}$.

The first amplitude analysis of the $B^{\pm }\to {\pi }^{\pm }{K}^{+}{K}^{-}$ decay is reported based on a data sample corresponding to an integrated luminosity of $3.0{\mathrm{fb}}^{-1}$ of $pp$ collisions recorded in 2011 and 2012 with the LHCb detector. The data are found to be best described by a coherent sum of five resonant structures plus a nonresonant component and a contribution from $\pi \pi \leftrightarrow KK$ $S$-wave rescattering. The dominant contributions in the ${\pi }^{\pm }$ $K^{\mp }$ and $K^{+}$ $K^{-}$ systems are the nonresonant and the $B^{\pm }\to \rho (1450{)}^0{\pi }^{\pm }$ amplitudes, respectively, with fit fractions around 30%. For the rescattering contribution, a sizable fit fraction is observed. This component has the largest $CP$ asymmetry reported to date for a single amplitude of $(-66\pm 4\pm 2)\%$, where the first uncertainty is statistical and the second systematic. No significant $CP$ violation is observed in the other contributions.