Observations of exotic structures in the $J/psi p$ channel, that we refer to as pentaquark-charmonium states, in $Lambda_b^0to J/psi K^- p$ decays are presented. The data sample corresponds to an integrated luminosity of 3/fb acquired with the LHCb d
etector from 7 and 8 TeV pp collisions. An amplitude analysis is performed on the three-body final-state that reproduces the two-body mass and angular distributions. To obtain a satisfactory fit of the structures seen in the $J/psi p$ mass spectrum, it is necessary to include two Breit-Wigner amplitudes that each describe a resonant state. The significance of each of these resonances is more than 9 standard deviations. One has a mass of $4380pm 8pm 29$ MeV and a width of $205pm 18pm 86$ MeV, while the second is narrower, with a mass of $4449.8pm 1.7pm 2.5$ MeV and a width of $39pm 5pm 19$ MeV. The preferred $J^P$ assignments are of opposite parity, with one state having spin 3/2 and the other 5/2.
Time-dependent CP violation is measured in the $B^0rightarrow J/psipi^+pi^-$ channel for each $pi^+pi^-$ resonant final state using data collected with an integrated luminosity of 3.0 fb$^{-1}$ in $pp$ collisions using the LHCb detector. The final st
ate with the largest rate, $J/psirho^0(770)$, is used to measure the CP-violating angle $2beta^{rm eff}$ to be $(41.7pm 9.6_{-6.3}^{+2.8})^{circ}$. This result can be used to limit the size of penguin amplitude contributions to CP violation measurements in, for example, $B_s^0rightarrow J/psiphi$ decays. Assuming approximate SU(3) flavour symmetry and neglecting higher order diagrams, the shift in the CP-violating phase $phi_s$ is limited to be within the interval [$-1.05^circ$, +$1.18^circ$] at 95% confidence level. Changes to the limit due to SU(3) symmetry breaking effects are also discussed.
We present a measurement of the ratio of the Bs meson lifetime, in the flavor-specific decay to $D_s^+pi^-$, to that of the B0 meson. The pp collision data used correspond to an integrated luminosity of 1/fb, collected with the LHCb detector, at a ce
nter-of-mass energy of 7 TeV. Combining our measured value of 1.010 +/- 0.010 +/- 0.008 for this ratio with the known lifetime, we determine the flavor-specific Bs lifetime to be tau(Bs) = 1.535 +/- 0.015 +/- 0.014 ps, where the uncertainties are statistical and systematic, respectively. This is the most precise measurement to date, and is consistent with previous measurements and theoretical predictions.
The mixing-induced CP-violating phase $phi_s$ in ${B}^0_s$ and $overline{B}^0_s$ decays is measured using the $J/psi pi^+pi^-$ final state in data, taken from 3,fb$^{-1}$ of integrated luminosity, collected with the LHCb detector in 7 and 8 TeV centr
e-of-mass $pp$ collisions at the LHC. A time-dependent flavour-tagged amplitude analysis, allowing for direct CP violation, yields a value for the phase $phi_s=70pm 68pm 8$,mrad. This result is consistent with the Standard Model expectation and previous measurements.
The resonant structure of the reaction $overline{B}^0rightarrow J/psi pi^+pi^-$ is studied using data from 3 fb$^{-1}$ of integrated luminosity collected by the LHCb experiment, one-third at 7 Tev center-of-mass energy and the remainder at 8 Tev. The
invariant mass of the $pi^+pi^-$ pair and three decay angular distributions are used to determine the fractions of the resonant and non-resonant components. Six interfering $pi^+pi^-$ states: $rho(770)$, $f_0(500)$, $f_2(1270)$, $rho(1450)$, $omega(782)$ and $rho(1700)$ are required to give a good description of invariant mass spectra and decay angular distributions. The positive and negative CP fractions of each of the resonant final states are determined. The $f_0(980)$ meson is not seen and the upper limit on its presence, compared with the observed $f_0(500)$ rate, is inconsistent with a model of tetraquark substructure for these scalar mesons at the eight standard deviation level. In the $qoverline{q}$ model, the absolute value of the mixing angle between the $f_0(980)$ and the $f_0(500)$ scalar mesons is limited to be less than $17^{circ}$ at 90% confidence level.
The resonant structure of the decay $overline{B}_s^0to J/psipi^+pi^-$ is studied using data corresponding to 3 fb$^{-1}$ of integrated luminosity from $pp$ collisions by the LHC and collected by the LHCb detector. Five interfering $pi^+pi^-$ states a
re required to describe the decay: $f_0(980),f_0(1500),f_0(1790),f_2(1270)$, and $f_2^{prime}(1525)$. An alternative model including these states and a non-resonant $J/psi pi^+pi^-$ component also provides a good description of the data. Based on the different transversity components measured for the spin-2 intermediate states, the final state is found to be compatible with being entirely $CP$-odd. The $CP$-even part is found to be $<2.3$% at 95% confidence level. The $f_0(500)$ state is not observed, allowing a limit to be set on the absolute value of the mixing angle with the $f_0(980)$ of $<7.7^{circ}$ at 90% confidence level, consistent with a tetraquark interpretation of the $f_0(980)$ substructure.
The LHCb measurement of the lifetime ratio of the $Lambda^0_b$ to the $overline{B}^0$ meson is updated using data corresponding to an integrated luminosity of 3.0 fb$^{-1}$ collected using 7 and 8 TeV centre-of-mass energy $pp$ collisions at the LHC.
The decay modes used are $overline{B}^0to J/psi p K^-$ and $overline{B}^0to J/psi pi^+ K^-$, where the $pi^+K^-$ mass is consistent with that of the $overline{K}^{*0}(892)$ meson. The lifetime ratio is determined with unprecedented precision to be $0.974pm0.006pm0.004$, where the first uncertainty is statistical and the second systematic. This result is in agreement with original theoretical predictions based on the heavy quark expansion. Using the current world average of the $overline{B}^0$ lifetime, the $Lambda^0_b$ lifetime is found to be $1.479 pm 0.009 pm 0.010$ ps.
A search for heavy Majorana neutrinos produced in the $B^- to pi^+mu^-mu^-$ decay mode is performed using 3 fb$^{-1}$ of integrated luminosity collected with the LHCb detector in $pp$ collisions at center-of-mass energies of 7 TeV and 8 TeV at the LH
C. Neutrinos with masses in the range 250-5000 MeV and lifetimes from zero to 1000 ps are probed. In the absence of a signal, upper limits are set on the branching fraction ${cal{B}}(B^- to pi^+mu^-mu^-)$ as functions of neutrino mass and lifetime. These limits are on the order of $10^{-9}$ for short neutrino lifetimes of 1 ps or less. Limits are also set on the coupling between the muon and a possible fourth-generation neutrino.
Decays of Bs and B0 mesons into J/psi pi +pi -pi +pi - final states, produced in pp collisions at the LHC, are investigated using data corresponding to an integrated luminosity of 3/fb collected with the LHCb detector. B^0_(s) -> Jpsi f_1(1285) decay
s are seen for the first time, and the branching fractions are measured. Using these rates, the f_1(1285) mixing angle between strange and non-strange components of its wave function in the q-qbar structure model is determined to be pm (24.0^{+3.1+0.6}_{-2.6-0.8}) degrees. Implications on the possible tetraquark nature of the f_1(1285) are discussed.
The first observation of the B0->J/psi K+K- decay is presented with a data sample corresponding to an integrated luminosity of 1.0/fb of pp collisions at a center-of-mass energy of 7 TeV collected with the LHCb detector. The branching fraction is mea
sured to be B(B0->J/psi K+K-) = (2.53 +/- 0.31 +/- 0.19)x10^{-6}, where the first uncertainty is statistical and the second is systematic. An amplitude analysis of the final state in the B0->J/psi K+K- decay is performed to separate resonant and nonresonant contributions in the K+K- spectrum. Evidence of the a0(980) resonance is reported with statistical significance of 3.9 standard deviations. The corresponding product branching fraction is measured to be B(B0->J/psi a0(980), a0(980)->K+K-)=(4.70 +/- 3.31 +/- 0.72)x10^{-7}, yielding an upper limit of B(B0->J/psi a0(980), a0(980)->K+K-)<9.0x10^{-7} at 90% confidence level. No evidence of the resonant decay B0->J/psiphi; is found, and an upper limit on its branching fraction is set to be B(B0->J/psiphi)< 1.9x10^{-7} at 90% confidence level.
