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Register a new userMeasurement of the CP-violating phase $phi_s$ in $overline{B}^0_srightarrow J/psi pi^+pi^-$ decays
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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 centre-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.
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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 are 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.
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 state 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.
A flavour-tagged decay-time-dependent amplitude analysis of $B_s^0to(K^+pi^-)(K^-pi^+)$ decays is presented in the $K^{pm}pi^{mp}$ mass range from 750 to 1600 MeV$/c^2$. The analysis uses $pp$ collision data collected with the LHCb detector at centre-of-mass energies of $7$ and $8$ TeV, corresponding to an integrated luminosity of $3.0$ fb$^{-1}$. Several quasi-two-body decay modes are considered, corresponding to $K^{pm}pi^{mp}$ combinations with spin 0, 1 and 2, which are dominated by the $K_0^*(800)^0$ and $K_0^*(1430)^0$, the $K^*(892)^0$ and the $K_2^*(1430)^0$ resonances, respectively. The longitudinal polarisation fraction for the $B_s^0to K^*(892)^0overline{K}^*(892)^0$ decay is measured as $f_L=0.208 pm 0.032 pm 0.046$, where the first uncertainty is statistical and the second is systematic. The first measurement of the mixing-induced $CP$-violating phase, $phi_s^{doverline{d}}$, in $bto doverline{d}s$ transitions is performed, yielding a value of $phi_s^{doverline{d}}=-0.10$ $pm$ $0.13$ (stat) $pm$ $0.14$ (syst) rad.
Measurement of the mixing-induced CP-violating phase phi_s in Bs decays is of prime importance in probing new physics. Here 7421 +/- 105 signal events from the dominantly CP-odd final state J/psi pi+ pi- are selected in 1/fb of pp collision data collected at sqrt{s} = 7 TeV with the LHCb detector. A time-dependent fit to the data yields a value of phi_s=-0.019^{+0.173+0.004}_{-0.174-0.003} rad, consistent with the Standard Model expectation. No evidence of direct CP violation is found.
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