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Register a new userStudy of B^0 -> rho^0 rho^0 decays, implications for the CKM angle phi_2 and search for other B^0 decay modes with a four-pion final state
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We present a study of the branching fraction of the decay B^0->rho0rho0 and the fraction of longitudinally polarized rho0 mesons in this decay. The results are obtained from the final data sample containing 772 million BBbar pairs collected at the Y(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider. We find 166 +- 59 B^0 -> rho0 rho0 events (including systematic uncertainties), corresponding to a branching fraction of B(B^0->rho0rho0) = (1.02 +- 0.30 (stat) +- 0.15 (syst)) x 10^{-6} with a significance of 3.4 standard deviations and a longitudinal polarization fraction fL = 0.21^{+0.18}_{-0.22} (stat) +- 0.15 (syst). We use the longitudinal polarization fraction to determine the Cabibbo-Kobayashi-Maskawa matrix angle phi_2 = (84.9 +- 13.5) degrees through an isospin analysis in the B->rhorho system. We furthermore find 149 +- 49 B^0->f0rho0 events, corresponding to B(B^0->f0rho0) x B(f0->pi+pi-) = (0.78 +- 0.22 (stat) +- 0.11 (syst)) x 10^{-6}, with a significance of 3.1 standard deviations. We find no other significant contribution with the same final state, and set upper limits at 90% confidence level on the (product) branching fractions, B(B^0->pi+pi-pi+pi-)<11.2 x 10^{-6}, B(B^0->rho0pi+pi-)<12.0 x 10^{-6}, B(B^0->f0pi+pi-) x B(f0->pi+pi-) <3.0 x 10^{-6} and B(B^0->f0f0) x B(f0->pi+pi-)^{2} < 0.2 x 10^{-6}.
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We present a measurement of the branching fraction and the longitudinal polarization fraction of $B^{0}rightarrowrho^+rho^-$ decays, as well as the time-dependent $CP$ violating parameters in decays into longitudinally polarized $rho^{+}rho^{-}$ pairs with Belles final data set of $772times 10^6$ $Bbar{B}$ pairs, at the $Upsilon(4S)$ resonance, collected at the asymmetric-energy $e^+ e^-$ collider KEKB. We obtain ${cal B}(B^0 rightarrow rho^+ rho^-)=(28.3pm 1.5;(rm stat) pm 1.5;(rm syst))times 10^{-6}$, $f_L = 0.988pm 0.012;(rm stat ) pm0.023;(rm syst)$, ${cal A}_{CP} = 0.00pm0.10;(rm stat ) pm0.06;(rm syst)$, ${cal S}_{CP} = -0.13pm0.15;(rm stat ) pm0.05;(rm syst).$ We perform an isospin analysis to constrain the CKM angle $phi_2$ and obtain two solutions with begin{eqnarray} phi_{2} = (93.7pm10.6)^{circ}, onumber end{eqnarray} being most compatible with other Standard-Model based fits to the data.
Proton-proton collision data recorded in 2011 and 2012 by the lhcb experiment, co-rres-pon-ding to an integrated luminosity of 3.0invfb, are a-na-lysed to search for the charmless ${B^0 to rho^0 rho^0}$ decay. More than 600 ${B^0 to (pi^+pi^-)(pi^+pi^-)}$ signal decays are selected and used to perform an amplitude analysis from which the ${B^0 to rho^0 rho^0}$ decay is observed for the first time with 7.1 standard deviations significance. The fraction of ${B^0 to rho^0 rho^0}$ decays yielding a longitudinally polarised final state is measured to be $fL = 0.745^{+0.048}_{-0.058} ({rm stat}) pm 0.034 ({rm syst})$. The ${B^0 to rho^0 rho^0}$ branching fraction, using the ${B^0 to phi K^*(892)^{0}}$ decay as reference, is also reported as ${BF(B^0 to rho^0 rho^0) = (0.94 pm 0.17 ({rm stat}) pm 0.09 ({rm syst}) pm 0.06 ({rm BF})) times 10^{-6}}$.
The first observation of the decay $bar{B}^0_s to D^0 K^{*0}$ using $pp$ data collected by the LHCb detector at a centre-of-mass energy of 7 TeV, corresponding to an integrated luminosity of 36 pb$^{-1}$, is reported. A signal of $34.4 pm 6.8$ events is obtained and the absence of signal is rejected with a statistical significance of more than nine standard deviations. The $bar{B}^0_s to D^0 K^{*0}$ branching fraction is measured relative to that of $bar{B}^0 to D^0 rho^0$: $frac{{cal B}(bar{B}^0_s to D^0 K^{*0})}{{cal B}(bar{B}^0 to D^0 rho^0)} = 1.48 pm 0.34 pm 0.15 pm 0.12$, where the first uncertainty is statistical, the second systematic and the third is due to the uncertainty on the ratio of the $B^0$ and $B^0_s$ hadronisation fractions.
An amplitude analysis of ${B^0to (pi^+pi^-) (K^+pi^-)}$ decays is performed in the two-body invariant mass regions ${300 < m(pi^+pi^-)<1100}$ MeV/$c^2$, accounting for the $rho^0$, $omega$, $f_0(500)$, $f_0(980)$ and $f_0(1370)$ resonances, and ${750 < m(K^+pi^-)<1200}$ MeV/$c^2$, which is dominated by the $K^{*}(892)^0$ meson. The analysis uses 3 fb$^{-1}$ of proton-proton collision data collected by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. The $CP$ averages and asymmetries are measured for the magnitudes and phase differences of the contributing amplitudes. The $CP$-averaged longitudinal polarisation fractions of the vector-vector modes are found to be $tilde{f}^0_{rho K^{*}} = 0.164 pm 0.015 pm 0.022$ and $tilde{f}^0_{omega K^{*}} = 0.68 pm 0.17 pm 0.16$, and their $CP$ asymmetries, $mathcal{A}^0_{rho K^{*}} = -0.62 pm 0.09 pm 0.09$ and $mathcal{A}^0_{omega K^{*}} = -0.13 pm 0.27 pm 0.13$, where the first uncertainty is statistical and the second systematic.
A search for previously unobserved decays of beauty baryons to the final states $K^0_{mathrm{S}}ppi^-$ and $K^0_{mathrm{S}}pK^-$ is reported. The analysis is based on a data sample corresponding to an integrated luminosity of $1.0,mathrm{fb}^{-1}$ of $pp$ collisions. The $Lambda^0_b rightarrow K^0_{mathrm{S}}ppi^-$ decay is observed for the first time with a significance of $8.6,sigma$, and a measurement is made of the $CP$ asymmetry, which is consistent with zero. No significant signals are seen for $Lambda^0_b rightarrow K^0_{mathrm{S}}pK^-$ decays, $Xi^0_b$ decays to both $K^0_{mathrm{S}}ppi^-$ and $K^0_{mathrm{S}}pK^-$ final states, and the $Lambda^0_b rightarrow D^-_s (K^0_{mathrm{S}}K^-)p$ decay, and upper limits on their branching fractions are reported.
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