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Register a new userStudy of $mathbf{B^{0}rightarrowrho^{+}rho^{-}}$ decays and implications for the CKM angle $mathbf{phi_2}$
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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.
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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}.
CP-violating asymmetries in $B to pi pi$ and $B to rho rho$ decays can help specify the weak phase $phi_2 = alpha$ of the Cabibbo-Kobayashi-% Maskawa (CKM) matrix. We discuss the impact of improved measurements of these processes such as will be available in the near future, finding special value in better measurement of the time-dependent CP violation parameter $S_{00}$ in $B^0 to pi^0 pi^0$ and $B^0 to rho^0 rho^0$. Reducing the errors on $B to rho rho$ measurements by a factor of two can potentially lead to an error in $phi_2 = alpha$ just above $2^circ$, at which level isospin-breaking corrections must be considered.
A sensitivity study for the measurement of the CKM angle $gamma$ from $B^0_srightarrow tilde{D}^{(*)0}phi$ decays is performed using $D$ meson reconstructed in the quasi flavour-specific modes $Kpi$, $K3pi$, $Kpipi^0$, and CP-eigenstate modes $KK$ and $pipi$, where the notation $tilde{D}^0$ corresponds to a $D^0$ or a ${tilde{D}^0}$ meson. The LHCb experiment is taken as a use case. A statistical uncertainty of about $8-19^{circ}$ can be achieved with the $pp$ collision data collected by the LHCb experiment from year 2011 to 2018. The sensitivity to $gamma$ should be of the order $3-8^{circ}$ after accumulating 23invfb of $pp$ collision data by 2025, while it is expected to further improve with 300~fb$^{-1}$ by the second half of the 2030 decade. The accuracy depends on the strong parameters $r^{(*)}_{B}$ and ${delta^{(*)}_{B}}$, describing, together with $gamma$, the interference between the leading amplitudes of the $B^0_srightarrow tilde{D}^{(*)0}phi$ decays.
The $beta$ decay of the odd-odd nucleus $^{70}$Br has been investigated with the BigRIPS and EURICA setups at the Radioactive Ion Beam Factory (RIBF) of the RIKEN Nishina Center. The $T=0$ ($J^{pi}=9^+$) and $T=1$ ($J^{pi}=0^+$) isomers have both been produced in in-flight fragmentation of $^{78}$Kr with ratios of 41.6(8)% and 58.4(8)%, respectively. A half-life of $t_{1/2}=2157^{+53}_{-49}$ ms has been measured for the $J^{pi}=9^+$ isomer from $gamma$-ray time decay analysis. Based on this result, we provide a new value of the half-life for the $J^{pi}=0^+$ ground state of $^{70}$Br, $t_{1/2}=78.42pm0.51$ ms, which is slightly more precise, and in excellent agreement, with the best measurement reported hitherto in the literature. For this decay, we provide the first estimate of the total branching fraction decaying through the $2^+_1$ state in the daughter nucleus $^{70}$Se, $R(2^+_1)=1.3pm1.1%$. We also report four new low-intensity $gamma$-ray transitions at 661, 1103, 1561, and 1749 keV following the $beta$ decay of the $J^{pi}=9^+$ isomer. Based on their coincidence relationships, we tentatively propose two new excited states at 3945 and 4752 keV in $^{70}$Se with most probable spins and parities of $J^{pi}=(6^+)$ and $(8^+)$, respectively. The observed structure is interpreted with the help of shell-model calculations, which predict a complex interplay between oblate and prolate configurations at low excitation energies.
The Belle experiment, running at the KEKB e^+ e^- asymmetric energy collider during the first decade of the century, has recorded 770 fb^-1 of data at the Upsilon(4S) resonance. A combination of recent Belle results obtained with this sample is used to perform a measurement of the CKM angle gamma. We use B^+- -> DK^+- and B^+- -> D^*K^+- decays where the D meson decays into K_S^0pi+pi-, Kpi, KK, pipi, K_S^0 pi^0 and K_S^0 eta final states and D^* decays into Dpi^0 and Dgamma. Belle obtains the most precise gamma measurement to date, gamma = (68^{+15}_{-14}) degree.
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