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Study of B^0 -> rho^0 rho^0 decays, implications for the CKM angle phi_2 and search for other four pion final states

I. Adachi, K. Adamczyk, H. Aihara, K. Arinstein, Yuji Arita, David M. Asner, T. Aso, V. Aulchenko, T. Aushev, T. Aziz, A. M. Bakich, Y. Ban, E. L. Barberio, M. Barrett, A. Bay, I. Bedny, M. Belhorn, K. Belous, V. Bhardwaj, B. Bhuyan, M. Bischofberger, S. Blyth, A. Bondar, G. Bonvicini, Andrzej Bozek, J. Brodzicka, O. Brovchenko, Thomas E. Browder, M. C. Chang, P. Chang, Y. Chao, Vladimir Chekelian, A. Chen, K. F. Chen, Pisin Chen, B. G. Cheon, K. Chilikin, R. Chistov, I. S. Cho, K. Cho, Ki-Seok Choi, S.-K. Choi, Y. Choi, J. Crnkovic, Jeremy Peter Dalseno, M. Danilov, J. Dingfelder, Zbyněk Drásal, A. Drutskoy, W. Dungel, D. Dutta, S. Eidelman, Denis A. Epifanov, S. Esen, J. E. Fast, M. Feindt, Ariane Frey, M. Fujikawa, V. Gaur, N. Gabyshev, A. Yu. Garmash, Y. M. Goh, B. Golob, M. Große Perdekamp, Hao Guo, J. Haba, P. Hamer, Y. L. Han, Koji Hara, T. Hara, Yuji Hasegawa, K. Hayasaka, Hisaki Hayashii, D. M. Heffernan, T. Higuchi, Y. Horii, Y. Hoshi, K. Hoshina, W.-S. Hou, Yee Bob Hsiung, H. J. Hyun, Y. Igarashi, Toru Iijima, Miki Imamura, K. Inami, A. Ishikawa, R. Itoh, M. Iwabuchi, M. Iwasaki, Y. Iwasaki, T. Iwashita, S. Iwata, I. Jaeglé, M. Jones, T. Julius, D. H. Kah, H. Kakuno, J. H. Kang

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Abstract

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-) rho0pi+pi-) f0pi+pi-) x B(f0->pi+pi-) f0f0) x B(f0->pi+pi-)^{2} < 0.2 x 10^{-6}.

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What this paper is about

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-) rho0pi+pi-) f0pi+pi-) x B(f0->pi+pi-) f0f0) x B(f0->pi+pi-)^{2} < 0.2 x 10^{-6}.

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Available abstract

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-) rho0pi+pi-) f0pi+pi-) x B(f0->pi+pi-) f0f0) x B(f0->pi+pi-)^{2} < 0.2 x 10^{-6}.

Key concepts: KEKB, Physics, Branching fraction, Electron–positron annihilation, Particle physics, Cabibbo–Kobayashi–Maskawa matrix, Pion, Nuclear physics

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