Measurement of the Lepton Forward-Backward Asymmetry in B rightarrow X_s ell^+ ell^- Decays with a Sum of Exclusive Modes

Y. Sato , A. Ishikawa , H. Yamamoto , A. Abdesselam , I. Adachi , K. Adamczyk , H. Aihara , D. M. Asner

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V. Aulchenko T. Aushev R. Ayad A. M. Bakich A. Bala V. Bhardwaj B. Bhuyan A. Bondar G. Bonvicini A. Bozek M. Bra\v T. E. Browder D. \v V. Chekelian A. Chen B. G. Cheon I.-S. Cho K. Cho V. Chobanova Y. Choi D. Cinabro J. Dalseno M. Danilov Z. Dole\v Z. Dr\'asal A. Drutskoy D. Dutta K. Dutta S. Eidelman H. Farhat J. E. Fast T. Ferber V. Gaur A. Garmash R. Gillard Y. M. Goh B. Golob J. Haba T. Hara K. Hayasaka H. Hayashii X. H. He Y. Hoshi W.-S. Hou H. J. Hyun T. Iijima R. Itoh Y. Iwasaki T. Iwashita I. Jaegle T. Julius J. H. Kang E. Kato Y. Kato H. Kawai T. Kawasaki H. Kichimi D. Y. Kim H. J. Kim J. B. Kim J. H. Kim M. J. Kim Y. J. Kim K. Kinoshita J. Klucar B. R. Ko P. Kody\v S. Korpar P. Kri\v P. Krokovny T. Kuhr T. Kumita A. Kuzmin Y.-J. Kwon S.-H. Lee Y. Li J. Libby C. Liu Y. Liu Z. Q. Liu D. Liventsev P. Lukin H. Miyata R. Mizuk G. B. Mohanty A. Moll R. Mussa M. Nakao Z. Natkaniec M. Nayak E. Nedelkovska N. K. Nisar S. Nishida O. Nitoh S. Ogawa P. Pakhlov H. Park H. K. Park T. K. Pedlar T. Peng R. Pestotnik M. Petri\v L. E. Piilonen E. Ribe\v M. Ritter M. R\"ohrken A. Rostomyan H. Sahoo T. Saito Y. Sakai S. Sandilya D. Santel L. Santelj T. Sanuki V. Savinov O. Schneider G. Schnell C. Schwanda A. J. Schwartz R. Seidl D. Semmler K. Senyo M. E. Sevior M. Shapkin C. P. Shen T.-A. Shibata J.-G. Shiu B. Shwartz A. Sibidanov F. Simon Y.-S. Sohn A. Sokolov E. Solovieva S. Stani\v M. Stari\v T. Sumiyoshi U. Tamponi G. Tatishvili Y. Teramoto K. Trabelsi M. Uchida S. Uehara T. Uglov Y. Unno S. Uno P. Urquijo Y. Ushiroda Y. Usov S. E. Vahsen C. Van Hulse P. Vanhoefer G. Varner K. E. Varvell V. Vorobyev C. H. Wang M.-Z. Wang P. Wang X. L. Wang Y. Watanabe E. Won J. Yamaoka Y. Yamashita S. Yashchenko Y. Yook Z. P. Zhang V. Zhilich V. Zhulanov A. Zupanc (The Belle Collaboration)

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classification ✦ hep-ex

keywords exclusiverightarrowsigmaasymmetryforward-backwardleptonmeasurementstandard

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We report the first measurement of the lepton forward-backward asymmetry ${\cal A}_{\rm FB}$ as a function of the squared four-momentum of the dilepton system, $q^2$, for the electroweak penguin process $B \rightarrow X_s \ell^+ \ell^-$ with a sum of exclusive final states, where $\ell$ is an electron or a muon and $X_s$ is a hadronic recoil system with an $s$ quark. The results are based on a data sample containing $772\times10^6$ $B\bar{B}$ pairs recorded at the $\Upsilon(4S)$ resonance with the Belle detector at the KEKB $e^+ e^-$ collider. ${\cal A}_{\rm FB}$ for the inclusive $B \rightarrow X_s \ell^+ \ell^-$ is extrapolated from the sum of 10 exclusive $X_s$ states whose invariant mass is less than 2 GeV/$c^2$. For $q^2 > 10.2$ GeV$^2$/$c^2$, ${\cal A}_{\rm FB} < 0$ is excluded at the 2.3$\sigma$ level, where $\sigma$ is the standard deviation. For $q^2 < 4.3$ GeV$^2$/$c^2$, the result is within 1.8$\sigma$ of the Standard Model theoretical expectation.

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Measurement of the Lepton Forward-Backward Asymmetry in B rightarrow X_s ell^+ ell^- Decays with a Sum of Exclusive Modes

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