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Study of B meson decays with J/ψ and φ in the final states
https://ir.soken.ac.jp/records/711
https://ir.soken.ac.jp/records/7118de8acac-f38b-4553-9d61-e431bc9cc314
名前 / ファイル | ライセンス | アクション |
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Item type | 学位論文 / Thesis or Dissertation(1) | |||||
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公開日 | 2010-02-22 | |||||
タイトル | ||||||
タイトル | Study of B meson decays with J/ψ and φ in the final states | |||||
タイトル | ||||||
タイトル | Study of B meson decays with J/ψ and φ in the final states | |||||
言語 | en | |||||
言語 | ||||||
言語 | eng | |||||
資源タイプ | ||||||
資源タイプ識別子 | http://purl.org/coar/resource_type/c_46ec | |||||
資源タイプ | thesis | |||||
著者名 |
LIU, YANG
× LIU, YANG |
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フリガナ |
リュウ, ヤン
× リュウ, ヤン |
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著者 |
LIU, Yang
× LIU, Yang |
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学位授与機関 | ||||||
学位授与機関名 | 総合研究大学院大学 | |||||
学位名 | ||||||
学位名 | 博士(理学) | |||||
学位記番号 | ||||||
内容記述タイプ | Other | |||||
内容記述 | 総研大甲第1196号 | |||||
研究科 | ||||||
値 | 高エネルギー加速器科学研究科 | |||||
専攻 | ||||||
値 | 14 素粒子原子核専攻 | |||||
学位授与年月日 | ||||||
学位授与年月日 | 2008-09-30 | |||||
学位授与年度 | ||||||
値 | 2008 | |||||
要旨 | ||||||
内容記述タイプ | Other | |||||
内容記述 | We study the decay modes of <i>B</i> meson decay to final states including <i>J/ψ</i> and <i>Φ</i> mesons based on a large amount of data sample at the ϒ(4S) state collected with Belle detector in KEKB asymmetric energy <i>e</i><sup>+</sup><i>e</i><sup>-</sup> collider. The decay <i>B</i><sup>0</sup> → <i>J /ψΦ</i></sup> is expected to involve W-exchange and final state interac- tion (FSI) processes. The mechanisms contributing to this decay can be divided into four categories: 1) The photo-production; 2) The tri-gluon fusion; 3) The rescattering<br />effect; 4) The <i>ω - Φ</i> mixing. The dominant contribution is from <i>ω- Φ</i> mixing and the branching fraction for this decay is estimated to be (1.8 ± 0.3) × 10<sup>-7</sup>. We perform a search for <i>B</i><sup>0</sup> → <i>J /ψΦ</i> decays using a data sample of 605 fb<sup>-1</sup> containing 657 × 10<sup>6</sup> <i>BB</i></span>pairs. We reconstruct <i>B</i> mesons from the decays <i>J/ψ</i> → <i>l<sup>+</sup>l<sup>-</sup> (l = e,μ)</i> and <i>Φ</i> → <i>K<sup>+</sup> K<sup>-</sup></i>. Events are required to pass a basic hadronic event selection. We identify <i>B</i> candidates using two widely used kinematic variable calculated in the center-of-mass system:the beam-energy constrained mass (<i>M</i><small>bc</small> ≡ <big>√</big>E<sup>2</sup><small>beam</small> ― P<sup>2</sup><small>B</small>) and the energy difference (△<i>E</i> ≡ <i>E<small>B</i></small> - <i>E</i><small>beam</small>), where <i>E</i><small>beam</small> is the beam energy, <i>P<small>B</i></small> and <i>E<small>B</small></i> are the reconstructed momentum and energy of the B<sup>0</sup> candidate. We select <i>B</i> candidates within the range -0.2 GeV < △<i>E</i> < 0.3 GeV and 5.27 GeV / <i>c</i><sup>2</sup> < <i>M</i><small>bc</small> < 5.29 GeV / <i>c</i><sup>2</sup> for final analysis. We study reconstruction efficiency and event selection criteria using a large signal Monte Calor (MC) sample. To study the background, we use a MC sample corre- sponding to 3.86 × 10<sup>6</sup>generic <i>BB</i> decays (59 times that of real data) that includes all known <i>B</i> → <i>J/ψX</i> processes as well as sideband region. The dominant background comes from <i>BB</i> events with <i>B</i> decays to <i>J/ψ</i>. We find that the dominant backgrounds come B<sup>0</sup> → <i>J/ψK</i>*<sup>0</sup>(892)[→<i>K</i><sup>-</sup>π<sup>+</sup>] and<br />B<sup>0-</sup> → <i>J/ψK</i><small>1</small>(1270)[→ <i>K</i><sup>-</sup>π<sup>+</sup>π<sup>0/-</sup>]. In both cases, a pion is misidentified as a kaon, and in the latter case, the other pion is missed. The former has a peak at △<i>E</i> ~0.1~<br />GeV, while the latter has a broad peak in the negative △<i>E</i> region. The remaining background is due to random combinations of <i>J/ψ</i>and <i>Φ</i> candidates and does not have structure in the △<i>E</i> distribution (referred to as combinatorial background). The signal yield is extracted by performing an unbinned extended maximum- likelihood fit to the △<i>E</i> distribution of candidate events. The signal PDF is mod- eled by a sum of two Gaussians. The background PDFs are two Gaussians for the <i>J/ψK</i><small>1</small> component, a bifurcated Gaussian for the <i>J/ψK</i><sup>*0</sup> component and a second- order polynomial for combinatorial background, respectively. The parameters of these PDFs are determined from MC simulations. We obtain a signal yield of 4.6<sup>+3.1</sup><small>-2.5</small> events with a statistical significance of 2.3σ. As no significant signal is found for the <i>B</i><sup>0</sup> → <i>J /ψΦ</i> decay mode, we an upper limit on the yield at the 90% confidence level by a frequentist method using ensembles of pseudo-experiments. Finally an upper limit at the 90% confidence level is obtained: <i>β</i>(<i>B</i><sup>0</sup> → <i>J /ψΦ</i>)< 9.4 × 10<sup>-7</sup>. (1) This result improves upon the previous result by about a factor of 10 and is consistent with the theory prediction. The result shows that a large enhancement from rescattering is not likely in this decay mode. To check the prediction more precisely, a larger data sample is needed. |
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値 | 有 |