Study of B meson decays with J/ψ　and φ in the final states

LIU, YANG; リュウ, ヤン; LIU, Yang

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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

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Item type

学位論文 / Thesis or Dissertation(1)

公開日

2010-02-22

タイトル

Study of B meson decays with J/ψ　and φ in the final states

タイトル

Study of B meson decays with J/ψ　and φ in the final states

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

フリガナ

リュウ, ヤン

著者

LIU, Yang

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

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

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 B meson decay to final states including J/ψ and
Φ mesons based on a large amount of data sample at the &upsih;(4S) state collected with
Belle detector in KEKB asymmetric energy e+e- collider.
　　The decay B0 → J /ψΦ 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 effect; 4) The ω - Φ mixing. The dominant contribution is from ω- Φ mixing and the
branching fraction for this decay is estimated to be (1.8 ± 0.3) × 10-7.
　　We perform a search for B0 → J /ψΦ decays using a data sample of 605 fb-1
containing 657 × 106 BBpairs.
　　We reconstruct B mesons from the decays J/ψ → l+l- (l = e,μ) and Φ →
K+ K-. Events are required to pass a basic hadronic event selection. We identify B
candidates using two widely used kinematic variable calculated in the center-of-mass
system:the beam-energy constrained mass (Mbc &equiv; <big>√</big>E2beam　―　P2B) and the energy
difference (△E &equiv; EB - Ebeam), where Ebeam is the beam energy, PB and EB are the
reconstructed momentum and energy of the B0 candidate. We select B candidates
within the range -0.2 GeV < △E < 0.3 GeV and 5.27 GeV / c2 ＜ Mbc < 5.29 GeV / c2
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 × 106generic BB decays (59 times that of real data) that includes
all known B →　J/ψX processes as well as sideband region.
　　The dominant background comes from BB events with B decays to J/ψ. We
find that the dominant backgrounds come B0 → J/ψK*0(892)[→K-π+] and B0- → J/ψK1(1270)[→ K-π+π0/-]. 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 △E ～0.1～ GeV, while the latter has a broad peak in the negative △E region. The remaining
background is due to random combinations of J/ψand Φ candidates and does not
have structure in the △E distribution (referred to as combinatorial background).
　　The signal yield is extracted by performing an unbinned extended maximum-
likelihood fit to the △E distribution of candidate events. The signal PDF is mod-
eled by a sum of two Gaussians. The background PDFs are two Gaussians for the
J/ψK1 component, a bifurcated Gaussian for the J/ψK*0 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+3.1-2.5 events with a statistical significance of 2.3σ.
As no significant signal is found for the B0 →　J /ψΦ 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:

　　　　　　　　　　　　　　β(B0 → J /ψΦ)< 9.4 × 10-7. 　　　　　 (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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Study of B meson decays with J/ψ　and φ in the final states

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× リュウ, ヤン

× LIU, Yang

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Study of B meson decays with J/ψ and φ in the final states

× LIU, YANG

× リュウ, ヤン

× LIU, Yang

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Cite as

エクスポート

Study of B meson decays with J/ψ　and φ in the final states