B+ 介子衰變至p Λ-bar K+ K−以及p-bar Λ K+ K+ 之分析

日本筑波KEK之B工廠(包括了KEKB 加速器以及BELLE 偵測器) 於1998 至2010 年間收集了772 百萬BB 介子對實驗數據，藉著準確的粒子分辨率以及粒子的四動量，我們使用了這些BB 介子對，量測了B+衰變至pΛK+K− 以及B+ 衰變至pΛK+K+ 四體衰變分支比及中間態衰變分支比。藉由分析各中間態的量測，我們能夠更清楚了解此衰變的結構。在此量測中，我們發現了四個新衰變態: genuine fourbody decay of B(B+ → pΛK+K−) = (4.10+0.45−0.43± 0.50)×10−6、genuine fourbody decay of B(B+ → pΛK+K+) = (3.70+0.39−0.37±0.44)×10−6、B(B+ → pΛϕ) = (7.95±2.09±0.77) × 10−7 and B(ηc → p¯ΛK− +c.c.) = (2.83+0.36−0.34± 0.35) × 10−3 )。這裡B指的是粒子的衰變分支比。根據我們對Λ−c 的了解，Λ−c 為udc 態，Λ−c 與Λ 皆為IJP = 0(1/2+)，以上量測與B(B0 → p¯Λ−c π+π−) > B(B+ → p¯Λ−c π+)的衰變分支比結構類似。新的魅粒子態也同時被發現，可根據此實驗結果對於魅粒子態有更進一步的了解。

關鍵字

B介子衰變；雙重子衰變；魅子中間態

並列摘要

From 1998 to 2010, the B factory (including KEKB accelerator and BELLE detector)at KEK collected 772 million BB pairs. With the precise identification and measurement of four-momentum of particles, we finished the studies: genuine four-body decay of B(B+ → pΛK+K−) = (4.10+0.45−0.43± 0.50)×10−6、genuine four-body-decay of B(B+ → pΛK+K+) = (3.70+0.39−0.37± 0.44)×10−6、B(B+ →pΛϕ) = (7.95 ± 2.09 ± 0.77) × 10−7 and B(ηc → p¯ΛK− +c.c.) = (2.83+0.36−0.34±0.35) × 10−3. Here B is the branching fraction of the particles. According to our understanding of Λ−c , Λ−c is udc state, Λ−c and Λ are IJP = 0(1/2+). The hierarchical structure seems to exist, e.g., B(B0 → p¯Λ−c π+π−) > B(B+ → p¯Λ−c π+). We also found a new charmonium decay mode, ηc → p¯ΛK− +c.c., which can be compared with the measured decay mode, J/ψ → p¯ΛK− +c.c., thus we could have a clearer understanding on charmonium system.