尋找中性K介子衰變至準純量sgoldstino粒子

Abstract

本論文尋找可能的中性K介子衰變至pi0介子以及輕準純量 sgoldstino(代稱X粒子)。所使用數據來自日本國家高能加速器 中心質子加速器的E391a 偵測器，於九十四年二月至三月間取 得。 經由事例重建，我們針對四組可能的質量範圍搜尋，並無發 現顯著訊號，因此給予90%信心水準之衰變分率上限，分別為 Br(KL->pi0X(181.7 MeV)) < 2.26e-6 Br(KL->pi0X(198.0 MeV)) < 1.97e-6 Br(KL->pi0X(214.3 MeV)) < 1.81e-6 Br(KL->pi0X(230.6 MeV)) < 1.17e-6

With mX = 214.3 MeV as hinted by a previous HyperCP experiment, we report the first search of the decay KL->pi0X using the Run2 data sample recorded with the E391a detector at KEK-PS. The particle X has a theoretical interpretation as the pseudoscalar sgoldstino. It is predicted to decay predominantly to two photons. As a result of this search, we set a 90% confidence-level upper limit for its branching ratio at B(KL->pi0X)<1.81e-6. We also performed a search for the same mode assuming different mX: 181.7MeV, 198MeV, 230.6MeV and set respective 90% confidence-level upper limits: B(KL->pi0X181.7)<2.26e-6, B(KL->pi0X198.0)<1.97e-6 and B(KL->pi0X230.6)<1.17e-6. The KL flux for the E391a Run2 data set is also measured to be (4.83+-0.21)e9 in the fiducial region.