Muon capture at PSI

详细信息    查看全文

• 作者：Peter Winter^a
• 关键词：pseudoscalar nucleon form factor ; time projection chamber ; muon capture
• 刊名：Physics Procedia
• 出版年：2011
• 出版时间：2011
• 年：2011
• 卷：17
• 期：Complete
• 页码：239-244
• 全文大小：796 K

文摘

Measuring the rate of muon capture in hydrogen provides one of the most direct ways to study the axial current of the nucleon. The MuCap experiment uses a negative muon beam stopped in a time projection chamber operated with ultra-pure hydrogen gas. Surrounded by a decay electron detector, the lifetime of muons in hydrogen can be measured to determine the singlet capture rate Λ_S to a final precision of 1 % . The capture rate determines the nucleon's pseudoscalar form factor gP. A first result, gP = 7.3 ± 1.1, has been published [1] and the final analysis of the full statistics will reduce the error by a factor of up to 3. Muon capture on the deuteron probes the weak axial current in the two-nucleon system. Within the framework of effective field theories the calculation of such two-nucleon processes involving the axial current requires the knowledge of one additional low energy constant which can be extracted from the doublet capture rate Λ_d. The same constant then allows to model-independently calculate related processes such as solar pp-fusion or _d scattering. The MuSun experiment will deduce Λ_S to better than 1.5 % . The experiment uses the MuCap detection setup with a new time projection chamber operated with deuterium at 30K and several hardware upgrades. The system is currently fully commissioned and the main physics data taking will start in 2011.