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arXiv 1202.4906hep-phhep-ex
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极小超对称标准模型中的Gamma(K -> e nu)/Gamma(K -> mu nu)

Gamma(K -> e nu)/Gamma(K -> mu nu) in the Minimal Supersymmetric Standard Model

Jennifer Girrbach, Ulrich Nierste

摘要:

在CERN的NA 62实验中研究的量R_K = Gamma(K -> e nu)/Gamma(K -> mu nu)被认为是探测最小超对称标准模型(MSSM)的轻子味破坏(LFV)参数。非零参数delta_{RR} ^{13}可以打开衰减通道K -> e nu_tau并将R_K增强到其标准模型值之上。在NA 62探测的参数空间的区域中,来自双态循环图的贡献在数值上占主导地位,左手态和右手态之间的混合是重要的。对于大的Stau混合角θ_tau值,通常采用的质量插入近似是不准确的。因此,我们用最轻的Stau本征态的质量、混合角θ_tau和其他相关的MSSM参数(如tan(beta)和带电希格斯玻色子质量M_H)来表示对R_K的超对称贡献,并绘制出受R_K约束的参数区域。我们进一步研究了当K -> eNu_e时,MSSM贡献对SM振幅的破坏性干扰能使R_K耗尽到什么程度。这种轻子味守恒(LFC)机制涉及参数组合|delta_{LL} ^{13} delta_{RR} ^{13}| LFC对R_K的影响是有限的,如果R_K的NA 62测量值显著低于标准模型的期望值,则表明物理超出了MSSM。

英文摘要:

The quantity R_K = Gamma(K -> e nu)/Gamma(K -> mu nu) studied by the experiment NA62 at CERN is known to probe lepton-flavour violating (LFV) parameters of the Minimal Supersymmetric Standard Model (MSSM). A non-zero parameter delta_{RR}^{13} can open the decay channel K -> e nu_tau and enhance R_K over its Standard-Model value. In the region of the parameter space probed by NA62 the contribution from a bino-stau loop diagram is numerically dominant and the mixing between left-handed and right-handed staus is important. For large values of the stau mixing angle theta_tau the commonly adopted mass insertion approximation is not accurate. We therefore express the supersymmetric contribution to R_K in terms of the mass of the lightest stau eigenstate, the mixing angle theta_tau, and other relevant MSSM parameter such as tan(beta) and the charged-Higgs boson mass M_H and plot the parameter regions constrained by R_K. We further study to which extent R_K can be depleted through MSSM contributions interfering destructively with the SM amplitude for K -> e nu_e. This lepton-flavour conserving (LFC) mechanism involves the parameter combination |delta_{LL}^{13} delta_{RR}^{13}|, which can be constrained with a naturalness consideration for the electron mass or with the measurement of the anomalous magnetic moment of the electron. The LFC effect on R_K is marginal, an NA62 measurement of R_K significantly below the Standard Model expectation would indicate physics beyond the MSSM.

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