Importance of d-wave contributions in the charge symmetry breaking reaction d d ? 4 He p 0
Importance of d-wave contributions in the charge symmetry breaking reaction d d ? 4 He p 0
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d 波在电荷对称性破缺反应中的重要性 d d ?
DOI：
10.1016/j.physletb.2018.04.037
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发表时间：
2018
影响因子：
4.4
通讯作者：
Adlarson P
中科院分区：
文献类型：
--
作者：
Adlarson P
在基本粒子的标准模型中，由于夸克质量差和电磁效应，同位旋对称性被破坏[1-3]。在强子水平上，这反映在例如质子-中子质量差上。由于夸克质量效应，质子比中子轻，因此是稳定的。强子反应中的同位旋破坏（IV）的观察原则上允许人们研究夸克质量的影响。然而，IV的大多数实验特征都是由π质量差mπ0− mπ±决定的，这是一个非常好的纯电磁起源的近似。一个例外是电荷对称破缺（CSB）的观测值。电荷对称性是同位旋对称性的一个子群，它是在上下夸克互换的同位旋空间中，围绕第二个轴旋转180度的哈密顿量的不变性。电荷对称算符不交换带电和中性π介子态，π介子质量差不进入（见，例如，[4]）。基于与QCD有直接联系的理论方法，如格点QCD和手征微扰论（ChPT），因此有可能将夸克质量效应与强子观测量联系起来。虽然CSB观测值具有直接与夸克质量差异相关的优势，但它们的微小性构成了实验挑战。报道了在非常接近反应阈值的束流能量下[5]，通过np→ dπ0中的非零前后不对称性[6]，对反应dd→ 4 He π0首次精确测量CSB。这两个结果引发了一系列的理论研究。在ChPT中，后者测量的信号与质子-中子质量差的夸克质量诱导部分成正比，直至次领先阶[7，8]。这成为可能的适应ChPT的π介子生产反应在参考。[9]的文件。形式主义最近被推到了s波的次-次-领先顺序[10，11]。P波的贡献已在Ref. [12]第10段。最近的评论见Ref。[13]第10段。
Within the Standard Model of elementary particles isospin symmetry is violated via quark mass differences as well as electromagnetic effects [1–3]. On the hadronic level this is reflected, for example, by the proton–neutron mass difference. It is due to quark-mass effects that the proton is lighter than the neutron and, therefore, stable. The observation of isospin violation (IV) in hadronic reactions in principle allows one to study the effects of quark masses. However, most experimental signatures of IV are dominated by the pion mass difference mπ0− mπ±, which is to a very good approximation of purely electromagnetic origin. An exception are observables that are charge symmetry breaking (CSB). Charge symmetry, a subgroup of isospin symmetry, is the invariance of the Hamiltonian under rotation by 180◦ around the second axis in isospin space that interchanges up and down quarks. The charge symmetry operator does not interchange charged and neutral pion states, and the pion mass difference does not enter (see, eg,[4]). On the basis of theoretical approaches with a direct connection to QCD, like lattice QCD and chiral perturbation theory (ChPT), it is, therefore, possible to link quark-mass effects to hadronic observables. While CSB observables have the advantage of being directly related to quark-mass differences, their smallness poses an experimental challenge. First precision measurements of CSB were reported for the reaction dd→ 4Heπ0 at beam energies very close to the reaction threshold [5] and, at the same time, via a nonvanishing forward–backward asymmetry in np→ dπ0 [6]. Both results triggered a series of theoretical investigations. The signal of the latter measurement was shown to be proportional to the quark-mass-induced part of the proton–neutron mass difference up to next-to-leading order in ChPT [7, 8]. This became possible by the adaption of ChPT to pion production reactions in Ref.[9]. The formalism has recently been pushed to next-to-next-to-leading order for s-waves [10, 11]. The contribution of p-waves has been investigated in Ref.[12]. For a recent review see Ref.[13].