Two-photon laser spectroscopy of antiprotonic helium and the antiproton-to-electron mass ratio
Two-photon laser spectroscopy of antiprotonic helium and the antiproton-to-electron mass ratio
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DOI：
10.1038/nature10260
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发表时间：
2011-07-28
期刊：
影响因子：
64.8
通讯作者：
Zurlo, Nicola
中科院分区：
文献类型：
--
作者：
Hori, Masaki;Soter, Anna;Zurlo, Nicola
物理定律被认为在电荷、宇称和时间反演的组合变换下是不变的（CPT对称性（1））。这意味着一个反物质粒子与它的粒子具有完全相同的质量和电荷的绝对值。亚稳反质子氦（（p）over bar He+）是一个三体原子（2），由一个正常的氦核、一个基态的电子和一个占据里德堡态的反质子（（p）over bar）组成，它们的主动量和角动量分别为n和l，使得n接近l + 1接近38。这些原子可以接受精确的激光光谱学的测量，其结果原则上可以用来确定反质子与电子的质量比，并限制反质子和质子的电荷和质量之间的相等性。本文报道了用两束反向传播的激光束照射反质子氦的双光子光谱，其中（p）对He-3（+）和（p）对He-4（+）同位素。这激发了反质子在深紫外波长（λ = 139.8，193.0和197.0 nm）的非线性双光子跃迁（n，l）->（n - 2，l - 2），这部分抵消了由原子热运动引起的激光共振的多普勒展宽。由此产生的窄谱线使我们能够测量三个跃迁频率，其分数精度为2.3-5/10（9）。通过将结果与三体量子电动力学计算进行比较，我们得出反质子与电子的质量比为1，836.1526736（23），其中括号误差代表一个标准差。这与已知的质子-电子值具有相似的精度。
Physical laws are believed to be invariant under the combined transformations of charge, parity and time reversal (CPT symmetry(1)). This implies that an antimatter particle has exactly the same mass and absolute value of charge as its particle counterpart. Metastable antiprotonic helium ((p) over bar He+) is a three-body atom(2) consisting of a normal helium nucleus, an electron in its ground state and an antiproton ((p) over bar) occupying a Rydberg state with high principal and angular momentum quantum numbers, respectively n and l, such that n approximate to l + 1 approximate to 38. These atoms are amenable to precision laser spectroscopy, the results of which can in principle be used to determine the antiproton-to-electron mass ratio and to constrain the equality between the antiproton and proton charges and masses. Here we report two-photon spectroscopy of antiprotonic helium, in which (p) over bar He-3(+) and (p) over bar He-4(+) isotopes are irradiated by two-counter-propagating laser beams. This excites nonlinear, two-photon transitions of the antiproton of the type (n, l) -> (n - 2, l - 2) at deep-ultraviolet wavelengths (lambda = 139.8, 193.0 and 197.0 nm), which partly cancel the Doppler broadening of the laser resonance caused by the thermal motion of the atoms. The resulting narrow spectral lines allowed us to measure three transition frequencies with fractional precisions of 2.3-5 parts in 10(9). By comparing the results with three-body quantum electrodynamics calculations, we derived an antiproton-to-electron mass ratio of 1,836.1526736(23), where the parenthetical error represents one standard deviation. This agrees with the proton-to-electron value known to a similar precision.