Physicists¹ Deliver The Most Precise Measurement Of The Helium Nucleus² Yet物理学家对氦核进行了迄今为止最精确的测量

Helium is a very important element, much more than just a way to make balloons float or increase the pitch of our voices. It is the second most abundant element in the universe and the lightest of the noble gases. Physicists have now announced a breakthrough in our understanding of this element: The most precise measurement of its nucleus yet.

氦是一个非常重要的元素，不仅仅是一种让气球浮起来或提高我们声音的方法。它是宇宙中第二丰富的元素，也是稀有气体中最轻的。物理学家们现在宣布我们对这种元素的理解有了突破:对其原子核的最精确的测量。

An international team of researchers has established that the radius³ of the helium nucleus is 1.67824 femtometers – or 1.67824×10-15 meters (5.506×10-15 feet). To give you a comparison, if the nucleus was the size of your thumbnail, your actual thumbnail would then be the size of the Earth’s orbit. This new measurement is 4.8 times more precise than previous estimates. The findings are reported in Nature.

一个国际研究团队已经确定氦原子核的半径为1.67824毫米，即1.67824×10-15米(5.506×10-15英尺)。给你一个比较，如果原子核是你的缩略图的大小，那么你实际的缩略图就是地球轨道的大小。新的测量方法比以前估计的精确4.8倍。研究结果发表在《自然》杂志上。

The helium atom, in its most abundant form, is made of a nucleus comprised of two protons and two neutrons⁴ surrounded by two electrons. The electrons have a negative electric charge, while the protons are positive. Neutrons have no electric charge but are key to keep the protons from repelling⁵ each other. Protons and neutrons are made of quarks, and quarks interact via the strong nuclear force.

最丰富的氦原子是由两个质子和两个中子组成的原子核组成的，原子核被两个电子包围着。电子带负电荷，而质子带正电荷。中子不带电荷，但它是阻止质子相互排斥的关键。质子和中子是由夸克组成的，夸克通过强核力相互作用。

Dr Alfredo Carpineti

This will tell you that the particles in the nucleus are not just staying still, and the nucleus hasn’t got a well-defined boundary. Its radius is estimated by working out the interaction between the nucleus and negatively charged particles.

这将告诉你，原子核中的粒子不仅仅是静止的，原子核也没有一个明确的边界。它的半径是通过计算原子核和带负电荷的粒子之间的相互作用来估计的。

In this latest experiment, researchers tweaked the helium by switching electrons with muons. Muons have the same electric charge as the electron but they are 200 times more massive. This difference allowed researchers to make more precise measurements.

在最新的实验中，研究人员通过交换电子和介子来调整氦。介子和电子的电荷是一样的，但是它们的质量是电子的200倍。这种差异使研究人员能够进行更精确的测量。

"We don't work with normal atoms, but with exotic atoms in which both electrons have been replaced by a single muon. So with muonic helium, we can draw conclusions about the structure of the atomic nucleus and measure its properties," senior author Aldo Antognini, from the Paul Scherrer Institute, said in a statement.

“我们研究的不是普通原子，而是两个电子都被一个μ子所取代的奇异原子。因此，有了介子氦，我们就可以得出有关原子核结构的结论，并测量其性质，”保罗·谢勒研究所的资深作者奥尔多·安托格尼尼在一份声明中说。

This same approach with muon was used a few years back to obtain a more precise measurement of the proton. This led to a bit of contradiction in the size of the proton. Researchers thought that this was just an experimental error in older measurements, but they were open to the idea that maybe it was a hint⁶ of more complex physics.

几年前，人们用同样的方法研究质子，以获得对质子的更精确的测量。这导致了质子大小的矛盾。研究人员认为这只是以前测量的一个实验误差，但他们也认为这可能是更复杂物理的一个暗示。

There is no disagreement in the measurement of the helium – the latest number is a clear and simple improvement on previous estimates. This strengthens the proton results, making it unlikely to be a product of unknown physics.

在氦的测量上没有分歧——最新的数字是对以前估计的一个明确而简单的改进。这增强了质子的结果，使得它不太可能是未知物理的产物。

"Our measurement can be used in different ways," says Julian Krauth, first author of the study. "The radius of the helium nucleus is an important touchstone for nuclear physics."“我们的测量方法可以用在不同的方面，”该研究的第一作者朱利安·克劳斯说。氦核的半径是核物理学的重要试金石。

This work is a perfect testbed for several physical theories, from theoretical models of nuclear structure to refining our understanding of the strong nuclear force in fundamental physics.

这项工作为多种物理理论提供了一个完美的实验平台，从核结构的理论模型到基础物理中增强我们对强核力的理解。