每天一篇经济学人 | Particle physics 粒子物理（2022...

The standard model of particle physics—completed in 1973—is the jewel in the crown of modern physics. It predicts the properties of elementary particles and forces with mind boggling accuracy. Take the magnetic moment of the electron, for example, a measure of how strongly a particle wobbles in a magnetic field. The Standard Model gives the correct answer to 14 decimal places, the most accurate prediction in science. But the Standard Model is not perfect.

1973年完成的粒子物理学标准模型是现代物理学皇冠上的一颗宝石。它预测基本粒子和力的性质的准确性令人难以置信。以电子的磁矩为例，它是衡量一个粒子在磁场中摆动强度的指标。标准模型给出了小数点后14位的正确答案，这是科学上最准确的预测。但是标准模型并不完美。

It cannot explain gravity, dark matter (mysterious stuff detectable only by its gravitational pull), or where all the antimatter in the early universe went. Physicists have spent much time, effort and money performing ever-more elaborate experiments in an effort to see where the Standard Model fails, in the hopes of finding a clue to the theory that will replace it. 

它无法解释引力、暗物质（只有通过引力才能探测到的神秘物质），也无法解释早期宇宙中所有反物质的去向。物理学家们花费了大量的时间、精力和金钱，进行了越来越精细的实验，试图找出标准模型的失败之处，希望找到替代标准模型的理论线索。

But the Standard Model has fought back, stubbornly predicting the results of every experiment physicists have thrown its way. But that may perhaps be changing. In a paper published last week in Science, a team of researchers from the Fermi National Accelerator Laboratory (Fermilab) in America announced that the mass of an elementary particle called the w boson appears to be greater than the Standard Model predicts.

但是标准模型进行了反击，它固执地预测物理学家们提出的每一个实验的结果。但这种情况可能正在改变。在上周《科学》杂志上发表的一篇论文中，美国费米国家加速器实验室(简称Fermilab)的一组研究人员宣布，一种名为w玻色子的基本粒子的质量似乎比标准模型预测的要大。

The difference is small—only a hundredth of a percent—but the measurement’s precision exceeds that of all previous experiments combined. It places the odds that the result is spurious at only one in a trillion (“seven sigma” , in the statistical lingo), well above the one in 3.5m (five sigma) that physicists require to consider a finding robust.

差别很小，只有百分之一，但测量的精度超过了所有以前的实验的总和。它将结果不可信的几率设定为一万亿分之一(用统计学术语来说就是“7西格玛”)，远高于物理学家认为这一发现可靠的350万分之一(5西格玛)。

The scientists at Fermilab analysed historical data from the Tevatron, a circular particle collider which was the most powerful in the world until the Large Hadron Collider (LHC) came online in 2009. between 2002 and 2011 (when it ran for the last time), the Tevatron produced approximately 4m w bosons in collisions between particles called quarks and their antimatter counterparts, antiquarks.

费米实验室的科学家分析了Tevatron的历史数据。Tevatron是一个圆形粒子对撞机，在2009年大型强子对撞机(LHC)投入使用之前，它是世界上最强大的粒子对撞机。在2002年到2011年(它最后一次运行的时候)，Tevatron在夸克和它们的反物质对位物反夸克之间的碰撞中产生了大约4m w的玻色子。

Using detailed recordings of the scattering trajectories of the menagerie of particles present in such collisions, the scientists could calculate the mass of the w boson with unprecedented accuracy. The finding has big implications. The w boson is a force-carrying particle. Together with its sibling the z boson, it mediates the weak nuclear force that governs radioactive decay.

利用这种碰撞中存在的大量粒子的散射轨迹的详细记录，科学家们可以以前所未有的精度计算出w玻色子的质量。这一发现具有重大意义。玻色子是一种携带力的粒子。它和它的兄弟粒子z玻色子一起，调节控制放射性衰变的弱核力。

Unlike other force-carrying particles, however, the w and z bosons have mass—and a lot of it. The w boson is 90 times heavier than a hydrogen atom. The z boson is even more massive. What really distinguishes the w boson, however, is its ability to change the type—or “flavour”—of other elementary particles it comes across. For example, it can transform the electron (and two of its cousins, the muon and tau) into neutrinos.

然而，与其他携带力的粒子不同，w和z玻色子有质量，而且质量很大。w玻色子比氢原子重90倍。z玻色子的质量更大。然而，真正区别w玻色子的是，它能够改变遇到的其他基本粒子的类型或“味道”。例如，它可以将电子(以及它的两个表亲，muon 和tau)转化为中微子。

It can also flip quarks from one type to another—up to down, top to bottom, and the whimsically named “strange” quark to a “charm” one. These protean powers mean that the mass of the w boson is linked to the mass of several other elementary particles. That allows scientists to use the w boson to calculate the mass of those other particles.

它还可以把夸克从一种类型翻转到另一种类型，从上到下，从上到下，从上到下，把名字古怪的“奇怪”夸克翻转到“迷人”夸克。这些千变万化的能力意味着w玻色子的质量与其他几种基本粒子的质量相联系。这使得科学家可以使用w玻色子来计算其他粒子的质量。

That is how they predicted the mass of the top quark (discovered in 1995) and the mass of the Higgs boson (discovered in 2012), before either particle had been detected. If the w boson is more massive than the Standard Model predicts, it implies that something else is tugging on it too—an as-yet-undiscovered particle or force. For particle physicists, that is an exciting prospect.

这就是他们如何预测顶夸克(发现于1995年)和希格斯玻色子(发现于2012年)的质量，在这两个粒子被探测到之前。如果w玻色子的质量比标准模型预测的要大，这就意味着还有其他的东西在拉着它——一种尚未发现的粒子或力。对于粒子物理学家来说，这是一个令人兴奋的前景。

It is not the only one. In March 2021 scientists from CERN—Europe’s particle-physics laboratory—reported evidence that the bottom quark decays into electrons and muons in uneven numbers, contradicting the Standard Model. Only three weeks later, Fermilab announced that the magnetic moment of the muon appears to be greater than predicted by the Standard Model too.

它不是唯一的一个。2021年3月，欧洲核子研究中心粒子物理实验室的科学家报告称，有证据表明，底部夸克衰变为数量不均匀的电子和介子，这与标准模型相矛盾。仅仅三周后，费米实验室宣布，介子的磁矩似乎也比标准模型预测的要大。

Like the mass of the w boson, the magnetic moment of the muon is partly determined by the properties of other particles. If it is greater than the Standard Model predicts, that hints at an as-yet-undiscovered particle or force too. Assuming, that is, the results are real. exciting as they were, neither result from 2021 crossed the 5-sigma threshold (they hit 3.1 and 4.2 sigma, respectively). That means further confirmation is necessary.

与w玻色子的质量一样，介子的磁矩部分取决于其他粒子的性质。如果它比标准模型预测的要大，那就意味着还有一种尚未被发现的粒子或力。也就是说，假设结果是真实的。令人兴奋的是，2021年的结果都没有超过5西格玛临界值(分别达到了3.1和4.2)。这意味着需要进一步确认。

The more recent Tevatron result, though, contradicts the previous best measurement of the w boson mass, made in 2017 at the LHC. That was in close agreement with the Standard Model, presenting a puzzle. On the other hand, the latest Tevatron result aligns well with previous data provided by the Large Electron-Positron Collider, the LHC’s predecessor.

然而，最近的Tevatron结果与2017年LHC对w玻色子质量的最佳测量结果相矛盾。这与标准模型非常接近，令人困惑。另一方面，Tevatron的最新结果与大型正电子对撞机(LHC的前身)提供的数据吻合得很好。

It is consequently the strongest evidence yet of the physics that must lie beyond the Standard Model. Anyone who prefers interesting errors over yet more dull confirmation will be hoping it holds up.

因此，这是迄今为止最有力的物理学证据，它必须超越标准模型。那些更喜欢有趣的错误而不是更乏味的确认的人会希望它能站得住脚。