经济学人下载:捕获希格斯粒子 敌军现身?

Science and Technology
科技

Looking for the Higgs
捕获希格斯粒子

Enemy in sight?
敌军现身？

The search for the Higgs boson is closing in on its quarry
希格斯玻色子的研究逼近其目标

ON JULY 22nd two teams of researchers based at CERN, Europe's main particle-physics laboratory, near Geneva, told a meeting of the European Physical Society in Grenoble that they had found the strongest hints yet that the Higgs boson does, in fact, exist.
7月22日，驻欧洲粒子物理研究所（CERN，邻近日内瓦的欧洲主要粒子物理实验室）的两组研究人员在格勒诺布尔(Grenoble)欧洲物理协会的一次会议上声称，他们已经得到迄今为止最有力的线索，将力证希格斯玻色子的确真实存在。

The Higgs (named after Peter Higgs, a British physicist who predicted its existence) is the last unobserved part of the Standard Model, a 40-year-old theory which successfully describes the behaviour of all the fundamental particles and forces of nature bar gravity.
希格斯粒子（它以预言其存在的英国物理学家彼得·希格斯的名字命名） 是"基础模型"中最后一个尚未观测到的组件，"基础模型"已有40年的历史，它成功地描述了所有基础粒子的行为及除重力以外的所有自然力。

Mathematically, the Higgs is needed to complete the model because, otherwise, none of the other particles would have any mass.
在数学层面上，希格斯粒子对于完成"模型"是必不可少的，这是因为，一旦缺少它，所有的其它粒子都将会失去质量。

The problem with the elusive boson is not creating it in the first place.
对于难于捉摸的玻色子而言，首要的问题并不是将其创造出来。

Two of the world's particle accelerators, the Large Hadron Collider (LHC) at CERN and its American rival, the Tevatron at Fermilab on the outskirts of Chicago, each have more than enough oomph to conjure up the Higgs—at least if it looks anything like theory suggests it should.
世界上现有两台粒子加速器，欧洲粒子物理研究所的大型强子对撞机（LHC），以及其美国竞争对手芝加哥市郊费米实验室的兆电子伏加速器（Tevatron），各自都有绰绰有余的充沛魔力去召唤希格斯粒子——如果一切符合理论，至少看来应该是这样。

The difficulty, rather, is spotting signs of it in the jetsam of subatomic debris these machines produce.
然而，困难在于如何在这些机器制造的亚原子碎片衍生物中辩认出它的踪迹来。

Both laboratories use similar approaches: smashing particles called hadrons into each other.
两个实验室都采用类似的方法：将称作强子的高能粒子彼此对撞。

The LHC collides beams of protons.
大型强子对撞机对轰质子束。

The Tevatron works with protons and antiprotons.
而兆电子伏加速器使用的是质子和反质子。

In each case the particles concerned are accelerated to within a whisker of the speed of light before they are forced, head-on, into each other.
在它们被强制彼此迎头撞击之前，各自所采用的那些粒子都要被加速至距离光速仅有一线之隔。

During such a collision, their kinetic energy is converted into other particles (since, as Einstein showed, energy and mass are but two sides of the same coin).
在这样的撞击过程中，它们的动能转换成额外的粒子（正如爱因斯坦所指出的那样，这是由于能量和质量只是同一个硬币的两面而已）。

The more kinetic energy there is, the heavier these daughter particles can be.
动能越大，越能产生更大质量的粒子。

Unfortunately hadrons, such as protons and antiprotons, are made of smaller bits called quarks.
不幸的是，强子，比如质子和反质子，是由名为夸克的更小单元所组成的。

As a result, hadron collisions can be messy and difficult to interpret.
结果，强子的撞击可能造成混乱且难于预测的局面。

If a Higgs were to be made in such a collision, the complexity of hadrons means that other particles would be created along with the boson.
如果一个希格斯粒子产生在这样的一次碰撞中，那么强子的复杂构造意味着另外的粒子也将会伴随这个玻色子而出现。

Both it and its companions would then decay almost instantly into a plethora of less fleeting bits, some of which could be detected.
玻色子与它的伙伴们将会几乎在瞬间衰变为大批寿命更短的微粒子，其中有一些能被检测出来。

In theory, analysing this shower of daughter particles should give away whether or not a Higgs was involved.
理论上，分析这批衰变所产生的粒子应该能轻松查明是否其中曾存在希格斯粒子。

But other sorts of subatomic process that do not involve the Higgs can produce precisely the same final readings as those the missing boson is predicted to generate.
然而其他类型的不含希格斯粒子的亚原子衰变过程也能够精确地产生相同的最终观测结果，就跟缺失的希格斯粒子预定产生的一般。

Finding a Higgs-like signal among the daughters is therefore not, by itself, enough to say you have discovered the Higgs.
因而在这些衍生粒子中发现类似希格斯粒子的迹象本身并不足以证明你已经发现希格斯粒子。

What is needed is an unexpected abundance of such signals.
这样的迹象出乎意料地频繁出现是一个必要条件。

And it is just such excess that two separate experiments at the LHC, known as CMS and ATLAS, have detected.
而在大型强子对撞机上的这两个独立实验（称为CMS和ATLAS）就已经检测到这样的反常频密现象。

Individually, each team's result could be a statistical fluke.
客观地说，每个研究团队所得出的结论可能只是统计意义上的偶然现象。

Neither reaches the exacting standard of proof that particle physicists require to accept a result unequivocally—namely one chance in 3.5m that it occurred by accident.
两者都达到粒子物理学家所提出能确定无疑地接受为证据的严苛标准——即三百五十万次实验中偶尔发生一次。

Instead, they each achieved a significance of somewhere between one chance in 1,000 and one in six, depending on which statistical test you use.
不止如此，它们各自都获得了显著的观测数据，从一千次发生一次到六次发生一次的范围之内，这取决于你所采用的统计学测试标准。

What set the scientists gathered in Grenoble aflutter, though, was that both experiments ascribed the excesses they observed to the same putative decay pattern—one involving W bosons, which mediate the weak nuclear force that is responsible for certain types of radioactive decay.
令到聚集在格勒诺布尔的科学家们兴奋不已的是，这两个实验中所观察到的反常频密现象都要归因于相同的公认衰变模式——一种涉及W玻色子的衰变，该玻色力是传递弱核力的媒介，而弱核力是某些特定种类放射性衰变的主因。

Both teams also ascribe the same mass to their putative Higgses, namely 130-150 gigaelectron-volts (the units in which particle physicists measure mass).
两个团队也认为他们所推定的希格斯粒子具有相同的质量，即130—150吉电子伏特（这是粒子物理学测量质量所采用的一种单位）。

That is at the low end of the predicted range.
这处在预测范围中的底部。

Sadly, even taken together these results are far from robust enough to claim the Higgs's discovery.
遗憾地是，即使是将这些结果一并考虑，也远不足于斩钉截铁地断言发现希格斯粒子。

With a little tweaking, the Standard Model might explain them in other ways.
只要稍作更改，"标准模型"可以用另一种方式去解释它们。

Guido Tonelli and Fabiola Gianotti, who head CMS and ATLAS respectively, therefore urge caution.
各自领导CMS和ATLAS的基多·汤内利（Guido Tonelli）及法比奥拉·贾诺蒂（Fabiola Gianotti）因而呼吁要格外的小心谨慎。

Their goal is to have enough data by the end of the year either to say definitely that the Higgs has a mass of 130-150 gigaelectron-volts, or that if it exists at all, then it must be heavier than that.
他们的目标是到今年年末获得足够的数据，要么证明希格斯粒子具有130—150吉电子伏特的质量，要么证明只要它确实存在，那么它必定要更重一些。

If this is the case, the hunt will continue at higher and higher energies (and therefore masses) until either the thing is found, or there is nowhere left in the energy landscape for it to be hiding.
如果是这样的话，追捕行动将在越来越高的能量（因此质量也是同样如此）层级上展开，直到发现它为止，否则的话，能量图谱中根本就不存在它的藏身之处。