在俄羅斯小鎮捕捉中微子

Just over the border from Georgia, in the Caucasus Mountains of southern Russia, lies a small town called Neytrino. For the last half-century, its main business has been the study of the tiniest insubstantial bit of matter in the universe, an ephemeral fly-by-night subatomic particle called the neutrino.

在俄羅斯南部高加索山脈比鄰格魯吉亞的地方，有一個名叫涅特里諾的小鎮。在過去的半個世紀裏，這個小鎮上的主要工作是研究宇宙中最微小、最虛無縹緲的物質，即很難捕捉到的、轉瞬即逝的中微子。

This is the home of the Baksan Neutrino Observatory, a warren of tunnels and laboratories burrowed two miles into a mountain, sheltered from the outside universe and cosmic rays underneath 12,000 feet of rock. There vats of liquid wait to record the flight of neutrinos from the center of the sun, from exploding stars, atomic reactors and the Big Bang itself, carrying messages through time. Neutrinos are the ghost riders of the cosmos, mostly impervious to the forces, like electromagnetism, with which other denizens of nature interact. Neutrinos cruise unmolested through rocks, the earth and even our bodies. In the words of a famous poem by John Updike, they “insult the stallion in his stall.”

巴克桑中微子觀測站就坐落在這個小鎮上。這個建在一座大山下的觀測站由狹小的隧道和實驗室組成，從山洞口進去約有3.6公里，上面覆蓋着3500多米厚的岩石，以減少來自宇宙外部的宇宙射線的影響。一桶桶的液體在這裏等待着記錄不同來源的、攜帶着穿越時空信息的中微子，它們有的來自太陽的中心，有的來自爆炸的恆星，有的來自核反應堆，也有的來自大爆炸本身。中微子是宇宙中的幽靈騎手，它們基本上不受電磁這樣的力量影響，不像其他的自然萬物那樣會與之相互作用。中微子能不受干擾地穿越岩石、土壤，甚至不知不覺地穿越我們的身體。正如約翰·厄普代克(John Updike)那句名詩所說，它們敢於“冒犯馬廄中的牡馬”。

The most delicate measurements so far indicate that an individual neutrino weighs less than a millionth what an electron weighs. Baksan is not the only place dedicated to their surreal pursuit.

目前爲止最精確的測量顯示，中微子的質量不到電子質量的百萬分之一。巴克桑不是唯一致力於這種超現實事業的地方。

The men and women in these photographs, taken by Maxim Babenko last year, share an underground union with scientists scattered around the world in equally deep places: the Sanford Underground Research Facility in the former Homestake gold mine in Lead, S.D.; the Gran Sasso National Laboratory, beneath the mountain of that name in Italy; the Sudbury Neutrino Observatory in Ontario, Canada; the Super-Kamiokande, deep within Mount Ikeno, Japan; and IceCube, an array of detectors buried in ice at the South Pole.

馬克西姆·巴本科(Maxim Babenko)去年拍攝的這些照片中的男男女女們，與世界各地的深地實驗室的科學家們同屬於一個地下聯盟。這些深地實驗室包括：位於美國南卡羅來納州里德一座廢棄金礦裏的桑福德地下研究所(Sanford Underground Research Facility)，位於意大利同名山脈下的格蘭薩索國家實驗室，位於加拿大安大略省的薩德伯裏中微子觀測站(Sudbury Neutrino Observatory)，位於日本池野山深處的超級神岡觀測站(Super-Kamiokande)，以及埋在南極下面冰層中的一個名爲冰立方(IceCube)的探測器陣列。

All of them are trying to listen to quantum whispers about the nature of reality. One of Baksan’s biggest claims to fame to date was to catch neutrinos emitted by thermonuclear reactions in the center of the sun in nearly 60 tons of liquid gallium. The experiment, called S.A.G.E., for Soviet-American Gallium Experiment, proved that scientists actually do know what powers our favorite star, source of our life and light.

所有這些中微子實驗室的工作者們都在試圖傾聽量子中透露的實在本質。到目前爲止，讓巴克桑最有名的成就之一是，用近60噸的液態鎵捕捉到了太陽中心的熱核反應發射的中微子。這個名爲“蘇聯-美國鎵實驗”（Soviet-American Gallium Experiment，簡稱SAGE）的實驗證明，科學家的確知道是什麼在驅動我們最愛的恆星，地球上生命和光的來源。

Since the fall of the Soviet Union, the scientists in Baksan have had to fend off both thieves and the Russian government to keep their gallium, an element that goes for some $500 a kilogram. Physicists know that neutrinos come in at least three flavors, known as electron, muon and tau neutrinos, depending on their subatomic origin. To add to the confusion, neutrinos have a kind of quantum superpower: They can molt from one type to another, sort of like a jail escapee changing clothes as he flees. An electron neutrino, say, can emerge from a nuclear reactor in one place and appear in a detector somewhere else as a muon neutrino. This complicates the cosmic accounting of these creatures.

自從蘇聯解體之後，巴克桑的科學家們爲了保護他們的鎵，不得不同時抵禦盜賊和俄羅斯政府，鎵是一種每公斤售價500美元的元素。物理學家們知道，中微子至少有三種，由於其不同的亞原子起源，中微子被分爲電子中微子、μ中微子和τ中微子。更讓其難以琢磨的是，中微子有一種量子超能：它們可以從一種變成另一種，就像是一個越獄者在逃跑過程中換了衣服似的。比如，一個地方的核反應堆中釋放的電子中微子，可以以μ中微子的形式出現在另一個地方的探測器中。這給計算宇宙中這種粒子的數量製造了困難。

Physicists are arguing intensely these days over whether there is evidence for a fourth type, called sterile neutrinos. That is the object of a new experiment called B.E.S.T., for Baksan Experiment on Sterile Transitions, now underway in the rusty Baksan tunnels. Although neutrinos are the lightest and flimsiest and perhaps most fickle particles of the universe, they are also among the most numerous, outnumbering the protons and electrons that make up us and ordinary matter by a billion to one. And so neutrinos contribute about as much mass to the universe as the visible stars.

如今的物理學家們一直在激烈爭論是否有證據表明存在着第四種中微子，即惰性中微子。這是正在巴克桑老舊隧道中進行的名爲“惰性轉換巴克桑實驗”（Baksan Experiment on Sterile Transitions，簡稱BEST）的新實驗所研究的對象。雖然中微子是宇宙中最輕、最透明、或許也是最易變的粒子，但它們也是數量最多的一種，比構成人和普通物質的質子和電子多十億倍。所以中微子對宇宙質量的貢獻與可見恆星的貢獻差不多。

An extra population of neutrinos discovered by scientists in a cave in the Caucasus would affect basic calculations of the expansion of the universe. The discovery this month of a high-energy neutrino from a far distant galaxy passing through the IceCube detector at the South Pole elicited headlines around the world.

如果科學家在高加索山脈的洞穴裏找到了以前不知道的中微子的話，那會影響宇宙膨脹的基本計算。南極的冰立方探測器本月檢測到從其中經過的、來自遙遠星系的高能中微子，這一發現引起了全世界的關注。

Meanwhile, unaware that they are being harassed by extraterrestrial visitors, horses graze outside Baksan, and life goes on, whether we understand it or not.

不知道自己受到外星訪客騷擾的馬兒們，正在巴克桑觀測站外面的山上吃草。不管我們瞭解與否，生命一如既往。