The atom is a process, not a thing. The interior of a proton is a kind of magical place, where matter can appear out of nowhere.
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|The New York Times, Jan 13, 2004 pA19 col 02
(19 col in)
Full Text: COPYRIGHT 2004 The New York Times Company
A fleeting, ultradense state of matter, comparable in some respects to a bizarre kind of subatomic pudding, has been discovered deep within the core of ordinary gold atoms, scientists from Brookhaven National Laboratory said at a conference here Monday.
The finding was described by some scientists here as a breakthrough in understanding the powerful, immensely complex forces that hold together the building blocks of atomic nuclei: protons and neutrons. Evidence for the new state of matter turned up when the scientists slammed heavy hydrogen, or deuterons, into the gold at nearly the speed of light and observed the spray of particles that flew out.
The data, from three separate particle detectors at Brookhaven's Relativistic Heavy Ion Collider, suggested that the tiny, hard, pointlike building blocks of the nucleus had briefly merged into a smeared-out pudding. No such effect had been seen before, although some theorists had predicted that it might occur because of the notoriously shifty properties of matter at minuscule scales.
''This is nothing short of a major discovery,'' said Dmitri Kharzeev, a theoretical physicist at Brookhaven who was not involved in the experiments. ''I think it's going to trigger a real revolution in nuclear physics.''
The nuclear pudding, as strange as it is, has a simple structure and could turn out to be a universal property of nuclei speeding at high energies, Dr. Kharzeev said. The simplicity stands in sharp contrast to the messy and sometimes incomprehensible structure of many atomic nuclei. The newly discovered state could let physicists cut through those complexities and find basic laws of nature.
Other scientists said they were still checking to see whether something more mundane within the complicated world of the nucleus could explain the new results.
''The observation is very interesting,'' said Xin-Nian Wang, a theorist at the Lawrence Berkeley National Laboratory who is an organizer of the conference, called Quark Matter 2004. ''I remain cautious about the exact implications.''
Physicists have long viewed protons and neutrons as something like bags of tiny marbles -- collections of hard, pointlike particles called quarks, as well as similarly pointlike particles called gluons, which carry the strong force that binds the quarks together.
Each proton (and each neutron) contains three quarks. Normally there is just a handful of gluons flitting among the quarks, said Dr. Larry McLerran, leader of Brookhaven's nuclear theory group.
That arrangement means that atomic nuclei, though comparatively dense, are something like little planetary systems: particles whirling through mostly empty space. But subatomic matter is nothing if not elusive, and other quarks and gluons can briefly pop into and out of existence in the emptiness, filling the nuclei up just a little more.
The effect is especially pronounced for the gluons, which can interact among themselves, split in two, split again and so on. Theorists had known that for vanishingly short instants of time, a trillionth of a trillionth of a second, the nucleus could be filled with hundreds of gluons that then disappear again.
At the Brookhaven accelerator, though, the gluons could feed off the high energies and be created much more easily, theorists predicted. And because, according to Einstein's theory of relativity, time slows down when particles move close to the speed of light, those brief fluctuations could in effect last longer.
In that state, according to work by Dr. Kharzeev, Dr. McLerran and others, there would be so many gluons that they would in some sense merge, creating the pudding that is known technically as a color glass condensate.
Although the condensate, Dr. McLerran suggested, would be ''much more dense than nuclear matter'' -- by a factor of 50 to 1,000 -- it should have one very clear property: particles that slam into it would be more inclined to shoot straight through than bounce sideways, just as it is easier to stick one's finger through chocolate pudding than through a bag of marbles.
And that is exactly what a particle detector called Brahms, for Broad Range Hadron Magnetic Spectrometer, saw at Brookhaven, said Dr. Ramiro Debbe, a physicist on the experiment. As deduced by the number of collision products shooting straight down the axis of the accelerator, deuterons did not have nearly as many collisions with gluons inside the gold as they would have if the gluons had all been flying about separately.
So, Dr. Debbe said, the Brahms data indicated that the deuterons probably struck a color glass condensate inside the gold nuclei. ''The agreement between the expectations, the predictions and the data, are quite good,'' he said.
The Brookhaven accelerator uses gold because it has enough protons and neutrons, 197 altogether, to make a substantial soup of particles when smashed together with other nuclei. And for technical reasons, the ease with which gold atoms pick up a negative electrical charge makes them prime candidates for being accelerated to high energies.