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discovered_01_2013

discovered 01.13 FOCUS WWW.Hzdr.DE in the lab setting. "It allows us to probe deep into the past, approximately 14 billion years all the way back to the Big Bang, albeit only its first few minutes," says Naumann. The scientists are assuming that, back then, all matter was highly concentrated into a "primordial soup," which ultimately gave rise to all elementary particles and then, later on, to all of the various chemical elements. "Quark-gluon plasma" is the proper term for this dense state of matter. To generate it, the CBM researchers are planning to get heavy atomic nuclei to collide with each other. "This happens if, for instance, an accelerated ion beam hits a gold target," Naumann explains. When individual heavy atomic nuclei containing lots of quarks and gluons – in contrast to lighter nuclei that contain fewer of these particles – collide, hundreds or even thousands of new particles can result. For this to work, high-performance accelerators like the ones that are planned at FAIR have to direct the nuclei at each other and they have to be able to overcome the strong forces between the nuclear constituents. If protons and neutrons then collide and overlap, quarks would be able to directly interact with each other – and, voilà, there you have a novel state of matter and your quark-gluon plasma. The particles they contain are much more densely arranged than they normally are in other types of matter. The CBM experiment will yield high-density plasma: The researchers accelerate the original particles to "moderate" levels of energy, which allows the particles to interact intensively. These kinds of states of plasma are also being examined at CERN and at Brookhaven National Laboratory in the US, albeit at higher particulate energies and lower densities. Ten million particle collisions per second Only a small portion of the newly created particles will result from the central collision of two atomic nuclei. The next step is to filter them from the multiplicity of signals given off by the individual particle collisions – on the order of up to ten million per second. To put it another way, the scientists are in need of extremely high-performance detectors. To develop these, they use new kinds of materials and technologies that will allow them to incorporate the vast number of particles. The CBM experiment is thus planned as the combination of several individual detector systems, each of which performs a different function. One of these includes measuring the time of flight for which Lothar Naumann and his HZDR colleagues are developing central detector components. At around 100 square meters, the entire time of flight detector is roughly as big as the area of a single-family home. Therefore, the underground bunker, which will house the CBM experiment, needs to have the proper dimensions. Construction of the new facility is expected to begin in 2017 at the earliest. Until then, what is important is to complete development, testing, and construction of the detectors. A detector consisting of many small individual segments with a total area of roughly one square meter is currently being built at the Helmholtz- Zentrum Dresden-Rossendorf. Using the electron beam at HZDR’s ELBE accelerator, the researchers have already very successfully finished testing the prototype. In addition, their CBM colleagues from Tsinghua University Beijing in China and the Institute for Theoretical and Experimental Physics in Moscow, Russia, and a number of other research groups, have started using the ELBE electron beam to test their respective detectors for FAIR. Special ceramic detectors According to Lothar Naumann, the HZDR components must meet two major requirements: "First, they must be able to register the speed of a large number of individual particles with – secondly – very high precision." In this, Naumann and his team proved successful a while ago – at this point, the tests are already three years old. The result: the new detectors are capable of determining with high precision up to one million particles per second in a one square centimeter area in the 100 picosecond range - the time it takes a particle moving at near the speed of light to travel a distance of 30 millimeters. Since most of the particles are passing through the gigantic time of flight detector’s center at a very high probability, the fast HZDR components are applied right there. "The detectors have exceeded all our expectations," Lothar Naumann admits. "We developed them in partnership with the Dresden Fraunhofer Institute for Ceramic Technologies and Systems IKTS and are very happy with our partners at the Institute." The test was preceded by an almost two-year period of development, during which time the scientists were actively searching for a suitable material to use. "In order to be able to build innovative detector components, we needed a kind of material with very unique electrical properties. Now, unfortunately, you can’t just go to the store and buy that sort „Our detectors have to be able to register the speed of a huge number of individual particles with very high precision.“

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