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The Warsaw Voice » Society » September 24, 2008
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In Search of the God Particle
September 24, 2008   
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The Large Hadron Collider (LHC) which started running at the European Organization for Nuclear Research (CERN) in Geneva, on the French-Swiss border, Sept. 10, after 20 years of preparatory tests, is expected to contribute to our understanding of antimatter, dark matter and the early days of the universe.

The LHC fires proton beams at each other at a velocity approaching that of light from opposite ends of a 3.8m wide 27 km circular tunnel located between 50 and 175 meters underground. There were no collisions in the LHC Sept. 10 though. This was merely a full dress rehearsal for 300 or so journalists. Scientists are hoping that the proton collisions will either prove or disprove several hypotheses including the existence of the Higgs boson-the so-called God Particle-the only particle in the standard model of particle physics that has not been observed. Should it exist, the Higgs boson would explain the difference between the large mass of the W and Z bosons compared with that of the photon.

The composition of dark matter is another mystery the LHC may be able to solve. The existence of dark matter has been hypothesized from otherwise inexplicable gravitational effects. There is believed to be several times more dark matter than visible matter in the universe. The LHC may help test the hypothesis that it is composed of elementary particles having unusual properties.

Antimatter is the third research topic the LHC may help clear up. Physicists have long been aware that every elementary particle has a corresponding antiparticle. Antiparticles differ from particles in that they have an opposite charge. For example, an antiproton has all the properties of a proton except a negative, instead of a positive, charge, and an anti-electron (also called a positron) is essentially a positively charged electron. Whenever a particle meets its anti-matter counterpart, both are annihilated to become photons: pure energy. There are equal numbers of particles and antiparticles whenever matter is created from energy. Why there is less antimatter than matter in the universe is therefore a mystery. Any new antimatter that appears as a result of radioactive decay or which is artificially created in laboratories is annihilated once it collides with its material equivalent. Scientists are convinced, however, that matter and antimatter existed in equal amounts at the beginning of the universe. Matter must somehow have prevailed over antimatter before particles and antiparticles starting colliding with, and annihilating, each other immediately after the Big Bang. This is because there was a surplus of matter which brought the material world of stars, planets and so on into existence. Scientists are trying to piece together where this surplus of matter came from and how the symmetry was broken. The miniature "Big Bangs" inside the LHC will enable the formation and disintegration of particles and antiparticles to be observed. Scientists are hoping that this will reveal why matter prevailed over antimatter at the start of the universe.

Dr. Andrzej Siemko, the Polish scientist who heads the CERN group responsible for starting up and operating the magnets that focus the proton beams, says that space technology is involved. "They have to be cooled down to 1.9 degrees Kelvin above absolute zero (-272 degrees Celsius)." It's colder in here than anywhere else in the world. "Even the cosmic vacuum is warmer," he says.

The Sept. 10 trial run had to be temporarily halted when some of the magnets started heating up. Siemko says that much of the credit for the equipment eventually functioning correctly has to go to the Polish scientists who were involved in preparing the magnets since the beginning of the accelerator's construction. "We had many collaborators from Poland who worked with CERN at the accelerator startup stage," he says. These were groups from the AGH University of Science and Technology and the Institute of Nuclear Physics, both in Cracow. One group was responsible for quality control of the system in the underground tunnel while the other saw to starting up the magnet safeguard system. In all, about 100 people from Poland were involved in the project.

A lot of Poles work elsewhere at the facility, most of them on the detectors that record the particles emerging from collisions. These detectors can be as large as a house and have a lot of sensors inside. Particles passing through leave traces recorded by computers for physicists to analyze later.

Dr. Piotr Traczyk is a Polish scientist working on experiments involving the Compact Muon Solenoid (CMS) detector, the second-largest particle detector at the LHC. "Poles are present in all LHC experiments," he says. "The CMS detector is a Warsaw specialty, and the ATLAS [Atoroidal LHC Aparatus] detector, the LHC's largest, is a Cracow specialty." The Warsaw group, comprising specialists from the University of Warsaw and the Institute for Nuclear Studies in ¦wierk near Warsaw, made the detector's trigger. This device has software that determines which of the data gathered by the sensors is worth recording.

"The machine works so that collisions occur every 25 nanoseconds, or 40 million times per second," Traczyk explains. "One batch of data from the detector from one collision, is roughly one megabyte. If we multiply that out, we get 40 million megabytes per second. We cannot even begin to look at such a massive amount of data. We have to reduce it to at least an amount that can be saved on disk, to say nothing of subsequent analysis," he says. "The trigger is a multi-level system that systematically analyzes the collisions and selects the more promising ones, because the processes that are of special interest to us are very rare. With 40 million collisions per second, they might only occur once a minute or a second."

The LHC would not run so smoothly were it not for the elaborate software controlling its each and every component. Polish computer scientist Marek Strzelczyk, one of the specialists who helped develop it, says the entire LHC can be run remotely without anyone having to leave their desks. Everything happening in the accelerator can be continuously monitored.

Computers also play a key role in storing and analyzing the experimental data. The sheer volume of data provided by the detectors called for the deployment of cutting-edge computing techniques like grid computing, a form of distributed computing designed to handle massive amounts of data. CERN came up with a multi-tiered grid computing system named GRID. Tier 0 is CERN's central computer network, Tier 1 clusters powerful computers from some of the world's front rank scientific centers, and Tier 2 clusters computers from smaller research centers. Computers from Polish institutions in Warsaw, Cracow and Poznań can be found in Tier 2. This will allow physicists in Poland to access data from the LHC experiments and analyze them with their foreign colleagues.

Marcin Rybicki

CERN, the European Organization for Nuclear Research, was officially established Sept. 29, 1954, when nine European countries ratified a convention on its inception. CERN was set up to find ways of utilizing the potential of countries that had participated in World War II for peaceful purposes. Switzerland and Sweden were two of the 12 founding members.

CERN currently has 20 members: Austria, Belgium, Bulgaria, the Czech Republic, Denmark, Finland, France, Germany, Greece, Hungary, Italy, the Netherlands, Norway, Poland, Portugal, Slovakia, Spain, Sweden, Switzerland, and the United Kingdom.

The European Commission, India, Israel, Japan, Russia, Turkey, UNESCO, and the United States have observer status.

Bilateral government agreements have been signed by 43 other countries. Poland has been a member of CERN since July 1, 1991. The ratification document was signed by then president Lech Wałęsa.
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