The greatest experiment in the world
LHC: The greatest experiment in the world has begun
10th September 2008. The wait is over: the engines of the LHC, the largest and most powerful particle accelerator ever built located underground near Geneva, a joint effort by an international group of scientists coordinated by CERN, the particle physics research center, have been turned on. The first beam of protons was started shortly after 9:30AM. Scientists from all over the world expect to make some great discoveries even though it might take a very long time. The LHC is attempting to go back billions of years, to a tiny fraction of a second following the Big Bang. In other words, to the time when the universe was born, when all the matter was condensed in a small lump no larger than an orange, and the particles that composed it collided at extremely high speeds. This will be recreated now with two beams of protons that are being accelerated at the speed of light in opposite directions in a 27 km. circular tunnel 100 meters below the ground near Geneva. Man's challenge to the mysteries of science has just begun and the answers that scientists dream of getting could come all of a sudden. It could be a matter of minutes as it could be a matter of years. However long it is going to take for about 100 research groups to gather and study the billions of data per second that will come from each collision. This huge task will enable either to confirm the most accredited theories on the birth of the universe, or else bring forth some totally new ones. Whatever the outcome, the world of physics will never the the same again.
A big project for big questions
In 1992 the Nobel prize winner Carlo Rubbia, at the time director of Cern, officially proposed the construction of a new super accelerator whose purpose would be to discover one of the greatest mysteries in physics. First and foremost: why do objects have a mass? According to the standard model, which is the most accredited theory so far on this issue, there is a particle which is responsible for object mass. It is the notorious Higgs’ Boson, named after the Scottish scientist who was the first to come forth with this theory in the ‘60s. The accelerator should finally be able to prove its existence along with that of another unapproachable particle, the neutrino, with which we might unravel the second great mystery of the cosmos: dark matter.
If the LHC should fail to discover the Higgs Boson and the neutrino it is most likely that nothing will happen, but the old theory will have to be re-addressed and we will have to be prepared to make new discoveries and elaborate new theories.
The heart of the issue
The Higgs’ Boson
Higgs Boson, whose existence was assumed in 1964 by the Scottish scientist Peter Higgs, is the only particle as yet unseen belonging to the standard model, the theory that was put forth during the 70’s and 80’s which describes all the elementary components of matter known to us today and three of the four basic forces that dominate it: strong nuclear interaction, weak nuclear interaction and electromagnetic force (gravity force is excluded, which is what makes this an incomplete theory, besides the fact that dark matter isn’t considered).
Higgs Boson, which was nicknamed “God’s particle” by the Physics Nobel prize winner Leon Max Lederman because of its importance in the theory of matter, is believed to play a leading role in object mass. Thanks to the unexplored energies which will be attained by the Lhc experiment, maybe it will be possible to find it and discover its proprieties, which will help to complete our understanding of matter.
It is there but you cannot see it. We know nothing about the characteristics of its mass except the fact that it keeps light originating in remote galaxies from reaching Earth. This is one of the few proofs we have of its existence. In fact, one of the latest theories is that only 4% of what makes up the universe can be seen, the other 96% is simply “dark” or invisible matter. Scientists began to suspect this in the ‘70s when they noticed that the laws of interaction between centrifugal force and gravity apparently didn’t apply in the case of certain galaxies formed by stars that instead of moving farther away according to prime force (the result of astronomic calculations between mass and velocity) appeared to be held by a gravity force which was apparently out of proportion with the size of the visible mass. Even though we are practically certain of its existence, we haven’t been able yet to understand exactly what it is. Probably, but it has yet to be proven (and this is the secret hope of the scientists that will be studying the vast amount of data produced by the LHC), it is made up of neutrinos, subatomic particles that have always remained hidden from scientists’ view but now, thanks to the high energy explosions produced by the neutron beams that will collide in the LHC tunnel, they may become visible. It would be a sensational discovery that could solve the mysteries about the future of our universe: whether it will expand further or not.
A close up view of the LHC
LHC stands for Large Hadron Collider, hadrons being scientific jargon for protons, those particles that combined with neutrons make up the atom’s nucleus.
Inside a 27 kilometer circular tunnel 50 to 100 meters below the ground, two proton beams travel through the accelerator at the speed of light. The two beams collide in four different locations, within huge collectors that will gather data from the 800 million collisions that will take place per second. Atlas and Cms, the two main collectors are as large as five floor buildings. The other two, Alice and Lhcb, are 10 meters high by 10 meters wide. The first two are supposed to collect data on Higgs’ boson, verify the supersymmetry theories and search for new particles. The others will analyze the collision between lead atoms to study quark characteristics and the matter-antimatter asymmetry in the Big Bang.
The LHC in numbers, the greatest experiment in history
27 kilometers: the length of the tunnel through which proton beams travel in opposite directions. To be exact the collisions will occur between bunches of 100 billion protons just a few centimeters in length by 1 to 3 millimeters in width.
2,500: the number of bunches of protons travelling through the tunnel per second.
50 – 100 meters underground: the depth at which the tunnel is built, a necessary feature to keep cosmic waves from interfering with the experiment.
1 Gigabyte of data per second: the abnormous amount of information gathered. To collect, filter, classify and examine this huge amount of data a gigantic computer system has been set up: the LHC computer grid, composed by a dozen sites that will perform back-ups of all the data supplied by over 100 different centers.
800,000: the number of people from 20 different countries of Europe as well as from Russia, the U.S., Japan, Israel and others that are involved directly or indirectly with the experiment.
7 TeV: as in 7 Tera electron volts, or 7 trillion electron volts, is the amount of energy reached by protons in the LHC, the highest ever reached by a particle accelerator.
800 million: the number of proton collisions per second.
-271.5 °C: the temperature that must be reached for the magnets in the machine to perform their duty as electricity conductors without using other sources of energy. This is quite close to the absolute zero temperature of –273 °C. Scientists are using liquid helium as the refrigerating agent because it stays in its fluid form at near absolute zero temperatures.
- 1992: The adventure begins. The Nobel Prize winner Carlo Rubbia, who was the Cern director at the time, proposed to build a new powerful accelerator to study the effects of proton collisions.
- 1996: The year when the Cern board of directors approved the project.
- 2002-2004: The time when the electric plants were installed.
- 2004-2005: the cryogenic cooling system and the first magnets were installed. The project was half way done.
- 2007: magnet installation and interconnection were completed. The first proton beam is sent through the machine.
- 10 September 2008: the machine becomes fully operational.
- 2028: data collection deadline.
written by Paolo Magliocco