A Large Ion Collider Experiment
For the ALICE experiment, the LHC will collide lead ions to recreate the conditions just after the Big Bang under laboratory conditions. The data obtained will allow physicists to study a state of matter known as quark‑gluon plasma, which is believed to have existed soon after the Big Bang.
All ordinary matter in today’s Universe is made up of atoms. Each atom contains a nucleus composed of protons and neutrons, surrounded by a cloud of electrons. Protons and neutrons are in turn made of quarks which are bound together by other particles called gluons. This incredibly strong bond means that isolated quarks have never been found.
Collisions in the LHC will generate temperatures more than 100 000 times hotter than the heart of the Sun. Physicists hope that under these conditions, the protons and neutrons will 'melt', freeing the quarks from their bonds with the gluons. This should create a state of matter called quark-gluon plasma, which probably existed just after the Big Bang when the Universe was still extremely hot. The ALICE collaboration plans to study the quark-gluon plasma as it expands and cools, observing how it progressively gives rise to the particles that constitute the matter of our Universe today.
A collaboration of more than 1000 scientists from 94 institutes in 28 countries works on the ALICE experiment (March 2006).
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fredag den 31. august 2007
mandag den 20. august 2007
The LHC experiments
The six experiments at the LHC are all run by international collaborations, bringing together scientists from institutes all over the world. Each experiment is distinct, characterised by its unique particle detector.
The two large experiments, ATLAS and CMS, are based on general-purpose detectors to analyse the myriad of particles produced by the collisions in the accelerator. They are designed to investigate the largest range of physics possible. Having two independently designed detectors is vital for cross-confirmation of any new discoveries made.
Two medium-size experiments, ALICE and LHCb, have specialised detectors for analysing the LHC collisions in relation to specific phenomena.
Two experiments, TOTEM and LHCf, are much smaller in size. They are designed to focus on ‘forward particles’ (protons or heavy ions). These are particles that just brush past each other as the beams collide, rather than meeting head-on
The ATLAS, CMS, ALICE and LHCb detectors are installed in four huge underground caverns located around the ring of the LHC. The detectors used by the TOTEM experiment are positioned near the CMS detector, whereas those used by LHCf are near the ATLAS detector.
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The two large experiments, ATLAS and CMS, are based on general-purpose detectors to analyse the myriad of particles produced by the collisions in the accelerator. They are designed to investigate the largest range of physics possible. Having two independently designed detectors is vital for cross-confirmation of any new discoveries made.
Two medium-size experiments, ALICE and LHCb, have specialised detectors for analysing the LHC collisions in relation to specific phenomena.
Two experiments, TOTEM and LHCf, are much smaller in size. They are designed to focus on ‘forward particles’ (protons or heavy ions). These are particles that just brush past each other as the beams collide, rather than meeting head-on
The ATLAS, CMS, ALICE and LHCb detectors are installed in four huge underground caverns located around the ring of the LHC. The detectors used by the TOTEM experiment are positioned near the CMS detector, whereas those used by LHCf are near the ATLAS detector.
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onsdag den 1. august 2007
How the LHC works
The LHC, the world’s largest and most powerful particle accelerator, is the latest addition to CERN’s accelerator complex. It mainly consists of a 27 km ring of superconducting magnets with a number of accelerating structures to boost the energy of the particles along the way.
Inside the accelerator, two beams of particles travel at close to the speed of light with very high energies before colliding with one another. The beams travel in opposite directions in separate beam pipes – two tubes kept at ultrahigh vacuum. They are guided around the accelerator ring by a strong magnetic field, achieved using superconducting electromagnets. These are built from coils of special electric cable that operates in a superconducting state, efficiently conducting electricity without resistance or loss of energy. This requires chilling the magnets to about ‑271°C – a temperature colder than outer space! For this reason, much of the accelerator is connected to a distribution system of liquid helium, which cools the magnets, as well as to other supply services.
Thousands of magnets of different varieties and sizes are used to direct the beams around the accelerator. These include 1232 dipole magnets of 15 m length which are used to bend the beams, and 392 quadrupole magnets, each 5–7 m long, to focus the beams. Just prior to collision, another type of magnet is used to 'squeeze' the particles closer together to increase the chances of collisions. The particles are so tiny that the task of making them collide is akin to firing needles from two positions 10 km apart with such precision that they meet halfway!
All the controls for the accelerator, its services and technical infrastructure are housed under one roof at the CERN Control Centre. From here, the beams inside the LHC will be made to collide at four locations around the accelerator ring, corresponding to the positions of the particle detectors.
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Inside the accelerator, two beams of particles travel at close to the speed of light with very high energies before colliding with one another. The beams travel in opposite directions in separate beam pipes – two tubes kept at ultrahigh vacuum. They are guided around the accelerator ring by a strong magnetic field, achieved using superconducting electromagnets. These are built from coils of special electric cable that operates in a superconducting state, efficiently conducting electricity without resistance or loss of energy. This requires chilling the magnets to about ‑271°C – a temperature colder than outer space! For this reason, much of the accelerator is connected to a distribution system of liquid helium, which cools the magnets, as well as to other supply services.
Thousands of magnets of different varieties and sizes are used to direct the beams around the accelerator. These include 1232 dipole magnets of 15 m length which are used to bend the beams, and 392 quadrupole magnets, each 5–7 m long, to focus the beams. Just prior to collision, another type of magnet is used to 'squeeze' the particles closer together to increase the chances of collisions. The particles are so tiny that the task of making them collide is akin to firing needles from two positions 10 km apart with such precision that they meet halfway!
All the controls for the accelerator, its services and technical infrastructure are housed under one roof at the CERN Control Centre. From here, the beams inside the LHC will be made to collide at four locations around the accelerator ring, corresponding to the positions of the particle detectors.
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