The LHC is up and running again at CERN

The Large Hadron Collider (LHC) is a gigantic scientific instrument near Geneva, where it spans the border between Switzerland and France about 100 m underground. It is a particle accelerator used by physicists to study the smallest known particles – the fundamental building blocks of all things. It will revolutionise our understanding, from the minuscule world deep within atoms to the vastness of the Universe.The LHC is operated by CERN, the European Organization for Nuclear Research….

“Two beams of subatomic particles called ‘hadrons’ – either protons or lead ions – will travel in opposite directions inside the circular accelerator, gaining energy with every lap. Physicists will use the LHC to recreate the conditions just after the Big Bang, by colliding the two beams head-on at very high energy. Teams of physicists from around the world will analyse the particles created in the collisions using special detectors in a number of experiments dedicated to the LHC…

“CERN directors decided to extend the run through the end of 2012, instead of shutting down in 2011 for repairs as previously planned, and spirits are running high among scientists working in the field of new physics.” (physorg.com)

Let’s take a look at the four main experiments at the LHC, ATLAS, ALICE, CMS, and LHCb.

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The ATLAS experiment is one of the four big experiments at the Large Hadron Collider (LHC) at CERN (Geneva, Switzerland). A collaboration of about 2500 scientists from all around the world aims at studying proton – proton collisions at very high energies and particle fluxes. New and exciting particles are to be discovered, deeper insight into the fundamental forces and structures of our universe to be gained. The experiment has been built and installed in Geneva in a joint effort over the last decade, has been thoroughly commissioned

The Mainz group aims at using data recorded by the ATLAS detector to resolve fundamental questions such as the nature of dark matter (search for Supersymmetry), the origin of electroweak symmetry breaking (discovery and study of the Higgs boson), and the quest for a unified theory of all interactions (detection of physics beyond the Standard Model).

We have made major contributions to detector and electronics design, in particular in the general area of the ATLAS Liquid Argon Calorimeter, as well as the readout and analysis infrastructure. Along with physics analyses, the Mainz group is currently working on the maintenance, optimization and further development of the high speed trigger electronics…

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“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…

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The CMS (Compact Muon Solenoid) experiment uses a general-purpose detector to investigate a wide range of physics, including the search for the Higgs boson, extra dimensions, and particles that could make up dark matter. Although it has the same scientific goals as the ATLAS experiment, it uses different technical solutions and design of its detector magnet system to achieve these.

The CMS detector is built around a huge solenoid magnet. This takes the form of a cylindrical coil of superconducting cable that generates a magnetic field of 4 teslas, about 100 000 times that of the Earth. The magnetic field is confined by a steel ‘yoke’ that forms the bulk of the detector’s weight of 12 500 tonnes. An unusual feature of the CMS detector is that instead of being built in-situ underground, like the other giant detectors of the LHC experiments, it was constructed on the surface, before being lowered underground in 15 sections and reassembled.
More than 2000 scientists collaborate in CMS, coming from 155 institutes in 37 countries….

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The LHCb experiment will help us to understand why we live in a Universe that appears to be composed almost entirely of matter, but no antimatter.
It specialises in investigating the slight differences between matter and antimatter by studying a type of particle called the ‘beauty quark’, or ‘b quark’.

Instead of surrounding the entire collision point with an enclosed detector, the LHCb experiment uses a series of sub-detectors to detect mainly forward particles. The first sub-detector is mounted close to the collision point, while the next ones stand one behind the other, over a length of 20 m. An abundance of different types of quark will be created by the LHC before they decay quickly into other forms. To catch the b-quarks, LHCb has developed sophisticated movable tracking detectors close to the path of the beams circling in the LHC. The LHCb collaboration has 650 scientists from 48 institutes in 13 countries.”