LHC Run 3 Starts Today At Cern
Today, the 17-mile Large Hadron Collider at Cern in Geneva begins its third physics campaign.
Travelling at 99 percent the speed of light, protons are smashed into each other as they circle the collider 11,000 times every second. The accelerator ring itself consists of 1232 dipole magnets 15 metres in length which bend the beams, and 392 quadrupole magnets, each 5–7 metres long, which focus the beams.
The complex is buried between 164 and 574 feet underground. The variation in depth was deliberate, to reduce the amount of tunnel that lies under the Jura Mountains to avoid having to excavate a vertical access shaft there.
A tunnel was chosen to avoid having to purchase expensive land on the surface, which would also have an impact on the landscape and to take advantage of the shielding against background radiation that the earth’s crust provides.
Image: Cern
The image below shows a simplified illustration of the LHC accelerator chain.
This third campaign sees the LHC operating at 13.6TeV (trillion electron volts), the highest energy ever achieved in a particle accelerator.
The proton beams are collided at four separate locations around the LHC, known as experimental areas, where four large detectors record the collisions for examination.
The LHC experimental areas
ATLAS
Image: Cern
ATLAS, which stands for A Toroidal LHC ApparatuS, looks for high-mass particles which were not observable using earlier lower-energy accelerators. ATLAS was one of the two LHC experiments involved in the discovery of the Higgs boson in July 2012. It has been, and will continue, investigating ‘Supersymmetry’ and matter-antimatter charge-parity violations.
ATLAS is 46 metres long, 25 metres in diameter, and weighs about 7,000 tonnes.
ALICE
Image: Ars Technica
ALICE stands for A Large Ion Collider Experiment. It is primarily used to investigate the quark-gluon plasma which we think constituted the infant universe in the moments after the Big Bang.
Collisions in the LHC generate temperatures more than 100 000 times hotter than the centre of the Sun. For part of each year the LHC provides collisions between lead ions, recreating in the laboratory conditions similar to those just after the Big Bang.
Under these extreme conditions, protons and neutrons “melt”, freeing the quarks from their bonds with the gluons. This is quark-gluon plasma. The ALICE collaboration studies this plasma as it expands and cools, observing how it progressively gives rise to the particles that constitute the matter of our universe today.
Conventional wisdom has it there were equal amounts of matter and antimatter created at the moment of the Big Bang. Had that been so, they would have annihilated themselves so the universe would have ended the moment it was created. There must have been more of one than the other, and that came to be the universe we see today. This imbalance is known as charge-parity violation.
ALICE is 26 m long, 16 m high, and 16 m wide. It weighs 10 000 tonnes.
LHCb
Image: Daily Express
The LHCb experiment is used primarily to measure the parameters of charge-parity violation in the interactions of hadrons that contain bottom (or beauty) quarks, and compliment the measurements recorded by the ATLAS detector. Such studies can help to explain the matter-antimatter asymmetry of the Universe.
It is 21 metres long, 10 metres high and 13 metres wide, and weighs 5600 tons.
CMS
Image: Nebraska Today
The Compact Muon Solenoid is the largest experiment in the LHC. The word ‘compact’ is a complete misnomer. The machine is 21 metres long, 15 m in diameter, and weighs 14,000 tonnes
The Compact Muon Solenoid (CMS) is a general-purpose detector, which has a broad physics programme ranging from studying the Standard Model (including the Higgs boson) to searching for extra dimensions and particles that could make up dark matter.
CMS and ATLAS use different technical solutions and design of its detector magnet system to achieve their goals.
Other experimental areas
There are several other parts of the LHC complex that investigate other nuclear phenomena. The image below shows where they are.
Image: Cern
The Antiproton Decelerator
Image: Wikipedia
The AD was built from the Antiproton Collector (AC) to be a successor to the Low Energy Antiproton Ring (LEAR) and started operation in the year 2000. Antiprotons are created by firing a proton beam from the Proton Synchrotron on a metal target. The AD decelerates the resultant antiprotons to an energy of 5.3 MeV, which are then ejected to one of several connected experiments.
The major goal of the AD is to study the effects of gravity on antimatter. Though each experiment at AD has varied aims ranging from testing antimatter for cancer therapy to charge-parity violation and anti-gravity research.
CNGS
Image: Cern
The Cern Neutrinos to Gran Sasso experiment ran between 2006 and 2012, to study how neutrinos interact with matter. A beam was redirected from the SPS to fire neutrinos through the Earth’s crust at two detectors at the Gran Sasso facility in Italy, some 455 miles away.
This experiment caused a furore in 2011 when it appeared they had detected neutrinos travelling faster than light. It turned out to be a data error and was rather embarrasing for both Cern and the Gran Sasso laboratories.
ISOLDE
Image: Cern
ISOLDE stands for Isotope Separator On-Line DEvice. It is the oldest experiment at Cern, beginning operations as long ago as 1967. It’s purpose was, and is, to study the properties of atomic nuclei. A high-intensity proton beam that could be directed into specially developed targets to yield lots of different atomic fragments.
Different devices could then be used to ionise, extract and separate these different nuclei according to their mass, forming a low-energy beam that could then be delivered to various experimental stations. Thus, the idea of “ISOLDE” was born.
LHC Run 3
This new campaign will be looking for particles that exist at energies the original LHC was not capable of seing, but which the standard model theories suggest should be there
These include up to four particles related to the Higgs bozon, and a seventh quark. The second run of the LHC gave hints of a seventh quark, so they will be looking to see if it is in fact real.
If they find it, they will have to search for an eighth, as all the other six quarks came in pairs. For each new quark, they will also have to hunt for its balancing lepton.
Failed projects
The Superconducting Supercollider had been partially constructed in Texas. It would have been 54 miles in diameter, with an energy of 20 TeV per beam, and was set to be the world’s largest and most energetic particle accelerator. After 14 miles of tunnel were bored, surface buildings constructed and nearly four billion dollars were spent, the project was cancelled in 1993.
Header image: Symmetry Magazine
About the author: Andy Rowlands is a university graduate in space science and British Principia Scientific International researcher, writer and editor who co-edited the new climate science book, ‘The Sky Dragon Slayers: Victory Lap‘
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