12 December 2014
British scientists are gearing up for the next running of the world’s biggest science experiment – the Large Hadron Collider at CERN. After a two-year upgrade to nearly double the power of the machine, scientists are hoping to unravel some of the secrets of dark matter.
“We have unfinished business with understanding the universe,” said Professor Tara Shears from Liverpool.
The LHC is the largest and most powerful particle accelerator in the world, and is expected to restart in Spring 2015 for a three-year run of experiments. The whole 27-kilometre long machine is now being cooled to just 1.9 degrees above absolute zero.
The first running of the machine confirmed the existence of the Higgs Boson in 2012, but scientists stress they still need to understand the properties of the important new particle, including how it gives mass to other particles, and whether it fully matches the current models of how the Universe works.
Other big questions in physics that this new run of the LHC might help answer include understanding why there is a lack of antimatter in the Universe, proving the existence of dark matter particles and also a better study of Supersymmetry, the theory that predicts the existence of a whole other set of ‘super’ particles.
There are four main experiments at the Large Hadron Collider at CERN: ALICE, LHCb, CMS and ATLAS.
Professor Tara Shears, who leads the University of Liverpool LHCb group makes it clear that
"We have unfinished business with understanding the universe. We want to see what the new data shows us about antimatter, and why there's so little in the universe. We want to chase the hints we've seen in previous measurements, whose behaviour didn't quite match our expectations, in case these hints turn into discoveries.”
“We've spent the shutdown readying and improving the LHCb detectors so that we can explore this new data with precision.”
Professor John Womersley, particle physicist and Chief Executive of the Science and Technology Facilities Council (STFC) said
“There’s been a huge amount of work done on the LHC over the past two years – for example, every single one of the electrical links between the thousand magnets in the accelerator ring has been reworked.”
“This means that it will be able to operate at almost double the previous beam energy, bringing huge potential for major new discoveries beyond the Higgs boson that was found in 2012. But it also means that the machine that’s now being started up is almost a new LHC, and it’s not a trivial challenge. Nonetheless, everything is on track for the LHC experiments to start collecting data in this new era by May 2015.”
Dr Victoria Martin of Edinburgh University and a member of the ATLAS team said that
“The ATLAS UK team are eagerly anticipating the extra data that LHC Run 2 will provide. Using data from LHC Run 1 we discovered the Higgs boson particle. However only a limited number of Higgs particles were produced and it has not yet been possible to test every prediction made by Peter Higgs and others. The higher energy and more frequent proton collisions in Run 2 will allow us to investigate the Higgs particle in much more detail. Higher energy may also allow the mysterious "dark matter" observed in galaxies to be made and studied in the lab for the first time.”
Professor David Evans leads the University of Birmingham team on the ALICE experiment at CERN and said
“With higher particle beam energies and intensities, Run 2 looks to be even more exciting than the first stage of the LHC. My team has been busy upgrading the Central Trigger Processor, or “electronic brain”, of the ALICE Detector which makes decisions within a tenth of a millionth of a second after each particle collision in order to decide which collisions are interesting and should be recorded.”
Doctor Sudan Paramesvaran from the University of Bristol and based at CERN where he works on the CMS instrument said
“We are all eagerly anticipating the start of Run 2 of the LHC. The full LHC energy in Run 2 will allow us to probe further than ever before in our search for new particles. The new Calorimeter trigger system for CMS, built in the UK, will be essential in handling the huge amount of data we expect".
For the first time on 9 December 2014, the magnets of one sector of the LHC, one eighth of the ring, were successfully powered to the level needed for beams to reach 6.5 TeV, the operating energy for Run 2. The goal for 2015 will be to run with two proton beams in order to produce 13 TeV collisions, an energy never achieved by any accelerator in the past.
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There are four main experiments at the Large Hadron Collider at CERN: ALICE, LHCb, CMS and ATLAS. Each one has been undergoing major preparatory work for run 2, after the long shutdown during which important programmes for maintenance and improvements were achieved. They will now enter their final commissioning phase.
ALICE was built in a cavern 100m below ground near St Genis-Pouilly in France. ALICE is a heavy-ion detector designed to investigate the properties of the Strong Force that keeps particles inside the atomic nucleus together, and how this energy generates mass. It is the force that we know least about.
ALICE recreates conditions that existed only 0.00001 seconds after the Big Bang; temperatures 300,000 times hotter than the Sun and densities 50 times greater than in the core of a neutron star.
LHCb was built in a cavern 100m below ground near Ferney-Voltaire in France. It is investigating the subtle differences between matter and antimatter. One of the most fundamental questions is why is our Universe made of matter? It is widely thought that initially equal amounts of matter and antimatter were created, and currently there is no evidence opposing this.
LHCb studies the decay of particles containing b and anti-b quarks, collectively known as ‘B mesons’. Physicists believe that by comparing these decays, they may be able to gain useful clues as to why nature prefers matter over antimatter.
Like ATLAS, CMS is a general purpose detector designed to investigate a wide range of physics including supersymmetry, extra dimensions and particles that could make up dark matter. The CMS detector is built around a huge solenoid magnet. This takes the form of a cylindrical coil of superconducting cable that generates a field of 4 tesla (about 100,000 times the magnetic field of the Earth). The field is confined by a steel ‘yoke’ that forms the bulk of the detector’s 12,500-tonne weight.
The scientific goals for the two experiments of CMS and ATLAS are the same, but they use different technical solutions. These similar science goals, but different designs allow the two experiments to cross-check results and confirm exciting discoveries such as a Higgs boson.
Like CMS, ATLAS is a general purpose detector designed to investigate a wide range of physics including supersymmetry, extra dimensions and particles that could make up dark matter. The main feature of ATLAS is its enormous magnet system; eight 25m long superconducting magnet coils forming a cylinder around the beam pipe at the heart of the detector. The magnets bend the paths of charged particles to measure their momentum.