The 2016 physics season starts at the LHC
CERN's Large Hadron Collider (LHC) and its experiments are back in action, and UK researchers and colleagues are now taking physics data for 2016 that will give us an improved understanding of fundamental physics.
UK particle physicists have been eagerly awaiting the move up to full energy so that they could get back to working on understanding the fundamental physics of the Universe. During the annual winter break of the LHC the accelerator complex and experiments have been fine-tuned using low-intensity beams and pilot proton collisions, and now the LHC and the experiments are ready to take an abundance of new data.
Following a short commissioning period, the LHC operators will now begin to increase the intensity of the beams so that the machine produces a larger number of collisions.
“For the UK team working on the ATLAS instrument at the LHC our focus now will be on using the larger number of even higher energy collisions to better understand the Higgs boson. Despite confirming its existence back in 2012, there is still a lot for us to learn about the Higgs boson to be able to fully test Peter Higgs' original theory." Dr Victoria Martin, University of Edinburgh Particle Physics Experiment group and a member of the ATLAS team at the LHC.
“The start of this new season of physics at the LHC means that the many UK researchers working both in CERN itself and back in the UK will have much more data to work with – much more of the information they need to start to answer some of the big questions that still remain in physics including why there is a lack of antimatter in the Universe, the nature of dark matter particles and whether Supersymmetry, the theory that predicts the existence of a whole other set of ‘super’ particles, is correct”Prof. John Womersley, particle physicist and Chief Executive of the UK’s Science and Technology Facilities Council (STFC).
The four largest LHC experimental collaborations, ALICE, ATLAS, CMS and LHCb, now start to collect and analyse the 2016 data. Their broad physics programme will be complemented by the measurements of three smaller experiments – TOTEM, LHCf and MoEDAL – which focus with enhanced sensitivity on specific features of proton collisions.
“The restart of the LHC always brings with it great emotion. With the 2016 data, the experiments will be able to perform improved measurements of the Higgs boson and other known particles and phenomena, and look for new physics with an increased discovery potential.” Fabiola Gianotti, CERN Director General and Honorary Professor in the School of Physics & Astronomy.
The Large Hadron Collider
This is the second year the LHC will run at a collision energy of 13 TeV. During the first phase of Run 2 in 2015, operators mastered steering the accelerator at this new higher energy by gradually increasing the intensity of the beams.
Beams are made of “trains” of bunches, each containing around 100 billion protons, moving at almost the speed of light around the 27-kilometre ring of the LHC. These bunch trains circulate in opposite directions and cross each other at the centre of experiments. Last year, operators increased the number of proton bunches up to 2244 per beam, spaced at intervals of 25 nanoseconds. These enabled the ATLAS and CMS collaborations to study data from about 400 million million proton–proton collisions. In 2016, operators will increase the number of particles circulating in the machine and the squeezing of the beams in the collision regions. The LHC will generate up to 1 billion collisions per second in the experiments.
The Higgs boson was the last piece of the puzzle for the Standard Model – a theory that offers us the best description of the known fundamental particles and the forces that govern them. In 2016, the ATLAS and CMS collaborations – who announced the discovery of the Higgs boson in 2012 – will study this boson in depth.
But there are still several questions that remain unanswered by the Standard Model, such as why nature prefers matter to antimatter, and what dark matter consists of, despite it potentially making up one quarter of our universe.
The huge amounts of data from the 2016 LHC run will enable physicists to challenge these and many other questions, to probe the Standard Model further and to possibly find clues about the physics that lies beyond it.
This new physics run with protons will last six months. The machine will then be set up for a four-week run colliding protons with lead ions.
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.
ATLAS is one of the four main experiments at the Large Hadron Collider at CERN. 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 scientific goals for the two experiments 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 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 scientific goals for the two experiments 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.