LHC media briefing

This briefing document is supposed to help CERN scientists prepare for interviews and visits. It lists frequently asked questions by journalists and the general public, suggests answers, and provides a chronology of events from 2008, as well as an outlook on the phase we have just entered in which we can expect first results from the LHC to be published.

Please note that these pages only provide suggestions for answers. Authenticity and enthusiasm are key characteristics of CERN and its scientists, so please continue to use your own voice when you reply to questions.

The main objective of the CERN communication strategy for the coming years is to build on the platform created by the public impact of the LHC start-up in 2008 to communicate CERN's key message of basic science as a knowledge and innovation driver.

We want to maintain CERN's position as a world leading centre for basic research, reinforcing awareness of the importance of basic research for society.

In this document

CERN's Key Communication Messages

  • CERN is world's leading centre for basic physics.
  • Basics physics is essential for progress of society.


  • To maintain CERN's reputation as a global laboratory and a world leader in fundamental physics research
  • To foster support for CERN and particle physics
  • To position fundamental science as essential to society
  • To place science on the popular agenda
  • Fundamental science satisfies the basic human instinct to explore
  • Fundamental science is a driving for technical innovation, collaboration and education

Key messages

  • Fundamental science satisfies the basic human instinct to explore the unknown
  • Fundamental science is a driving force for technical innovation, collaboration and education
  • Fundamental science transcends barriers of age, religion, gender and nationality
  • CERN is a world leader in fundamental research
  • The LHC is launching a new era of discovery and understanding of fundamental questions about the Universe
  • CERN physics has the capacity to inspire, and to attract young people into science

Frequently Asked Questions

For general information about CERN and the LHC download the LHC Guide.

What follows is a series of genuine questions that are regularly asked, complete with short answers. These are backed up with longer articles treating the same subject, where they exist. For answers to the question "Isn't it all a bit expensive?" you can draw inspiration from this article in the Guardian: What price the secrets of the Universe?

1) On the first LHC run and future plans

What are the plans for the future?

The LHC will run at an energy of 7 TeV in 2011 and 2012, followed by a long technical stop from 2013. There will also be a short technical stop at the end of 2011. The long run gives the LHC's experiments a good chance of finding new physics in the next two years, before the LHC goes into a long shutdown to prepare for higher-energy running starting 2014.

For more info:

What are the discoveries that can be made with 7-TeV collisions?

Collisions at 7 TeV mark the start of the physics programme of the LHC - at these energies scientists will be able to cross-check data and predictions from previous experiments and potentially discover predicted or unpredicted particles that will help us understand how the universe works. Discoveries will not be made on the first day - science is a long process, and the First Physics day marks the start of an exciting new era in particle physics.

During 2011 and 2012, the experiments will gather enough data to make important analyses or even discoveries. At 7 TeV and the amount of data to be collected over two years scientists at the LHC's experiments will be able to:

  • set the limit for or discover supersymmetric particles up to 700 GeV;
  • improve the exclusion limit of the Higgs - or find it (this will only happen if is heavy; a light Higgs will not be found with (1 fb-1));
  • confirm that quarks are elementary, or discover compositeness;
  • search for new heavy partners to the gauge Z boson, a Z', up to a mass of at least 1.5 TeV;
  • test the structure of spacetime up to a new energy scale, with the potential discovery of large extra dimensions.

What happened during and after the technical stop following the incident from 19 September 2008?

The machine was prepared for running at 3.5 TeV, which involved changing some 4000 connectors of the new Quench Protection System and powering the magnets to 6 kAmps. For a summary of work that was carried out on the LHC, please see the Bulletin article The LHC enters a new phase from 25 January 2010.

A chronology of LHC events

Regarding each of the experiments, please look at their homepages.

2) On the LHC damage and repairs

Why do you need to shut down for a year in 2013? What it due to a design flaw?

The LHC will run through 2011 and 2012 at 7 TeV before shutting down to prepare for higher-energy running.

This change from the original schedule is due to the machine's excellent performance in its first full year of operation. Expected performance improvements in 2011 should increase the rate that the experiments can collect data by at least a factor of three compared to 2010. That would lead to enough data being collected to bring tantalising hints of new physics, if there is new physics currently within reach of the LHC operating at its current energy. However, to turn those hints into a discovery would require more data than can be delivered in one year, hence the decision to postpone the long shutdown. If there is no new physics in the energy range currently being explored by the LHC, running through 2012 will give the LHC experiments the data needed to fully explore this energy range before moving up to higher energy.

Traditionally, CERN has operated its accelerators on an annual cycle, running for seven to eight months with a four- to five-month shutdown each year. The LHC however takes about a month to bring up to room temperature and another month to cool down. A four-month shutdown as part of an annual cycle no longer makes sense for such a machine.

The longer operational cycle of the LHC is good for the experiments. By abandoning CERN's traditional annual cycle the Laboratory is increasing the overall running time and potential for new discoveries over the next three years.

See also:

Why did the repairs take so long?

We had to ensure that such an incident could not happen again. As a result, we have not only repaired the damaged sector, but also installed a very sophisticated monitoring and protection system.

Why didn't you do this before switching on in 2008?

We have had to develop new techniques that were not possible at that time.

Have you found the person responsible for the fault?

We are more interested in moving on than seeking a scapegoat. It is more important to ensure that we've done all that's necessary to ensure that a similar incident cannot reoccur.

Was the breakdown caused by you being too hasty in 2008?

If we had to do it all again, we would probably follow a very similar procedure. We tested every step of the way, and the incident occurred during one of the final tests. You have to remember that the LHC is a prototype. We have learned a painful lesson, and moved on. That is how technological progress is made.

What did the experiments do through 2009?

The experiments are more ready than any experiments in the history of particle physics have ever been. The time has been spent ensuring that the detectors and algorithms are ready for data.

In the following article, reprinted from The Times' Eureka Magazine, CERN's Director for Accelerators and Technology Steve Myers explains what caused the failure in the LHC on September 19, 2008, the repairs that ensued, and why such a failure won't happen again. The original article can be viewed online at: http://www.timesonline.co.uk/tol/news/science/eureka/article6904270.ece

CERN: what went wrong the first time?

The LHC shut down in 2008 when one of 10,000 soldered joints failed. A CERN expert explains why it probably won't again

By Steve Myers, November 2009

How do you know it won't just break again? It's a question I've been asked many times and the short answer is that the Large Hadron Collider is a much better understood and instrumented machine than it was a year ago. For the long answer, we need to understand what actually happened on September 19, 2008.

The original fault was a poor solder splice in a superconducting cable that failed at around 8,000 amps. This generated an electrical arc that perforated the vessel containing the ultra-cold liquid helium; superconductivity being a low-temperature phenomenon. The liquid helium leaked, became gaseous, expanded and thereby generated a high pressure inside the LHC vacuum enclosures. This high pressure resulted in damage to 53 of the machine's 1,600 "arc" magnets. Recovering from this accident required much more than a simple repair: it meant that we had to do some serious re-engineering to make sure that this could never happen again.

A year ago, we didn't think it was possible to monitor for such an event: the precursor of a failure of this type would be a fast increase of an almost vanishingly small electrical resistance across the splice. The resistance seemed too small to measure with sufficient accuracy. However, necessity being the mother of invention, we needed to make it possible. The LHC's new monitoring system is 3,000 times more sensitive than its predecessor, and it's already been tested on two of the machine's eight sectors*. These tests validated a measurement precision of splice resistance to a fraction of a nano-ohm (one billionth of an ohm). The absolute results indicated maximum splice resistances of 1 nano-ohm, 220 times lower than the resistance of the one that failed. Furthermore, after the September incident, using a less precise measurement technique, we found another bad splice. This one had 50 nano-ohms of resistance, and we've been "hard-testing" on a special test bench ever since to try to reproduce the critical failure. The splice quality has not deteriorated in spite of stringent testing, so we are convinced that 50 nano-ohms is safe. A factor of at least 50 is a very comfortable margin. Consequently the probability of a repeat rupture of a splice is vanishingly small. However, zero probability does not exist and risk analysis coefficients are defined by the product of the risk probability and the resulting impact. In our case the impact was high because of the resulting collateral damage to the magnets.

For this reason we have also attacked reduction of the resulting collateral damage. We've added extra pressure relief valves all around the ring so that even in the worst case the pressure build up would be greatly lessened and damage would be limited to the immediate area. The combination of these two measures makes us certain that a repeat of the September 19 incident can never occur.

CERN is usually thought of as a laboratory that pushes the frontiers of physics, but this is not strictly true. Our user community does that, but in order for them to do so, CERN has to push the frontiers of engineering. The calibre of the engineers needed to design, construct and operate a collider such as the LHC is incredibly high. CERN employs and trains some of the best engineers in the world today. This is another reason I'm confident the LHC will work as designed this time. Over the coming months, we'll be strengthening our technical and engineering base, adding to the human capital that has allowed us to recover so rapidly from the September 2008 incident.

All this makes the LHC a better machine than it was a year ago. We've learnt from our experience and engineered the technology that allows us to move on. That's how progress is made. We like to think that we accelerate technical innovation as well as particles.

*Note from November 19, 2009: By the time the first collisions happen in the LHC, the new monitoring system will have been tested and qualified in all eight sectors for the energy at which beams will circulate before collisions.

Did a baguette cause an LHC power cut?

This information is excerpted from the CERN Bulletin article titled The truth about Birds and Baguettes by James Gillies.

On 3 November 2009, a power cut caused by a malfunction in an electrical substation made headlines around the world. Such things happen all the time and the media rarely take notice, but this one was different. The substation in question was one that supplied part of the LHC's cryogenic systems, and the media spotted it instantly.

What's more, the notion that the power cut might have been caused by a piece of bread dropped by a passing bird on the substation in question started to spread. A power cut suddenly became a story too good to ignore. Before you could say 'crumbs', the press office phones were ringing off the hook as journalists demanded to know how it could be that a piece of bread could lay low the world's mightiest machine. Of course, no such thing had happened.

To this day, we do not know what caused the power cut, but it is true that feathers and bread were found at the site. The truth about birds and baguettes is that two sectors of the LHC warmed by a few degrees while the substation was repaired, and were then cooled back to 1.9K. There was no damage, and no delay. Had we been running, we'd have lost a day or two's worth of beam time, which is nothing unusual when operating a frontier research machine like the LHC. Power cuts are, of course, something that the LHC has been designed to cope with, as have all its predecessors.

3) On Safety

Much of the following is taken from http://public.web.cern.ch/public/en/LHC/Safety-en.html

How do you know that the LHC is safe?

The LHC, like other particle accelerators, recreates the natural phenomena of cosmic rays under controlled laboratory conditions, enabling them to be studied in more detail. Cosmic rays are particles produced in outer space, some of which are accelerated to energies far exceeding those of the LHC. The energy and the rate at which they reach the Earth's atmosphere have been measured in experiments for some 70 years. Over the past billions of years, Nature has already generated on Earth as many collisions as about a million LHC experiments – and the planet still exists. Astronomers observe an enormous number of larger astronomical bodies throughout the Universe, all of which are also struck by cosmic rays. The Universe as a whole conducts more than 10 million million LHC-like experiments per second. The possibility of any dangerous consequences contradicts what astronomers see - stars and galaxies still exist.

Will microscopic black holes destroy the Earth?

Nature forms black holes when certain stars, much larger than our Sun, collapse on themselves at the end of their lives. They concentrate a very large amount of matter in a very small space. Speculations about microscopic black holes at the LHC refer to particles produced in the collisions of pairs of protons, each of which has an energy comparable to that of a mosquito in flight. Astronomical black holes are much heavier than anything that could be produced at the LHC.

According to the well-established properties of gravity, described by Einstein's relativity, it is impossible for microscopic black holes to be produced at the LHC. There are, however, some speculative theories that predict the production of such particles at the LHC. All these theories predict that these particles would disintegrate immediately. Black holes, therefore, would have no time to start accreting matter and to cause macroscopic effects.

Although stable microscopic black holes are not expected in theory, study of the consequences of their production by cosmic rays shows that they would be harmless. Collisions at the LHC differ from cosmic-ray collisions with astronomical bodies like the Earth in that new particles produced in LHC collisions tend to move more slowly than those produced by cosmic rays. Stable black holes could be either electrically charged or neutral. If they had electric charge, they would interact with ordinary matter and be stopped while traversing the Earth, whether produced by cosmic rays or the LHC. The fact that the Earth is still here rules out the possibility that cosmic rays or the LHC could produce dangerous charged microscopic black holes. If stable microscopic black holes had no electric charge, their interactions with the Earth would be very weak. Those produced by cosmic rays would pass harmlessly through the Earth into space, whereas those produced by the LHC could remain on Earth. However, there are much larger and denser astronomical bodies than the Earth in the Universe. Black holes produced in cosmic-ray collisions with bodies such as neutron stars and white dwarf stars would be brought to rest. The continued existence of such dense bodies, as well as the Earth, rules out the possibility of the LHC producing any dangerous black holes.

What are strangelets?

Strangelet is the term given to a hypothetical microscopic lump of 'strange matter' containing almost equal numbers of particles called up, down and strange quarks. According to most theoretical work, strangelets should change to ordinary matter within a thousand-millionth of a second. But could strangelets coalesce with ordinary matter and change it to strange matter? This question was first raised before the start up of the Relativistic Heavy Ion Collider, RHIC, in 2000 in the United States. A study at the time showed that there was no cause for concern, and RHIC has now run for eight years, searching for strangelets without detecting any. At times, the LHC will run with beams of heavy nuclei, just as RHIC does. The LHC's beams will have more energy than RHIC, but this makes it even less likely that strangelets could form. It is difficult for strange matter to stick together in the high temperatures produced by such colliders, rather as ice does not form in hot water. In addition, quarks will be more dilute at the LHC than at RHIC, making it more difficult to assemble strange matter. Strangelet production at the LHC is therefore less likely than at RHIC, and experience there has already validated the arguments that strangelets cannot be produced.

What are vacuum bubbles?

There have been speculations that the Universe is not in its most stable configuration, and that perturbations caused by the LHC could tip it into a more stable state, called a vacuum bubble, in which we could not exist. If the LHC could do this, then so could cosmic-ray collisions. Since such vacuum bubbles have not been produced anywhere in the visible Universe, they will not be made by the LHC.

What are magnetic monopoles?

Magnetic monopoles are hypothetical particles with a single magnetic charge, either a north pole or a south pole. Some speculative theories suggest that, if they do exist, magnetic monopoles could cause protons to decay. These theories also say that such monopoles would be too heavy to be produced at the LHC. Nevertheless, if the magnetic monopoles were light enough to appear at the LHC, cosmic rays striking the Earth's atmosphere would already be making them, and the Earth would very effectively stop and trap them. The continued existence of the Earth and other astronomical bodies therefore rules out dangerous proton-eating magnetic monopoles light enough to be produced at the LHC.

Is the LHC being sabotaged from the future?

(adapted from letter to New York Times by Michelangelo Mangano)

The Nielsen/Ninomiya theory is excluded by the fact that cosmic rays hit the Earth's atmosphere at energies equal to and far above what the LHC can achieve. If their hypothesis that the Higgs cannot be produced were correct, then whatever prevents the LHC from starting up would also prevent high-energy cosmic rays colliding with the Earth's atmosphere. This is because those collisions are exactly like those at the LHC, and if the LHC can produce a Higgs, then cosmic rays can do it as well. Since we know that cosmic rays hit the Earth's atmosphere, we know that Nielsen and Ninomiya's ideas are wrong.

Copyright CERN 2008 - Press Office, DG-CO


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