Welcome to the Big Bang Experience
A Brief History and Future of the Large Hadron Collider
Dr Stephen Gibson
Royal Holloway University of London, Physics Department
My notes from the lecture (if they don’t make sense then it is entirely my fault)
Perceptions of physicists in the media
The Big Bang Theory: how not to give a public talk:
Personally, I can’t stand the programme. A friend suggested I watch it when she learnt I had a physics degree. I did not find it funny at all. It depicted the stereotypical physicist, all-male and incapable of doing ordinary things.
In reality, physicists are normal people with interests other than physics.
Ok, we are the wrong side of 50 but we both have physics degrees (my husband has a physics PhD). He has a lot of interests besides physics such as music, theatre, literature. My interests besides physics include science fiction (and picking holes in the science), detective stories and music. My plans include making my own jewellery.
A brief history of the Large Hadron Collider
What are we made of?
All the known matter particles
The Standard Model of Particle Physics describes the fundamental building blocks of matter and their interactions:
Why do they exist?
The Higgs Boson was predicted to exist and give mass to the other subatomic particles. The LHC was proposed to hunt for the Higgs Boson – the last missing piece of the puzzle
The Higgs field and boson
The following image seeks to explain the behaviour of the Higgs field and the Higgs particle
Imagine you’re at a Hollywood party. The crowd is evenly distributed around the room, chatting. The room is like space filled with the Higgs field.
When the big star arrives, the people nearest the door gather around him
As he moves through the party, he attracts the people close to him. This increases his resistance to movement. In other words, he acquires mass, just like a particle moving through the Higgs field.
If a rumour crosses the room ….
….it creates the same kind of clustering, but this time among the people themselves. In this analogy, these clusters are the Higgs particles
Due to Einstein’s famous equation, E = mc2, we need high-energy particle collisions to generate massive particles and test the theory.
The Large Hadron Collider
Reusing the existing LEP tunnel for LHC saved the major excavation cost.
The Large Electron-Positron Collider (LEP) was one of the largest particle accelerators ever constructed.
It was built at CERN, a multi-national centre for research in nuclear and particle physics near Geneva, Switzerland. LEP collided electrons with positrons at energies that reached 209 GeV. It was a circular collider with a circumference of 27 kilometres built in a tunnel roughly 100 m underground and passing through Switzerland and France. LEP was used from 1989 until 2000. Around 2001 it was dismantled to make way for the Large Hadron Collider, which re-used the LEP tunnel. To date, LEP is the most powerful accelerator of leptons ever built.
Digging the LEP tunnel in 1988
This accelerator was used for beautiful studies of the Z boson (45.5 GeV per beam)
It managed to create a 104.5 GeV beam, but still not enough energy to find the Higgs boson
Discovered in 1983 by physicists at the Super Proton Synchrotron at CERN, the Z boson is a neutral elementary particle. Like its electrically charged cousin, the W, the Z boson carries the weak force.
The weak force is essentially as strong as the electromagnetic force, but it appears weak because its influence is limited by the large mass of the Z and W bosons. Their mass limits the range of the weak force to about 10-18 metres, and it vanishes altogether beyond the radius of a single proton.
Enrico Fermi was the first to put forth a theory of the weak force in 1933, but it was not until the 1960s that Sheldon Glashow, Abdus Salam and Steven Weinberg developed the theory in its present form, when they proposed that the weak and electromagnetic forces are actually different manifestations of one electroweak force.
By emitting an electrically charged W boson, the weak force can cause a particle such as the proton to change its charge by changing the flavour of its quarks. In 1958, Sidney Bludman suggested that there might be another arm of the weak force, the so-called “weak neutral current,” mediated by an uncharged partner of the W bosons, which later became known as the Z boson.
Physicists working with the Gargamelle bubble chamber experiment at CERN presented the first convincing evidence to support this idea in 1973. Neutrinos are particles that interact only via the weak interaction, and when the physicists shot neutrinos through the bubble chamber they were able to detect evidence of the weak neutral current and hence indirect evidence for the Z boson.
At the end of the 1970s, CERN converted what was then its biggest accelerator, the Super Proton Synchrotron, to operate as a proton-antiproton collider, with the aim of producing W and Z bosons directly. Both types of particle were observed there for the first time in 1983. The bosons were then studied in more detail at CERN and at Fermi National Accelerator Laboratory in the US.
During the 1990s, the Large Electron-Positron collider at CERN and the SLAC Linear Collider in the US produced millions of Z bosons for further study.
Where do we get hadrons?
A proton is the centre of a hydrogen atom.
We start simply with a bottle of hydrogen, H2
Above right shows linac2 at CERN
How can we move particles? For instance, we need to accelerate protons
The particle’s electric charge is used:
A plasma globe or plasma lamp (also called plasma ball, dome, sphere, tube or orb, depending on shape) is a clear glass container filled with a mixture of various noble gases with a high-voltage electrode in the centre of the container.
When voltage is applied, a plasma is formed within the container. Plasma filaments extend from the inner electrode to the outer glass insulator, giving the appearance of multiple constant beams of coloured light
Van de Graaff generator
A Van de Graaff generator is an electrostatic generator which uses a moving belt to accumulate electric charge on a hollow metal globe on the top of an insulated column, creating very high electric potentials.
The Van de Graaff generator was developed as a particle accelerator for physics research; its high potential is used to accelerate subatomic particles to great speeds in an evacuated tube. It was the most powerful type of accelerator of the 1930s until the cyclotron was developed. Van de Graaff generators are still used as accelerators to generate energetic particle and X-ray beams for nuclear research and nuclear medicine.
The Westinghouse Atom Smasher, the 5 MeV Van de Graaff generator built in 1937 by the Westinghouse Electric company in Forest Hills, Pennsylvania
Van de Graff generator can accelerate tin foil pastry cases
It can produce a 20000Vcm-1 electromagnetic spark
Salad Bowl Accelerator https://www.youtube.com/watch?v=RiAWrH3-xFk&t=171s
A proton can move 11000 times a second at the LHC running at 7TeV
Charge-discharge experiment https://www.youtube.com/watch?v=_aUfss0SyRY
There used to be a Van de Graff generator at Oxford
At the LHC a wave is used to launch particles
Chambers along the LHC use radio waves to pass energy to the protons as they hurtle past, making them move faster and faster. Then, at four points along the LHC tunnel, the bunches of protons – each containing 100bn particles – are made to cross and collide.
Vortex cannon – Make your own! https://www.sciencefriday.com
Trapping a sound wave
The Kundt’s tube resonator
Kundt’s tube is an experimental acoustical apparatus invented in 1866 by German physicist August Kundt for the measurement of the speed of sound in a gas or a solid rod. The experiment is still taught today due to its ability to demonstrate longitudinal waves in a gas (which can often be difficult to visualise). It is used today only for demonstrating standing waves and acoustical forces.
The LHC traps an em wave in the radio frequency cavity. There are eight of them
LHC Radio Frequency Cavity
The standing wave allows the particle to accelerate. The particle acts like a surfer
The LHC uses eight super-cooled cavities per beam, at 4.5 K — the LHC magnets use superfluid helium at 1.9 K.
Every time a proton passes through the cavities it receives an extra energy: 8 x 2 MV = 16 MeV
Each proton does 11,245 laps of the LHC per second, and it takes 28 minutes to ramp up the energy to 6,500 MeV.
Accelerating gradient is 5 MV/m at 400 MHz
Credit to Graeme Burt, Lancaster
Riding the wave
DC voltage (above left) Radio frequency cavity (above right)
LHC superconducting magnets
To keep the beam on track, the particle beams are steered using strong, 8 Tesla, superconducting magnets
Stored LHC beam energy
The individual 7 TeV energy of each proton is tiny:
• 1 TeV is about the energy of motion of a flying mosquito
• There are over 300,000,000,000,000 protons per beam.
• This gives an enormous stored beam energy: 362 MJ
• Equivalent to a 200 m long TGV train at around 150 km/h
• The energy could melt nearly one tonne of copper
Collimation at HL-LHC
A collimator is a device which narrows a beam of particles or waves. To narrow can mean either to cause the directions of motion to become more aligned in a specific direction (i.e., make collimated light or parallel rays), or to cause the spatial cross-section of the beam to become smaller (beam limiting device).
The High Luminosity Large Hadron Collider (HL-LHC; formerly SLHC, Super Large Hadron Collider) is an upgrade to the Large Hadron Collider started in June 2018 that will boost the accelerator’s potential for new discoveries in physics, starting in 2026. The upgrade aims at increasing the luminosity of the machine by a factor of 10, up to 1035 cm−2s−1, providing a better chance to see rare processes and improving statistically marginal measurements.
LHC magnet quench incident
On the 19th September 2008 (9 days after the first operation)
An electrical fault caused a puncture of the cooling apparatus
6 tonnes of helium evaporated and there was an explosion
53 magnets were damaged
The LHC restarted on the 20th November 2009
Let’s make a cloud
Boiling water is poured into a container of liquid nitrogen
How do we accelerate particles?
The “balls in a bin” demonstration simulates high energy collisions
In particle accelerators the speed of the particles is increased by using electric fields – this is the case whether the accelerator is a synchrotron in a lab, a linear particle accelerator in a hospital or the Large Hadron Collider.
Protons colliding in ATLAS
The beams of protons arrive at ATLAS
Protons colliding at ATLAS
23 collisions produce energy that generates new particles, which then decay
Construction of the ATLAS particle tracker in UK and CERN
Installing delicate fibres inside the centre of ATLAS
Beam arrives in ATLAS
A Higgs Event
On the 4th of July 2012, it was announced that a 5s Higgs-like boson was found
5 sigma is a measure of how confident scientists feel their results are. If experiments show results to a 5 sigma confidence level, that means if the results were due to chance and the experiment was repeated 3.5 million times then it would be expected to see the strength of conclusion in the result no more than once.
So, what’s the LHC doing now?
Every year, we take more particle collision data to measure the properties of the Higgs Boson and search for exciting exotic physics [Dark Matter, Extra Dimensions, Super symmetry]
Processes are very rare, so we need lots of collisions = luminosity!
160 fb-1 achieved in L
The future: High Luminosity LHC
LHC will be upgraded in 2025. To provide more collisions
Crab Cavities for fast beam rotation
The crab cavities, a new technology to brighten up the future, will play an important role in the High-Luminosity LHC
The beams in the LHC are made of bunches, each containing billions of protons. They are similar to trains with carriages full of billions of passengers. In the LHC, the two counter-circulating proton beams meet at a small crossing angle at the collision point of the experiments.
What makes the crab cavities special is their ability to “tilt” the proton bunches in each beam, maximising their overlap at the collision point. Тhis way every single proton in the bunch is forced to pass through the whole length of the opposite bunch, which increases the probability that it will collide with another particle. After being tilted, the motion of the proton bunches appears to be sideways – just like a crab.
How to measure the rotation of the beam?
Frequency scanning interferometry was chosen for this task, whereby a laser beam is sent inside the cryomodule and reflected off several reflectors placed on the cavity interfaces to track their movements. The optical path of the measurement beam is then compared with a beam from a reference interferometer, offering absolute interferometric distance measurements with sub-micrometre precision.
RHUL has developed detailed models to simulate how particles travel around LHC
Future Circular Collider
The Future Circular Collider (FCC) is a conceptual study that aims to develop designs for a post-LHC particle accelerator with an energy significantly above that of previous circular colliders (SPS, Tevatron, LHC). After injection at 3.3 TeV, each beam would have a total energy of 560 MJ. At collision energy of 100 TeV, this increases to 16.7 GJ. These total energy values exceed the present LHC by nearly a factor of 30.
Reuse the LHC as an injector for an 80 – 100 km accelerator: the FCC
Design studies show:
• collision energy of 80 – 100 TeV
• stored beam energy = 8.5 GJ, equivalent to Airbus A380 at 850 km/h
Future Circular Collider hh: 100 TeV pp collider
Future Circular Collider e+e- collider
Applications of Accelerators
Low energy accelerators
• Diamond light source (3 GeV)
• ISIS (800 MeV proton synchrotron on target)
Diamond Light Source (or Diamond) is the UK’s national synchrotron light source science facility located at the Harwell Science and Innovation Campus in Oxfordshire. Its purpose is to produce intense beams of light whose special characteristics are useful in many areas of scientific research. In particular it can be used to investigate the structure and properties of a wide range of materials from proteins (to provide information for designing new and better drugs), and engineering components (such as a fan blade from an aero-engine) to conservation of archaeological artefacts (for example Henry VIII’s flagship the Mary Rose).
Of approximately 70 dedicated synchrotron facilities in the world, Diamond (3 GeV) is the largest medium energy synchrotron. The four larger facilities are classed as high energy.
• Proton therapy (~320 MeV)
In the field of medical procedures, proton therapy, or proton radiotherapy, is a type of particle therapy that uses a beam of protons to irradiate diseased tissue, most often in the treatment of cancer. The chief advantage of proton therapy over other types of external beam radiotherapy is that as a charged particle the dose is deposited over a narrow range of depth, and there is minimal entry, exit, or scattered radiation dose.
• Industrial applications (~MeV range)
• Medical isotope production
12 March 2019 is the 30 year anniversary of the invention of the Web @ CERN by UK Physicist, Tim Berners-Lee