APPEAL 10 Future Accelerator Projects

After the Higgs Discovery

Linear Colliders for Higgs Factories!

Philip Burrows

Interim Director,

John Adams Institute for Accelerator Science

Oxford University


My notes from the lecture (if they don’t make sense then it is entirely my fault)

John Adams Institute

A centre of excellence for advanced and novel accelerator technology, providing expertise, research, development and training in accelerator techniques, and promoting advanced accelerator applications in science and society


Oxford University, Royal Holloway, Imperial College

One of two UK national academic centres of excellence in accelerator science, set up in 2004

23 faculties

30 staff

37 PhD students

Research projects at: CERN, DESY, KEK, Daresbury, Diamond, ISIS, CLF …

A comprehensive PhD training programme

Smashing matter apart

We want to see what matter is made of. To do that we need to smash matter apart and look for the building blocks

Basically, take small pieces of matter, accelerate them in opposite directions and then crash them into each other


At the LHC the pieces of matter usually used are protons

Scientific importance of accelerators

30% of physics Nobel Prizes have been awarded for work based on accelerators and an increasing number of non-physics Nobel Prizes have been awarded for work reliant on accelerators!

Accelerator-related Physics Nobel Prizes

1901 Roentgen: X rays

1905 Lenard: cathode rays

1906 JJ Thomson: electron

1914 von Laue: X-ray diffraction

1915 WH+WL Bragg: X-ray crystallography

1925 Franck, Hertz: laws of impact of electrons on atoms

1927 Compton: X-ray scattering

1937 Davisson, Germer: diffraction of electrons

1939 Lawrence: cyclotron

1943 Stern: magnetic moment of a proton

1951 Cockcroft, Walton: artificial acceleration

1959 Segre, Chamberlain: antiproton discovery

1961 Hofstadter: structure of nucleons

1968 Alvarez: discovery of particle resonances

1969 Gell-Mann: classification of el. particles

1976 Richter, Ting: charmed quark

1979 Glashow, Salam, Weinberg: Standard Model

1980 Cronin, Fitch: symmetry violation in kaons

1984 Rubbia, van der Meer: W + Z particles

1986 Ruska: electron microscope

1988 Ledermann, Schwartz, Steinberger: mu nu

1990 Friedmann, Kendall, Taylor: quarks

1992 Charpak: multi-wire proportional chamber

1994 Brockhouse, Shull: neutron scattering

1995 Perl: tau lepton discovery

2004 Gross, Pollitzer, Wilczek: asymptotic freedom

2008 Nambu, Kobayashi, Maskawa: broken symmetries

2013 Englert, Higgs: Higgs boson

Large Hadron Collider (LHC)


The LHC is the best window we have on matter in the universe, at ultra-early times and at ultra-small scales

The new boson discovered 2012


Led to the Nobel Prize in 2013

Before LHC

Large Electron-Positron (LEP): c. 100 GeV electrons + positrons

Super Large Electron-Positron collider?

500 GeV beams? (5 x LEP)

The problem would be synchrotron radiation

LHC: accelerate protons with energy E = 7000 GeV

Synchrotron radiation

Synchrotron radiation (also known as magnetobremsstrahlung radiation) is the electromagnetic radiation emitted when charged particles are accelerated radially, e.g., when they are subject to an acceleration perpendicular to their velocity. It is produced, for example, in synchrotrons using bending magnets, undulators and/or wigglers. If the particle is non-relativistic, then the emission is called cyclotron emission. If, on the other hand, the particles are relativistic, sometimes referred to as ultrarelativistic, the emission is called synchrotron emission. Synchrotron radiation may be achieved artificially in synchrotrons or storage rings, or naturally by fast electrons moving through magnetic fields. The radiation produced in this way has a characteristic polarization and the frequencies generated can range over the entire electromagnetic spectrum which is also called continuum radiation.

Syncradiation was named after its discovery in Schenectady, New York from a General Electric synchrotron accelerator built in 1946 and announced in May 1947 by Frank Elder, Anatole Gurewitsch, Robert Langmuir and Herb Pollock in a letter entitled “Radiation from Electrons in a Synchrotron”. Pollock recounts:

“On April 24, Langmuir and I were running the machine and as usual were trying to push the electron gun and its associated pulse transformer to the limit. Some intermittent sparking had occurred and we asked the technician to observe with a mirror around the protective concrete wall. He immediately signalled to turn off the synchrotron as “he saw an arc in the tube.” The vacuum was still excellent, so Langmuir and I came to the end of the wall and observed. At first, we thought it might be due to Cherenkov radiation, but it soon became clearer that we were seeing Ivanenko and Pomeranchuk radiation.”


The team behind the first observation of man-made Synchrotron radiation at the GE laboratories: Left to Right: Robert Langmuir, Frank Elder, Anatole Gurewitsch, Ernest Charlton and Herb Pollock.


Power lost due to synchrotron radiation is P ~ E 4/r 2 where E = beam energy and r = radius of trajectory

For LEP each electron lost ~ 3 GeV per turn (3%! Lost per turn)

P = 10-6 Watts/electron  –> 18 MW total

–> Must be compensated by accelerating cavities

Suppose we increase LEP beam energy (100 GeV) by factor 5: E –> 500 GeV, in the same tunnel. E increases by factor 5, so P increases by 54 this would give P = 54 x 18 MW = 11 GW!

Compensate by increasing radius r?

You would need 10 x r to reduce P by 100 –> 270km tunnel!


100km tunnel for proton-proton collision would cost 5.5 billion Swiss francs

First purpose-built SR source

SRS Daresbury, UK 1967


The Synchrotron Radiation Source (SRS) at the Daresbury Laboratory in Cheshire, England was the first second-generation synchrotron radiation source to produce X-rays.


Applications of synchrotron radiation

Structures of crystalline materials

Protein structures

Phase transitions

Diffusion in solids

Interfaces in solids

Magnetic properties


Defect structures (stress + fatigue)

X-ray diffraction


Max Theodor Felix von Laue (9 October 1879 – 24 April 1960) was a German physicist who won the Nobel Prize in Physics in 1914 for his discovery of the diffraction of X-rays by crystals. In addition to his scientific endeavours with contributions in optics, crystallography, quantum theory, superconductivity, and the theory of relativity, he had a number of administrative positions which advanced and guided German scientific research and development during four decades. A strong objector to Nazism, he was instrumental in re-establishing and organizing German science after World War II.


Constructive interference:

2 d sin q = n l

X-ray diffraction today


Protein structures


Above right = HIV glycoprotein, above middle = mosquito immune system and above right = yeast enzyme

> 50,000 protein structures solved with X rays (2009)

Diamond: synchrotron source of X-rays


500m circumference

Nobel Prizes based on X-ray work


2009 Chemistry Nobel Prize


Ramakrishnan, Steitz, Yonath

‘studies of the structure and function of the ribosome’

Ribosomes comprise a complex macromolecular machine, found within all living cells, that serves as the site of biological protein synthesis (translation). Ribosomes link amino acids together in the order specified by messenger RNA (mRNA) molecules. Ribosomes consist of two major components: the small ribosomal subunits, which read the mRNA, and the large subunits, which join amino acids to form a polypeptide chain. Each subunit consists of one or more ribosomal RNA (rRNA) molecules and a variety of ribosomal proteins (r-protein or rProtein). The ribosomes and associated molecules are also known as the translational apparatus.

Synchrotron radiation: LHC?

Why isn’t this a problem for LHC?

Remember P ~ ( E/m )4/r2

The mass of a proton is about 2000 times the mass of an electron. This leads to the power lost by the proton is about 2000-4 of the power lost by the electron

Even for LHC, E lost = 70 x LEP, each proton loses only 5 keV per turn (0.000 000 1% negligible!)

The new boson


Finger-printing the new boson

You need to produce a large sample

Is it: The Standard Model Higgs boson? Another type of Higgs boson? Not a Higgs boson at all?

Its “profile” needs to be determined:

Mass; Width; Spin; CP nature; Coupling to fermions (quarks + leptons); Coupling to gauge bosons (W + Z); Yukawa coupling to top quark; Self-coupling –> Higgs potential

The LHC has started this endeavour!

and next ….

Microscope on the new boson


Higgs Factory

e+e- annihilations:


Above left: E > 91 + 125 = 216 GeV; E ~ 250 GeV Above right: E > 91 + 250 = 341 GeV; E ~ 350 – 500 GeV

e+e- colliders

Produce annihilations of point-like particles under controlled conditions:

There is a well-defined centre of mass-energy: 2E

There is complete control of event kinematics:

p = 0, M = 2E

Electron beam(s) are polarised

The experimental environment must be clean

The operation gives us a precision microscope to look for:

masses, decay-modes, couplings, spins, CP properties … of new particles

e+e- annihilations

A beam of electrons is polarised when the electron spins have a preferential orientation. In other words the beams have the same spin direction, either left (L) or right (R)


At these energies, the electrons are like tiny billiard balls

Unfortunately, the Super Large Electron-Positron Collider is not being considered

250 GeV beams? (2.5 x LEP) will give 700MW or synchrotron radiation


After LHC?

Future 100km tunnel???


For high energy electron-positron colliders, the path ahead is … linear

SLAC Linear Collider


c. 50 GeV per beam to study the Z boson in the 1990s

International Linear Collider (ILC)


Compact Linear Collider (CLIC)


The Compact Linear Collider (CLIC) is a concept for a future linear particle accelerator that aims to explore the next energy frontier. CLIC would collide electrons with positrons and is currently the only mature option for a multi-TeV linear collider (about 1.5TeV). The accelerator would be between 11 and 50 km long, more than ten times longer than the existing Stanford Linear Accelerator (SLAC) in California, USA. CLIC is proposed to be built at CERN, across the border between France and Switzerland near Geneva, with first beams starting by the time the Large Hadron Collider (LHC) has finished operations around 2035.

The aim is to investigate SUSY and dark matter

Ingredients for a linear collider


2 x 1010 electrons

Like firing bullets to hit in middle …


Except that …

… it is very difficult

A Higgs and top factory


European particle physics strategy 2013

There is a strong scientific case for an electron-positron collider, complementary to the LHC, that can study the properties of the Higgs boson and other particles with unprecedented precision and whose energy can be upgraded.

The Technical Design Report of the International Linear Collider (ILC) has been completed, with large European participation. The initiative from the Japanese particle physics community to host the ILC in Japan is most welcome, and European groups are eager to participate.

Europe looks forward to a proposal from Japan to discuss a possible participation. It is expected to cost between 5 and 6 billion dollars


CLIC Collaboration January 2019


500 people are in the team

The first stage of CLIC is expected to cost 5.9 billion Swiss francs.

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