COLLIDERS FOR HIGH ENERGY PHYSICS

W. C. MadusankaDept. Of PhysicsUniversity of Ruhuna

Content IntroductionParticle acceleratorsColliders CM EnergyLuminosityHistoryPast CollidersPresent Colliders Future Colliders References

IntroductionParticle accelerators have been widely

used for physics research since the early 20th century and have greatly progressed both scientifically and technologically since then.

To gain an insight into the physics of elementary particles, one accelerates them to very high kinetic energy, let them impact on other particles, and detect products of the reactions that transform the particles into other particles.

Particle acceleratorsParticle accelerators are devices that

accelerate charged particles using electromagnetic fields.

Particle accelerators can be split into two fundamental types, electrostatic accelerators and oscillating field accelerators.◦ Electrostatic accelerators : Make use of an

electrostatic field. Electrostatic fields are simply electric fields that do not change with time.

◦ Oscillating field accelerator : Requires electric fields that periodically change with time.

Particle accelerators (cont)Particle accelerators come in many different shapes

and sizes and they are used for many different things.

According to shape there are two main types of particle accelerators, straight line(linear) and circular (cyclic/ring accelerators).

1 Straight Line

1.1 Linear

1.2 Tandem Electrostatic

2 Circular

2.1 Cyclotron

2.2 Synchrocyclotron

2.3 Betatron

2.4 Synchrotron

Particle accelerators (cont)But they all have one thing in common - they

accelerate charged particles.These machines use electric fields to

accelerate particles.   A lot of particle accelerators accelerate

fundamental particles like protons and electrons, but there are also accelerators which accelerate ions (ions are atoms with some electrons removed or added to make them charged).

The most famous application of particle accelerator is the collider.

Colliders A collider is a type of particle accelerator

involving directed beams of particles. Colliders may either be ring accelerators or

linear accelerators, and may collide a single beam of particles against a stationary target or two beams head-on.

As a research tool in particle physics, accelerating particles to very high kinetic energy and letting them impact other particles.

Analysis of the by-products of these collisions gives scientists good evidence of the structure of the subatomic world and the laws of nature governing it.

Colliders (cont)

Fixed Target Colliding beam

A beam of particles (the projectiles) is accelerated with a particle accelerator, and as collision partner, one puts a stationary target into the path of the beam. ◦ SLC

◦ TESLA

◦ CLIC

Two beams of particles are accelerated and the beams are directed against each other, so that the particles collide while flying in opposite directions. ◦ Large Electron–Positron

Collider

◦ Large Hadron Collider

To do such experiments there are two possible setups:

CM Energy The center of mass (CM) energy Ecm for a head-on

collision of two particles with masses m1, m2 and energies E1 and E2 is

For many decades, the only arrangement of accelerator experiments was a fixed target setup.

In this case, as follows from above Eq. , for high energy accelerators E >> mc2, the CM energy is Ecm≈ (2Emc2)1/2.

◦ For example, E=1000 GeV protons hitting stationary protons mc2 ≈ 1 GeV can produce reactions with about 43 GeV energy.

2/1422

22

421

21

422

2121 ]2)(2[ cmEcmEcmmEEEcm

CM Energy (cont) In colliding beam set-up, has much higher

center of mass energy, Ecm ≈ 2(E1E2)1/2.

◦ In the case of two equal masses of particles (e.g. protons and protons, or protons and antiprotons) colliding with the same energy E of 1000 GeV, one gets Ecm=2E or 2000 GeV.

Such an obvious advantage led to the first practical proposals of colliding-beam storage rings in the late 1950’s.

LuminosityLuminosity (L) is the ratio of the number of

events detected (N) in a certain time (t) to the interaction cross-section (σ).

A related quantity is integrated luminosity (Lint), which is the integral of the luminosity with respect to time.

The luminosity and integrated luminosity are useful values to characterize the performance of

a particle accelerator.

History The first colliding lepton beam facilities were

built in the early 1960s almost simultaneously at three laboratories: ◦ e-e+ colliders AdA at the Frascati laboratory near Rome in Italy,

◦ the VEP-1 collider in the Novosibirsk Institute of Nuclear Physics (USSR)

◦ the Princeton-Stanford Colliding Beam Experiment at Stanford (USA).

Their center of mass energies were 1 GeV or less.

In 1966, work began on the Intersecting Storage Rings at CERN (Switzerland) , and in 1971, this collider was operational.◦ The ISR was a pair of storage rings that accumulated particles

injected by the CERN Proton Synchrotron.

This was the first hadron (proton-proton) collider.

Center of mass energy eventually reached 63 GeV.

History (cont) The first linear collider was the e-e+ SLAC Linear

Collider (SLC) constructed at Stanford in the late 1980’s◦ The experimental physics program using the SLC started

with the MarkII detector in 1989, which demonstrated that same year the first evidence that only three families of matter particles exist. 

History (cont)

The energy of colliders has been increasing over the years as demonstrated in Figure.

Past, present and future collidersPast, present and possible future colliders; hadron colliders are in bold, lepton colliders in Italic, facilities under construction or in decisive design and planning stage are listed in parenthesis (…)

Past CollidersLarge Electron–Positron Collider (CERN,1989 – 2000)

The Large Electron–Positron Collider (LEP) was one of the largest and powerful particle accelerator of leptons ever built.

It was built at CERN, a multi-national centre for research in nuclear and particle physics near Geneva, Switzerland.

LEP was a circular collider with a circumference of 27 km built in a tunnel roughly 100 m underground and passing through Switzerland and France.

It was used from 1989 until 2000. When the LEP collider started operation in August

1989 it accelerated the electrons and positrons to a total energy of 45 GeV each to enable production of the Z boson, which has a mass of 91 GeV.

LEP (cont)

The accelerator was upgraded later to enable production of a pair of W bosons, each having a mass of 80 GeV.

LEP collider energy eventually topped at 209 GeV. At the end of 2000, LEP was shut down and then

dismantled in order to make room in the tunnel for the construction of the Large Hadron Collider (LHC).

Past Colliders (cont)Tevatron (Fermilab, 1983–2011)

Tevatron (cont)

The Tevatron was a circular particle accelerator in the United States, at the Fermi National Accelerator Laboratory (also known as Fermilab), just east of Batavia, Illinois.

The second highest energy particle collider in the world after the Large Hadron Collider (LHC).

The Tevatron was a synchrotron that accelerated protons and antiprotons in a 6.86 km ring to energies of up to 1 TeV, hence its name.

Completed in 1983 at a cost of $120 million and significant upgrade investments were made in 1983–2011.

The main achievement of the Tevatron was the discovery in 1995 of the top quark—the last fundamental fermion predicted by the standard model of the particle physics.

Present Colliders

The Large Hadron Collider (CERN,1998 –201?)

LHC (cont)

The Large Hadron Collider (LHC) is the world's largest and most powerful particle collider, built by the European Organization for Nuclear Research (CERN).

The LHC was built in collaboration with over 10,000 scientists and engineers from over 100 countries, as well as hundreds of universities and laboratories.

The collider is contained in a circular tunnel, with a circumference of 27 km, at a depth ranging from 50 to 175 metres underground.

Proton–proton collisions are the main operation mode.

The LHC operated at 3.5 TeV per beam in 2010 and 2011, and at 4 TeV in 2012.

LHC (cont)

The discovery of a particle matching the Higgs boson was confirmed by data from the LHC in 2013.

The LHC went into shutdown for upgrades to increase beam energy to 6.5 TeV per beam, with reopening planned for early 2015.

Future CollidersInternational Linear Collider (ILC,2015-

202?)

ILC (cont)

The International Linear Collider (ILC) is a proposed linear particle accelerator.

It is planned to have a collision energy of 500 GeV initially, with the possibility for a later upgrade to 1000 GeV (1 TeV).

The host country for the accelerator has not yet been chosen, and proposed locations are Japan, Europe (CERN) and the USA (Fermilab).

Japan is considered the most likely candidate, as the Japanese government is willing to contribute half of the costs, according to the coordinator of study for detectors at the ILC .

Construction could begin in 2015 or 2016 and will not be completed before 2026.

The ILC would collide electrons with positrons.

ILC (cont)

It will be between 30 km and 50 km long, more than 10 times as long as the 50 GeV Stanford Linear Accelerator, the longest existing linear particle accelerator.

At the ILC physicists hope to be able to:◦ Measure the mass, spin, and interaction strengths of the

Higgs boson◦ If existing, measure the number, size, and shape of any

TeV-scale extra dimensions◦ Investigate the lightest supersymmetric particles,

possible candidates for dark matter

References http://en.wikipedia.org/wiki/Collider, accessed on

10/08/2014 High energy particle colliders: past 20 years, next 20

years and beyond, VLADIMIR D. SHILTSEV http://arxiv.org/ftp/arxiv/papers/1409/1409.5464.pdf ,

accessed on 10/08/2014 http://en.wikipedia.org/wiki/

Particle_accelerator#Oscillating_field_particle_accelerators, accessed on 11/08/2014

http://www.accelerators-for-society.org/about-accelerators/index.php?id=21 , accessed on 11/08/2014

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