Accelerator

A machine in which beams of charged particles are accelerated to high energies. Electric fields are used to accelerate the particles whilst magnets steer and focus them. A collider is a special type of accelerator where counter-rotating beams are accelerated and interact at designated collision points. A synchrotron is an accelerator in which the magnetic field bending the orbits of the particles increases with the energy of the particles. This keeps the particles moving in a closed orbit.

ALICE (A Large Ion Collider Experiment)

One of the four major experiments that uses the LHC.

AMS-IX (Amsterdam Internet Exchange)

The main place in the Netherlands for Internet Service Providers to interconnect and exchange IP traffic with each other at a national or international level.

Annihilation

A process in which a particle meets its corresponding antiparticle and both disappear. The resulting energy appears in some other form: as a different particle and its antiparticle (and their energy), as many mesons, or as a single neutral boson such as a Z boson. The produced particles may be any combination allowed by conservation of energy and momentum.

ANTARES (Astronomy with a Neutrino Telescope and Abyss Environmental Research)

Large area water Cherenkov detector in the deep Mediterranean Sea near Toulon, optimised for the detection of muons resulting from interactions of high-energy cosmic neutrinos.

Antimatter

Every kind of matter particle has a corresponding antiparticle. Charged antiparticles have the opposite electric charge as their matter counterparts. Although antiparticles are extremely rare in the Universe today, matter and antimatter are believed to have been created in equal amounts in the Big Bang.

Antiproton

The antiparticle of the proton.

ATLAS (A Toroidal LHC ApparatuS)

One of the four major experiments that uses the LHC.

BaBar

Detector at SLAC’s B Factory. Named for the elephant in Laurent DeBrunhoff’s children’s books. Operation stopped in 2008.

Baryon

See Particles.

Beam

The particles in an accelerator are grouped together in a beam. Beams can contain billions of particles and are divided into discrete portions called bunches. Each bunch is typically several centimeters long and can be just a few µm in diameter.

Big Bang

The name given to the explosive origin of the Universe.

Boson

The general name for any particle with a spin of an integer number (0, 1 or 2…) of quantum units of angular momentum (named for Indian physicist S.N. Bose). The carrier particles of all interactions are bosons. Mesons are also bosons.

Calorimeter

An instrument for measuring the amount of energy carried by a particle.

Cherenkov radiation

Light emitted by fast-moving charged particles traversing a dense transparent medium faster than the speed of light in

that medium.

CLIC (Compact LInear Collider)

A feasibility study aiming at the development of a realistic technology at an affordable cost for an electron-positron linear collider for physics at multi-TeV energies.

Collider

See Accelerator.

Cosmic ray

A high-energy particle that strikes the Earth’s atmosphere from space, producing many secondary particles, also called cosmic rays.

CP violation

A subtle effect observed in the decays of certain particles that betrays nature’s preference for matter over antimatter.

D0 (named for location on the Tevatron Ring)

Collider detector, studies proton-antiproton collisions at Fermilab’s Tevatron.

Dark matter and dark energy

Only 4% of the matter in the Universe is visible. The rest is known as dark matter and dark energy. Finding out what it consists of is a major question for modern science.

Detector

A device used to measure properties of particles. Some detectors measure the tracks left behind by particles, others measure energy. The term ‘detector’ is also used to describe the huge composite devices made up of many smaller detector elements. Examples are the ATLAS, the ALICE and the LHCb detectors.

Electron

See Particles.

eLISA (evolved LISA)

ESA-only gravitational wave space mission, orbiting around the Sun as a giant equilateral triangle 1 million km on a side. Candidate for launch in 2028.

ET

Einstein Telescope. Design project for a third generation gravitational wave observatory consisting of three underground and typically 10 km long cryogenic xylophone interferometers in a triangular shape.

eV (Electronvolt)

A unit of energy or mass used in particle physics. One eV is extremely small, and units of million electronvolts, MeV, thousand MeV = 1 GeV, or million MeV = 1 TeV, are more common in particle physics. The latest generation of particle accelerators reaches up to several TeV. One TeV is about the kinetic energy of a flying mosquito.

Fermion

General name for a particle that is a matter constituent, characterised by spin in odd half integer quantum units. Named for Italian physicist Enrico Fermi. Quarks, leptons and baryons are all fermions.

Forces

There are four fundamental forces in nature. Gravity is the most familiar to us, but it is the weakest. Electromagnetism is the force responsible for thunderstorms and carrying electricity into our homes. The two other forces, weak and strong, are connected to the atomic nucleus. The strong force binds the nucleus together, whereas the weak force causes some nuclei to break up. The weak force is important in the energy-generating processes of stars, including the Sun. Physicists would like to find a theory that can explain all these forces in one common framework. A big step forward was made in the late 1970s when the electroweak theory uniting the electromagnetic and weak forces was proposed. This was later confirmed in a Nobel prize winning experiment at CERN.

Gluon

See Particles.

Gravitational wave

The gravitational analog of an electromagnetic wave whereby gravitational radiation is emitted at the speed of light from any mass that undergoes rapid acceleration.

Grid

A service for sharing computer power and data storage capacity over the Internet.

Hadron

A subatomic particle that contains quarks, antiquarks, and gluons, and so experiences the strong force (see also Particles).

High-Energy Physics

A branch of science studying the interactions of fundamental particles; called ‘high energy’ because very powerful accelerators produce very fast, energetic particles probing deeply into other particles.

Higgs boson

A particle predicted in 1964 independently by theoreticians Brout, Englert and Higgs in order to explain the mechanism by which particles acquire mass. In 2012 the ATLAS and CMS experiments at the LHC announced the discovery of a particle with mass 125 GeV that fits the properties of this Higgs boson. The particle plays a central role in the Standard Model of elementary particle physics. In 2013 Englert and Higgs received the Nobel Prize for the theoretical discovery of a mechanism that contributes to our understanding of the origin of mass of subatomic particles, and which recently was confirmed through the discovery of the predicted fundamental particle, by the ATLAS and CMS experiments at CERN’s Large Hadron Collider.

HiSPARC (High School Project on Astrophysics Research with Cosmics)

Cosmic ray experiment with schools in the Netherlands.

ILC

International Linear Collider, now under study. A possible future electron-positron accelerator, proposed to be built as an international project.

Kaon

A meson containing a strange quark (or antiquark). Neutral kaons come in two kinds, long-lived and short-lived. The long-lived ones occasionally decay into two pions, a CP-violating process (see also Particles).

KM3NeT (Cubic Kilometre Neutrino Telescope)

European deep sea neutrino telescope with a volume of several cubic kilometres at the bottom of the Mediterranean Sea, distributed over three locations offshore the coasts of France, Italy and Greece

LEP

The Large Electron-Positron collider at CERN which ran until 2000. Its tunnel has been reused for the LHC.

Lepton

A class of elementary particles that includes the electron. Leptons are particles of matter that do not feel the strong force. (See also Particles).

LHC (Large Hadron Collider)

CERN’s biggest accelerator, started in 2008.

HL-LHC (High Luminosity Large Hadron Collider)

Proposed upgrade of CERN’s LHC to increase its luminosity (rate of collisions) by a factor of 10 beyond its design value.

LHCb (Large Hadron Collider beauty)

One of the four major experiments that uses the LHC.

LOFAR (Low Frequency Array)

First radio telescope of a new generation of astronomical facilities, mainly in the Netherlands.

Medipix

A family of photon counting pixel detectors based on the Medipix CMOS read-out chips that can be provided with a signal from either a semi-conductor sensor or ionisation products in a gas volume. The detectors are developed by an international collaboration, hosted by CERN, and including Nikhef. Medipix-3 is the prototype that is currently in the development phase.

Meson

See Particles.

Muon

A particle similar to the electron, but some 200 times more
massive (see also Particles).

Muon chamber

A device that identifies muons, and together with a magnetic system creates a muon spectrometer to measure momenta.

Neutrino

Uncharged, weakly interacting lepton, most commonly produced in nuclear reactions such as those in the Sun. There are three known flavours of neutrino, corresponding to the three flavours of leptons. Recent experimental results indicate that all neutrinos have tiny masses (see also Particles).

NLO (Next-to-Leading Order)

Second-order calculations in perturbative QED and QCD.

NWO

The Netherlands Organisation for Scientific Research funds thousands of top researchers at universities and institutes and steers the course of Dutch science by means of subsidies and research programmes.

Nucleon

The collective name for protons and neutrons.

Particles

There are two groups of elementary particles, quarks and leptons, with three families each. The quarks are named up and down, charm and strange, top and bottom (or beauty). The leptons are electron and electron neutrino, muon and muon neutrino, tau and tau neutrino. There are four fundamental forces, or interactions, between particles, which are carried by special particles called bosons. Electromagnetism is carried by the photon, the weak force by the charged W and neutral Z bosons, the strong force by the gluons and gravity is probably carried by the graviton, which has not yet been discovered. Hadrons are particles that feel the strong force. They include mesons, which are composite particles made up of a quark-antiquark pair, and baryons, which are particles containing three quarks. Pions and kaons are types of meson. Neutrons and protons (the constituents of ordinary matter) are baryons; neutrons contain one up and two down quarks; protons two up and one down quark.

Photon

See Particles.

Pierre Auger Observatory

International experiment in Argentina to track down the origin of ultra-high-energy cosmic rays.

Pion

See Particles.

Positron

The antiparticle of the electron.

Quantum electrodynamics (QED)

The theory of the electromagnetic interaction.

Quantum chromodynamics (QCD)

The theory for the strong interaction analogous to QED.

Quark

The basic building block of matter (see also Particles).

Quark-gluon plasma (QGP)

A new kind of plasma, in which protons and neutrons are believed to break up into their constituent parts. QGP is believed to have existed just after the Big Bang.

RASNIK (Red Alignment System Nikhef)

Optical alignment system where a pattern is projected by a lens on a CCD and deviations measured.

RHIC

Brookhaven’s Relativistic Heavy Ion Collider; began operation in 2000. RHIC collides beams of gold ions to study what the Universe looked like in the first few moments after the Big Bang.

Spectrometer

In particle physics, a detector system containing a magnetic field to measure momenta of particles.

Spin

Intrinsic angular momentum of a particle.

Standard Model

A collection of theories that embodies all of our current understanding about the behaviour of fundamental particles.

STAR

Experiment at RHIC.

String Theory

A theory of elementary particles incorporating relativity and quantum mechanics in which the particles are viewed not as points but as extended objects. String theory is a possible framework for constructing unified theories that include both the microscopic forces and gravity (see also Forces).

Supersymmetry

Supersymmetry (often abbreviated SUSY) is a symmetry that relates elementary particles of one spin to other particles that differ by half a unit of spin and are known as superpartners.

SURFnet

Networking organisation in the Netherlands.

Tevatron

Fermilab’s 2-TeV proton-antiproton accelerator near Chicago, ceased operation in 2011.

Tier 1

First tier (category) in the LHC regional computing centers. Tier 0 is the facility at CERN collecting, reconstructing and storing the data.

Trigger

An electronic system for spotting potentially interesting collisions in a particle detector and triggering the detector’s read-out system.

Vertex detector

A detector placed close to the collision point in a colliding beam experiment so that tracks coming from the decay of a short-lived particle produced in the collision can be accurately reconstructed and seen to emerge from a ‘vertex’ point that is different from the collision point.

Virgo

Detector near Pisa for gravitational waves: a Michelson laser interferometer made of two orthogonal arms, each 3 km long.

W boson

A carrier particle of weak interactions; involved in all electric-charge-changing weak processes.

WIMP

Weakly Interacting Massive Particles are the most compelling candidates for dark matter particles. They can interact with normal matter through the weak nuclear force and through gravity and are often inherent to models extending the Standard Model.

WLCG (Worldwide LHC Computing Grid)

The mission of the WLCG is to provide data-storage and analysis infrastructure for the entire high-energy physics community using the LHC.

XENON

A series of experiments aiming at direct detection of Weakly Interacting Massive Particles (WIMPs). The detectors are located in the Gran Sasso laboratory in Italy and use xenon as the target material.

Z boson

A carrier particle of weak interactions; involved in all weak processes that do not change flavour and charge.