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ATLAS Visits

How to visit in person

To schedule an onsite visit to the ATLAS experiment, please contact the CERN Visits Service.

The ATLAS Visitor Center has a permanent exhibit with interactive screens outside the Control Room and a 3D movie which explains how the detector works and why the collaboration pursues its quest for fundamental knowledge. CERN also has two permanent exhibitions Universe of Particles and Microcosm that provide unique experiences in understanding the secrets of matter and exploring the mysteries in our universe.

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ATLAS Virtual Visits

How to visit remotely

An ATLAS Virtual Visit connects a classroom, exhibition or other public venues with scientists at the experiment using web-based video conferencing. It is a chance for you to have a conversation with the scientists working on ATLAS.

Group Visits

For groups of at least 10 visitors, you can schedule a Virtual Visit by completing this form.

Schedule a Group Virtual Visit

Open Visits

We also schedule periodic visits for individuals or small groups to join. You can see a list of upcoming Open Virtual Visits here. Select the one you want and register.

ATLAS Virtual Tours

Studying vision

A team of ATLAS collaborators developed a system that can record the neural activity of retinal cells.

Inspired by the silicon microstrip detector technology employed in ATLAS, the team created an advanced multi-electrode array system that can simultaneously record the neural activity of hundreds of the retinal output (ganglion) cells.

The heart of the system is a two-dimensional array of 512 microscopic electrodes densely packed together in an area of 1.7 mm² (about the size of a pinhead). Over the years, additional designs have been implemented, allowing neurobiologists to study retinal cells with a variety of spatial densities.

This system led to the discovery a new functional type of retinal ganglion cell. They are believed to play a role in the perception of motion. These cells are rare and difficult to spot with traditional one-electrode technology.

Researchers are now applying this ATLAS technology to retinal prosthesis studies, to convey visual information to the brain when photoreceptors are degenerated. But that’s not all – similar technology is now being used to study the electrical activity of neurons in the brain, helping to reveal how visual information is processed and encoded.

HADRON THERAPY

Diamond sensors used in the ATLAS detector have been successfully applied to hadron therapy.

Diamond sensors are made of synthetic diamonds, called CVD (chemical vapours deposition). They are installed in ATLAS’ Beam Conditions Monitor and Diamond Beam Monitor, in the pixel detector region. They have many advantages for their application as beam monitors: increased resistance to radiation, a quicker response time and the ability to operate at room temperature. These qualities make them ideals as tools for hadron therapy. Hadron therapy is a medical treatment that uses charged particles (like protons or carbon ions) to irradiate tumours, killing the cancer cells while trying to spare the surrounding healthy tissues. Diamond sensors are used to precisely monitor the particle beams in hadron therapy, measuring their intensity and time structure.

ULTRASOUND GAS ANALYSIS

Ultrasonic instruments, developed to monitor the composition of gas mixtures in the ATLAS silicon tracker cooling environment, are currently being adapted as tools for clinical anaesthesia.

These devices transmit ultrasonic pulses through a mixture of two gases, measuring their propagation times in opposite directions. Since sound velocity is affected by the composition of the medium, the instrument is then able to estimate the ratio of the gases in the mixture and can simultaneously measure the gas flow rate.

This technology was developed to detect the presence of leaks in the ATLAS inner detector cooling system. This system uses two coolant fluids: octa-fluoropropane (C₃F₈) for the SCT and Pixel sub-detectors and carbon dioxide (CO₂) for the Insertable B-Layer. Surrounding these sub-detectors are volumes of nitrogen that help to minimise the presence of water vapour in the detector.

Using these ultrasonic devices, ATLAS engineers can detect the presence of C₃F₈and CO₂ in the nitrogen volumes, revealing if there are any leaks in the system.

Researchers are now exploring possible biomedical applications. In particular, the device could be used to control the composition of anaesthetic gases in real time. It is especially suitable for a new type of anaesthesia that uses mixtures of xenon and oxygen, which normally require two different measurement techniques to analyse.

MEDICAL IMAGING

3D silicon sensors developed for the ATLAS Insertable B-Layer could have a bright future in medical imaging.

Unlike traditional sensors, the electrodes in 3D sensors are processed inside the silicon bulk instead of being implanted on the wafer’s surface. This particular structure gives them an enhanced resistance to radiation, and for this reason they were developed specifically for the ATLAS pixel region.

If used in medical imaging, one of the most important characteristics of 3D sensors would be their ability to provide a high image resolution with low-dose radiation. This could be beneficial as exposure to X-rays is potentially dangerous and, consequently, the radiation dose should be as low as possible. These sensors could also deliver fast and focussed signals - useful for X-ray imaging and Positron Emission Tomography (PET) - and precise volume definition - needed in micro-dosimetry during cancer therapy.

Scientists are experimenting with other possible applications, including neutron imaging, a scanning technique that uses beams of neutrons instead of X-rays.

SOUND REPRODUCTION

Inspired by ATLAS’ optical metrology technology, a team of researchers developed a new system to recover sound from old records.

In ATLAS’ SemiConductor Tracker there are 16,000 carefully aligned silicon detectors. Their accurate position was obtained thanks to optical metrology tools, which can give measurements with a precision of a few micrometres.

This same technology was applied to audio digitizing by a team of scientists from Lawrence Berkeley National Lab, headed by ATLAS collaborator Carl Haber. They developed a machine (called IRENE) which is able to extract sounds from old audio devices such as phonograph discs and cylinder records. These devices represent sounds as grooves on their surface. Optical metrology was used to reconstruct the exact shape of the grooves and, consequently, to create a digital version of the recording. All this was achieved without actually touching the records, so that there is no risk of damage.

Haber’s team restored many important historical recordings. For instance, thanks to IRENE we were able to hear Alexander Graham Bell’s voice for the first time.

The ATLAS Computing System analyses the data produced by the ATLAS detector

The ATLAS software and computing system processes and stores the vast amounts of collision data collected by the detector. The data are then distributed to physicists at institutes around the world.

All members of the ATLAS Collaboration have equal access possibilities to all ATLAS data

Independently of their geographical location, thanks to the Worldwide LHC Computing Grid. ATLAS computing infrastructure and software are constantly evolving – with the help of members of the Collaboration.

ATLAS records over 10,000 TB of data per year

ATLAS records over 10,000 TB of data per year – that’s equivalent to 320,000 hours of 4K streaming. The data are distributed to over 130 computing centres worldwide – located on every inhabited continent – and filtered according to the needs of individual physics analyses. As part of these analyses, ATLAS processes 25,000 TB of data every week.

The ATLAS computing system uses custom software that converts the raw signals from the detector into information that physicists can study. By piecing together individual detector signals, the software is able to reconstruct the paths of particles, identify their particle type (e.g. electrons or muons) and much more.

Open Software

ATLAS software is public under an APACHE 2.0 license and totals more than 5 million lines of code. It is under constant development by members of the Collaboration, as they implement the latest technologies and analysis techniques.

Selects events with distinguishing characteristics that make them interesting for physics analyses.

ATLAS is designed to observe up to 1.7 billion proton-proton collisions per second, with a combined data volume of more than 60 million megabytes per second. However, only some of these events will contain interesting characteristics that might lead to new discoveries. The Trigger and Data Acquisition system ensures optimal data-taking conditions and selects the most interesting collision events for study.

The billions of collisions in ATLAS have a combined data volume of more than 60 million megabytes per second – that’s equivalent to 5400 simultaneous streams of 4K video. However, only some of these events will contain interesting characteristics that might lead to new discoveries. To reduce the flow of data to manageable levels, ATLAS uses a special event selection system – the “trigger” – which picks events with distinguishing characteristics for physics analyses.

The ATLAS trigger system carries out the selection process in two stages.

One The first-level hardware trigger, constructed with custom-made electronics located on the detector, works on a subset of information from the calorimeters and the Muon Spectrometer. The decision to keep the data from an event is made less than 2.5 microseconds after the event occurs. During this time the event data is kept in storage buffers. If the event is selected it is passed on to the second-level trigger, which can accept up to 100,000 events per second.

Two The second-level software trigger operates from a large farm of about 40,000 CPU cores. In just 200 microseconds, it conducts very detailed analyses of each collision event, examining data from specific detector regions. The second-level trigger finally selects about 1000 events per second and passes them on to a data storage system for offline analysis.

Installing the ATLAS calorimeter — The eight toroid magnets can be seen surrounding the calorimeter that is later moved into the middle of the detector. This calorimeter will measure the energies of particles produced when protons collide in the centre of the detector. (Image: CERN)

Bends particles around the various layers of detector systems

By bending the trajectories of charged particles, ATLAS can measure their momentum and charge. This is done using two different types of superconducting magnet systems – solenoidal and toroidal. These impressive systems are cooled to about 4.5 K (–268°C) in order to provide the necessary strong magnetic fields.

The main sections of the magnet system are: Central Solenoid Magnet, Barrel Toroid and End-cap Toroids.

Central Solenoid Magnet

The ATLAS solenoid surrounds the inner detector at the core of the experiment. This powerful magnet is 5.8 m long, 2.56 m in diameter and weighs over 5 tonnes. It provides a 2 Tesla magnetic field in just 4.5 cm thickness. This is achieved by embedding over 9 km of niobium-titanium superconductor wires into strengthened, pure aluminum strips, thus minimising possible interactions between the magnet and the particles being studied.

Bends charged particles for momentum measurement
5.8 m long, 2.56 m outer diameter, 4.5 cm thick
5 tonne weight
2 tesla (T) magnetic field with a stored energy of 38 megajoules (MJ)
9 km of superconducting wire
Nominal current: 7.73 kiloampere (kA)

Toroid Magnet

The ATLAS toroids use a series of eight coils to provide a magnetic field of up to 3.5 Tesla, used to measure the momentum of muons. There are three toroid magnets in ATLAS: two at the ends of the experiment, and one massive toroid surrounding the centre of the experiment.

At 25.3 m in length, the central toroid is the largest toroidal magnet ever constructed. It is unique in particle physics and an iconic element of ATLAS. It uses over 56 km of superconducting wire and weighs about 830 tonnes. The end-cap toroids extend the magnetic field to particles leaving the detector close to the beam pipe. Each end-cap is 10.7 m in diameter and weighs 240 tonnes

Installation of the first of the big wheels of the ATLAS muon spectrometer, a thin gap chamber (TGC) wheel — The muon spectrometer will include four big moving wheels at each end, each measuring 25 metres in diameter. Of the eight wheels in total, six will be composed of thin gap chambers for the muon trigger system and the other two will consist of monitored drift tubes (MDTs) to measure the position of the muons (Image: CERN)

Identifies and measures the momenta of muons

The outer layer of the ATLAS experiment is made of muon detectors. They identify and measure the momenta of muons – particles similar to electrons but 200 times heavier, which allows them to cross the thick layers of the ATLAS Calorimeters.

Five different detector technologies are used: Thin Gap Chambers, Resistive Plate Chambers, Monitored Drift Tubes, Small-Strip Thin-Gap Chambers and Micromegas.

Precision Detectors

The precision detectors of the Muon Spectrometer are able to determine the position of a muon, to an accuracy of less than a 10th of a millimetre!

Monitored Drift Tube (MDTs) detectors are composed of 3 cm wide aluminium tubes filled with a gas mixture. Muons pass through the tubes, knocking electrons out of the gas. These then drift to a wire at the tube’s centre to induce a signal. Over 380,000 aluminium tubes are stacked up in several layers in order to precisely trace the trajectory of each muon.

Fast-Response Detectors

ATLAS uses fast-response detectors to quickly select collision events that are potentially interesting for physics analysis. They make this decision within 2.5 μs (400,000th of a second).

The Resistive Plate Chambers (RPCs) surround the central region of the ATLAS experiment. They consist of pairs of parallel plastic plates at an electric potential difference, separated by a gas volume. Thin Gap Chambers (TGCs) are found at the ends of the ATLAS experiment and consist of parallel 30 μm wires in a gas mixture. Both chambers detect muons when they ionise the gas mixture and generate a signal.

Micromegas and Small-Strip Thin-Gap Chambers (sTGCs) are two additional detector technologies specially designed for high-intensity LHC collisions. These detectors can track muons in high-density areas on either side of the experiment close to the LHC beam pipe, both quickly and with high precision.

The combined data from fast-response detectors gives a coarse measurement of a muon’s momentum, allowing ATLAS to choose whether to keep or discard a collision event.

Measures the energy a particle loses as it passes through the detector

They are designed to absorb most of the particles coming from a collision, forcing them to deposit all of their energy and stop within the detector. ATLAS calorimeters consist of layers of an “absorbing” high-density material that stops incoming particles, interleaved with layers of an “active” medium that measures their energy.

Electromagnetic calorimeters measure the energy of electrons and photons as they interact with matter. Hadronic calorimeters sample the energy of hadrons (particles that contain quarks, such as protons and neutrons) as they interact with atomic nuclei. Calorimeters can stop most known particles except muons and neutrinos.

The components of the ATLAS calorimetry system are: the Liquid Argon (LAr) Calorimeter and the Tile Hadronic Calorimeter.

Liquid Argon Calorimeter

The Liquid Argon (LAr) Calorimeter surrounds the ATLAS Inner Detector and measures the energy of electrons, photons and hadrons. It features layers of metal (either tungsten, copper or lead) that absorb incoming particles, converting them into a “shower” of new, lower energy particles. These particles ionise liquid argon sandwiched between the layers, producing an electric current that is measured. By combining all of the detected currents, physicists can determine the energy of the original particle that hit the detector.

The central region of the calorimeter is specially designed to identify electrons and photons. It features a characteristic accordion structure, with a honeycomb pattern, to ensure that no particle escapes unchallenged.

To keep the argon in liquid form, the calorimeter is kept at -184°C. Specially-designed, vacuum-sealed cylinders of cables bring the electronic signals from the cold liquid argon to the warm area where the readout electronics are located.

Tile Hadronic Calorimeter

The Tile Calorimeter surrounds the LAr calorimeter and measures the energy of hadronic particles, which do not deposit all of their energy in the LAr Calorimeter. It is made of layers of steel and plastic scintillating tiles. As particles hit the layers of steel, they generate a shower of new particles. The plastic scintillators in turn produce photons, which are converted into an electric current whose intensity is proportional to the original particle’s energy.

The Tile Calorimeter is made up of about 420,000 plastic scintillator tiles working in sync. It is the heaviest part of the ATLAS experiment, weighing almost 2900 tonnes!

Combining two major ATLAS inner detector components — The semiconductor tracker is inserted into the transition radiation tracker for the ATLAS experiment at the LHC. These make up two of the three major components of the inner detector. They will work together to measure the trajectories produced in the proton-proton collisions at the centre of the detector when the LHC is switched on in 2008. (Image: CERN)

It is the first part of ATLAS to see the decay products of the collisions

It is very compact and highly sensitive. It consists of three different systems of sensors all immersed in a magnetic field parallel to the beam axis. The Inner Detector measures the direction, momentum, and charge of electrically-charged particles produced in each proton-proton collision.

The main components of the Inner Detector are: Pixel Detector, Semiconductor Tracker (SCT), and Transition Radiation Tracker (TRT).

Pixel Detector

Located just 3.3 cm from the LHC beam line, the Pixel Detector is the first point of detection in the ATLAS experiment. It is made up of four layers of silicon pixels, with each pixel smaller than a grain of sand. As charged particles burst out from the collision point, they leave behind small energy deposits in the Pixel Detector. These signals are measured with a precision of almost 10 μm to determine the origin and momentum of the particle. The Pixel Detector is incredibly compact, with over 92 million pixels and almost 2000 detector elements.

92 million pixels (92 million electronic channels).
Silicon area approx. 1.9m². 15 kW power consumption
Pixel size 50 x 400μm² for the external layers and 50 x 250 μm²for the innermost layer (IBL)
4-barrel layers with 1736 sensor modules
3 disks in each end-cap with 288 modules

Semiconductor Tracker

The Semiconductor Tracker surrounds the Pixel Detector and is used to detect and reconstruct the tracks of charged particles produced during collisions. It consists of over 4,000 modules of 6 million “micro-strips” of silicon sensors. Its layout is optimised such that each particle crosses at least four layers of silicon. This allows scientists to measure particle tracks with a precision of up to 25 μm - that’s less than half the width of a human hair!

4,088 two-sided modules and over 6 million implanted readout strips (6 million channels)
60m² of silicon distributed over 4 cylindrical barrel layers and 18 planar endcap discs
Readout strips every 80μm on the silicon

Transition Radiation Tracker

The third and final layer of the Inner Detector is the Transition Radiation Tracker (TRT). Unlike its neighbouring sub-detectors, the TRT is made up of 300,000 thin-walled drift tubes (or “straws”). Each straw is just 4 mm in diameter, with a 30 μm gold-plated tungsten wire in its centre. The straws are filled with a gas mixture. As charged particles cross through the straws, they ionise the gas to create a detectable electric signal. This is used to reconstruct their tracks and, owing to the so-called transition radiation, provides information on the particle type that flew through the detector, i.e. if it is an electron or pion.

350,000 read-out channels
Volume 12m³
Straw tubes with 4mm diameter, with centred 0.03mm diameter gold-plated tungsten wire
50,000 straws in Barrel, each straw 144 cm long.
250,000 straws in both endcaps, each straw 39 cm long
Precision measurement of 0.17 mm (particle track to wire)

The first ATLAS inner detector end-cap after complete insertion within the Liquid Argon Cryostat.

The installation of the ATLAS inner detector end-cap C.

Inner — An ATLAS inner detector end-cap is placed in its cryostat. The instrumentation housed inside the inner end-cap must be kept cool to avoid thermal noise. This cooling is achieved on ATLAS by placing the end-cap inside a liquid argon cryostat. The end-cap measures particles that are produced close to the direction of the beam pipe and would otherwise be missed.

This colorful 3D animation is an excerpt from the film "ATLAS-Episode II, The Particles Strike Back." Shot with a bug's eye view of the inside of the detector. The viewer is taken on a tour of the inner workings of the transitional radiation tracker within the ATLAS detector. Subjects covered include what the tracker is used to measure, its structure, what happens when particles pass through the tracker, how it distinguishes between different types of particles within it. (Video: CERN)

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Looking for the extended family of the Higgs boson

Menu of the day: Di-Higgs soup!

ATLAS explores Z boson production with heavy-flavour quarks

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ATLAS Visits

How to visit in person

ATLAS Virtual Visits

How to visit remotely

Group Visits

Open Visits

ATLAS Virtual Tours

Explore ATLAS virtually

Technology Transfer

Studying vision

A team of ATLAS collaborators developed a system that can record the neural activity of retinal cells.

FIND OUT MORE

“What Does the Eye Tell the Brain?...”

“From eye to sight”

“A second chance at sight”

HADRON THERAPY

Diamond sensors used in the ATLAS detector have been successfully applied to hadron therapy.

FIND OUT MORE

“A sparkling tale of spin-off”

ULTRASOUND GAS ANALYSIS

Ultrasonic instruments, developed to monitor the composition of gas mixtures in the ATLAS silicon tracker cooling environment, are currently being adapted as tools for clinical anaesthesia.

FIND OUT MORE

“A combined ultrasonic flow meter ...”

“The cooling capabilities of ...”

“Implementation of Ultrasonic Sensing ...”

MEDICAL IMAGING

3D silicon sensors developed for the ATLAS Insertable B-Layer could have a bright future in medical imaging.

FIND OUT MORE

“3D Silicon Sensors: Design, Large ...”

SOUND REPRODUCTION

Inspired by ATLAS’ optical metrology technology, a team of researchers developed a new system to recover sound from old records.

FIND OUT MORE

“A voice from the past”

“Reconstruction of Mechanically ...”

LEARN MORE

Software & Computing

The ATLAS Computing System analyses the data produced by the ATLAS detector

All members of the ATLAS Collaboration have equal access possibilities to all ATLAS data

ATLAS records over 10,000 TB of data per year

Open Software

PARTNERSHIPS

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Trigger and Data Acquisition

Selects events with distinguishing characteristics that make them interesting for physics analyses.

The ATLAS trigger system carries out the selection process in two stages.

LEARN MORE

Magnet System

Bends particles around the various layers of detector systems

Central Solenoid Magnet

Toroid Magnet

Barrel Toroid

End-cap Toroid

More

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Muon Spectrometer

Identifies and measures the momenta of muons

Precision Detectors

Fast-Response Detectors

Detector Technologies

Resistive Plate Chambers

Thin Gap Chambers

Monitored Drift Tubes

Micromegas

More

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Calorimeter

Measures the energy a particle loses as it passes through the detector

Liquid Argon Calorimeter

Tile Hadronic Calorimeter

More

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The Inner Detector