Switch on to the LHC!

The LHC is preparing to collide beams at 3.5 TeV for the first time ever! Be part of the event and follow live what goes on at the world’s most powerful particle accelerator by connecting to LHC1. Hereafter we give you a key to understand the display as well as a typical event display from the ATLAS and CMS experiments.

1. This is the energy of beams. 1 TeV=1000 GeV. The LHC set the energy world’s record of 3.48 TeV per beam, today, 19 March 2010.

2. Intensity of, respectively, B1 (blue) and B2 (red).

3. The information in these boxes can vary. Operators display the graphs that are relevant to the specific operation.

4. Most of the flags are set automatically. They provide a quick summary of the machine status. In order to have collisions the ‘Stable Beams’ flag must be set to green.

5. Here operators write down their messages to the experiments. Often, they write the ongoing activity, followed by the plan for the coming hours.

6. Machine Mode, indicating what the machine is currently doing. Operators can choose among several modes of operation, such as: circulate and dump, inject and dump, cycling, injection of physics beam, injection probe beam, prepare ramp, ramp, stable beams, etc.

7. Progressive number used for archiving purposes.

ATLAS Event Display: A Jet Event at 2.36 TeV

This ATLAS event display shows the production of jets in a proton-proton collision. Jets—sprays of particles —are an indication of a head-on proton collision.

A, B, C: This event display shows three different views of the same collision. View A shows the ATLAS detector from the side; view B shows a beams-eye view; and view C shows the energy deposited in calorimeters.

1. Collision point — The point at which two protons collided in this event.

2. Direction of the particle beams In view A, the proton beams travel horizontally. In view B, the beams travel into and out of the display through the collision point.

3. Trackers — Colored lines radiating from the collision point show the passage of a particle that registered in all three tracking detectors, which measure the momentum of charged particles. Directly above and below the collision point are the pixel detectors; slightly farther away is the Semiconductor Tracker system; in purple is the Transition Radiation Tracker.

4. Central Solenoid Magnet — The Central Solenoid magnet curves the tracks of particles as they pass through the tracking detectors.

5. Liquid argon calorimeter This detector measures the energies of particles such as electrons and photons.

6. Tile calorimeter — This detector measures the energies of hadrons such as protons and neutrons. In both calorimeters, yellow dots in views A and B indicate that a particle has left an energy deposit. In view C, the energy deposits are shown as red (hadronic) and green (electromagnetic) bars. Yellow circles in view C indicate the energy deposited by jets.

7. Muon spectrometer — Yellow dots show deposits of energy by muons in the muon spectrometer. This detector system is only partially shown in this event display.

8. Jet — The white circles show how the same jet appears in views A, B and C.

A detailed explanation can be found here:

CMS Event Display: A Candidate Dimuon Event at 2.36 TeV


This event display illustrates the production of two muons in a proton-proton collision. The paths of the muons are shown by the thin red lines on each screen. The muons left signals that were reconstructed into tracks in the silicon tracker, deposited a little energy in the calorimeters, and passed through the muon chambers.

A, B, C: The event display is divided into different screens to give you different views of the split second when the proton-proton collision occurred.

1. Collision point
— The collision point, or what particle physicists call the interaction point, is where the protons collided in this event. Collisions occur along the beam line at the center of the detector.

2. Beam line — The beam line is the path that protons travel along in opposite directions and into collision.

3. Silicon tracker — The innermost portion of the detector is the silicon tracker, which includes the pixel and silicon strip detectors. The tracker follows the movement of charged particles point by point; these are represented by yellow dots. When we connect the dots we can see the particle track, tracing a particle’s movement.

4. Calorimeters
— Just outside of the tracker are the electromagnetic and hadron calorimeters. When particles strike one or both, they leave an energy deposit. These deposits are represented by the bars just outside of the tracker data. The height of the bar corresponds to the amount of energy deposited.

5. Muon chambers — The third and outermost component of the detector are muon chambers. The chambers are visible as red and blue blocks on screen B, and the chambers through which a particle has passed have been highlighted. Screen C shows only those chambers through which a muon has passed.

6. Muons — The path of the muons can be followed in red from the point of the collision through the tracker and calorimeters to the muon chambers.

A detailed explanation can be found here:

by CERN Bulletin