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25 Nov 2016
One of the biggest puzzles in physics is that eighty-five percent of the matter in our universe is “dark”: it does not interact with the photons of the conventional electromagnetic force and is therefore invisible to our eyes and telescopes. Although the composition and origin of dark matter are a mystery, we know it exists because astronomers observe its gravitational pull on ordinary visible matter such as stars and galaxies.
Some theories suggest that, in addition to gravity, dark matter particles could interact with visible matter through a new force, which has so far escaped detection. Just as the electromagnetic force is carried by the photon, this dark force is thought to be transmitted by a particle called “dark” photon which is predicted to act as a mediator between visible and dark matter.
Image above: An overview of the NA64 experimental set-up at CERN. NA64 hunts down dark photons, hypothetic dark matter particles. (Image: Maximilien Brice/CERN).
“To use a metaphor, an otherwise impossible dialogue between two people not speaking the same language (visible and dark matter) can be enabled by a mediator (the dark photon), who understands one language and speaks the other one,” explains Sergei Gninenko, spokesperson for the NA64 collaboration.
CERN’s NA64 experiment looks for signatures of this visible-dark interaction using a simple but powerful physics concept: the conservation of energy. A beam of electrons, whose initial energy is known very precisely, is aimed at a detector. Interactions between incoming electrons and atomic nuclei in the detector produce visible photons. The energy of these photons is measured and it should be equivalent to that of the electrons. However, if the dark photons exist, they will escape the detector and carry away a large fraction of the initial electron energy.
Hunting the mysterious dark photon: the NA64 experiment
Video above: View of the NA64 experiment set-up. (Video: Christoph Madsen/Noemi Caraban/CERN).
Therefore, the signature of the dark photon is an event registered in the detector with a large amount of “missing energy” that cannot be attributed to a process involving only ordinary particles, thus providing a strong hint of the dark photon’s existence.
If confirmed, the existence of the dark photon would represent a breakthrough in our understanding the longstanding dark matter mystery.
Meet TIM, the LHC tunnel’s robot
TIM the Robot: Monitoring the LHC tunnel
Video Credits: Noemi Caraban/Ronaldus Suykerbuyk/Christoph Madsen/CERN.
The name’s TIM, Robot TIM – meet the spy patrolling the 27-km tunnel of the Large Hadron Collider (LHC). TIM, the Train Inspection Monorail, is a mini vehicle transporting a set of instruments along tracks suspended from the tunnel’s ceiling. This smart machine is used for real-time monitoring of the LHC tunnel: the tunnel structure, the oxygen percentage, the communication bandwidth and the temperature.
Image above: TIM uses the tracks of the former Large Electron Positron (LEP) monorail. This image from 1991 shows the LEP monorail, which carried materials and workers when the tunnel housed the LEP collider. LEP was closed down in 2000 to make way for the construction of the LHC in the same tunnel. (Image: Patrice Loiez/CERN).
TIM provides visual and infrared imaging of the LHC tunnel and can move up to 6 km/h. It can also pull small wagons for specific tasks.
Two TIM units are currently running in the LHC tunnel, parked in a service tunnel of one of the LHC experiment, waiting for commands.
CERN, the European Organization for Nuclear Research, is one of the world’s largest and most respected centres for scientific research. Its business is fundamental physics, finding out what the Universe is made of and how it works. At CERN, the world’s largest and most complex scientific instruments are used to study the basic constituents of matter — the fundamental particles. By studying what happens when these particles collide, physicists learn about the laws of Nature.
The instruments used at CERN are particle accelerators and detectors. Accelerators boost beams of particles to high energies before they are made to collide with each other or with stationary targets. Detectors observe and record the results of these collisions.
Founded in 1954, the CERN Laboratory sits astride the Franco–Swiss border near Geneva. It was one of Europe’s first joint ventures and now has 22 Member States.
Dark matter: http://home.cern/about/physics/dark-matter
Large Hadron Collider (LHC): http://home.cern/topics/large-hadron-collider
Large Electron Positron (LEP): http://home.cern/about/accelerators/large-electron-positron-collider
For more information about European Organization for Nuclear Research (CERN), Visit: http://home.cern/
Images (mentioned), Videos (mentioned), Text, Credits: CERN/Stefania Pandolfi/Corinne Pralavorio.
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