Science & Environment

Large Hadron Collider can be 'world's biggest rain meter'

LHC diagram
Image caption The LHC ring is 175m below the surface in places

The LHC is not just the world's most powerful particle accelerator, it could also be its biggest rain meter, scientists say.

They are investigating tiny changes in the length of the collider's 27km-circumference ring, which occur on a daily and a seasonal basis.

The short cycle is explained by normal tidal forces.

But the winter-summer pattern which affects the huge underground facility is not so obvious.

Except researchers think they can now show that winter rain and snow is gravitationally pulling on the ring.

"My hypothesis is that in winter there's a lot more water in the ground, and even snow sitting on the ground. So, basically, this mass pulls on the ring. And when that extra mass melts away and evaporates away in summer - the ring stretches a bit," said Rolf Hut from Delft University of Technology, Netherlands.

If that's true, you could use the LHC to study precipitation and other aspects of hydrology - not just the secrets of the Universe.

"I can make a rain gauge out of anything," said Dr Hut. He was speaking here at the European Geosciences Union General Assembly.

Space sensors

Changes in the size of the LHC's ring are known from the behaviour of the beam of particles whizzing around inside it at near-light-speed.

The length of the particles' orbit is fixed and controlled by the collider's operators such as to position the beam in the centre of the ring's vacuum chamber.

An alteration in the circumference will force the particles to move inwards or outwards relative to this centre point.

This movement can be measured with micrometre accuracy and is corrected. The adjustments made by the operators therefore represent a very precise measure of the change in the circumference of the LHC.

This issue was first noticed in the LEP accelerator, which occupied the mighty tunnel under the Franco-Swiss border before the LHC.

The daily changes were quickly attributed to the flexure of the surrounding rock by the Moon's tides, but the longer seasonal cycle could have a number of explanations.

One of these is the change in temperature between summer and winter months: the rock could simply be flexing as it warms and cools. Except, temperatures ought to be pretty stable at the ring's depth, which can reach 175m below the surface.

Image copyright CERN
Image caption The particle beams are carefully managed and kept in the centre of the vacuum chamber

Dr Hut finds a more compelling solution in the observations of the US-German Grace space mission.

This is a pair of satellites that measure the small variations in gravity across the Earth.

The duo are especially good at sensing changes in the mass of water stored in the ground.

"And there's a very nice correlation that when Grace says there's not a lot of mass, not a lot of water, then the LHC is expanding a little bit," explained Dr Hut.

Unfortunately, the view from Grace has quite a low resolution and the LHC hasn't been operating so long that there is much data to drive home the association.

The Delft scientist wants to put some low-cost gravimeters in the LHC to investigate the idea further.

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Media captionRolf Hut: "The Grace satellites track variations in Earth's gravity field"

If the conjecture holds up, it's another example of "gold in the noise" - of one group of scientists finding value in the data that another group ordinarily discards.

And the same may hold true for other big physics experiments, such as the Advanced Ligo laser facilities in the US that have just made the historic first detection of gravitational waves.

"If it's really the amount of water that we're measuring then suddenly we have a 27km-circumference circle that integrates, and that's unique in geoscience," said Dr Hut.

"You either have point measurements that have a footprint of centimetres, metres or tens of meters; or you have a satellite that has a footprint of kilometres.

"Now all of a sudden we could have something on the ground that has a large footprint, and we could use that to help calibrate Grace or future gravity satellites to make them more accurate."

Dr Hut's co-investigators are Jorg Wenninger from Cern (the LHC's home), and Ivo van Vulpen from the University of Amsterdam.

"By the way, the LHC is also a brilliant earthquake detector," said Dr Wenninger. "We saw the Ecuador earthquake (on Saturday) about 20 minutes after it happened (the seismic travel time to Europe)," he told BBC News.

Smashing particles

Image copyright View Pictures
  • Best known for discovering the Higgs Boson, the Large Hadron Collider (LHC) is the world's biggest science experiment.
  • The LHC underwent upgrade work between 2013 and 2015. Now more powerful than ever, it forces particles into high energy collisions and detects the results.
  • Mysterious particles such as pentaquarks, gravitons and dark matter may be waiting to be discovered.

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