LHC studies uncover possible evidence of elusive ‘odderon’

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Researchers at the Large Hadron Collider have discovered what could be evidence of a quasiparticle they’ve been chasing for nearly 50 years.

Physicists have been looking for a type of subatomic quasiparticle called an ‘odderon’ since the 1970s, when it was first theorized.

While scientists have previously observed collisions that involve an even number of subatomic particles known as gluons exchanged between protons, the latest findings show potential evidence of an odd number.

The experiment, dubbed TOTEM, was designed to spot protons that are not destroyed in the collisions, but ‘slightly deviated. To do this, the detectors are placed at a few millimetres from the beams of protons that did not interact

According to the researchers, the discovery could help to clear up some of the ‘opaque regions’ in the Standard Model.

‘We’ve been looking for this since the 1970s,’ said Christophe Royon, Foundation Distinguished Professor in the KU Department of Physics & Astronomy.

The experiments at the LHC involved scenarios in which the protons remained intact after the collision.

In all other experiments before this, scientists detected collisions in which protons exchanged an even number of gluons – which act as the ‘glue’ that holds quarks together.

‘The protons interact like two big semi-trucks that are transporting cars, the kind you see on the highway,’ said Timothy Raben, a particle theorist at KU who has worked on the odderon.

‘If those trucks crashed together, after the crash you’d still have the trucks, but the cars would now be outside, no longer aboard the trucks – and also new cars are produced (energy is transformed into matter).’

Researchers at the Large Hadron Collider have discovered what could be evidence of a quasiparticle they’ve been chasing for nearly 50 years. Physicists have been looking for a type of subatomic quasiparticle called an ‘odderon’ since the 1970s, when it was first theorized

Researchers at the Large Hadron Collider have discovered what could be evidence of a quasiparticle they’ve been chasing for nearly 50 years. Physicists have been looking for a type of subatomic quasiparticle called an ‘odderon’ since the 1970s, when it was first theorized

Using higher-energy and more precise collisions than in the past, the researchers detected possible evidence of an odd number of gluons.

The results of the experiments are published pre-print on arXiv and CERN servers in two separate papers.

‘Until now, most models were thinking there was a pair of gluons – always an even number,’ Royon said.

‘Now we measure for the first time the higher number of events and properties and at a new energy.

‘We found measurements that are incompatible with this traditional model of assuming an even number of gluons.

‘It’s a kind of discovery that we might have seen for the first time, this odd exchange of the number of gluons. There may be three, five, seven or more gluons.’

WHAT ARE ELEMENTARY PARTICLES?

Atoms are usually made of protons, neutrons and electrons.

These are made of even smaller elementary particles.

Elementary particles, also known as fundamental particles, are the smallest particles we know to exist.

They are subdivided into two groups, the first being fermions, which are said to be the particles that make up matter.

The second are bosons, the force particles that hold the others together.

Within the group of fermions are subatomic particles known as quarks.

When quarks combine in threes, they form compound particles known as baryons.

Protons are probably the best-known baryons.

Sometimes, quarks interact with corresponding anti-particles (such as anti-quarks), which have the same mass but opposite charges.

When this happens, they form mesons.

Mesons often turn up in the decay of heavy man-made particles, such as those in particle accelerators, nuclear reactors and cosmic rays.

Mesons, baryons, and other kinds of particles that take part in interactions like these are called hadrons.

According to the researchers, the odderon is essentially the total contribution from all types of odd gluon exchange.

This includes three, five, seven, and other odd numbers.

The earlier models assume contributions from all even numbers, such as two, four, six, and so on.

More than 100 physicists from eight countries collaborated on the experiment, which is now said to add new detail to the Standard Model.

‘This doesn’t break the Standard Model, but there are very opaque regions of the Standard Model, and this work shines a light on one of those opaque regions,’ said Raben.

‘These ideas date back to the ‘70s, but even at that time it quickly became evident we weren’t close technologically to being able to see the odderon, so while there are several decades of predictions, the odderon has not been seen,’ Raben said.

Using higher-energy and more precise collisions than in the past, the researchers detected possible evidence of an odd number of gluons. The results of the experiments are published pre-print on arXiv and CERN servers in two separate papers

Using higher-energy and more precise collisions than in the past, the researchers detected possible evidence of an odd number of gluons. The results of the experiments are published pre-print on arXiv and CERN servers in two separate papers

The experiment, dubbed TOTEM, was designed to spot protons that are not destroyed in the collisions, but ‘slightly deviated.

To do this, the detectors are placed at a few millimetres from the beams of protons that did not interact.

They then compared the results with previous measurements made at lower energies.

‘If you go to really high energies, there are signatures of the behaviour of beams collided at a high energy that can be measured,’ said Raben.

‘But there are different types of high-energy growth signatures. Up until now, we’ve only had to think about one type of high-energy growth behaviour.

‘Essentially these quantities might change as a function of the amount of energy. The rho parameter is essentially measuring the ratio of one signature to another of this high energy growth.’





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