Dark matter appears to dictate the gravitational effects of rotating galaxies and holds a majority stake in the universe at large. Physicists estimate up to 85 percent of the cosmos is built from the mystery substance whereas ordinary or baryonic matter – the kind we are built from – only accounts for about five percent. Despite this certainty, no one has ever been able to directly observe dark matter in the universe and there is no real consensus on what it is or how it works. Because of this, the hunt for dark matter is one of the most exciting and pressing cosmological conundrums scientists worldwide are hoping to solve.

At CERN in Geneva, Switzerland, the Large Hadron Collider (LHC) particle accelerator could be one of the tools used to detect the dark matter surrounding us.

Running 328ft (100m) underground beneath France and Switzerland, the LHC accelerates beams of proton particles to near the speed of light before colliding them at seven incredible machines.

The LHC’s most famous experiments are ATLAS and CMS, which independently and yet collaboratively confirmed the discovery of the Higgs Boson particle in 2012.

But another of the LHC’s experiments, the Large Hadron Collider beauty experiment (LHCb), is making its own leaps and bounds towards explaining the universe on the smallest scale imaginable.

Dark Matter: The LHCb experiment at CERN

Dark Matter: The LHCb experiment is one of seven particle detectors at CERN’s LHC (Image: [email protected])

Unlike the particle detectors of ATLAS and CMS, which create new particles from proton collisions, LHCb is concerned with the minute differences between particles of matter and antimatter.

Mark Williams, a CERN physicist from the University of Manchester Particle Physics Research Group, likened the work done by ATLAS and CMS to watching a ship slowly disappear over the horizon.

The LHCb on the other hand, observes the motions of the waves and the slight differences caused by the ship’s journey.

The physicist, who is a Royal Society University Research Fellow with the University of Manchester, told Express.co.uk: “This allows us to see over the horizon and what’s actually happening, is we’re producing these new particles virtually and they survive for a very short time and then decay.

“But those virtual reactions can affect things like the lifetime, or masses or symmetries of processes that we’re measuring.”

So how does the question of dark matter fit into the work done by the LHCb and is there any hope for its eventual discovery?

According to Dr Williams, tracking down the elusive substance is not as easy as postulating the existence of a new particle, which we are yet to detect.

Dark matter does not appear to interact with the electromagnetic force, meaning it does not emit or reflect light, making it virtually impossible to detect.

Instead, what scientists can do is assume a broader theory of particle physics, which incorporates particles whose interactions are too weak to be immediately evident.

We’re scientists, not philosophers, so we have to make testable predictions

Mark Williams, LHCb experiment at CERN

Such a broader theory, for instance, could oppose the widely accepted Standard Model of particle physics, which categorises the fundamental building blocks of the universe into fermions, such as electrons and quarks, and bosons such as photos and gluons.

Dr Williams said: “Supersymmetry is a good example. This normally has a very light particle that everything will decay into but which can’t decay into anything else so it’s stable, much like an electron is stable, and which only interacts very weakly with the other particles and the non-supersymmetry particles in our universe.

“These kinds of theories naturally give you a dark matter candidate and if you can demonstrate that these theories are correct, then you can start to characterise them and you can give confidence that there is a dark matter candidate.

Dark matter at CERN: LHCb experiment

Dark matter: The incredible machine detects minute differences between matter and antimatter (Image: CERN)

Dark matter at CERN: Pentaquark particle at LHCb

Dark matter: The LHCb discovered the short-lived pentaquark particles this year (Image: CERN)

“For these very rare processes, the presence of supersymmetric particles in these virtual quantum loops can really change the prevalence of decays.”

But Supersymmetry is only one of many theoretical candidates hoping to explain the nature of dark matter.

One such theory, proposed by the late theoretical physicist Stephen Hawking, proposed dark matter is the remnants of primordial dark holes peppered throughout the cosmos.

Another theory recently postulated by US astrophysicist Paul Sutter, suggests dark matter can be explained by axions – a theoretical particle, which is yet to be discovered.

Whatever the case may be, Dr Williams argued the theories and their effects have to be observable in one way or another in our universe to be confirmed.

He said: “There’s no point in postulating a theory, which cannot be tested. We’re scientists, not philosophers, so we have to make testable predictions.”

Fellow colleague Dr Sarah Williams, who works on CERN’s ATLAS experiment, recently spoke to Express.co.uk about one of these theories and how the Higgs Boson discovery could be a portal to dark matter.

The LHCb is currently silent and undergoing a raft of crucial repairs, upgrades and maintenance procedures.

Dark matter at CERN: Large Hadron collider

Dark matter: The LHC’s tunnels run underneath Switzerland and France (Image: SEBASTIAN KETTLEY)

The LHC at CERN operates on a three-year cycle of proton acceleration, followed by a cool down period of two years, during which thousands of engineers descend into the tunnels to upgrade and maintain the accelerator and its seven experiments.

The Hadron Collider will kick back into work in the spring of 2021 for so-called Run 3.

But the data collected during the LHCb’s previous runs has already led to the incredible discovery of the pentaquark – a subatomic particle first theorised in the 1960s – in March this year.

In the same month, the LHCb experiment observed CP violation in charm decays, an accomplishment which the CERN Courier described as a “milestone” in particle physics.

When the LHC is powered up again in 2021, Dr Williams said the LHCb will be more efficient, more precise and better geared to understand how our universe operates.

Hopefully, this will help physicists hone in on the mysterious processes behind dark matter.

source: express.co.uk


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