Results announced by the LHCb experiment at CERN has revealed further tips for phenomena that cannot be explained with our current theory of basic physics.
In March 2020, the same experiment released evidence that particles break one of the basic models of the standard model – our best theory of particles and forces – suggesting the possible existence of new fundamental particles and forces.
Now, further measurements by physicists at Cambridge’s Cavendish Laboratory have found similar effects, raising the bar for new physics.
“The fact that we’ve seen the same effect as our colleagues did in March certainly increases the chances that we’re really on the verge of discovering something new.” – Harry Cliff
The standard model describes all the known particles that make up the universe and the forces through which they interact. It has passed all experimental tests to date, and yet physicists know that it must be incomplete. It does not include gravity, nor can it account for how matter was produced under Big bang, and contains no particles that could explain the mysterious dark matter that astronomy tells us is five times more abundant than the things that make up the visible world around us.
As a result, physicists have long been looking for signs of physics beyond the standard model that can help us solve some of these mysteries.
One of the best ways to search for new particles and forces is to study particles known as beauty quarks. These are exotic cousins to the up and down quarks that make up the core of each atom.
Beauty quarks do not exist in large numbers in the world, as they are incredibly short-lived — surviving on average only a trillion a second before being transformed or decaying into other particles. However, billions of beauty quarks are produced each year by CERN’s giant particle accelerator, the Large Hadron Collider, which is detected by a specially built detector called the LHCb.
The way beauty quarks decay can be affected by the existence of undiscovered forces or particles. In March, a team of physicists at the LHCb published results showing signs that beauty quarks decay to particles called muons less frequently than to their lighter cousins, electrons. This is impossible to explain in the standard model, which treats electrons and muons alike, except that electrons are about 200 times lighter than muons. As a result, beauty quarks should decay to muons and electrons at equal speeds. Instead, physicists at the LHCb found that muon decay occurred only about 85% as often as electron decay.
The difference between the LHCb result and the standard model was about three units with experimental error, or ‘3 sigma’ as it is known in particle physics. This means that there is only about one in a thousand chances that the result is due to a statistical error.
Assuming the result is correct, the most likely explanation is that a new force pulling on electrons and muons of different strengths is disrupting how these beauty quarks decay. To be sure if the effect is real, more data is needed to reduce the experimental error. Only when a result reaches the ‘5 sigma’ threshold, when there is less than one in a million chance that it is due to a random coincidence, will particle physicists begin to regard it as a real discovery.
“The fact that we have seen the same effect as our colleagues did in March certainly increases the chances that we are really on the verge of discovering something new,” said Dr. Harry Cliff of Cavendish Laboratory. “It’s nice to shed a little more light on the puzzle.”
Today’s result examined two new beauty quark decays from the same decay family that were used in the March result. The team found the same effect – the muon decay occurred only about 70% as often as the electron decays. This time the error is larger, which means that the deviation is around ‘2 sigma’, which means that there is a little over 2% chance that it is due to a statistical ingenuity of the data. While the outcome is not crucial in itself, it adds further support to a growing pile of evidence that there are new fundamental forces waiting to be discovered.
“The tension at the Large Hadron Collider is growing, and the upgraded LHCb detector is being turned on and additional data is being collected that will provide the necessary statistics to either claim or refute a major discovery,” said Professor Val Gibson, also of the Cavendish Laboratory. .