June 10, 2023

The Standard Model of Particle Physics May Be Broken – A Physicist at the Large Hadron Collider Explains

We often talk about development in terms of finding new particles, and this is frequently real. Studying a brand-new, very heavy particle assists us see underlying physical procedures– often without irritating background noise. Comprehensive research studies from the LHCb experiment discovered that a particle understood as a charm quark (quarks make up the protons and neutrons in the atomic nucleus) “decomposes” (falls apart) into an electron much more often than into a muon– the electrons much heavier, but otherwise similar, sibling. According to the basic design, this shouldnt happen– hinting that new particles or even forces of nature may affect the procedure.
The newest surprising outcome is a measurement of the mass of a fundamental particle called the W boson, which carries the weak nuclear force that governs radioactive decay.

A recent series of precise measurements of already known, basic particles and processes have actually threatened to shake up physics.
As a physicist working at the Large Hadron Collider (LHC) at CERN, one of the most regular questions I am asked is “When are you going to find something?” Resisting the temptation to sarcastically reply “Aside from the Higgs boson, which won the Nobel Prize, and a lot of brand-new composite particles?” I understand that the factor the question is postured so often is down to how we have actually depicted progress in particle physics to the wider world.
We often discuss development in regards to discovering new particles, and this is regularly real. Studying a new, extremely heavy particle assists us see underlying physical processes– often without frustrating background sound. That makes it simple to describe the worth of the discovery to the public and political leaders.
Just recently, nevertheless, a series of accurate measurements of ordinary already known, standard particles and procedures have threatened to shake up physics. And with the LHC getting prepared to perform at greater energy and intensity than ever previously, it is time to start going over the implications widely.

The storage-ring magnet for the Muon G-2 experiment at Fermilab Credit: Reidar Hahn, Fermilab.
In truth, particle physics has actually always proceeded in 2 ways, of which new particles is one. The other is by making really exact measurements that evaluate the forecasts of theories and look for discrepancies from what is anticipated.
The early evidence for Einsteins theory of basic relativity, for example, originated from finding little variances in the apparent positions of stars and from the motion of Mercury in its orbit.
3 essential findings
Particles follow a hugely successful however counter-intuitive theory called quantum mechanics. This theory reveals that particles far too massive to be made straight in a laboratory accident can still influence what other particles do (through something called “quantum fluctuations.”) Measurements of such impacts are very intricate, however, and much harder to explain to the general public.
Current results hinting at unusual brand-new physics beyond the standard design are of this second type. Detailed research studies from the LHCb experiment discovered that a particle known as a beauty quark (quarks make up the protons and neutrons in the atomic nucleus) “decomposes” (falls apart) into an electron a lot more frequently than into a muon– the electrons much heavier, however otherwise similar, brother or sister. According to the standard design, this shouldnt take place– hinting that brand-new particles and even forces of nature might influence the procedure.
The LHCb experiment at CERN Credit: CERN.
Intriguingly, though, measurements of comparable procedures including “leading quarks” from the ATLAS experiment at the LHC program this decay does happen at equivalent rates for electrons and muons.
On the other hand, the Muon g-2 experiment at Fermilab in the United States has just recently made very precise research studies of how muons “wobble” as their “spin” (a quantum property) connects with surrounding electromagnetic fields. It found a small however significant discrepancy from some theoretical predictions– again suggesting that unidentified forces or particles may be at work.
The most recent unexpected outcome is a measurement of the mass of an essential particle called the W boson, which carries the weak nuclear force that governs radioactive decay. After several years of data taking and analysis, the experiment, likewise at Fermilab, suggests it is considerably heavier than theory anticipates– deviating by a quantity that would not occur by possibility in more than a million experiments. Again, it might be that yet undiscovered particles are contributing to its mass.
Remarkably, nevertheless, this also disagrees with some lower-precision measurements from the LHC (presented in this research study and this one).
The verdict
While we are not absolutely specific these results require an unique explanation, the proof appears to be growing that some brand-new physics is required.
Of course, there will be almost as lots of new mechanisms proposed to discuss these observations as there are theorists. These may involve additional Higgs bosons (associated with the field that gives fundamental particles their mass).
Others will surpass this, conjuring up less just recently fashionable ideas such as “technicolor,” which would imply that there are additional forces of nature (in addition to gravity, electromagnetism and the weak and strong nuclear forces), and might suggest that the Higgs boson is in fact a composite item made from other particles. Only experiments will reveal the reality of the matter– which is good news for experimentalists.
The experimental teams behind the new findings are all well appreciated and have worked on the issues for a long time. It may be that when we do more precise computations, some of the brand-new findings will fit with the standard design.
Equally, it might be the researchers are using subtly different analyses and so finding irregular results. Comparing 2 speculative outcomes needs mindful checking that the same level of approximation has actually been utilized in both cases.
These are both examples of sources of “methodical unpredictability,” and while all concerned do their best to measure them, there can be unanticipated complications that under- or over-estimate them.
None of this makes the existing results any less crucial or fascinating. What the outcomes highlight is that there are multiple pathways to a deeper understanding of the brand-new physics, and they all need to be checked out.
With the restart of the LHC, there are still potential customers of brand-new particles being made through rarer procedures or discovered hidden under backgrounds that we have yet to uncover.
Written by Roger Jones, Professor of Physics, Head of Department, Lancaster University.
This short article was first released in The Conversation.