Searching for the Universe's Missing Pieces

Scientists at the Large Hadron Collider are probing new particles beyond the Standard Model of Particle Physics, aiming to unravel its limitations and foster advancements in technology.

It seemed like the Standard Model of Particle Physics was complete with the discovery of the Higgs boson particle in 2012. The Standard Model is physicists’ current best explanation of the major building blocks of the universe and three out of four of the major forces. 

But there are still a number of mysteries that the Standard Model simply can’t explain. These include dark matter and dark energy. Physicists supported by the Department of Energy (DOE) are trying to figure out if there are particles and forces beyond those in the Standard Model, and if so, what they are.   READ MORE...

Exploring the Quantum Universe

After a multi-year review, the U.S. particle physics community has announced its vision for research spanning the next five to ten years. The various projects could, if funded, help researchers develop a much better understanding of the laws of nature.

The recommendations were released in a report called “Exploring the Quantum Universe: Pathways to Innovation and Discovery in Particle Physics.” It was written by the Particle Physics Projects Prioritization Panel (P5), a sub-panel of the High Energy Physics Advisory Panel (HEPAP), and will be submitted to funding agencies like the U.S. Department of Energy Office of Science and the Natioce Foundation to guide their funding decisions over the next decade.  READ MORE...

An Alternative Picture of Particle Physics

All of nature springs from a handful of components — the fundamental particles — that interact with one another in only a few different ways. In the 1970s, physicists developed a set of equations describing these particles and interactions. Together, the equations formed a succinct theory now known as the Standard Model of particle physics.

The Standard Model is missing a few puzzle pieces (conspicuously absent are the putative particles that make up dark matter, those that convey the force of gravity, and an explanation for the mass of neutrinos), but it provides an extremely accurate picture of almost all other observed phenomena.

Yet for a framework that encapsulates our best understanding of nature’s fundamental order, the Standard Model still lacks a coherent visualization. Most attempts are too simple, or they ignore important interconnections or are jumbled and overwhelming.

A New Approach
Chris Quigg, a particle physicist at the Fermi National Accelerator Laboratory in Illinois, has been thinking about how to visualize the Standard Model for decades, hoping that a more powerful visual representation would help familiarize people with the known particles of nature and prompt them to think about how these particles might fit into a larger, more complete theoretical framework. 

Quigg’s visual representation shows more of the Standard Model’s underlying order and structure. He calls his scheme the “double simplex” representation, because the left-handed and right-handed particles of nature each form a simplex — a generalization of a triangle. We have adopted Quigg’s scheme and made further modifications.   READ MORE...

Playing Quantum Billards

Protons accelerated almost to the speed of light can collide similarly to billiard balls. However, since protons are quantum particles, from measuring such collisions we can learn unobvious things about the strong interaction. Credit: IFJ PAN




A study conducted by the ATLAS experiment at the Large Hadron Accelerator has gained insights into the properties of strong interactions between protons at ultra-high energies by exploring elastic scattering in proton-proton collisions. The research found discrepancies with pre-existing theoretical models, prompting a reconsideration of current understanding of these interactions.

The quantum nature of interactions between elementary particles allows drawing non-trivial conclusions even from processes as simple as elastic scattering. The ATLAS experiment at the LHC accelerator reports the measurement of fundamental properties of strong interactions between protons at ultra-high energies.

The physics of billiard ball collisions is taught from early school years. In a good approximation, these collisions are elastic, where both momentum and energy are conserved. The scattering angle depends on how central the collision was (this is often quantified by the impact parameter value – the distance between the centers of the balls in a plane perpendicular to the motion). In the case of a small impact parameter, which corresponds to a highly central collision, the scattering angles are large. As the impact parameter increases, the scattering angle decreases.

In particle physics, we also deal with elastic collisions, when two particles collide, maintaining their identities, and scatter a certain angle to their original direction of motion. Here, we also have a relationship between the collision parameter and the scattering angle. By measuring the scattering angles, we gain information about the spatial structure of the colliding particles and the properties of their interactions.    READ MORE...

A New Force

Harry Cliff, a Cambridge particle physicist writes...

After years without particle physics making the news, recent announcements suggest a breakthrough. Could a new fundamental force also explain the mystery of the three generations of matter? Harry Cliff weighs up the case.

Most of my colleagues would probably admit, at least in private, that it’s been an anxious time to be a particle physicist. Thirteen years ago, when the world’s largest (and most expensive) scientific instrument, the Large Hadron Collider (LHC), fired up for the first time, hopes were high that we would soon discover new particles and forces that could help address some of the most profound mysteries in science.

Things got off to a spectacular start with the discovery of the long-sought Higgs boson in 2012, but momentous as its discovery was, the Higgs belongs to the well-established ‘standard model’ of particle physics, which took shape more than half a century ago in the 1960s and 70s. Now, I don’t want to do the standard model down. It is without a doubt the most successful scientific theory ever devised, describing everything we know about the fundamental building blocks that makes up the world around us with stunning precision. You could make a good case for it being the greatest intellectual achievement of humankind. But we know it can’t be the end of the story.

The standard model has no solutions for numerous thorny problems, including how matter survived annihilation during the Big Bang, or indeed why we observe the set of particles that we do. Perhaps its most glaring omission is its failure to account for a whopping 95% of universe, which astronomy tells us is dominated by enigmatic substances known as dark matter and dark energy. So, when the LHC switched on in September 2008, particle physicists like me were itching to see something altogether new, something that might show us the way to an expanded picture of the subatomic world.

Yet almost a decade later, after literally thousands of searches performed by the four big LHC experiments, nature has stubbornly refused to give up its secrets. After the discovery of the Higgs, the LHC experiments continued to verify the predictions of the standard model, while ruling out a whole host of speculative new theories that were intended to extend it into new territory.

Some began to talk about a crisis in particle physics. Could it be that the long quest for an ever-deeper understanding of the fundamental constituents of our universe had reached a dead end? However, amid the gathering gloom, a series of unexpected chinks of light were beginning to appear.

Once again, particle physics made headline news around the world. Major discoveries seemed to be arriving like buses.

The LHCb experiment, one of the four giant detectors that study particle collisions produced by the LHC and the experiment on which I work, was reporting a growing number of ‘anomalies’; measurements that seemed to be in tension with the predictions of the standard model. While intriguing, for a long while these deviations were too subtle for physicists to have much confidence that they were anything other than random statistical wobbles in the data. That is until the 23rd March of this year.

On that day, my colleagues at LHCb announced they had found firm evidence for exotic particles known as beauty quarks decaying in ways that the standard model can’t explain. If borne out, these results suggest the existence of a brand-new force of nature, which would make it arguably the most momentous scientific discovery of the 21st century so far. The story broke out into the mainstream media, quickly making it one of the most widely covered particle physics stories since the discovery of the Higgs in 2012.

Then, just two weeks later on the 7th April, a completely different experiment at Fermilab in the United States announced a second result that seemed to suggest that fundamental particles called muons were also experiencing the tug of a hitherto undiscovered force. Once again, particle physics made headline news around the world. Major discoveries seemed to be arriving like buses.  READ MORE

A Quantum Reality

QUANTUM MECHANICS

Quantum Mechanics or QM, describes how the Universe works at the level smaller than atoms. It is also called "quantum physics" or "quantum theory". A quantum of energy is a specific amount of energy, and Quantum Mechanics describes how that energy moves and interacts at the sub-atomic level.

The new theory ignored the fact that electrons are particles and treated them as waves. By 1926 physicists had developed the laws of quantum mechanics, also called wave mechanics, to explain atomic and subatomic phenomena.  When X-rays are scattered, their momentum is partially transferred to the electrons.

The world as we know it has three dimensions of space—length, width and depth—and one dimension of time. But there's the mind-bending possibility that many more dimensions exist out there. According to string theory, one of the leading physics model of the last half century, the universe operates with 10 dimensions.

String theory is a set of attempts to model the four known fundamental interactions—gravitation, electromagnetism, strong nuclear force, weak nuclear force—together in one theory.  Einstein had sought a unified field theory, a single model to explain the fundamental interactions or mechanics of the universe.

One notable feature of string theories is that these theories require extra dimensions of spacetime for their mathematical consistency. In bosonic string theory, spacetime is 26-dimensional, while in superstring theory it is 10-dimensional, and in M-theory it is 11-dimensional.

M-theory is a new idea in small-particle physics that is part of superstring theory that was initially proposed by Edward Witten. The idea, or theory, often causes arguments among scientists, because there is no way to test it to see if it is true.

A type of spacetime symmetry, supersymmetry is a possible candidate for undiscovered particle physics, and seen by some physicists as an elegant solution to many current problems in particle physics if confirmed correct, which could resolve various areas where current theories are believed to be incomplete.