World of Dark Photons

Illustration of two types of long-lived particles decaying into a pair of muons, showing how the signals of the muons can be traced back to the long-lived particle decay point using data from the tracker and muon detectors. Credit: CMS/CERN




This search for exotic long-lived particles looks at the possibility of “dark photon” production, which would occur when a Higgs boson decays into muons displaced in the detector.

The CMS experiment has presented its first search for new physics using data from Run 3 of the Large Hadron Collider. The new study looks at the possibility of “dark photon” production in the decay of Higgs bosons in the detector. 

Dark photons are exotic long-lived particles: “long-lived” because they have an average lifetime of more than a tenth of a billionth of a second – a very long lifetime in terms of particles produced in the LHC – and “exotic” because they are not part of the Standard Model of particle physics.

The Standard Model is the leading theory of the fundamental building blocks of the Universe, but many physics questions remain unanswered, and so searches for phenomena beyond the Standard Model continue. 

CMS’s new result defines more constrained limits on the parameters of the decay of Higgs bosons to dark photons, further narrowing down the area in which physicists can search for them.  READ MORE...

Preventing Our Universe From Collapsing

Physicists have proposed our universe might be a tiny patch of a much larger cosmos that is constantly and rapidly inflating and popping off new universes. In our corner of this multiverse, the mass of the Higgs boson was low enough that this patch did not collapse like others may have. (Image credit: MARK GARLICK/SCIENCE PHOTO LIBRARY via Getty Images)

The Higgs boson, the mysterious particle that lends other particles their mass, could have kept our universe from collapsing. And its properties might be a clue that we live in a multiverse of parallel worlds, a wild new theory suggests.

That theory, in which different regions of the universe have different sets of physical laws, would suggest that only worlds in which the Higgs boson is tiny would survive.

If true, the new model would entail the creation of new particles, which in turn would explain why the strong force — which ultimately keeps atoms from collapsing — seems to obey certain symmetries. And along the way, it could help reveal the nature of dark matter — the elusive substance that makes up most matter.

A tale of two Higgs
In 2012, the Large Hadron Collider achieved a truly monumental feat; this underground particle accelerator along the French-Swiss border detected for the first time the Higgs boson, a particle that had eluded physicists for decades. The Higgs boson is a cornerstone of the Standard Model; this particle gives other particles their mass and creates the distinction between the weak nuclear force and the electromagnetic force.

But with the good news came some bad. The Higgs had a mass of 125 gigaelectronvolts (GeV), which was orders of magnitude smaller than what physicists had thought it should be.

To be perfectly clear, the framework physicists use to describe the zoo of subatomic particles, known as the Standard Model, doesn't actually predict the value of the Higgs mass. For that theory to work, the number has to be derived experimentally. But back-of-the-envelope calculations made physicists guess that the Higgs would have an incredibly large mass. So once the champagne was opened and the Nobel prizes were handed out, the question loomed: Why does the Higgs have such a low mass?  READ MORE...

Dark Energy On Earth

DARK ENERGY ISN’T just dark — it's nigh invisible.

Hypothesized by physicists to drive the accelerating expansion of the universe, dark energy has never been directly observed or measured. Instead, scientists can only make inferences about it from its effects on the space and matter we can see.


Finding measurable hints of dark energy’s effects on distance objects — and the shape of space itself — is a major goal of major NASA missions, such as the upcoming Nancy Grace Roman Space Telescope.

But in a new paper published September 15 in the journal Physical Review D a group of cosmologists suggests researchers might not need to peer deep into the cosmos to make second-hand observations of dark energy — it may have been detected right here on Earth.

WHAT’S NEW — In the paper, the researchers claim that hints of dark energy were detected at the Gran Sasso National Laboratory in Italy during an experiment designed to detect dark matter.

The team, comprised mostly of theorists, looked at data from the XENON1T, an experiment designed to detect rare interactions between hypothetical dark matter particles and components of the noble gas xenon held in a special detector.

The odds that dark energy has been detected directly are admittedly low, Jeremy Sakstein, assistant professor of theoretical physics at the University of Hawaii and one of the paper’s authors, tells Inverse.

“There are other explanations for this signal as well,” he says, and at the moment, “we don't know whether it's just a statistical anomaly.”

Statistically, there is a 5 percent chance the detection was an anomaly. The detection of the 2012 discovery Higgs Boson, by comparison, was much more certain — there was only a chance in about 3.5 million that detection was anomalous.  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