Scientists narrow down the search for dark photons using decade-old particle collider data

November 8, 2017, Lawrence Berkeley National Laboratory
The BaBar detector at SLAC National Accelerator Laboratory. Credit: SLAC National Accelerator Laboratory

In its final years of operation, a particle collider in Northern California was refocused to search for signs of new particles that might help fill in some big blanks in our understanding of the universe.

A fresh analysis of this data, co-led by physicists at the Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab), limits some of the hiding places for one type of theorized particle - the , also known as the heavy photon - that was proposed to help explain the mystery of dark matter.

The latest result, published in the journal Physical Review Letters by the roughly 240-member BaBar Collaboration, adds to results from a collection of previous experiments seeking, but not yet finding, the theorized dark photons.

"Although it does not rule out the existence of dark photons, the BaBar results do limit where they can hide, and definitively rule out their explanation for another intriguing mystery associated with the property of the subatomic particle known as the muon," said Michael Roney, BaBar spokesperson and University of Victoria professor.

Dark matter, which accounts for an estimated 85 percent of the total mass of the universe, has only been observed by its gravitational interactions with normal matter. For example, the rotation rate of galaxies is much faster than expected based on their visible matter, suggesting there is "missing" mass that has so far remained invisible to us.

So physicists have been working on theories and experiments to help explain what dark matter is made of - whether it is composed of undiscovered , for example, and whether there may be a hidden or "dark" force that governs the interactions of such particles among themselves and with visible matter. The dark photon, if it exists, has been put forward as a possible carrier of this dark force.

Using data collected from 2006 to 2008 at SLAC National Accelerator Laboratory in Menlo Park, California, the analysis team scanned the recorded byproducts of particle collisions for signs of a single particle of light - a photon - devoid of associated particle processes.

The BaBar experiment, which ran from 1999 to 2008 at SLAC, collected data from collisions of electrons with positrons, their positively charged antiparticles. The collider driving BaBar, called PEP-II, was built through a collaboration that included SLAC, Berkeley Lab, and Lawrence Livermore National Laboratory. At its peak, the BaBar Collaboration involved over 630 physicists from 13 countries.

BaBar was originally designed to study the differences in the behavior between matter and antimatter involving a b-quark. Simultaneously with a competing experiment in Japan called Belle, BaBar confirmed the predictions of theorists and paved the way for the 2008 Nobel Prize. Berkeley Lab physicist Pier Oddone proposed the idea for BaBar and Belle in 1987 while he was the Lab's Physics division director.

The latest analysis used about 10 percent of BaBar's data - recorded in its final two years of operation. Its data collection was refocused on finding particles not accounted for in physics' Standard Model - a sort of rulebook for what particles and forces make up the known universe.

"BaBar performed an extensive campaign searching for dark sector particles, and this result will further constrain their existence," said Bertrand Echenard, a research professor at Caltech who was instrumental in this effort.

This chart shows the search area (green) explored in an analysis of BaBar data where dark photon particles have not been found, compared with other experiments' search areas. The red band shows the favored search area to show whether dark photons are causing the so-called "g-2 anomaly," and the white areas are among the unexplored territories for dark photons. Credit: Muon g-2 Collaboration

Yury Kolomensky, a physicist in the Nuclear Science Division at Berkeley Lab and a faculty member in the Department of Physics at UC Berkeley, said, "The signature (of a dark photon) in the detector would be extremely simple: one high-energy photon, without any other activity."

A number of the dark photon theories predict that the associated would be invisible to the detector. The single photon, radiated from a beam particle, signals that an electron-positron collision has occurred and that the invisible dark photon decayed to the dark matter particles, revealing itself in the absence of any other accompanying energy.

When physicists had proposed dark photons in 2009, it excited new interest in the physics community, and prompted a fresh look at BaBar's data. Kolomensky supervised the data analysis, performed by UC Berkeley undergraduates Mark Derdzinski and Alexander Giuffrida.

"Dark photons could bridge this hidden divide between dark and our world, so it would be exciting if we had seen it," Kolomensky said.

The dark photon has also been postulated to explain a discrepancy between the observation of a property of the muon spin and the value predicted for it in the Standard Model. Measuring this property with unprecedented precision is the goal of the Muon g-2 (pronounced gee-minus-two) Experiment at Fermi National Accelerator Laboratory.

Earlier measurements at Brookhaven National Laboratory had found that this property of muons - like a spinning top with a wobble that is ever-slightly off the norm - is off by about 0.0002 percent from what is expected. Dark photons were suggested as one possible particle candidate to explain this mystery, and a new round of experiments begun earlier this year should help to determine whether the anomaly is actually a discovery.

The latest BaBar result, Kolomensky said, largely "rules out these dark theories as an explanation for the g-2 anomaly, effectively closing this particular window, but it also means there is something else driving the g-2 anomaly if it's a real effect."

It's a common and constant interplay between theory and experiments, with theory adjusting to new constraints set by experiments, and experiments seeking inspiration from new and adjusted theories to find the next proving grounds for testing out those theories.

Scientists have been actively mining BaBar's data, Roney said, to take advantage of the well-understood experimental conditions and detector to test new theoretical ideas.

"Finding an explanation for is one of the most important challenges in physics today, and looking for dark photons was a natural way for BaBar to contribute," Roney said, adding that many experiments in operation or planned around the world are seeking to address this problem.

An upgrade of an experiment in Japan that is similar to BaBar, called Belle II, turns on next year. "Eventually, Belle II will produce 100 times more statistics compared to BaBar," Kolomensky said. "Experiments like this can probe new theories and more states, effectively opening new possibilities for additional tests and measurements."

"Until Belle II has accumulated significant amounts of data, BaBar will continue for the next several years to yield new impactful results like this one," Roney said.

Explore further: NA64 hunts the mysterious dark photon

More information: J. P. Lees et al, Search for Invisible Decays of a Dark Photon Produced in e+e− Collisions at BaBar, Physical Review Letters (2017). DOI: 10.1103/PhysRevLett.119.131804

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17 comments

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rrwillsj
2.3 / 5 (3) Nov 08, 2017
Ahhh, 'dark photon', i.e. 'dark light'?

A funny punny, honey.
ursiny33
1 / 5 (6) Nov 08, 2017
Theres no such thing as dark photons they are a balanced magnetic construction of 3 electrons and 2 positrons fused tpgether in a magnetic bond they can only come apart over time outside the realm of a negative charged environment back into there quantum parts, they are not eternal in there construction but do have a long life span of dozens of billions of years
ursiny33
1 / 5 (4) Nov 08, 2017
I sorry i mean 3 positrons and 2 electrons
Gigel
not rated yet Nov 09, 2017
Shouldn't those be easy to detect by magnetic deflection, since they have electric charge?
antialias_physorg
5 / 5 (5) Nov 09, 2017
construction of 3 electrons and 2 positrons fused tpgether in a magnetic bond

If such a structure would be possible (which it isn't) it would produce a lot of gamma rays at the latest when it hits the detector.

Oh, and the word 'fuse' doesn't mean what you think it means.
baudrunner
1 / 5 (2) Nov 09, 2017
Scientists are still taking "slice of time" samples to predict the behavior of galaxies, as if the current state of the universe is a function of only the current relationships of masses in space. But that is just so wrong. The universe is behaving in ways that we can't explain because of the events of a past history that occurred when we weren't even around. The behavior of those rotating galaxies, that seem to defy our predictions, are just still responding to influences experienced during times of universal history unknown to us. Sometimes we think too highly of ourselves and our presumed state of knowledge, but it's still a fact that mainstream science is largely theoretical.
Parsec
5 / 5 (4) Nov 09, 2017
@baudrunner - seriously dude? 1st rule of posting. Post first, THEN smoke crack. Reversing the order works less than well.
rrwillsj
1 / 5 (2) Nov 10, 2017
Parsec, at this stage of my ignorance, I have to disagree with your comment about baudrunner.

Frankly and Ernestly, I agree with what he wrote. There is an obvious abundance of hubris and over-weening pride among scientists, engineers, technologist, researchers of all types.

However, considering all that they have accomplished the last few centuries. How far forward they have dragged the kicking and screaming mass of Humanity-in-Denial. I grudgingly salute them with a toast wishing them continued success.

P, perhaps you know b, personally? And know his motivations for his comments? I do not and just agree with what was posted above.

If it turns out b was trying to postulate crankery or superstition? I still agree with what I have read. Even if eventually, I disagree with why he wrote the above comment.

Monkeys and typewriters!
nikola_milovic_378
Nov 11, 2017
This comment has been removed by a moderator.
nikola_milovic_378
Nov 11, 2017
This comment has been removed by a moderator.
nikola_milovic_378
Nov 11, 2017
This comment has been removed by a moderator.
tallenglish
not rated yet Nov 11, 2017
Proposal for the dark photon - its exactly the same as a photon, just travelling backwards in time relative to the observer. I think we get too stuck up on things only going forward in time, because we measure everything using photons or effect after cause, suggest an effect can happen before the cause break most peoples brains, easy if you assume mass/light can move in either direction, i.e. +c and -c (and +/- ic)
rrwillsj
3.7 / 5 (6) Nov 11, 2017
Interesting, those of the comments pointing out all the hypothesis that have failed testing. And therefore letting loose the loons of crankery repeating baseless claims of ancient wisdom.

Reminds me of Thomas Edison's reply to those adulating his 'genius' discovering the incandescent light bulb.

Peeved that the flatters were ignoring the years of hard work it took to develop a commercially successful product.

Edison replied "That he had NOT discovered the light bulb. Instead he discovered a thousand ways NOT to make a light bulb!"

Sooner or later the EU/Aether dolts will have to put away their childish toys and learn to accept reality. Comicbooks, fictional stories, video-games and cinema are entertainment. Relaxing fun when you want a break from real life and nothing more.

Benni
1 / 5 (4) Nov 12, 2017
If Dark Energy actually exists, by necessity so must Dark Photons........this simply because PHOTONS & ENERGY are exactly the same, but I imagine there are those who would try concocting a different descriptor between the two because they don't comprehend Special Relativity.
TrollBane
5 / 5 (2) Nov 12, 2017
Dark photons? I expect these to be finally discovered by a team led by Professor Palpatine of Naboo University.
Da Schneib
3 / 5 (2) Nov 12, 2017
Well, @TrollBane, maybe, and these findings argue against them, but there's still some regimes where they're not ruled out according to the graph in the article.
rrwillsj
2.3 / 5 (3) Nov 12, 2017
m, what proof can you offer that Tesla discovered anything pertaining to this article? Or, that based on his real-life, 19th century knowledge, that he would even comprehend the subject?

And, since you brought it up... Equating outright, criminal frauds such as N-Rays with the great Tesla's work? I'd have to opinionate that anything you post is suspect!

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