New Study: Scientists Narrow Down a Search for Dark Photons Using Decade-Old Particle Collider Data

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In a final years of operation, a molecule collider in Northern California was refocused to hunt for signs of new particles that competence assistance fill in some large blanks in a bargain of a universe.

Photo - Data collected from molecule collider experiments regulating a BaBar detector during SLAC National Accelerator Laboratory, graphic here, were analyzed to hunt for traces of theorized dim matter particles famous as dim photons. (Credit: SLAC National Accelerator Laboratory)

The BaBar detector during SLAC National Accelerator Laboratory. (Credit: SLAC)

A uninformed investigate of this data, co-led by physicists during a Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), boundary some of a stealing places for one form of theorized molecule – the dim photon, also famous as a complicated photon – that was due to assistance explain a poser of dim matter.

The latest result, published in a journal Physical Review Letters by a roughly 240-member BaBar Collaboration, adds to formula from a collection of prior experiments seeking, though not nonetheless finding, a theorized dim photons.

“Although it does not order out a existence of dim photons, a BaBar formula do extent where they can hide, and definitively order out their reason for another intriguing poser compared with a skill of a subatomic molecule famous as a muon,” conspicuous Michael Roney, BaBar orator and University of Victoria professor.

Dark matter, that accounts for an estimated 85 percent of a sum mass of a universe, has usually been celebrated by a gravitational interactions with normal matter. For example, a revolution rate of galaxies is many faster than approaching formed on their manifest matter, suggesting there is “missing” mass that has so distant remained invisible to us.

So physicists have been operative on theories and experiments to assistance explain what dim matter is done of – whether it is stoical of undiscovered particles, for example, and either there might be a dim or “dark” force that governs a interactions of such particles among themselves and with manifest matter. The dim photon, if it exists, has been put brazen as a probable conduit of this dim force.

Using information collected from 2006 to 2008 during SLAC National Accelerator Laboratory in Menlo Park, California, a investigate group scanned a available byproducts of molecule collisions for signs of a singular molecule of light – a photon – abandoned of compared molecule processes.

The BaBar experiment, that ran from 1999 to 2008 during SLAC, collected information from collisions of electrons with positrons, their definitely charged antiparticles. The collider pushing BaBar, called PEP-II, was built by a partnership that enclosed SLAC, Berkeley Lab, and Lawrence Livermore National Laboratory. At a peak, a BaBar Collaboration concerned over 630 physicists from 13 countries.

BaBar was creatively designed to investigate a differences in a function between matter and antimatter involving a b-quark. Simultaneously with a competing examination in Japan called Belle, BaBar reliable a predictions of theorists and paved a approach for a 2008 Nobel Prize. Berkeley Lab physicist Pier Oddone proposed a idea for BaBar and Belle in 1987 while he was a Lab’s Physics multiplication director.

The latest investigate used about 10 percent of BaBar’s information – available in a final dual years of operation. Its information collection was refocused on anticipating particles not accounted for in physics’ Standard Model – a arrange of rulebook for what particles and army make adult a famous universe.

“BaBar achieved an endless debate acid for dim zone particles, and this outcome will serve constrain their existence,” conspicuous Bertrand Echenard, a investigate highbrow during Caltech who was instrumental in this effort.

Chart - This draft shows a hunt area (green) explored in an investigate of BaBar information where dim photon particles have not been found, compared with other experiments hunt areas. The red rope shows a adored hunt area to establish either dim photons are causing a supposed g-2 anomaly, and a white areas are among a unexplored territories for dim photons. (Credit: Muon g-2 Collaboration)

This draft shows a hunt area (green) explored in an investigate of BaBar information where dim photon particles have not been found, compared with other experiments’ hunt areas. The red rope shows a adored hunt area to establish either dim photons are causing a supposed “g-2 anomaly,” and a white areas are among a unexplored territories for dim photons. (Credit: Muon g-2 Collaboration)

Yury Kolomensky, a physicist in a Nuclear Science Division during Berkeley Lab and a imagination member in a Department of Physics during UC Berkeley, said, “The signature (of a dim photon) in a detector would be intensely simple: one high-energy photon, though any other activity.”

A series of a dim photon theories envision that a compared dim matter particles would be invisible to a detector. The singular photon, radiated from a lamp particle, signals that an electron-positron collision has occurred and that a invisible dim photon unkempt to a dim matter particles, divulgence itself in a deficiency of any other concomitant energy.

When physicists had due dim photons in 2009, it vehement new seductiveness in a production community, and stirred a uninformed demeanour during BaBar’s data. Kolomensky supervised a information analysis, achieved by UC Berkeley undergraduates Mark Derdzinski and Alexander Giuffrida.

“Dark photons could overpass this dim order between dim matter and a world, so it would be sparkling if we had seen it,” Kolomensky said.

The dim photon has also been presumed to explain a inequality between a regard of a skill of a muon spin and a value likely for it in a Standard Model. Measuring this skill with rare pointing is a idea of the Muon g-2 (pronounced gee-minus-two) Experiment during Fermi National Accelerator Laboratory.

Earlier measurements during Brookhaven National Laboratory had found that this skill of muons – like a spinning tip with a stagger that is ever-slightly off a normal – is off by about 0.0002 percent from what is expected. Dark photons were suggested as one probable molecule claimant to explain this mystery, and a new turn of experiments begun progressing this year should assistance to establish either a curiosity is indeed a discovery.

The latest BaBar result, Kolomensky said, mostly “rules out these dim photon theories as an reason for a g-2 anomaly, effectively shutting this sold window, though it also means there is something else pushing a g-2 curiosity if it’s a genuine effect.”

It’s a common and consistent interplay between speculation and experiments, with speculation adjusting to new constraints set by experiments, and experiments seeking impulse from new and practiced theories to find a subsequent proof drift for contrast out those theories.

Scientists have been actively mining BaBar’s data, Roney said, to take advantage of a well-understood initial conditions and detector to exam new fanciful ideas.

“Finding an reason for dim matter is one of a many critical hurdles in production today, and looking for dim photons was a healthy approach for BaBar to contribute,” Roney said, adding that many experiments in operation or designed around a star are seeking to residence this problem.

An ascent of an examination in Japan that is identical to BaBar, called Belle II,  turns on subsequent year. “Eventually, Belle II will furnish 100 times some-more statistics compared to BaBar,” Kolomensky said. “Experiments like this can examine new theories and some-more states, effectively opening new possibilities for additional tests and measurements.”

“Until Belle II has amassed poignant amounts of data, BaBar will continue for a subsequent several years to produce new impactful formula like this one,” Roney said.

The investigate featured appearance by a general BaBar collaboration, that includes researchers from about 66 institutions in a U.S., Canada, France, Spain, Italy, Norway, Germany, Russia, India, Saudi Arabia, U.K., a Netherlands, and Israel. The work was upheld by a U.S. Department of Energy’s Office of Science and a National Science Foundation; a Natural Sciences and Engineering Research Council in Canada; CEA and CNRS-IN2P3 in France; BMBF and DFG in Germany; INFN in Italy; FOM in a Netherlands; NFR in Norway; MES in Russia; MINECO in Spain; STFC in a U.K.; and BSF in Israel and a U.S. Individuals concerned with this investigate have perceived support from a Marie Curie EIF in a European Union, and a Alfred P. Sloan Foundation in a U.S.


Lawrence Berkeley National Laboratory addresses a world’s many obligatory systematic hurdles by advancing tolerable energy, safeguarding tellurian health, formulating new materials, and divulgence a start and predestine of a universe. Founded in 1931, Berkeley Lab’s systematic imagination has been famous with 13 Nobel Prizes. The University of California manages Berkeley Lab for a U.S. Department of Energy’s Office of Science. For more, visit

DOE’s Office of Science is a singular largest believer of simple investigate in a earthy sciences in a United States, and is operative to residence some of a many dire hurdles of a time. For some-more information, greatfully visit

Source: Berkeley Lab

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