Abstract Particle Physics Concept

University of Chicago researchers hunt for proposed particles that could describe peculiarities of deep space.

A team of scientists at the University of Chicago recently embarked on the search of a life time– or rather, a search for the lifetime of long-lived supersymmetric particles.

Supersymmetry is a proposed theory to broaden the Requirement Design of particle physics. Comparable to the periodic table of aspects, the Requirement Design is the best description we have for subatomic particles in nature and the forces acting on them.

But physicists know this design is insufficient– it doesn’t make space for gravity or dark matter.

” Supersymmetry really is the most promising theory we have for solving as numerous issues as possible in the Standard Model,” stated Tova Holmes, assistant professor at the University of Tennessee, Knoxville, who dealt with the experiment as a postdoctoral scientist at UChicago. “Our work fits into a larger effort at the Large Hadron Collider to reassess how we search for brand-new physics.”

Lesya Horyn

Inside of the ATLAS detector with UChicago researcher Lesya Horyn, who recently completed her dissertation on the search for long-lived sleptons, supersymmetric partners of the existing electron, muon, and tau leptons. Credit: University of Chicago

The Large Hadron Collider, situated in Europe at CERN, accelerates protons to nearly the speed of light prior to forcing them to collide. These proton-proton collisions produce a variety of additional particles where researchers want to discover new physics.

” However at the Big Hadron Collider, new physics events are very unusual and hard to identify in the particles of clashing particles,” said Prof. Young-Kee Kim, chair of the UChicago physics department and co-author of the study, an effort led totally by ladies.

The UChicago team searched for the production of sleptons– assumed superpartners of the existing electron, muon, and tau leptons– utilizing data gathered in ATLAS, a particle detector at CERN. In the evaluated supersymmetry design, sleptons are thought to have long life times, suggesting they can take a trip far before decomposing into something noticeable by ATLAS.

Tova Holmes

Physicist Tova Holmes in the ATLAS counting space, where much of the information acquisition and set off infrastructure lives. Eventually in the next years, these systems will be upgraded for improvements to next-generation supersymmetry searches. Credit: University of Chicago

” One of the ways we can miss out on brand-new physics is if the particle doesn’t decay promptly when it’s produced,” said Holmes. “Normally, we’re blind to long-lived particles in our searches, due to the fact that we essentially cut out anything that does not look like a basic prompt decay in our detector.”

Sleptons are expected to ultimately decay into their routine lepton partners.

In 4 years of collected ATLAS information, however, UChicago scientists discovered no displaced lepton occasions. That absence of discovery allowed them to set what is called a limitation, dismissing a series of masses and lifetimes that long-lived sleptons might have.

” We are at least 95%sure that, ought to a slepton in this design exist, it does not have the masses and lifetimes in the shaded portions of this plot,” said Lesya Horyn, recently minted PhD from UChicago who just recently completed her dissertation on this measurement.

Does a null outcome disappoint the team? Not at all.

” Finding nothing informs you so much,” Horyn said. Knowing that long-lived sleptons don’t have particular masses and life times notifies scientists on where to focus future searches.

” Supersymmetry truly is the most promising theory we have for resolving as lots of problems as possible in the Standard Model.”

Tova Holmes, assistant teacher at the University of Tennessee, Knoxville

” From my point of view, this search was the number one thing theorists were calling out to have covered,” Holmes stated. “It looked like we might do it– and we did!”

The result has stimulated the group to push the borders even further. At some time in the next decade, the Large Hadron Collider will enter its routine shutdown, leaving ample time for ATLAS hardware to be updated.

” This was a first pass at the analysis, so there are certainly positions to improve,” Horyn said.

One pushing upgrade will be a revamp of the trigger system, which selects whether occasions must be saved or thrown away. The trigger is currently optimized to save decays from temporary particles, not the long-lived sleptons central to this supersymmetry search.

More instant enhancements can be made without awaiting the shutdown.

” Future steps might consist of searching for the very same design using more robust data from the next runs of the Big Hadron Collider,” stated Xiaohe Jia, a college student at Harvard who worked on the experiment as a UChicago undergrad. Another route to check out, she said, could be utilizing similar methods to expand the long-lived particle search beyond simply sleptons.

For now, the completion of the Requirement Design stays a secret, but the team is proud to have actually led a first look for this supersymmetry design in ATLAS.

” Discovering brand-new physics resembles discovering a needle in a haystack,” Kim said. “Although we did not see anything in the current information, there is fantastic opportunity for the future!”

Recommendation: “Search for displaced leptons in √ s=13 TeV pp collisions with the ATLAS detector” by The ATLAS Partnership, 6 October 2020, ATLAS CONF Note.

Funding: National Science Structure.


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