University of Chicago scientists hunt for proposed particles that might describe peculiarities of deep space.
A group of scientists at the University of Chicago just recently started the search of a life time—or rather, a look for the life time of long-lived supersymmetric particles.
Supersymmetry is a proposed theory to broaden the Standard Model of particle physics. Akin to the table of elements of components, the Standard Model is the very best description we have for subatomic particles in nature and the forces acting upon them.
But physicists understand this design is insufficient—it doesn’t include gravity or dark matter, for instance. Supersymmetry intends to finish the photo by matching each Standard Model particle with a supersymmetric partner, opening a brand-new class of theoretical particles to discover and find. In a brand-new research study, UChicago physicists have actually revealed restrictions for what residential or commercial properties these superpartners, if they exist, might have.
“Supersymmetry really is the most promising theory we have for solving as many problems as possible in the Standard Model,” stated Tova Holmes, assistant teacher 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 reconsider how we search for new physics.”
Inside of the ATLAS detector with UChicago scientist Lesya Horyn, who just recently finished her argumentation on the look 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, speeds up protons to almost the speed of light prior to requiring them to clash. These proton-proton accidents produce a variety of extra particles where scientists wish to discover brand-new physics.
“But at the Large Hadron Collider, new physics events are extremely rare and difficult to identify in the debris of colliding particles,” stated Prof. Young-Kee Kim, chair of the UChicago physics department and co-author of the research study, an effort led completely by ladies.
The UChicago group looked for the production of sleptons—assumed superpartners of the existing electron, muon, and tau leptons—utilizing information gathered in ATLAS, a particle detector at CERN. In the evaluated supersymmetry design, sleptons are thought to have long life times, indicating they can take a trip far prior to decomposing into something noticeable by ATLAS.
Physicist Tova Holmes in the ATLAS counting space, where much of the information acquisition and set off facilities lives. At some point in the next years, these systems will be updated for enhancements to next-generation supersymmetry searches. Credit: University of Chicago
“One of the ways we can miss new physics is if the particle doesn’t decay promptly when it’s produced,” stated Holmes. “Typically, we’re blind to long-lived particles in our searches, because we basically cut out anything that doesn’t look like a standard prompt decay in our detector.”
Sleptons are anticipated to ultimately decay into their routine lepton partners. But unlike traditional decays, these leptons will be displaced, indicating they won’t point back to the initial proton-proton crash point. It was this distinct function that physicists were searching for.
In 4 years of gathered ATLAS information, nevertheless, UChicago scientists discovered no displaced lepton occasions. That absence of discovery permitted them to set what is called a limitation, dismissing a variety of masses and life times that long-lived sleptons may have.
“We are at least 95% sure that, should a slepton in this model exist, it doesn’t have the masses and lifetimes in the shaded portions of this plot,” stated Lesya Horyn, recently minted PhD from UChicago who just recently finished her argumentation on this measurement.
Does a null outcome dissatisfy the group? Not at all.
“Finding nothing tells you so much,” Horyn stated. Knowing that long-lived sleptons don’t have particular masses and life times notifies scientists on where to focus future searches.
“Supersymmetry really is the most promising theory we have for solving as many 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 seemed like we could do it—and we did!”
The result has actually stimulated the group to press the limits even further. At some point in the next years, the Large Hadron Collider will enter its regular shutdown, leaving sufficient time for ATLAS hardware to be updated.
“This was a first pass at the analysis, so there are definitely places to improve,” Horyn stated.
One pushing upgrade will be a revamp of the trigger system, which chooses whether occasions need to be conserved or discarded. The trigger is presently enhanced to save decays from temporary particles, not the long-lived sleptons main to this supersymmetry search.
More instant enhancements can be made without awaiting the shutdown.
“Future steps might include searching for the same model using more robust data from the next runs of the Large Hadron Collider,” stated Xiaohe Jia, a college student at Harvard who dealt with the experiment as a UChicago undergrad. Another path to check out, she stated, might be utilizing comparable strategies to broaden the long-lived particle search beyond simply sleptons.
For now, the conclusion of the Standard Model stays a secret, however the group is happy to have actually led a very first look for this supersymmetry design in ATLAS.
“Discovering new physics is like finding a needle in a haystack,” Kim stated. “Although we did not see anything in the current data, there is great opportunity for the future!”
Reference: “Search for displaced leptons in √ s = 13 TeV pp collisions with the ATLAS detector” by The ATLAS Collaboration, 6 October 2020, ATLAS CONF Note.
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Funding: National Science Foundation.
