physical with CMS Collaboration at the Large Hadron Collider (LHC) at CERN presented its first search for new physics using data from the LHC Run 3.
Illustration of two types of long-lived particles decaying into a pair of muons, showing how muon signals can be traced back to the decay point of long-lived particles using data from the tracker and muon detectors. Image credit: CMS/CERN.
dark photons They are hypothetical long-lived dark sector particles proposed as carriers of photon-like force in electromagnetism.
“Long-lived” because they have a half-life of more than one-tenth of a billionth of a second.
It may seem like an incredibly short period of time, but in terms of the particles produced in the LHC collisions, it is actually quite long.
The Higgs boson, for example, has a lifespan ten billion times shorter!
In fact, particles with a lifetime longer than a thousandth of a billionth of a second are already classified as “long-lived.”
In terms of the CMS detector, this means that a dark photon would travel a measurable distance before decaying, making it potentially detectable.
“Exotic” because they are not part of the Standard Model of particle physics, which is the main theory that guides our understanding of the fundamental building blocks of the Universe.
However, the Standard Model does not answer all questions within particle physics, so searches for phenomena “beyond the Standard Model” continue.
The new CMS result defines tighter limits on the parameters of the decay of Higgs bosons into dark photons, further narrowing the area in which physicists can search for them.
In theory, dark photons would travel a measurable distance in the CMS detector before decaying into “displaced muons.”
If scientists were to retrace the tracks of these muons, they would discover that they do not reach the point of collision, because the tracks come from a particle that has already moved away some distance, without leaving a trace.
LHC Run 3 began in July 2022 and has a higher instantaneous luminosity than previous LHC runs, meaning more collisions occur at any time for researchers to analyze.
The LHC produces tens of millions of collisions per second, but only a few thousand of them can be stored, since recording each collision would quickly consume all available data storage.
That’s why CMS is equipped with a real-time data selection algorithm called a trigger, which decides whether a given collision is interesting or not.
Therefore, it is not only a greater volume of data that could help reveal evidence of the dark photon, but also the way in which the activation system is tuned to look for specific phenomena.
“We have really improved our ability to activate displaced muons,” said Dr. Juliette Alimena, member of the CMS Collaboration.
“This allows us to collect many more events than before with muons traveling from the collision point at distances ranging from a few hundred micrometers to several meters.”
“Thanks to these improvements, if dark photons exist, CMS is now much more likely to find them.”
CMS physicists will continue to use the most powerful techniques to analyze all data taken in the remaining years of Run 3 operations, with the goal of further exploring physics beyond the Standard Model.
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CMS Collaboration. 2023. Search for long-lived particles that decay into a pair of muons in pp collisions at √s= 13.6 TeV with data from 2022. CMS-PAS-EXO-23-014
