Dark matter is one of the biggest mysteries of modern physics. It is a form of matter that does not interact with light or ordinary matter, but only with gravity. It makes up about 27% of the universe, while ordinary matter makes up only 5%. The rest is dark energy, another mysterious force that drives the expansion of the universe. Scientists have been trying to detect and identify dark matter for decades, using various methods and experiments. One of the most powerful tools for this quest is the Large Hadron Collider (LHC), the world’s largest and most powerful particle accelerator, located at CERN in Switzerland.
The Large Hadron Collider and Dark Matter
The LHC is a 27-kilometer ring of superconducting magnets that can accelerate protons to near the speed of light and collide them at four points, creating mini Big Bangs. These collisions produce a shower of particles, some of which are very rare and exotic, such as the Higgs boson, the particle that gives mass to other particles. The LHC can also produce dark matter particles, if they exist, by converting some of the energy of the collisions into mass, according to Einstein’s famous equation E=mc2. However, detecting dark matter particles is very challenging, as they do not leave any traces in the detectors. The only way to infer their presence is by measuring the missing energy and momentum in the collisions, which indicate that something invisible has escaped.
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A Novel Approach to Search for Dark Matter
Researchers at CERN’s ATLAS experiment, one of the four main detectors at the LHC, have introduced a novel approach to search for dark matter through semi-visible jets, marking a significant paradigm shift in the field. Their work provides new directions and stringent upper bounds in the ongoing quest to understand dark matter.
Semi-visible jets are a new type of signature that could reveal the production of dark matter particles inside a jet of ordinary particles. A jet is a collimated spray of particles that results from the fragmentation and hadronization of a quark or a gluon, the elementary constituents of protons. Normally, a jet is composed of visible particles, such as pions, kaons, and protons, that can be detected by the ATLAS calorimeter, a device that measures the energy and direction of particles. However, if a jet contains dark matter particles, some of the energy and momentum of the jet will be missing, creating a gap in the jet’s profile. This gap is what makes the jet semi-visible, as opposed to fully visible or fully invisible.
The researchers used a technique called machine learning, a branch of artificial intelligence, to train a computer program to identify semi-visible jets from simulated data. They then applied the program to the real data collected by the ATLAS detector from 2015 to 2018, corresponding to an integrated luminosity of 139 fb-1, a measure of the number of collisions. They found no evidence of semi-visible jets, which means that no dark matter particles were produced inside the jets. However, they were able to set the most stringent limits to date on the mass and interaction strength of dark matter particles that could produce semi-visible jets, ruling out a large region of the parameter space that was previously unconstrained.
The Implications and Future Prospects
The search for semi-visible jets is a revolutionary approach that opens up a new window to explore the dark matter sector, which could be composed of multiple types of particles with different properties. Semi-visible jets could also be a signature of other exotic phenomena, such as dark photons, dark QCD, or dark showers. The researchers plan to continue their search for semi-visible jets with the upcoming run of the LHC, which will start in 2022 and will increase the collision energy and luminosity, enhancing the chances of producing and detecting dark matter particles. They also hope to collaborate with other experiments and theorists to optimize their search strategy and interpretation
Frequently Asked Questions (FAQs) – Dark Matter Detective Work at the Large Hadron Collider
Q: What is dark matter, and why is it challenging to detect?
A: Dark matter is an invisible and undetectable substance that makes up about 27% of the universe’s mass. It doesn’t emit or absorb light, posing challenges for detection using traditional observational methods. Its presence is inferred through gravitational effects on visible matter.
Q: How does the Large Hadron Collider (LHC) contribute to dark matter detection?
A: The LHC, a powerful particle accelerator, simulates conditions similar to those in the early universe by colliding protons at high energies. Scientists at the LHC conduct experiments to explore fundamental particles, including potential dark matter candidates, by analyzing data from these collisions.
Q: What are WIMPs, and how are they related to dark matter detection at the LHC?
A: Weakly Interacting Massive Particles (WIMPs) are hypothesized dark matter candidates. The LHC experiments, such as ATLAS and CMS, aim to detect WIMPs by analyzing collision data for missing energy signatures, which could indicate the presence of undetected dark matter particles.
Q: Can you explain the role of the ATLAS and CMS experiments at the LHC?
A: ATLAS (A Toroidal LHC ApparatuS) and CMS (Compact Muon Solenoid) are two major experiments at the LHC. These detectors capture and analyze particles produced in high-energy collisions, providing crucial data for understanding particle behavior and potential clues about dark matter.
Q: How do scientists at the LHC deal with the elusive nature of dark matter particles?
A: Dark matter particles interact weakly with regular matter, making their detection challenging. Scientists look for missing energy signatures in collision data, indicating the potential presence of undetected dark matter particles escaping the detectors.
Q: What is the significance of precision measurements in dark matter detection?
A: Precision measurements are crucial for refining detection techniques and increasing the sensitivity of detectors. Ongoing upgrades and future enhancements at the LHC aim to improve measurement accuracy, pushing the boundaries of particle physics and dark matter research.
Q: How does global collaboration contribute to dark matter research at the LHC?
A: Thousands of scientists from around the world collaborate on the design, construction, and operation of the LHC and its experiments. This global collaboration accelerates progress, pooling expertise and resources for a more comprehensive exploration of dark matter.
Q: What technological innovations are involved in dark matter detection at the LHC?
A: Dark matter detection requires cutting-edge technology, including advanced detectors and sophisticated data analysis algorithms. The technological innovations developed for LHC experiments contribute to broader scientific and technological advancements.
Q: How do theoretical frameworks guide dark matter detection at the LHC?
A: Theoretical frameworks guide the interpretation of data from LHC experiments. As experiments progress, theoretical models are refined, creating a dynamic interplay between theory and experiment in the ongoing quest to understand dark matter.
- Q: What would the discovery of dark matter at the LHC mean for our understanding of the universe?
A: The discovery of dark matter particles at the LHC would be a historic moment in physics. It could reshape our understanding of the universe’s composition, gravitational interactions, and fundamental forces, impacting not only particle physics but also cosmology and astrophysics.
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