The Dark Dinner Exam With The Higgs Boson
Visible matter – everything from pollen to stars and galaxies – makes up approximately 15% of the total mass of the Universe. The remaining 85% is made from something completely different from the things we can touch and see: dark matter. Despite dizzying evidence from the observation of gravitational effects, the nature of dark matter and its composition remain unknown.
How can physicists study dark matter beyond gravitational effects if it is practically invisible? Three different approaches are followed: indirect detection with astronomical observations, search for decay products of dark matter disposal in galactic centers; direct detection with very sensitive experiments in low background, looking for dark matter that disperses nuclei; and creating dark matter in the Large Hadron Collider (LHC) controlled laboratory environment in CERN.
Although successful in describing elementary particles and their interactions at low energies, the Standard Model of particle physics does not include a stable particle of matter. The only possible candidates, the neutrinos, do not have the proper properties to explain the dark matter observed. To solve this problem, a simple theoretical extension of the Standard Model predicts that existing particles, such as the Higgs boson, act as a “portal” between known particles and dark matter particles. Since Higgs boson pairs in mass, massive particles of dark matter must interact with it. Higgs boson still has great uncertainties related to the strength of its interaction with Standard Model particles; up to 30% of Higgs-boson faults can be potentially invisible, according to the latest Higls-boson combined ATLAS measurements.
Can some of Higgs bosons be destroyed in dark matter? Since dark matter does not interact directly with the ATLAS detector, physicists are looking for signs of “invisible particles” ascertained through the preservation of the moment of proton-proton collision products. According to the Standard Model, the fraction of Higgs bosons rotting to an invisible final state (four neutrinos!) Accounts for only 0.1% and is thus negligible. If such events are observed, it would be a direct indicator of new physics and possible evidence of the decay of Higgs bosons into particles of dark matter.
Can Higgs rot in dark material? The ATLAS collaboration checked the complete LHC Run 2 data to set the strongest boundaries on the Higgs boson decay in invisible dark matter particles.
At the LHC, the most sensitive channel for looking for direct decay of the Higgs boss in invisible particles is through the so-called boson ovary fusion production (VBF) of the Higgs boson. The output of the VBF Higgs-boson results in two particle sprays (called “jets”) pointing one direction further on the ATLAS detector. This, combined with a large missing moment in the perpendicular (“transverse”) direction on the axis of the beam from invisible particles of matter, creates a unique signature that ATLAS physicists may require.
In the recently presented results, the ATLAS Collaboration studied the complete LHC Run 2 data collected by the ATLAS Detector in 2015–2018 to look for Higgs-boson decay to dark matter particles at VBF events. No significant overstepping of events over the expected background by known Standard Model processes was found in the analysis. ATLAS issued, at a 95% confidence level, an exclusion limit of Higgs-boson decay to invisible particles of 13%. This analysis included approximately 75% more data than the previous ATLAS search, and the team implemented several improvements including:
- Faster filtering algorithms to generate more simulated collisions with equivalent computing power. The lack of simulated events was the main uncertainty in the first 13 TeV version of this analysis.
- Optimized collision selection to receive ~ 50% more Higgs-boson events on the same data.
- Categorize refined events to result in a higher signal-to-background ratio in search regions. This can be seen in Figure 1, as the red curve in the bottom panel increases with the higher invariant mass of the two main planes (mJJ).
- Improved acceptance for collisions enriched in background processes, allowing analysts to improve process process modeling.
This observed exception is consistent with no sign of Higgs breast decay in dark matter. New results advance the search for poorly interacting mass particles (WIMPs), a popular candidate for dark matter. ATLAS set additional exclusion limits for lower WIMP measures, which are comparable to other direct detection experiments in Figure 2. These limits are competitive with the best direct detection experiments for WIMP measures up to half the Higgs mass -boson, assuming Higgs boson interacts directly with dark matter.
This new analysis sets the strongest existing boundaries in Higgs turkey decay to invisible particles to date. As research continues, physicists will continue to increase sensitivity to this fundamental investigation of dark matter.