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Can the boson Higgs decay into dark matter?



Concept of dark atomic matter small particle artist

Exploration of dark matter with Boson Higgs particle

Visible matter – everything from pollen to stars and galaxies – makes up about 15% of the Universe’s total mass. The remaining 85% is made of something completely different from what we can touch and see: dark matter. Although there is much evidence from observations of gravitational effects, the nature of dark matter and its composition is unknown.

How can physicists study dark matter in addition to the gravitational effect if it is practically invisible? Three different approaches are pursued: indirect detection with astronomical observatories, searching for the decay products of dark matter destruction in galactic centers; direct detection with highly sensitive low-background experiments, looking for dark matter scattering away from the nucleus; and by generating dark matter in the Large Hadron Collider (LHC) controlled laboratory environment at Cern.

Although successful in describing elementary particles and their interactions at low energies, the Standard Model of particle physics does not include a viable dark matter particle. The only possible candidate, the neutrino, does not have the properties suitable to explain observable dark matter. To overcome this problem, a simple theoretical extension of the Standard Model poses that existing particles, such as the Higgs boson, act as a “portal” between known particles and particles. dark matter. Because the Higgs boson has mass, large dark matter particles will interact with it. The Higgs boson still has a large degree of uncertainty regarding the intensity of its interaction with the Standard Model particles; According to ATLAS’s latest combined Higgs-boson measurements, up to 30% of Higgs-boson decay is stealthy.

Can some Higgs bosons decay into dark matter? Since dark matter does not interact directly with the ATLAS detector, physicists look for signs of “invisible particles”, which are inferred through the kinetic conservation of proton- collision products. proton. According to the Standard Model, the part of the Higgs boson that decays to its final invisible state (four neutrinos!) Is only 0.1% and therefore negligible. If such events are observed, it would be a direct indication of new physics and potential evidence of the Higgs boson decay into dark matter particles.

Could the Higgs boson decay into dark matter? ATLAS Collaboration searched the entire LHC Run 2 dataset to place the strongest limit on the decay of the Higgs boson into invisible dark matter particles to date.

At the LHC, the most sensitive channel to seek the direct decay of the Higgs boson into invisible particles is through the production of the so-called vector boson fusion (VBF) of the Higgs boson. The creation of the Higgs-boson VBF resulted in two more forward sprayings (called “jets”) in the ATLAS detector. This, combined with a large momentum missing in a perpendicular (“horizontal”) direction to the beam axis from invisible dark matter particles, produces a unique signature that ATLAS physicists have. can be searched.

The Higgs boson signal in the Decline to an invisible final state

Figure 1: Masses of two top jets (x-axis) in search area with all background processes stacked and compared with data. A hypothetical Higgs boson signal that is decaying to the last invisible state is shown in red. Credit: ATLAS Collaboration / CERN

In the recently presented results, ATLAS Collaboration studied the entire LHC Run 2 dataset, collected by the ATLAS detector in 2015–2018, to look for Higgs-boson decay into dark matter particles. in VBF events. No significant redundancy of the expected background was found from known Standard Model procedures in the analysis. ATLAS obtained, at a 95% confidence level, the exclusion limit of the Higgs-boson decay into invisible particles is 13%. This analysis included about 75% more data than the previous ATLAS search, and the team made a number of improvements including:

  • Faster filtering algorithms to generate more simulated collisions with equal computational power. Lack of simulation events was the leading factor of uncertainty in the first 13 TeV version of this analysis.
  • The collision selection is optimized to accept ~ 50% more Higgs-boson events on the same data set.
  • The event categorization is tweaked to result in a higher signal-to-background ratio in the search areas. This can be seen in Figure 1 when the red curve in the bottom panel increases with the higher constant mass of the first two jets (mJJ).
  • Improved collisions tolerance is enriched in background processes, allowing analysts to improve background process models.
Upper limit of WIMP-Nucleon cross section

Figure 2: Upper limit of WIMP-nucleon cross section at 90% confidence level obtained in this analysis compared with direct detection tests. Credit: ATLAS Collaboration / CERN

This observed exclusion is consistent with no indication that the Higgs boson is decaying into dark matter. The new results drive the search for weakly interacting mass particles (WIMPs), a common candidate for dark matter. ATLAS establishes additional exclusion limits for lower WIMP volumes, which are compared with other direct detection experiments in Figure 2. These bounds compete with the best direct detection tests for WIMP mass is up to half of the Higgs-boson mass, assuming the Higgs boson is interacting directly with dark matter.

This new analysis places the strongest limit available to date on the decay of the Higgs boson into invisible particles. As the search continues, physicists will continue to increase sensitivity to this basic dark matter probe.




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