The Lux-Zeplin direct dark matter detection experiment continues to squeeze the parameter space of WIMP dark matter, which has for all practical purposes, been ruled out.
We report results of a search for nuclear recoils induced by weakly interacting massive particle (WIMP) dark matter using the LUX-ZEPLIN (LZ) two-phase xenon time projection chamber. This analysis uses a total exposure of 4.2 ± 0.1 tonne-years from 280 live days of LZ operation, of which 3.3 ± 0.1 tonne-years and 220 live days are new. A technique to actively tag background electronic recoils from 214Pb β decays is featured for the first time. Enhanced electron-ion recombination is observed in two-neutrino double electron capture decays of 124Xe, representing a noteworthy new background. After removal of artificial signal-like events injected into the data set to mitigate analyzer bias, we find no evidence for an excess over expected backgrounds. World-leading constraints are placed on spin-independent (SI) and spin-dependent WIMP-nucleon cross sections for masses ≥9 GeV/c^2. The strongest SI exclusion set is 2.1×10^−48 cm^2 at the 90% confidence level at a mass of 36 GeV/c^2, and the best SI median sensitivity achieved is 5.0×10^−48 cm^2 for a mass of 40 GeV/c^2.
J. Aalbers, et al., "Dark Matter Search Results from 4.2 Tonne-Years of Exposure of the LUX-ZEPLIN (LZ) Experiment" arXiv:2410.17036 (October 22, 2024).
The cross-section of interaction of a neutrino with a nucleon is a little less than 10^-38 cm^2. The maximum cross-section of dark matter particles with masses from 9 GeV to 10,000 GeV in light of the latest Lux-Zeplin data is 10^-45 cm^2 (i.e. ten million times smaller), and for masses of 11 GeV to 150 GeV it is 10^-47 cm^2 (i.e. a billion times smaller). This is far below the threshold for dark matter candidates such as Higgs portal, Z portal, W portal, and millicharged dark matter candidates. Those thresholds were already passed in 2018.
Basically, if 9 GeV to 10 TeV mass dark matter particles exist, they have to have be "sterile", i.e. have no non-gravitational interactions with ordinary matter.
By comparison, the heaviest atom currently known, Oganesson (element 118) has a mass of about 274 GeV, and the heaviest fundamental particle, the top quark, has a mass of about 173 GeV. Any hypothetical stable hexaquark candidate (and there is no credible evidence than any hadron other than the proton and neutron are ever stable) would still be under 50 GeV and would have a strong cross-section of interaction with ordinary matter. The top of exclusion range reaches up to the mass of a large molecule with several hundred atoms in it, while the bottom of the exclusion range is about half the mass of a water molecule.
Particle physics experiments place tight complementary bounds on the exclusion range for dark matter particles that have a cross section of interaction with ordinary matter that is even a small fraction of the weak force interaction, from the meV mass scale of neutrino masses to hundreds of GeVs. The collective experience of particle physics is particularly compelling in the mass range from the mass of an electron (511 keV) to half of the mass of the Z boson (about 45 GeV) and the Higgs boson (about 62.5 GeV), which has been throughly explored experimentally for decades.
Basically, in light of these experimental non-detections of dark matter, any dark matter particle with a mass on the meV scale or up has to have no non-gravitational interactions with ordinary matter strong enough to be discernible experimentally. This direct detection dull results do not rule out, however, a fifth force interaction between dark matter particles and other dark matter particles, a category of dark matter which is called self-interacting dark matter (SIDM).
The correlations between ordinary matter distributions and inferred dark matter distributions, and the shape of inferred dark matter halos, however, strongly disfavors both "sterile" and SIDM dark matter particle candidates.
A variety of other data disfavors heavier dark matter particle candidates (including wave-like dynamics from astronomy data, and the non-detection of the gravitational effects of compact objects in a sufficient quantity in a mass range that covers basically everything more massive than an asteroid), such as primordial black hole dark matter candidates.
A viable dark matter particle candidate must be both very low in mass and have some sort of interaction with ordinary matter beyond gravity (and must reproduce the radial acceleration relation over many orders of magnitude of galaxy sizes, and must also replicate the external field effect of MOND).
Collectively, these points argue strongly in favor of a gravitational explanation for dark matter phenomena rather than a dark matter particle theory.
5 comments:
A viable dark matter particle candidate must be both very low in mass and have some sort of interaction with ordinary matter beyond gravity (and must reproduce the radial acceleration relation over many orders of magnitude of galaxy sizes, and must also replicate the external field effect of MOND).
Stacy McGaugh favors MOND for individual galaxies and massive neutrinos for galaxies clusters
That won't work and he acknowledge that this theory was in trouble due to low neutrino masses in a recent comment at his blog.
I ask if massive neutrinos are the same as sterile neutrinos and he agreed
The point is the ordinary neutrinos aren't massive enough (in addition to the lack of a mechanism to make them much more common in clusters than elsewhere).
if you fine turning the mass and velocities of sterile neutrinos it might work to make them much more common in clusters than elsewhere
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