We present searches for light dark matter (DM) with masses 3-9 GeV/$c^2$ in the presence of coherent elastic neutrino-nucleus scattering (CE$ν$NS) from $^{8}$B solar neutrinos with the LUX-ZEPLIN experiment. This analysis uses a 5.7 tonne-year exposure with data collected between March 2023 and April 2025. In an energy range spanning 1-6 keV, we report no significant excess of events attributable to dark matter nuclear recoils, but we observe a significant signal from $^{8}$B CE$ν$NS interactions that is consistent with expectation. We set world-leading limits on spin-independent and spin-dependent-neutron DM-nucleon interactions for masses down to 5 GeV/$c^2$. In the no-dark-matter scenario, we observe a signal consistent with $^{8}$B CE$ν$NS events, corresponding to a $4.5σ$ statistical significance. This is the most significant evidence of $^{8}$B CE$ν$NS interactions and is enabled by robust background modeling and mitigation techniques. This demonstrates LZ's ability to detect rare signals at keV-scale energies.
90% CL WIMP SI cross sections, including sensitivities
90% CL WIMP SDn cross sections, including sensitivities and nuclear structure uncertainties
90% CL WIMP SDp cross sections, including sensitivities and nuclear structure uncertainties
While dual-phase xenon time projection chambers (TPCs) have driven the sensitivity towards weakly interacting massive particles (WIMPs) at the GeV/c^2 to TeV/c^2 mass scale, the scope for sub-GeV/c^2 dark matter particles is hindered by a limited nuclear recoil energy detection threshold. One approach to probe for lighter candidates is to consider cases where they have been boosted by collisions with cosmic rays in the Milky Way, such that the additional kinetic energy lifts their induced signatures above the nominal threshold. In this Letter, we report first results of a search for cosmic ray-boosted dark matter (CRDM) with a combined 4.2 tonne-year exposure from the LUX-ZEPLIN (LZ) experiment. We observe no excess above the expected backgrounds and establish world-leading constraints on the spin-independent CRDM-nucleon cross section as small as 3.9 * 10^{-33} cm^2 at 90% confidence level for sub-GeV/c^2 masses.
90% CL CRDM-nucleon cross sections
The formation of light (anti)nuclei with mass number A of a few units (e.g., d, $^3$He, and $^4$He) in high-energy hadronic collisions presents a longstanding mystery in nuclear physics [1,2]. It is not clear how nuclei bound by a few MeV can emerge in environments characterized by temperatures above 100 MeV [3-5], about 100,000 times hotter than the center of the Sun. Despite extensive studies, this question remained unanswered. The ALICE Collaboration now addresses it with a novel approach using deuteron-pion momentum correlations in proton-proton (pp) collisions at the Large Hadron Collider (LHC). Our results provide model-independent evidence that about 80% of the observed (anti)deuterons are produced in nuclear fusion reactions [6] following the decay of short-lived resonances, such as the $\Delta (1232)$. These findings resolve a crucial gap in our understanding of nucleosynthesis in hadronic collisions. Beyond answering the fundamental question on how nuclei are formed in hadronic collisions, the results can be employed in the modeling of the production of light and heavy nuclei in cosmic rays [7] and dark matter decays [8,9].
Measured $\pi^{+}$–d$\oplus\pi^{-}$–$\overline{\mathrm{d}}$ (left panel) correlation function.
Measured $\pi^{-}$–d$\oplus\pi^{+}$–$\overline{\mathrm{d}}$ (right panel) correlation function.
The extracted kinetic decoupling temperature is derived from $\pi^{+}$–d correlation functions.
We report results from a 2018 pilot run to study the feasibility of nuclear fragmentation measurements with the NA61/SHINE experiment at the CERN SPS. These results are important for the interpretation of the production of light secondary cosmic-ray nuclei (Li, Be, and B) in the Galaxy. The specific focus here is on cross sections important for the production of boron in the Galaxy from the interactions of $^{12}$C nuclei with hydrogen in the interstellar medium, including the contribution from the decay of the short-lived $^{11}$C fragments. The data were taken with the secondary $^{12}$C beam at beam momentum of 13.5 GeV/c per nucleon and two fixed targets, polyethylene (CH$_2$) and graphite (C), from which we derive the cross sections of carbon on hydrogen. We present the measurement of the fragmentation cross sections of $^{11}$C, $^{11}$B, and $^{10}$B as well as the mass- and charge-changing cross sections.
Mass-changing, charge-changing and production cross sections of $^{11}\mathrm{C}$, $^{11}\mathrm{B}$ and $^{10}\mathrm{B}$ nuclei in $^{12}\mathrm{C}$ + p interactions at 13.5 GeV/c per nucleon. Graphite (C) and polyethylene (CH2) targets were used. The cross section on a proton target (p) was derived from the measurements on the CH2 and C targets according to the formula $\sigma_p = \frac{1}{2}\left( \sigma_{\mathrm{CH2}} - \sigma_{\mathrm{C}} \right).$ Notation for the type of cross section in the table: mc – mass-changing, cc – charge-changing, prod – production.
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 $4.2\pm0.1$ tonne-years from 280 live days of LZ operation, of which $3.3\pm0.1$ tonne-years and 220 live days are new. A technique to actively tag background electronic recoils from $^{214}$Pb $β$ decays is featured for the first time. Enhanced electron-ion recombination is observed in two-neutrino double electron capture decays of $^{124}$Xe, 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 $\geq$9 GeV/$c^2$. The strongest SI exclusion set is $2.2\times10^{-48}$ cm$^{2}$ at the 90% confidence level and the best SI median sensitivity achieved is $5.1\times10^{-48}$ cm$^{2}$, both for a mass of 40 GeV/$c^2$.
90% CL WIMP SI cross sections, including sensitivities
90% CL WIMP SI cross sections, including sensitivities
90% CL WIMP SDn cross sections, including sensitivities and nuclear structure uncertainties
Weakly interacting massive particles (WIMPs) may interact with a virtual pion that is exchanged between nucleons. This interaction channel is important to consider in models where the spin-independent isoscalar channel is suppressed. Using data from the first science run of the LUX-ZEPLIN dark matter experiment, containing 60 live days of data in a 5.5~tonne fiducial mass of liquid xenon, we report the results on a search for WIMP-pion interactions. We observe no significant excess and set an upper limit of $1.5\times10^{-46}$~cm$^2$ at a 90% confidence level for a WIMP mass of 33~GeV/c$^2$ for this interaction.
WIMP-Pion interaction cross section at the 90% CL
The first science run of the LUX-ZEPLIN (LZ) experiment, a dual-phase xenon time project chamber operating in the Sanford Underground Research Facility in South Dakota, USA, has reported leading limits on spin-independent WIMP-nucleon interactions and interactions described from a non-relativistic effective field theory (NREFT). Using the same 5.5~t fiducial mass and 60 live days of exposure we report on the results of a relativistic extension to the NREFT. We present constraints on couplings from covariant interactions arising from the coupling of vector, axial currents, and electric dipole moments of the nucleon to the magnetic and electric dipole moments of the WIMP which cannot be described by recasting previous results described by an NREFT. Using a profile-likelihood ratio analysis, in an energy region between 0~keV$_\text{nr}$ to 270~keV$_\text{nr}$, we report 90% confidence level exclusion limits on the coupling strength of five interactions in both the isoscalar and isovector bases.
Isoscalar interaction coupling limit for Lagrangian 1
Isovector interaction coupling limit for Lagrangian 19
Isoscalar interaction coupling limit for Lagrangian 19
A search for high-mass resonances decaying into a $\tau$-lepton and a neutrino using proton-proton collisions at a center-of-mass energy of $\sqrt{s}=13$ TeV is presented. The full Run 2 data sample corresponding to an integrated luminosity of 139 fb$^{-1}$ recorded by the ATLAS experiment in the years 2015-2018 is analyzed. The $\tau$-lepton is reconstructed in its hadronic decay modes and the total transverse momentum carried out by neutrinos is inferred from the reconstructed missing transverse momentum. The search for new physics is performed on the transverse mass between the $\tau$-lepton and the missing transverse momentum. No excess of events above the Standard Model expectation is observed and upper exclusion limits are set on the $W^\prime\to \tau \nu$ production cross-section. Heavy $W^\prime$ vector bosons with masses up to 5.0 TeV are excluded at 95% confidence level, assuming that they have the same couplings as the Standard Model $W$ boson. For non-universal couplings, $W^\prime$ bosons are excluded for masses less than 3.5-5.0 TeV, depending on the model parameters. In addition, model-independent limits on the visible cross-section times branching ratio are determined as a function of the lower threshold on the transverse mass of the $\tau$-lepton and missing transverse momentum.
Observed and predicted $m_{\rm T}$ distributions including SSM and NU (cot$\theta$ = 5.5) $W^{\prime}$ signals with masses of 4 TeV. Please note that in the paper figure the bin content is divided by the bin width, but this is not done in the HepData table.
Observed and expected 95% CL upper limits on cross section times $\tau\nu$ branching fraction for $W^{\prime}_{\rm SSM}$.
Regions of the non-universal parameter space excluded at 95% CL.
Searches for dark matter with liquid xenon time projection chamber experiments have traditionally focused on the region of the parameter space that is characteristic of weakly interacting massive particles, ranging from a few GeV/$c^2$ to a few TeV/$c^2$. Models of dark matter with a mass much heavier than this are well motivated by early production mechanisms different from the standard thermal freeze-out, but they have generally been less explored experimentally. In this work, we present a re-analysis of the first science run (SR1) of the LZ experiment, with an exposure of $0.9$ tonne$\times$year, to search for ultraheavy particle dark matter. The signal topology consists of multiple energy deposits in the active region of the detector forming a straight line, from which the velocity of the incoming particle can be reconstructed on an event-by-event basis. Zero events with this topology were observed after applying the data selection calibrated on a simulated sample of signal-like events. New experimental constraints are derived, which rule out previously unexplored regions of the dark matter parameter space of spin-independent interactions beyond a mass of 10$^{17}$ GeV/$c^2$.
Upper limit on the WIMP-nucleon scattering cross section from the multiple-scatter analysis.
Upper limit on the WIMP-nucleus scattering cross section from the multiple-scatter analysis.
Upper limit on the WIMP-nucleon scattering cross section from the single-scatter analysis.
Strong interactions preserve an approximate isospin symmetry between up ($u$) and down ($d$) quarks, part of the more general flavor symmetry. In the case of $K$ meson production, if this isospin symmetry were exact, it would result in equal numbers of charged ($K^+$ and $K^-$) and neutral ($K^0$ and $\overline K^{\,0}$) mesons in the final state. Here, we report results on the relative abundance of charged over neutral $K$ meson production in argon and scandium nuclei collisions at a center-of-mass energy of 11.9 GeV per nucleon pair. We find that the production of $K^+$ and $K^-$ mesons at mid-rapidity is $(18.4\pm 6.1)\%$ higher than that of the neutral $K$ mesons. Although with large uncertainties, earlier data on nucleus-nucleus collisions in the collision center-of-mass energy range $2.6 < \sqrt{s_{NN}} < 200$~\GeV are consistent with the present result. Using well-established models for hadron production, we demonstrate that known isospin-symmetry breaking effects and the initial nuclei containing more neutrons than protons lead only to a small (few percent) deviation of the charged-to-neutral kaon ratio from unity at high energies. Thus, they cannot explain the measurements. The significance of the flavor-symmetry violation beyond the known effects is 4.7$\sigma$ when the compilation of world data with uncertainties quoted by the experiments is used. New systematic, high-precision measurements and theoretical efforts are needed to establish the origin of the observed large isospin-symmetry breaking.
Numerical data for $K^0_S$ from Figure 1.
Numerical data for $K^0_S$ from Figure 1.
Numerical data for $(K^+ + K^-)/2$ from Figure 1.
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