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The field of dark matter detection is a highly visible and highly competitive one. In this paper, we propose recommendations for presenting dark matter direct detection results particularly suited for weak-scale dark matter searches, although we believe the spirit of the recommendations can apply more broadly to searches for other dark matter candidates, such as very light dark matter or axions. To translate experimental data into a final published result, direct detection collaborations must make a series of choices in their analysis, ranging from how to model astrophysical parameters to how to make statistical inferences based on observed data. While many collaborations follow a standard set of recommendations in some areas, for example the expected flux of dark matter particles (to a large degree based on a paper from Lewin and Smith in 1995), in other areas, particularly in statistical inference, they have taken different approaches, often from result to result by the same collaboration. We set out a number of recommendations on how to apply the now commonly used Profile Likelihood Ratio method to direct detection data. In addition, updated recommendations for the Standard Halo Model astrophysical parameters and relevant neutrino fluxes are provided. The authors of this note include members of the DAMIC, DarkSide, DARWIN, DEAP, LZ, NEWS-G, PandaX, PICO, SBC, SENSEI, SuperCDMS, and XENON collaborations, and these collaborations provided input to the recommendations laid out here. Wide-spread adoption of these recommendations will make it easier to compare and combine future dark matter results.

New neutrino–nucleus interaction cross-section measurements are required to improve nuclear models sufficiently for future long baseline neutrino experiments to meet their sensitivity goals. A time projection chamber (TPC) filled with a high-pressure gas is a promising detector to characterise the neutrino sources used for such experiments. A gas-filled TPC is ideal for measuring low-energy particles, which travel further in gas than in solid or liquid detectors and using high-pressure increases the target density, resulting in more neutrino interactions. We examine the suitability of multiwire proportional chambers (MWPCs) from the ALICE TPC for use as the readout chambers of a high-pressure gas TPC. These chambers were previously operated at atmospheric pressure. We report the successful operation of an ALICE TPC outer readout chamber (OROC) at pressures up to 4.2 bar absolute (barA) with Ar-CH 4 mixtures with a CH 4 content between 2.8 and 5.0%, and so far up to 4 bar absolute with Ar-CO 2 (90-10). The charge gain of the OROC was measured with signals induced by an 55 Fe source. The largest gain achieved at 4.2 bar was ( 29 ± 1 ) · 10 3 in Ar-CH 4 with 4.0% CH 4 with an anode voltage of 2975 V . In Ar-CO 2 with 10% CO 2 at 4 barA, a gain of ( 4.2 ± 0.1 ) · 10 3 was observed with anode voltage 2975 V . We extrapolate that at 10 barA, an interesting pressure for future neutrino experiments, a gain of 5000 in Ar-CO 2 with 10% CO 2 (10,000 in Ar-CH 4 with ∼ 4 % CH 4 ) may be achieved with anode voltage of 4.6 kV ( ∼ 3.6 kV ).

We present studies of proton fluxes in the T10 beamline at CERN. A prototype high pressure gas time projection chamber (TPC) was exposed to the beam of protons and other particles, using the 0.8 GeV/c momentum setting in T10, in order to make cross section measurements of low energy protons in argon. To explore the energy region comparable to hadrons produced by GeV-scale neutrino interactions at oscillation experiments, i.e., near 0.1 GeV of kinetic energy, methods of moderating the T10 beam were employed: the dual technique of moderating the beam with acrylic blocks and measuring scattered protons off the beam axis was used to decrease the kinetic energy of incident protons, as well as change the proton/minimum ionising particle (MIP) composition of the incident flux. Measurements of the beam properties were made using time of flight systems upstream and downstream of the TPC. The kinetic energy of protons reaching the TPC was successfully changed from ∼0.3 GeV without moderator blocks to less than 0.1 GeV with four moderator blocks (40 cm path length). The flux of both protons and MIPs off the beam axis was increased. The ratio of protons to MIPs vary as a function of the off-axis angle allowing for possible optimisation of the detector to select the type of required particles. Simulation informed by the time of flight measurements show that with four moderator blocks placed in the beamline, (5.6 ± 0.1) protons with energies below 0.1 GeV per spill traversed the active TPC region. Measurements of the beam composition and energy are presented.

The charge-conjugation and parity-reversal (CP) symmetry of fundamental particles is a symmetry between matter and antimatter. Violation of this CP symmetry was first observed in 1964 1 , and CP violation in the weak interactions of quarks was soon established 2 . Sakharov proposed 3 that CP violation is necessary to explain the observed imbalance of matter and antimatter abundance in the Universe. However, CP violation in quarks is too small to support this explanation. So far, CP violation has not been observed in non-quark elementary particle systems. It has been shown that CP violation in leptons could generate the matter–antimatter disparity through a process called leptogenesis 4 . Leptonic mixing, which appears in the standard model’s charged current interactions 5 , 6 , provides a potential source of CP violation through a complex phase δ CP , which is required by some theoretical models of leptogenesis 7 – 9 . This CP violation can be measured in muon neutrino to electron neutrino oscillations and the corresponding antineutrino oscillations, which are experimentally accessible using accelerator-produced beams as established by the Tokai-to-Kamioka (T2K) and NOvA experiments 10 , 11 . Until now, the value of δ CP has not been substantially constrained by neutrino oscillation experiments. Here we report a measurement using long-baseline neutrino and antineutrino oscillations observed by the T2K experiment that shows a large increase in the neutrino oscillation probability, excluding values of δ CP that result in a large increase in the observed antineutrino oscillation probability at three standard deviations (3 σ ). The 3 σ confidence interval for δ CP , which is cyclic and repeats every 2π, is [−3.41, −0.03] for the so-called normal mass ordering and [−2.54, −0.32] for the inverted mass ordering. Our results indicate CP violation in leptons and our method enables sensitive searches for matter–antimatter asymmetry in neutrino oscillations using accelerator-produced neutrino beams. Future measurements with larger datasets will test whether leptonic CP violation is larger than the CP violation in quarks. The T2K experiment constrains CP symmetry in neutrino oscillations, excluding 46% of possible values of the CP violating parameter at a significance of three standard deviations; this is an important milestone to test CP symmetry conservation in leptons and whether the Universe’s matter–antimatter imbalance originates from leptons.

New neutrino–nucleus interaction cross-section measurements are required to improve nuclear models sufficiently for future long baseline neutrino experiments to meet their sensitivity goals. A time projection chamber (TPC) filled with a high-pressure gas is a promising detector to characterise the neutrino sources used for such experiments. A gas-filled TPC is ideal for measuring low-energy particles, which travel further in gas than in solid or liquid detectors and using high-pressure increases the target density, resulting in more neutrino interactions. We examine the suitability of multiwire proportional chambers (MWPCs) from the ALICE TPC for use as the readout chambers of a high-pressure gas TPC. These chambers were previously operated at atmospheric pressure. We report the successful operation of an ALICE TPC outer readout chamber (OROC) at pressures up to 4.2 bar absolute (barA) with$$\\text {Ar-CH}_4$$Ar-CH 4 mixtures with a$$\\text {CH}_{4}$$CH 4 content between 2.8 and 5.0%, and so far up to 4 bar absolute with$${\\text {Ar-CO}}_2$$Ar-CO 2 (90-10). The charge gain of the OROC was measured with signals induced by an$$^{55}\\text {Fe}$$55 Fe source. The largest gain achieved at 4.2 bar was$$(29\\pm 1)\\cdot 10^{3}$$( 29 ± 1 ) · 10 3 in$$\\text {Ar-CH}_4$$Ar-CH 4 with 4.0%$$\\text {CH}_{4}$$CH 4 with an anode voltage of$${2975}\\,\\hbox {V}$$2975 V . In$${\\text {Ar-CO}}_2$$Ar-CO 2 with 10%$$\\text {CO}_{2}$$CO 2 at 4 barA, a gain of$$(4.2\\pm 0.1)\\cdot 10^{3}$$( 4.2 ± 0.1 ) · 10 3 was observed with anode voltage$${2975}\\,\\hbox {V}$$2975 V . We extrapolate that at 10 barA, an interesting pressure for future neutrino experiments, a gain of 5000 in$${\\text {Ar-CO}}_2$$Ar-CO 2 with 10%$$\\text {CO}_{2}$$CO 2 (10,000 in$$\\text {Ar-CH}_4$$Ar-CH 4 with$$\\sim \\!{4}{\\%}$$∼ 4 %$$\\text {CH}_{4}$$CH 4 ) may be achieved with anode voltage of$${4.6}\\,\\hbox {kV}$$4.6 kV ($$\\sim \\!{3.6}\\,\\hbox {kV}$$∼ 3.6 kV ).

Bayesian analysis results require a choice of prior distribution. In long-baseline neutrino oscillation physics, the usual parameterisation of the mixing matrix induces a prior that privileges certain neutrino mass and flavour state symmetries. Here we study the effect of privileging alternate symmetries on the results of the T2K experiment. We find that constraints on the level of CP violation (as given by the Jarlskog invariant) are robust under the choices of prior considered in the analysis. On the other hand, the degree of octant preference for the atmospheric angle depends on which symmetry has been privileged.

Bayesian analysis results require a choice of prior distribution. In long-baseline neutrino oscillation physics, the usual parameterisation of the mixing matrix induces a prior that privileges certain neutrino mass and flavour state symmetries. Here we study the effect of privileging alternate symmetries on the results of the T2K experiment. We find that constraints on the level of CP violation (as given by the Jarlskog invariant) are robust under the choices of prior considered in the analysis. On the other hand, the degree of octant preference for the atmospheric angle depends on which symmetry has been privileged.

This report describes the experimental strategy and technologies for XLZD, the next-generation xenon observatory sensitive to dark matter and neutrino physics. In the baseline design, the detector will have an active liquid xenon target of 60 tonnes, which could be increased to 80 tonnes if the market conditions for xenon are favorable. It is based on the mature liquid xenon time projection chamber technology used in current-generation experiments, LZ and XENONnT. The report discusses the baseline design and opportunities for further optimization of the individual detector components. The experiment envisaged here has the capability to explore parameter space for Weakly Interacting Massive Particle (WIMP) dark matter down to the neutrino fog, with a 3σ evidence potential for WIMP-nucleon cross sections as low as 3 x 10–49 cm2 (at 40 GeV/c2 WIMP mass). The observatory will also have leading sensitivity to a wide range of alternative dark matter models. It is projected to have a 3σ observation potential of neutrinoless double beta decay of 136Xe at a half-life of up to 5.7 x 1027 years. Additionally, it is sensitive to astrophysical neutrinos from the sun and galactic supernovae.

We present new results with a prototype detector that is being developed by the DMTPC collaboration for the measurement of the direction tag ( head-tail ) of dark matter wind. We use neutrons from a 252Cf source to create low-momentum nuclear recoils in elastic scattering with the residual gas nuclei. The recoil track is imaged in low-pressure time-projection chamber with optical readout. We measure the ionization rate along the recoil trajectory, which allows us to determine the direction tag of the incoming neutrons.