Spin-independent Elastic Scattering Cross Section Research Articles

Lighting up the LHC with Dark Matter

We show that simultaneously explaining dark matter and the observed value of the muon’s magnetic dipole moment may lead to yet unexplored photon signals at the LHC. We consider the Minimal Supersymmetric Standard Model with electroweakino masses in the few-to-several hundred GeV range, and opposite sign of the Bino mass parameter with respect to both the Higgsino and Wino mass parameters. In such region of parameter space, the spin-independent elastic scattering cross section of a Bino-like dark matter candidate in direct detection experiment is suppressed by cancellations between different amplitudes, and the observed dark matter relic density can be realized via Bino-Wino co-annihilation. Moreover, the observed value of the muon’s magnetic dipole moment can be explained by Bino and Wino loop contributions. Interestingly, “radiative” decays of Wino-like neutralinos into the lightest neutralino and a photon are enhanced, whereas decays into leptons are suppressed. While these decay patterns weaken the reach of multi-lepton searches at the LHC, the radiative decay opens a new window for probing dark matter at the LHC through the exploration of parameter space regions beyond those currently accessible. To complement the current electroweakino searches, we propose searching for a single (soft) photon plus missing transverse energy, accompanied by a hard initial state radiation jet.

Constraining the spin-independent elastic scattering cross section of dark matter using the Moon as a detection target and the background neutrino data

Our Moon is a natural giant direct-detection target for constraining dark matter. By considering the dark matter capture rate of the Moon, we obtain some constraints of the spin-independent elastic scattering cross section of dark matter particles on nucleons $\sigma_p^{\rm SI}$ using the background neutrino data. The upper limits of $\sigma_p^{\rm SI}$ can be constrained to $\sim 10^{-38}-10^{-36}$ cm$^2$ for certain `resonance dark matter mass' ranges. These stringent astrophysical constraints are complementary to the constraints obtained by the direct-detection experiments.

Energy response and position reconstruction in the DEAP-3600 dark matter experiment

DEAP-3600 is a dark matter WIMP (Weakly Interacting Massive Particles) search experiment, which aims to detect nuclear recoils from WIMP scattering in a liquid argon target. At WIMP masses of 100 GeV, DEAP-3600 has a projected sensitivity of 10−46 cm2 for the spin-independent elastic scattering cross section of WIMPs. The beta emissions from the intrinsic 39 Ar present in the natural Ar target, as well as external calibration sources, can be used to tune the energy calibration and position reconstruction in the energy region of interest (ROI) for WIMP signals. These proceedings will present the techniques used to determine the energy response and position reconstruction in DEAP-3600. Using these techniques, the light yield was found to be LY = (math) (fit syst.) ± 0.22(SPE syst.) PE/keVee with a fiducial mass for WIMP detection of 2 223 ± 74 kg for the first data set.

Latest results from the XENON1T experiment

The most successful class of direct detection of WIMPs with masses from few GeV/c2 to TeV/c2 have utilized Liquid Xenon time projection chambers (TPCs). The XENON project adopted dual phase TPCs using ultra-pure liquid Xenon as both target and detection medium for WIMPs. The first ton-scale Liquid Xenon based TPC, XENON1T, is running at the Gran Sasso Laboratory. With an active mass inside the TPC of 2 tonnes, data were collected for 278.8 days live time. Within a fiducial mass of 1.3 tonne, this results in 1.0 tonne×year exposure. In the energy region of interest, the detector exhibits the lowest background ever obtained in direct dark matter search experiment. In these data no significant excess over background is found and the most stringent limits on WIMP-nucleon spin-independent elastic scattering cross section has been set for masses above 6 GeV/c2 with a minimum of 4.1×10−47cm2 at 30 GeV/c2.

Effective interaction of electroweak-interacting dark matter with Higgs boson and its phenomenology

We study phenomenology of electroweak-interacting fermionic dark matter (DM) with a mass of O(100) GeV. Constructing the effective Lagrangian that describes the interactions between the Higgs boson and the SU(2)L isospin multiplet fermion, we evaluate the electric dipole moment (EDM) of electron, the signal strength of Higgs boson decay to two photons and the spin-independent elastic-scattering cross section with proton. As representative cases, we consider the SU(2)L triplet fermions with zero/nonzero hypercharges and SU(2)L doublet fermion. It is found that the electron EDM gives stringent constraints on those model parameter spaces. In the cases of the triplet fermion with zero hypercharge and the doublet fermion, the Higgs signal strength does not deviate from the standard model prediction by more than a few % once the current DM direct detection constraint is taken into account, even if the CP violation is suppressed. On the contrary, O(10–20)% deviation may occur in the case of the triplet fermion with nonzero hypercharge. Our representative scenarios may be tested by the future experiments.

Neutrino mass and dark matter in light of recent AMS-02 results

We study a simple extension of the Standard Model supplemented by an electroweak triplet scalar field to accommodate small neutrino masses by the type-II seesaw mechanism, while an additional singlet scalar field can play the role of cold dark matter (DM) in our Universe. This DM candidate is leptophilic for a wide range of model parameter space, and the lepton flux due to its annihilation carries information about the neutrino mass hierarchy. Using the recently released high precision data on positron fraction and flux from the AMS-02 experiment, we examine the DM interpretation of the observed positron excess in our model for two kinematically distinct scenarios with the DM and triplet scalar masses (a) non-degenerate ($m_{\rm DM}\gg m_{\Delta}$), and (b) quasi-degenerate ($m_{\rm DM} \simeq m_\Delta$). We find that a good fit to the AMS-02 data can be obtained in both cases (a) and (b) with a normal hierarchy of neutrino masses, while the inverted hierarchy case is somewhat disfavored. Although we require a larger boost factor for the normal hierarchy case, this is still consistent with the current upper limits derived from Fermi-LAT and IceCube data for case (a). Moreover, the absence of an excess anti-proton flux as suggested by PAMELA data sets an indirect upper limit on the DM-nucleon spin-independent elastic scattering cross section which is stronger than the existing DM direct detection bound from LUX in the AMS-02 preferred DM mass range.

Originally asymmetric dark matter

We propose a scenario with a fermion dark matter, where the dark matter particle used to be the Dirac fermion, but it takes the form of the Majorana fermion at a late time. The relic number density of the dark matter is determined by the dark matter asymmetry generated through the same mechanism as leptogenesis when the dark matter was the Dirac fermion. After efficient dark matter annihilation processes have frozen out, a phase transition of a scalar field takes place and generates Majorana mass terms to turn the dark matter particle into the Majorana fermion. In order to address this scenario in detail, we propose two simple models. The first one is based on the Standard Model (SM) gauge group and the dark matter originates the $SU(2)_L$ doublet Dirac fermion, analogous to the Higgsino-like neutralino in supersymmetric models. We estimate the spin-independent/dependent elastic scattering cross sections of this late-time Majorana dark matter with a proton and find the possibility to discover it by the direct and/or indirect dark matter search experiments in the near future. The second model is based on the $B-L$ gauged extension of the SM, where the dark matter is a SM singlet. Although this model is similar to the so-called Higgs portal dark matter scenario, the spin-independent elastic scattering cross section can be large enough to detect this dark matter in future experiments.