This paper describes the physics case for a new fixed target facility at CERN SPS. The SHiP (search for hidden particles) experiment is intended to hunt for new physics in the largely unexplored domain of very weakly interacting particles with masses below the Fermi scale, inaccessible to the LHC experiments, and to study tau neutrino physics. The same proton beam setup can be used later to look for decays of tau-leptons with lepton flavour number non-conservation, [Formula: see text] and to search for weakly-interacting sub-GeV dark matter candidates. We discuss the evidence for physics beyond the standard model and describe interactions between new particles and four different portals-scalars, vectors, fermions or axion-like particles. We discuss motivations for different models, manifesting themselves via these interactions, and how they can be probed with the SHiP experiment and present several case studies. The prospects to search for relatively light SUSY and composite particles at SHiP are also discussed. We demonstrate that the SHiP experiment has a unique potential to discover new physics and can directly probe a number of solutions of beyond the standard model puzzles, such as neutrino masses, baryon asymmetry of the Universe, dark matter, and inflation.
We present the results of a search for dark matter weakly interacting massive particles (WIMPs) in the mass range below 20 GeV/c^{2} using a target of low-radioactivity argon with a 6786.0 kg d exposure. The data were obtained using the DarkSide-50 apparatus at Laboratori Nazionali del Gran Sasso. The analysis is based on the ionization signal, for which the DarkSide-50 time projection chamber is fully efficient at 0.1 keVee. The observed rate in the detector at 0.5 keVee is about 1.5 event/keVee/kg/d and is almost entirely accounted for by known background sources. We obtain a 90% C.L. exclusion limit above 1.8 GeV/c^{2} for the spin-independent cross section of dark matter WIMPs on nucleons, extending the exclusion region for dark matter below previous limits in the range 1.8-6 GeV/c^{2}.
Dark sectors, consisting of new, light, weakly-coupled particles that do not interact with the known strong, weak, or electromagnetic forces, are a particularly compelling possibility for new physics. Nature may contain numerous dark sectors, each with their own beautiful structure, distinct particles, and forces. This review summarizes the physics motivation for dark sectors and the exciting opportunities for experimental exploration. It is the summary of the Intensity Frontier subgroup "New, Light, Weakly-coupled Particles" of the Community Summer Study 2013 (Snowmass). We discuss axions, which solve the strong CP problem and are an excellent dark matter candidate, and their generalization to axion-like particles. We also review dark photons and other dark-sector particles, including sub-GeV dark matter, which are theoretically natural, provide for dark matter candidates or new dark matter interactions, and could resolve outstanding puzzles in particle and astro-particle physics. In many cases, the exploration of dark sectors can proceed with existing facilities and comparatively modest experiments. A rich, diverse, and lowcost experimental program has been identified that has the potential for one or more game-changing discoveries. These physics opportunities should be vigorously pursued in the US and elsewhere.
When ultralight axion dark matter encounters a static magnetic field, it sources an effective electric current that follows the magnetic field lines and oscillates at the axion Compton frequency. We propose a new experiment to detect this axion effective current. In the presence of axion dark matter, a large toroidal magnet will act like an oscillating current ring, whose induced magnetic flux can be measured by an external pickup loop inductively coupled to a SQUID magnetometer. We consider both resonant and broadband readout circuits and show that a broadband approach has advantages at small axion masses. We estimate the reach of this design, taking into account the irreducible sources of noise, and demonstrate potential sensitivity to axionlike dark matter with masses in the range of 10 −14 -10 −6 eV. In particular, both the broadband and resonant strategies can probe the QCD axion with a GUT-scale decay constant. DOI: 10.1103/PhysRevLett.117.141801 A broad class of well-motivated dark matter (DM) models consists of light pseudoscalar particles a coupled weakly to electromagnetism [1][2][3]. The most famous example is the QCD axion [4][5][6][7], which was originally proposed to solve the strong CP problem. More generally, string compactifications often predict a large number of axionlike particles (ALPs) [8], with Planck-suppressed couplings to electric (E) and magnetic (B) fields of the form aE · B. Unlike QCD axions, generic ALPs do not necessarily couple to the QCD operator GG, where G is the QCD field strength. The masses and couplings of ALP DM candidates are relatively unconstrained by theory or experiment (see Refs. [9-11] for reviews). It is therefore important to develop search strategies that cover many orders of magnitude in the axion parameter space.The ADMX experiment [12][13][14] has already placed stringent constraints on axion DM in a narrow mass range around m a ∼ few × 10 −6 eV. However, ADMX is only sensitive to axion DM whose Compton wavelength is comparable to the size of the resonant cavity. For the QCD axion, the axion mass m a is related to the PecceiQuinn (PQ) symmetry-breaking scale f a viawhere m π ≈ 140 MeV (f π ≈ 92 MeV) is the pion mass (decay constant). Lighter QCD axion masses therefore correspond to higher-scale axion decay constants f a . The GUT scale (f a ∼ 10 16 GeV, m a ∼ 10 −9 eV) is particularly well motivated, but well beyond the reach of ADMX as such small m a would require much larger cavities. More general ALPs can also have lighter masses and larger couplings than in the QCD case.In this Letter, we propose a new experimental design for axion DM detection that targets the mass range m a ∈ ½10 −14 ; 10 −6 eV. Like ADMX, this design exploits the fact that axion DM, in the presence of a static magnetic field, produces response electromagnetic fields that oscillate at the axion Compton frequency. Whereas ADMX is based on resonant detection of a cavity excitation, our design is based on either broadband or resonant detection of an oscillating magnetic flux with sensit...
We show that axion dark matter (DM) may be detectable through narrow radio lines emitted from neutron stars. The neutron star magnetosphere hosts a strong magnetic field and a plasma frequency that increases towards the neutron star surface. As the axions pass through the magnetosphere, they can resonantly convert into radio photons in a narrow region around the radius at which the plasma frequency equals the axion mass. The bandwidth of the signal is set by the small DM velocity dispersion far away from the neutron star. We solve the axion-photon mixing equations, including a full treatment of the magnetized plasma and associated anisotropic dielectric tensor, to obtain the conversion probability. We discuss possible neutron-star targets and how they may probe the QCD axion parameter space in the mass range of ∼0.2-40 µeV.arXiv:1804.03145v1 [hep-ph] 9 Apr 2018 for collaboration in the early stages of this project. We thank Anatoly Spitkovsky for detailed discussions regarding NS magnetospheres, and
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