Dib Venturelli, Claudio Omar

The Search for Hidden Particles (SHiP) Collaboration has shown that the CERN SPS accelerator with its 400 GeV c proton beam offers a unique opportunity to explore the Hidden Sector [1–3]. The proposed experiment is an intensity frontier experiment which is capable of searching for hidden particles through both visible decays and through scattering signatures from recoil of electrons or nuclei. The high-intensity experimental facility developed by the SHiP Collaboration is based on a number of key features and developments which provide the possibility of probing a large part of the parameter space for a wide range of models with light long-lived superweakly interacting particles with masses up to O¹10º GeV c2 in an environment of extremely clean background conditions. This paper describes the proposal for the experimental facility together with the most important feasibility studies. The paper focuses on the challenging new ideas behind the beam extraction and beam delivery, the proton beam dump, and the suppression of beam-induced background.

ANDES (Agua Negra Deep Experiment Site) is an underground laboratory, proposed to be built inside the Agua Negra road tunnel that will connect Chile (IV Region) with Argentina (San Juan Province) under the Andes Mountains. The Laboratory will be 1750 meters under the rock, becoming the 3rd deepest underground laboratory of this kind in the world, and the first in the Southern Hemisphere. ANDES will be an international Laboratory, managed by a Latin American consortium. The laboratory will host experiments in Particle and Astroparticle Physics, such as Neutrino and Dark Matter searches, Seismology, Geology, Geophysics and Biology. It will also be used for the development of low background instrumentation and related services. Here we present the general features of the proposed laboratory, the current status of the proposal and some of its opportunities for science.

In this work, we explore an extension of the Standard Model designed to elucidate the fermion mass hierarchy, account for the dark matter relic abundance, and explain the observed matter-antimatter asymmetry in the universe. Beyond the Standard Model particle content, our model introduces additional scalars and fermions. Notably, the light active neutrinos and the first two generations of charged fermions acquire masses at the one-loop level. The model accommodates successful low-scale leptogenesis, permitting the mass of the decaying heavy right-handed neutrino to be as low as 10 TeV. We conduct a detailed analysis of the dark matter phenomenology and explore various interesting phenomenological implications. These include charged lepton flavor violation, muon and electron anomalous magnetic moments, constraints arising from electroweak precision observables, and implications for collider experiments.

We study the process pp¯ → γγγ as a signal for associated photon–technipion production at the Tevatron. This is a clean signature with relatively low background. Resonant and non-resonant contributions are included and we show that technicolor models can be effectively probed in this mode

The phenomenon of neutrino flavor oscillations motivates searches for sterile neutrinos in a broad range of masses and mixing-parameter values. A sterile neutrino 𝑁 that mixes predominantly with the 𝜏 neutrino is particularly challenging experimentally. To address this challenge, we propose a new method to search for a 𝜈𝜏-mixing 𝑁 that is lighter than the 𝜏 lepton. The method uses the large 𝑒+⁢𝑒−→𝜏+⁢𝜏− samples collected at 𝐵-factory experiments to produce the 𝑁 in 𝜏-lepton decays. We exploit the long lifetime of a sterile neutrino in this mass range to suppress background and apply kinematic and vertexing constraints that enable measuring the sterile-neutrino mass. Estimates for the sensitivities of the BABAR, Belle, and Belle II experiments are calculated and presented.

The Search for Hidden Particles (SHiP) experiment proposal at CERN demands a dedicated dipole magnet for its scattering and neutrino detector. This requires a very large volume to be uniformly magnetized at B > 1:2 T, with constraints regarding the inner instrumented volume as well as the external region, where no massive structures are allowed and only an extremely low stray field is admitted. In this paper we report the main technical challenges and the relevant design options providing a comprehensive design for the magnet of the SHiP Scattering and Neutrino Detector.

We study two- and three-body lepton flavor violating (LFV) decays involving leptons and neu- tral vector bosons V = ρ0, ω, φ, J/ψ, Υ, Z0, as well as pseudoscalar P = π0, η, η′, ηc and scalar S = f0(500), f0(980), a0(980), χc0(1P ) mesons, without referring to a specific mechanism of LFV realization. In particular, we relate the rates of the three-body LFV decays τ (μ) → 3`, where ` = μ or e, to the two-body LFV decays (V, P ) → τ μ(τ e, μe), where V and P play the role of intermediate resonances in the decay process τ (μ) → 3`. From the experimental upper bounds for the branching ratios of τ (μ) → 3` decays, we derive upper limits for the branching ratios of (V, P ) → τ μ(τ e, μe). We compare our results to the available experimental data and known theoretical upper limits from previous studies of LFV processes and find that some of our limits are several orders of magnitude more stringent. Using the idea of quark-hadron duality, we extract limits on various quark-lepton dimension-six LFV operators from data on lepton decays. Some of these limits are either new or stronger than those existing in the literature.

We obtain results for the average number of muons at sea level in a proton-initiated vertical atmospheric cascade using a simple model of hadronic interactions based on the Hillas splitting algorithm. We study the muon yield at sea level as a function of the proton primary energy, varying the parameters of the interaction model in order to see the behavior of our results. We find that our results are in agreement with experimental data and with those of more sophisticated simulation models for some particular values of the model parameters.

Magnetars are a subclass of neutron stars whose intense soft-gamma-ray bursts and quiescent X-ray emission are believed to be powered by the decay of a strong internal magnetic field. We reanalyze neutrino emission in such stars in the plausibly relevant regime in which the Landau band spacing $\Delta E$ of both protons and electrons is much larger than kT (where k is the Boltzmann constant and T is the temperature), but still much smaller than the Fermi energies. Focusing on the direct Urca process, we find that the emissivity oscillates as a function of density or magnetic field, peaking when the Fermi level of the protons or electrons lies about $\sim$3 kT above the bottom of any of their Landau bands. The oscillation amplitude is comparable to the average emissivity when $\Delta E$ is roughly the geometric mean of kT and the Fermi energy (excluding mass), i.e., at fields much weaker than required to confine all particles to the lowest Landau band. Since the density and magnetic field strength vary continuously inside the neutron star, there will be alternating surfaces of high and low emissivity. Globally, these oscillations tend to average out, making it unclear whether there will be any observable effects.

We propose to study the leptonic decays W± → e±e±μ∓ν and W± → μ±μ±e∓ν at the LHC to discover sterile neutrinos with masses below MW , and discriminate their Majorana or Dirac character. These decays are induced by a sterile neutrino N that goes on mass shell in the intermediate state. We find that, even though the final (anti-)neutrino goes undetected and thus lepton number is unchecked, one can distinguish between the Majorana vs. Dirac character of the intermediate sterile neutrino by comparing the production of e±e±μ∓ vs. μ±μ±e∓, provided the N-e and N-μ mixings are different enough. Alternatively, one can also distinguish the Majorana vs. Dirac character by studying the energy spectra of the opposite charge lepton, a method that works even if the N-e and N-μ mixings are equal.