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.

We study the feasibility to observe sterile neutrinos with masses in the range 5 GeV

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.

In scenarios of strongly coupled electroweak symmetry breaking, heavy composite particles of different spin and parity may arise and cause observable effects on signals that appear at loop levels. The recently observed process of Higgs to γγ at the LHC is one of such signals. We study the new constraints that are imposed on composite models from , together with the existing constraints from the high precision electroweak tests. We use an effective chiral Lagrangian to describe the effective theory that contains the Standard Model spectrum and the extra composites below the electroweak scale. Considering the effective theory cutoff at , consistency with the T and S parameters and the newly observed can be found for a rather restricted range of masses of vector and axial-vector composites from 1.5 TeV to 1.7 TeV and 1.8 TeV to 1.9 TeV, respectively, and only provided a non-standard kinetic mixing between the and fields is included.

We study leptonic decays W± → e±e±μ∓ν and W± → μ±μ±e∓ν which would occur at the LHC if there exist sterile neutrinos with masses below MW . We also study ways to discriminate their Majorana or Dirac character, a rather non trivial task, because lepton number conservation cannot be checked due to the missing neutrino in the final state. We find that it is indeed possible to discriminate between Majorana vs. Dirac sterile neutrinos by comparing the production of e±e±μ∓ vs. μ±μ±e∓ if the N-e and N-μ mixings are sufficiently different. Alternatively, one could also distinguish the Majorana vs. Dirac character by studying the energy spectra of the opposite charge lepton, a method that works even for equal N-e and N-μ mixings.

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.

AbstractThe SHiP-charm project was proposed to measure the associated charm production induced by 400 GeV/c protons in a thick target, including the contribution from cascade production. An optimisation run was performed in July 2018 at CERN SPS using a hybrid setup. The high resolution of nuclear emulsions acting as vertex detector was complemented by electronic detectors for kinematic measurements and muon identification. Here we present first results on the analysis of nuclear emulsions exposed in the 2018 run, which prove the capability of reconstructing proton interaction vertices in a harsh environment, where the signal is largely dominated by secondary particles produced in hadronic and electromagnetic showers within the lead target.

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.

Some of the outstanding questions of particle physics today concern the neutrino sector, in particular whether there are more neutrinos than those already known and whether they are Dirac or Majorana particles. There are different ways to explore these issues. In this article we describe neutrino-mediated decays of charged pseudoscalar mesons such as π±,K± and B±, in scenarios where extra neutrinos are heavy and can be on their mass shell. We discuss semileptonic and leptonic decays of such kinds. We investigate possible ways of using these decays in order to distinguish between the Dirac and Majorana character of neutrinos. Further, we argue that there are significant possibilities of detecting CP violation in such decays when there are at least two almost degenerate Majorana neutrinos involved. This latter type of scenario fits well into the known neutrino minimal standard model (νMSM) which could simultaneously explain the Dark Matter and Baryon Asymmetry of the Universe.

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.