Heavy Neutral Leptons (HNLs) are hypothetical particles predicted by many extensions of the Standard Model. These particles can, among other things, explain the origin of neutrino masses, generate the observed matter-antimatter asymmetry in the Universe and provide a dark matter candidate. The SHiP experiment will be able to search for HNLs produced in decays of heavy mesons and travelling distances ranging between O(50 m) and tens of kilometers before decaying. We present the sensitivity of the SHiP experiment to a number of HNL's benchmark models and provide a way to calculate the SHiP's sensitivity to HNLs for arbitrary patterns of flavour mixings. The corresponding tools and data files are also made publicly available.

We propose to install a storage ring at an ISOL-type radioactive beam facility for the first time. Specifically, we intend to install the heavy-ion, low-energy ring TSR at the HIE-ISOLDE facility in CERN, Geneva. Such a facility will provide a capability for experiments with stored secondary beams that is unique in the world. The envisaged physics programme is rich and varied, spanning from investigations of nuclear groundstate properties and reaction studies of astrophysical relevance, to investigations with highly-charged ions and pure isomeric beams. The TSR can also be used to remove isobaric contaminants from stored ion beams and for systematic studies within the neutrino beam programme. In addition to experiments performed using beams recirculating within the ring, cooled beams can also be extracted and exploited by external spectrometers for high-precision measurements. The existing TSR, which is presently in operation at the Max-Planck Institute for Nuclear Physics in Heidelberg, is well-suited and can be employed for this purpose. The physics cases, technical details of the existing ring facility and of the beam requirements at HIE-ISOLDE, together with the cost, time and manpower estimates for the transfer, installation and commissioning of the TSR at ISOLDE are discussed in the present technical design report.

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 super-weakly interacting particles with masses up to 𝒪(10) 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.

Complex morphologies in lipid membranes typically arise due to chemical heterogeneity, but in the tilted gel phase, complex shapes can form spontaneously even in a membrane containing only a single lipid component. We explore this phenomenon via experiments and coarse-grained simulations on giant unilamellar vesicles of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine. When cooled from the untilted L α liquid-crystalline phase into the L β′ tilted gel phase, vesicles deform from smooth spheres to disordered, highly crumpled shapes. We propose that this shape evolution is driven by nucleation of complex membrane microstructure with topological defects in the tilt orientation that induce nonuniform membrane curvature. Coarsegrained simulations demonstrate this mechanism and show that kinetic competition between curvature change and defect motion can trap vesicles in deeply metastable, defect-rich structures.C omplex morphologies in lipid membranes arise typically due to chemical heterogeneities. For example, clustering of different lipid species can result in membrane domains with different intrinsic curvatures (1) and transmembrane proteins can induce local curvature (2). Here we explore another mechanism that produces complex shapes in membranes of a single lipid component without chemical heterogeneity: the formation of topological defects in a membrane with in-plane orientational order and their trapping to produce highly disordered morphologies.In this paper, we present coordinated experimental and computational studies of giant unilamellar vesicles (GUVs), i.e., singlebilayer shells, as they cool from the untilted liquid-crystalline phase (L α ) into the tilted gel phase ðL β′ Þ. In the gel phase, the local molecular tilt has orientational order; i.e., the molecules point in a particular direction within the 2D plane. Hence, the gel phase exhibits microstructural point defects, vortices in the tilt direction, which can be considered as positive or negative topological "charges" according to which way the tilt direction rotates about the defect core (3). A spherical vesicle must have defects with a total topological charge of +2, as shown by the Gauss-Bonnet theorem (just as one cannot comb the hair on a coconut without leaving at least two defects). In general, there is a fundamental geometric connection between 2D order and defects within a membrane and the 3D shape of the membrane: Curvature drives formation of topological defects, and conversely, defects can induce curvature (4-6). This interaction has been explored in liquid crystals (7,8), faceted block copolymer vesicles (9), liquid-crystalline elastomers (10), colloidal crystals (11), and superfluids (12), and we investigate how it affects the shape of GUVs. Results and DiscussionPrevious theories have predicted that a lipid vesicle with in-plane tilt order will have a smooth and elongated ground state with a defect of charge +1 at each end (13,14). To test this prediction experimentally, we prepare GUVs in water from the lipid 1,2-dipalmitoyl-sn-glycero-3...

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