The discovery of the Higgs boson during the LHC Run 1 completes the experimental validation of the Standard Model (SM) of high-energy particle physics. Its particle spectrum is fully established, and definite predictions are available for all interactions. At the quantum level, the SM relates the masses of the heaviest particles the W and Z gauge bosons, the Higgs boson, and the top quark. The Z boson mass is precisely known since LEP1, and the measurement precision of the top quark mass has vastly improved at the TeVatron and LHC. In 2014, the ATLAS and CMS collaborations produced a precise measurement of the Higgs boson mass, based on the full 7 and 8 TeV datasets; in 2016, ATLAS completed a first measurement of mW, using 7 TeV data only, that matches the precision of the best previous results. The present proposal aims at further improvement in the measurements of mW, mZ and the weak mixing angle with ATLAS, exploiting all data available at 8 and 13 TeV. Leptonic final states play a particular role, and improving the measurement of electrons and muons is our main focus on the experimental side. A set of dedicated measurements is foreseen to bring our understanding of strong interaction effects to the required level. Finally, a global analysis of the electroweak parameters is proposed, accounting for correlations of QCD uncertainties across the different measurements, extending traditional electroweak fits. The involved scientists and institutes have recognized expertise and achievements in the fields spanned by this project. The present call provides a unique opportunity to strengthen our collaboration over a timescale matching the needs of our ambition.

The aim of the CUPID-1 project is the development of a complete bolometric detector system capable of investigating neutrinoless double beta decay – 2b0n- with unprecedented sensitivity. The project will be dedicated to the design of a detector tower capable to be operated in a next generation 2b0n experiment at the ton scale and to test one of these towers as a final validation of the technology. The crucial innovative feature of the project is to fully develop and optimize an integrated bolometric system combining thermal and mechanical considerations, optimization of light collection, MC simulations and selection of radiopure materials, including an extensive cryogenic tests campaign, that will allow to reach the background goal below 10-4 counts/(keV kg y). This single tower will be also a competitive 2ß0n experiment at the international level and the most sensitive ever for 100Mo.

The HIGGSENLIGHTENED project proposes to deepen understanding of electroweak symmetry breaking by studying the 125 GeV Higgs boson in the high-precision diphoton decay channel, in the areas of the Higgs boson self-coupling, its CP nature and natural width, studies which could also serve to search for indirect evidence of BSM physics. A fourth area of work is a direct search for additional low-mass Higgs bosons in the diphoton channel. Underlying these objectives are proposed novel reconstruction techniques for electromagnetically interacting particles and novel background estimation techniques. The measurement of the Brout-Englert-Higgs boson potential form has not yet been performed directly. It can be accessed via the Higgs boson self-couplings, and measured through the pair production of Higgs bosons (HH), requiring at least the Run 3 data. The most recent CMS paper, in the non-resonant case using the process HH bb, when combined with other channels, reaches a sensitivity of ~2.5 times the SM HH production cross section. We plan to improve the bb sensitivity by at least an additional ~20%, using ‘deep’ machine learning technologies. In combination with other channels, we hope to exclude a null value of the Higgs boson trilinear self-coupling. Higgs boson width constraint: The combined data of Runs 2 and 3 may permit an indirect constraint of the 125 GeV Higgs boson width through the diphoton decay channel, via a method independent from the ‘off-shell’ method using the HZZ*4 lepton channel. The interference between the Higgs boson production process ggH and the direct diphoton process ggintroduces a downward shift in the invariant diphoton mass and a suppression of the production cross section. Both observables depend on the width of the H, but also on the transverse momentum of the diphoton system, making possible a width constraint via a differential measurement in diphoton transverse momentum. An upward mass shift, corresponding to constructive interference, would be evidence of BSM physics. Higgs boson CP studies in the diphoton channel: After having demonstrated that constraints from the study of the CP structure in the VBF production mode could be achieved in the diphoton decay channel, we are now pursuing a publication planned for the full Run 2 data set. In the Hff sector, CP-odd couplings have have been studied in Run 2 in the ttH production mode by ATLAS and CMS with 3σ level exclusions of the pure CP-odd coupling. Obtaining stronger exclusions will require the data of Run 3. The ttH CP analysis in the diphoton channel could be improved in several ways: with the addition of categories targeting specifically the tH production mode and with global fits within EFT or the anomalous couplings framework including other production modes. Pursuing these studies may allow to pinpoint small deviations not yet within reach. Direct search for a second low-mass Higgs boson: An excess of 2.8 at an invariant mass of 95.3 GeV has been observed in the CMS data of 2012 and 2016 in the diphoton channel. The analysis of the remaining Run 2 data should give a strong indication, but Run 3 will allow a final response, also permitting an increase in search sensitivity by a factor ~3. Novel ECAL reconstruction techniques could make possible increased rejection of electrons from the ppe+e- Drell-Yan background process. We plan a purely data-driven modeling of this process, and to extend the search zone’s lower mass boundary to ~20 GeV via the use of alternative triggering methods or subpopulations of boosted events. Novel ECAL reconstruction techniques, under development in the CMS ECAL using advanced machine learning methods, have shown possible improvements regarding both energy resolution and particle identification in particular, discrimination between photons/electrons/jets. These algorithms could have widespread impact, notably for our four areas of work.

The aim of the ClearMind project is to develop a monolithic gamma ray detector (0.5 MeV to few MeV) with a large surface area (= 25 cm2), high efficiency, high spatial accuracy (< 4 mm3 FWHM ) and high timing accuracy ( < 20 ps FWHM, excluding contributions of the collection and amplification of photoelectrons). Our motivation is to improve the performance of Positron Emission Tomography scanners (PET). We propose to develop a position-sensitive detector consisting of a scintillating crystal on which is directly deposited a photo-electric layer of refractive index greater than that of the crystal. This "scintronic" crystal, which combines scintillation and photoelectron generation, optimizes the transmission of scintillation photons and Cherenkov light photons to the photoelectric layer. We expect a factor 4 gain on the probability of optical photon transmission between the crystal and the photoelectric layer, compared to conventional assemblies using optical contact gels. The crystal will be encapsulated with a micro-channel plate multiplier tube (MCP-MT) in order to amplify the signal and optimize the transit time of the photo-electrons towards the plane of detection anodes (densely pixelated) and thus the temporal and spatial resolutions of the detection chain. The originality of our detector consists in: - Improve the efficiency of light collection in a high-density, and high-effective atomic number crystal by depositing a photoelectric layer directly on the scintillating crystal. - Use the Cherenkov light emission for detection. The gain in optical coupling optimizes the measurement of time based Cherenkov photons, inherently very fast. - Use the map of photoelectrons produced at the surface of the crystal to reconstruct the properties of the gamma interactions by means of robust statistical estimators and information processing using machine learning algorithms. The scintillation photons provide the necessary statistics for a measurement of the energy deposited in the crystal, modest but compatible with a use on a PET imager, and a precise measurement of the coordinates of the interaction position of the gamma ray. - The fast acquisition of signal shapes (SAMPIC technology), which facilitates the optimization of the detector. - The effort to reduce the number of electronic channels (and associated constraints) while keeping optimal performance. We propose to develop the ClearMind prototypes in two phases. Phase 1 consists in producing a "thin" detector, ~ 10 mm, instrumented on one side. The objective is a proof of principle of the technology, the characterization of the performances of this prototype, and its confrontation with a Monte Carlo model, using the GATE simulation tool. This should allow us to set up all the technologies and to concretely understand their stakes. Deadline 18 months. Phase 2 involves the production of a ~ 20 mm thick detector, instrumented on both sides. The objective will then be to produce a detector module of optimized efficiency, spatial and temporal resolutions, close to what would be used in future PET machines. Deadline 30 months. The GATE Monte Carlo simulation will then allow us to assess the potential of the technology to design an enhanced cerebral Time-Of-Flight PET imager, (and alternatively whole body TOF-PET). Our efforts with the manufacturers involved in the development of the prototypes resulted in quotations and delivery times compatible with the schedule and the budget presented in this project.

The SPHINX project binds atomic and antimatter physics with an application to astrophysics. It revolves around the charge exchange reaction between a hydrogen (H) atom and a positronium (Ps) atom, leading to the formation of a negative hydrogen ion (H–) and a free positron. This encompasses the charge conjugate reaction involving antihydrogen and yielding the positive antihydrogen ion, at the heart of the GBAR experiment at CERN, as well as the reverse reaction of Ps formation from positron impact on H–, a process of interest in the study of positron annihilation in the interstellar medium (ISM). The experimental part of the project proposes an extensive program of cross section measurements for a H beam colliding with a Ps target. The results will put disagreeing theoretical models at test and provide validated values for the applications. The needed dense Ps target is only available from GBAR at CERN, which also offers the opportunity of making a pulsed neutral hydrogen beam with energies from 6 to 10 keV. The measurement advantageously relies on the detection of produced H–. A beamline extension has to be built and equipped for that purpose. The H beam will be obtained by photo-detachment of a H- beam provided by CERN. For further investigations at low energy beam (1 to 2 keV) a detailled study of this neutralisation device is required. This will then allow to measure the cross sections for H(2S), Ps(3D), with the current set-up, and Ps(2p), which requires to finalise a laser system. The second part of the project will use the experimentally validated cross sections in the following simulations: 1) optimisation of the antihydrogen ion production in GBAR, a direct application of the measured cross sections; 2) Ps formation from H– in the ISM. For the latter, the simulation will first focus on predicted H– rich plasmas, with a special interest for the transition region of planetary nebulae. The goal is to estimate the impact of H– on the features of the positron annihilation spectra for this particular case, before generalising the application to more extended phases of the interstellar medium.