The project aims to study the impact of the time accuracy in calorimeters on the reconstruction quality of Particle Flow Algorithms (PFA) and in particular to determine which time accuracy is necessary to improve the separation of close by hadronic and electromagnetic showers. To do so, the modelling of the timing response of the prototype calorimeters SiWECAL (electromagnetic) and SDHCAL (hadronic) equipped with MGRPC detectors (Multi-layer Glass Resistive Plate Chambers) will be performed and included as input to the ARBOR and APRIL PFA algorithm.

Since the discovery of the Higgs boson at the CERN LHC, the hunt for new physics - new particles that are not predicted in the standard model (SM) of particle physics - has continued. In parallel, increasingly precise measurements of the Higgs boson and other SM particles are being performed. So far, this search for new physics has not led to a discovery. It is therefore important to consider the possibility that the new particles we are looking for are heavier than can be produced at the LHC. In this case, it is only through precise measurements of the Higgs boson, and other SM particles, that we can learn about the presence of new physics, and so this avenue must be explored. In this project, we propose to develop a new method to perform measurements of the Higgs and electroweak sectors at the LHC, to be as sensitive as possible to the effects from new physics whilst providing sufficient information for the results of a measurement to be included in a global combination of measurements, which provides the best constraints on the presence of new physics. The novel measurement approach will be demonstrated through a measurement of Higgs bosons and Z bosons, paving the way for wider adoption of this method.

Diffuse emission is the most prominent observational signature from the sky at Gigaelectronvolt (GeV) energies. Galactic diffuse emission was established before individual gamma-ray sources started to emerge and constitute a prime source of knowledge about cosmic-ray particle interactions and radiation processes ever since. Diffuse GeV gamma-ray emission still constitutes the systematic limit of source detection near instrumental threshold. In contrast to the GeV domain the search for diffuse emission at Teraelectronvolt (TeV) energies is still in its infancy, largely due to the predominant charged particle background that constitutes a principal instrumental challenge of the atmospheric Cherenkov technique. Diffuse emission is expected in the VHE domain, too: on Galactic scale primarily from hadronic particle interactions with interstellar gas and Inverse Compton scattering of high energy electrons with interstellar radiation fields, but also when encountering intense radiation fields or dense molecular clouds in the local vicinity of cosmic accelerators. Both processes are indicative for particle escape from their acceleration regions. This last, most energetic window for astronomical investigation, the domain of Very High Energies (VHE) gamma-rays, was unveiled by the systematic observations with the H.E.S.S. telescope array, a breakthrough recognized by the award of the Descartes Prize in 2006 and Rossi Prize in 2010. One of the major achievements of H.E.S.S. was the survey of the inner regions of our Galaxy, which led to the discovery of more than 50 new energetic sources. The proposed project aims at establishing the existence, spatial and spectral signature of diffuse emission at TeV energies. H.E.S.S. observations are to be compared with predictions from a model of diffuse VHE emission that will be specifically developed for the project. On the instrumental side, the investigation will push the limits of atmospheric Cherenkov imaging in sensitivity and energy through the development of more precise reconstruction techniques, and more effective background subtraction methods. Advanced modelling of the isotropic charged particle background and development of a likelihood-based analysis technique is proposed, the latter being a novelty for investigating VHE data. Systematics induced by the geomagnetic field and inhomogeneities of the night sky background on the instrument response will be addressed with particular care. The construction of a model of diffuse emission at TeV energies appears to be demanding due to competing phenomena, such as the energy-dependent escape of charged particles from the acceleration region vs. particle transport on larger scales inside our Galaxy. Detection and study of diffuse VHE emission will constitute a major scientific breakthrough, allowing the community to further understand particle propagation in the Galaxy up to the knee (1015 eV) and how particles are released into the interstellar medium. It will allow a closer connection to GeV measurements, benefiting from orthogonal observational techniques – satellite-based direct pair conversion vs. ground-based indirect air shower detections – deployed on a large scale, non-source related investigation. Consequently, the intensity and energy dependence of different constituents of the diffuse emission will extend our understanding of common physics processes to the most energetic end of the electromagnetic spectrum. Through an assessment of the irreducible background it will prepare the advent of the Cherenkov Telescope Array by establishing the hard detection limit for gamma-ray sources and will allow investigation of a putative dark matter component in the suspected WIMP rest mass region. The project results will allow generalizing from single-source detection to source population studies, and, for the first time, estimating the unresolved source component in a comprehensive way.

The precise reconstruction of all products of a particle interaction is of critical importance for the discovery reach and the potential for precision measurements of fundamental aspects of the properties and interactions of elementary particles. The detectors at future particle colliders use highly granular “imaging calorimeters” to provide detailed three-dimensional spatial information of the energy deposited by the passage and the showering of particle in the detector. This information is exploited with sophisticated particle flow algorithms, which optimally combine the information available from the different subsystems of the detector. The capability of the calorimeters to detect, separate and measure individual final-state particles is critical. Modern timing devices that achieve precisions of a few 10 to 100 ps turn imaging calorimeters into five-dimensional detectors, covering space, energy and time. This precision is comparable to the calorimeter cell size divided by the speed of light (1 cm = 30 ps × c). To capitalise on these new technologies existing particle flow algorithms will be extended beyond the state of the art, both classically and by integrating machine learning techniques to enable the full exploitation of the added complexity. These algorithms typically use a standardised set of features extracted from the calorimeter information (shower profiles, hit energy distribution etc.). These features will be enhanced by the timing information, owing to the fact that a shower is not a simple cluster, but a time ordered cluster similar to a tree with cell connections slower than light. This process will also inform the requirements for timing elements in calorimeter systems at future e+e–-colliders (Higgs Factories), by combining the developed algorithms with detailed performance studies for key physics channels in the area of Higgs physics and electroweak precision measurements. The CALO5D project will build on the current state of the art of calorimetry and event reconstruction for Higgs factories. The participants of the project are renowned national and international experts for highly granular electromagnetic and hadronic calorimeters and reconstruction techniques including machine learning techniques as well as for physics analysis and phenomenology. For the success of this project, it is essential to put together this expertise in order to estimate reliably the gain from the use of timing in object reconstruction ranging from simple objects such as electrons and photons to complex objects such as jets.

Quarks and gluons (named partons) traversing a QCD medium – either quark-gluon plasma but also confined, cold nuclear matter – are expected to lose energy dominantly through gluon radiation, leading to the phenomenon of jet quenching observed in high-energy heavy ion collisions. Understanding quantitatively parton energy loss is thus a central question of this field, which the present proposal addresses. More specifically, the objective of the project is a systematic investigation of parton energy loss processes in cold nuclear matter. This ambitious program will be carried out through detailed and complementary theoretical, phenomenological, and experimental studies, with measurements performed in hadron-nucleus collisions from fixed-target facilities (COMPASS at the CERN Super Proton Synchrotron, SPS) to colliders (CMS at the Large Hadron Collider, LHC). The synergy between theory, phenomenology and experiment is at the heart of this proposal. The effects of energy loss in the fully coherent regime on various QCD processes will be investigated, such as forward production of light hadrons, heavy hadrons (D and B mesons) and Drell-Yan lepton pairs, in pi-A and p-A collisions at different center-of-mass energies. Another important task is the development of a unified framework enabling the rigorous treatment of parton energy loss in the two most relevant dynamical regimes, namely the Landau-Pomeranchuk-Migdal (partially coherent) regime and the fully coherent regime. In addition, both radiative energy loss processes and parton saturation – expected in nuclei at small values of Bjorken-x and an important topic in the phenomenology of high-energy nuclear collisions – will also be implemented in a unified approach based on first principles. Resulting from this theoretical work, detailed phenomenology of QCD processes in hadron-nucleus collisions will allow for the interpretation of the present data and for providing reliable predictions on future measurements. Closely related to radiative energy loss, the transverse momentum broadening of partons propagating through cold QCD matter will also be investigated, at both theoretical and phenomenological levels. On the experimental side, the measurements of Drell-Yan lepton pairs and quarkonium production will be performed in pion-nucleus collisions at SPS energy by the COMPASS experiment. At the LHC, Drell-Yan, quarkonia and heavy mesons will be measured by the CMS collaboration, as well as forward dijet production. The measurements performed at both SPS and LHC, together with past measurements at Fermilab (FNAL) and Brookhaven (RHIC), will allow for the extraction of the cold nuclear matter transport coefficient at different energies and using different processes. In fine, the phenomenological and experimental results will clarify the contributions of radiative energy loss (in both LPM and fully coherent regimes) on the production of hard processes in nuclear collisions. On top of these research studies, an important aspect of the proposal is that of education of young researchers. This project will allow for the organization of two international high-level schools on QCD, in 2019 and 2021, gathering PhD students and young researchers together with world-class lecturers. The proposal will also lead to outreach activities through the publication of brochures on particle physics and astrophysics, intended to a general audience, as well as for the organization of conferences in high-schools and during public events.