Turning precise measurements at particle colliders into searches for new physics
Project description
Top quark, Higgs and heavy flavor physics with the CMS experiment at the LHC at CERN
With the discovery of the Higgs boson in 2012 at CERN, the Standard Model of particle physics marked its final triumph by adding a unique particle that relates to the masses of elementary particles. At the same time, this discovery opened a variety of new questions, which are potentially even more fundamental. In many ways the scalar or Higgs sector provides a unique window to search for new physics phenomena that would address these open questions (e.g. Excellence of Science project, https://be-h.be). The interplay of the Higgs boson with the heaviest fundamental particle, the top quark, provides a powerful tool to explore phenomena at energy scales not yet directly achievable in particle collisions. The Large Hadron Collider at CERN will continue to provide high-energy proton collisions in which Higgs bosons and top quarks emerge together. By confronting precise measurements of these processes with precise predictions, a novel search can be conducted into yet unknown territory.
Very recently, the interplay between the Higgs boson and the top quark is made concrete at the LHC in the collision processes in which both particles appear. Due to the decay of the top quark and the Higgs boson and due to the main features of the background processes, these studies involve the reconstruction of several heavy quarks in the final state, like bottom and charm quarks. A coherent understanding of proton collision processes resulting in a variety of final states, such as ttH, tHq, tt+heavy flavor, is key towards a solid interpretation in light of new physics. Additionally, the research will contribute to a better understanding of the interaction between the Higgs boson and bottom (or even charm) quarks.
The HEP@VUB team welcomed a long list of leaders of the heavy-flavour identification or b/c- tagging team at the CMS experiment pioneering for example the development of Machine Learning algorithms for the classification of bottom quark jets from other jets (e.g. JINST 13 (2018) 05) and the development of charm tagging algorithms. Turning precise measurements into searches evolves through the use of Effective Field Theories (EFT) which we frequently used for example for top quark FCNC searches. Moreover, taking into account our experience in the application of Machine Learning tools, we pioneered the novel use of Machine Learning tools to optimize searches using precise measurements in an EFT approach (e.g. JHEP 11 (2018) 131). Our involvement in top quark physics and related searches resulted in about 20 PhD theses.
The collision data to be collected by the CMS experiment during the LHC Run 3 will provide a unique opportunity to measure precisely the top-Higgs sector and related processes. Via an EFT approach and novel Machine Learning tools they can be transformed into powerful searches for deviations from Standard Model predictions. On the phenomenological front we collaborate frequently with the groups of Fabio Maltoni and Benjamin Fuks, while we have direct access to our major TIER-2 computing facility deployed in Brussels.
About the research Group
High Energy Physics
Unique on the Belgian scale, about 23 professors at the VUB perform fundamental research towards a profound and comprehensive understanding of both the largest and smallest structures around us. Combining theoretical and experimental research of high-energy phenomena in the universe and on the quantum scale we aim to unravel the laws of nature at the most fundamental level. This effort is concerted in a flourishing HEP@VUB Research Centre which excels internationally. To achieve a coherent global picture of the reality around us, puzzling features that challenge the underlying basic principles in physics on large and small scales have to be studied and understood. The foundations of the Standard Models of both particle physics and cosmology face problems to explain for example the omnipresence of dark matter and dark energy, as well as the apparent need for fine-tuning in several corners of our models and the difficulty to unite all forces. Novel theoretical reasoning and further experimental explorations will provide insights towards solutions. The recent creation and now further consolidation of our phenomenological research activities are essential to profoundly connect theory and experiment, as well as to connect the studies of large-scale and small-scale features.
At the foundation of the HEP@VUB Research Centre is the involvement in a variety of large-scale research infrastructures around the world. At colliders our long-term engagement is focused on the studies of proton collisions with the CMS experiment at the LHC at CERN both for precise measurements and for searches. We develop analysis and reconstruction techniques and take responsibility in the upgrade of the all-silicon CMS Tracker. Recently, we started to explore physics studies at future colliders. For neutrino physics our research revolves around the very-short baseline SoLid experiment at the BR2 nuclear reactor at the SCK-CEN, Belgian’s leading nuclear laboratory. The IceCube Neutrino Observatory at the South Pole is our main infrastructure for astroparticle physics with a focus on multi-messenger astrophysics, complemented with the Auger observatory in Argentina for cosmic ray studies and novel radio detector arrays being installed on the South Pole and on Greenland in the search for ultra-high-energy neutrinos. The radio interferometric array of LOFAR, situated mainly in the Netherlands, allows us to observe and study high-energy astrophysics phenomena. Recently we engaged in gravitational wave research with the Virgo/LIGO interferometers, in the USA and Italy, and towards the new Einstein Telescope potentially situated partially in Belgium. Additionally, a broad range of theoretical topics in the area of string theory and holography is offered, often involving links to other fields in physics. Through phenomenological research we develop methods and tools towards an overall interpretation of the experimental results in existing theories and to build novel models to be confronted with experimental observations. The explicit phenomenological research has a focus on beyond Standard Model physics related to supersymmetry, dark matter, cosmology and inflation, but in astroparticle and collider physics.
The concrete research projects mentioned in the abstracts are embedded in the HEP@VUB Research Centre.The HEP@VUB Research Centre - https://hep.research.vub.be