The Compact Muon Solenoid (CMS) experiment at CERNs is one of four big particle collider experiments at the Large Hadron Collider (LHC) on the border between France and Switzerland. The LHC accelerates protons (or heavy Ions) to near the speed of light, colliding them at energies that allow us a glimpse into the interactions between natures most fundamental particles. We describe these interactions covering three out of four fundamental forces of nature (all except gravity) with the Standard Model of particle physics (SM). The SM (up to now) describes almost all observations near perfectly. At the same time we know it is not complete and there must me physics beyond the SM (BSM) as its in its current form not describing gravity (currently described by Einsteins theory of general relativity) and Astrophysical/Cosmological observations give us hints at “Dark Matter” and “Dark Energy“, particles and/or forces outside our current (particle physics) understanding of the world. Since 2012 all predicted fundamental particles of the SM have been found, now the hunt begins for hints where the new physics (we know must exist) hides.
Our analysis group lead by Torben Lange works on data analysis of data taken with the CMS experiment with a focus on the 2012 discovered Higgs boson and leptonic final states (including hadronically decaying taus). Since 2012 many of the properties of the Higgs boson have been investigated and constrained up to a few percent to be in good agreement with the Standard model of particle physics (SM). One notable exception is the trilinear Higgs boson self coupling λ. While having an indirect effect on the production cross section and branching fraction of single Higgs boson processes, it can only be directly measured through the study of Di-Higgs events, the simultaneous production of two Higgs at once. Studying Di-Higgs events does not only give us insight into λ which is directly related to the Higgs boson potential and the stability of our universe, but also other SM couplings such as the quartic coupling between two Higgs and two vector bosons C2V, but also several BSM scenarios studied in effective field theory (for example HEFT with C2, Cg and C2g) as well as resonant production X->HH.
The figure shows an overview of these processes, all of which we aim to study in our group.
Overall we currently focus on three main efforts:
Di-Higgs analysis in Run3: We are contributing actively to ongoing Run3 analysis such as HH->bbττ and HH->Multilepton. This is done in strong collaboration with the group of Prof. Peter Schleper University of Hamburg among others. The driving force here is Norman, who’s PhD. thesis is on HH->bbττ.
General Di-Higgs efforts: Torben is currently the CMS internal contact person for Di-Higgs, coordinating between different analysis, working on the development of common tools used in all CMS Di-Higgs such as hh-inference as well as tools for modeling signal processes in various interpretations expanding the physics coverage to new scenarios in HEFT/SMEFT and UV complete models. We are also participating heavily in all Di-Higgs related combination efforts of CMS. Torben is also Estonias representative in the COST action COMETA on multi boson interactions.
In anticipation of the future we are interested in the long term developments of Di-Higgs studies including projections for the HL-LHC, reconstruction algorithms for future colliders (done in collaboration with our ML group under Joosep Pata) and eventually preliminary studies of Di-Higgs and sensitivity at future colliders.
If you want to know more, inquire about open positions or want todo a thesis or student internship with us (we work with both TalTech and Tartu University), please get in touch [Email].
“Prospects for di-Higgs boson searches with multilepton final states in the qqHH production mode”, Masters this by Norman Seeba [link]
“Combination of searches for nonresonant Higgs boson pair production in proton-proton collisions at sqrt(s) = 13 TeV”, the CMS collaboration, CMS-PAS-HIG-20-011, Conference pre-print, [link]
“A portrait of the Higgs boson by the CMS experiment ten years after the discovery”, the CMS collaboration, doi:10.1038/s41586-022-04892-x, published in nature, [link]
“Search for Higgs boson pairs decaying to WW*WW*, WW*ττ, and ττττ in proton-proton collisions at Sqrt( = 13 TeV”, the CMS collaboration, doi:10.1007/JHEP07(2023)095, published in JHEP, [link]
Constraints on the Higgs boson self-coupling from the combination of single and double Higgs boson production in proton-proton collisions at Sqrt( = 13 TeV, the CMS collaboration, arXiv:2407.13554, submitted to PLB, [link]
Searches for Higgs boson production through decays of heavy resonances, the CMS collaboration, arXiv:2403.16926, submitted to Physics Reports, [link]
Tau lepton identification and reconstruction: A new frontier for jet-tagging ML algorithms, Lange, Torben and Nandan, Saswati and Pata, Joosep and Tani, Laurits and Veelken, Christian, doi:10.1016/j.cpc.2024.109095, Comput. Phys. Commun., [Link]
A unified machine learning approach for reconstructing hadronically decaying tau leptons, Tani, Laurits and Seeba, Nalong-Norman and Vanaveski, Hardi and Pata, Joosep and Lange, Torben, arXiv:2407.06788, submitted to Comput. Phys. Commun., [Link]
