Spandan Mondal, a postdoctoral researcher in Ulrich Heintz's Elementary Particle Experiment group, is a recipient of a CERN CMS Thesis Award for his thesis, "Charming decays of the Higgs, Z, and W bosons: Development and deployment of a new calibration method for charm jet identification." The highly competitive award recognizes the result of distinct efforts made by thesis authors in writing an exceptionally clear, effective and original documentation of their research work.

When describing his research on CERN.com, Spandan said, "The Higgs boson decaying to a charm quark-antiquark pair is a particularly interesting process, as its rate can be significantly altered by the presence of new physics beyond the Standard Model, due to the small mass (~1.3 GeV) of the charm quark. However, the small mass of the charm quark also makes this process extremely rare. Moreover, identifying charm quarks at the CMS experiment is difficult, making the search extremely challenging.

In my thesis, “Charming decays of the Higgs, Z, and W bosons: Development and deployment of a new calibration method for charm jet identification,” I developed a novel calibration algorithm for charm jet identification that enables maximal use of the available information related to jets arising from charm quarks. The new method is used to correct the entire distribution expected as output when jet flavor identification algorithms are applied to jets of different flavors. The calibrated results improve upon traditional efficiency measurements and help enhance the sensitivities of searches involving charm quarks.

The second part of my thesis focuses on analyzing data collected by the CMS experiment to search for events where a Higgs boson, produced in association with a leptonically-decaying Z or W boson, decays to a charm quark-antiquark pair. The charm quarks are reconstructed using two separate (“resolved”) small-radius jets whose flavors are predicted using modern machine-learning (ML) based flavor tagging algorithms calibrated using the aforementioned novel method. Upon a statistical combination with a complementary merged-jet-based search, an upper limit on the process of interest is obtained, which is the most stringent direct limit to date. The analysis is validated by studying the decay of the Z boson into charm quarks and the corresponding process is observed for the first time at a hadron collider experiment. I further extended my thesis by studying the decay of W bosons into charm-strange quark pairs, leveraging correlated tagging of charm and strange jets. This marked the first observation of charmed W boson decays in the diboson channel at a hadron collider experiment.

I am currently a postdoctoral fellow in the Department of Physics at Brown University, working with the group led by Profs. Heintz and Barone. Within the CMS Collaboration, I serve as a convener of the flavor tagging physics group. My work focuses on developing new ML-based reconstruction and calibration methods for identifying heavy-flavor hadronic decays. Additionally, I continue to work on the search for the Higgs boson decaying into a charm quark-antiquark pair and explore other topics in Higgs physics, such as its production in the vector boson fusion and scattering modes, as well as its decay into leptonic final states. My goal is to extend the use of novel data analysis techniques across a broad range of studies within the CMS Collaboration."