Chang Lab

The quartic couplings between two Higgs bosons and vector bosons (HHWW and HHZZ) remain among the least constrained in the Higgs sector. This CMS study presents the first direct search for production of a Higgs boson in association with two vector bosons via vector boson scattering (VBS), using 138 fb⁻¹ of 13 TeV data. It sets the most stringent limits yet on the VVHH (κ₂V) coupling relative to the SM and independently constrains the HHWW (κ₂W) and HHZZ (κ₂Z) quartic couplings—marking a significant advance in our ability to probe Higgs self-interactions at the LHC.

We led the study of first simultaneous measurement of nonresonant WWZ and ZH (H→WW) production at √s = 13 and 13.6 TeV. This study delivered the most precise determination of the WWZ cross section to date and provided the first evidence for triboson production at 13.6 TeV. These results are a critical milestone in testing the Standard Model's self-consistency and probing the dynamics of multi-boson interactions, which are uniquely sensitive to subtle effects from new physics at higher scales.

We led the study of first simultaneous measurement of nonresonant WWZ and ZH (H→WW) production at √s = 13 and 13.6 TeV. This study delivered the most precise determination of the WWZ cross section to date and provided the first evidence for triboson production at 13.6 TeV. These results are a critical milestone in testing the Standard Model's self-consistency and probing the dynamics of multi-boson interactions, which are uniquely sensitive to subtle effects from new physics at higher scales.

The simultaneous production of three massive gauge bosons (VVV with V = W, Z) is an extremely rare phenomenon predicted by the Standard Model of particle physics. Observing such events provides a direct window into the self-interactions of the electroweak force, one of the least tested aspects of the theory. The first observation of VVV production, including evidence for WWW and evidence for WWZ, marks a significant milestone: it confirms a key prediction of the Standard Model and opens a new triboson physics program at the LHC. These measurements will enable increasingly precise studies of multi-boson dynamics and offer sensitivity to subtle effects of new physics at higher energy scales.

The High-Luminosity LHC will deliver an unprecedented volume of collision data, demanding new approaches to charged-particle tracking. The Line Segment Tracking algorithm is a highly parallelizable method designed to run efficiently on modern architectures such as GPUs. By reconstructing tracks from short, local segments, LST dramatically reduces combinatorial complexity, enabling fast and scalable track finding in high-pileup environments. This development is central to ensuring that the full discovery potential of the HL-LHC can be realized.

The production of three W bosons (WWW) is one of the rarest processes predicted by the Standard Model, providing a sensitive window into the structure of quartic electroweak gauge couplings and the dynamics of multi-boson interactions. Studying this channel tests the self-interactions of the weak force in extreme conditions and offers a pathway to uncover deviations that could signal new physics. In addition to probing the Standard Model, the analysis also set the first experimental limits on photophobic axion-like particle models, expanding the search for new phenomena beyond the electroweak sector.

The Higgs boson, discovered in 2012, plays a central role in explaining how fundamental particles acquire mass. One of the most important ways to study its properties is through its decay into a pair of W bosons (H → WW*). Observations in this channel provided some of the earliest and most precise tests of the Higgs mechanism, including the first evidence for vector boson fusion production of the Higgs boson. These measurements placed strong constraints on the Higgs boson's Yukawa coupling strength, sharpening our understanding of its interaction with other particles. In addition, searches for an extended Higgs sector through the WW decay mode explored possible links between the Higgs boson and dark matter, highlighting its potential as a tool to probe new physics.