W Boson Mass and Transverse Momentum Spectrum
With CDF’s recent measurement of the W mass 7 standard deviations away from the Standard Model value, this analysis has the attention of the whole particle physics community: will we see something in agreement with the theory, or will we confirm the CDF result, thereby providing one of the strongest indications of new physics to date?
Image credit: Science.org
Dark Matter: Soft Unclustered Energy Patterns (SUEP)
As many simpler models and signatures of possible beyond Standard Model physics have been ruled out in recent searches at the LHC and beyond, models like Hidden Sectors have gained increasingly more attention. These models assume a dark sector that is only weakly coupled to our Standard Model sector via some ‘portal’ – a particle – perhaps a new one or perhaps something like our Higgs. This particular dark matter model assumes a QCD-like group in the dark sector that would generate ‘dark showers’, which promptly decay back to Standard Model particles, in a diffuse and isotropic ‘soft bomb’ that would be very hard to distinguish from typical QCD events. Our analysis thus seeks to identify very high multiplicity and the particular shape of the jets to gain sensitivity to possible SUEPs.
Dark Photon Searches
Several BSM predicted particles could give rise to resonant particle pair production, with dimuon being one of the most promising final states. In those predictions, a new particle emerges in the pp collision and subsequently decays into dimuon. One of the most exciting candidates is the dark photon, a new gauge field predicted by the dark matter theory. Another intriguing candidate is a pseudo-scalar particle predicted in the extended two-Higgs-doublet model. Recent searches have so far yielded null results for the new particles in the large mass value, interest has therefore grown in extending resonance searches to explore the phase space of lower masses. Our analysis thus broadens the exploration of dimuon resonances, now reaching scales as low as GeV.
Analysis of Rare B Decays
Rare B meson decays provide a sensitive probe for BSM effects and allow exploring energy scales much higher than the ones directly accessible at the CERN LHC. The Bs → μμ and B0 → μμ represent such a case, where precise theoretical predictions can be matched with a clear experimental signature. These rare decays are examples of FCNC processes, which are strongly suppressed in the SM, making them sensitive to BSM physics contributions. The Bs -> μμ is particularly interesting because it contains the process of b->sll, where 2-3σ disagreements from the SM were observed.
We have measured the Bs → μμ branching fraction and effective lifetime, as well as the results of a search for the B0 → μμ decay using CMS Run 2 data. The measurements are the most precise single measurements to date, exhibiting greater consistency with the SM prediction compared to the measurements from other experiments, thus reducing the overall tension. A more precise measurement is on going with Run 3 data.
Search for Rare Higgs Boson Decays
The announcement of the discovery of the Higgs boson by the CMS [1] and ATLAS [2] collaborations on July 4th, 2012 was not the final verdict on the Standard Model (SM), but gave physicists a pile of homework for the coming decades. In particular, there has been an ongoing effort to test the interaction strength of the Higgs boson with other particles. According to the SM, the coupling of the Higgs boson is proportional to the mass of the particle; hence, the heavier the mass, the better chance of observing it. So far, experiments have measured the Higgs coupling to heavy gauge bosons (Z, W bosons [3, 4, 5]), to 3rd generation massive fermions (tau lepton [6, 7] and top, bottom [8, 9] quarks), and to the 2nd generation lepton (muon). Recent efforts have extended to the 2nd generation charm quark [10, 11]. However, as the mass of the fermions become smaller, the chances of observing their decays become increasingly sparse.
In our analyses, we test the SM hypothesis of the Higgs coupling to the up, down, and strange quarks. Having masses that are about 104-105 times smaller than that of the heaviest quark, decays into these 1st and 2nd generation fermions occur very rarely. We focus primarily on decays of the Higgs boson into a photon and a light vector meson, as these processes yield clearer experimental signatures. By scrutinizing these exotic decays, we aim to uncover any deviations from the predicted values by the SM, hinting at the existence of new particles and phenomena beyond our current understanding. This research has the potential to unveil groundbreaking discoveries in particle physics, expanding our knowledge of the fundamental constituents of the universe.