Speaker
Description
We present a selection of recent measurements of electromagnetic probes conducted by CMS to probe initial-state aspects of the heavy ion collision. The Z boson has a very short lifetime and can decay to dimuon final states that can be precisely measured. These properties make it a valuable tool for studying the initial state of heavy ion collisions. It has been proposed that the momentum of muons resulting from a Z decay, and therefore the experimentally observed mass and width of the Z boson, may be modified by the presence of the immense initial-state electromagnetic fields that are thought to be created in heavy ion collisions. Using the CMS experiment, we report the first search for a modification of the observed Z boson mass and width in PbPb collisions at $\sqrt{s_{{\mathrm{NN}}}} = 5.02$ TeV relative to those observed in pp collisions. In addition, measurements of Z boson yields and azimuthal anisotropy, $v_2$, will be discussed. The centrality and rapidity dependence of the measurements are compared to theoretical models. Taken together, these measurements provide new insights into the role of initial electromagnetic fields, nuclear parton distribution functions, and initial-state geometry in heavy ion collisions. The production of top quarks in heavy ion collisions serves as a novel tool for investigating nuclear parton distribution functions at high Bjorken-x. Although being a quark, the top has a short lifetime, decaying predominantly to a W boson and b quark pair, before hadronizing. Leptonic final states from the subsequent W boson decay are thus effectively electroweak probes of the medium they traverse before reaching the detector. The CMS collaboration has reported evidence of top quark pair ($\mathrm{t\bar{t}}$) production using data from lead-lead (PbPb) collisions during Run 2. This talk will present the first measurement of $\mathrm{t\bar{t}}$ production utilizing $1.63~\mathrm{nb}^{-1}$ of PbPb data collected by CMS at 5.36 TeV in 2023 and derived using kinematic variables from leptons and jets.
| Category | Experiment |
|---|---|
| Collaboration (if applicable) | CMS |
