Search for anomalous couplings in WW and WZ production with single-lepton final states in proton-proton collisions at = 13 TeV
Using 138 fb of 13 TeV proton-proton collision data from the CMS experiment, this study constrains anomalous triple gauge boson and vector boson-quark couplings via an effective field theory approach in WW and WZ production with single-lepton final states, achieving the most stringent constraints to date on triple gauge couplings by focusing on high-energy hadronic decays reconstructed as large-radius jets.
Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer
The universe is built on a set of rules that physicists call the Standard Model. This framework acts like a periodic table for the fundamental particles that make up everything we see, from the air we breathe to the stars above. It describes how these particles interact through forces carried by other particles, such as the photon for light or the W and Z bosons for the weak nuclear force. For decades, this model has been incredibly successful, predicting experimental results with stunning precision. Yet, it is incomplete. It cannot explain phenomena like dark matter or why the universe has more matter than antimatter. Scientists suspect that there are heavier, hidden particles or new forces waiting to be discovered, but these might be too massive to create directly in our current machines. Instead of looking for these heavy particles head-on, researchers often look for subtle ripples they might leave behind in the behavior of known particles, much like noticing a heavy boat passing by by watching the wake it leaves on the water.
To find these ripples, physicists at the Large Hadron Collider in Switzerland smash protons together at nearly the speed of light. In a recent study, the CMS collaboration analyzed data from these collisions to search for deviations in how pairs of W and Z bosons are produced. These bosons are heavy carriers of the weak force, and when they are created together, they should behave in a very specific way according to the Standard Model. The researchers focused on a particular scenario where one of these bosons decays into a charged particle, like an electron or a muon, and a neutrino, while the other boson decays into a spray of particles that merge into a single, large, energetic clump. By examining the energy and direction of these collisions, the team could test whether the interactions between these bosons matched the predictions of the Standard Model or if they showed signs of new physics.
The team examined a massive collection of data corresponding to 138 inverse femtobarns of collisions, a volume of information that represents the most comprehensive look at this specific process to date. Because the signals they were looking for would be most visible at very high energies, the researchers focused their search on the most energetic events, where the bosons are moving so fast that their decay products are squeezed together. In these high-speed collisions, the particles from the second boson do not spread out into separate streams but instead merge into a single, large jet. To distinguish these rare, high-energy signals from the overwhelming background of ordinary particle collisions, the team employed a sophisticated machine-learning tool. This tool acts like a highly trained eye, analyzing the internal structure of the large jets to determine if they originated from a decaying W or Z boson or from a common background process.
After carefully filtering the data and removing events that were likely caused by known background processes, such as the production of top quarks, the researchers compared their observations against the predictions of the Standard Model. They found that the number of events and their energy distribution matched the Standard Model predictions almost perfectly. There was no evidence of the strange deviations that would indicate the presence of new, heavy particles or modified forces. This result allows the scientists to place strict limits on how much the behavior of these bosons can differ from the established theory. They calculated that if new physics exists in this area, its effects must be incredibly small, confined to energy scales far beyond what the current collider can directly reach.
The study also tested a specific mathematical framework known as effective field theory, which allows scientists to describe the potential influence of unknown heavy particles without needing to know exactly what those particles are. By analyzing the data through this lens, the researchers constrained the possible values of the parameters that would describe these hypothetical new interactions. The limits they set are the most stringent to date for certain types of interactions between the W and Z bosons, effectively ruling out a wide range of theoretical models that predicted larger deviations. While the search for new physics continues, this work confirms that the Standard Model remains robust even under the extreme conditions of high-energy collisions, narrowing the path for future discoveries by telling scientists exactly where not to look.
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