The discovery of the Higgs boson in 2012 marked a significant milestone in particle physics, completing the puzzle known as the Standard Model. However, this achievement also raised questions about what lies beyond this framework. Scientists are now on a quest to uncover new phenomena that could provide answers to the universe’s remaining mysteries, such as dark matter and matter-antimatter asymmetry.
One parameter that holds clues about potential new physics phenomena is the “width” of the W boson, which is the electrically charged carrier of the weak force. The width of a particle is directly related to its lifetime and describes how it decays into other particles. If the W boson decays in unexpected ways, such as into undiscovered particles, it would influence the measured width. Any significant deviation from the Standard Model prediction of the W-boson width could indicate the presence of unaccounted phenomena.
A recent study published by the ATLAS collaboration on the arXiv preprint server has provided valuable insights into the W-boson width. This study involved measuring the W-boson width at the Large Hadron Collider (LHC) for the first time. Previous measurements had been conducted at other colliders, such as CERN’s Large Electron–Positron (LEP) collider and Fermilab’s Tevatron collider, yielding an average value consistent with the Standard-Model prediction.
Using proton-proton collision data collected during Run 1 of the LHC, ATLAS measured the W-boson width with unprecedented precision. The new measurement, which is the most accurate to date from a single experiment, slightly deviates from the Standard Model prediction but remains within 2.5 standard deviations. This achievement was made possible through a detailed particle-momentum analysis of W-boson decays into electrons, muons, and neutrinos, which are key indicators of missing energy in collision events.
To achieve such high precision, physicists had to calibrate the ATLAS detector’s response to particles accurately, accounting for background processes and theoretical predictions. Understanding W-boson production in proton-proton collisions and the inner structure of protons through parton distribution functions were essential components of the measurement. By incorporating these factors and leveraging statistical methods to constrain uncertainties directly from measured data, the ATLAS collaboration was able to improve the precision of the measurement.
The updated measurement of the W-boson mass, along with the width, is consistent with the predictions of the Standard Model. However, future measurements using larger datasets are expected to further reduce statistical and experimental uncertainties. Advances in theoretical predictions and a deeper understanding of parton distribution functions will also help refine the measurements and minimize theoretical uncertainties.
As physicists continue to enhance the precision of their measurements, they will be able to conduct more rigorous tests of the Standard Model and explore the possibility of new particles and forces. The exploration of the W-boson width serves as a crucial step towards unraveling the mysteries of the universe and pushing the boundaries of our understanding of particle physics.
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