ATLAS Measures W-boson Width With Unprecedented Precision

The W-boson, an electrically charged carrier of the weak force, plays a crucial role in understanding particle physics.

In a recent study, the ATLAS collaboration— an international team of scientists and engineers working on the ATLAS experiment at CERN— conducted the first-ever measurement of the W-boson width at the Large Hadron Collider (LHC).

Previous measurements carried out at CERN’s Large Electron–Positron (LEP) collider and Fermilab’s Tevatron collider resulted in an average value of 2085 ± 42 million electronvolts (MeV). This result aligns closely with the Standard-Model prediction of 2088 ± 1 MeV.

Utilizing data from proton-proton collisions at an energy of 7 TeV gathered during Run 1 of the LHC, ATLAS determined the W-boson width to be 2202 ± 47 MeV. This is the most precise measurement by a single experiment to date. While slightly larger, it remains consistent with the Standard Model prediction within 2.5 standard deviations.

A window to new physics beyond the Standard Model

One key factor that might provide insights into new phenomena is the “width” of the W-boson, a particle responsible for carrying weak nuclear force. This width indicates how long the W boson exists before it decays.

f it decays into unfamiliar particles, it alters the width observed in measurements. Since the Standard Model predicts this width accurately, any deviation from this prediction could suggest the presence of unexplored phenomena in physics.

The ATLAS collaboration measured both the W-boson width and mass at the same time. They used a statistical method that directly constrained some uncertainty parameters based on the measured data, which helped enhance the precision of the measurement.

Researchers achieve breakthrough precision

The new measurement of the W-boson mass is 80367 ± 16 MeV, surpassing the previous measurement by ATLAS using the same data.

Additionally, researchers successfully unveiled a groundbreaking outcome: the precise measurement of W boson decays into electrons or muons, alongside their elusive neutrinos, which, while undetectable, leave a distinct energy gap in collision events.

To do this, scientists carefully adjusted the ATLAS detector to detect particles better, considering factors like efficiency, energy, and momentum, and taking into account background processes.

They used a mix of theoretical predictions and measurements of W and Z bosons to do their research. 

Understanding how protons work was also crucial, and they did this by studying parton distribution functions. ATLAS scientists tested these functions thoroughly using data from many different particle physics experiments.

Furthermore, this milestone represents a significant step forward in looking for future breakthroughs in particle physics research.

Enhanced data analysis promises breakthroughs in particle physics

As ATLAS collects more data, it is likely to improve W-boson’s width and mass measurements, making them more accurate. Better predictions and understanding of parton distribution functions will also help reduce guesswork.

As these measurements improve, physicists can, in turn, conduct more rigorous tests on the Standard Model, potentially uncovering new particles or forces.