Scientists from the LHCb collaboration at CERN’s Large Hadron Collider (LHC) today made an exciting announcement. They have recently produced a joint and unprecedented measurement of the mass of the Z boson, a key particle that mediates the weak nuclear force. This precision measurement validates that the Z boson has a mass of about 91,184.2 million electronvolts (MeV). That’s about 91 billion electronvolts (GeV) – about the mass of a Z boson. This is a remarkable precision for such a measurement. It has an uncertainty of only 9.5 MeV, equivalent to about one-hundredth of a percent.
These neutral force carriers, collectively called Z bosons, are one of the heaviest known elementary particles. This alone would make its measurement extremely important for the field of particle physics. The LHCb team’s results were based on data collected during high-energy proton collisions in 2016, during the LHC’s second run. Most impressively, the experiment’s analysis focused on a sample of 174,000 Z bosons that decayed into pairs of muons—heavier cousins of electrons.
Implications for Fundamental Physics
The Z boson plays a crucial role in mediating the weak nuclear force, one of nature’s fundamental forces that underpins various processes in particle interactions. All of the surprising recent results are now in line with expectations from the Standard Model of particle physics. The accuracy of this model hopes for an uncertainty of 8.8 MeV.
This exact calculation of the Z boson’s mass matches our theoretical predictions. It opens the door to thrilling new research possibilities. Scientists hope that additional improvements in measurement approaches would reveal a richer picture of the cascade of forces at play in particle collisions.
“The High-Luminosity LHC has the potential to challenge the precision of the Z boson mass measurement from LEP—something that seemed inconceivable at the beginning of the LHC program.” – Vincenzo Vagnoni
As the LHCb collaboration has shown, tremendous strides have already been made. This achievement is a transformative step forward for scientists who are probing the strange world of elementary particles and their interactions.
The Role of Muons in Measurement
Muons are electrically charged unstable particles similar to electrons but roughly 200 times heavier. They were instrumental in measuring the mass of the Z boson. When Z bosons decay they almost always produce a pair of muons, which we can detect and use to study the Z bosons themselves. Through meticulous experiments, scientists can begin to look at these decay processes. This allows them to collect important data on the Z boson’s properties.
As Z bosons are produced mostly through high-energy collisions at the LHC, this setting is perfect for generating extreme quantities of Z bosons. By measuring decay patterns, researchers are able to derive very precise measurements. For these research pioneers, these discoveries deepen their grasp of profound forces and particles.
Looking Ahead
While researchers interpret these results, they look forward to continued measurements and discoveries with optimism. The High-Luminosity LHC will be well positioned to make deepening precision measurements of particles such as the Z boson. This new phase holds great potential to deepen our understanding of particle physics. It will very likely even discover new phenomena outside of our current theoretical understanding.