Determining the mass of W bosons took 10 years– and the result was not what physicists anticipated.
” You can do it rapidly, you can do it cheaply, or you can do it right. We did it right.” These were some of David Toback opening remarks when the leader of Fermilabs Collider Detector unveiled the outcomes of a decade-long experiment to measure the mass of a particle understood as the W boson.
I am a high energy particle physicist, and I become part of the team of numerous researchers that built and ran the Collider Detector at Fermilab in Illinois– understood as CDF.
After trillions of crashes and years of information collection and number crunching, the CDF team discovered that the W boson has a little more mass than expected. The inconsistency is tiny, the results, described in a paper released in the journal Science on April 7, 2022, have actually electrified the particle physics world. It is yet another strong signal that there are missing out on pieces to the physics puzzle of how the universe works if the measurement is undoubtedly correct.
These were some of David Toback opening remarks when the leader of Fermilabs Collider Detector revealed the results of a decade-long experiment to measure the mass of a particle understood as the W boson.
It likewise postulated that a 3rd particle, the Higgs boson, is what offers all other particles– including W and Z bosons– mass.
It is only because the measurement of the Higgs boson– since it offers mass to all other particles– that scientists could check the determined mass of W bosons against the mass anticipated by the Standard Model. In order to calculate the W bosons mass, physicists utilize the mass of the Higgs boson. That leaves the last choice: There are unusual particles or forces causing the upward shift in the W bosons mass.
The Standard Model of particle physics describes the particles that comprise the mass and forces of deep space. MissMJ/WikimediaCommons The Standard Model of particle physics describes the particles that make up the mass and forces of deep space. Credit: MissMJ/WikimediaCommons
A particle that brings the weak force
The Standard Model of particle physics is sciences existing finest structure for the standard laws of deep space and describes 3 standard forces: the electro-magnetic force, the weak force, and the strong force.
Atomic nuclei are held together by the strong force. Nevertheless, certain nuclei are unstable and go through radioactive decay, slowly launching energy by particle emission. This process is driven by the weak force, and researchers have actually been trying to find out why and how atoms decay given that the early 1900s.
According to the Standard Model, forces are transferred by particles. In the 1960s, a series of theoretical and speculative developments proposed that the weak force is transferred by particles called W and Z bosons. It also postulated that a 3rd particle, the Higgs boson, is what gives all other particles– consisting of W and Z bosons– mass.
Given that the arrival of the Standard Model in the 1960s, scientists have actually been working their method down the list of anticipated yet undiscovered particles and determining their homes. In 1983, two experiments at CERN in Geneva, Switzerland, captured the first evidence of the presence of the W boson. It appeared to have the mass of roughly a medium-sized atom such as bromine.
By the 2000s, there was simply one piece missing to finish the Standard Model and connect everything together: the Higgs boson. I helped look for the Higgs boson on three successive experiments, and at last we discovered it in 2012 at the Large Hadron Collider at CERN.
The Standard Model was complete, and all the measurements we made hung together magnificently with the forecasts.
The Collider Detector at Fermilab collected data from trillions of collisions that produced countless W bosons. Credit: Bodhita/WikimediaCommons, CC BY-SA
Determining W bosons
Its a lot of fun to smash particles together at actually high energies to test the Standard Model. These crashes produce much heavier particles for a quick time period prior to decaying back into lighter particles. To examine the homes and interactions of the particles developed in these accidents, physicists use huge and incredibly delicate detectors at centers such as Fermilab and CERN.
In CDF, W bosons are produced about one out of every 10 million times when an antiproton and a proton clash. W bosons decay so quick that they are difficult to determine directly. Physicists track the energy produced from their decay to measure the mass of W bosons.
In the 40 years given that scientists first discovered proof of the W boson, succeeding experiments have actually achieved ever more accurate measurements of its mass. It is only given that the measurement of the Higgs boson– considering that it gives mass to all other particles– that researchers could examine the determined mass of W bosons against the mass forecasted by the Standard Model. The prediction and the experiments always compared– till now.
The new measurement of the W boson (red circle) is much further from the mass predicted by the Standard Model (purple line) and likewise higher than the initial measurement from the experiment. Credit: CDF Collaboration via Science Magazine, CC BY
Suddenly heavy
Fermilabs CDF detector is excellent at precisely measuring W bosons. In between 2001 and 2011, the accelerator smashed antiprotons and protons trillions of times, developing millions of W bosons and gathering as much data as possible from each collision.
In 2012, the Fermilab team reported preliminary outcomes based on a subset of the information. We discovered that the mass was somewhat off, but close to the prediction.
When the physics world finally saw the outcome on April 7, 2022, we were all surprised. Physicists measure primary particle masses in systems of countless electron volts– shortened to MeV. The W bosons mass came out to be 80,433 MeV– 70 MeV greater than what the Standard Model predicts it must be. This might appear like a small excess, however the measurement is accurate to within 9 MeV. This is a variance of nearly eight times the margin of error. When my associates and I saw the outcome, our reaction was a definite “wow!”.
The reality that the measured mass of the W boson differs from the anticipated mass in the Standard Model could show one of three things. Either the math is inaccurate, the measurement is inaccurate, or something is missing from the Standard Model.
What this means for the Standard Model.
The fact that the determined mass of the W boson does not match the anticipated mass within the Standard Model could mean three things. Either the mathematics is incorrect, the measurement is incorrect or there is something missing out on from the Standard Model.
In order to determine the W bosons mass, physicists utilize the mass of the Higgs boson. Furthermore, theoretical physicists have actually been working on the W boson mass calculations for years.
The next possibility is a defect in the experiment or analysis. Physicists all over the world are already evaluating the outcome to try to poke holes in it. In addition, future experiments at CERN may eventually accomplish a more accurate outcome that will either validate or refute the Fermilab mass. In my viewpoint, the experiment is as good a measurement as is currently possible.
That leaves the last choice: There are unexplained particles or forces causing the upward shift in the W bosons mass. Even prior to this measurement, some theorists had actually proposed prospective new particles or forces that would lead to the observed deviation. In the coming months and years, I anticipate a raft of new documents seeking to discuss the puzzling mass of W bosons.
As a particle physicist, I am positive in saying that there need to be more physics waiting to be found beyond the Standard Model. It will be the latest in a series of findings revealing that the Standard Model and real-world measurements often dont rather match if this new outcome holds up. It is these secrets that provide physicists new factors and new ideas to keep looking for a fuller understanding of matter, time, space, and energy.
Written by John Conway, Professor of Physics, University of California, Davis.
This article was first released in The Conversation.