It is disappointing news for the particle physics community coming out of Fermilab, we’re afraid. Fermilab has confirmed that the earlier bump seen in the data, presumed to be a new particle, is not significant enough to be considered a detection. We broke the news in emphatic fashion of a new particle discovered in Fermilab in an earlier post.
Story So Far
We had reported that there was a bump found at about 145 GeV with a 5 GeV spread. Data acquired from proton-antiproton collisions with semi-leptonic dijet emissions showed a peak at 145 GeV. The curve was Gaussian in nature with a spread of 5 GeV on either side of the peak. Initial analysis showed that the curve had a three-sigma confidence level (More on confidence levels later). There was thus a strong possibility that a new particle was on the way, since no boson is known having a mass of 145 GeV. The new particle was named as the Z’ or the W’ (Z-primed or W-primed) boson. The Standard Model, wildly successful in particle physics, did not predict this and to fit this in would have required a serious rethinking of known physics. Physicists were naturally excited.
This detection was made at Fermilab at their CDF detector.
Fermilab was the biggest particle accelerator till the Large Hadron Collider came onto the scene. It has been a major progressive force for particle physics over the last three decades, also serving to etch the American superiority in the particle physics arena. It is however expected to be closed down forever late this year. Data recovered from it over the years is still being analysed, and as such will continue for the next five years. One of the two detectors at Fermilab the CDF had detected the anomalous bump of our present interest.
So What’s Wrong?
There are two problems with the CDF data it cannot be corroborated and it falls outside the required confidence levels.
The other detector at Fermilab, named DZero, repeated the experiment, but failed to come up with any conclusive evidence of detection. The negative DZero result would definitely cast shadows over the CDF discovery. Scientists are now baffled as to how the two detectors extremely alike could give such widely varying results under the same experimental conditions. However this is a very good safeguard.
Problem 2: Remember that earlier we had said something about a three-sigma confidence level? It means that the data is reliable and the chances of it being wrong are one-in-a-thousand (99.9% accurate). Confidence levels measure reliability of data. For a discovery to be accepted by the scientific community, the event must have at least a five-sigma confidence level or higher, which means that doubts must reduce to less than one-in-a-million. The problem with the current bump is that it lies just below the five-sigma confidence level.
Take a look at the above graph. Never mind the mathematics and abstruse symbols. Know that the horizontal axis represents the mass of the particles and the vertical axis represents the number of particles detected. At the 145-150 GeV range (point 145 GeV on the horizontal axis), you’d have expected a curve if the previous CDF results were replicated. This is marked with the dotted curve. There is nothing there as far as DZero is concerned. The red regions represent detections and these are in complete agreement with the Standard Model. There is no anomaly to be seen anywhere.
On both counts, the bump is rejected as a new discovery.
What changes then?
Practically nothing changes. The 145 GeV particle, if discovered, would have been interesting, as the Standard Model doesn’t predict it. Further, it could have provided a mechanism for particles acquiring mass without the need of the Higgs boson (essentially becoming the new God particle’). With it being ruled out, the Standard Model stands as it is with the Higgs mechanism being the most favoured mechanism for mass generation.
The discovery would have been exciting, but the field’s exciting even without it. After all, science is like this. DZero spokesperson Stefan Soldner-Rembold put it approproiately in a Fermilab press conference:
This is exactly how science works. Independent verification of any new observation is the key principle of scientific research.
So very true!