Synopsis: Perhaps no “bump” in the data

Potential signs of new physics in an earlier particle collision experiment are now being questioned in a report from Fermilab.
Synopsis figure
Credit: V. Abazov et al., Phys. Rev. Lett. (2011)

An unexpected finding in a particle physics experiment must be reproduced to rule out the possibility that it is only a statistical fluctuation or due to something other than new physics.  This is a primary reason for having more than one experiment studying the same kind of signal at a high-energy particle collider.  At Fermilab, there are two such experiments: CDF and D0.

In April 2011, the CDF collaboration reported a 3.2 standard deviation excess in the number of events with a W boson and a pair of jets whose invariant mass was in the 120160 giga-electron-volt (GeV) range (see T. Aaltonen et al., Phys. Rev. Lett. 106, 171801). One possible explanation for that excess was an unexpected new particle, with a cross section of approximately 4 picobarn (pb). Now, the D0 collaboration reports in Physical Review Letters their analysis of the same type of events. They see no evidence for such an excess, ruling out a particle with a 4pb cross section at the 4.3 standard deviation level.

The two Fermilab experiments appear to disagree, but it’s not yet clear why. To facilitate comparison between the results, D0 made their search parallel to the CDF search to a good approximation, but there were small differences in how the two collaborations handled systematic errors, and of course the detectors are different.  

It is also possible that CDF saw an upward fluctuation in the production of some new particle while D0 saw a downward fluctuation. D0 addresses this possibility, showing their p values for a range of potential signal cross sections. For example, there is only a 2% chance that a particle with a 2pb cross section is compatible with D0’s data.  Further results are needed to clarify the situation. – Robert Garisto


More Announcements »

Subject Areas

Particles and Fields

Previous Synopsis

Nuclear Physics

Pairing in nuclei

Read More »

Next Synopsis

Related Articles

Synopsis: Little Higgs Gives Warm Inflaton a Hand

Synopsis: Little Higgs Gives Warm Inflaton a Hand

A concept borrowed from particle physics models called little Higgs gives new strength to the theory of warm inflation. Read More »

Synopsis: Spotting Dark Matter with Supermaterials
Particles and Fields

Synopsis: Spotting Dark Matter with Supermaterials

Superconducting aluminum or superfluid helium could be used to detect superlight dark matter particles. Read More »

Synopsis: Strange Mesonic Atoms Detected
Particles and Fields

Synopsis: Strange Mesonic Atoms Detected

The DIRAC collaboration at CERN reports the first statistically significant observation of an atom formed from a 𝜋 meson and a K meson. Read More »

More Articles