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D0 fails to reproduce CDF’s mysterious bump

By James Dacey

In April the CDF collaboration at the Tevatron triggered excitement and frantic speculation when it announced the discovery of a mysterious bump in its data that could not be explained by the Standard Model of particle physics. But alas, it appears that this mysterious bump will now fade into the night, following the announcement today by the D0 collaboration – CDF’s sister experiment – that it has failed to reproduce the result.

Two months ago the CDF collaboration reported the unexplained signal, which was spotted in a study of W and Z boson pairs that are created when protons and antiprotons collide in Fermilab’s Tevatron collider. The researchers noted a bump between 120 and 160 GeV /C2 in the jets of W bosons with a statistical significance of about “three sigma”.

Within days, speculation surrounding CDF’s bump was rife. People quickly ruled out the possibility that this was the elusive Higgs boson, but some were suggesting that it could be explained by a kind of hybrid force dubbed “technicolour”. A separate theory, proposed by Dan Hooper at Fermilab, was that the excess of events could be explained by a new force responsible for interactions between dark matter and normal matter.

And excitement grew even stronger last week when further analysis by the CDF collaboration saw the significance of its result upgraded to almost five sigma. In everyday terms, this means that there was just a one-in-a-million chance of the bump being due to a statistical fluke.

But earlier today, the D0 collaboration may have killed the party following its analysis of a similar data selection. Publishing a related paper on their website and on arXiv, the researchers report that they find no evidence for the same rare boson production in the mass range 110–170 GeV/c2.

In a statement published on Fermilab’s website, D0 co-spokesperson Dmitri Denisov is quoted as saying: “Our data for collisions that produce a W boson plus two jets are in agreement with the predictions from the Standard Model.

“We have looked among two hundred trillion particle collisions, and we don’t see the excess reported by CDF.”

The D0 collaboration will report its result and the details of its analysis at 4 p.m (CDT). today at a seminar at Fermilab. You will be able to watch a live webcast.

So is this the end of the bump? I’m not sure but it will be very interesting to hear what CDF makes of the developments.

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