CDF search for new physics using six energy clusters

CDF looked for new particles that decay into three jets. Physicists calculated the invarient mass of all possible three-jet combinations and plucked out the triplet that could have come from the decay of a massive particle. There is an excess at around 175 GeV/c2 due to the decay of the top quark, but there is no sign of a new particle.

Experiments at the Tevatron have carried out the hunt for exotic new particles decaying to electrons, photons, muons and even particles that leave no trace in the detector. Physicists find these particles by examining the momentum that disappears when the particles exit the detector.

But few searches for new phenomena concentrate solely on quarks and gluons, which are the basic building blocks of protons and neutrons. Physicists avoid searching these areas because it is hard to sort out new phenomena from the overwhelming abundance of quarks and gluons that come from just standard model physics.

A CDF team worked with theory colleague Scott Thomas to develop a technique that allows them to extract the signature of a massive new particle decaying only to quarks.

If these new particles exist, physicists think that they would be produced in pairs, which would each decay to three quarks. These quarks create showers of secondary particles called jets. The challenge in this analysis is to identify the three jets coming from decay of the hypothetical new particle in the midst of myriad other jets from unrelated particle decays.

Physicists used the technique to examine all possible three-jet combinations and pluck out the triplet that could have come from the decay of a massive particle. Although the team did not find any new particles decaying to three jets, they identified three jet combinations that came from the decay of top quarks (see figure).

The observation of the top quark decays demonstrates that this technique can extract new physics signatures from within very busy events should these new physics signatures exist. Physicists are adapting this technique for use in detecting other types of particle decays.

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edited by Andy Beretvas

Top row from left: Daryl Hare, Claudia Seitz and Amitabh Lath. Also pictured are Eva Halkiadakis (inset left) and Hou-Keong (Tim) Lou (inset right). All members of this analysis group are from Rutgers University.