DZero confirms newly observed particle

A magician’s feats are not meant to be repeatable, but the reproducibility of results, such as this confirmation of a newly observed particle, is key to the scientific process.

When a magician produces a rabbit out of an empty hat during a performance, you don’t expect to go home and repeat the feat yourself. When a scientist claims to see something new, the expectation is that the observation can be repeated. Reproducibility is a key aspect of scientific inquiry and motivates having independent but complementary experiments that can verify each other’s results. The DZero and CDF experiments perform complimentary studies of the Tevatron data while ATLAS and CMS play those roles at the LHC. Independent verification is not limited to data taken from the same particle collider, though, as demonstrated by a new DZero result that has verified an exciting recent result from ATLAS.

In the Standard Model, the strong force binds quarks by twos or by threes into particles called mesons and baryons, respectively. Most of these particles are short lived, but can be identified by their mass and the type and behavior of their decay products. Recently the ATLAS collaboration observed a new particle that they interpret as an excited state of bottomonium, or a bottom and anti-bottom quark pair.

To verify this new particle, DZero analyzers started by looking for events containing a lower energy state of bottomonium that had decayed into a pair of muons. Next they looked for a photon, a sign of an excited state of bottomonium dropping down to a lower energy state. A precise energy measurement of this low-energy photon is critical to resolving the mass of the excited bottomonium states and verifying the new particle. To improve the energy measurement of these low-energy photons, the analyzers looked for photons that converted into electron-positron pairs inside of the DZero tracking system. This lets the tracking system determine the photon energy measurement, yielding the best resolution at this low energy.

The DZero experimenters verified the observation of a particle with a mass consistent with that reported by the ATLAS collaboration. Further analysis is underway to determine if this new particle is an excited state of bottomonium or perhaps something more exotic.

—Mike Cooke

These physicists made major contributions to this analysis.

The DZero mechanical crew facilitated efficient operation of the DZero detector around the clock throughout the Tevatron run and provided essential support for detector and infrastructure maintenance and upgrades. The impressive reliable operation of the infrastructure that supported the DZero experiment is a testament to the dedication and effectiveness of this team.