DØ at Lancaster

The D0 experiment was based at the Fermilab Tevatron in Chicago, Illinois, USA. Our research addresses the fundamental nature of the Universe:

  • What is it made of?
  • Where is the anti-matter?
  • Where does mass come from?

The D0 Collaboration in Lancaster July 2013.

The Lancaster group takes particular interest in the investigation of B-hadrons (particles containing b-quarks) and the search for the Higgs. We hope that this research will provide some answers to why the Universe is made of matter. We are currently investigating CP violation (the difference between matter and anti-matter) in the decays of particles containing bottom (b)-quarks and charm (c)-quarks.

Members of the Lancaster group were also involved in the Search for the Higgs boson. The combination of the D0 and CDF results were the first to place limits on the mass of the standard model Higgs Boson ruling out masses around 165 GeV.

The latest cross section limits for the process Higgs → WW.

Lancaster Contributions

Lancaster was responsible for developing and maintaining the key tracking algorithm used by the experiment (the AA algorithm). This work is an essential component of nearly all of the physics results produced by D0 since 2001.

Lancaster was also responsibe for supporting the computer workflow packages (mc_runjob and d0_runjob) which have been used for all of the experiments Monte Carlo event simulation and all of its computer processing on the Grid.

Recent Results

The Lancaster group has taken advantage of two key features of the D0 detector. One is its ability to efficiently reconstruct muons and the the second is the ability to reverse the magnetic fields of the solenoid and the toroid. These two features allow us to minimise the reconstruction asymmetries between positively and negatively charged particles and provide the ideal environment for investigating CP-violation.

One of the most intriguing measurements of recent years is “Evidence for an Anomalous Like-Sign Dimuon Charge Asymmetry” which found a difference from the standard model predictions of 3.2 standard deviations. Since the publication of this result the Lancaster group has investigated this, updating the original measurement and measuring the exclusive semi-leptonic asymmetries in the decays Bs → μDs and Bd → μD(*). These measurements hover 3 standard deviations from the SM providing a tantalising hint of physics beyond the SM.

Combination of measurements of the semi-leptonic charge asymmetries and the two impact-parameter-binned constraints from the same-charge dimuon asymmetry. The bands represent the ±1 standard deviation uncertainties on each measurement. The ellipses represent the 1, 2, 3, and 4 standard deviation two- dimensional confidence level regions of the combination.

Our most recent result is the most precise measurement of CP-violation in the decays B± → J/ψK± and B± → J/ψπ± decays.

The polarity-weighted J/ψh± invariant mass distribution, where the h± is assigned the charged kaon mass

We are currently working on updating the anomalous dimuon measurement and investigating CP-violation in the decay of mesons containing charm-quarks.