Mark Williams

The jet energy scale correction is used to determine the true energies of particle jets from the measured energy deposits in the DZero calorimeter. It accounts for many types of experimental effects, such as electronic noise, uninstrumented parts of the detector and interactions of particles before they reach the calorimeter. Such corrections are essential for almost all analyses performed at the DZero experiment. Disponible en español The most visible legacy of the two Tevatron experiments is the still-expanding set of…

The direction of positive (blue) and negative (red) W bosons produced in proton-antiproton collisions gives information about the underlying quark structure of these nucleons. For the best possible measurement, the momentum of the neutrinos (the fuzzy gray objects) is needed. This requires some clever techniques and a detailed understanding of the detector. Disponible en español The above figure may look familiar. That’s because I used a very similar one for an article in September, describing a measurement of the muon…

The top figure is the invariant mass distribution of all Ds± meson candidates, with a clear signal peak shown in red, together with a number of background processes. For the lower figure, each point is the difference between the number of positive (Ds+) and negative (Ds–) candidates, for a set of 10 simulations showing what a negative charge asymmetry of 1 percent would look like for the signal. Disponible en español Our understanding of particle physics is grounded in the…

By using the well-known Z boson as a standard candle to calibrate the detector response, scientists can measure the W boson mass to very high precision. The plot in this figure shows just how well the Z boson data (points) agree with the simulation (line) for the Z boson mass, even in the tricky ‘tails’ of the distribution, which are sensitive to many subtle detector effects. Disponible en español Last year, both CDF and DZero released their latest measurements of…

The new measurement uses the DZero detector like a set of scales, weighing the amount of matter and antimatter. However, the scales are themselves asymmetric, and the main challenge is to understand and quantify the effect of this behavior. Disponible en español Experiments at particle colliders are often described as "recreating the big bang": making new particles out of energy, and then watching to see what happens. In almost all such experiments, we find that matter and antimatter are produced…

DZero has now surpassed 300 publications submitted in Run II. The milestone paper is a comprehensive study of W boson-plus-jet production, pushing our understanding of quark interactions and, in turn, enabling the particle physics community to perform better measurements, including extracting properties of the Higgs boson. Nine years after the DZero collaboration published their first measurement using Run II Tevatron data, they have now reached the milestone of submitting 300 Run II papers. Considering the amount of effort that goes…

X marks the what?

The peak on the left indicates an excess of events consistent with the X(4140) state, which could be a new type of particle composed of two quarks and two antiquarks. A second possible excess can also be seen, although this is more consistent with a background fluctuation. Physicists at particle colliders often perform searches for specific particles that are predicted to exist in our models. The Higgs boson is an excellent example of such a focused search effort, and indeed…

When protons and antiprotons collide, W bosons are produced asymmetrically, since the up quark carries more momentum than the down. By looking at the directions of positively (blue) and negatively (red) charged muons from W decay, we gain deeper understanding about the quark interactions. The inside of a proton is a tough place to see, but that doesn’t stop us from trying to learn more about the quarks and gluons that make it up. A proton contains two up quarks…