Calibrating jets to measure particle energies

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.

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The most visible legacy of the two Tevatron experiments is the still-expanding set of many hundred publications, describing world-leading measurements of the particles and forces that govern our universe. A less obvious, but still vital accomplishment is the innovation, development, and verification of the fundamental analysis techniques required to perform these measurements — techniques that have already been exported for use at the next generation of experiments at the LHC and beyond.

The DZero collaboration has made it a priority to curate and document the most important of these analysis tools to safeguard years of intellectual investment for future reference. Several DZero publications in recent months have been dedicated to the documentation of these analysis tools. Today’s article is devoted to a recent publication on the calibration of jet energies. In simple terms, this calibration enables the signals recorded in the DZero calorimeter detector to be converted into the true energies of particles produced in the initial proton-antiproton collision. It is crucial for any analysis that uses calorimeter information, including measurements of top quark and Higgs boson properties, searches for new particles and precision investigations of electroweak and quantum chromodynamic interactions.

A jet is a ubiquitous concept in collider physics: any time a quark or gluon is produced, the subsequent fragmentation and interactions generate a burst of high-energy particles, propagating through the detector in an expanding cone. Within the DZero detector, it is the calorimeter’s job to detect these particles and measure the energy that they deposit in the process. Translating the measured energy deposits back into true particle energies is a daunting task. For example, some particles will leave their energy in parts of the calorimeter that are uninstrumented; others will interact and lose energy before reaching the calorimeter. To make things worse, the effects are generally dependent on the type of particle and its properties (including the energy itself!). As an idea of the size of this effect, the measured calorimeter energy typically underestimates the particle jet energy by around 30 percent.

The jet calibration procedure is designed to account for all such effects and is determined using dedicated samples of events with well-known properties, such as back-to-back production of a photon and a single particle jet. In this case, the known energy of the photon effectively allows the jet energy to be calibrated. By using a wealth of such data-driven techniques, along with dedicated simulations, the required corrections are obtained with excellent precision at the one percent level, as testified by the many measurements that have already been published using these very techniques.

Mark Williams

These DZero scientists made important contributions to this paper. From left to right, top row: Dmitry Bandurin, group leader (University of Virginia), Gianluca Petrillo, group leader (University of Rochester), Leo Bellantoni (Fermilab), Amitabha Das (University of Arizona). Second row: Georgy Golovanov (JINR, Dubna, Russia), Bob Hirosky (University of Virginia), Aurelio Juste (IFIA, Barcelona, Spain), Bob Kehoe (Southern Methodist University). Third row: Alexander Kupco (Institute of Physics, Prague, Czech Republic), Huanzhao Liu (Southern Methodist University), Alexander Lobodenko (Petersburg Nuclear Physics Institute, Russia), Yun-Tse Tsai (University of Rochester). Bottom row: Alexander Verkheev (JINR, Dubna, Russia), Mike Wang (Fermilab), Zhenyu Ye (UIC).