Jet physics at DZero

For more than 10 years we are participating in the DZero experiment which detects and analyzes the results of the proton-antiproton interactions provided by Tevatron collider in Fermilab. We are focusing on jets - collimated sprays of particles which are fingerprints of violently scattered proton constituents, quarks and gluons. In events where the jets are produced with large transverse momenta we can study proton structure at scales thousand times smaller than the proton actual size. Data [2] confirms the validity of quantum chromodynamics (theory of strong interaction) and the assertion that the proton’s constituents, quarks, appear point-like even at those small distances.

Precise energetic calibration was crucial in order to obtain this result. Our Prague group which includes colleagues from Charles University and Czech Technical University played an important role in the derivation of jet energy scale. At the end we were able to calibrate jet energies with almost 1% precision, a level not reached at hadron colliders before. Uncertainty in jet energy calibration is usually dominant systematic uncertainty for most of the measurements, since jets are almost always present in the final state at hadron colliders. Our contribution thus had a large impact on the quality and precision of many published DZero results.

In paper [1], we studied finer details of multi-jet radiation and showed that also this aspect is well described within the framework of quantum chromodynamics. The results are being used for tuning phenomenological models of quark and gluon multi-emission showers in various Monte Carlo event generators.

Alexander Kupco was primary author of [1] and one of the main authors of [2]. He was also responsible for derivation of calorimeter response of jets and evaluation of correlations in jet energy scale uncertainty. Later on, he was co-leading the effort of Jet Energy Scale group as one of the convenors. In the past, he was responsible for developing a code for calculation of luminosity in physics samples.

WWW pages of Czech D0 group: http://www-hep2.fzu.cz/d0/hep2.fzu.cz/d0/

Important publications:

[1] V. M. Abazov, …, A. Kupco, et al. (DZero Collaboration): Measurement of dijet azimuthal decorrelations at central rapidities in p anti-p collisions at √s = 1.96 TeV. Phys. Rev. Lett. 94:2218018, 2005
[2] V. M. Abazov, …, A. Kupco, et al. (DZero Collaboration): Measurement of the inclusive jet cross-section in p anti-p collisions at √s = 1.96 TeV. Phys. Rev. Lett. 101:062001, 2008

Researcher:
Alexander Kupčo