Fyzikální ústav Akademie věd ČR

In order to investigate properties of matter at the smallest distances, we need to initiate, according to Heisenberg principle of uncertainty, processes with the largest possible changes in momentum. Before LHC, the best place to study such processes was collider Tevatron in Fermilab. There, the protons were collided with antiprotons at center of mass energy of √s=1.96 TeV, which was at that time the largest energy available at laboratory.Protons interact with antiprotons mostly through strong interaction. Therefore, we observe the most violent processes with the highest momenta transfers in the events induced by the strong interaction. In those events, the proton constituents, partons (quarks or gluons), are violently kicked out of proton. Ejected partons arewrapped up in clouds of hadrons (strongly interacting particles, like pions or protons). At the end, we observe in the detector strongly collimated sprays of particles – so called jets (see figure on the left). Measured cross section of jet production (see figure on the right) was in good agreement with the theoretical predictions of quantum chromodynamics (NLO pQCD) even for jets with the transverse momenta pT above 600 GeV. From the data, we can draw the conclusion that our ideas about properties of matter and space remain valid even at distances more than thousand times smaller than the actual size of proton.

Published measurement of the inclusive jet cross section was the most precise measurement at that time. Work presented here follows the previous publication which contained only short presentation of the results. Extended paper contains detailed information about used methods that lead to the final good precision of the measurement. In particular, strong emphasis was given on determination of jet energy calibration which was the dominant systematic uncertainty for the inclusive jet cross section measurement. Calibration of jet energies is an area where physicists from our institute played a leading role.

Left: One of the most violent interaction of proton with antiproton observed in D0 detector, transverse momentum of the leading jet exceeded 600 GeV. Right: Measured inclusive jet cross section and comparison with the theoretical prediction of quantum chromodynamics (NLO pQCD).

¹Joint Institute for Nuclear Research, Dubna, Russia
²Institute of Physics, Academy of Sciences of the Czech Republic, Praha, Czech Republic