Jet production in hadron collisions

High-energy proton-proton collisions that take place at the LHC create very energetic quarks and gluons. As these elementary particles travel away from the collision point, they emit more gluons, which can split into even more quarks and gluons. This results in a relatively narrow jet of particles.

LHC measurements are often separated into bins with a particular number of jets of energetic hadrons. An EU-funded team investigated the effects of jet binning, which affects the precision with which couplings of standard model particles to Higgs bosons are extracted. One of the most exciting aspects of Higgs bosons in the standard model is that couplings to all other particles are fixed. Any deviation from this picture points to new and unknown physical states.

Within the PRECISIONJETS4LHC (Precise predictions for Higgs and new physics signals with jets at the Large Hadron Collider) project, physicists employed resummation to improve the description of jets for Higgs and new physics searches, exploiting the excellent performance of LHC detectors. The soft-collinear effective theory (SCET) provides an efficient framework for resummation at higher orders.

Beam and jet functions in SCET describe initial- and final-state radiation. The physicists showed that they could be easily calculated at next-to-leading order. At next-to-next-to-leading order, they reproduced the quark jet function and calculated the fragmenting quark jet function for the first time.

The physicists also improved the description of jets' substructure using resummation and factorisation, rather than solely relying on Monte Carlo simulations. Specifically, the effort covered jets' angularity, charge and mass; and the results were compared with measurements from LHC detectors.

The production of hadronic jets in proton-proton collisions is one of the most basic processes at the LHC. They form a significant standard model background for many new physics processes. Project results will contribute to correctly accounting for both beam and central jets in future efforts to better understand hadronic final states at the LHC.