An Algorithm to Measure Parton Fragmentation at Large Hadron Colliders

Abstract

The Standard Model of particle physics is discussed with emphasis on light quark QCD, and existing data on light quark fragmentation from e+eð€€€ annihilation and deep inelastic scattering experiments. A method is developed to measure the directionally correlated pionic scaled momentum distribution, or partonic fragmentation function, in large hadron collider conditions. Jet algorithms are used to provide partonic momentum estimates, which in turn scale the hadronic momenta. The associated resolution is unfolded. Hadronic profiles about the parton are examined at Monte Carlo "truth" level. There is found to be a uniform uncorrelated background, which may be estimated event-by-event in regions away from jets and then subtracted statistically from the final distributions. A variable radius cone sampling method is used to count correlated charged hadrons and this also provides a method of coping with any poor directional resolution of jet algorithms. Extrapolation techniques make an estimated measurement possible when the largest safe sampling radius is not large enough to include all correlated hadrons. A novel method to calculate jet mass using jet collimation information available from the FAPS method is demonstrated. The algorithm was tested over an order of magnitude in hard scale ( 100GeV ! 1TeV) with two standard ATLAS reconstructed level Monte Carlos, Pythia and HERWIG, and the calculated fragmentation function is found to be in agreement with the trend of previous data at the hard scale overlap. These models have very different hadronisation models, so may be used to estimate systematic error and test feasibility for a possible full large scale measurement in data. Such work could support the concept of quark universality by establishing propagator invariance.