Jet-fragmentation properties inp¯pcollisions at √s=1.8 TeV

Abstract

The charged-particle fractional momentum distribution within jets, D(z), has been measured in dijet events from 1.8-TeV pp collisions in the Collider Detector at Fermilab. As expected from scale breaking in quantum chromodynamics, the fragmentation function D(z) falls more steeply as dijet invariant mass increases from 60 to 200 GeV/c 2 . The average fraction of the jet momentum carried by charged particles is 0.65 ± 0.02(stat) ± 0.08(syst).

Measurement of jet fragmentation into charged particles in pp and PbPb collisions at $ \sqrt{{{s_{\mathrm{NN}}}}} = 2.76 $ TeV

“…As done in previous measurements at hadron colliders [36], the fragmentation function is presented as a function of the variable…”

Neural filters for jet analysis

“…We note that in real applications, the network should be trained on-line with actual pp jet data where the PQCD jet distribution is known to be correct from a large body of prior experiments [3,4]. With those data, the learning dynamics may train the network to a dierent point in weight space to compensate for the actual eciencies of the detector, the inuence of noise, and physical dierences from the LUND model.…”

“…However, identifying jets and estimating their total energy in AA reactions poses a practical challenge because of the large background of low-transverse-energy hadrons produced along with the rare jets. Conventional methods of jet analysis developed for pp collisions [3,4] begin to fail in pA collisions [5] due to the enhanced nuclear background and can be expected to fail completely for future applications to nuclear collisions at the relativistic heavy-ion collider (RHIC) and the large hadron collider (LHC) [6]. The question addressed in this paper is whether the powerful pattern-recognition techniques recently developed in the eld of articial neural networks [7] could help overcome this problem.…”

“…Conventional methods for jet identication utilize the fact that most jet fragments are collimated into an angular cone [3] ( a 0 0 ) 2 + ( a 0 0 ) 2 < R 2 0:5 : (1) Therefore, the jet energy, as determined for example by a segmented calorimeter, is approximately given by E R = X a2R e a = X a e a (R 2 0 ( a 0 0 ) 2 0 ( a 0 0 ) 2 )…”

QCD Tests in Proton-Antiproton Collisions

“…The same mechanism for the evolution of parton densities, namely soft and collinear parton emission, is responsible for the logarithmic evolution of F (z). Figure 11 shows the evolution of different bins of F (z) as a function of dijet invariant mass (M jj ) from CDF data [79]. The data agree well with a logarithmic evolution with M jj and have a distinct similarity with data from e + e − [80], which are plotted as a function of √ s. M jj appears to be a sensible variable to express this evolution insomuch as it is a measure of the hardness of the scattering, particularly in the central pseudorapidity region.…”