Jet mass dependence of fragmentation in positron-proton collisions

Abstract

We propose the characterization of fragmentation functions by the energy fractionx, a hadron takes away from the energy of the jet measured in the frame co-moving with the jet. Besides, we propose the usage of the jet mass as the fragmentation scaleQ. We show that these two Lorentzinvariant variables emerge naturally in a microcanonical ensemble with conserved fourmomentum. Then, we construct a statistical hadronisation model, in which, two features of the hadronic final states in various high-energy reactions (power law spectra and negative-binomial multiplicity distributions) can be connected simply. Finally, we analyse the scale dependence of the parameters of the model (power of the spectrum and mean energy per hadron) in the φ 3 theory. Fitting fragmentation functions in diffractive positron-proton collisions, we obtain a prediction for the jet mass dependence of the hadron multiplicity distribution inside jets.

Jet Mass Fluctuations and Fragmentation Functions

“…Although the scale evolution of FFs can be obtained using perturbation theory, a non-perturbative input is needed, namely the form of FFs at an initial scale Q 0 . I use the statistical fragmentation model [5,3] for this purpose. In this model, the microcanonical ensemble is used (as in many cases in the literature [3,14,15,16,17,18,19,20,21,22,23]) to account for the finiteness of the energy and multiplicity of jets.…”

“…In Sec. 2, I briefly summarise the statistical fragmentation model and its scale evolution discussed in detailes in [5,3]. Furtheremore, I obtaine the jet mass-averaged FF, and compare it experimental data measured in pp collisions at √ s = 7…”

“…The masses of such jets are typically of the order of 60-100 GeV/c 2 . According to [5,3], in case of such "fat" jets, it is reasonable to parametrise FFs by the variablex = 2P jet…”

“…The masses of such jets are typically of the order of 60-100 GeV/c 2 . According to [5,3], in case of such "fat" jets, it is reasonable to parametrise FFs by the variable x = 2P jet µ p µ h /M 2 jet (p µ h being the fourmomentum of the hadon) and use Q = M jet as fragmentation scale instead of x = p 0 h /P 0 jet and Q = θ c P 0 jet (θ c being the jet opening angle) which are most often used in the literature (eg. [6,7,8,9,10,11,12,13]).…”