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Estimating the color lifetime of energetic quarks

W. Brooks,Jorge A. L'opez

Published 2020 in Physics Letters B

ABSTRACT

A new analysis of published experimental data from the HERMES experiment has been performed. This analysis extracts new information on the space-time properties of color propagation through fitting to a geometric model of the interaction with a realistic nuclear density distribution. Our approach uses a fit to the transverse momentum broadening observable and the hadronic multiplicity ratio; the simultaneous fit to two different observables strongly constrains the outcome. Using the known sizes of the target nuclei, we extract the color lifetime, finding a $z_\mathrm{h}$-dependent range of values from 2 to 8 fm/c for these data. We also extract estimates for the $\hat{q}$ transport coefficient characterizing the strength of the interaction between the quark and the cold nuclear medium, finding an average value of 0.038$\pm$0.026 GeV$\rm^2$/fm. With a two-parameter model we obtain satisfactory fits to the data for the kinematic conditions approximately corresponding to the current fragmentation region. In a secondary fit of the results from that model we independently find a value for the Lund String Model string tension of 1.04 $\pm$0.06 GeV/fm, consistent with the results from many previous analyses, validating our approach. We evaluated the sensitivity for extracting quark energy loss and effective in-medium hadronic cross sections using three-parameter variants of the model, finding large uncertainties in both cases. Our results suggest that hadronic interaction of forming hadrons in the nuclear medium is the primary dynamical cause of meson attenuation in the HERMES data, with quark energy loss playing a more minor role. The method developed here will be applicable for future data from Jefferson Lab and the Electron Ion Collider.

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