Extracting sigma_effective from the CDF gamma+3jets measurement

TL;DR

This work revisits CDF's 1997 σ_eff measurement for double parton scattering in γ+3 jets, identifying the non-standard exclusive-two-scatter definition as problematic for comparisons. Through a detailed parton-level correction and a jet-level correction quantified with multiple Monte Carlo generators, the authors derive a largely process-independent σ_eff. Their corrected result, σ_eff = 12.0 ± 1.4^{+1.3}_{-1.5} mb, carries smaller overall uncertainties than the original CDF value and constrains MPI modeling. The findings motivate refinements to parton-overlap models in MC tunes, including potential x-dependence, and provide context for related heavy-flavor and LHC measurements.

Abstract

In their 1997 paper, CDF measured sigma_effective, the normalization factor that relates the cross section for double parton scattering to the product of the inclusive cross sections of the two individual scatters, in a model in which they are assumed to be independent. In his 2007 paper, Treleani pointed out that CDF used a non-standard definition, in which the double parton scattering cross section corresponds to exactly two scatters, rather than the more conventional one in which it is the inclusive two-scatter cross section. He also estimated the correction from one definition to the other, to give a corrected value of sigma_effective. Treleani's form would be correct under the assumption that CDF were able to uniquely identify and count the number of scatters in an event, which is certainly not the case. In this publication we consider CDF's event definition in more detail to provide an improved correction.