Study of double parton interactions in diphoton + dijet events in $p\bar{p}$ collisions at $\sqrt{s} = 1.96$ TeV

TL;DR

This study measures double parton scattering in the gamma gamma + dijet final state using 8.7 fb^-1 of p-pbar data from the D0 detector at sqrt(s)=1.96 TeV. A data-driven technique compares DPS and DI events to extract the effective cross section sigma_eff, carefully accounting for acceptances, efficiencies, and photon purity to minimize theoretical uncertainties. The analysis yields sigma_eff = 19.3 ± 1.4 (stat) ± 7.8 (syst) mb and finds that about 21% of the selected events arise from DPS, consistent with prior DPS measurements across other final states and energies. The work demonstrates a robust, data-driven approach to characterizing DPS and informs understanding of parton spatial distribution in the nucleon.

Abstract

We use a sample of diphoton + dijet events to measure the effective cross section of double parton interactions, which is found to be $σ_{\rm eff} = 19.3$ $\pm$ $1.4({\rm stat})$ $\pm$ $7.8({\rm syst})$ mb. The sample was collected by the D0 detector at the Fermilab Tevatron collider in $p\bar{p}$ collisions at $\sqrt{s} = 1.96$ TeV and corresponds to an integrated luminosity of 8.7 fb$^{-1}$.

Figures (5)

• Figure 1: Schematic view of DP scattering processes producing $\gamma\gamma+{\rm dijet}$ final state. The $\gamma \gamma$ process is shown for the $q \bar{q}$ scattering (above, light, blue online) and box $gg$ diagram (below, light, blue online). The additional dijet scattering is a darker diagram (red online).
• Figure 2: Fraction of the $gg \to \gamma\gamma$ contribution to the total direct cross section comprising the $q\bar{q} \to \gamma\gamma$ and $gg \to \gamma\gamma$ processes. $M_{\gamma \gamma}$ is the invariant mass of the diphoton.
• Figure 4: A diagram illustrating the orientation of photon and jet transverse momenta vectors in $\gamma\gamma+{\rm dijet}$ events. Vectors $q_T^{~1}$ and $q_T^{~2}$ are the $p_T$ imbalance vectors of diphoton and dijet pairs, respectively.
• Figure 5: The fit of the 1VTX data $\Delta S$ distribution with SP and DP templates to extract the DP fraction. The black points correspond to data, red boxes to the DP signal MIXDP model normalized to the $f_{\mathrm{DP}}$ fraction obtained from the fit, and the blue triangles are the SP background template (SP1VTX) normalized to its fraction ($1 -$$f_{\mathrm{DP}}$). The pink open boxes correspond to the sum of the signal and background (total).
• Figure 6: Existing measurements of the effective cross section, $\sigma_{\rm eff}$, compared to the result presented here (AFS: no uncertainty is reported; UA2: only a lower limit is provided). Results of the measurements are grouped by the final state.