Measurement of the differential cross sections for isolated direct photon pair production in $p \bar p$ collisions at $\sqrt{s} = 1.96$ TeV

Abstract

We present measurements of direct photon pair production cross sections using 8.5 fb$^{-1}$ of data collected with the D0 detector at the Fermilab Tevatron $p \bar p$ collider. The results are presented as differential distributions of the photon pair invariant mass $dσ/dM_{γγ}$, pair transverse momentum $d σ/dp^{γγ}_T$, azimuthal angle between the photons $dσ/dΔφ_{γγ}$, and polar scattering angle in the Collins-Soper frame $dσ/d|\cos θ^*|$. Measurements are performed for isolated photons with transverse momenta $p^γ_T>18 ~(17)$ GeV for the leading (next-to-leading) photon in $p_T$, pseudorapidities $|η^γ|<0.9$, and a separation in $η-φ$ space $Δ\mathcal R_{γγ} > 0.4$. We present comparisons with the predictions from Monte Carlo event generators {\sc diphox} and {\sc resbos} implementing QCD calculations at next-to-leading order, $2γ${\sc nnlo} at next-to-next-to-leading order, and {\sc sherpa} using matrix elements with higher-order real emissions matched to parton shower.

Figures (3)

• Figure 1: (Color online) The differential cross section as a function of (a) $M_{\gamma\gamma}$, (b) $p_{T}^{\gamma\gamma}$, (c) $\Delta\phi_{\gamma\gamma}$, and (d) $|\cos \theta^{*}|$ for the full $\Delta\phi_{\gamma\gamma}$ region from data (black points) and theory predictions (curves) are shown in the upper plots. The lower plots show the ratio of data and diphox, resbos, and $2\gamma$ nnlo predictions to the sherpa predictions. The inner line for the error bars in data points shows the statistical uncertainty, while the outer line shows the total (statistical and systematic added in quadrature) uncertainty after subtracting the 7.4% normalization uncertainty.
• Figure 2: (Color online) The differential cross section as a function of (a) $M_{\gamma\gamma}$, (b) $p_{T}^{\gamma\gamma}$, and (c) $|\cos \theta^{*}|$ for the $\Delta\phi_{\gamma\gamma}$$<\pi/2$ region. The notations for points, lines and shaded regions are the same as in Fig. \ref{['fig:fulldphi']}.
• Figure 3: (Color online) The differential cross section as a function of (a) $M_{\gamma\gamma}$, (b) $p_{T}^{\gamma\gamma}$, and (c) $|\cos \theta^{*}|$ for the $\Delta\phi_{\gamma\gamma}$$\geq\pi/2$ region. The notations for points, lines and shaded regions are the same as in Fig. \ref{['fig:fulldphi']}.