Measurement of direct photon pair production cross sections in ppbar collisions at sqrt(s)=1.96 TeV

Abstract

We present a measurement of direct photon pair production cross sections using 4.2 fb-1 of data collected with the D0 detector at the Fermilab Tevatron proton-antiproton Collider. We measure single differential cross sections as a function of the diphoton mass, the transverse momentum of the diphoton system, the azimuthal angle between the photons, and the polar scattering angle of the photons, as well as the double differential cross sections considering the last three kinematic variables in three diphoton mass bins. The results are compared with different perturbative QCD predictions and event generators.

Figures (7)

• Figure 1: The fraction of events produced via $gg \to \gamma\gamma$ scattering relative to total diphoton production as a function of $M_{\gamma\gamma}$, as predicted by the pythia event generator using the CTEQ6.1L PDF set. Photons are required to have transverse momentum $p_T > 21(20)$ GeV for the highest (next-to-highest) $p_T$ photon and pseudorapidity $|\eta| < 0.9$d0_coordinate.
• Figure 2: Comparison of the normalized $O_{\rm NN}$ spectra for photons from DPP MC and $Z\to\ell^+\ell^-\gamma$ data and for misidentified jets from dijet MC.
• Figure 3: Comparison of the normalized $O_{\rm NN}$ spectra for jets misidentified as photons in data and in dijet MC.
• Figure 4: The measured differential diphoton production cross sections as functions of (a) $M_{\gamma\gamma}$, (b) $p_T^{\gamma\gamma}$, (c) $\Delta\phi_{\gamma\gamma}$, and (d) $|\cos \theta^{*}|$. The data are compared to the theoretical predictions from resbos, diphox, and pythia. The predictions from resbos, and diphox use the CTEQ6.6M PDF set CTEQ and renormalization, factorization, and fragmentation scales $\mu_{R} = \mu_{F} = \mu_f =$$M_{\gamma\gamma}$, while pythia uses the Tune A settings. Theoretical predictions are obtained using the following selections: two photons with $p_T>21(20)$ GeV, $|\eta|<0.9$, $30<$$M_{\gamma\gamma}$$<350$ GeV, $M_{\gamma\gamma}$$>p_{T}^{\gamma\gamma}$, ${\Delta\cal{R}}>0.4$, $\Delta \phi_{\gamma \gamma}>0.5\pi$, and $E^{\text{iso}}_{T}<2.5$ GeV. The ratio of differential cross sections between data and resbos are displayed as black points with uncertainties in the bottom plots. The inner line for the uncertainties in data points shows the statistical uncertainty, while the outer line shows the total (statistical and systematic added in quadrature) uncertainty after removing the 7.4% normalization uncertainty. The solid (dashed) line shows the ratio of the predictions from diphox ( pythia) to those from resbos. In the bottom plots, the scale uncertainties are shown by dash-dotted lines and the PDF uncertainties by shaded regions.
• Figure 5: The measured double differential diphoton production cross sections as functions of (a) $p_T^{\gamma\gamma}$, (b) $\Delta\phi_{\gamma\gamma}$, and (c) $|\cos \theta^{*}|$ for $30<$$M_{\gamma\gamma}$$<50$ GeV. The notations for points, lines and shaded regions are the same as in Figure \ref{['fig:xsec_ratio']}.