Abstract
We present a q_T-resummed calculation of diphoton production at order N^3LL^prime + NNLO. To reach the primed level of accuracy we have implemented the recently published three-loop {mathcal {O}}(alpha _s^3) virtual corrections in the qbar{q} channel and the three-loop transverse momentum dependent beam functions and combined them with the existing infrastructure of CuTe-MCFM, a code performing resummation at order N{}^3LL. While the primed predictions are parametrically not more accurate, one typically observes from lower orders and other processes that they are the dominant effect of the next order. We include in both the qbar{q} and loop-induced gg channel the hard contributions consistently together at order alpha _s^3 and find that the resummed qbar{q} channel without matching stabilizes indeed. Due to large matching corrections and large contributions and uncertainties from the gg channel, the overall improvements are small though. We furthermore study the effect of hybrid-cone photon isolation and hard-scale choice on our fully matched results to describe the ATLAS text {8} TeV data and find that the hybrid-cone isolation worsens agreement at small q_T compared to smooth-cone isolation.
Highlights
The production of prompt isolated photon pairs at hadron colliders is a test of QCD with a clean experimental signature and constitutes as a background to the h → γ γ decay
This is in part due to a new loop-induced gg channel entering at NNLO [15,16,17,18], but even true for just the Bornlevel induced qqchannel
Since the bulk of the cross-section comes from small qT, the resummation can, in principle, improve the prediction and uncertainties
Summary
The production of prompt isolated photon pairs at hadron colliders is a test of QCD with a clean experimental signature and constitutes as a background to the h → γ γ decay. NNLO calculations [14,15] for diphoton production have shown large perturbative corrections with uncertainties that significantly underestimate the difference going from NLO to NNLO, estimated by using typical scale-variation procedures This is in part due to a new loop-induced gg channel entering at NNLO [15,16,17,18], but even true for just the Bornlevel induced qqchannel. The hybrid-cone isolation and natural scale choice can not help to address the large difference between αs and αs results, but they raise valid concerns about previous assumptions This current situation makes a calculation of higher-order (αs3) effects necessary. Both channels have to be added separately together, which means to reach the αs accuracy for the “constant” part, we add the N3LL resummed qqchannel to the N2LL resummed gg loop-induced channel
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