Abstract
We consider the transverse-momentum (q T ) distribution of a diphoton pair produced in hadron collisions. At small values of q T , we resum the logarithmically-enhanced perturbative QCD contributions up to next-to-next-to-leading logarithmic accuracy. At intermediate and large values of q T , we consistently combine resummation with the known next-to-leading order perturbative result. All perturbative terms up to order α S 2 are included in our computation which, after integration over q T , reproduces the known next- to-next-to-leading order result for the diphoton pair production total cross section. We present a comparison with LHC data and an estimate of the perturbative accuracy of the theoretical calculation by performing the corresponding variation of scales. In general we observe that the effect of the resummation is not only to recover the predictivity of the calculation at small transverse momentum, but also to improve substantially the agreement with the experimental data.
Highlights
The method has so far been applied to the production of the Standard Model (SM) Higgs boson [44, 45, 47,48,49], Higgs boson production in bottom quark annihilation [50], Higgs boson production via gluon fusion in the MSSM [51], single vector bosons at next-to-leading leading logarithmic (NLL)+LO [52] and at NNLL+NLO [53], W W [54, 55] and ZZ [56] pairs, slepton pairs [57], and DY lepton pairs in polarized collisions [58,59,60,61]
The effect of the fragmentation contributions is sizeably reduced by the photon isolation criteria that are necessarily applied in hadron collider experiments to suppress the very large irreducible background
At small values of qT, the calculation includes the resummation of all logarithmically-enhanced perturbative QCD contributions, up to next-to-next-to-leading logarithmic accuracy; at intermediate and large values of qT, it combines the resummation with the fixed next-to-leading order perturbative result
Summary
We briefly recall the main points of the transverse-momentum resummation formalism of refs. [42, 44, 45], referring to the original papers for the full details. To reduce the impact of unjustified higher-order contributions in the large-qT region, the logarithmic variable L in eq (2.6) is replaced by L ≡ ln μ2resb2/b20 + 1 [44, 47] This (unitarity related) replacement has an additional and relevant consequence: after inclusion of the finite component (see eq (2.9)), we exactly recover the fixed-order perturbative value of the total cross section upon integration of the qT distribution over qT (i.e., the resummed terms give a vanishing contribution upon integration over qT ). Introducing the subscript f.o. to denote the perturbative truncation of the various terms, we have: This matching procedure between resummed and finite contributions guarantees to achieve uniform theoretical accuracy over the region from small to intermediate values of transverse momenta.
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