Abstract
If supersymmetry near the TeV scale is realized in Nature, the pair production of scalar top squarks is expected to be observable at the Large Hadron Collider. Recently, effective field-theory methods were employed to obtain approximate predictions for the cross section for this process, which include soft-gluon emission effects up to next-to-next-to-leading order (NNLO) in perturbation theory. In this work we employ the same techniques to resum soft-gluon emission effects to all orders in perturbation theory and with next-to-next-to-logarithmic (NNLL) accuracy. We analyze the effects of NNLL resummation on the stop-pair production cross section by obtaining NLO+NNLL predictions in pair invariant mass and one-particle inclusive kinematics. We compare the results of these calculations to the approximate NNLO predictions for the cross sections.
Highlights
Leading order in supersymmetric quantum chromodynamics (SUSY-QCD)
In order to isolate these corrections, we select the part of the next-to-next-to-leading logarithmic (NNLL) resummed formula for the hardscattering kernels which arises from s(1) (i. e. the next-to-leading order (NLO) contribution to the soft function), evaluate the contribution of these terms to the total cross section, and divide what we find by the next-to-leading logarithmic (NLL) cross section
I) we compare the results obtained in pair invariant mass” (PIM) and 1PI kinematics and their average, ii) we investigate the dependence of the predictions on the variation of the hard, soft and factorization scales, iii) we provide numerical tables for different values of the stop mass and for different choices of the parton distribution functions (PDFs) sets, and iv) we compare the predictions with NLO+NNLL accuracy to the approximate next-tonext-to-leading order (NNLO) cross section studied in [29]
Summary
The production of top-squark pairs is described by the scattering process N1(P1) + N2(P2) → t1(p3) + t∗1(p4) + X(k). A fact which is relevant for resummation purposes is that in the soft limit the partonic cross section factors into products of hard and soft functions Each of these two factors satisfies known RGEs. The anomalous dimensions entering these equations are know up to NNLO [30, 31], while the matching coefficients are known up to NLO. The 1PI soft functions, which differ from those derived in PIM kinematics, depend on plus distributions which are singular in the limit s4 → 0 They were originally computed up to NLO in [22] for the top-quark pair production cross section. The RGEs satisfied by the hard and soft functions are identical to the ones discussed in [22], all of the elements are in place to implement the resummation up to NNLL accuracy
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