Abstract
We present a calculation of slepton pair production at the LHC at next-to-next- to-leading logarithmic (NNLL) accuracy, matched to approximate next-to-next-to-leading order (aNNLO) QCD corrections. We collect the relevant analytical formulae, discuss the matching of logarithmically enhanced and fixed-order results and describe the transformation of parton densities and hadronic cross sections to and from Mellin space. Numerically, we find a moderate increase of invariant-mass distributions and total cross sections with respect to our previous results at next-to-leading logarithmic (NLL) accuracy matched to next-to-leading order (NLO), and more importantly a further significant reduction of the factorisation and renormalisation scale dependence that stabilises our predictions to the permil level. The dependence on other supersymmetric parameters like squark and gluino masses and sbottom mixing that enter only at NLO is found to be weak, i.e. less than two percent, as expected.
Highlights
We present a calculation of slepton pair production at the LHC at next-to-nextto-leading logarithmic (NNLL) accuracy, matched to approximate next-to-next-to-leading order QCD corrections
We find a moderate increase of invariant-mass distributions and total cross sections with respect to our previous results at next-to-leading logarithmic (NLL) accuracy matched to next-to-leading order (NLO), and more importantly a further significant reduction of the factorisation and renormalisation scale dependence that stabilises our predictions to the permil level
The increase from NLO+NLL to approximate next-to-next-to-leading order (aNNLO)+NNLL is much smaller as expected for a converging expansion, and most visible at low invariant masses, where the constant terms at aNNLO induce an increase by about 1%
Summary
The hadronic invariant mass distribution for the production of slepton pairs, M dσAB dM 2. Is obtained from a convolution of the parton density functions (PDFs) fa,b/A,B, that depend on the longitudinal momentum fractions xa,b of the partons a, b in the external hadrons A, B and the factorisation scale μF , with the partonic cross section σab, that depends on the squared invariant mass of the produced sleptons M 2, its ratio z = M 2/s Of the PDFs and partonic cross section in eq (2.1), the hadronic cross section σAB factorises, the singular terms in eq (2.2) turn into large logarithms of the Mellin variable N , lnm(1 − z) → lnm+1 N + . The exponent Gab is universal and contains all the logarithmically enhanced contributions in the Mellin variable N , while the hard function Hab is independent of N , though process-dependent
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