A search is presented for new physics in events with two low-momentum, oppositely charged leptons (electrons or muons) and missing transverse momentum in protonproton collisions at a centre-of-mass energy of 13 TeV. The data collected using the CMS detector at the LHC correspond to an integrated luminosity of 35.9 fb −1 . The observed event yields are consistent with the expectations from the standard model. The results are interpreted in terms of pair production of charginos and neutralinos ( χ ± 1 and χ 0 2 ) with nearly degenerate masses, as expected in natural supersymmetry models with light higgsinos, as well as in terms of the pair production of top squarks ( t), when the lightest neutralino and the top squark have similar masses. At 95% confidence level, wino-like χ ± 1 / χ 0 2 masses are excluded up to 230 GeV for a mass difference of 20 GeV relative to the lightest neutralino. In the higgsino-like model, masses are excluded up to 168 GeV for the same mass difference. For t pair production, top squark masses up to 450 GeV are excluded for a mass difference of 40 GeV relative to the lightest neutralino. Data and simulated samplesThe data used in this search correspond to an integrated luminosity of 35.9 fb −1 of protonproton (pp) collisions at a centre-of-mass energy of 13 TeV, recorded in 2016 using the CMS detector. The data are selected using two triggers: an inclusive p miss T trigger, which is used for signal regions (SRs) with an offline p miss T cut > 200 GeV and an additional trigger which requires two muons to lower the offline p miss T cut to 125 GeV. Both the muon p T and the muon pair p T have a trigger online cut of p T > 3 GeV. The inclusive p miss T triggers correspond to an integrated luminosity of 35.9 fb −1 , whereas the events recorded with the dimuon+p miss T trigger correspond to 33.2 fb −1 .Simulated signal and major background processes, such as tt, W+jets, and Z+jets are generated with the MADGRAPH5 aMC@NLO 2.2.2 [32, 33] event generator at leading order (LO) precision in perturbative QCD using the MLM merging scheme [34]. Additional partons are modelled A The CMS Collaboration
The MadGraph5 aMC@NLO framework aims to automate all types of leading-and next-to-leading-order-accurate simulations for any user-defined model that stems from a renormalisable Lagrangian. In this paper, we present all of the key ingredients of such models in the context of supersymmetric theories. In order to do so, we extend the FeynRules package by giving it the possibility of dealing with different renormalisation options that are relevant to supersymmetric models. We also show how to deal with the problem posed by the presence of narrow resonances, thus generalising the so-called on-shell subtraction approaches. We extensively compare our total rate results with those of both Prospino2 and Resummino, and present illustrative applications relevant to the 13 TeV LHC, both at the total-rate and differential levels. The computer programs that we have used to obtain the predictions presented here are all publicly available. arXiv:1907.04898v1 [hep-ph] 10 Jul 2019 7 Conclusions 47 A Conventions for one-point and two-point functions 49 B The MoGRe package 50 B.1 The main method MoGRe$Renormalize and its options 50 B.2 Simplifying the procedure 51 B.3 Restrictions 52 B.4 Specifying the renormalisation scheme 52 B.5 Clearing a renormalisation scheme 52 B.6 Technical details on the functioning of the method 53 C Decoupling of heavy SUSY particles in MG5 aMC 55 -1 -which allows for the cancellation of chiral anomalies and to generate masses for all up-type and down-type particles.
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 (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.
We present simplified MSSM models for light neutralinos and charginos with realistic mass spectra and realistic gaugino-higgsino mixing, that can be used in experimental searches at the LHC. The formerly used naive approach of defining mass spectra and mixing matrix elements manually and independently of each other does not yield genuine MSSM benchmarks. We suggest the use of less simplified, but realistic MSSM models, whose mass spectra and mixing matrix elements are the result of a proper matrix diagonalisation. We propose a novel strategy targeting the design of such benchmark scenarios, accounting for user-defined constraints in terms of masses and particle mixing. We apply it to the higgsino case and implement a scan in the four relevant underlying parameters {µ, tan β, M1, M2} for a given set of light neutralino and chargino masses. We define a measure for the quality of the obtained benchmarks, that also includes criteria to assess the higgsino content of the resulting charginos and neutralinos. We finally discuss the distribution of the resulting models in the MSSM parameter space as well as their implications for supersymmetric dark matter phenomenology.
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