Introduction¶
(From the original SModelS paper, arXiv:1312.4175 )
Searches at the ATLAS and CMS experiments at the LHC show no signs of physics beyond the Standard Model (BSM). After the first phase of LHC operation at centre-of-mass energies of 7–8 TeV in 2010–2012, the limits for the masses of supersymmetric particles, in particular of 1st/2nd generation squarks and gluinos, have been pushed well into the TeV range [1,2]. Likewise, precision measurements in the flavor sector, in particular in B-physics, are well consistent with Standard Model (SM) expectations [3,4] and show no sign, or need, of new physics. At the same time the recent discovery [5,6] of a Higgs-like particle with mass around 125 GeV makes the question of stability of the electroweak scale—the infamous gauge hierarchy problem—even more imminent. Indeed, supersymmetry (SUSY) is arguably the best-motivated theory to solve the gauge hierarchy problem and to explain a light SM-like Higgs boson. So, the Higgs has very likely been discovered—but where is supersymmetry?
Looking closely [7–12] one soon realizes that many of the current limits on SUSY particles are based on severe model assumptions, which impose particular relations between particle masses, decay branching ratios, etc. The prime example is the interpretation of the search results within the Constrained Minimal Supersymmetric Standard Model (CMSSM). The interpretation of the search results within a much more general realization of the MSSM is perfectly feasible, see [7,8,13], but computationally very demanding and certainly not suitable for a “quick” survey.
An approach which has therefore been adopted systematically by the ATLAS and CMS collaborations, is to interpret the results within so-called Simplified Model Spectra [14,15]. Simplified Model Spectra, or SMS for short, are effective-Lagrangian descriptions involving just a small number of new particles. They were designed as a useful tool for the characterization of new physics, see e.g. [16,17]. A large variety of results on searches in many different channels are available from both ATLAS and CMS, providing general cross section limits for SMS topologies. However, using these results to constrain complex SUSY (or general BSM) scenarios is not straightforward. In this paper, we present a method to decompose the signal of an arbitrary SUSY spectrum into simplified model topologies and test it against all the existing LHC bounds in the SMS context.
This document describes the computer package that does all this. SModelS can be used just like an application, running runSModelS.py. In addition, SModelS is also usable as a library, providing functionality to
- decompose models into simplified models,
- confront input models with LHC constraints,
- compute LO, NLO, NLL SUSY cross sections,
- identify missing topologies,
- browse the SModelS database of SMS results
- and a few more tasks.
For example code for various tasks, see How To’s
References:
[1] https://twiki.cern.ch/twiki/bin/view/AtlasPublic/SupersymmetryPublicResults
[2] https://twiki.cern.ch/twiki/bin/view/CMSPublic/PhysicsResultsSUS
[3] Heavy Flavor Averaging Group Collaboration, Y. Amhis et al., Averages of B-Hadron, C-Hadron, and tau-lepton properties as of early 2012, 1207.1158. and HFAG2013 update at http://www.slac.stanford.edu/xorg/hfag/
[4] LHCb Collaboration, R. Aaij et al., First evidence for the decay Bs → μ+ μ- , Phys. Rev. Lett. 110, 021801 (2013), 1211.2674
[5] ATLAS Collaboration, G. Aad et al., Observation of a new particle in the search for the Standard Model Higgs boson with the ATLAS detector at the LHC. Phys. Lett. B 716, 1–29 (2012), 1207.7214
[6] CMS Collaboration, S. Chatrchyan et al., Observation of a new boson at a mass of 125 GeV with the CMS experiment at the LHC. Phys. Lett. B 716, 30–61 (2012), 1207.7235
[7] S. Sekmen, S. Kraml, J. Lykken, F. Moortgat, S. Padhi, et al., Interpreting LHC SUSY searches in the phenomenological MSSM. JHEP 1202, 075 (2012), 1109.5119
[8] A. Arbey, M. Battaglia, F. Mahmoudi, Implications of LHC searches on SUSY particle spectra: the pMSSM parameter space with neutralino dark matter. Eur. Phys. J. C 72, 1847 (2012), 1110.3726
[9] M. Papucci, J.T. Ruderman, A. Weiler, Natural SUSY endures. JHEP 1209, 035 (2012), 1110.6926
[10] M.W. Cahill-Rowley, J.L. Hewett, A. Ismail, T.G. Rizzo, More energy, more searches, but the pMSSM lives on, Phys. Rev. D 88, 035002 (2013), 1211.1981
[11] H.K. Dreiner, M. Krämer, J. Tattersall, How low can SUSY go? Matching, monojets and compressed spectra. Europhys. Lett. 99, 61001 (2012), 1207.1613
[12] R. Mahbubani, M. Papucci, G. Perez, J.T. Ruderman, A. Weiler, Light non-degenerate squarks at the LHC. Phys. Rev. Lett. 110, 151804 (2013), 1212.3328
[13] CMS Collaboration, Phenomenological MSSM interpretation of the CMS 2011 5fb-1 results, Tech. Rep. CMS-PAS-SUS-12-030, CERN, Geneva (2013)
[14] ATLAS Collaboration, H. Okawa, Interpretations of SUSY searches in ATLAS with simplified models, 1110.0282 Page 21 of 23 2868
[15] CMS Collaboration, S. Chatrchyan et al., Interpretation of searches for supersymmetry with simplified models. Phys. Rev. D 88, 052017 (2013), 1301.2175
[16] J. Alwall, P. Schuster, N. Toro, Simplified models for a first characterization of new physics at the LHC. Phys. Rev. D 79, 075020 (2009), 0810.3921
[17] LHC New Physics Working Group Collaboration, D. Alves et al., Simplified models for LHC new physics searches, J. Phys. G 39, 105005 (2012), 1105.2838