Discovery potential for supersymmetry in CMS*

Abstract

This work summarizes and puts in an overall perspective studies done within CMS concerning the discovery potential for squarks and gluinos, sleptons, charginos and neutralinos, SUSY dark matter, lightest Higgs, sparticle mass determination methods and the detector design optimisation in view of SUSY searches. It represents the status of our understanding of these subjects as of Summer 1997.As a benchmark model we used the minimal supergravity-inspired supersymmetric standard model (mSUGRA) with a stable LSP. Discovery of supersymmetry at the LHC should be relatively straightforward. It may occur through the observation of a large excesses of events in missing E T plus jets, or with one or more isolated leptons. An excess of trilepton events or of isolated dileptons with missing E T , exhibiting a characteristic signature in the l + l − invariant mass distribution could also be the first manifestation of SUSY production. Squarks and gluinos can be discovered for masses in excess of 2 TeV. Charginos and neutralinos can be discovered from an excess of events in dilepton or trilepton final states. Inclusive searches can give early indications from their copious production in squark and gluino cascade decays. Indirect evidence for sleptons can be obtained also from inclusive dilepton studies. Isolation requirements and a jet veto would allow detection of both, the direct chargino/neutralino production and of directly-produced sleptons. Squark and gluino production may also represent a copious source of Higgs bosons through cascade decays. The lightest SUSY Higgs h → bb may be reconstructed with a signal/background ratio of order 1 thanks to hard cuts on E miss T justified by escaping LSP's. The lightest supersymmetric particle of SUSY models with conserved R-parity represents a very good candidate for the cosmological dark matter. The region of parameter space where this is true is well-covered by our searches, at least for tanβ = 2.If supersymmetry exists at electroweak scale it could hardly escape detection in CMS, and the study of supersymmetry will form a central part of our physics program.

Search for gauge extensions of the MSSM at the LHC

“…The resulting 0 lepton þ 1 jet þ E 6 T signal can be unambiguously established at the LHC [16]. The situation in the Uð1Þ 0 model is strikingly different than in the MSSM.…”

“…If bino is not the LSP, then it further decays into~0 1 emitting at least one dilepton ' þ ' À [16]. In either case, the decay mode above has 100% branching fraction as there is no other open decay channel for theq R in the MSSM.…”

“…The cascade decays (14) are the key processes for determining the sparticle properties from the decay rates and topologies at the LHC [16]. In the MSSM they involve the hypercharge and the isospin gauginos as well as the Higgsinos.…”

“…In fact, the SUð2Þ L breaking effects that split them in mass turn out to be small so that~0 2 and~AE 1 have approximately the same mass [3,16]. Hence, in the MSSM the decay ofW 3 dominantly gives a dilepton signal.…”

“…However, since all the SUSY processes end with a debris containing~0 1 , which escapes detection in the detector, a complete reconstruction of the masses and couplings of the sparticles is not possible. Therefore, observability is based on the criterion of having a significant excess of events of a given topology over a predetermined background [16,18]. For extracting information on a possible Uð1Þ 0 group, one has to determine the squark/gluino decay channels pertaining to the Uð1Þ 0 model, and compare the signal with the MSSM prediction, as will be done explicitly in the next section.…”