Search for long-lived particles in ATLAS and CMS

Heavy stable charged particles are predicted by many models of physics beyond the Standard Model [1], in which one or more new states carry a new conserved, or almost conserved, global quantum number, like for example Rparity or KK-parity. Stable heavy charged sleptons appear for example in Gauge Mediated Supersymmetry Breaking (GMSB) models, when the lightest supersymmetric particle (NLSP), typically the stau slepton, couples weakly with the gravitino LSP. Production of sleptons at the LHC proceeds mainly via decay chains of heavier supersymmetric particles, with typical cross-section at LHC ranging from 100 fb to 1 pb depending on the mass of the slepton particle. Stable leptons are also predicted by the Universal Extra Dimensions model (UED), where for each Standard Model particle exists a corresponding so-called Kaluza-Klein (KK) state in extra dimensions, with the same quantum numbers and spin as the Standard Model partner. KK leptons are directly produced in pairs in p-p collisions, with cross-section at LHC of the order of 20-30 fb. In addition to lepton-like particles, also hadron-like stable particles (R-hadrons) can be produced at LHC. R-hadrons are predicted in Split-SUSY models, or in the framework of the gravitino LSP scenario of SUGRA models, and can be copiously produced at the LHC, with cross-sections up to few nb. A common and largely model independent signature for all these processes is the existence of one or more stable massive charged particles, with low velocity and high transverse momentum, that behave similarly to "massive" muons in the LHC detectors.