Search for long-lived neutral particles decaying to quark-antiquark pairs in proton-proton collisions ats=8  TeV

Abstract

A search is performed for long-lived massive neutral particles decaying to quark-antiquark pairs. The experimental signature is a distinctive topology of a pair of jets, originating at a secondary vertex. Events were collected with the CMS detector at the CERN LHC in proton-proton collisions at a center-of-mass energy of 8 TeV. The data analyzed correspond to an integrated luminosity of 18.5 fb −1 . No significant excess is observed above standard model expectations. Upper limits at 95% confidence level are set on the production cross section of a heavy neutral scalar particle, H, in the mass range of 200 to 1000 GeV, decaying promptly into a pair of long-lived neutral X particles in the mass range of 50 to 350 GeV, each in turn decaying into a quark-antiquark pair. For X with mean proper decay lengths of 0.4 to 200 cm, the upper limits are typically 0.5-200 fb. The results are also interpreted in the context of an R-parity-violating supersymmetric model with long-lived neutralinos decaying into a quark-antiquark pair and a muon. For pair production of squarks that promptly decay to neutralinos with mean proper decay lengths of 2-40 cm, the upper limits on the cross section are typically 0.5-3 fb. The above limits are the most stringent on these channels to date.

Probing light stops with stoponium

“…Note also that if the RPV coupling is extremely small, λ O(10 −7 ) then the stop will have a macroscopic lifetime. In this case, there are additional strong constraints from searches for displaced dijets [75,80] or long-lived colored/charged particles [75,81,82]. In figure 10 we display the RPV stop LSP phase diagram.…”

Displaced vertex searches for sterile neutrinos at future lepton colliders

“…This effect of a secondary vertex from the decays of the heavy neutrino, that is displaced from the primary vertex, yields an exotic signature and constitutes a powerful search channel for heavy neutrinos at particle colliders. This type of signature is being looked for by the ATLAS and CMS collaborations in their searches for long-lived neutral particles [10,11].…”

Long-lived colored scalars at the LHC

“…In this scenario, a light stop decays to a gravitino a W gauge boson and a b-quark through an off-shell top. They find that for a nearly massless gravitino, the displaced dijet analysis by CMS [5] and the displaced muon plus tracks analysis by ATLAS [6] can exclude colored scalars with masses between 100 and 200 GeV with lifetimes all the way down to 0.1 mm. However, for larger dark fermion masses, the gravitino in their context, the fourbody decay mode of the colored scalar mode dominates leading to softer jets and a lower value of H T .…”

“…Therefore, to probe long-lived particle decays, especially within the inner detector, analyses must incorporate dedicated triggers and beyond the accustomed particle reconstruction algorithms. The latter should have the potential to pin down the origin of many particles (tracks) to one single displaced vertex [5,6,9].…”

“…Other searches look for interesting topologies that arise within SUSY scenarios with Rparity violation. In [5,6], the CMS and ATLAS collaborations search for long-lived neutral particles that decay to quarkantiquark pairs and a muon. These long-lived exotic particles are pair produced via the decay of a non-SM Higgs boson or the decay of a scalar quark to the lightest neutralino and a light quark.…”