Search For Stable Particles Research Articles

Search for millicharged particles using optically levitated microspheres.

We report results from a search for stable particles with charge ≳10^{-5}e in bulk matter using levitated dielectric microspheres in high vacuum. No evidence for such particles was found in a total sample of 1.4 ng, providing an upper limit on the abundance per nucleon of 2.5×10^{-14} at the 95% confidence level for the material tested. These results provide the first direct search for single particles with charge ≲0.1e bound in macroscopic quantities of matter and demonstrate the ability to perform sensitive force measurements using optically levitated microspheres in vacuum.

Lower limits on R-parity-violating couplings in supersymmetric models with light squarks.

We interpret the results of searches for strongly interacting massive particles to place absolute lower limits on R-parity-violating couplings for squarks with mass (m(q) below 100 GeV. Recent searches for anomalous isotopes require that there be a baryon-number-violating or lepton-number-violating coupling larger than 10(-22)-10(-21) if m(q)>18 GeV. Using data from searches for stable particles at the CERN Large Electron Positron Collider (LEP) we demonstrate that this lower limit increases by 14 orders of magnitude, to an R-parity-violating coupling larger than 10(-8)-10(-7) for any squarks of mass less than 90 GeV. In the presence of an R-parity-violating coupling of this magnitude, neutralinos cannot explain the dark matter density in the Universe.

Cross sections for lepton- and baryon-number-violating processes from supersymmetry at p-p-bar colliders.

In the standard minimal low-energy supersymmetric model, superpartners are produced only in pairs and the lightest superpartner is stable. At hadron colliders missing transverse energy is the most important signature for this model. There are two other minimal supersymmetric models: one has lepton-number violation, the other baryon-number violation. In both models superpartners can be singly produced and the lightest superpartner is unstable. At hadron colliders missing transverse energy is a poor signature for these models. However, there are several important signatures. The most spectacular signatures have two charged leptons without jets. There are also events with two or more isolated charged leptons and jets. Superpartner masses may be reconstructed from combinations of lepton-lepton or lepton-jet invariant masses and from jet spectroscopy. Cross sections are presented for the most important single and pair superparticle production mechanisms in {ital p}-{ital {bar p}} collisions. Present limits from CERN collider data are given and a variety of signatures, events, and backgrounds at {radical}{ital s} =2 TeV are discussed. For example, Drell-Yan fusion of a single superpartner gives a bump in the cross section for {ital e}{sup +}{ital e}{sup {minus}} pairs or jet pairs with invariant mass at the superpartner mass. Squark pair production couldmore » yield events with two jets and two isolated charged leptons. If the lightest superpartner is long lived, it can give rise to secondary vertices or to signatures in stable-particle searches. A run of 10 pb{sup {minus}1} at {radical}{ital s} =2 TeV will enable a large region of the parameter space to be explored.« less