Search For Massive Long-lived Particles Research Articles

Search for massive long-lived particles decaying semileptonically at {sqrt{s}}=13,hbox {TeV}

A search is performed for massive long-lived particles (LLPs) decaying semileptonically into a muon and two quarks. Two kinds of LLP production processes were considered. In the first, a Higgs-like boson with mass from 30 to 200text {,GeV!/}c^2 is produced by gluon fusion and decays into two LLPs. The analysis covers LLP mass values from 10text {,GeV!/}c^2 up to about one half the Higgs-like boson mass. The second LLP production mode is directly from quark interactions, with LLP masses from 10 to 90text {,GeV!/}c^2. The LLP lifetimes considered range from 5 to 200 ps. This study uses LHCb data collected from proton-proton collisions at sqrt{s} = 13text {,TeV} , corresponding to an integrated luminosity of 5.4text {,fb} ^{-1}. No evidence of these long-lived states has been observed, and upper limits on the production cross-section times branching ratio have been set for each model considered.

Search for massive long-lived particles decaying semileptonically in the LHCb detector

A search is presented for massive long-lived particles decaying into a muon and two quarks. The dataset consists of proton-proton interactions at centre-of-mass energies of 7 and 8 TeV, corresponding to integrated luminosities of 1 and 2,hbox {fb}^{-1}, respectively. The analysis is performed assuming a set of production mechanisms with simple topologies, including the production of a Higgs-like particle decaying into two long-lived particles. The mass range from 20 to 80 mathrm{{GeV}}/c^2 and lifetimes from 5 to 100{,mathrm{{ps}}} are explored. Results are also interpreted in terms of neutralino production in different R-Parity violating supersymmetric models, with masses in the 23–198 GeV/c^2 range. No excess above the background expectation is observed and upper limits are set on the production cross-section for various points in the parameter space of theoretical models.

Search for Long-Lived Heavy Particles

We have performed a high-sensitivity search for massive long-lived particles produced at 2.5 mrad by 400-GeV/c protons on a beryllium target using time-of-flight, Cherenkov, and calorimetric techniques. A total of ${10}^{11}$ light particles (${\ensuremath{\pi}}^{\ensuremath{-}},{K}^{\ensuremath{-}},\overline{p}$) was sampled at 70 GeV/c. This experiment places a limit of 1.1\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}37}$ ${\mathrm{cm}}^{2}$/${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^{2}$ \ifmmode\cdot\else\textperiodcentered\fi{} nucleon on the invariant cross section for the production of stable particles in the mass range of 4 to 10 ${\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c}}^{2}$.

Further search for massive long-lived particles produced by 400-GeV protons

We report the negative result of a search for the decay products of long-lived particles having lifetimes in the range 50 milliseconds to 10 hours. The upper limit for the "cross section for production and capture" of such particles in a 33-cm aluminum target irradiated with 400-GeV protons is set at less than ${10}^{\ensuremath{-}36}$ ${\mathrm{cm}}^{2}$.

Search for massive long-lived particles in aluminum targets irradiated by 300- and 400-GeV protons

A directional gas Cherenkov counter, which employed six phototubes to sample Cherenkov light from single particles having a gamma greater than ~10 was used to achieve accidental rates of less than one per day if operated near targets with surface radiation levels of as high as 10/sup +3/ r/hr. The cosmic ray background measured by the apparatus was reduced to less than one per day by mounting our directional Cherenkov counter above the irradiated targets and facing toward the earth. Two searches of a few days duration, after bombardments at energies of 300 and 400 GeV with >10/sup 16/ protons at NAL, were made in four inch thick targets of aluminum, mounted just down stream from another aluminum target. No long-lived particles were observed with cross sections for production and capture of approximately less than a micro-micro barn in a lifetime range of a few to a few thousand hours. (auth) from the decay of a long-lived intermediate state. (auth)