Search results for "Neutral particle"
showing 7 items of 17 documents
Future Aspects of Positron Spectroscopy
1987
In the first week of this conference experimentalists made us familiar with the features of the positron peaks observed in the collision of very heavy ions with atoms. We learned that these peaks are not understandable in terms of known positron production mechanisms like monoenergetic pair decay of excited nuclear levels or the proposed spontaneous positron production in superheavy atoms. In addition, theorists told us that, at present, also the interpretation that the positron peak structures originate from the decay of a previously not observed neutral particle is in contradiction to well-known experimental facts. Some of you may have, in addition, become confused by the results of the t…
Search for the Production of a Long-Lived Neutral Particle Decaying within the ATLAS Hadronic Calorimeter in Association with a Z Boson from pp Colli…
2019
This Letter presents a search for the production of a long-lived neutral particle (Zd) decaying within the ATLAS hadronic calorimeter, in association with a standard model (SM) Z boson produced via an intermediate scalar boson, where Z→+ (=e, μ). The data used were collected by the ATLAS detector during 2015 and 2016 pp collisions with a center-of-mass energy of s=13 TeV at the Large Hadron Collider and correspond to an integrated luminosity of 36.1±0.8 fb-1. No significant excess of events is observed above the expected background. Limits on the production cross section of the scalar boson times its decay branching fraction into the long-lived neutral particle are derived as a function of …
Search for Neutral, Long-Lived Particles Decaying into Two Muons inpp¯Collisions ats=1.96 TeV
2006
We present a search for a neutral particle, pair-produced in p-pbar collisions at sqrt(s)=1.96 TeV, which decays into two muons and lives long enough to travel at least 5 cm before decaying. The analysis uses ~380 pb^-1 of data recorded with the D0 detector. The background is estimated to be about one event. No candidates are observed, and limits are set on the pair production cross section times branching fraction into dimuons + X for such particles. For a mass of 10 GeV and lifetime of 4x10^-11 s, we exclude values greater than 0.14 pb (95% C.L.). These results are used to limit the interpretation of NuTeV's excess of di-muon events.
Search for a Heavy Neutral Particle Decaying toeμ,eτ, orμτinppCollisions ats=8 TeVwith the ATLAS Detector
2015
This Letter presents a search for a heavy neutral particle decaying into an opposite-sign different-flavor dilepton pair, e(+/-) mu(-/+), e(+/-) tau(-/+), or mu(+/-) tau(-/+) using 20.3 fb(-1) of pp collision data at root s = 8 TeV collected by the ATLAS detector at the LHC. The numbers of observed candidate events are compatible with the standard model expectations. Limits are set on the cross section of new phenomena in two scenarios: the production of (nu) over tilde (tau) in R-parity-violating supersymmetric models and the production of a lepton-flavor-violating Z' vector boson.
Coulomb Fourier Transformation: Application to a Three-Body Hamiltonian with One Attractive Coulomb Interaction
2003
Consider a three-body system consisting of one neutral particle 1 and two charged particles characterized by the indices 2 and 3 with charges of opposite sign, i.e., e2e3 < 0. We use the following notation: (x ν , y ν ), v = 1, 2, 3, denotes the (mass-renormalized) coordinate vector within the pair ν, and between the center of mass of the pair ν and particle ν, respectively. The corresponding canonically coniugate momenta are (k ν , p ν ).
Search for New Phenomena intt¯Events with Large Missing Transverse Momentum in Proton-Proton Collisions ats=7 TeVwith the ATLAS Detector
2012
A search for new phenomena in tt events with large missing transverse momentum in proton-proton collisions at a center-of-mass energy of 7 TeV is presented. The measurement is based on 1.04 fb-1 of data collected with the ATLAS detector at the LHC. Contributions to this final state may arise from a number of standard model extensions. The results are interpreted in terms of a model where new top-quark partners are pair produced and each decay to an on-shell top (or antitop) quark and a long-lived undetected neutral particle. The data are found to be consistent with standard model expectations. A limit at 95% confidence level is set excluding a cross section times branching ratio of 1.1 pb …
A new measurement of direct CP violation in the neutral kaon system
1993
A new measurement of the ratio of the CP-violating amplitudes for $K_{L} \to 2\pi^{0}$ and $K_{L} \to \pi^{+}\pi^{-}$ is reported. The measured value for $\Re = |\eta_{00} / \eta_{ +-}|^{2}$ is $0.9878 \pm 0.0026 \pm 0.0030$, where the first error is the statistical uncertainty and the second is the estimate of the systematic uncertainty. This gives a value for the parameter describing direct CP violation: $\Re$ $\epsilon'/\epsilon = (2.0 \pm 0.7) \times 10^{−3}$ .