Dilepton Decay Channel Research Articles

Leptonic and Charged Kaon Decay Modes of theϕMeson Measured in Heavy-Ion Collisions at the CERN Super Proton Synchrotron

We report on results of a measurement of meson production in central Pb-Au collisions at E(lab) = 158A GeV. For the first time in the history of high energy heavy-ion collisions, phi mesons were reconstructed both in the K+K- and the dilepton decay channels in the same experiment. This measurement yields rapidity densities near midrapidity, from the two decay channels, of 2.05 +/- 0.14(stat) +/- 0.25(syst) and 2.04 +/- 0.49(stat) +/- 0.32(syst), respectively. The shape of the measured transverse momentum spectrum is also in close agreement in both decay channels. The data rule out a possible enhancement of the phi yield in the leptonic over the hadronic decay channel of a factor 1.6 or larger at the 95% C.L. This rules out the discrepancy reported in the literature between measurements of the hadronic and dimuon decay channels by two different experiments.

Analytical solution oftt¯dilepton equations

The top quark antiquark production system in the dilepton decay channel is described by a set of equations which is nonlinear in the unknown neutrino momenta. Its most precise and least time consuming solution is of major importance for measurements of top quark properties like the top quark mass and $t\overline{t}$ spin correlations. The initial system of equations can be transformed into two polynomial equations with two unknowns by means of elementary algebraic operations. These two polynomials of multidegree two can be reduced to one univariate polynomial of degree four by means of resultants. The obtained quartic equation is solved analytically.

Algebraic approach to solvett¯dilepton equations

The set of non-linear equations describing the Standard Model kinematics of the top quark antiqark production system in the dilepton decay channel has at most a four-fold ambiguity due to two not fully reconstructed neutrinos. Its most precise solution is of major importance for measurements of top quark properties like the top quark mass and $t\bar{t}$ spin correlations. Simple algebraic operations allow to transform the non-linear equations into a system of two polynomial equations with two unknowns. These two polynomials of multidegree eight can in turn be analytically reduced to one polynomial with one unknown by means of resultants. The obtained univariate polynomial is of degree sixteen. The number of its real solutions is determined analytically by means of Sturm's theorem, which is as well used to isolate each real solution into a unique pairwise disjoint interval. The solutions are polished by seeking the sign change of the polynomial in a given interval through binary bracketing.

Measurement of theW+W−Production Cross Section inpp¯Collisions ats=1.96 TeVusing Dilepton Events

We present a measurement of the W+W- production cross section using 184/pb of ppbar collisions at a center-of-mass energy of 1.96 TeV collected with the Collider Detector at Fermilab. Using the dilepton decay channel W+W- -> l+l-vvbar, where the charged leptons can be either electrons or muons, we find 17 candidate events compared to an expected background of 5.0+2.2-0.8 events. The resulting W+W- production cross section measurement of sigma(ppbar -> W+W-) = 14.6 +5.8 -5.1 (stat) +1.8 -3.0 (syst) +-0.9 (lum) pb agrees well with the Standard Model expectation.

Heavy-flavor measurements with the PHENIX experiment at RHIC

The PHENIX experiment has measured the contribution of heavy-flavor decays to single-electron spectra in Au + Au collisions at √s NN = 130GeV and 200 GeV at RHIC, providing a first measure of the total charm yield and its dependence on collision centrality at the se energies. In addition, J/Ψ charmonium states were reconstructed by PHENIX in their dilepton decay channels in p+p and Au+Au collisions at √s NN = 200GeV .

Top quark search with the D0 1992-1993 data sample.

We present results on the search for the top quark in {ital p{bar p}} collisions at {radical}{ital s} =1.8 TeV with an integrated luminosity of 13.5{plus_minus}1.6 pb{sup {minus}1}. We have considered {ital t{bar t}} production in the standard model using electron and muon dilepton decay channels ({ital t{bar t}}{r_arrow}{ital e}{mu}+jets, {ital ee}+jets, and {mu}{mu}+jets) and single-lepton decay channels ({ital t{bar t}}{r_arrow}{ital e}+jets and {mu}+jets) with and without tagging of {ital b} quark jets. An analysis of these data optimized for top quark masses below 140 GeV/{ital c}{sup 2} gives a lower top quark mass limit of 128 GeV/{ital c}{sup 2}. An analysis optimized for higher top quark masses yields 9 events with an expected background of 3.8{plus_minus}0.9. If we assume that the excess is due to {ital t{bar t}} production, and assuming a top quark mass of 180 GeV/{ital c}{sup 2}, we obtain a cross section of 8.2{plus_minus}5.1 pb.

Observation of the Top Quark.

The D0 Collaboration reports on a search for the standard model top quark in pp¯ collisions at s=1.8TeV at the Fermilab Tevatron with an integrated luminosity of approximately 50pb−1. We have searched for tt¯ production in the dilepton and single-lepton decay channels with and without tagging of b-quark jets. We observed 17 events with an expected background of 3.8±0.6 events. The probability for an upward fluctuation of the background to produce the observed signal is 2×10−6 (equivalent to 4.6 standard deviations). The kinematic properties of the excess events are consistent with top quark decay. We conclude that we have observed the top quark and measured its mass to be 199−21+19 (stat) ±22 (syst) GeV/c2 and its production cross section to be 6.4±2.2pb.Received 24 February 1995DOI:https://doi.org/10.1103/PhysRevLett.74.2632©1995 American Physical Society

Search for high mass top quark production in pp-bar collisions at sqrt s=1.8 TeV.

We present new results on the search for the top quark in p anti-p collisions at S**(1/2) = 1.8 TeV with an integrated luminosity of 13.5 +- 1.6 pb**(-1). We have considered t anti-t production in the Standard Model using electron and muon dilepton decay channels (t anti-t -> e mu + jets, e e + jets, and mu mu + jets) and single-lepton decay channels (t anti-t -> e + jets and mu + jets) with and without tagging of b quark jets. From all channels, we have 9 events with an expected background of 3.8 +- 0.9. If we assume that the excess is due to t anti-t production, and assuming a top mass of 180 GeV/c**2, we obtain a cross section of 8.2 +- 5.1 pb.

Dynamical Likelihood Method for Reconstruction of Events with Missing Momentum. III. Analysis of a CDF HighPTeµEvent ast\bartProduction

A high P T dilepton event observed in 1.8 TeV \bar p p collisions at CDF is analyzed with Dynamical Likelihood Method. A likelihood function for the dilepton decay channel in the t \bar t production is given. We illustrate how the method can be applied to eliminate some typical Standard Model processes that could generate spurious events. By assuming that the event comes from the t \bar t production, the maximum likelihood mass and the expectation value of mass are evaluated as 124 and 136 GeV/c 2 , respectively, and a mass range at the 68% confidence level is estimated to be (119,151) GeV/c 2 , including measurement errors.