We report the first observation and cross-section measurement of νe+e−→νe+e−. Using neutrinos of energy less than 53 MeV, we observed 63±17 events consistent with ν+e−→ν+e−, of which 51±17 events are assigned to νe+e−→νe+e−. The resulting cross section, {[8.9±3.2(statistical) ±1.5(systematic)]×10−45 cm2/MeV} Eν, agrees with standard electroweak theory, rules out constructive interference between weak charged-current and neutral-current interactions, and begins to indicate the existence of interference between these two interactions.
No description provided.
Neutrino-electron elastic scattering was observed with a 15-ton fine-grained tracking calorimeter exposed to electron neutrinos from muon decay at rest. The measured νee−→νee− elastic scattering rate of 236±35 events yields the total elastic scattering cross section 10.0±1.5(stat)±0.9(syst)×10−45 cm2×[Eν (MeV)], and a model-independent measurement of the strength of the destructive interference between the charged and neutral currents, I=−1.07±0.21, that agrees well with the standard model (SM) prediction I=−1.08. The agreement between the measured electroweak parameters and SM expectations is used to place limits on neutrino properties, such as neutrino flavor-changing neutral currents and neutrino electromagnetic moments. Limits are placed on the masses of new bosons that interact with leptons: for a neutral tensor boson, MT>105 GeV; for a neutral (pseudo)scalar boson, MP,S>47 GeV; for a charged Higgs boson, Mχ+>87 GeV; and for a purely left-handed charged (neutral) vector boson, Mx>239 (119) GeV.
No description provided.
No description provided.
A measurement of the reaction νe+e−→νe+e− was performed using a beam-stop source of νe. Based upon 234±35 events, we obtain a cross section of σ(νee)=[9.9±1.5(stat)±1.0(syst)]×10−42 cm2 ×[Eν (GeV)]. This reaction is mediated by the exchange of W and Z bosons and is thus sensitive to the interference between them. This interference is measured to be -1.07±0.17(stat)±0.11(syst), consistent with the destructive interference (-1.08) predicted by the standard model.
No description provided.
We present the results of a search in p¯p collisions at s=1.8 TeV for the top quark decaying to a charged Higgs boson (H±). We search for dilepton final states from the decay chain tt¯→HH (or HW, or WW) + bb¯→ll+X. In a sample of 19.3 pb−1 collected during 1992-93 with the Collider Detector at Fermilab, we observe 2 events with a background estimation of 3.0 ± 1.0 events. Limits at 95% C.L. in the (Mtop,MH±) plane are presented. For the case Mtop<MW+Mb, we exclude at 95% C.L. the entire (Mtop,MH±) plane for the branching ratio B(H→τν) larger than 75%. We also interpret the results in terms of the parameter tan β of two-Higgs-doublet models.
Upper limits on the cross section at 95PCT CL. CONST(TAN(BETA)) is model parameter describing the charged Higgs decay (see text).
Upper limits on the cross section at 95PCT CL. CONST(TAN(BETA)) is model pameter describing the charged Higgs decay (see text).
Upper limits on the cross section at 95PCT CL. CONST(TAN(BETA)) is model pameter describing the charged Higgs decay (see text).
The total cross sections for the elastic electroproduction of $\rh0$ and $J/\Psi$ mesons for $Q~2$ $>$ 8 GeV$~2$ and $\langle W \rangle \simeq 90$ GeV/c$~2$ are measured at HERA with the H1 detector. The measurements are for an integrated electron$-$proton luminosity of $\simeq$3pb$~{-1}$. The dependences of the total virtual photon$-$proton ($\gamma~* p$) cross sections on $Q~2$, $W$ and the momentum transfer squared to the proton ($t$), and, for the $\rho$, the dependence on the polar decay angle ($\cos \theta~*$), are presented. The $J/\Psi$ : $\rh0$ cross section ratio is determined. The results are discussed in the light of theoretical models and of the interplay of hard and soft physics processes.
Overall EP cross section for M(PI+PI-) < 1.5 GEV.
Overall EP cross section, taking into account the J/PSI --> LEPTON+ LEPTON - branching fraction 0.12.
Integrated EP cross section.
This paper reports the measurement of the B meson and b quark cross sections through the decay chain B0→J/ψ K*(892)0, J/ψ→μ+μ−, K*(892)0→K+π−, using 4.3 pb−1 of data collected at the Collider Detector at Fermilab in p¯p collisions at qrts=1.8 TeV. We obtain σB=1.5±0.7(stat)±0.6(syst) μb for B0 mesons with transverse momentum PT>9.0 GeV/c and rapidity ‖y‖<1.0. Using this result, we find σb=3.7±1.6(stat)±1.5(syst) μb for b quarks with PT>11.5 GeV/c and rapidity ‖y‖<1.0. The b quark cross section is compared to next-to-leading order QCD calculations and previous measurements.
B0 meson cross section.
Bquark cross section.
We present the results of a search for the top quark in 19.3 pb−1 of p¯p collisions at √s =1.8 TeV. The data were collected at the Fermilab Tevatron collider using the Collider Detector at Fermilab (CDF). The search includes standard model tt¯ decays to final states eeνν¯, eμνν¯, and μμνν¯ as well as e+ν+jets or μ+ν+jets. In the (e,μ)+ν+jets channel we search for b quarks from t decays via secondary vertex identification and via semileptonic decays of the b and cascade c quarks. In the dilepton final states we find two events with a background of 0.56−0.13+0.25 events. In the e,μ+ν+jets channel with a b identified via a secondary vertex, we find six events with a background of 2.3±0.3. With a b identified via a semileptonic decay, we find seven events with a background of 3.1±0.3. The secondary vertex and semileptonic-decay samples have three events in common. The probability that the observed yield is consistent with the background is estimated to be 0.26%. The statistics are too limited to firmly establish the existence of the top quark; however, a natural interpretation of the excess is that it is due to tt¯ production. We present several cross-checks. Some support this hypothesis; others do not. Under the assumption that the excess yield over background is due to tt¯, constrained fitting on a subset of the events yields a mass of 174±10−12+13 GeV/c2 for the top quark. The tt¯ cross section, using this top quark mass to compute the acceptance, is measured to be 13.9−4.8+6.1 pb.
Cross section refers to top quark mass equals 174 +- 10 +13 - 12 GeV. Two events in the dilepton final states and six events in the electron or muon nu jets final states.
We present a measurement of $\sigma \cdot B(W \rightarrow e \nu)$ and $\sigma \cdot B(Z~0 \rightarrow e~+e~-)$ in proton - antiproton collisions at $\sqrt{s} =1.8$ TeV using a significantly improved understanding of the integrated luminosity. The data represent an integrated luminosity of 19.7 pb$~{-1}$ from the 1992-1993 run with the Collider Detector at Fermilab (CDF). We find $\sigma \cdot B(W \rightarrow e \nu) = 2.49 \pm 0.12$nb and $\sigma \cdot B(Z~0 \rightarrow e~+e~-) = 0.231 \pm 0.012$nb.
First systematic error is due to detector effects, the second is due to uncertainty in the luminosity.
We present a measurement of the ratio σB(W→eν)σB(Z0→e+e−) in p¯p collisions at s=1.8 TeV The data represent an integrated luminosity of 21.7 pb−1 from the 1992-1993 run of the Collider Detector at Fermilab. We find σB(W→eν)σB(Z0→e+e−)=10.90±0.32(stat)±0.29(syst). From this value, we extract a value for the W width, Γ(W)=2.064±0.061(stat)±0.059(syst) GeV, and the branching ratio, Γ(W→eν)Γ(W)=0.1094±0.0033(stat)±0.0031(syst), and we set a decay-mode-independent limit on the top quark mass mtop>62 GeV/c2 at the 95% C.L.
No description provided.
We present a measurement of the forward-backward charge asymmetry of the process pp¯→Z0/γ+X,Z0/γ→e+e− at Mee>MZ, using 110pb−1 of data at s=1.8TeV collected at the Collider Detector at Fermilab. The measured charge asymmetries are 0.43±0.10 in the invariant mass region Mee>105GeV/c2, and 0.070±0.016 in the region 75<Mee<105GeV/c2. These results are consistent with the standard model values of 0.528±0.009 and 0.052±0.002, respectively.
The forward-backward asymmetry resuts from angular differential cross section : D(SIG)/D(COS(THETA*) = A*(1 + COS(THETA*)**2) + B*COS(THETA*), where THETA * is the emission angle of the E- relative to the quark momentum in the rest frame of the E+ E- pair.
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