We have searched for the annihilation of e+e− into the exclusive channels e±τ∓ and μ±τ∓ at √s =29 GeV, using 226 and 133 pb−1, respectively, of data taken with the Mark II detector at the SLAC storage ring PEP. The resulting candidate sample is compatible with the expected background from τ pair production. Our analysis yields 95%-C.L. cross-section limits of σeτ/σμμ<1.8×10−3 and σμτ/σμμ<6.1×10−3, where σμμ is the QED cross section for production of a lepton pair. This is the first high-Q2 test of lepton-flavor conservation involving τ leptons.
95 pct confidence upper limits.
A measurement of the cross section for e + e - → hadrons using 11 000 hadronic decays of the Z boson at ten different center-of-mass energies is presented. A three-parameter fit gives the following values for the Z mass M z , the total width Γ z , the product of the electronic and hadronic partial widths Γ e Γ h , and the unfolded pole cross section σ 0 : M Z =91.171±0.030(stat)±0.030 (beam) GeV, Γ Z =2.511±0.065 GeV, Γ e Γ h =0.148±0.006 (stat.)±0.004 (syst.) GeV 2 , σ 0 =41.6±0.7(stat.)±1.1 (syst.) nb,
No description provided.
Resonance production in the γγ reactionse+e−→e+e+e−π0π0 ande+e−π0η has been studied with the JADE detector at PETRA. The decay widths into γγ of thef2(1270),a0(980) anda2(1320) were measured to be\(\Gamma _{\gamma \gamma } (f_2 (1270)) = 3.19 \pm 0.09_{ - 0.38}^{ + 0.22} \) Kev,Γλλ(a0(980))=0.28±0.04±0.10 KeV/BR(a0(980)→π0η) andΓλλ(a2(1320))=1.01±0.14±0.22KeV. For thef0(975) andf4(2050) upper limits of the widths were obtained,Γλλ(f0(975))<0.6 KeV, andΓλλ(f4(2050))<1.1 KeV, both at the 95% C.L. Assuming that the spin 0 background under thef2(1270) is small, thef2(1270) was found to be produced exclusively in a helicity 2 state. The helicity 0 contribution is <15% at the 95% C.L. The cross section forλλ→π0π0 in the mass range 2.0–3.5 GeV/c2 was measured for the first time. Since the cross section forλλ→π+π− is a factor ∼2 larger, ππ production in this range can be interpreted as taking place via isospin 0 production.
Cross section for ABS(COS(THETA*)) < 0.3.
Cross section under assumptions of spin 2, helicity 2 production.
Cross section under assumption of spin 0 production.
Measurements are presented of the cross section ratios R ℓ = σ ℓ ( e + e − →ℓ + ℓ − ) σ h ( e + e − →hadrons) for ℓ=e, μ and τ using data taken from a scan around the Z 0 . The results are R e =(5.09± o .32±0.18)%, R μ =(0.46±0.35±0.17)% and R τ =(4.72±0.38±0.29)% where, for the ratio R e , the t -channel contribution has been subtracted. These results are consistent with the hypothesis of lepton universality and test this hypothesis at the energy scale s ∼8300 GeV 2 . The absolute cross sections σ ℓ (e + e − →ℓ + ℓ − ) have also been measured. From the cross sections the leptonic partial widths Γ e =(83.2±3.0±2.4) MeV, (Γ e Γ μ ) 1 2 =(84.6±3.0±2.4) MeV and (Γ e Γ τ ) 1 2 =(82.6±3.3±3.2) MeV have been extracted. Assuming lepton universality the ratio Γ ℓ Γ h =(4.89±0.20±0.12) × 10 −2 w was obtained, together with Γ ℓ =(83.6±1.8±2.2) MeV. The number of light neutrino species is determined to be N v =3.12±0.24±0.25. Al the data are consistent with the predictions of the standard model.
E+ E- final state is t-channel subtracted.
No t-channel subtraction. Statistical errors only.
Statistical errors only.
We report results of a study of four-lepton final states produced in e + e − collisions at center-of-mass energies from 50 to 61.4 GeV using the AMY detector at the TRISTAN collider. For the cases where two or three charged tracks are produced at large angles relative to the beam direction, the cross sections agree with QED. However, we observe an excess of e + e − → e + e − μ + μ − events with four tracks at wide angles and with dimuon mass less than 1.0 GeV / c 2 .
No description provided.
None
No description provided.
No description provided.
No description provided.
The ratio R of the total cross section for e+e− annihilation into hadrons to the lowest-order QED cross section for e+e−→μ+μ− has been measured for center-of-mass energies ranging from 50 to 61.4 GeV. If we allow for an overall shift of —4.9%, about 1.5 times our estimated normalization error, the results are consistent with the standard-model predictions.
Error quoted contains point-to-point systematics. There is also an additional 3.2 pct systematic error.
Jet properties ine+e− annihilation at center of mass energies of 14, 22, 35 and 43.7 GeV were studied with the data collected in the TASSO detector at PETRA, using the same evaluation procedures for all the energies. The total hadronic cross section ratio for the center of mass energy interval 39–47 GeV was determined to be ℛ=4.11±0.05 (stat)±0.18(syst.) at\(\langle \sqrt s \rangle= 43 - 7\) GeV. Corrected distributions of global shape variables are presented as well as the inclusive charged particle distributions for scaled momentum and transverse momentum. The center of mass energy evolution of the average sphericity, thrust, aplanarity and particle momentum is shown.
R values. First systematic error comes from selection cuts and Monte Carlo, the second from the luminosity measurement and missing terms in the radiative correction calculations.
Normalised scaled momentum distributions. Data have combined statistical and systematic errors. These data superceded previous TASSO data (ZP C22 (84) 307 (<a href=http://durpdg.dur.ac.uk/scripts/reacsearch.csh/TESTREAC/red+1279> RED = 1279 </a>)).
Normalised scaled momentum distributions. Data have combined statistical and systematic errors. The binning is as used in fits in the paper. These data superceded previous TASSO data (ZP C22 (84) 307 (<a href=http://durpdg.dur.ac.uk/scripts/reacsearch.csh/TESTREAC/red+1279> RED = 1279 </a>)).
We report on a measurement of the mass of the Z 0 boson, its total width, and its partial decay widths into hadrons and leptons. On the basis of 25 801 hadronic decays and 1999 decays into electrons, muons or taus, selected over eleven energy points between 88.28 GeV and 95.04 GeV, we obtain from a combined fit to hadrons and leptons a mass of M z =91.154±0.021 (exp)±0.030 (LEP) GeV, and a total width of Γ z =2.536±0.045 GeV. The errors on M z have been separated into the experimental error and the uncertainty due to the LEP beam energy. The measured leptonic partial widths are Γ ee =81.2±2.6 MeV, Γ μμ =82.6± 5.8 MeV, and Γ ττ =85.7±7.1 MeV, consistent with lepton universality. From a fit assuming lepton universality we obtain Γ ℓ + ℓ − = 81.9±2.0 MeV. The hadronic partial width is Γ had =1838±46 MeV. From the measured total and partial widths a model independent value for the invisible width is calculated to be Γ inv =453±44 MeV. The errors quoted include both the statistical and the systematic uncertainties.
Errors are statistical and point to point systematic luminosity error of 1 pct.
Measured values of e+ e- --> e+ e- cross section.
Corrected cross section. Corrections are for t-channel effects and loss of acollinear events near the boundary of the acceptance.
The pure QED reaction e + e − → γγ has been studied at centre of mass energies around the mass of the Z 0 boson using data recorded by the OPAL detector at LEP. The results are in good agreement with the QED prediction. Lower limits on the cutoff parameters of the modified electron propagator are found to be Λ + >89 GeV and Λ. The lower limit on the mass of an excited electron is 82 GeV assuming the coupling constant λ =1. Upper limits on the branching ratios of Z 0 → γγ , Z 0 → π 0 γ and Z 0 → ηγ are set at 3.7×10 −4 , 3.9×10 −4 and 5.8×10 −4 respectively. Two events from the reaction e + e − → γγγ have been observed, consistent with the QED prediction. An upper limit on the branching ratio of Z 0 → γγγ is set at 2.8×10 −4 . All the limits are given at 95% confidence level.
No description provided.
Data read from graph.
We have measured the properties of Z 0 → b b decays using a sample of 944 inclusive muon events, corresponding to 18 000 hadron events obtained with the L3 detector at LEP. We measured the partial decay width of the Z 0 into b b , Γ b b =353±48 MeV , and we determined the vector coupling of the Z 0 to the b quark; g rmv 2 (b)=0.095±0.047. We measured the forward-backward charge asymmetry in e + e − → b b events at √ s ≈ M v , and obtained A b b =13.3±9.9% .
BOTTOM quark charge asymmetry measurement.
Production of charmed mesons in γγ-interactions at PETRA energies has been observed in the TASSO detector. Cross sections for inclusiveD*± and\(D^0 \bar D^0 \) production have been measured. Neutral and charged meson pairs are estimated to be produced with comparable cross sections, and their sum seems to account for a sizeable fraction of σtot(γγ→hadrons) near the\(c\bar c\) threshold.
No description provided.
No description provided.
Statistical error only.
Hadronic decays of Z 0 bosons are studied in the Delphi detector. Global event variables and singel particles inclusive distributions are compared with QCD-based predictions. The mean charged multiplicity is found to be 20.6±1.0 (stat+syst). The mean values of the sphericity, aplanarity, thrust, minor value, p in T and p out T are compared with values found at lower energy e + e − colliders.
Corrected Sphericity distribution. Statistical errors only.
Corrected Aplanarity distribution. Statistical errors only.
Corrected Q3-Q2 distribution. Statistical errors only.
Using data onvp and\(\bar vp\) charged current interactions from a bubble chamber experiment with BEBC at CERN, the average multiplicities of charged hadrons and pions are determined as functions ofW2 andQ2. The analysis is based on ∼20000 events with incidentv and ∼10000 events with incident\(\bar v\). In addition to the known dependence of the average multiplicity onW2 a weak dependence onQ2 for fixed intervals ofW is observed. ForW>2 GeV andQ2>0.1 GeV2 the average multiplicity of charged hadrons is well described by〈n〉=a1+a2ln(W2/GeV2)+a3ln(Q2/GeV2) witha1=0.465±0.053,a2=1.211±0.021,a3=0.103±0.014 for thevp anda1=−0.372±0.073,a2=1.245±0.028,a3=0.093±0.015 for the\(\bar vp\) reaction.
No description provided.
No description provided.
No description provided.
The NA24 experiment at CERN investigated inclusive γγ, π0π0, and γπ0 final states in the mass range between 4 and 9 GeV/c2 produced in π−p, π+p, and pp reactions at a c.m.-system energy s=23.7 GeV. The π0π0 cross sections agree well with expectations of the quark-parton model. For γπ0 production in π−p and pp reactions, a clear signal is observed and cross sections are shown. The production of γγ events was observed with a statistical significance of 2.9σ in π−p reactions. The cross section is in agreement with a higher-order QCD prediction.
Cross sections are averaged over the transverse momentum differences up to a value which is 1.10 GeV for all points except the first two which are 0.5 and 0.75 GeV respectively.
No description provided.
Maximum accepted transverse momentum difference of pi0 pair is 1 GeV. Inclusive cross section integrated over the total geometrical acceptance of the detector.
Energy spectra of protons, deuterons and tritons from the annihilation of antiprotons stopped in 12 C, 40 Ca, 63 Cu, 92,98 Mo and 238 U have been measured with a Ge-detector telescope. Parameters related to the shape of the spectra were calculated and their dependence on target and ejectile mass number was determined. Yields per p̄ of directly emitted protons, deuterons and tritons and of evaporated protons were estimated.
THE PROTON SPECTRA WERE FITTED WITH THE EXPRESSION N(E)=N1*EXP( -SLOPE(Q=1)*E)+N2*EXP(-SLOPE(Q=2)*E).
Axis error includes +- 0.0/0.0 contribution (?////).
Axis error includes +- 0.0/0.0 contribution (?////).
The reaction e+e−→e+e−π0π0 has been analyzed using 97 pb−1 of data taken with the Crystal Ball detector at the DESY e−e+ storage ring DORIS II at beam energies around 5.3 GeV. For the first time we have measured the cross section for γγ→π0π0 for π0π0 mvariant masses ranging from threshold to about 2 GeV. We measure an approximately flat cross section of about 10 nb for W=mπ0π0<0.8 GeV, which is below 0.6 GeV, in good agreement with a theoretical prediction based on an unitarized Born-term model. At higher invariant masses we observe formation of the f2(1270) resonance and a hint of the f0(975). We deduce the following two-photon widths: Γγγ(f2(1270))=3.19±0.16±0.280.29 keV and Γγγ(f0(975))<0.53 keV at 90% C.L. The decay-angular distributions show the π0π0 system to be dominantly spin 0 for W<0.7 GeV and spin 2, helicity 2 in the f2(1270) region, with helicity 0 contributing at most 22% (90% C.L.).
Statistical errors only.
Statistical errors only.
We have measured the analyzing power in π+, π−, and KS0 production by a polarized proton beam at 13.3 and 18.5 GeV/c. The data cover the central and the beam fragmentation region, in the transverse-momentum range up to 2 GeV/c. The results indicate that sizable effects are present at high xF and also persist into the hard-scattering region for KS0 and π+. A zero value of the analyzing power was observed for π− production.
No description provided.
No description provided.
No description provided.
The inclusive production of neutral kaons is studied inK+p and π+p interactions at 250 GeV/c. Total and semi-inclusive cross sections and average kaon multiplicities are presented and compared with the data at lower energies. The longitudinal and transverse momentum distributions and their energy dependence are analyzed. The results are interpreted in the framework of recent parton models.
No description provided.
No description provided.
No description provided.
We report on a study of ρ0, ρ+, ω,\(\bar K^{*0} (892)\) andK*0 (892) inclusive production in π+p interactions at 250 GeV/c, for ρ+,\(\bar K^{*0} (892)\) for the first time in a π+p experiment. The data are compared withK+p data in the same experiment, with results of other experiments and with quark-parton models. Interesting differences are found between ρ+,0 and ω production.
Inclusive cross sections and average multiplicity per inelastic collision.
No description provided.
No description provided.
We have observed four unambiguous decays of the charmed strange baryon Ξ c o in the NA32 experiment at CERN. Charge- coupled devices and silicon microstrip detectors were used to reconstruct the decay mode Ξ c o → pK − K ∗ (892) o seen in events produced by the interaction of 230 GeV/ c negative poins and kaons on a copper target. We present the first measurement of the lifetime of the Ξ c o , together with a determination of its mass and production cross section. The resonant components of the Ξ c o decay are studied. We use our earlier measurement of the mass of the Ξ c + in the determination of the isospin mass splitting of the Ξ c states.
No description provided.
The first kinematically complete, good-statistics data for the (π,2π) reaction on the proton are presented. They involve double- and triple-differential cross sections as well as π+π− angular correlations. At energies around the Δ resonance, they exhibit a marked difference from phase space. The data are qualitatively described within the framework of an extension of Weinberg’s effective chiral Lagrangian.
No description provided.
No description provided.
We present measurements of the pseudorapidity (η) distribution of charged particles (dNchdη) produced within |η|≤3.5 in proton-antiproton collisions at s of 630 and 1800 GeV. We measure dNchdη at η=0 to be 3.18±0.06(stat)±0.10(syst) at 630 GeV, and 3.95±0.03 (stat)±0.13(syst) at 1800 GeV. Many systematic errors in the ratio of dNchdη at the two energies cancel, and we measure 1.26±0.01±0.04 for the ratio of dNchdη at 1800 GeV to that at 630 GeV within |η|≤3. Comparing to lower-energy data, we observe an increase faster than ln(s) in dNchdη at η=0.
General rapidity densities.
No description provided.
Differential pseudorapidity distribution.. The numbers here at 1800 GeV have been taken from the HZTool routine hzf89201e provded by Arthur Moraes.
We present results on a high statistics study of the nucleon structure functions F 2 ( x , Q 2 ) and R = σ L / σ T measured in deep inelastic scattering of muons on a deuterium target. The analysis is based on 8×10 5 events after all cuts, recorded at beam energies of 120, 200 and 280 GeV in the kinematic range 0.06⩽ × ⩽0.80 and 8GeV 2 ⩽ Q 2 ⩽260GeV 2 . Scaling violations observed in the data are in agreement with predictions of perturbative QCD and allow to determine the QCD mass scale parameter Λ.
No description provided.
R=SIG(L)/SIG(T) is taken to be zero.
R=SIG(L)/SIG(T) is taken to be zero.
We have measured inclusive distributions for charged particles in hadronic decays of the Z boson. The variables chosen for study were charged-particle multiplicity, scaled momentum, and momenta transverse to the sphericity axes. The distributions have been corrected for detector effects and are compared with data from e+e− annihilation at lower energies and with the predictions of several QCD-based models. The data are in reasonable agreement with expectations.
Mean corrected charged particle multiplicity.
Corrected charged particle X distributions. Errors are statistical and systematic combined.
Corrected charged particle PTIN distributions. Errors are statistical and systematic combined.
Forum