The differential cross sections of π−p→γn at center-of-mass energy Ẽ=1363, 1337, and 1245 MeV are presented. The angular distributions are compared with recent γn→π−p experiments. Though the cross sections for π−p→γn are somewhat lower than those for the inverse reaction, when all uncertainties are considered, we find that our data are in acceptable agreement at all three energies with the inverse reaction determined from π−π+ ratio measurements, in support of time-reversal invariance. The agreement with bubble-chamber measurements at Ẽ=1363 and 1337 MeV is less satisfactory. The isotensor dip test applied to our data is inconclusive. Our measurements are compared with many multipole analyses, disagreeing with most, in particular with pure fixed- t dispersion relation calculations. We find no evidence, in the sense suggested by Donnachie, for the classification of the P11(1470) resonance in an SU(3) antidecuplet. The data are consistent with a small radiative decay of the P11(1470) resonance, as predicted by quark models.
Axis error includes +- 6/6 contribution.
Axis error includes +- 4.5/4.5 contribution.
Axis error includes +- 4.2/4.2 contribution.
Differential cross-section measurements for π − p → γ n, consisting of three angular distributions at 618, 676 and 718 MeV/ c , and the energy dependence at θ γ = 90° for seven incident pion momenta between 502 and 888 MeV/ c , are presented. Our data qualitatively support recent multipole analyses. Agreement with the Scheffler et al. results for the inverse reaction, γ n → π − p, using a ( π − -recoil p) coincidence technique is good excluding a large violation of time reversal invariance. The agreement with γ n → π − p data obtained using the R ( π − / π + ) ratio technique or a deuterium bubble chamber is only qualitative.
Axis error includes +- 6.6/6.6 contribution.
Axis error includes +- 6.2/6.2 contribution.
Axis error includes +- 6.0/6.0 contribution.
Measurements have been made of the inclusive scattering of 96, 147, and 219 GeV muons from hydrogen, and of 147 GeV muons from deuterium. Results are presented for the nucleon structure function F2(x,Q2) [≡νW2(x,Q2)] for 10<ν<200 GeV and 0.2<Q2<80 GeV2. The value of F2 rises with Q2 at small x, and falls with Q2 at large x, in agreement with the ideas of quantum chromodynamics. An average value of the ratio σLσT≡R=0.52±0.35 has been obtained for the region 0.003<x<0.10 and 0.4<Q2<30 GeV2. The values of F2 from this experiment have been combined with those from other charged-lepton scattering experiments to determine moments of the structure functions. The variation with Q2 of these moments is used to derive values for Λ, taking into account corrections up to second order in αs. The fit to the data is very good.
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Seventeen differential cross sections of the pion-nucleon charge-exchange reaction have been measured at total center-of-mass energies of 1245, 1337, and 1363 MeV. Most measurements are based on the neutron-photon coincidence method, using carefully calibrated neutron counters and an efficient, large-area photon detector. The results are used to test the predictions of charge independence, with which they agree. The results also confirm the Ayed-Bareyre-Sonderegger phase-degeneracy hypothesis at θ̃π0=180°.
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This paper reports measurements of the hadrons produced in the inelastic scattering of 147-GeV muons by protons and deuterons in an experiment carried out at Fermi National Accelerator Laboratory. Both the scattered muon and the hadrons were measured in a large spectrometer. Properties of the hadron spectra are presented for proton, deuteron, and neutron targets and compared with theoretical models and with hadron spectra from related processes. Emphasis is placed on the quark-parton model and the data are found to be in substantial agreement with it. The average transverse momentum of the hadrons with respect to the virtual photon direction shows no dependence on the muon scattering variables. The data display "jet behavior" of the inclusive hadrons comparable to that found in e+e− annihilations.
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Differential cross sections for π−p→π0n at five angles for 239, 264, 295, 323, and 375 MeV/c incident pions are presented. The measurements employ the neutron-photon coincidence method, using carefully calibrated neutron counters and an efficient, large-area photon detector. Good agreement is found with the results of the CERN phase-shift analysis.
Axis error includes +- 6.3/6.3 contribution.
Axis error includes +- 5.5/5.5 contribution.
Axis error includes +- 5.2/5.2 contribution.
Differential cross-section measurements are presented for π−p→γn at five energies around the p33(1232) resonance. A detailed comparison is made with γn→π−p deduced from γd experiments. In general, the results are in support of detailed balance. Using the Christ-Lee-Donnachie-Shaw model, our new data indicate that the T-violating phase in the isovector part of the M1+ multipole is less than 2°, which is a very sensitive test of time-reversal invariance. No evidence is found for a possible isotensor component of the electromagnetic current. Our data are compared to various multipole analyses. In general, the agreement is poor.
Axis error includes +- 6.3/6.3 contribution.
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We have studied muon-produced hadrons from a deuterium target. The structure functions and the charge ratios are reported for neutrons; the transverse momentum and azimuthal distributions are reported for deuterons. The structure function for the neutron is similar to that of the proton. The charge ratio of produced hadrons follows the expectation of a simple spin-½ quark model. Transverse-momentum results agree with those at lower energy and are similar to those from hadron-hadron interactions. No azimuthal anisotropy is seen.
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Inclusive hadron production in muon-proton inelastic scattering has been measured for q2>0.5 (GeV/c)2 and 10<ν<135 GeV. The results are presented in the form of the transverse momentum distribution of charged hadrons and the hadron invariant structure function F(x′). Results are given for different regions of q2 and s.
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Double-tag events in two-photon collisions are studied using the L3 detector at LEP centre-of-mass energies from root(s)=189 GeV to 209 GeV. The cross sections of the e+e- -> e+e- hadrons and gamma*gamma* -> hadrons processes are measured as a function of the photon virtualities, Q1^2 and Q2^2, of the two-photon mass, W_gammagamma, and of the variable Y=ln(W_gammagamma^2/(Q1 Q2)), for an average photon virtuality <Q2> = 16 GeV2. The results are in agreement with next-to-leading order calculations for the process gamma*gamma* -> q qbar in the interval 2 <= Y <= 5. An excess is observed in the interval 5 < Y <= 7, corresponding to W_gammagamma greater than 40 GeV . This may be interpreted as a sign of resolved photon QCD processes or the onset of BFKL phenomena.
Differential cross section as a function of the photon virtualities Qi**2. Here Q1 is the virtuality w.r.t the electron vertex, and Q2 w.r.t the positron vertex. Data are given both before and after radiative corrections.
Differential cross section as a function of W, the invariant mas of the virtual GAMMA*GAMMA* system. Data are given both before and after radiative corrections.
Differential cross section as a function of the variable LN(W**2/Q1*Q2). Data are given both before and after radiative corrections.
Results are presented from a study of the structure of high energy hadronic events recorded by the L3 detector at sqrt(s)>192 GeV. The distributions of several event shape variables are compared to resummed O(alphaS^2) QCD calculations. We determine the strong coupling constant at three average centre-of-mass energies: 194.4, 200.2 and 206.2 GeV. These measurements, combined with previous L3 measurements at lower energies, demonstrate the running of alphaS as expected in QCD and yield alphaS(mZ) = 0.1227 +- 0.0012 +- 0.0058, where the first uncertainty is experimental and the second is theoretical.
The measured ALPHA_S at three centre-of-mass energies from fits to the individual event shape distributions. The first error is statistcal, the first DSYS error is the experimental systematic uncertainty, and the second DSYS error is the theoryuncertainty.
Updated ALPHA_S measurements from the BT, BW and C-Parameter distributions,from earlier L3 data at lower centre-of-mass energies.. The first error is the total experimental error (stat+sys in quadrature) and the DSYS error is the theory uncertainty.
Combined ALPHA_S values from the five event shape variables. The first error is statistical, the first DSYS error is the experimental systematic uncertainity, the second DSYS error is the uncertainty from the hadronisdation models, andthethird DSYS errpr is the uncertainty due to uncalculated higher orders in the QCDpredictions.
The charged-particle multiplicity distribution is measured for all hadronic events as well as for light-quark and b-quark events produced in e+e- collisions at the Z pole. Moments of the charged-particle multiplicity distributions are calculated. The H moments of the multiplicity distributions are studied, and their quasi-oscillations as a function of the rank of the moment are investigated.
Moments of the charged particle multiplicity distribution with KOS and LAMBDA decay for all events.
Moments of the charged particle multiplicity distribution without KOS and LAMBDA decay for all events.
Moments of the charged particle multiplicity distribution with KOS and LAMBDA decay for light quark events.
A search was made among ν μ charged current events collected in the NOMAD experiment for the reaction: ν μ +N→μ − +D ★+ + hadrons ↪ D 0 +π + ↪ K − +π + . A high purity D ★+ sample composed of 35 events was extracted. The D ★+ yield in ν μ charged current interactions was measured to be T =(0.79±0.17(stat.)±0.10(syst.))%. The mean fraction of the hadronic jet energy taken by the D ★+ is 0.67±0.02(stat.)±0.02(syst.). The distributions of the fragmentation variables z, P T 2 and x F for D ★+ are also presented.
Distribution in Feynman X.
Distribution in transverse momentum.
Distribution in fractional energy Z.
The reaction e+e- -> e+e- gamma* gamma* -> e+e- hadrons for quasi-real photons is studied using data from root(s) = 183 GeV up to 202 GeV. Results on the total cross sections sigma(e+e- -> e+e- hadrons) and sigma(+e- gamma* gamma* -> e+e- hadrons) are given for the two-photon centre-of-mass energies 5 GeV < Wgammagamma < 185 GeV. The total cross section of two real photons is described by a Regge parametrisation. We observe a steeper rise with the two-photon centre-of-mass energy as compared to the hadron-hadron and the photon-proton cross sections. The data are also compared to the expectations of different theoretical models.
The measured total cross section for E+ E- --> E+ E- HADRONS. The first DSYS error is the total experimental systematic uncertainty and the second DSYS error is the uncertainty introduced by unfolding the data with PYTHIA and PHOJET corrections seperately.
The total cross section for two photon production of hadrons. The final column gives the data averaged over all energies together with the experimental systematic error (first DSYS) and the difference between the average and the data unfolded with PHOJET (lower sign) and PYTHIA (upper sign) seperately (second DSYS).
The production of c and b quarks in gamma-gamma collisions is studied with the L3 detector at LEP with 410 pb^-1 of data, collected at centre-of-mass energies from 189 GeV to 202 GeV. Hadronic final states containing c and b quarks are identified by detecting electrons or muons from their semileptonic decays. The cross sections sigma(e+e- -> e+e- c c~ X) and sigma(e+e- -> e+e- b b~ X) are measured and compared to next-to-leading order perturbative QCD calculations. The cross section of b production is measured in gamma-gamma collisions for the first time. It is in excess of the QCD prediction by a factor of three.
Total cross section for charm production.
Total cross section for beauty production.
We search for a Higgs particle with anomalous couplings in the e+e- -> H gamma, e+e- -> HZ and e+e- -> He+e- processes with the L3 detector at LEP. We explore the mass range 70GeV < m_H < 170GeV using 176pb^-1 of integrated luminosity at a center-of-mass energy of \sqrt{s} = 189GeV. The Higgs decays H -> bb, H -> gamma gamma and H -> Z gamma are considered in the analysis. No evidence for anomalous Higgs production is found. This is interpreted in terms of limits on the anomalous couplings d, d_B, Delta g_1^Z and Delta kappa_gamma. Limits on the Gamma(H -> gamma gamma) and Gamma(H -> Z gamma) partial widths in the explored Higgs mass range are also obtained.
The cross section times BR(HIGGS --> 2GAMMA).
The cross section times BR(HIGGS --> BQ BQBAR).
The cross section times BR(HIGGS --> Z GAMMA).
The cross section for the production of Z boson pairs is measured using the data collected by the L3 detector at LEP in 1999 in e^+e^- collisions at centre-of-mass energies ranging from 192 GeV up to 202 GeV. Events in all the visible final states are selected, measuring the cross section of this process. The special case of final states containing b quarks is also investigated. All results are in agreement with the Standard Model predictions.
Two methodics are used for evaluation of the cross section's values.
The result is combination for different energies.
The process e+e- -> W+W-gamma is analysed using the data collected with the L3 detector at LEP at a centre-of-mass energy of 188.6GeV, corresponding to an integrated luminosity of 176.8pb^-1. Based on a sample of 42 selected W+W- candidates containing an isolated hard photon, the W+W-gamma cross section, defined within phase-space cuts, is measured to be: sigma_WWgamma = 290 +/- 80 +/- 16 fb, consistent with the Standard Model expectation. Including the process e+e- -> nu nu gamma gamma, limits are derived on anomalous contributions to the Standard Model quartic vertices W+W- gamma gamma and W+W-Z gamma at 95% CL: -0.043 GeV^-2 < a_0/Lambda^2 < 0.043 GeV^-2 0.08 GeV^-2 < a_c/Lambda^2 < 0.13 GeV^-2 0.41 GeV^-2 < a_n/Lambda^2 < 0.37 GeV^-2.
Measured cross section within the limits of the cuts. THETA(C=GAMMA) is the angle between the photon and the beam axis. ALPHA(C=GAMMA) is the angle between the photon and that of the closest charged lepton or jet.
95 PCT confidence limits on the anomolous contributions.
The data collected by the L3 experiment at LEP at a centre-of-mass energy of 188.6 GeV are used to measure the W-pair production cross section and the W-boson decay branching fractions. These data correspond to an integrated luminosity of 176.8pb^-1. The total cross section for W-pair production, combining all final states, is measured to be sigma_WW = 16.24 +/- 0.37(stat.) +/- 0.22(syst.) pb. Including our data collected at lower centre-of-mass energies, the hadronic branching fraction of the W-boson is determined to be B(W ->qq) = [68.20 +/- 0.68 (stat.) +/- 0.33 (syst.) ] %. The results agree with the Standard Model predictions.
Quoted cross sections with W-boson decays (i.e. W +- < ... >) mean the cross sections times the corresponding branching ratios.
VCS is the CKM matrix element.
Open charm production in gamma-gamma collisions is studied with data collected at e+e- centre-of-mass energies from 189 GeV to 202 GeV corresponding to a total integrated luminosity of 410 pb-1. The charm cross section sigma(gamma gamma ---> c c~ X) is measured for the first time as a function of the two-photon centre-of-mass energy in the interval from 5 GeV to 70 GeV and is compared to NLO QCD calculations.
The total cross section for the process E+ E- --> E+ E- CQ CQBAR X.
The total cross section for the process GAMMA GAMMA --> CQ CQBAR X.
Correlation matrix of the data after unfolding.
The reactions ee->ee+pi0+X and ee->ee+K0s+X are studied using data collected at LEP with the L3 detector at centre-of-mass energies between 189 and 202 GeV. Inclusive differential cross sections are measured as a function of the particle transverse momentum pt and the pseudo-rapidity. For pt < 1.5 GeV, the pi0 and K0s differential cross sections are described by an exponential, typical of soft hadronic processes. For pt > 1.5 GeV, the cross sections show the presence of perturbative QCD processes, described by a power-law. The data are compared to Monte Carlo predictions and to NLO QCD calculations.
The PI0 differential cross section as a function of PT.
The PI0 differential cross section as a function of pseudorapidity.
The K0S differential cross section as a function of PT.
Single W boson production in electron-positron collisions is studied with the L3 detector at LEP. The data sample collected at a centre-of-mass energy of \sqrt{s} = 188.7GeV corresponds to an integrated luminosity of 176.4pb^-1. Events with a single energetic lepton or two acoplanar hadronic jets are selected. Within phase-space cuts, the total cross-section is measured to be 0.53 +/- 0.12 +/- 0.03 pb, consistent with the Standard Model expectation. Including our single W boson results obtained at lower \sqrt{s}, the WWgamma gauge couplings kappa_gamma and lambda_gamma are determined to be kappa_gamma = 0.93 +/- 0.16 +/- 0.09 and lambda_gamma = -0.31 +0.68 -0.19 +/- 0.13.
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Measurements of inclusive production of the Lambda, Xi- and Xi*(1530) baryons in two-photon collisions with the L3 detector at LEP are presented. The inclusive differential cross sections for Lambda and Xi- are measured as a function of the baryon transverse momentum, pt, and pseudo-rapidity, eta. The mean number of Lambda, Xi- and Xi*(1530) baryons per hadronic two-photon event is determined in the kinematic range 0.4 GeV < pt< 2.5 GeV, |eta| < 1.2. Overall agreement with the theoretical models and Monte Carlo predictions is observed. A search for inclusive production of the pentaquark theta+(1540) in two-photon collisions through the decay theta+ -> proton K0s is also presented. No evidence for production of this state is found.
Differential cross section for LAMBDA production.
Differential cross section for LAMBDA production.
Differential cross section for XI- production.
The structure functions of real and virtual photons are derived from cross section measurements of the reaction e^+e^ -> e^+e^- + hadrons at LEP. The reaction is studied at \sqrt{s} ~ 91 GeV with the L3 detector. One of the final state electrons is detected at a large angle relative to the beam direction, leading to Q^2 values between 40 GeV^2 and 500 GeV^2. The other final state electron is either undetected or it is detected at a four-momentum transfer squared P^2 between 1 GeV^2 and 8 GeV^2. These measurements are compared with predictions of the Quark Parton Model and other QCD based models.
Measured values of F2 for the single-tag data as a function of X for the full Q**2 range.
Measured values of F2 for the single-tag data as a function of Q**2 for different X ranges.
The effective F2 measured in double-tag events as a function of X.
We report on measurements of hadronic and leptonic cross sections and leptonic forward-backward asymmetries performed with the L3 detector in the years 1993-95. A total luminosity of 103 pb^-1 was collected at centre-of-mass energies \sqrt{s} ~ m_Z and \sqrt{s} ~ m_Z +/- 1.8 GeV which corresponds to 2.5 million hadronic and 245 thousand leptonic events selected. These data lead to a significantly improved determination of Z parameters. From the total cross sections, combined with our measurements in 1990-92, we obtain the final results: m_Z = 91189.8 +/- 3.1 MeV, Gamma_Z = 2502.4 +/- 4.2 MeV, Gamma_had = 1741.1 +/- 3.8 MeV, Gamma_l = 84.14 +/- 0.17 MeV. An invisible width of Gamma_inv = 499.1 +/- 2.9 MeV is derived which in the Standard Model yields for the number of light neutrino species N_nu = 2.978 +/- 0.014. Adding our results on the leptonic forward-backward asymmetries and the tau polarisation, the effective vector and axial-vector coupling constants of the neutral weak current to charged leptons are determined to be \bar{g}_V^l = -0.0397 +/- 0.0017 and \bar{g}_A^l = -0.50153 +/- 0.00053.Including our measurements of the Z -> b \bar{b} forward-backward and quark charge asymmetries a value for the effective electroweak mixing angle of sin^2\bar{\theta}_W = 0.23093 +/- 0.00066 is derived. All these measurements are in good agreement with the Standard Model of electroweak interactions. Using all our measurements of electroweak observables an upper limit on the mass of the Standard Model Higgs boson of m_H < 133 GeV is set at 95% confidence level.
Updated values of coupling constants and electroweak mixing angle.
Cross sections for hadron production from the 1993 data. The first DSYS error is the uncorrelated part of the systematic error. The second DSYS error is from the statistical error on the absolute luminosity. In addition there is a fully correlated multiplicative contribution to the systematic error of 0.039 PCT plus an absolute uncertainty of 3.2pb together with an additional error from the absolute luminosity of 0.105 PCT.
Cross sections for hadron production from the 1994 data. The first DSYS error is the uncorrelated part of the systematic error. The second DSYS error is from the statistical error on the absolute luminosity. In addition there is a fully correlated multiplicative contribution to the systematic error of 0.039 PCT plus an absolute uncertainty of 3.2pb together with an additional error from the absolute luminosity of 0.088 PCT.
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