Differential cross sections as a function of transverse momentum are presented for the production at ∼90° (in the c.m. system) of π±, K±, p, and p¯ in p-nucleus collisions at incident proton energies of 200 and 300 GeV.
No description provided.
No description provided.
No description provided.
We have measured, as a function of transverse momentum (p⊥), the invariant cross section Edσd3p for the production of π±, K±, p, p¯, d, and d¯ in proton collisions with a tungsten (W) target at incident proton energies of 200, 300, and 400 GeV. The measurements were made in the region of 90° in the c.m. system of the incident proton and a single nucleon at rest. Measurements were also made with 300-GeV protons incident on Be, Ti, and W targets of equal interaction length. These p-nucleus measurements, which show a strong dependence on atomic number at high p⊥, were used to extract effective proton-nucleon cross sections by extrapolation to atomic number unity. At large values of the scaling variable x⊥=2p⊥s, where s is the square of the c.m. energy, the pion data are found to be well represented by the expression (s)−ne−ax⊥, with n=11.0±0.4 and a=36.0±0.4. x⊥<0.35, where similar measurements have been made at the CERN ISR, our data are in good agreement with the ISR data.
No description provided.
No description provided.
No description provided.
We have observed muons produced directly in Cu and W targets by 300-GeV incident protons. We find a yield of muons which is approximately a constant fraction (0.8·10−4) of the pion yield for both positive and negative charges and for transverse momenta between 1.5 and 5.4 GeV/c.
No description provided.
Measurements of the midrapidity transverse energy distribution, $d\Et/d\eta$, are presented for $p$$+$$p$, $d$$+$Au, and Au$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV and additionally for Au$+$Au collisions at $\sqrt{s_{_{NN}}}=62.4$ and 130 GeV. The $d\Et/d\eta$ distributions are first compared with the number of nucleon participants $N_{\rm part}$, number of binary collisions $N_{\rm coll}$, and number of constituent-quark participants $N_{qp}$ calculated from a Glauber model based on the nuclear geometry. For Au$+$Au, $\mean{d\Et/d\eta}/N_{\rm part}$ increases with $N_{\rm part}$, while $\mean{d\Et/d\eta}/N_{qp}$ is approximately constant for all three energies. This indicates that the two component ansatz, $dE_{T}/d\eta \propto (1-x) N_{\rm part}/2 + x N_{\rm coll}$, which has been used to represent $E_T$ distributions, is simply a proxy for $N_{qp}$, and that the $N_{\rm coll}$ term does not represent a hard-scattering component in $E_T$ distributions. The $dE_{T}/d\eta$ distributions of Au$+$Au and $d$$+$Au are then calculated from the measured $p$$+$$p$ $E_T$ distribution using two models that both reproduce the Au$+$Au data. However, while the number-of-constituent-quark-participant model agrees well with the $d$$+$Au data, the additive-quark model does not.
Et EMC distributions for sqrt(sNN) = 62.4 GeV Au+Au collisions shown in 5% wide centrality bins.
Et EMC distributions for sqrt(sNN) = 62.4 GeV Au+Au collisions shown in 5% wide centrality bins.
Et EMC distributions for sqrt(sNN) = 62.4 GeV Au+Au collisions shown in 5% wide centrality bins.
We study the processes $e^+ e^-\to K_S^0 K_L^0 \gamma$, $K_S^0 K_L^0 \pi^+\pi^-\gamma$, $K_S^0 K_S^0 \pi^+\pi^-\gamma$, and $K_S^0 K_S^0 K^+K^-\gamma$, where the photon is radiated from the initial state, providing cross section measurements for the hadronic states over a continuum of center-of-mass energies. The results are based on 469 fb$^{-1}$ of data collected with the BaBar detector at SLAC. We observe the $\phi(1020)$ resonance in the $K_S^0 K_L^0$ final state and measure the product of its electronic width and branching fraction with about 3% uncertainty. We present a measurement of the $e^+ e^-\to K_S^0 K_L^0 $ cross section in the energy range from 1.06 to 2.2 GeV and observe the production of a resonance at 1.67 GeV. We present the first measurements of the $e^+ e^-\to K_S^0 K_L^0 \pi^+\pi^-$, $K_S^0 K_S^0 \pi^+\pi^-$, and $K_S^0 K_S^0 K^+K^-$ cross sections, and study the intermediate resonance structures. We obtain the first observations of \jpsi decay to the $K_S^0 K_L^0 \pi^+\pi^-$, $K_S^0 K_S^0 \pi^+\pi^-$, and $K_S^0 K_S^0 K^+K^-$ final states.
Cross section measurement for PHI(1020).
Mass measurement for PHI(1020).
Measurement of the PHI(1020) width.
3roton-antiproton elastic scattering at cm energy 540 GeV has been studied in the t range 0.14 ⩽ − t ⩽ 0.26 GeV 2 . The data is well fitted by an exponential form exp( bt ) with b = 13.3 ± 1.5 GeV −2 .
Elastic Differentiaol Cross Section (545 events). DATA REQUESTED 21 FEB 1983. Data read from plot in paper (29 JAN 2015).
No description provided.
From a sample of about 75000 τ decays identified with the ALEPH detector, K 0 production in 1-prong hadronic decays is investigated by tagging the K L 0 component in a hadronic calorimeter. Results are given for the final states ν τ h − K 0 and ν τ h − π 0 K 0 where the h − is separated into π and K contributions by means of the dE / dx measurement in in the central detector. The resulting branching ratios are: ( Bτ → ν τ π − K 0 ) = (0.88±0.14±0.09)%, ( Bτ → ν τ K − K 0 ) = (0.29±0.12±0.03)%, ( Bτ → ν τ π − π 0 K 0 ) = (0.33±0.14±0.07)% aand ( Bτ → ν τ K − π 0 K 0 ) = (0.05±0.05±0.01)%. The K ∗ decay rate in the K 0 π channel agrees with that in the Kπ 0 mode: the combined value for the branching ratio is (Bτ → ν τ K ∗− ) = (1.45±0.13±0.11)% .
Invariant mass distribution for the $K^0\pi$ system data. The numbers have been read from the plot in the paper.
Form a sample of about 75000 τ decays measured in the ALEPH detector, 1-prong charged kaon decays are identified by the dE / dx measurement in the central detector. The resulting branching ratios for the inclusive and exclusive modes are: B ( τ → ν τ K − ≥ 0 π 0 ≥ 0 K 0 ) = (1.60±0.07±0.12)%, B ( τ → ν τ K − = (0.64±0.05±0.05)%, B ( τ → ν τ − π 0 = (0.53±0.05±0.07)% and B ( τ → ν τ K − π 0 π 0 ) = (0.04±0.03±0.02)%. Exclusive modes are corrected for measured K L 0 production. The rate for τ → ν τ K − agrees well with the prediction based on τ - μ universality.
Invariant mass distribution of the $K\pi^0$ final state, as obtained from a $dE/dx$ fit in each mass bin. The numbers have been read from the plot in the paper, with the errors simply set to zero if they are smaller than the point size.
Single top production via flavour changing neutral currents in the reactions e + e − → t ̄ c / u is searched for in approximately 411 pb −1 of data collected by ALEPH at centre-of-mass energies in the range between 189 and 202 GeV. In total, 58 events are selected in the data to be compared with 50.3 expected from Standard Model backgrounds. No deviation from the Standard Model expectation is observed. Upper limits at 95% CL on single top production cross sections at s =189 –202 GeV are derived. A model-dependent limit on the sum of branching ratios BR(t→Zc)+BR(t→Zu)<17% is obtained.
SIG(C=LEPT) and SIG(C=HADR) are the cross sections upper limits evaluated for leptonic and hadronic decay modes of the W-boson, while SIG(C=COMB) are the values obtained by combining the leptonic and hadronic W-boson decay channels. All cross sections values are obtained under assumption of BR(TQ --> W+ BQ) = 100 %.
We search for lepton flavour violating events (e mu, e tau and mu tau) that could be directly produced in e+e- annihilations, using the full available data sample collected with the OPAL detector at centre-of-mass energies between 189 GeV and 209 GeV. In general, the Standard Model expectations describe the data well for all the channels and at each sqrt(s). A single e mu event is observed where according to our Monte Carlo simulations only 0.019 events are expected from Standard Model processes. We obtain the first limits on the cross-sections sigma(e+e- -> e mu, e tau and mu tau) as a function of sqrt(s) at LEP2 energies.
No description provided.
The triple gauge-boson couplings involving the W are determined using data samples collected with the ALEPH detector at mean centre-of-mass energies of 183 GeV and 189 GeV, corresponding to integrated luminosities of 57 pb^-1 and 174 pb^-1, respectively. The couplings, g^Z_1, Kappa_gamma and lambda_gamma, are measured using W-pair events, single-W production and single-gamma production. Each coupling is measured individually with the other two coupling fixed at their Standard Model value. Including ALEPH results from lower energies, the 95% confidence level intervals for the deviation to the Standard Model are -0.087 < Dg^Z_1 < 0.141 -0.200 < DKappa_gamma < 0.258 -0.062 < Lambda_gamma < 0.147. Fits are also presented where two or all three couplings are allowed to vary. In addition, W-pair events are used to set limits on the C- or P-violating couplings g^V_4, g^V_5, Kappa_V, and Lambda_V, where V denotes either gamma or Z. No deviations from the Standard Model expectations are observed.
The errors included the statistical and systematic uncertainties. Deviation from SM values.
The errors included the statistical and systematic uncertainties. Combined results, lower sqrt(s) data are also included.
The errors included the statistical and systematic uncertainties. Combined results, lower sqrt(s) data are also included. Three-parameter fit.
A new precise measurement of |V_{cb}| and of the branching ratio BR(\bar{B^0} -> D^{*+} \ell^- \bar{\nu_\ell}) has been performed using a sample of about 5000 semileptonic decays \bar{B^0} -> D^{*+} \ell^- \bar{\nu_\ell}, selected by the DELPHI detector at LEP I by tagging the soft pion from D^{*+} -> D^0 \pi^+. The results are: V_{cb}=(39.0 +/- 1.5 (stat.) ^{+2.5}_{-2.6} (syst. exp.) +/- 1.3 (syst. th.)) x 10^{-3} BR(\bar{B^0} -> D^{*+} \ell^- \bar{\nu_\ell})=(4.70 +/- 0.13 (stat.) ^{+0.36}_{-0.31} (syst. exp.))% The analytic dependences of the differential cross-section and of the Isgur Wise form factor as functions of the variable w = v_{B^0}.v_{D^*} have also been obtained by unfolding the experimental resolution.
The formfactors are evaluated at zero recoil of D meson. VCB is the V-CKM (Cabibbo-Kobayashi-Maskawa) mixing matrix element. The value of FORMFACTOR(1) = 0.91 +- 0.03.
A test of the QED process e+e- -> gamma gamma (gamma) is reported. The data analysed were collected with the DELPHI detector in 1998 and 1999 at the highest energies achieved at LEP, reaching 202 GeV in the centre-of-mass. The total integrated luminosity amounts to 375.7 pb^{-1}. The differential and total cross-sections for the process e+e- -> gamma gamma were measured, and found to be in agreement with the QED prediction. 95% Confidence Level (C.L.) lower limits on the QED cut-off parameters of Lambda+ > 330 GeV and Lambda- > 320 GeV were derived. A 95% C.L. lower bound on the mass of an excited electron of 311 GeV/c^2 (for lambda_gamma = 1) was obtained. s-channel virtual graviton exchange was searched for, resulting in 95% C.L. lower limits on the string mass scale, M_S: M_S > 713 GeV/c^2 (lambda = 1) and M_S > 691 GeV/c^2 (lambda = -1).
No description provided.
No description provided.
No description provided.
The rates are measured per hadronic Z decay for gluon splitting to bb(bar) quark pairs, g_bb, and of events containing two bb(bar) quark pairs, g_4b, using a sample of four-jet events selected from data collected with the OPAL detector. Events with an enhanced signal of gluon splitting to bb(bar) quarks are selected if two of the jets are close in phase-space and contain detached secondary vertices. For the event sample containing two bb(bar) quark pairs, three of the four jets are required to have a significantly detached secondary vertex. Information from the event topology is combined in a likelihood fit to extract the values of g_bb and g_4b, namely g_bb = (3.07 +- 0.53(stat) +- 0.97(syst))x10^-3 g_4b = (0.36 +- 0.17(stat) +- 0.27(syst))x10^-3
No description provided.
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.
The magnitude of the CKM matrix element Vub is determined by measuring the inclusive charmless semileptonic branching fraction of beauty hadrons at OPAL based on b -> Xu l nu event topology and kinematics. This analysis uses OPAL data collected between 1991 and 1995, which correspond to about four million hadronic Z decays. We measure Br(b -> Xu l) to be (1.63 +/- 0.53 +0.55/-0.62) x 10^(-3). The first uncertainty is the statistical error and the second is the systematic error. From this analysis, Vub is determined to be: |Vub| = (4.00 +/- 0.65(stat) +0.67/-0.76(sys) +/- 0.19(HQE)) x 10^(-3). The last error represents the theoretical uncertainties related to the extraction of |Vub| from Br(b -> Xu l) using the Heavy Quark Expansion.
CKM is Cabibbo-Kobayashi-Maskawa (CKM) matrix element. The last DSYS error comes from the theoretical uncertainty.
The production of charm quarks is studied in deep-inelastic electron-photon scattering using data recorded by the OPAL detector at LEP at normal e+e- centre-of-mass energies from 183 to 209 GeV. The charm quarks have been identified by full reconstruction of charged D* mesons using their decays into D0pi with the D0 observed in two decay modes with charged particle final states, Kpi and K3pi. The cross-section sigma(D*) for production of charged D* in the reaction e+e- -> e+e-D*X is measured in a restricted kinematical region using two bins in Bjorken x, 0.0014 < x < 0.1 and 0.1 < x < 0.87. From sigma(D*) the charm production cross-section sigma(e+e- -> e+e- ccbar X) and the charm structure function of the photon F 2,c are determined in the region 0.0014 < x < 0.87 and 5 < Q2 < 100 GeV2. For x > 0.1 the perturbative QCD calculation at next-to-leading order agrees perfectly with the measured cross-section. For x < 0.1 the measured cross-section is 43.8 +- 14.3 +- 6.3 +- 2.8 pb with a next-to-leading order prediction of 17.0+2.9-2.3 p.b
The inclusive D* production cross section.
The inclusive charm quark pair cross section. The second DSYS error is due to extrapolation.
The measured structure function F2(C=CHARM). The second DSYS error is due to extrapolation.
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.
Inclusive branching ratios involving b to tau transitions are measured in approximately four million hadronic Z decays collected by the ALEPH detector at LEP. The fully-inclusive branching ratio b -> tau nu X and the semi-inclusive branching ratio b -> tau nu D*+/- X are measured to be (2.43 +/- 0.20 +/- 0.25)% and (0.88 +/- 0.31 +/- 0.28)%, in agreement with the standard model predictions. Upper limits on the branching fractions b -> tau nu and b -> s nu nubar are set to 8.3 10**-4 and 6.4 10**-4 at the 90% C.L. These results allow a 90% C.L. lower limit of 0.40 (GeV/c**2)**-1 to be set on the tan(beta)/mH+/- ratio, in the framework of type-II two-Higgs-doublet mode
TAN(BETA) is the two-Higgs-doublet model parameter, while M_H is the mass of charged Higgs.
Using about 3.9 million hadronic Z decays from e+e- collisions recorded by the OPAL detector at LEP at centre-of-mass energies near MZ the branching ratio for the decay D_s -> tau nu_tau has been measured to be (7.0 +/- 2.1(stat) +/- 2.0 (syst))%. This result can be used to derive the decay constant of the D_s meson: f(D_s) = 286 +/- 44(stat) +/- 41(syst) MeV.
FORMFACTOR(NAME=FP,C=DECAY CONSTANT) is pseudoscalar meson decay constant.
Measurements of the tau lepton polarization and forward-backward polarization asymmetry near the Z resonance using the OPAL detector are described. The measurements are based on analyses of tau -> e nu_e nu_tau, tau -> mu nu_mu nu_tau, tau -> pi nu_tau, tau -> rho nu_tau and tau -> a1 nu_tau decays from a sample of 144810 e+e- -> tau+ tau- candidates corresponding to an integrated luminosity of 151 pb-1. Assuming that the tau lepton decays according to V-A theory, we measure the average tau polarization near Ecm = MZ to be <Ptau> = (-14.10 +/- 0.73 +/- 0.55)% and the tau polarization forward-backward asymmetry to be Afb = (-10.55 +/- 0.76 +/- 0.25)%, where the first error is statistical and the second systematic. Taking into account the small effects of the photon propagator, photon-Z interference and photonic radiative corrections, these results can be expressed in terms of the lepton neutral current asymmetry parameters: Atau = 0.1456 +/- 0.0076 +/- 0.0057, Ae = 0.1454 +/- 0.0108 +/- 0.0036. These measurements are consistent with the hypothesis of lepton universality and combine to give Al = 0.1455 +/- 0.0073. Within the context of the Standard Model this combined result corresponds to sin^2(theta)(lept,effective) = 0.23172 +/- 0.00092. Combing these results with those from the other OPAL neutral current measurements yields a value of sin^2(theta)(lept,effective) = 0.23211 +/- 0.00068.
No description provided.
The charged particle multiplicities of two- and three-jet events from the reaction e+e- -> Z0 -> hadrons are measured for Z0 decays to light quark (uds) flavors. Using recent theoretical expressions to account for biases from event selection, results corresponding to unbiased gluon jets are extracted over a range of jet energies from about 11 to 30 GeV. We find consistency between these results and direct measurements of unbiased gluon jet multiplicity from upsilon and Z0 decays. The unbiased gluon jet data including the direct measurements are compared to corresponding results for quark jets. We perform fits based on analytic expressions for particle multiplicity in jets to determine the ratio r = Ng/Nq of multiplicities between gluon and quark jets as a function of energy. We also determine the ratio of slopes, r(1) = (dNg/dy)/(dNq/dy), and of curvatures, r(2) = (d2Ng/dy2)/(d2Nq/dy2), where y specifies the energy scale. At 30 GeV, we find r = 1.422 +/- 0.051, r(1) = 1.761 +/- 0.071 and r(2) = 1.98 +/- 0.13, where the uncertainties are the statistical and systematic terms added in quadrature. These results are in general agreement with theoretical predictions. In addition, we use the measurements of the energy dependence of Ng and Nq to determine an effective value of the ratio of QCD color factors, CA/CF. Our result, CA/CF = 2.23 +/- 0.14 (total), is consistent with the QCD value of 2.25.
Measurements of the mean charged particle multiplicity of biased two-jet uds flavour events from Z0 decays as a function of the transverse momentum cutoff PT(C=LU) used to separate two- and three-jet events.
Measurements of the mean charged particle multiplicity of three-jet uds flavour 'Y events' from Z0 decays, as a function of the angle THETA1 between the lowest two energy jets. The results for the quark jet scale SQRT(S(C=QQBAR)) and the gluon jet scales PT(C=LU) and PT(C=LE) are also given.
Measurements of the unbiased gluon multiplicity as a function of the energy scale Q=PT(C=LU). The corresponding bins of THETA1 in 'Y events' are also indicated.
The photon structure function F2-gamma(x,Q**2) has been measured using data taken by the OPAL detector at centre-of-mass energies of 91Gev, 183Gev and 189Gev, in Q**2 ranges of 1.5 to 30.0 GeV**2 (LEP1), and 7.0 to 30.0 GeV**2 (LEP2), probing lower values of x than ever before. Since previous OPAL analyses, new Monte Carlo models and new methods, such as multi-variable unfolding, have been introduced, reducing significantly the model dependent systematic errors in the measurement.
Results of F2/ALPHAE for the LEP1 data using the SW for Q**2 = 1.9 GeV**2.
Results of F2/ALPHAE for the LEP1 data using the SW for Q**2 = 3.7 GeV**2.
Results of F2/ALPHAE for the LEP1 data using the FD for Q**2 = 8.9 GeV**2.
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.
Muon pair production in the process e+e- -> e+e-mu+mu- is studied using the data taken at LEP1 (sqrt(s) \simeq m_Z) with the DELPHI detector during the years 1992-1995. The corresponding integrated luminosity is 138.5 pb^{-1}. The QED predictions have been tested over the whole Q^2 range accessible at LEP1 (from several GeV^2/c^4 to several hundred GeV^2/c^4) by comparing experimental distributions with distributions resulting from Monte Carlo simulations using various generators. Selected events are used to extract the leptonic photon structure function F_2^\gamma. Azimuthal correlations are used to obtain information on additional structure functions, F_A^\gamma and F_B^\gamma, which originate from interference terms of the scattering amplitudes. The measured ratios F_A^\gamma/F_2^\gamma and F_B^\gamma/F_2^\gamma are significantly different from zero and consistent with QED predictions.
The measured QED photon structure function at Q**2 = 12.5 GeV for the combine SAT and STIC data.
The measured QED photon structure function at Q**2 = 120 GeV for the combine SAT and STIC data.
Ratio of the structure functions FA and FB to F2.
The decay B0 -> J/psi K0_S is reconstructed with J/psi -> e+ e- or mu+ mu- and K0_S -> pi+ pi-. From the full ALEPH dataset at LEP1 of about 4 million hadronic Z decays, 23 candidates are selected with an estimated purity of 71%. They are used to measure the CP asymmetry of this decay, given by sin 2beta in the Standard Model, with the result sin 2beta = 0.84 +0.82-1.04 +-0.16. This is combined with existing measurements from other experiments, and increases the confidence level that CP violation has been observed in this channel to 98%.
Standard Model predicts the time-dependent rate asymmetry as follows: A(t) = (B0(t)-BBAR0(t))/(B0(t)+BBAR0(t)) = SIN(2*BETA)*SIN(Delta(M)*t), where Delta(M) is the mass difference between the two B0 mass eigenstates.
Measurements of the trilinear gauge boson couplings WWgamma and WWZ are presented using the data taken by DELPHI in 1998 at a centre-of-mass energy of 189 GeV and combined with DELPHI data at 183 GeV. Values are determined for Delta(g_1^Z) and Delta(kappa_gamma), the differences of the WWZ charge coupling and of the WWgamma dipole coupling from their Standard Model values, and for lambda_gamma, the WWgamma quadrupole coupling. A measurement of the magnetic dipole and electric quadrupole moment of the W is extracted from the results for Delta(kappa_gamma) and lambda_gamma. The study uses data from the final states jjlv, jjjj, lX, jjX and gammaX, where j represents a quark jet, l an identified lepton and X missing four-momentum. The observations are consistent with the predictions of the Standard Model.
No description provided.
The inclusive branching ratio for the process b -> tau nu X has been measured using hadronic Z decays collected by the OPAL experiment at LEP in the years 1992-2000. The result is: BR(b -> tau nu X) = (2.78 +/- 0.18 +/- 0.51)% This measurement is consistent with the Standard Model expectation and puts a constraint of tan(beta) / M(H+/-) < 0.53 GeV-1 at the 95% confidence level on Type II Two Higgs Doublet Models.
TAN(BETA) is the two-Higgs-doublet model parameter, while M_H is the mass of charged Higgs.
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.
The cross-sections for the production of single charged and neutral intermediate vector bosons were measured using integrated luminosities of 52 pb^{-1} and 154 pb^{-1} collected by the DELPHI experiment at centre-of-mass energies of 182.6 GeV and 188.6 GeV, respectively. The cross-sections for the reactions were determined in limited kinematic regions. The results found are in agreement with the Standard Model predictions for these channels.
Cross sections for single-W production in the (E- NUEBAR Q QBAR + CC) and (E- NUEBAR LEPTON LEPTONBAR) + CC) channels.
Cross sections for the E NU E NU channel, which includes contributions from both single-W and from single-Z0 with a large interference bewteen the two processes.
Cross sections for single-Z0 production in the hadronic channel.
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.
This final analysis of hadronic and leptonic cross-sections and of leptonic forward-backward asymmetries in e+e- collisions with the OPAL detector makes use of the full LEP1 data sample comprising 161 pb^-1 of integrated luminosity and 4.5 x 10^6 selected Z decays. An interpretation of the data in terms of contributions from pure Z exchange and from Z-gamma interference allows the parameters of the Z resonance to be determined in a model-independent way. Our results are in good agreement with lepton universality and consistent with the vector and axial-vector couplings predicted in the Standard Model. A fit to the complete dataset yields the fundamental Z resonance parameters: mZ = 91.1852 +- 0.0030 GeV, GZ = 2.4948 +- 0.0041 GeV, s0h = 41.501 +- 0.055 nb, Rl = 20.823 +- 0.044, and Afb0l = 0.0145 +- 0.0017. Transforming these parameters gives a measurement of the ratio between the decay width into invisible particles and the width to a single species of charged lepton, Ginv/Gl = 5.942 +- 0.027. Attributing the entire invisible width to neutrino decays and assuming the Standard Model couplings for neutrinos, this translates into a measurement of the effective number of light neutrino species, N_nu = 2.984 +- 0.013. Interpreting the data within the context of the Standard Model allows the mass of the top quark, mt = 162 +29-16 GeV, to be determined through its influence on radiative corrections. Alternatively, utilising the direct external measurement of mt as an additional constraint leads to a measurement of the strong coupling constant and the mass of the Higgs boson: alfa_s(mZ) = 0.127 +- 0.005 and mH = 390 +750-280 GeV.
The cross section for hadron production corrected to the simple kinematic acceptance region defined by SPRIME/S > 0.01. Statistical errors only are shown. Also given is the cross section value corrected for the beam energy spread to correspond to the physical cross section at the central value of SQRT(S).
The cross section for E+ E- production corrected to the simple kinematic acceptance region defined by ABS(COS(THETA(C=E-))) < 0.7 and THETA(C=ACOL) < 10 degrees. Statistical errors only are shown. Also given is the cross section value corrected for the beam energy spread to correspond to the physical cross sectionat the central value of SQRT(S).
The cross section for mu+ mu- production corrected to the simple kinematic acceptance region defined by N = M(P=3_4)**2/S > 0.01. Statistical errors only are shown. Also given is the cross section value corrected for the beam energy spread to correspond to the physical cross section at the central value of SQRT(S).
A measurement of triple gauge boson couplings is presented, based on W-pair data recorded by the OPAL detector at LEP during 1998 at a centre-of-mass energy of 189 GeV with an integrated luminosity of 183 pb^-1. After combining with our previous measurements at centre-of-mass energies of 161-183 GeV we obtain k_g=0.97 +0.20 -0.16, g_1^z=0.991 +0.060 -0.057 and lambda_g=-0.110 +0.058 -0.055, where the errors include both statistical and systematic uncertainties and each coupling is determined by setting the other two couplings to their SM values. These results are consistent with the Standard Model expectations.
Triple gauge boson couplings. All systematic errors are added in quadrature.
The polarisation of $\tau$'s produced in Z decay is measured using 160 pb$^{-1}$ of data accumulated at LEP by the ALEPH detector between 1990 and 1995. The variation of the polarisation with polar angle yields the two parameters ${\cal A}_e = 0.1504 \pm 0.0068 $ and ${\cal A}_{\tau} = 0.1451 \pm 0.0059$ which are consistent with the hypothesis of $e$-$\tau$ universality. Assuming universality, the value ${\cal A}_{e{-}\tau} = 0.1474 \pm 0.0045$ is obtained from which the effective weak mixing angle $\sin^2 {\theta_{\mathrm{W}}^{\mathrm{eff}}} =0.23147 \pm 0.00057 $ is derived.
No description provided.
The interaction of virtual photons is investigated using double tagged gammagamma events with hadronic final states recorded by the ALEPH experiment at e^+e^- centre-of-mass energies between 188 and 209 GeV. The measured cross section is compared to Monte Carlo models, and to next-to-leading-order QCD and BFKL calculations.
Differential cross section as a function of the relative energy of the scattered electrons.
Differential cross section as a function of the polar angle THETA of the scattered electrons.
Differential cross section as a function of the virtuality Q**2 of the photons.
Hadronic Z decay data taken with the ALEPH detector at LEP1 are used to measure the three-jet rate as well as moments of various event-shape variables. The ratios of the observables obtained from b-tagged events and from an inclusive sample are determined. The mass of the b quark is extracted from a fit to the measured ratios using a next-to-leading order prediction including mass effects. Taking the first moment of the y3 distribution, which is the observable with the smallest hadronization corrections and systematic uncertainties, the result is: mb(MZ) = [3.27+-0.22(stat) +-0.22(exp)+-0.38(had)+-0.16(theo)] GeV/c2. The measured ratio is alternatively employed to test the flavour independence of the strong coupling constant for b and light quarks.
No description provided.
The hadronic structure of the photon F2gamma is measured as a function of Bjorken x and of the photon virtuality Q2 using deep-inelastic scattering data taken by the OPAL detector at LEP at e+e- centre-of-mass energies from 183 to 209 GeV. Previous OPAL measurements of the x dependence of F2gamma are extended to an average Q2 of <Q2>=780GeV2 using data in the kinematic range 0.15 < x < 0.98. The Q2 evolution of F2gamma is studied for 12.1 < <Q2> < 780GeV2 using three ranges of x. As predicted by QCD, the data show positive scaling violations in F2gamma for the central x region 0.10-0.60. Several parameterisations of F2gamma are in qualitative agreement with the measurements whereas the quark-parton model prediction fails to describe the data.
F2 and DSIG/DX for the EE sample in the high Q**2 region as a function of X.
Statistical correlations between the bins in the preceding table.
The measured value of F2 and DSIG/DX for the SW data sample in the Q**2 range 9 to 15 GeV**2.
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.
Measurements are presented of the polarisation of W+W- boson pairs produced in e+e- collisions, and of CP-violating WWZ and WWGamma trilinear gauge couplings. The data were recorded by the OPAL experiment at LEP during 1998, where a total integrated luminosity of 183 pb^-1 was obtained at a centre-of-mass energy of 189 GeV. The measurements are performed through a spin density matrix analysis of the W boson decay products. The fraction of W bosons produced with longitudinal polarisation was found to be sigma_L/sigma_total = (21.0 +- 3.3 +- 1.6)% where the first error is statistical and the second systematic. The joint W boson pair production fractions were found to be sigma_TT/sigma_total = (78.1 +- 9.0 +- 3.2) %, sigma_LL/sigma_total = (20.1 +- 7.2 +- 1.8) % and sigma_TL/sigma_total = (1.8 +- 14.7 +- 3.8) %. In the CP-violating trilinear gauge coupling sector we find kappa_z = -0.20 +0.10 -0.07, g^z_4 = -0.02 +0.32 -0.33 and lambda_z = -0.18 +0.24 -0.16, where errors include both statistical and systematic uncertainties. In each case the coupling is determined with all other couplings set to their Standard Model values except those related to the measured coupling via SU(2)_LxU(1)_Y symmetry. These results are consistent with Standard Model expectations.
Individual W-boson transverse polarised cross-sections.
Individual W-boson longitudinal polarised cross-sections.
W pair polarized cross-sections. (C=TT), (C=LL), and (C=TL) stand for both W transversely polarised, for both W longitudinally polarised, and for transversely and longitudinally polarisedW-bosons, respectively.
Exclusive production of π and K meson pairs in two photon collisions is measured with ALEPH data collected between 1992 and 2000. Cross-sections are presented as a function of cos θ ∗ and invariant mass, for | cos θ ∗ |<0.6 and invariant masses between 2.0 and 6.0 GeV/ c 2 (2.25 and 4.0 GeV/ c 2 ) for pions (kaons). The shape of the distributions are found to be well described by QCD predictions but the data have a significantly higher normalization.
Measured angular distribution for pion production.
Measured angular distribution for kaon production.
Measured cross section for pion production as a function of W.
The process e+ e- -> e+ e- Z/gamma* is studied with the OPAL detector at LEP at a centre of mass energy of sqrt(s) = 189 GeV. The cross-section times the branching ratio of the Z/gamma* decaying into hadrons is measured within Lorentz invariant kinematic limits to be (1.2 +/- 0.3 +/- 0.1) pb for invariant masses of the hadronic system between 5 GeV and 60 GeV and (0.7 +/- 0.2 +/- 0.1) pb for hadronic masses above 60 GeV. The differential cross-sections of the Mandelstam variables s-hat, t-hat, and u-hat are measured and compared with the predictions from the Monte Carlo generators grc4f and PYTHIA. From this, based on a factorisation ansatz, the total and differential cross-sections for the subprocess e gamma -> e Z/gamma* are derived.
Measured values of the cross section times the branching ratio for the (Z0/GAMMA*) decay into hadrons within the restricted kinematic limits.
Differential cross-section dsig_ee/dm_qq.
Differential cross-section dsigma_ee/dsqrt(shat).
About 4.4 million hadronic decays of Z bosons, recorded by the OPAL detector at LEP at a centre-of-mass energy of around sqrt(s) = 91.2 GeV, are used to determine the mean charged particle multiplicities for the three light quark flavours. Events from primary u, d, and s quarks are tagged by selecting characteristic particles which carry a large fraction of the beam energy. The charged particle multiplicities are measured in the hemispheres opposite to these particles. An unfolding procedure is applied to obtain these multiplicities for each primary light quark flavour. This yields <n_u> = 17.77 +- 0.51 +0.86 -1.20, <n_d> = 21.44 +- 0.63 +1.46 -1.17, <n_s> = 20.02 +- 0.13 +0.39 -0.37, where statistical and systematic errors are given. The results for <n_u> and <n_d> are almost fully statistically anti-correlated. Within the errors the result is consistent with the flavour independence of the strong interaction for the particle multiplicities in events from the light up, down, and strange quarks.
No description provided.
No description provided.
Di-jet producion is studied in collisions of quasi-real photons at e+e- centre- of-mass energies sqrt(s)ee from 189 to 209 GeV at LEP. The data were collected with the OPAL detector. Jets are reconstructed using an inclusive k_t clustering algorithm for all cross-section measurements presented. A cone jet algorithm is used in addition to study the different structure of the jets resulting from either of the algorithms. The inclusive di-jet cross-section is measured as a function of the mean transverse energy Etm(jet) of the two leading jets, and as a functiuon of the estimated fraction of the photon momentum carried by the parton entering the hard sub-process, xg, for different regions of Etm (jet). Angular distribution in di-jet events are measured and used to demonstrate the dominance of quark and gluon initiated processes in different regions of phase space. Furthermore the inclusive di-jet cross-section as a function of |eta(jet)| and |delta eta (jet)| is presented where eta(jet) is the jet pseudo-rapidity. Different regions of the xg+ -xg- -space are explored to study and control the influence of an underlying event. The results are compared to next-to-leading order perturbative QCD calculations and to the predictions of the leading order Monte Carlo generator PYTHIA.
The di-jet cross section as a function of the angle between the jet and thedirection of the incoming parton in the centre-of-mass frame for the region whe re both X(C=GAMMA+) and X(C=GAMMA-) are > 0.75.
The di-jet cross section as a function of the angle between the jet and thedirection of the incoming parton in the centre-of-mass frame for the region whe re both X(C=GAMMA+) and X(C=GAMMA-) are < 0.75.
The di-jet cross section as a function of the mean transverse energy of thedi-jet system for the full X(C=GAMMA+) and X(C=GAMMA-) region.
The data recorded at a centre-of-mass energy of 189GeV by the OPAL detector at LEP are used to search for trilinear couplings of the neutral gauge bosons in the process e+e- --> Z-gamma. The cross-sections are measured for multihadronic events with an energetic isolated photon and for events with a high energy photon accompanied by missing energy. These cross-sections and the photon energy, polar angle and isolation angle distributions are compared to the Standard Model predictions and to the theoretical expectations of a model allowing for Z-gamma-Z and Z-gamma-gamma vertices. Since no significant deviations with respect to the Standard Model expectations are found, constraints are derived on the strength of neutral trilinear gauge couplings.
Total sysytematic error for Q Qbar (NU NUbar) channel is 0.154 (0.048) pb.
See text for Z(GAMMA) anomalous coupling definitions. Statistical and systematic errors are combined in quadrature.
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