11 research outputs found

    FIRST EVIDENCE OF HARD SCATTERING PROCESSES IN SINGLE TAGGED GAMMA-GAMMA-COLLISIONS

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    For the first time, multihadronic production from single tagged gamma gamma collisions has been studied, where one of the scattered leptons was tagged at very low virtual photon absolute mass squared ([Q(2)] = 0.06 (GeV/c(2))(2)). Data collected during 1991 and 1992 in the DELPHI experiment at LEP are shown to agree well with predictions which included the non-perturbative vector meson dominance model in which the interacting photons are assumed to have converted into a vector meson (rho, omega or pi), a quark-parton model which describes direct photon interactions and a QCD-based model which considers the photon to have quark and gluon structure functions. Five different parametrizations of these structure functions were used and the predictions compared with the data. This study confirms recent results from no-tag experiments in requiring a QCD-based component to successfully describe the data, indicating that the photon has a significant partonic content

    FIRST EVIDENCE OF HARD SCATTERING PROCESSES IN SINGLE TAGGED GAMMA-GAMMA-COLLISIONS

    No full text
    For the first time, multihadronic production from single tagged γγ collisions has been studied, where one of the scattered leptons was tagged at very low virtual photon absolute mass squared (〈Q2〉 = 0.06 (GeV/c2)2). Data collected during 1991 and 1992 in the DELPHI experiment at LEP are shown to agree well with predictions which included the non-perturbative vector meson dominance model in which the interacting photons are assumed to have converted into a vector meson (ρ{variant}, ω or π), a quark-parton model which describes direct photon interactions and a QCD-based model which considers the photon to have quark and gluon structure functions. Five different parametrizations of these structure functions were used and the predictions compared with the data. This study confirms recent results from no-tag experiments in requiring a QCD-based component to successfully describe the data, indicating that the photon has a significant partonic content. © 1995

    Search for pair production of heavy objects in 4 jet events at s**(1/2) = 130-GeV - 136-GeV

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    Results are presented of a search for pair production of heavy objects decaying into four hadronic jets, as expected for example from associated or pair production of MSSM Higgs bosons, \hA ~or \HH, using a data sample of 5.9  5.9\;pb1^{-1} of e+ee^+ e^- collisions at s=130136  GeV\sqrt{s}=130-136\;{\mathrm {GeV}} collected with the DELPHI detector at LEP in November 1995. The data and expectations from standard processes agree after four-jet selections. An analysis based on bb-tagging finds no \hA ~candidate with high mass. A study optimized to search for \HH ~events with mass in the 4050  GeV/c240-50 \; {\mathrm{GeV}}/c^2 range also finds no candidate. Finally a comparison is made with a recent ALEPH analysis which found an excess of four-jet events with high multiplicity and high mass. Such a signal is not observed in the DELPHI data, although a slight excess in the mass region around 105  GeV/c2105 \; {\mathrm{GeV}}/c^2 is seen

    Search for stable heavy charged particles in e+ e- collisions at s**(1/2) = 130-GeV to 136-GeV, 161-GeV and 172-GeV

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    A search for stable or long-lived heavy charged particles in e+ee^+e^- interactions at energies of 130-136, 161 and 172 GeV has been performed using the data taken by the DELPHI experiment at LEP. The search is based on particle identification provided by the Time Projection Chamber and the Ring Imaging Cherenkov detector. Upper limits at 95\% confidence level are derived on the cross-section for heavy long-lived pair-produced charge ±e\pm e and ±2/3e\pm 2/3e particles in the range of 0.4-2.3 pb for masses from 45 to 84 GeV/c2c^2. Within supersymmetric extensions of the Standard Model, long-lived charginos with masses from 45 to 84 (80)~GeV/c2c^2 for high (low) sneutrino masses can be excluded at 95\% confidence level. %Mass limits for long-lived sleptons are obtained. %For selectrons no general mass limits can be given. Left-handed (right-handed) long-lived or stable smuons and staus with masses between 45 and 68 (65)~GeV/c2c^2 can be excluded at 95\% confidence level

    Search for high mass gamma gamma resonances in e+ e ---> lepton+ lepton- gamma gamma, neutrino anti-neutrino gamma gamma and q anti-q gamma gamma at LEP-1

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    A search for high mass photon pairs from the processes e+e+γγ {\mathrm e}^+ {\mathrm e}^- \to \ell^+ \ell^- \gamma \gamma\ , ${\mathrm e}^+ {\mathrm e}^- \to {\mathrm \nu} \overline {\mathrm \nu} \gamma \gamma

    Cross-sections and leptonic forward backward asymmetries from the Z0 running of LEP

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    info:eu-repo/semantics/publishe

    Charged particle multiplicity in e+ e- ---> q anti-q events at 161-GeV and 172-GeV and from the decay of the W boson

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    The data collected by DELPHI in 1996 have been used to measure the average charged particle multiplicities and dispersions in qqˉq\bar{q} events at centre-of-mass energies of s=161\sqrt{s}=161~GeV and s=172\sqrt{s}=172~GeV, and the average charge multiplicity in WW events at s=172\sqrt{s}=172~GeV. The multiplicities in qqˉq\bar{q} events are consistent with the evolution predicted by QCD. The dispersions in the multiplicity distributions are consistent with Koba-Nielsen-Olesen (KNO) scaling. The average multiplicity of charged particles in hadronic W decays has been measured for the first time; its value, 19.23±0.74(stat+syst)19.23 \pm 0.74 (stat+syst), is consistent with that expected for an e+ee^+e^- interaction at a centre-of-mass energy equal to the W mass. The charged particle multiplicity in W decays shows no evidence of effects of colour reconnection between partons from different W's at the present level of statistics

    Measurement of the triple gluon vertex from double quark tagged four jet events

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    The 4-jet events collected by the DELPHI experiment at LEP1 in 1992, 1993 and 1994 are analysed to determine the contribution of the triple-gluon vertex. Two of the four jets are tagged as jets from bb- or cc-quarks using lifetime and lepton transverse momentum information. The 4-jet contributions from double-gluon bremsstrahlung, the triple-gluon vertex, and secondary quark-antiquark pair production then yield significantly different two-dimensional distributions in the generalized Nachtmann Reiter angle %ΘNR\Theta^{*}_{NR} versus the opening angle of the two secondary jets. These distributions are used to fit CA/CFC_A/C_F, the ratio of the coupling strength of the triple-gluon vertex to that of gluon bremsstrahlung, and NC/NAN_C/N_A, the ratio of the number of quark colours to the number of gluons, giving \begin{center} CA/CF=2.51±0.28C_A/C_F=2.51 \pm 0.28 ~and~ NC/NA=0.38±0.10N_C/N_A=0.38 \pm 0.10 \end{center} in agreement with the values expected from QCD: \begin{center} CA/CF=9/4=2.25C_A/C_F = 9/4 = 2.25 ~and~ NC/NA=3/8=0.375N_C/N_A = 3/8 = 0.375. \end{center

    Search for the B(c) Meson

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    constant over the range of predicted B_c\upm lifetimes

    FIRST EVIDENCE OF HARD SCATTERING PROCESSES IN SINGLE TAGGED GAMMA-GAMMA-COLLISIONS

    No full text
    For the first time, multihadronic production from single tagged gamma gamma collisions has been studied, where one of the scattered leptons was tagged at very low virtual photon absolute mass squared ([Q(2)] = 0.06 (GeV/c(2))(2)). Data collected during 1991 and 1992 in the DELPHI experiment at LEP are shown to agree well with predictions which included the non-perturbative vector meson dominance model in which the interacting photons are assumed to have converted into a vector meson (rho, omega or pi), a quark-parton model which describes direct photon interactions and a QCD-based model which considers the photon to have quark and gluon structure functions. Five different parametrizations of these structure functions were used and the predictions compared with the data. This study confirms recent results from no-tag experiments in requiring a QCD-based component to successfully describe the data, indicating that the photon has a significant partonic content
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