1. |
- Schael, S., et al.
(författare)
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Electroweak measurements in electron positron collisions at W-boson-pair energies at LEP
- 2013
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Ingår i: Physics Reports. - : Elsevier BV. - 0370-1573 .- 1873-6270. ; 532:4, s. 119-244
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Forskningsöversikt (refereegranskat)abstract
- Electroweak measurements performed with data taken at the electron positron collider LEP at CERN from 1995 to 2000 are reported. The combined data set considered in this report corresponds to a total luminosity of about 3 fb(-1) collected by the four LEP experiments ALEPH, DELPHI, 13 and OPAL, at centre-of-mass energies ranging from 130 GeV to 209 GeV. Combining the published results of the four LEP experiments, the measurements include total and differential cross-sections in photon-pair, fermion-pair and four-fermion production, the latter resulting from both double-resonant WW and ZZ production as well as singly resonant production. Total and differential cross-sections are measured precisely, providing a stringent test of the Standard Model at centre-of-mass energies never explored before in electron positron collisions. Final-state interaction effects in four-fermion production, such as those arising from colour reconnection and Bose Einstein correlations between the two W decay systems arising in WW production, are searched for and upper limits on the strength of possible effects are obtained. The data are used to determine fundamental properties of the W boson and the electroweak theory. Among others, the mass and width of the W boson, m(w) and Gamma(w), the branching fraction of W decays to hadrons, B(W -> had), and the trilinear gauge-boson self-couplings g(1)(Z), K-gamma and lambda(gamma), are determined to be: m(w) = 80.376 +/- 0.033 GeV Gamma(w) = 2.195 +/- 0.083 GeV B(W -> had) = 67.41 +/- 0.27% g(1)(Z) = 0.984(-0.020)(+0.018) K-gamma - 0.982 +/- 0.042 lambda(gamma) = 0.022 +/- 0.019. (C) 2013 Elsevier B.V. All rights reserved.
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2. |
- Schael, S, et al.
(författare)
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Precision electroweak measurements on the Z resonance
- 2006
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Ingår i: Physics Reports. - : Elsevier BV. - 0370-1573 .- 1873-6270. ; 427:5-6, s. 257-454
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Forskningsöversikt (refereegranskat)abstract
- We report on the final electroweak measurements performed with data taken at the Z resonance by the experiments operating at the electron-positron colliders SLC and LEP. The data consist of 17 million Z decays accumulated by the ALEPH, DELPHI, L3 and OPAL experiments at LEP, and 600 thousand Z decays by the SLID experiment using a polarised beam at SLC. The measurements include cross-sections, forward-backward asymmetries and polarised asymmetries. The mass and width of the Z boson, m(Z) and Gamma(Z), and its couplings to fermions, for example the p parameter and the effective electroweak mixing angle for leptons, are precisely measured: m(Z) = 91.1875 +/- 0.0021 GeV, Gamma(Z) = 2.4952 +/- 0.0023 GeV, rho(l) = 1.0050 +/- 0.0010, sin(2)theta(eff)(lept) = 0.23153 +/- 0.00016. The number of light neutrino species is determined to be 2.9840 +/- 0.0082, in agreement with the three observed generations of fundamental fermions. The results are compared to the predictions of the Standard Model (SM). At the Z-pole, electroweak radiative corrections beyond the running of the QED and QCD coupling constants are observed with a significance of five standard deviations, and in agreement with the Standard Model. Of the many Z-pole measurements, the forward-backward asymmetry in b-quark production shows the largest difference with respect to its SM expectation, at the level of 2.8 standard deviations. Through radiative corrections evaluated in the framework of the Standard Model, the Z-pole data are also used to predict the mass of the top quark, m(t) = 173(+10)(+13) GeV, and the mass of the W boson, m(W) = 80.363 +/- 0.032 GeV. These indirect constraints are compared to the direct measurements, providing a stringent test of the SM. Using in addition the direct measurements of m(t) and m(W), the mass of the as yet unobserved SM Higgs boson is predicted with a relative uncertainty of about 50% and found to be less than 285 GeV at 95% confidence level. (c) 2006 Elsevier B.V. All rights reserved.
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3. |
- Abdallah, J., et al.
(författare)
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Study of double-tagged gamma gamma events at LEPII
- 2006
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 46:3, s. 559-568
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Tidskriftsartikel (refereegranskat)abstract
- Double-tagged interactions of photons with virtualities Q(2) between 10 GeV2 and 200 GeV2 are studied with the data collected by DELPHI at LEPII from 1998 to 2000, corresponding to an integrated luminosity of 550 pb(-1). The gamma*gamma* -> mu(+)mu(-) data agree with QED predictions. The cross-section of the reaction gamma*gamma* -> hadrons is measured and compared to the LO and NLO BFKL calculations.
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4. |
- Abdallah, J, et al.
(författare)
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A precise measurement of the B+, B-0 and mean b-hadron lifetime with the DELPHI detector at LEP I
- 2004
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 33:3, s. 307-324
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Tidskriftsartikel (refereegranskat)abstract
- Final results from the DELPHI Collaboration on the lifetime of B+ and B-0 mesons and the mean b-hadron lifetime, are presented using the data collected at the Z(0) peak in 1994 and 1995. Elaborate, inclusive, secondary vertexing methods have been employed to ensure a b-hadron reconstruction with good efficiency. To separate samples of B+ and B-0 mesons, high performance neural network techniques are used that achieve very high purity signals. The results obtained are: tau(B+) = 1.624+/-0.014 (stat)+/-0.018 (syst) ps tau(B)0 = 1.531+/-0.021 (stat)+/-0.031 (syst) ps tau(B+)/tau(B)0 = 1.060+/-0.021 (stat)+/-0.024 (syst) and for the average b-hadron lifetime: taub/tau(B)0 = 1.570+/-0.005 (stat)+/-0.008 (syst) ps.
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5. |
- Abdallah, J, et al.
(författare)
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Bose-Einstein correlations in W+W- events at LEP2
- 2005
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 44:2, s. 161-174
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Tidskriftsartikel (refereegranskat)abstract
- Bose-Einstein correlations (BEC) between final state particles in the reaction e(+)e(-) -> W+ W- -> q(1)(q(2)) over barq(3)(q(4)over bar>) over bar) have been studied. Data corresponding to a total integrated luminosity of 550 pb(-1), recorded by the DELPHI detector at centre-of-mass energies ranging from 189 to 209 GeV, were analysed. An indication for inter-W BEC between like-sign particles has been found at the level of 2.4 standard deviations of the combined statistical and systematic uncertainties.
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6. |
- Abdallah, J, et al.
(författare)
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Determination of the e(+)e(-)->gamma gamma(gamma) cross-section at LEP 2
- 2004
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 37:4, s. 405-419
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Tidskriftsartikel (refereegranskat)abstract
- A test of the benchmark QED process e(+) e(-) -->gammagamma(gamma) is reported, using the data collected with the DELPHI detector at LEP 2. The data analysed were recorded at centre-of-mass energies ranging from 161 GeV to 208 GeV and correspond to a total integrated luminosity of 656.4 pb(-1). The Born cross-section for the process e(+) e(-)-->gammagamma(gamma) was determined, confirming the validity of QED at the highest energies ever attained in electron-positron collisions. Lower limits on the parameters of a number of possible deviations from QED, predicted within theoretical frameworks expressing physics beyond the Standard Model, were derived.
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7. |
- Abdallah, J, et al.
(författare)
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Measurement of the energy dependence of hadronic jet rates and the strong coupling alpha(s) from the four-jet rate with the DELPHI detector at LEP
- 2005
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 38:4, s. 413-426
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Tidskriftsartikel (refereegranskat)abstract
- Hadronic events from the data collected with the DELPHI detector at LEP within the energy range from 89 GeV to 209 GeV are selected, their jet rates are determined and compared to predictions of four different event generators. One of them is the recently developed APACIC++ generator which performs a massive matrix element calculation matched to a parton shower followed by string fragmentation. The four-jet rate is used to measure alpha(s) in the next-to-leading-order approximation yielding alpha(s)(M-Z(2)) = 0.1175 +/- 0.0030. The running of alpha(s) determined by using four-jet events has been tested. The logarithmic energy slope is measured to be dalpha(s)(-1)/d log E-cm = 1.14 +/- 0.36. Since the analysis is based on four-jet final states it represents an alternative approach to previous DELPHI alpha(s) measurements using event shape distributions.
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8. |
- Abdallah, J, et al.
(författare)
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Measurement of the forward-backward asymmetries of e(+)e(-)-> Z -> b(b)over-bar and e(+)e(-)-> Z -> c(c)over-bar using prompt leptons
- 2004
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 34:2, s. 109-125
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Tidskriftsartikel (refereegranskat)abstract
- The forward-backward asymmetries of the processes e(+) e(-) --> Z --> b (b) over bar and e(+)e(-) --> Z --> c (c) over bar were measured from a sample of hadronic Z decays collected by the DELPHI experiment between 1993 and 1995. Enriched samples of b (b) over bar and c (c) over bar events were obtained using lifetime information. The tagging of b and c quarks in these samples was based on the semileptonic decay channels b/c --> X + mu and b/c --> X + e combined with charge flow information from the hemisphere opposite to the lepton. Combining the A(FB)(b (b) over bar) and A(FB)(c (c) over bar) measurements presented in this paper with published results based on 1991 and 1992 DELPHI data samples, the following pole asymmetries were obtained: A(FB)(0,b) = 0.1021 +/- 0.0052 (stat) +/- 0.0024 (syst) A(FB)(0,c) = 0.0728 +/- 0.0086 (stat) +/- 0.0063 (syst) The effective value of the weak mixing angle derived from these measurements is sin(2) theta(W,eff)(lept) = 0.23170 +/- 0.00097.
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9. |
- Abdallah, J, et al.
(författare)
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Measurement of the W-pair production cross-section and W branching ratios in e(+)e(-) collisions at root s=161-209 GeV
- 2004
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 34:2, s. 127-144
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Tidskriftsartikel (refereegranskat)abstract
- These final results on e(+) e(-) W+ W- production cross-section measurements at LEP2 use data collected by the DELPHI detector at centre-of-mass energies up to 209 GeV. Measurements of total cross-sections, W angular differential distributions and decay branching fractions, and the value of the CKM element |V-cs| are compared to the expectations of the Standard Model. These results supersede all values previously published by DELPHI.
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10. |
- Abdallah, J, et al.
(författare)
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Measurement of vertical bar Vcb vertical bar using the semileptonic decay (B)d(0))over-bar -> D*+l(-)(nu)over-barl
- 2004
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 33:2, s. 213-232
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Tidskriftsartikel (refereegranskat)abstract
- Data from Z decays in DELPHI have been searched for <(B-d(o))over bar> --> D*+ l(-) (ν) over bar (l) with the D*+ decaying to D(0)pi(+) and D-0 --> K(-)pi(+), K(-)pi(+)pi(+)pi(-) or K- pi(+)(pi(0)). These events are used to measure the CKM matrix element V-cb and the form factor slope, rho(A1)(2): F-D*(1) V-cb = 0.0392 +/- 0.0018 +/- 0.0023; rho(A1)(2) = 1.32 +/- 0.15 +/- 0.33 corresponding to a branching fraction: BR(<(B-d(0))over bar> --> D(*+)l(-)(ν) over bar (l)) = (5.90 +/- 0.22 +/- 0.50)%. Combining these and previous DELPHI measurements gives: FD*(1)V-cb = 0.0377 +/- 0.0011 +/- 0.0019, rho(A1)(2) = 1.39 +/- 0.10 +/- 0.33 and BR(<(B-d(0))over bar> --> D(*+)l(-)(ν) over bar (l)) = (5.39 +/- 0.11 +/- 0.34)% Using F-D*(1) = 0.91 +/- 0.04, yields: V-cb = 0.0414 +/- 0.0012(stat.) +/- 0.0021(syst.) +/- 0.0018 (theory). The b-quark semileptonic branching fraction into a D*+ emitted from higher mass charmed excited states has also been measured to be: BR(b --> D*+ Xl(-)(ν) over bar (l)) = (0.67 +/- 0.08 +/- 0.10)%.
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11. |
- Abdallah, J, et al.
(författare)
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Search for B-s(0)-(B-s(0))over-bar oscillations in DELPHI using high-p(t) leptons
- 2004
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 35:1, s. 35-52
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Tidskriftsartikel (refereegranskat)abstract
- Oscillations in the B-s(0)- <(B-s(0))over bar> system were studied in events selected from about 4.3 million hadronic Z(0) decays registered by DELPHI between 1992 and 2000. This paper presents updates of two published analyses ([11, 12]). The first analysis, which utilizes leptons emitted with large momentum transverse to a jet, was improved by means of a better algorithm for the vertex reconstuction and a new algorithm for flavour-tagging at production time. The second analysis, which utilizes D-s-lepton events, was improved by optimizing the treatment of proper time resolution. No signal of B-s(0) oscillations was observed and limits on the mass difference between the physical B-s(0) states were obtained to be: Deltam(s)>8.0 ps-1 at the 95% C.L. with a sensitivity of Deltam(s)= 9.1 ps(-1) in the high p(t) lepton analysis and Deltam(s)>4.9 ps(-1) at the 95% C.L. with a sensitivity of Deltam(s)=8.6 ps(-1) in the D-s-lepton analysis. Previously published results on these analyses are superseded. The combination of these results with those obtained in other independent analyses previously performed in DELPHI (D-s-hadron, exclusive B-s(0), inclusive vertex) gives: Deltam(s)>8.5 ps(-1) at the 95% C.L. with a sensitivity of Deltam(s)=12.0 ps(-1).
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12. |
- Abdallah, J, et al.
(författare)
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Search for fermiophobic Higgs bosons in final states with photons at LEP 2
- 2004
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 35:3, s. 313-324
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Tidskriftsartikel (refereegranskat)abstract
- Higgs boson production with subsequent decay to photons was searched for in the data collected by the DELPHI detector at centre-of-mass energies between 183 GeV and 209 GeV, corresponding to a total integrated luminosity of nearly 650 pb(-1). No evidence for a signal was found, and limits were set on h(0)Z(0) and h(0)A(0) production with h(0) decay to photons. These results were used to exclude regions in the parameter space of fermiophobic scenarios of Two Higgs Doublet Models.
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13. |
- Abdallah, J, et al.
(författare)
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Search for SUSY in the AMSB scenario with the DELPHI detector
- 2004
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 34:2, s. 145-156
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Tidskriftsartikel (refereegranskat)abstract
- The DELPHI experiment at the LEP e (+) e(-) collider collected almost 700 pb(-1) at centre-of-mass energies above the Z(0) mass pole and up to 208 GeV. Those data were used to search for SUSY in the Anomaly Mediated SUSY Breaking (AMSB) scenario with a flavour independent common sfermion mass parameter. The searches covered several possible signatures experimentally accessible at LEP, with either the neutralino, the sneutrino or the stau being the Lightest Supersymmetric Particle (LSP). They included: the search for nearly mass-degenerate chargino and neutralino, which is a typical feature of AMSB; the search for Standard-Model-like or invisibly decaying Higgs boson; the search for stable staus; the search for cascade decays of SUSY particles resulting in the LSP and a low multiplicity final state containing neutrinos. No evidence of a signal was found, and thus constraints were set in the space of the parameters of the model.
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14. |
- Abdallah, J, et al.
(författare)
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Study of tau-pair production in photon-photon collisions at LEP and limits on the anomalous electromagnetic moments of the tau lepton
- 2004
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 35:2, s. 159-170
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Tidskriftsartikel (refereegranskat)abstract
- Tau-pair production in the process e(+)e(-) --> e(+)e(-) tau(+)tau(-) was studied using data collected by the DELPHI experiment at LEP2 during the years 1997 - 2000. The corresponding integrated luminosity is 650 pb(-1). The values of the cross-section obtained are found to be in agreement with QED predictions. Limits on the anomalous magnetic and electric dipole moments of the tau lepton are deduced.
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15. |
- Abdallah, J, et al.
(författare)
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A study of the energy evolution of event shape distributions and their means with the DELPHI detector at LEP
- 2003
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 29:3, s. 285-312
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Tidskriftsartikel (refereegranskat)abstract
- Infrared and collinear safe event shape distributions and their mean values are determined in e(+)e(-) collisions at centre-of-mass energies between 45 and 202GeV. A phenomenological analysis based on power correction models including hadron mass effects for both differential distributions and mean values is presented. Using power corrections, alpha(s) is extracted from the mean values and shapes. In an alternative approach, renormalisation group invariance (RGI) is used as an explicit constraint, leading to a consistent description of mean values without the need for sizeable power corrections. The QCD beta-function is precisely measured using this approach. From the DELPHI data on Thrust, including data from low energy experiments, one finds beta(0) = 7.86 +/- 0.32 for the one loop coefficient of the beta-function or, assuming QCD, n(f) = 4.75 +/- 0.44 for the number of active flavours. These values agree well with the QCD expectation of beta(0) = 7.67 and n(f) 5. A direct measurement of the full logarithmic energy slope excludes light gluinos with a mass below 5GeV.
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16. |
- Abdallah, J, et al.
(författare)
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Coherent soft particle production in Z decays into three jets
- 2005
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 605:1-2, s. 37-48
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Tidskriftsartikel (refereegranskat)abstract
- Low-energy particle production perpendicular to the event plane in three-jet events produced in Z decays in e(+)e(-) annihilation is measured and compared to that perpendicular to the event axis in two-jet events. The topology dependence of the hadron production ratio is found to agree with a leading-order QCD prediction. This agreement and especially the need for the presence of a destructive interference term gives evidence for the coherent nature of gluon radiation. Hadron production in three-jet events is found to be directly proportional to a single topological scale function of the inter-jet angles. The slope of the dependence of the multiplicity with respect to the topological scale was measured to be 2.211 +/- 0.014(stat.) +/- 0.053(syst.) in good agreement with the expectation given by the colour-factor ratio C-A/C-F = 9/4. This result strongly supports the assumption of local parton-hadron duality, LPHD, at low hadron momentum.
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17. |
- Abdallah, J, et al.
(författare)
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Final results from DELPHI on the searches for SM and MSSM neutral Higgs bosons
- 2004
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 32:2, s. 145-183
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Tidskriftsartikel (refereegranskat)abstract
- These final results from DELPHI searches for the Standard Model (SM) Higgs boson, together with benchmark scans of the Minimal Supersymmetric Standard Model (MSSM) neutral Higgs bosons, used data taken at centre-of-mass energies between 200 and 209 GeV with a total integrated luminosity of 224 pb(-1). The data from 192 to 202 GeV are reanalysed with improved b-tagging for MSSM final states decaying to four b-quarks. The 95% confidence level lower mass bound on the Standard Model Higgs boson is 114.1 GeV/c(2). Limits are also given on the lightest scalar and pseudo-scalar Higgs bosons of the MSSM.
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18. |
- Abdallah, J, et al.
(författare)
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Inclusive b decays to wrong sign charmed mesons
- 2003
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - 0370-2693. ; 561:1-2, s. 26-40
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Tidskriftsartikel (refereegranskat)abstract
- The production of wrong sign charmed mesons b --> (D) over bar X-(s), D-(s) = (D-0, D+, D-s), is studied using the data collected by the DELPHI experiment in the years 1994 and 1995. Charmed mesons in Z --> b (b) over bar events are exclusively reconstructed by searching for the decays D-0 --> K(-)pi(+), D+ --> K(-)pi(+)pi(+) and D-s(+) --> phipi(+) --> K(+)K(-)pi(+). The wrong sign contribution is extracted by using two discriminant variables: the charge of the b-quark at decay time, estimated from the charges of identified particles, and the momentum of the charmed meson in the rest frame of the b-hadron. The inclusive branching fractions of b-hadrons into wrong sign charm mesons are measured to be: B(b --> (D) over bar X-0) + B(b --> D-X) = (9.3 +/- 1.7(stat) +/- 1.3(syst) +/- 0.4(B))%, B(b --> Ds-X) = (10.1 +/- 1.0(stat) +/- 0.6(syst) +/- 2.8(B))% where the first error is statistical, the second and third errors are systematic. (C) 2003 Published by Elsevier Science B.V.
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19. |
- Abdallah, J, et al.
(författare)
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Measurement of inclusive f(1) (1285) and f(1) (1420) production in Z decays with the DELPHI detector
- 2003
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 569:3-4, s. 129-139
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Tidskriftsartikel (refereegranskat)abstract
- DELPHI results are presented on the inclusive production of two (K(K) over bar π)(0) states in the mass region 1.2-1.6 GeV/c(2) in hadronic Z decays at LEP I. The measured masses (widths) are 1274 +/- 6 MeV/c(2) (29 +/- 12 MeV/c(2)) and 1426 +/- 6 MeV/c(2) (51 +/- 14 MeV/c(2)), respectively. A partial-wave analysis of the (K(K) over bar π)(0) system shows that the first peak is consistent with the I-G (J(PC)) = 0(+)(1(++))/(0(-+))a(0)(980)pi and the second with the I-G (J(PC)) = 0(+)(1(++))K*(892)(K) over bar + c.c. assignments. The total hadronic production rates per hadronic Z decay are (0.165 +/- 0.051) and (0.056 +/- 0.012), respectively. These measurements are consistent with the two states being the f(1) (1285) and f(1) (1420) mesons. (C) 2003 Published by Elsevier B.V.
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20. |
- Abdallah, J, et al.
(författare)
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Measurement of the e(+)e(-)-> W+W- gamma cross-section and limits on anomalous quartic gauge couplings with DELPHI
- 2003
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 31:2, s. 139-147
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Tidskriftsartikel (refereegranskat)abstract
- W(+)W(-)gamma production at LEP2 is studied using data collected with the DELPHI detector at centre-of-mass energies between 189 GeV and 209 GeV, corresponding to an integrated luminosity of about 600 pb(-1). Cross-sections are measured for the production of W+W- with a hard, central and isolated photon in the final state, and are found to be compatible with the Standard Model prediction. The photon energy spectra are used to derive limits on anomalous contributions to the W(+)W(-)Z(o)gamma and W(+)W(-)gammagamma vertices.
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21. |
- Abdallah, J, et al.
(författare)
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Measurement of the Lambda(0)(b) decay form factor
- 2004
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 585:1-2, s. 63-84
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Tidskriftsartikel (refereegranskat)abstract
- The form factor of A(o)(b) baryons is estimated using 3.46 x 10(6) hadronic Z decays collected by the DELPM experiment between 1992 and 1995. Charmed A(c)(+) baryons fully reconstructed in the pK(-)pi(+), pK(o)(s), and Api(+)pi(+)pi(-) modes, are associated to a c S lepton with opposite charge in order to select A(o)(b) --> A(c)(+)l(-)v(l) decays. From a combined likelihood and event rate fit to the b C distribution of the Isgur-Wise variable w, and using the Heavy Quark Effective Theory (HQET), the slope of the b-baryon form factor is measured to be p(2)=2.03+/-0.46(stat)(-1.00)(+0.72)(syst). The exclusive semileptonic branching fraction Br(A(b)(o) --> A(c)(+)l(-)v(l)) can be derived from p(2) and is found to be (5.0(-0.8)(+1.1)(stat)(-1.2)(+1.6) (syst))%. Limits on other branching fractions are also obtained. (C) 2004 Published by Elsevier B.V.
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22. |
- Abdallah, J, et al.
(författare)
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Rapidity-alignment and p(T) compensation of particle pairs in hadronic Z(0) decays
- 2002
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - 0370-2693. ; 533:3-4, s. 243-252
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Tidskriftsartikel (refereegranskat)abstract
- Observation is made of rapidity-alignment of K+K- and (p) over barp pairs which results from their asymmetric orientation in rapidity, with respect to the direction from primary quark to antiquark. The K+K- and (p) over barp data are consistent with predictions from the fragmentation string model. However, the (p) over barp data strongly disagree with the conventional implementation of the cluster model. The non-perturbative process of 'gluon splitting to diquarks' has to be incorporated into the cluster model for it to agree with the data. Local conservation of PT between particles nearby in rapidity (i.e., p(T) compensation) is analysed with respect to the thrust direction for pi(+)pi(-), K+K-, and (p) over barp pairs. In this case, the string model provides fair agreement with the data. The cluster model is incompatible with the data for all three particle pairs. The model with its central premiss of isotropically-decaying clusters predicts a p(T) correlation not seen in the data. (C) 2002 Elsevier Science B.V. All rights reserved.
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23. |
- Abdallah, J, et al.
(författare)
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Search for an LSP gluino at LEP with the DELPHI detector
- 2003
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 26:4, s. 505-525
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Tidskriftsartikel (refereegranskat)abstract
- In some supersymmetric models, the gluino ((g) over tilde) is predicted to be light and stable. In that case, it would hadronize to form R-hadrons. In these models, the missing energy signature of the lightest supersymmetric particle is no longer valid, even if R-parity is conserved. Therefore, such a gluino is not constrained by hadron collider results, which looked for the decay (g) over tilde --> q (q) over bar(χ) over tilde (0)(1). Data collected by the DELPHI detector in 1994 at 91.2 GeV have been analysed to search for q (q) over bar(gg) over tilde events. No deviation from Standard Model predictions is observed and a gluino mass between 2 and 18 GeV/c(2) is excluded at the 95% confidence level in these models. Then, R-hadrons produced in the squark decays were searched for in the data collected by DELPHI at the centre-of-mass energies of 189 to 208 GeV, corresponding to an overall integrated luminosity of 609 pb(-1). The observed number of events is in agreement with the Standard Model predictions. Limits at 95% confidence level are derived on the squark masses from the excluded regions in the plane (m((q) over tilde1),m((g) over bar)): m((t) over tilde1) > 90 GeV/c(2) and m((b) over tilde1) > 96 GeV/c(2) for purely left squarks. m((t) over tilde1) > 87 GeV/c(2) and m((b) over tilde1) > 82 GeV/c(2) independent of the mixing angle.
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24. |
- Abdallah, J, et al.
(författare)
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Search for B-s(0)-(B-s(0))over-bar oscillations and a measurement of B-d(0)-(B-d(0))over-bar oscillations using events with an inclusively reconstructed vertex
- 2003
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 28:2, s. 155-173
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Tidskriftsartikel (refereegranskat)abstract
- Neutral B meson oscillations in the B-s(0) - <(B-s(0))over bar>, and B-d(0) - <(B-d(0))over bar> systems were studied using a sample of about 4.0 million hadronic Z decays recorded by the DELPHI detector between 1992 and 2000. Events with a high transverse momentum lepton were removed and a sample of 770 k events with an inclusively reconstructed vertex was selected. The mass difference between the two physical states in the B-d(0) - <(B-d(0))over bar>system was measured to be: Deltam(d) = (0.531 +/- 0.025(stat.) +/- 0.007(syst.))ps(-1). The following limit on the width difference of these states was also obtained: DeltaGamma(Bd)/Gamma(Bd) < 0.18 at 95% CL. As no evidence for B-s(0) -<(B-s(0))over bar> oscillations was found, a limit on the mass difference of the two physical states was given:, Deltam(s) > 5.0 ps(-1) at 95% CL. The corresponding sensitivity of this analysis is equal to 6.6 ps(-1).
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25. |
- Abdallah, J, et al.
(författare)
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Search for charged Higgs bosons in e(+)e(-) collisions root s=189-202 GeV
- 2002
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - 0370-2693. ; 525:1-2, s. 17-28
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Tidskriftsartikel (refereegranskat)abstract
- A search for pair-produced charged Higgs bosons was performed in the high energy data collected by the DELPHI detector at LEP II at centre-of-mass energies from 189 GeV to 202 GeV. The three different final states, taunutaunu, c (s) over bar(c) over bars and c (s) over bar taunu were considered. New methods were applied to reject wrong hadronic jet pairings and for the tau identification, where a discriminator based on tau polarisation and polar angles was used. No excess of data compared to the expected Standard Model processes was observed and the existence of a charged Higgs boson with mass lower than 71.5 GeV/c(2) is excluded at the 95% confidence level. (C) 2002 Published by Elsevier Science B.V.
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