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Journal articleAcciarri M, Achard P, Adriani O, et al., 1999,
Measurement of the e<SUP>+</SUP>e<SUP>-</SUP>→Z→b(b)over-bar forward-backward asymmetry and the B<SUP>0</SUP>(B)over-bar<SUP>0</SUP> mixing parameter using prompt leptons
, PHYSICS LETTERS B, Vol: 448, Pages: 152-162, ISSN: 0370-2693- Author Web Link
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- Citations: 21
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Journal articleBarate R, Buskulic D, Decamp D, et al., 1999,
Search for the standard model Higgs boson at the LEP2 collider near √<i>s</i>=183 GeV (vol 440, pg 403, 1998)
, PHYSICS LETTERS B, Vol: 447, Pages: 336-351, ISSN: 0370-2693- Author Web Link
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- Citations: 13
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Conference paperAlbergo S, Azzi P, Babucci E, et al., 1999,
Test results of heavily irradiated Si detectors
, 9th Symposium on Radiation Measurements and Applications, Publisher: ELSEVIER SCIENCE BV, Pages: 238-241, ISSN: 0168-9002 -
Journal articleAcciarri M, Achard P, Adriani O, et al., 1999,
The <i>Q</i><SUP>2</SUP> evolution of the hadronic photon structure function <i>F</i><sub>2</sub><SUP>γ</SUP> at LEP
, PHYSICS LETTERS B, Vol: 447, Pages: 147-156, ISSN: 0370-2693- Author Web Link
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- Citations: 50
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Journal articleAbbiendi G, Ackerstaff K, Alexander G, et al., 1999,
Search for baryon and lepton number violating Z<SUP>0</SUP> decays
, PHYSICS LETTERS B, Vol: 447, Pages: 157-166, ISSN: 0370-2693- Author Web Link
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- Citations: 4
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Journal articleAbbiendi G, Ackerstaff K, Alexander G, et al., 1999,
A measurement of the τ<SUP>-</SUP>→e<SUP>-</SUP>(ν)over-bar<sub>e</sub>ν<sub>τ</sub> branching ratio
, PHYSICS LETTERS B, Vol: 447, Pages: 134-146, ISSN: 0370-2693- Author Web Link
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- Citations: 20
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Journal articleBarate R, Buskulic D, Decamp D, et al., 1999,
Analysis of transverse momentum correlations in hadronic Z decays
, PHYSICS LETTERS B, Vol: 447, Pages: 183-198, ISSN: 0370-2693 -
Journal articleAcciarri M, Adriani O, Aguilar-Benitez M, et al., 1999,
Search for charged Higgs bosons in e<SUP>+</SUP>e<SUP>-</SUP> collisions at centre-of-mass energies between 130 and 183 GeV
, PHYSICS LETTERS B, Vol: 446, Pages: 368-377, ISSN: 0370-2693- Author Web Link
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- Citations: 9
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Journal articleAbreu P, Adam W, Adye T, et al., 1999,
Search for Leptoquarks and FCNC in <i>e</i><i><SUP>+</SUP></i><SUP>e</SUP><SUP>-</SUP> annihilations √<i>s</i> = 183 GeV
, PHYSICS LETTERS B, Vol: 446, Pages: 62-74, ISSN: 0370-2693- Author Web Link
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- Citations: 41
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Journal articleAbreu P, Adam W, Adye T, et al., 1999,
Search for charginos, neutralinos and gravitinos in e<SUP>+</SUP>e<SUP>-</SUP> interactions at √<i>s</i> = 183 GeV
, PHYSICS LETTERS B, Vol: 446, Pages: 75-91, ISSN: 0370-2693- Author Web Link
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- Citations: 24
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Journal articleAcciarri M, Adriani O, Aguilar-Benitez M, et al., 1999,
Searches for scalar top and scalar bottom quarks in e<sup>+</sup>e<sup>-</sup> interactions at 161 GeV ≤ √s ≤ 183 GeV
, Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics, Vol: 445, Pages: 428-438, ISSN: 0370-2693Searches for scalar top and scalar bottom quarks have been performed at center-of-mass energies between 161 GeV and 183 GeV using the L3 detector at LEP. No signal is observed. Model-independent limits on production cross sections are determined for the two decay channels t̃1 → cχ̃01 and b̃1 → b χ̃01. Within the framework of the Minimal Supersymmetric extension of the Standard Model mass limits are derived. For mass differences between t̃1 and χ̃01 greater than 10 GeV a 95% C.L. limit of 81.5 GeV is set on the mass of the Supersymmetric partner of the left-handed top. A supersymmetric partner of the left-handed bottom with a mass below 80 GeV is excluded at 95% C.L. if the mass difference between b̃1 and χ̃1 is greater than 20 GeV. © 1999 Published by Elsevier Science B.V. All rights reserved.
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Journal articleAcciarri M, Adriani O, Aguilar-Benitez M, et al., 1999,
Searches for scalar top and scalar bottom quarks in e<SUP>+</SUP>e<SUP>-</SUP> interactions at 161GeV≤√<i>s</i>≤183GeV
, PHYSICS LETTERS B, Vol: 445, Pages: 428-438, ISSN: 0370-2693- Author Web Link
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- Citations: 12
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Journal articleAckerstaff K, Alexander G, Allison J, et al., 1999,
Production of K<sup>0</sup><inf>S</inf> and Λ in quark and gluon jets from Z<sup>0</sup> decay
, European Physical Journal C, Vol: 8, Pages: 241-254, ISSN: 1434-6044The production of K0S mesons and Λ baryons in quark and gluon jets has been investigated using two complementary techniques. In the first approach, which provides high statistical accuracy, jets were selected using different jet finding algorithms and ordered according to their energy. Production rates were determined taking into account the dependences of quark and gluon compositions as a function of jet energy as predicted by Monte Carlo models. Selecting three-jet events with the k⊥ (Durham) jet finder (Ycut = 0.005), the ratios of K0S and Λ production rates in gluon and quark jets relative to the mean charged particle multiplicity were found to be 1.10 ± 0.02 ± 0.02 and 1.41 ± 0.04 ± 0.04, respectively, where the first uncertainty is statistical and the second is systematic. In the second approach, a new method of identifying quark jets based on the collimation of energy flow around the jet axis is introduced and was used to anti-tag gluon jets in symmetric (Y-shaped) three-jet events. Using the cone jet finding algorithm with a cone size of 30°, the ratios of relative production rates in gluon and quark jets were determined to be 0.94 ± 0.07 ± 0.07 for K0S and 1.18 ± 0.10 ± 0.17 for Λ. The results of both analyses are compared to the predictions of Monte Carlo models.
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Journal articleAbbiendi G, Ackerstaff K, Alexander G, et al., 1999,
Bose-Einstein correlations in e<sup>+</sup>e<sup>-</sup> → W<sup>+</sup>W<sup>-</sup> at 172 and 183 GeV
, European Physical Journal C, Vol: 8, Pages: 559-571, ISSN: 1434-6044Bose-Einstein correlations between like-charge pions are studied in hadronic final states produced by e+e- annihilations at center-of-mass energies of 172 and 183 GeV. Three event samples are studied, each dominated by one of the processes W+W- →qq̄ℓν̄e, W+W- qq̄qq̄, or (Z0/γ)* → qq̄. After demonstrating the existence of Bose-Einstein correlations in W decays, an attempt is made to determine Bose-Einstein correlations for pions originating from the same W boson and from different W bosons, as well as for pions from (Z0/γ)* → qq̄ events. The following results are obtained for the individual chaoticity parameters λ, assuming a common source radius R: λsame= 0.63 ± 0.19 ± 0.14 λdiff = 0.22 ± 0.53 ±0.14, λ Z* = 0.47 ± 0.11 ± 0.08, R = 0.92 ± 0.09 ± 0.09 fm. In each case, the first error is statistical and the second is systematic. At the current level of statistical precision it is not established whether Bose-Einstein correlations, between pions from different W bosons exist or not.
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Journal articleAbbiendi G, Ackerstaff K, Alexander G, et al., 1999,
A measurement of the product branching ratio f(b → Λ<inf>b</inf>) · BR(Λ<inf>b</inf> → ΛX) in Z<sup>0</sup> decays
, European Physical Journal C, Vol: 9, Pages: 1-9, ISSN: 1434-6044The product branching ratio, f(b → Λb) · BR(Λb → ΛX), where Λb denotes any weakly-decaying b-baryon, has been measured using the OPAL detector at LEP. Λb's are selected by the presence of energetic Λ particles in bottom events tagged by the presence of displaced secondary vertices. A fit to the momenta of the Λ particles separates signal from B meson and fragmentation backgrounds. The measured product branching ratio is f(b → Λb) · BR(Λb → ΛX) = (2.67) ± 0.38(stat)+0.67-0.60(sys))%. Combined with a previous OPAL measurement, one obtains f(b → Λb) · BR(Λb → ΛX) = (3.50) ± 0.32(stat) ± 0.35(sys))%.
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Journal articleAbbiendi G, Ackerstaff K, Alexander G, et al., 1999,
W<sup>+</sup>W<sup>-</sup> production and triple gauge boson couplings at LEP energies up to 183 GeV
, European Physical Journal C, Vol: 8, Pages: 191-215, ISSN: 1434-6044A study of W-pair production in e+e- annihilations at LEP is presented, based on 877 W+W- candidates corresponding to an integrated luminosity of 57pb-1 at √s = 183 GeV. Assuming that the angular distributions of the W-pair production and decay, as well as their branching fractions, are described by the Standard Model, the W-pair production cross-section is measured to be 15.43 ± 0.61(stat.) ± 0.26(syst.) pb. Assuming lepton universality and combining with our results from lower centre-of-mass energies, the W branching fraction to hadrons is determined to be 67.9 ± 1.2(stat.) ± 0.5(syst.)%. The number of W-pair candidates and the angular distributions for each final state (qq̄l̄νl, qq̄qq̄, l̄νll′ν̄l′) are used to determine the triple gauge boson couplings. After combining these values with our results from lower centre-of-mass energies we obtain Δκγ = 0.11+0.52-0.37, Δgz1 = 0.01+0.13-0.12 and λ = -0.10+0.13-0.12, where the errors include both statistical and systematic uncertainties and each coupling is determined by setting the other two couplings to the Standard Model value. The fraction of W bosons produced with a longitudinal polarisation is measured to be 0.242 ± 0.091(stat.) ± 0.023(syst.). All these measurements are consistent with the Standard Model expectations.
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Journal articleAckerstaff K, Alexander G, Allison J, et al., 1999,
Measurements of flavour-dependent fragmentation functions in Z<sup>0</sup> → qq̄ events
, European Physical Journal C, Vol: 7, Pages: 369-381, ISSN: 1434-6044Fragmentation functions for charged particles in Z0 → qq̄ events have been measured for bottom (b), charm (c) and light (uds) quarks as well as for all flavours together. The results are based on data recorded between 1990 and 1995 using the OPAL detector at LEP. Event samples with different flavour compositions were formed using reconstructed D*± mesons and secondary vertices. The ξP = ln(1/xp) distributions and the position of their maxima ξ0 are also presented separately for uds, c and b quark events. The fragmentation function for b quarks is significantly softer than for uds quarks.
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Conference paperDavies G J, 1999,
RECENT RESULTS FROM PBWO4 CRYSTALS AND MSGCS IN CMS
, European Physical Society, 1997, Pages: 1109-1113 -
Conference paperI Liubarsky et al, 1999,
DARK MATTER SEARCH AT BOULBY MINE
, Dark matter in astrophysics and particle physics, Pages: 780-784 -
Journal articleScannavini MG, Speller RD, Royle GJ, et al., 1999,
Design of a small laboratory Compton camera for the imaging of positron emitters
, IEEE Nuclear Science Symposium and Medical Imaging Conference, Vol: 2, Pages: 1120-1126A small laboratory prototype has been designed for the Compton imaging of annihilation photons produced from positron emitters. Considerations on the design of the scatter collimator are presented and the system configuration is described. The system features a stack of four AC coupled, double-sided silicon strip detectors (6 × 6 cm2 area, 500 μm thickness, 470 μm strip pitch, 128 channels/side) in a double Compton configuration and externally triggered readout mode. Signal readout is obtained by bonding two 128-channel low-noise APV6 chips to each detector. Custom electronics have been developed for the chip readout. The system is currently being assembled. The estimated angular resolution of the camera is approximately 4 degrees. High sensitivity could be achieved by extending the number of stack elements and by improving the design of the trigger detector, which presently consists of a small area germanium crystal.
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Journal articleFortunato E, Becker U, Dinner R, et al., 1999,
Systematic study of electron drift for gaseous chamber design
, IEEE Nuclear Science Symposium and Medical Imaging Conference, Vol: 1, Pages: 106-110We present a consistent set of measurements of electron drift velocities and Lorentz deflection angles in all noble gases with methane and ethane as quenchers in magnetic fields up to 0.8 Tesla. These and many other results are available in a searchable database on World Wide Web at http: //cyclotron.mit.edu/drift/ to allow for guided design and optimization of future detectors. A simple model is used to form an empirical parameterization of the results. This compact form unifies the drift characteristics of a gas mixture over a range of electric (0 - 1.5 kV/cm) and magnetic (0-0.8 Tesla) fields. A more detailed model is presented which explains the surprisingly large effect of even modest (and inevitable) nitrogen contamination on electron drift velocity. Additional measurements and simulations confirm the validity of the model's predictions and show possible applications.
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Journal articleAndrés E, Askebjer P, Barwick SW, et al., 1999,
Status of the AMANDA experiment
, Nuclear Physics B - Proceedings Supplements, Vol: 70, Pages: 448-452, ISSN: 0920-5632The AMANDA high energy neutrino telescope has successfully been increased in size from four detector strings to ten detector strings during the 1996/1997 season. The first upward going muon-neutrino candidates have been reconstructed from the 1996 year's four-string data. Three new detector strings will be deployed during 1997/1998 to 2350 metres depth.
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Journal articleAcciarri M, Achard P, Adriani O, et al., 1999,
Search for low scale gravity effects in e<sup>+</sup>e<sup>-</sup> collisions at LEP
, Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics, Vol: 464, Pages: 135-144, ISSN: 0370-2693Recent theories propose that quantum gravity effects may be observable at LEP energies via gravitons that couple to Standard Model particles and propagate into extra spatial dimensions. The associated production of a graviton and a photon is searched for as well as the effects of virtual graviton exchange in the processes: e+e-→ γγ, W+W-, μ+μ-, τ+τ-, qq and e+e-. No evidence for this new interaction is found in the data sample collected by the L3 detector at LEP at centre-of-mass energies up to 183 GeV. Limits close to 1 TeV on the scale of this new scenario of quantum gravity are set. © 1999 Published by Elsevier Science B.V. All rights reserved.
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Journal articleAcciarri M, Achard P, Adriani O, et al., 1999,
The Q<sup>2</sup> evolution of the hadronic photon structure function F<inf>2</inf><sup>γ</sup> at LEP
, Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics, Vol: 447, Pages: 147-156, ISSN: 0370-2693New measurements at a centre-of-mass energy √s ≃ 183 GeV of the hadronic photon structure function F2γ(x) in the Q2 interval, 9 GeV2 ≤ Q2 ≤ 30 GeV2, are presented. The data, collected in 1997 with the L3 detector, correspond to an integrated luminosity of 51.9 pb-1. Combining with the data taken at a centre-of-mass energy of 91 GeV, the evolution of F2γ with Q2 is measured in the Q2 range from 1.2 GeV2 to 30 GeV2. F2γ shows a linear growth with InQ2; the value of the slope α-1dF2γ(Q2)/dlnQ2 is measured in two x bins from 0.01 to 0.2 and is somewhat higher than predicted. © 1999 Published by Elsevier Science B.V. All rights reserved.
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Journal articleBarate R, Decamp D, Ghez P, et al., 1999,
A direct measurement of
, Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics, Vol: 465, Pages: 349-362, ISSN: 0370-2693The inclusive charm production rate in W decays is measured from a study of the properties of final state particles. The sample of W pairs is selected from 67.7 pb-1collected by ALEPH in 1996 and 1997 at centre-of-mass energies near 172 and 183 GeV in the channels W+W-→ 4q and W+W-→ℓvqq̄. The branching fraction of hadronic W decays to a final state containing a c quark, RcW= Γ(W→cX)/Γ(W→hadrons), is measured to be 0.51 ± 0.05stat+ 0.03syst.This allows a direct determination of the CKM matrix element |Vcs| = 1.00 ± 0.11stat± 0.07syst. © 1999 Published by Elsevier Science B.V. All rights reserved.
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Journal articleAcciarri M, Achard P, Adriani O, et al., 1999,
Measurement of the e<sup>+</sup>e → Z → bb̄ forward-backward asymmetry and the B<sup>0</sup>B̄<sup>0</sup> mixing parameter using prompt leptons
, Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics, Vol: 448, Pages: 152-162, ISSN: 0370-2693The time-integrated B0B̄0 mixing parameter and the forward-backward charge asymmetry in the process e+e-→ bb are measured in hadronic Z events containing prompt muons or electrons, collected by the L3 experiment in the years 1990 to 1995. The total sample of 3.3 milion hadronic Z events with a mean centre-of-mass energy of 91.26 GeV yields: AFBb = 0.0960 ± 0.0066(stat.) ± 0.0033(sys.), Xb = 0.1192 ± 0.0068(stat.) ± 0.0051(sys.). This asymmetry measurement together with measurements at energies away from the Z pole energy yield a pole asymmetry and corresponding effective electroweak mixing angle of: AFB0,b = 0.1015 ± 0.0064(stat.) + 0.0035(.sy.s.), sin20W = 0.2318 ± 0.0013. © 1999 Published by Elsevier Science B.V. All rights reserved.
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Journal articleAcciarri M, Achard P, Adriani O, et al., 1999,
Search for the standard model Higgs boson in e<sup>+</sup>e<sup>-</sup> interactions at √S = 189 GeV
, Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics, Vol: 461, Pages: 376-386, ISSN: 0370-2693A search for the Standard Model Higgs boson is carried out on 176.4pb-1 of data collected by the L3 detector at a center-of-mass energy of 189 GeV. The data are consistent with the expectations of Standard Model processes and no evidence of a Higgs signal is observed. Combining the results of this search with those at lower center-of-mass energies, a lower limit on the mass of the Standard Model Higgs boson of 95.3 GeV is set at the 95% confidence level. © 1999 Elsevier Science B.V. All rights reserved.
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Journal articleAcciarri M, Achard P, Adriani O, et al., 1999,
Search for heavy isosinglet neutrinos in e<sup>+</sup>e<sup>-</sup> annihilation at 130 < √s < 189 GeV
, Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics, Vol: 461, Pages: 397-404, ISSN: 0370-2693A search for heavy neutrinos that are isosinglets under the standard SU(2)L gauge group is made at center-of-mass energies 130 < √s < 189 GeV with the L3 detector at LEP. Such heavy neutrinos are expected in many extensions of the Standard Model. The search is performed for the first generation heavy singlet neutrino, Ne, through the decay mode Ne → e + W. We set upper limits on the mixing parameter between the heavy and light neutrino for the heavy neutrino mass range from 80 GeV to 185 GeV. © 1999 Elsevier Science B.V. All rights reserved.
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Journal articleAcciarri M, Achard P, Adriani O, et al., 1999,
Search for charged Higgs bosons in e<sup>+</sup> e<sup>-</sup> collisions at √s = 189 GeV
, Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics, Vol: 466, Pages: 71-78, ISSN: 0370-2693A search for pair-produced charged Higgs bosons is performed with the L3 detector at LEP using data collected at a centre-of-mass energy of 188.6 GeV, corresponding to an integrated luminosity of 176.4 pb-1. Higgs decays into a charm and a strange quark or into a tau lepton and its associated neutrino are considered. The observed events are consistent with the expectations from Standard Model background processes. A lower limit of 65.5 GeV on the charged Higgs mass is derived at 95% confidence leva, independent of the decay branching ratio Br(H ± → τν). ©1999 Published by Elsevier Science B.V. All rights reserved.
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Journal articleBarate R, Buskulic D, Decamp D, et al., 1999,
Search for the standard model Higgs boson at the LEP2 Collider near √s = 183 GeV
, Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics, Vol: 447, Pages: 336-351, ISSN: 0370-2693During 1997 the ALEPH experiment at LEP gathered 57pb-1 of data at centre-of-mass energies near 183 GeV. These data are used to look for possible signals from the production of the Standard Model Higgs boson in the reaction e+e-→ HZ. No evidence of a signal is found in the data; seven events are selected, in agreement with the expectation of 7.2 events from background processes. This observation results in an improved lower limit on the mass of the Higgs boson: mH > 87.9GeV/c2 at 95% confidence level. © 1999 Elsevier Science B.V. All rights reserved.
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