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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 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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Conference paperI Liubarsky et al, 1999,
DARK MATTER SEARCH AT BOULBY MINE
, Dark matter in astrophysics and particle physics, Pages: 780-784 -
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 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 cm<sup>2</sup> 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 articleAckerstaff K, Alexander G, Allison J, et al., 1999,
Production of K0S and Λ in quark and gluon jets from Z0 decay
, European Physical Journal C, Vol: 8, Pages: 241-254, ISSN: 1434-6044The production of K<sup>0</sup><inf>S</inf> 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<inf>⊥</inf> (Durham) jet finder (Y<inf>cut</inf> = 0.005), the ratios of K<sup>0</sup><inf>S</inf> 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 K<sup>0</sup><inf>S</inf> 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+e- → W+W- 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<sup>+</sup>e<sup>-</sup> annihilations at center-of-mass energies of 172 and 183 GeV. Three event samples are studied, each dominated by one of the processes W<sup>+</sup>W<sup>-</sup> →qq̄ℓν̄e, W<sup>+</sup>W<sup>-</sup> qq̄qq̄, or (Z<sup>0</sup>/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 (Z<sup>0</sup>/γ)* → qq̄ events. The following results are obtained for the individual chaoticity parameters λ, assuming a common source radius R: λ<sup>same</sup>= 0.63 ± 0.19 ± 0.14 λ<sup>diff</sup> = 0.22 ± 0.53 ±0.14, λ <sup>Z</sup>* = 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 → Λb) · BR(Λb → ΛX) in Z0 decays
, European Physical Journal C, Vol: 9, Pages: 1-9, ISSN: 1434-6044The product branching ratio, f(b → Λ<inf>b</inf>) · BR(Λ<inf>b</inf> → ΛX), where Λ<inf>b</inf> denotes any weakly-decaying b-baryon, has been measured using the OPAL detector at LEP. Λ<inf>b</inf>'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 → Λ<inf>b</inf>) · BR(Λ<inf>b</inf> → ΛX) = (2.67) ± 0.38(stat)<sup>+0.67</sup><inf>-0.60</inf>(sys))%. Combined with a previous OPAL measurement, one obtains f(b → Λ<inf>b</inf>) · BR(Λ<inf>b</inf> → ΛX) = (3.50) ± 0.32(stat) ± 0.35(sys))%.
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Journal articleAbbiendi G, Ackerstaff K, Alexander G, et al., 1999,
W+W- 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<sup>+</sup>e<sup>-</sup> annihilations at LEP is presented, based on 877 W<sup>+</sup>W<sup>-</sup> candidates corresponding to an integrated luminosity of 57pb<sup>-1</sup> 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 (qq̄l̄ν<inf>l</inf>, qq̄qq̄, l̄ν<inf>l</inf>l′ν̄<inf>l</inf>′) are used to determine the triple gauge boson couplings. After combining these values with our results from lower centre-of-mass energies we obtain Δκ<inf>γ</inf> = 0.11+<sup>0.52</sup><inf>-0.37</inf>, Δg<sup>z</sup><inf>1</inf> = 0.01<sup>+0.13</sup><inf>-0.12</inf> and λ = -0.10<sup>+0.13</sup><inf>-0.12</inf>, 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 Z0 → qq̄ events
, European Physical Journal C, Vol: 7, Pages: 369-381, ISSN: 1434-6044Fragmentation functions for charged particles in Z<sup>0</sup> → 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*<sup>±</sup> mesons and secondary vertices. The ξ<inf>P</inf> = ln(1/x<inf>p</inf>) distributions and the position of their maxima ξ<inf>0</inf> 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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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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Conference paperDavies G J, 1999,
RECENT RESULTS FROM PBWO4 CRYSTALS AND MSGCS IN CMS
, European Physical Society, 1997, Pages: 1109-1113 -
Journal articleAbreu P, Adam W, Adye T, et al., 1999,
Search for scalar fermions and long-lived scalar leptons at centre-of-mass energies of 130 GeV to 172 GeV
, EUROPEAN PHYSICAL JOURNAL C, Vol: 6, Pages: 385-401, ISSN: 1434-6044- Author Web Link
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- Citations: 23
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Journal articleAbreu P, Adam W, Adye T, et al., 1999,
Measurement of the quark and gluon fragmentation functions in Z<SUP>0</SUP> hadronic decays
, EUROPEAN PHYSICAL JOURNAL C, Vol: 6, Pages: 19-33, ISSN: 1434-6044- Author Web Link
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- Citations: 39
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Journal articleBarate R, Buskulic D, Decamp D, et al., 1999,
Determination of |V<sub>ub</sub>| from the measurement of the inclusive charmless semileptonic branching ratio of b hadrons
, EUROPEAN PHYSICAL JOURNAL C, Vol: 6, Pages: 555-574, ISSN: 1434-6044- Author Web Link
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- Citations: 53
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Journal articleAckerstaff K, Alexander G, Allison J, et al., 1999,
Search for scalar top and scalar bottom quarks at √s = 183 GeV at LEP
, EUROPEAN PHYSICAL JOURNAL C, Vol: 6, Pages: 225-238, ISSN: 1434-6044- Author Web Link
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- Citations: 16
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Journal articleTorii HA, Hayano RS, Hori M, et al., 1999,
Laser measurements of the density shifts of resonance lines in antiprotonic helium atoms and stringent constraint on the antiproton charge and mass
, PHYSICAL REVIEW A, Vol: 59, Pages: 223-229, ISSN: 1050-2947- Author Web Link
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- Citations: 80
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Journal articleAbbiendi G, Ackerstaff K, Alexander G, et al., 1999,
Tests of the Standard Model and constraints on new physics from measurements of fermion-pair production at 183 GeV at LEP
, EUROPEAN PHYSICAL JOURNAL C, Vol: 6, Pages: 1-18, ISSN: 1434-6044- Author Web Link
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- Citations: 87
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Conference paperSumner TJ, Quenby JJ, Bewick A, et al., 1999,
Current limits on the cold dark matter interaction cross section obtained by the UK collaboration
, 5th International Workshop on Topics in Astroparticle and Underground Physics (TAUP 97), Publisher: ELSEVIER SCIENCE BV, Pages: 74-78, ISSN: 0920-5632- Author Web Link
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- Citations: 11
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Journal articleAbreu P, Adye T, Adzic P, et al., 1999,
Search for pair-produced neutralinos in events with photons and missing energy from e<SUP>+</SUP>e<SUP>-</SUP> collisions at √<i>s</i>=130-183 GeV
, EUROPEAN PHYSICAL JOURNAL C, Vol: 6, Pages: 371-384, ISSN: 1434-6044- Author Web Link
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- Citations: 10
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Journal articleAckerstaff K, Alexander G, Allison J, et al., 1999,
Inclusive production of charged hadrons and K<SUP>0</SUP><sub>S</sub> mesons in photon-photon collisions
, EUROPEAN PHYSICAL JOURNAL C, Vol: 6, Pages: 253-264, ISSN: 1434-6044- Author Web Link
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- Citations: 23
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Journal articleFoudas C, Butterworth I, Long KR, et al., 1999,
Measurement of the inclusive D*+/- and associated dijet cross sections in photoproduction at HERA
, European Physical Journal B, Vol: C, Pages: 67-83 -
Journal articleVirdee TS, 1999,
Experimental techniques
, CERN 99-04, Vol: INFO NEEDED, Pages: 347-419 -
Journal articleBecker U, Uchida Y, 1999,
Consistent measurements comparing the drift features of noble gas mixtures
, Nucl.Instrum.Meth.A, Vol: 421, Pages: 54-59 -
Journal articleLong KR, Butterworth I, Foudas C, et al., 1999,
Measurement of high-Q(2) neutral-current e(+)p deep inelastic scattering cross-sections at HERA
, European Physical Journal C, Vol: 11, Pages: 427-445, ISSN: 1434-6044 -
Conference paperSumner TJ, 1999,
Techniques for detecting WIMPS operating above 100 K
, The Identification of Dark Matter, Publisher: World Scientific, Pages: 227-240 -
Journal articleThompson JC, Binnie DM, Dornan PJ, et al., 1999,
Measurements of the W mass in e+e- collisions at 183 GeV
, Physics Letters B, Vol: 453, Pages: 121-137
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