A search for a Higgs boson produced in e+e− collisions in association with a Z boson and decaying into invisible particles is performed. Data collected at LEP with the L3 detector at centre-of-mass ...energies from 189 to 209 GeV are used, corresponding to an integrated luminosity of 0.63 fb−1. Events with hadrons, electrons or muons with visible masses compatible with a Z boson and missing energy and momentum are selected. They are consistent with the Standard Model expectations. A lower limit of 112.3 GeV is set at 95% confidence level on the mass of the invisibly-decaying Higgs boson in the hypothesis that its production cross section equals that of the Standard Model Higgs boson. Relaxing this hypothesis, upper limits on the production cross section are derived.
Performance tests of some aspects of the CMS ECAL were carried out on modules of the "barrel" sub-system in 2002 and 2003. A brief test with high energy electron beams was made in late 2003 to ...validate prototypes of the new Very Front End electronics. The final versions of the monitoring and cooling systems, and of the high and low voltage regulation were used in these tests. The results are consistent with the performance targets including those for noise and overall energy resolution, required to fulfil the physics programme of CMS at the LHC.
The measurements of hadron and lepton-pair production cross sections and leptonic forward–backward asymmetries performed with the L3 detector at centre-of-mass energies between 130
GeV
and 189
GeV
...are used to search for new physics phenomena such as: contact interactions, exchange of virtual leptoquarks, scalar quarks and scalar neutrinos, effects of
TeV
strings in models of quantum gravity with large extra dimensions and non-zero sizes of the fermions. No evidence for these phenomena is found and new limits on their parameters are set.
Search for excited leptons at LEP Aloisio, A.; Alviggi, M.G.; Arefiev, A. ...
Physics letters. B,
08/2003, Letnik:
568, Številka:
1-2
Journal Article
Recenzirano
Odprti dostop
A search for charged and neutral excited leptons is performed in 217 pb−1 of e+e− collision data collected with the L3 detector at LEP at centre-of-mass energies from 202 up to 209 GeV. The pair- and ...single-production mechanisms of excited electrons, muons and taus, as well as of excited electron-, muon- and tau-neutrinos, are investigated and no signals are detected. Combining with L3 results from searches at lower centre-of-mass energies, gives improved limits on the masses and couplings of excited leptons.
Final results of the search for the standard model Higgs boson are presented for the data collected by the L3 detector at LEP at centre-of-mass energies up to about 209 GeV. These data are compared ...with the expectations of standard model processes for Higgs boson masses up to 120 GeV. A lower limit on the mass of the standard model Higgs boson of 112.0 GeV is set at the 95% confidence level. The most significant high mass candidate is a Hνν̄ event. It has a reconstructed Higgs mass of 115 GeV and it was recorded at s=206.4 GeV.
The forward muon detector of L3 Adam, A.; Aguilar-Benitez, M.; Alarcon, J. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
12/1996, Letnik:
383, Številka:
2
Journal Article
Recenzirano
Odprti dostop
The forward-backward muon detector of the L3 experiment is presented. Intended to be used for LEP 200 physics, it consists of 96 self-calibrating drift chambers of a new design enclosing the magnet ...pole pieces of the L3 solenoid. The pole pieces are toroidally magnetized to form two independent analyzing spectrometers. A novel trigger is provided by resistive plate counters attached to the drift chambers. Details about the design, construction and performance of the whole system are given together with results obtained during the 1995 running at LEP.
The evolution of the electromagnetic coupling, α, in the momentum-transfer range 1800 GeV2<−Q2<21600 GeV2 is studied with about 40 000 Bhabha-scattering events collected with the L3 detector at LEP ...at centre-of-mass energies s=189–209 GeV. The running of α is parametrised as: α(Q2)=α01−CΔα(Q2), where α0≡α(Q2=0) is the fine-structure constant and C=1 corresponds to the evolution expected in QED. A fit to the differential cross section of the e+e−→e+e− process for scattering angles in the range |cosθ|<0.9 excludes the hypothesis of a constant value of α, C=0, and validates the QED prediction with the result: C=1.05±0.07±0.14, where the first uncertainty is statistical and the second systematic.
Aims.Several experiments have reported observations on possible correlations between the flux of high energy muons and intense solar flares. If confirmed, these observations would have significant ...implications for acceleration processes in the heliosphere able to accelerate protons and other ions to energies of at least tens of GeV. Methods.The solar flare of the 14 of July 2000 offered a unique opportunity for the L3+C experiment to search for a correlated enhancement in the flux of muons using the L3 precision muon spectrometer. Its capabilities for observing a directional excess in the flux of muons above 15 GeV (corresponding to primary proton energies above 40 GeV) are presented along with observations made on the 14th of July 2000. Results.We report an excess which appeared at a time coincident with the peak increase of solar protons observed at lower energies. The probability that the excess is a background fluctuation is estimated to be 1%. No similar excess of the muon flux was observed up to 1.5 h after the solar flare time.
Anomalous couplings of the Higgs boson are searched for through the processes e+e−→Hγ, e+e−→e+e−H and e+e−→HZ. The mass range 70 GeV<mH<190 GeV is explored using 602 pb−1 of integrated luminosity ...collected with the L3 detector at LEP at centre-of-mass energies s=189–209 GeV. The Higgs decay channels H→ff̄, H→γγ, H→Zγ and H→WW(∗) are considered and no evidence is found for anomalous Higgs production or decay. Limits on the anomalous couplings d, dB, Δg1Z, Δκγ and ξ2 are derived as well as limits on the H→γγ and H→Zγ decay rates.
The process e+e−→Zγ, where the Z boson decays into hadrons or neutrinos, is studied with data collected with the L3 detector at LEP at centre-of-mass energies from 189 up to 209 GeV. The cross ...sections are measured and found to be in agreement with the Standard Model predictions. Limits on triple neutral-gauge-boson couplings, forbidden in the Standard Model at tree level, are derived. Limits on the energy scales at which the anomalous couplings could be manifest are set. They range from 0.3 to 2.3 TeV depending on the new physics effect under consideration.
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