Bose–Einstein correlations in W-pair production at LEP are investigated in a data sample of 629 pb−1 collected by the L3 detector at s=189–209 GeV. Bose–Einstein correlations between pions within a W ...decay are observed and found to be in good agreement with those in light-quark Z decay. No evidence is found for Bose–Einstein correlations between hadrons coming from different W's in the same event.
Extra spatial dimensions are proposed by recent theories that postulate the scale of gravity to be of the same order as the electroweak scale. A sizeable interaction between gravitons and Standard ...Model particles is then predicted. Effects of these new interactions in boson and fermion pair production are searched for in the data sample collected at centre-of-mass energies above the Z pole by the L3 detector at LEP. In addition, the direct production of a graviton associated with a Z boson is investigated. No statistically significant hints for the existence of these effects are found and lower limits in excess of
1
TeV
are derived on the scale of this new theory of gravity.
Measurement of W polarisation at LEP Aguilar-Benitez, M.; Alcaraz, J.; Aloisio, A. ...
Physics letters. B,
04/2003, Letnik:
557, Številka:
3-4
Journal Article
Recenzirano
Odprti dostop
The three different helicity states of W bosons produced in the reaction e+e−→W+W−→ℓνqq̄′ at LEP are studied using leptonic and hadronic W decays. Data at centre-of-mass energies s=183–209 GeV are ...used to measure the polarisation of W bosons, and its dependence on the W boson production angle. The fraction of longitudinally polarised W bosons is measured to be 0.218±0.027±0.016 where the first uncertainty is statistical and the second systematic, in agreement with the Standard Model expectation.
The charged-particle multiplicity distribution is measured for all hadronic events as well as for light-quark and b-quark events produced in e+e- collisions at the Z pole. Moments of the ...charged-particle multiplicity distributions are calculated. The H moments of the multiplicity distributions are studied, and their quasi-oscillations as a function of the rank of the moment are investigated.
The QED processes e+e−→e+e−μ+μ− and e+e−→e+e−τ+τ− are studied with the L3 detector at LEP using an untagged data sample collected at centre-of-mass energies 161 GeV⩽s⩽209 GeV. The τ-pairs are ...observed through the associated decay of one τ into eνν and the other into ππν. The cross sections are measured as a function of s. For muon pairs, the cross section of the γγ→μ+μ− process is also measured as a function of the two-photon centre-of-mass energy for 3 GeV⩽Wγγ⩽40 GeV. Good agreement is found between these measurements and the O(α4) QED expectations. In addition, limits on the anomalous magnetic and electric dipole moments of the τ lepton are extracted.
Z boson pair-production at LEP Aloisio, A.; Alviggi, M.G.; Arefiev, A. ...
Physics letters. B,
10/2003, Letnik:
572, Številka:
3-4
Journal Article
Recenzirano
Odprti dostop
Events stemming from the pair-production of Z bosons in e+e− collisions are studied using 217.4 pb−1 of data collected with the L3 detector at centre-of-mass energies from 200 GeV up to 209 GeV. The ...special case of events with b quarks is also investigated. Combining these events with those collected at lower centre-of-mass energies, the Standard Model predictions for the production mechanism are verified. In addition, limits are set on anomalous couplings of neutral gauge bosons and on effects of extra space dimensions.
Recent 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, ZZ, W
+W
−,
μ
+
μ
−,
τ
+
τ
−,
q
q
̄
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.
A search, in e+e− collisions, for chargino, neutralino, scalar lepton and scalar quark pair-production is performed, without assuming R-parity conservation in decays, in the case that only one of the ...coupling constants λ or λ″ is non-negligible. No signal is found in data up to a centre-of-mass energy of 208 GeV. Limits on the production cross sections and on the masses of supersymmetric particles are derived.
We measure Bose-Einstein correlations between like-sign charged pion pairs in hadronic Z decays with the
l3 detector at
lep. The analysis is performed in three dimensions in the longitudinal ...center-of-mass system. The pion source is found to be elongated along the thrust axis with a ratio of transverse to longitudinal radius of 0.81±0.02
+0.03
−0.19.
The reaction e+e−→e+e−pp̄ is studied with the L3 detector at LEP. The analysis is based on data collected at e+e− center-of-mass energies from 183 GeV to 209 GeV, corresponding to an integrated ...luminosity of 667 pb−1. The γγ→pp̄ differential cross section is measured in the range of the two-photon center-of-mass energy from 2.1 to 4.5 GeV. The results are compared to the predictions of the three-quark and quark–diquark models.
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