We have studied the structure of hadronic events with a hard, isolated photon in the final state (e
+e
− → Z → hadrons + γ) in the 3.6 million hadronic events collected with the L3 detector at ...centre-of-mass energies around 91 GeV. The centre-of-mass energy of the hadronic system is in the range 30 GeV to 86 GeV. Event shape variables have been measured at these reduced centre-of-mass energies and have been compared with the predictions of different QCD Monte Carlo programs. The event shape variables and the energy dependence of their mean values are well reproduced by QCD models. We fit distributions of several global event shape variables to resummed
O
(α
s
2) calculations to determine the strong coupling constant
α
s over a wide range of energies. We find that the strong coupling constant
α
s decreases with increasing energy, as expected from QCD.
We report measurements of the inclusive production of heavy quarkonium states in Z decays based on the analysis of 3.6 million hadronic events collected by the L3 detector at LEP. The measurement of ...inclusive J production and an improved 95% confidence level upper limit on
ϒ production are presented. In addition, two independent measurements of the ratio,
f
p, of prompt J mesons to those from B decay are made using two different isolation cuts to separate prompt J mesons from J mesons produced in the decays of b hadrons. The results are:
Br(
Z→
J+
X)=(3.21±0.21
(stat.)
+0.19
−0.28
(sys.))×10
−3
, Br(Z→
ϒ(1S)+
X)<4.4×10
−5,
f
p
=(7.1±2.1
(stat.)
±1.2
(sys.)
+1.5
−0.8
(theo.))×10
−2
.
A search for the lightest neutral CP-even and neutral CP-odd Higgs bosons of the Minimal Supersymmetric Standard Model is performed using 216.6 pb-1 of data collected with the L3 detector at LEP at ...centre-of-mass energies between 203 and 209 GeV. No indication of a signal is found. Including our results from lower centre-of-mass energies, lower limits on the Higgs boson masses are set as a function of tan(beta) for several scenarios. For tan(beta) greater than 0.7 they are mh 84.5 GeV and mA 86.3 GeV at 95% confidence level.
Production of single W bosons at LEP Alcaraz, J; Alverson, G; Ambrosi, G ...
Physics letters. B,
06/1997, Letnik:
403, Številka:
1
Journal Article
Recenzirano
Odprti dostop
We report on the observation of single W boson production in a data sample collected by the L3 detector at LEP2. The signal consists of large missing energy final states with a single energetic ...lepton or two hadronic jets. The cross-section is measured to be 0.61
−0.33
+0.43 ± 0.05 pb at the centre of mass energy
s
= 172
GeV
, consistent with the Standard Model expectation. From this measurement the following limits on the anomalo γWW gauge couplingsare derived at 95% CL: −3.6 <
Δκ
γ
< 1.5 and −3.6 <
λ
γ
< 3.6.
The cross section of the process e^+ e^- -> Z \gamma\gamma -> qq~ \gamma \gamma is measured with 215 pb^-1 of data collected with the L3 detector during the final LEP run at centre-of-mass energies ...around 205 GeV and 207 GeV. No deviation from the Standard Model expectation is observed. The full data sample of 713 pb^-1, collected above the Z resonance, is used to constrain the coefficients of anomalous quartic gauge boson couplings to: -0.02 GeV^-2 a_0/\Lambda^2 0.03 GeV^-2 and -0.07 GeV^-2 a_c/\Lambda^2 0.05 GeV^-2, at 95% confidence level.
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