Tests of QED at LEP energies using e+ e- --> gamma gamma (gamma) and e+ e- --> lepton+ lepton- gamma gamma

The L3 collaboration Acciarri, M. ; Adam, A. ; Adriani, O. ; et al.
Phys.Lett.B 353 (1995) 136-144, 1995.
Inspire Record 394354 DOI 10.17182/hepdata.47938

Total and differential cross sections for the process e + e − → γγ ( γ ), and the total cross section for the process e + e − → γγγ , are measured at energies around 91 GeV using the data collected with the L3 detector from 1991 to 1993. We set lower limits, at 95% CL, on a contact interaction energy scale parameter Λ > 602 GeV, on the mass of an excited electron m e ∗ >146 GeV and on the QED cut-off parameters Λ + > 149 GeV and Λ _ > 143 GeV. Upper limits are also set o branching fractions of Z decaying into γγ , π ° and ηγ of 5.2 × 10 −5 , 5.2 × 10 −5 and 7.6 × 10 −5 respectively. The reactions e + e − → ℓ + ℓ − nγ (ℓ = e , μ , τ ) are studied using the data collected from 1990 to 1994. The data are consistent with the QED expectations.

3 data tables

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Determination of the number of light neutrino species

The L3 collaboration Adriani, O. ; Aguilar-Benitez, M. ; Ahlen, S. ; et al.
Phys.Lett.B 292 (1992) 463-471, 1992.
Inspire Record 339090 DOI 10.17182/hepdata.29030

We have measured the cross-section of the production of single photon events in e + e − collisions near the Z 0 resonance. For an integrated luminosity of 9.6 pb −1 , we have observed 202 single photon candidates with energy between 0.9 and 3.5 GeV in the polar angular region between 45° and 135°. Assuming that the only stable weakly interacting particles are light neutrinos with standard model couplings, we determine the number of light neutrino species to be N v = 3.14 ± 0.24 (stat.)±0.12 (syst.). This corresponds to an invisible Z 0 width of Γ inv = 524 ± 40 ± 20 MeV.

1 data table

Corrected cross section.


Measurement of the e+ e- --> b anti-b and e+ e- --> c anti-c forward backward asymmetries at the Z0 resonance

The L3 collaboration Adriani, O. ; Aguilar-Benitez, M. ; Ahlen, S. ; et al.
Phys.Lett.B 292 (1992) 454-462, 1992.
Inspire Record 339089 DOI 10.17182/hepdata.29017

We have measured the forward-backward asymmetry in e + e − → b b and e + e − → c c processes using hadronic events containing muons or electrons. The data sample corresponds to 4100000 hadronic decays of the Z 0 . From a fit to the single lepton and dilepton p and p T spectra, we determine A b b =0.086±0.015±0.007 and A c c =0.083±0.038±0.027 at the effective center-of-mass energy √ s =91.24 GeV. These measurements yield a value of the electroweak mixing angle sin 2 θ w =0.2336±0.0029 .

4 data tables

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A Test of quantum electrodynamics in the reaction e+ e- ---> gamma gamma (gamma)

The L3 collaboration Adriani, O. ; Aguilar-Benitez, M. ; Ahlen, S. ; et al.
Phys.Lett.B 288 (1992) 404-411, 1992.
Inspire Record 336900 DOI 10.17182/hepdata.29221

We have measured the total and differential cross sections of the reaction e + e − → γγ ( γ ) at center-of-mass energies around 91 GeV, with an integrated luminosity of 14.2 pb −1 . The results are in good agreement with QED predictions. We set lower limits, at 95% confidence level, on the QED cutoff parameters of Λ + > 139 GeV, Λ − > 108 GeV and on the mass of an excited electron of m e∗ > 127 GeV . We searched for Z 0 rare decays with photonic signitures in the final state. Upper limits, at 95% confidence level, for branching ratio of Z 0 decaying into π 0 γ / γγ , νγ and γγγ are 1.2 × 10 −4 , 1.8 × 10 −4 , 3.3 × 10 −5 respectively.

3 data tables

Measured cross section for the 1991 data.

Measured cross section for the 1990 data.

Measured differential cross sections of combined 1990 and 1991 data.


Measurement of inclusive eta production in hadronic decays of the Z0

The L3 collaboration Adriani, O. ; Aguilar-Benitez, M. ; Ahlen, S. ; et al.
Phys.Lett.B 286 (1992) 403-412, 1992.
Inspire Record 336180 DOI 10.17182/hepdata.29161

We present a study of the inclusive η production based on 300 000 hadronic Z 0 decays. The measured inclusive momentum distribution can be reproduced by parton shower Monte Carlo programs and also by an analytical QCD calculation. Comparing our results with low energy e + e − data, we find that QCD describes both the shape and the energy evolution of the η spectrum. The comparison of η production rates in quark- and gluon-enriched jet samples does not show statistically significant evidence for more abundant production of η mesons in gluon fragmentation.

2 data tables

Differential cross section for inclusive eta production, normalized to the total hadronic cross section.

Differential cross section for inclusive eta production, normalized to the total hadronic cross section.


Determination of alpha-s from hadronic event shapes measured on the Z0 resonance

The L3 collaboration Adrian, O. ; Aguilar-Benitez, M. ; Ahlen, S. ; et al.
Phys.Lett.B 284 (1992) 471-481, 1992.
Inspire Record 334951 DOI 10.17182/hepdata.29157

We present a study of the global event shape variables thrust and heavy jet mass, of energy-energy correlations and of jet multiplicities based on 250 000 hadronic Z 0 decays. The data are compared to new QCD calculations including resummation of leading and next-to-leading logarithms to all orders. We determine the strong coupling constant α s (91.2 GeV) = 0.125±0.003 (exp) ± 0.008 (theor). The first error is the experimental uncertainty. The second error is due to hadronization uncertainties and approximations in the calculations of the higher order corrections.

3 data tables

Measured EEC distribution corrected for detector effects and photon radiation. Errors are combined statistical and systematic uncertainties.

Measured average jet multiplicities for the K_PT algorithm. All numbers are corrected for detector effects and photon radiation. Errors are combined statistical and systematic uncertainties.

Value of strong coupling constant, alpha_s, determined from the data. First error is experimental, the second is theoretical.


A Direct determination of the number of light neutrino families from e+ e- ---> neutrino anti-neutrino gamma at LEP

The L3 collaboration Adeva, B. ; Adriani, O. ; Aguilar-Benitez, M. ; et al.
Phys.Lett.B 275 (1992) 209-221, 1992.
Inspire Record 324176 DOI 10.17182/hepdata.29260

The L3 detector at LEP has been used to determine the number of light neutrino families by measuring the cross section of single photon even in e + e − collisions at energies near the Z 0 resonance. We have observed 61 single photon candidates with more than 1.5 GeV of deposited energy in the barrel electromagnetic calorimeter, for a total integrated luminosity of 3.0 pb −1 . From a likelihood fir to the single photon cross sections, we determin N ν =3.24 ± 0.46 ( statistical ) ±0.22 ( systematic ).

1 data table

Corrected single photon cross sections. Errors represent 68 pct CL intervals and take into account the background fluctuations.


Measurement of the strong coupling constant alpha-s for bottom quarks at the Z0 resonance

The L3 collaboration Adeva, B. ; Adriani, O. ; Aguilar-Benitez, M. ; et al.
Phys.Lett.B 271 (1991) 461-467, 1991.
Inspire Record 318981 DOI 10.17182/hepdata.38288

We have measured the ratio of the strong coupling constants α s for bottom quarks and light quarks at the Z 0 resonance, in order to test the flavour independence of the strong interaction. The coupling strength α s has been determined from the fraction of events with three jets, measured for a sample of all hardronic events, and for inclusive muon and electron events. The b purity is evaluated to be 22% for the first data set and 87% for the inclusive lepton sample. We find α s ( b ) α s ( udsc ) =1.00± 0.05 ( stat. )±0.06 ( syst. ) .

1 data table

No description provided.


Decay properties of tau leptons measured at the Z0 resonance

The L3 collaboration Adeva, B. ; Adriani, O. ; Aguilar-Benitez, M. ; et al.
Phys.Lett.B 265 (1991) 451-461, 1991.
Inspire Record 318230 DOI 10.17182/hepdata.40873

From 2540 Z 0 → τ + τ − events, we determine the inclusive decay branching fractions of the τ -lepton into one and three charged particles to be 0.856 ± 0.006 (stat.) ± 0.003 (syst.) and 0.144 ± 0.006 (stat.) ± 0.003 (syst.), respectively. The leptonic branching fractions are measured to be 0.175 ± 0.008 (stat.) ± 0.005 (syst.) for τ → μν μ ντ and 0.177 ± 0.007 (stat.) ± 0.006 (syst.) for τ → eν e ν τ . We determined the τ lifetime both from three-prong decays using the decay length and from one-prong decays using the impact parameter. The results from the two independent methods agree and yield a combined value of [0.309 ± 0.023 (stat.) ± 0.030 (syst.)] × 10 −12 s.

1 data table

ALPHAS extracted from the ratio of the branching fractions.


A Test of QCD based on three jet events from Z0 decays

The L3 collaboration Adeva, B. ; Adriani, O. ; Aguilar-Benitez, M. ; et al.
Phys.Lett.B 263 (1991) 551-562, 1991.
Inspire Record 315954 DOI 10.17182/hepdata.38291

We present a study of 43 000 3-jet events from Z 0 boson decays. Both the measured jet energy distributions and the event orientation are reproduced by second order QCD. An alternative model with scalar gluons fails to describe the data.

1 data table

Jets are ordered according their energy: E1 > E2 > E3.