HEPData Search

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A measurement of the Z0 invisible width by single photon counting.

The OPAL collaboration Akrawy, M.Z. ; Alexander, G. ; Allison, John ; et al.

Z.Phys.C 50 (1991) 373-384, 1991.

Inspire Record 302586 DOI 10.17182/hepdata.14980

The OPAL detector at LEP is used to measure the branching ratio of theZ0 into invisible particles by measuring the cross section of single photon events ine+e− collisions at centre-of-mass energies near theZ0 resonance. In a data sample of 5.3 pb−1, we observe 73 events with single photons depositing more than 1.5 GeV in the electromagnetic calorimeter, with an expected background of 8±2 events not associated with invisibleZ0 decay. With this data we determine theZ0 invisible width to be 0.50±0.07±0.03 GeV, where the first error is statistical and the second systematic. This corresponds to 3.0±0.4±0.2 light neutrino generations in the Standard Model.

1 data table

Table 1

No description provided.

Inclusive jet cross-section and a search for quark compositeness at the CERN $\bar{p} p$ collider

The UA2 collaboration Alitti, J. ; Ansari, R. ; Autiero, D. ; et al.

Phys.Lett.B 257 (1991) 232-240, 1991.

Inspire Record 302588 DOI 10.17182/hepdata.29493

The inclusive jet cross-section has been measured at the CERN p p Collider ( s = 630 GeV ) as a function of the jet transverse momentum ( p T ) and pseudorapidity ( η ) for p T values up to 180 GeV and for−2< η <2. The results are consistent with leading order QCD calculations, and a lower limit Λ c >825 GeV (95% CL ) is set on the quark compositeness scale Λ c .

2 data tables

Table 1

No description provided.

Table 2

No description provided.

Measurement of the cross-sections of the reactions e+ e- ---> gamma gamma and e+ e- ---> gamma gamma gamma at LEP

The OPAL collaboration Akwawy, M.Z. ; Alexander, G. ; Allison, J. ; et al.

Phys.Lett.B 257 (1991) 531-540, 1991.

Inspire Record 302587 DOI 10.17182/hepdata.29464

The cross section of the pure QED process e + e − → γγ has been measured using data accumulated during the 1989 and 1990 scans of the Z 0 resonance at LEP. Both the energy dependence and the angular distribution are in good agreement with the QED prediction. Upper limits on the branching ratios of Z 0 → γγ , Z 0 → π 0 γ and Z 0 → ηγ have been set at 1.4×10 −4 , 1.4×10 −4 and 2.0×10 −4 respectively. Lower limits on the cutoff parameters of the modified electron propagator have been found to be Λ + > 117 GeV and Λ − > 110 GeV. The reaction e + e − → γγγ has also been studied and was found to be consistent with the QED prediction. An upper limit on the branching ratio of Z 0 → γγγ has been set at 6.6 × 10 −5 . All the limits are given at 95% confidence level.

3 data tables

Table 1

No description provided.

Table 2

No description provided.

Table 3

No description provided.

Measurement of alpha-s from the structure of particle clusters produced in hadronic Z decays

The ALEPH collaboration Decamp, D. ; Deschizeaux, B. ; Goy, C. ; et al.

Phys.Lett.B 257 (1991) 479-491, 1991.

Inspire Record 302771 DOI 10.17182/hepdata.29466

Using 106 000 hadronic events obtained with the ALEPH detector at LEP at energies close to the Z resonance peak, the strong coupling constant α s is measured by an analysis of energy-energy correlations (EEC) and the global event shape variables thrust, C -parameter and oblateness. It is shown that the theoretical uncertainties can be significantly reduced if the final state particles are first combined in clusters using a minimum scaled invariant mass cut, Y cut , before these variables are computed. The combined result from all shape variables of pre-clustered events is α s ( M Z 2 = 0.117±0.005 for a renormalization scale μ= 1 2 M Z . For μ values between M Z and the b-quark mass, the result changes by −0.009 +0.006 .

2 data tables

Table 1

No description provided.

Table 2

Error contains both experimental and theoretical errors.

Subthreshold K+ production in heavy ion collisions

Julien, J. ; Lebrun, D. ; Mougeot, A. ; et al.

Phys.Lett.B 264 (1991) 269-273, 1991.

Inspire Record 304290 DOI 10.17182/hepdata.29376

The cross section for K + meson production in collisions of 36 Ar ions on a 48 Ti target has been measured at an incident energy of 92 MeV per nucleon. A description of the experimental set-up is given. Twelve events attributed to monoenergetic muons following the decay of stopped kaons have been identified. From these events, one infers a production cross section of 240 pb. Data are briefly discussed.

1 data table

Table 1

No description provided.