A sample of 25000 Z 0 → τ + τ − events collected by the DELPHI experiment at LEP in 1991 and 1992 is used to measure the leptonic branching fractions of the τ lepton. The results are B(τ → eν ν ) = (17.51 ± 0.39) % and B(τ → μν ν ) = (17.02 ± 0.31) %. The ratio of the muon and electron couplings to the weak charged current is measured to be g μ g e = 1.000 ± 0.013 , satisfying e-μ universality. The leptonic branching fraction corrected to the value for a massless lepton, assuming e-μ universality, is found to be B(τ → lν ν ) = (17.50 ± 0.25) %.
Axis error includes +- 0.23/0.23 contribution (Data statistics).
Axis error includes +- 0.19/0.19 contribution (Data statistics).
Combined from the two branching fractions above. E-MU universality assumed.
An absolute measurement of π0 photoproduction on the proton has been carried out in the threshold region (from 144.7 to 173 MeV) by use of tagged annihilation photons. The measured cross sections, differential in the recoiling-proton energy, are used to perform a multipole analysis which gives a value & &, in disagreement with low-energy-theorem predictions. Total cross sections and coefficients of the π0 angular distribution are presented.
No description provided.
A measurement of the cross section for e + e - → hadrons using 11 000 hadronic decays of the Z boson at ten different center-of-mass energies is presented. A three-parameter fit gives the following values for the Z mass M z , the total width Γ z , the product of the electronic and hadronic partial widths Γ e Γ h , and the unfolded pole cross section σ 0 : M Z =91.171±0.030(stat)±0.030 (beam) GeV, Γ Z =2.511±0.065 GeV, Γ e Γ h =0.148±0.006 (stat.)±0.004 (syst.) GeV 2 , σ 0 =41.6±0.7(stat.)±1.1 (syst.) nb,
No description provided.
We have measured the cross section for e + e − →hadrons over the center of mass energy range of the Z 0 peak, from 88.22 to 95.03 GeV. We determine the Z 0 mass M z =91.164±0.013 (experiment) ±0.030 (LEP) GeV. Within the framework of the standard model we determine the invisible width, Γ invisible =0.502±0.018 GeV, and the number of light neutrino species, N ν =3.01±0.11. We exclude the existence of a supersymmetric scalar neutrino having a mass less than 31.4 GeV, at the 95% confidence level. We performed a model independent combined fit to the e + e − →hadrons and e + e − → μ + μ − data to determine total width, leptonic width and hadronic width of the Z 0 .
Cross sections from 1990 data. Additional systematic error 1.5 pct.
Cross sections from 1989 data. This data has been rescaled by 0.96 from original publication PL B237 (90) 136. Additional systematic error 2.0 pct.
The two-photon production of the η meson has been observed, and a value has been determined for the two-photon η decay width by a measurement of the cross section σ(e+e−→e+e−η) where η→γγ. The measurement was made with the TPC/Two-Gamma facility at the SLAC e+e− collider PEP, with an accumulated data sample of 64.5 pb−1. The η→γγ events were both triggered and detected by the pole-tip calorimeter. The measured two-photon η decay width is Γη→γγ=0.64±0.14 (statistical) ±0.13 (systematic) keV, in agreement with earlier similarly determined values.
No description provided.
A search for excited states of the standard model fermions was performed using the ZEUS detector at the HERA electron-proton collider, operating at a centre of mass energy of 296 GeV. In a sample corresponding to an integrated luminosity of 0.55 pb−1, no evidence was found for any resonant state decaying into final states composed of a fermion and a gauge boson. Limits on the coupling strength times branching ratio of excited fermions are presented for masses between 50 GeV and 250 GeV, extending previous search regions significantly.
The cross sections times branching ratio.
We have measured the inclusive cross-section as a function of missing energy, due to the production of neutrinos or new weakly interacting neutral particles in 450 GeV/c proton-nucleus collisions, using calorimetric measurements of visible event energy. Upper limits are placed on the production of new particles as a function of their energy. These upper limits are typically an order
Differential single diffraction cross section.
Differential single diffraction cross section.
Differential single diffraction cross section.
The e+e- -> p anti-p cross section is determined over a range of p anti-p masses, from threshold to 4.5 GeV/c^2, by studying the e+e- -> p anti-p gamma process. The data set corresponds to an integrated luminosity of 232 fb^-1, collected with the BABAR detector at the PEP-II storage ring, at an e+e- center-of-mass energy of 10.6 GeV. The mass dependence of the ratio of electric and magnetic form factors, |G_E/G_M|, is measured for p anti-p masses below 3 GeV/c^2: its value is found to be significantly larger than 1 for masses up to 2.2 GeV/c^2. We also measure J/psi -> p anti-p and psi(2S) -> p anti-p branching fractions and set an upper limit on Y(4260) -> p anti-p production and decay.
The cross section and effective form factor for E+ E- --> PBAR P.
The cross section and effective form factor for E+ E- --> PBAR P.
Nearly 40000 neutrino and antineutrino interactions in BEBC are compared to measure the differences between neon and deuterium in the quark and antiquark distributions and in the nucleon structure functions. The ratio of Ne to D cross sections indicates some decrease betweenx∼0.2 andx∼0.6. They distributions show there is no significant increase in the neon sea, but prefer a small decrease. Taken altogether, thex andy distributions and the measured total cross-sections indicate some change in the shape of the valence distributions. No significant dependence onA is observed for either the shape of the sea or the ratio of longitudinal to transverse cross-sections.
No description provided.
No description provided.
No description provided.
None
292+-7 MUB - CORRECTED VALUE FOR FIRST REACTION (SLOW PROTONS). M(P 4PI) <= 3.5 GEV FOR REACTIONS WITH FOUR PIONS.
No description provided.
No description provided.
Forum