Results are presented on the exclusive production of four-prong final states in photon-photon collisions from the TPC/Two-Gamma detector at the SLAC e+e− storage ring PEP. Measurement of dE/dx and momentum in the time-projection chamber (TPC) provides identification of the final states 2π+2π−, K+K−π+π−, and 2K+2K−. For two quasireal incident photons, both the 2π+2π− and K+K−π+π− cross sections show a steep rise from threshold to a peak value, followed by a decrease at higher mass. Cross sections for the production of the final states ρ0ρ0, ρ0π+π−, and φπ+π− are presented, together with upper limits for φρ0, φφ, and K*0K¯ *0. The ρ0ρ0 contribution dominates the four-pion cross section at low masses, but falls to nearly zero above 2 GeV. Such behavior is inconsistent with expectations from vector dominance but can be accommodated by four-quark resonance models or by t-channel factorization. Angular distributions for the part of the data dominated by ρ0ρ0 final states are consistent with the production of JP=2+ or 0+ resonances but also with isotropic (nonresonant) production. When one of the virtual photons has mass (mγ2=-Q2≠0), the four-pion cross section is still dominated by ρ0ρ0 at low final-state masses Wγγ and by 2π+2π− at higher mass. Further, the dependence of the cross section on Q2 becomes increasingly flat as Wγγ increases.
UNTAGGED DATA.
TAGGED DATA, RESULTS OBTAINED USING TRANSVERSE-TRANSVERSE LUMINOSITY ONLY. DATA FOR Q2=0 ARE FROM UNTAGGED SAMPLE, ERRORS DUE TO RELATIVE NORMALISATION OF THESE SAMPLES IS INCLUDED INTO ERRORS QUOTED.
UNTAGGED DATA.
We report on measurements of the triple-gauge-boson couplings of the W boson in e+e- collisions with the L3 detector at LEP. W-pair, single-W and single-photon events are analysed in a data sample corresponding to a total luminosity of 76.7 pb^{-1} collected at centre-of-mass energies between 161 GeV and 183 GeV. CP-conserving as well as both C- and P-conserving triple-gauge-boson couplings are determined. The results, in good agreement with the Standard-Model expectations, confirm the existence of the self coupling among the electroweak gauge bosons and constrain its structure.
The errors are statistical. Two-parameter fit.
The errors are statistical. Two-parameter fit.
The errors are statistical. Two-parameter fit.
First results on the measurement of the elastic and total cross section at the CERN pp̄ Collider are presented. Combining the measurement of elastic scattering at low momentum transfer with the rate of inelastic interactions, a value of the total cross section of 66 mb with a 10% statistical error was obtained.
STATISTICAL ERROR ONLY.
Proton-antiproton elastic scattering at CM energy 540 GeV has been studied in the t -range 0.04 < − t < 0.45 GeV 2 . The data are well fitted by the form exp ( bt ) with b = 17.1 ± 1.0 GeV −2 for | t | = 0.04 − 0.18 GeV su 2 and b = 13.7 ± 0.2 ± 0.2 GeV −2 for | t | = 0.21−0.45 GeV 2 . A luminosity measurement combined with the optical theorem gives σ tot = 67.6 ± 5.9 ± 2.7 mb and σ e1 / σ tot = 0.209 ± 0.018 ± 0.008.
No description provided.
No description provided.
ELASTIC RATIO ASSUMES RHO=0.
Results on charged particle production in pp̄ collision at s 1 2 = 540 GeV are presented. The data were obtained at the CERN pp̄ collider using the UA1 detector, operated without magnetic field. The central particle density is 3.3 + - 0.2 per unit o pseudo-rapidity for non-diffractive events. KNO scaling of the multiplicity distributions withresults from ISR energies is observed.
Pseudorapidity density distribution for all charged multiplicities corrected for acceptance and backgrounds by excluding NSD events. Data have been read from the plot.
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We have measured transverse momentum spectra up to 10 GeV/ c for charged particles produced centrally in proton-antiproton collisions at 540 GeV in the centre of mass at the CERN collider. Our results are compared with data at ISR energies and with the predictions of a QCD model. The charged particle spectrum shows a clear dependence on charged track multiplicity.
No description provided.
No description provided.
We present measurements of the αα elastic scattering differential cross section at √ s = 126 GeV in the range 0.05 ⩽ ‖ t ‖
ERRORS ARE STATISTICAL ONLY.
EXPONENTIAL FIT TO CROSS SECTION BELOW T = 0.075 GEV**2.
OPTICAL THEOREM CALCULATION OF THE TOTAL CROSS SECTION ASSUMING RHO IS ZERO.
We present results on dijet production via hard color-singlet exchange in proton-antiproton collisions at root-s = 630 GeV and 1800 GeV using the DZero detector. The fraction of dijet events produced via color-singlet exchange is measured as a function of jet transverse energy, separation in pseudorapidity between the two highest transverse energy jets, and proton-antiproton center-of-mass energy. The results are consistent with a color-singlet fraction that increases with an increasing fraction of quark-initiated processes and inconsistent with two-gluon models for the hard color-singlet.
Colour-singlet fraction at 1.8 TeV.
Ratio of colour-singlet fractions between 630 and 1800 GeV.
The first measurement of the neutron form factor in the time-like region has been performed by the FENICE experiment at the ADONE e + e − storage ring. Results at q 2 = 4.0 and 4.4 (GeV/ c ) 2 , together with a new measurement of the proton form factor are presented here.
Neutron form factor and cross section.
Preliminary analysis of proton form factor and cross section.
The large sample of W→eν events collected by the UA2 experiment at the CERN pp̄ collider between 1988 and 1990 has been used to determine the strong coupling constant α s . From a measurement of the ratio of the production rate of W events with one jet to that with no jets, α s has been extracted to second order in the MS ̄ scheme: α s (M 2 w )=0.123±0.0.18( stat .)±0.017 ( syst .) .
ALP_S extracted to second order in the MSbar scheme.
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