QED Prediction Research Articles

Observation of direct soft photon production in π−p interactions at 280 GeV/ c

The OMEGA spectrometer, equipped with a hydrogen target and two electromagnetic calorimeters, was used to investigate the production of soft gammas in hadronic collisions. The E γ and P T distributions of the measured γ's are compared with the corresponding distributions of γ's arising from hadronic decays and of γ's expected from QED inner bremsstrahlung. An excess of gammas by a factor of 7.9 ± 1.4 over the QED prediction is measured in the low energy (0.2< E γ <1.0 GeV) and low P T (< 10 MeV/ c) kinematic region, and confirms the original observation of a similar effect in a bubble chamber experiment.

Studies of e +e −→ γγ and γγγ reactions

We have measured the cross section for γγ production with the TOPAZ detector in the energy region √ s=50.0–61.4 GeV. The observed cross section for γγ production integrated over |cos θ| ⩽ 0.77 is 50.2±0.8±2.2 pb at 〈√ s〉=57.6 GeV and the ratio of this value to the QED prediction is 1.01±0.02±0.04. The angular distribution is in good agreement with the QED predictions, thereby setting limits on the compositeness scales, Λ L+R +=168 GeV, Λ L+R −=97 GeV, Λ L,R=141 GeV, Λ L,R −=81 GeV, and Λ L−R ±=68 GeV, at the 95% confidence level. The reaction e +e −→ γγγ was also studied and was found consistent with the QED prediction.

Observation of the decay mode KL0--> gamma gamma ee.

Results of a search for the decay mode {ital K}{sub {ital L}}{sup 0}{r arrow}{gamma}{gamma}{ital ee} ({ital K}{sub {ital L}}{sup 0}{r arrow}{gamma}{ital ee} with a hard internal bremsstrahlung) are reported. The measured branching ratio is (6.6{plus minus}3.2){times}10{sup {minus}7}, in agreement with the QED prediction of 5.8{times}10{sup {minus}7}. The infrared cutoff for both branching ratios is the requirement that both photons have an energy of at least 5 MeV in the center of mass.

The reaction e +e − → γγ(γ) at Z 0 energies

The total and differential cross-sections for the reaction e +e − → γγ( γ) are measured at centre of mass energies around 91 GeV using an integrated luminosity of 4.7 pb −1. The aggreement with QED prediction is good. Consequently there is no evidence for non-standard channels which would have the same experimental signature. The lower limits on the QED cuttoff parameters are Λ + > 113 GeV and Λ − > 95 GeV. An upper limit on the effective coupling between a possible excited electron and the gamma is derived. At 95% confidence level the branching ratios for Z 0 decay into π 0γ, ηψ and γγγ are below 1.5 × 10 −4, 2.8 × 10 −4 and 1.4 × 10 −4 respectively.

Study of the e+e− → μ+μ−γ reaction at center-of-mass energies between 54 and 64 GeV

Abstract The cross section and forward-backward muon charge asymmetry for the e+e−→μ+μ−γ reaction were measured to be σ=2.82±0.35 pb and A=−0.34±0.10 with the VENUS detector at TRISTAN at 〈√s〉=59.2GeV for an integrated luminosity of 53.5 pb−1. The measured cross section agrees with the theoretical prediction. The asymmetry result is consistent with the electroweak prediction but not with the QED prediction at the level of 2σ.

Measurement of the cross sections of the reactions e +e − → γγ and e +e − → γγγ at LEP

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.

A study of the reaction e +e −→ γγ at LEP

The pure QED reaction e +e −→ γγ has been studied at centre of mass energies around the mass of the Z 0 boson using data recorded by the OPAL detector at LEP. The results are in good agreement with the QED prediction. Lower limits on the cutoff parameters of the modified electron propagator are found to be Λ +>89 GeV and Λ. The lower limit on the mass of an excited electron is 82 GeV assuming the coupling constant λ=1. Upper limits on the branching ratios of Z 0→ γγ, Z 0→ π 0 γ and Z 0→ ηγ are set at 3.7×10 −4, 3.9×10 −4 and 5.8×10 −4 respectively. Two events from the reaction e +e −→ γγγ have been observed, consistent with the QED prediction. An upper limit on the branching ratio of Z 0→ γγγ is set at 2.8×10 −4. All the limits are given at 95% confidence level.

A measurement of muon pair production ine + e ? annihilation at centre of mass energies 35.0? $$\sqrt s $$ ?46.8 GeV

The reactione+e−→µ+µ− has been studied at centre of mass energies between 35.0 and 46.8 GeV using the TASSO detector at PETRA. We present measurements of the forward-backward charge asymmetry (Aμμ) and cross section σμμ for this reaction at three energies. At 35.0 GeV we obtain a cross section relative to the QED prediction ofRμμ=σμμ/σo=0.932±0.018±0.044 andAμμ=(−10.6−2.3+2.2±0.5)%. At 38.3 GeV we findRμμ=0.951±0.072−0.057+0.063 andAμμ=(+1.7−8.6+8.5±0.5)%. At 43.6 GeV we measureRμμ=0.921±0.037±0.055 andAμμ=(−17.6−4.3+4.4±0.5)%. Our results are in good agreement with the predictions of the standard model. Including previous TASSO data we present improved determinations of muonic electroweak parameters. We also report on lower limits of possible contributions from contact interactions.

Laser excitation of the muonium 1S-2S transition.

We present evidence for the excitation of the two-photon Doppler-free $1S\ensuremath{-}2S$ transition in muonium. Thermal muonium atoms were produced in vacuum by a 27.5-MeV/c pulsed positive-muon beam incident on a powdered Si${\mathrm{O}}_{2}$ target. Transitions were induced by the light from a frequency-doubled pulsed dye laser and were detected by photoionization of the $2S$ state. The $1S(F=1)\ensuremath{\rightarrow}2S(F=1)$ transition frequency is within 300 MHz of the QED prediction.

Measurement of the Positronium1S13−2S13Interval by Doppler-Free Two-Photon Spectroscopy

We have measured the $1^{3}S_{1}\ensuremath{-}2^{3}S_{1}$ interval in positronium (Ps) to be 1 233 607 185 \ifmmode\pm\else\textpm\fi{} 15 MHz, in agreement to within 1% of the ${\ensuremath{\alpha}}^{3}{R}_{\ensuremath{\infty}}$ QED prediction. The quoted 12-ppb uncertainty has equal contributions from the measurement of the Ps resonance relative to a ${\mathrm{Te}}_{2}$ absorption line and the calibration of the ${\mathrm{Te}}_{2}$ line relative to the deuterium $2{S}_{\frac{1}{2}}\ensuremath{-}4{P}_{\frac{3}{2}}$ Balmer line.

Measurement of the reactione + e −→μ + μ − for $$14 \leqq \sqrt S \leqq 36.4$$ GeV

The reaction (e+e−→μ+μ−) has been measured between\(\sqrt S = 14.0\) and\(\sqrt S = 36.4\). The total cross section result is in good agreement with the QED prediction and the following Λ values have been obtained:Λ+=186 GeV,Λ−=101 GeV. The angular distribution at high energy (\(\left( {\left. {\left\langle {\sqrt S } \right.} \right\rangle = 34.2 GeV} \right)\)) shows a fitted charge asymmetry of −0.064±0.064 in agreement with theW-S model prediction of −0.092, corresponding to an axial coupling parametera2=4ga2=0.69±0.69.