Large impact parameter cut-off in the process e+e−→e+e−γ

In investigating the e⁺e^? → e⁺e^?γ process the radiation probability is oberved to be substantially less than that calculated in the standard QED. The effect is due to the fact that the characteristic impact parameters in the process are much greater than the transverse sizes of the colliding beams. The Compton scattering γ-spectrum of the synchrotron radiation by a colliding beam is measured.     

A search for excited electrons in the e+e− reactions up to the √s of 56 GeV

Excited electrons, e^1's, have been searched for by making use of the processes e⁺e⁻→e⁺e⁻γγ and eγ(e) (quasi-real Compton scattering). From the former process, we have obtained the lower limit for the mass of e^1', 27.9 GeV/c. A good agreement with QED is observed in the latter process, and new upper limits have been set for the coupling strength λ as a function of the mass of e¹.     

Accurate measurement of the energy dependence of the process e+ + e- → e±+e∓, in the s-range 1.44−9.0 GeV2

The analysis of 12827 e⁺ + e^- → e^± + e^-+ events observed in the s-range 1.44?9.0 GeV² allows measurement of the energy dependence of the cross-section for the most typical QED process, with ±2% accuracy. Within this limit the data follow QED, with first-order radiative corrections included.     

QCD and QED corrections to the longitudinal polarization asymmetry

The interplay between QED and QCD corrections to the longitudinal polarization asymmetry,A _LR, ine ⁺ e ^?, annihilation is studied. It is found that measurements with hadronic final states will be well suited for precision tests of the standard model. QCD corrections to the asymmetry are particularly small on top of theZ ⁰, with the leading terms induced by quark mass effects. The influence of initial state radiation inA _LR is essentially accounted for by a slight shift in beam energy. Initial/final state QED bremsstrahlung interference (QED boxes) is studied in detail and its influence onA _LR is found to be negligibly small, especially close to the top of theZ ⁰ peak. A comment on the importance of helicity nonconservation for polarized beams in the presence of photon emission is also included.     

An investigation of the processes e+e−→μ+μ−γ and e+e−→e+e−γ

The reactions e⁺e^?→μ⁺μ^?γ and e⁺e^?→e⁺e^?γ have been studied with the CELLO detector at the PETRA storage ring. Data have been collected from $\text{s}\text{=14}\text{GeV up to}\text{46.8}\text{GeV}$. In a Dalitz plot analysis of the data, good agreement is found with QED, except for the region Mx_μγe>0.8 where the probability that QED describes the high energy data is at the percent level.     

Production ofW-bosons in high energye + e − ande − p collisions

We study the processe ⁺ e ^?→W+hadrons from theZ ⁰-pole to the threshold region forW-pair production, keeping the widths of theZ ⁰ andW finite. Already slightly below threshold the cross section is strongly depressed. Also the total cross section at theZ ⁰-peak is very small. We present a simple model to account for this. We also give exact results to lowest order for the weak Compton processese ⁺ e ^?→e ⁺ W ^? v _e ande ^? p→pW ^? v _e and compare them with results obtained with the equivalent photon approximation.     

Acoplanar (e+e−) pairs and radiative corrections

Further proof is given for the inadequacy of the peaking approximation in first-order radiative corrections, via the observation of 429 non-coplanar (e⁺e^?) events. The energy dependence of this effects is measured in the s-range 1.44 to 9.0 GeV², and represents another proof of the validity of QED.     

QED polarization asymmetries fore + e − scattering due to helicity flips

The polarization asymmetries for thee ⁺ e ^? scattering with polarized incoming and outgoing beams, which are proportional to the amplitudes? ₅ describing one helicity flip and? ₅ describing two helicity flips, have been calculated including their pure QED radiative corrections. These asymmetries are partly large and can be observed well at low energies.     

Distributions in the process e+e− → μ+μ−(γ)

Analytical expressions for a number of distributions in the process e⁺e^? → μ⁺μ^?(γ) are given. A procedure is outlined to simulate events for this reaction by using the analytical distributions. This method then numerically provides any other distribution and makes it possible to impose any experimental constraint to radiative correction calculations. Besides examples for pure QED situations, the corrections to R and to the thrust distribution for hadronic events are also discussed.     

Comparison of π±, K± and p,p production in the central rapidity region in hadron-hadron collisions and in e+e− annihilation

We compare the p_T dependence of pion, kaon and proton production cross sections in the central rapidity region in e⁺e⁻ annihilation events and in proton-proton collisions at ISR energies. We find similarities both in the p_T dependence of cross sections and in the particle composition as a function of p_T, in agreement with the hypothesis of a universal mechanism of particle production.     

QED corrections to the forward backward asymmetry with extraZ bosons fore + e −→f + f −

The complete standard model corrections together with the QED contributions from an additionalZ boson to the forward backward asymmetry of the reactione ⁺ e ^?→(ψ,Z, Z′, ...)→f ⁺ f ⁺ are calculated. They include soft photon exponentiation and a cut on the photon energy. Some numerical applications are considered forE ₆ generated extraZ bosons. Though being small at TRISTAN and LEP1 energies, the QED corrections due toZ′ exchange are very important near and above theZ′ peak.     

The three photon final state produced in e+e− collision at 3.6 GeV and at the ψ′

The three photon final state produced in e⁺e^? collisions at 3.6 GeV and at the mass of the ψ′ resonance has been measured using the nonmagnetic part of the double arm spectrometer DASP. A total of 31 events is observed outside the resonance region compared to 35.1 events predicted from QED. At the mass of the ψ′ 49 events are observed compared to 37.2 events expected from QED. Limits on radiative decays via intermediate states are given.     

Electron correlation effects in the momentum distribution of highly oriented pyrolytic graphite

Absolute Compton profiles of highly oriented pyrolytic graphite have been determined using ¹⁹⁸Au 412 keV gamma radiation. The anisotropy in the electron momentum density between Compton profiles measured parallel to the c-axis and averaged over the basal plane have been compared with a recent pseudopotential calculation of Chou et al. Excellent agreement is found over the entire momentum range studied. Differences between absolute Compton profiles J_theory(p_z − J_exp (p_z) vindicates a correlation correction to take account of the electron-electron Coulomb interactions.     

Determination of the electronic branching ratio of the ϒ(9.46) and an upper limit for its total width

We have measured the reaction e⁺e^? → e⁺e^? at the ? Using athe excess of electron pairs over the QED expectation we obtain an electronic branching ratio of B_ee = (5.1 ± 3.0) %. Combining this with publishe values of the muonic branching ratio B_μμ we conclude that the ? is a narrow state with a total width < 180 keV at 95% C.L.     

Heavy quark production at a photon linear collider

Heavy quark production at future Compton colliders is investigated. The impact of polarization has been studied. Perturbative QCD corrections to the effective cross section are calculated and found to be at the level of 40% for ae ⁺ e ^? collider of 500 GeV and a top quark mass of 150 GeV. The η _t resonance structure is incorporated.     

Resonant mechanism of axion photoproduction in a magnetized electron gas

It was shown that the contribution of diagrams with electron-positron vacuum excitation in a strong magnetic field B ? B ₀ = m ²/e = 4.41 × 10¹³ G in the Compton mechanism of axion production γe → ae at temperatures on the order of the axion mass exceeds the contribution of the “simple” Compton diagram and the contribution of the neutrino production γe → (ν\(\bar \nu \))e to the radiation power by many orders of magnitude. The conclusion is made on the probable axionic nature of the cold hidden mass of the Universe.     

Deep inelastic Compton scattering and large-p T pion photoproduction in QCD hard collision model

Inclusive photon(pion) production at large-p _T in γp collisions is studied in the framework of QCD perturbation theory, taking into account the effects due to parton transverse momenta. The contributions from various components of photons are equally important at relatively smallp _T (e.g.,p _T?4 Ge V/c at \(\sqrt s = 17GeV\) ). At largep _T, however, the contributions from the subprocesses with direct photon coupling are most important; quark Compton scattering is the dominant subprocess in inelastic Compton scattering.     

Influence of the transverse beam sizes on theep→epγ cross section at the HERA and a FUTURE CERN electron-proton collider

In the processep→epγ, proposed for luminosity measurements at HERA, impact parameters occur which are larger than the transverse beam sizes in theep-colliders of HERA and a CERN option (LHC+LEP). This decreases the number of observed photons compared to the standard QED calculation. The difference is larger than 10% at photon energiesE _γ<0.4E _e for the CERN option andE _γ<0.01E _e for HERA.     

Optimizing Higgs factories by modifying the recoil mass

It is difficult to measure the WW-fusion Higgs production process(e~+e~-→νh)at a lepton collider with a center of mass energy of 240-250 Ge V due to its small rate and the large background from the Higgsstrahlung process with an invisible Z(e~+e~-→h Z,Z→ν).We construct a modified recoil mass variable,m~p_(recoil),defined using only the 3-momentum of the reconstructed Higgs particle,and show that it can separate the WW-fusion and Higgsstrahlung events better than the original recoil mass variable m_(recoil).Consequently,the m~p_(recoil)variable can be used to improve the overall precisions of the extracted Higgs couplings,in both the conventional framework and the effective-field-theory framework.We also explore the application of the m~p_(recoil)variable in the inclusive cross section measurements of the Higgsstrahlung process,while a quantitive analysis is left for future studies.     

Indication of an onset of hard-like effects in K+p, π+p and pp collisions at 250 GeV/c: EHS/NA22 Collaboration Aachen-Antwerp/Brussel-Berlin (Zeuthen)-Helsinki-Cracow-Moscow-Nijmegen-Rio de Janeiro- Serpukhov-Warsaw-Yerevan

Similarly as in lepton-hadron scattering, but less pronounced than in e⁺e⁻ annihilation at comparable energies, we observe a rise of the “sea-gull” wings with CMS energy. The large average transverse momenta around Feynman |x_F|=0.4 are mainly due to high multiplicity events, for which also a tail develops in the multiplicity distribution. Neither of these effects can be reproduced by currently used low-p_T fragmentation models.