Hadron production from photon-photon interactions in the CM energy range from 1 to 5 GeV

We present the first data on photon-photon annihilation into hadrons for CM energies > 1 GeV obtained with the detector PLUTO at the e⁺e^? storage ring PETRA. Cross sections are extracted using an inelastic eγ scattering formalism. The results are compared to expectations from Regge-like models.     

The total hadronic cross section for e+e− annihilation between 3.1 and 4.8 GeV center of mass energy

Using the solenoidal magnetic detector PLUTO, we have measured the total cross section for e⁺e^? annihilation into hadrons. Results are presented for center of mass energies between 3.6 and 4.8 GeV, and in the regions of the $\text{J}\text{ψ}$(3.1) and ψ(3.7) resonances. We also present results for the 2 prong cross section in the energy range 3.6 to 4.8 GeV.     

Measurement of the branching ratios for the decays J/ψ(3.1) → fω and J/ψ(3.1) → Bπ

Decays of the J/ψ (3.1) resonance into final states with four charged and one neutral pion have been investigated. We measured the branching ratios J/ψ (3.1) → fω/all = 0.40 ± 0.14)% and J/ψ (3.1) → (B⁺π^? + B^?π⁺)/all = (0.28 ± 0.07)%.     

The hadronic cross section of electron-positron annihilation at 9.5 GeV and the ϒ and ϒ′ resonance parameters

The reaction e⁺e^?→ hadrons has been measured in the ? and ?′ region using the DASP detector at the DESY storage ring DORIS. The following final results are obtained: R_had(9.5 GeV)=3.73±0.16±0.28, Γ_ee(?)=(1.23 ± 0.08 ± 0.12) keV, B_μμ(?)=(3.2±1.3±0.3)%, $\text{Γ}{}_{\mathrm{<mtext>ee</mtext>}}\text{Γ}{}_{\mathrm{<mtext>had</mtext>}}\text{Γ}{}_{\mathrm{<mtext>tot</mtext>}}\text{(?′)=(0.55±0.11 ±0.06)}\text{keV}$, and M(?′)?M(?)=(556 ±10) MeV.     

Measurement of the J/ψ radiative decay into f0(1270)γ

The J/ψ decay modes f⁰(1270)γ and ρπ have been studied in e⁺e^? collision at 3.1 GeV center of mass energy leading to the π⁺π^?γ and π⁺π^?π⁰ final states. The f⁰γ decay branching ratio is measured to be (0.20 ± 0.07) × 10^?2, a value comparable to the J/ψ radiative decay rates into the ηγ and η′γ channels. The J/ψ decay branching ratio into ?π is measured to be (1.6 ± 0.4) × 10^?2.     

Observation of antideuteron production in electron-positron annihilation at 10 GeV center of mass energy

The production of antideuterons has been observed in electron-positron annihilations at center-of-mass energies around 10 GeV. Antideuterons have been identified unambiguously by their energy loss in the drift chamber, their time-of-flight and the pattern of their energy deposition in the shower counters of the ARGUS detector. The production rate in the momentum range (0.6?1.8) GeV/c is (1.6_?0.7^+1.0) × 10^?5 per hadronic event.     

Tests of quantum chromodynamics in the decay of the τ-lepton and in electron positron annihilation into hadrons

We present a method to derive upper and lower bounds for a large class of quantities measurable ine ⁺ e ^? annihilation into hadrons and in τ-decay. The theoretical input are the asymptotic expansions for the vacuum polarization functions of vector and axial vector currents in the euclidean region as given by QCD. Since our method allows straightforward inclusion of (as yet uncalculated) higher order terms in α _s , there is the potential of making high precision tests of QCD even with experiments at rather moderate energies. We argue, therefore, that it may be very worthwhile to pursue experiments ate ⁺ e ^? storage rings below theJ/Ψ resonance and to measure the branching ratios for the decays of the τ-lepton with high accuracy. In the latter case we can also get information on the behaviour of the weak axial vector current which should be very interesting in connection with chiral symmetry breaking.     

Inclusive electron production from heavy quarks in e+e− annihilation at 34.6 GeV center of mass energy

The production of electrons by bottom and charm hadrons has been studied in e⁺e^? annihilation at 34.6 GeV center of mass energy. It is observed that the b quark fragmentation function is peaked at large values of the scaling variable z with 〈z_b〉 = 0.84^{+0.15 + 0.15}_{?0.10 ? 0.11}. For c quarks 〈z_c〉 = 0.57^{+0.10 + 0.05}_{?0.09 ? 0.06} is observed. A forward-backward charge asymmetry of A = ?0.25 ± 0.22 was measured in b production.     

Measurement of the f0(1270) polarization in the J/ψ → f0γ decay

The polarization of the f⁰(1270) and ?⁰(770) produced in the J/ψ decays into f⁰γ and ?⁰π⁰ are measured in e⁺e^? collisions at 3.1 GeV. A fit to the f⁰ production and decay angular distributions yields the values A₁/A₀ = 0.6 ± 0.3 and A₂/A₀ = 0.3 _?1.6^+0.6, where A_λ are the f⁰ helicity amplitudes. These results are in good agreement with the values predicted from a QCD two-gluon-exchange model. In addition an upper limit of 2.3 × 10^?4 is obtained for the J/ψ → f′⁰(1514) γ decay branching ratio which implies Γ(J/ψ → f′γ)/Γ(J/ψ → f⁰γ) ? 0.12 ± 0.05.     

The large N limit of the O(N) Heisenberg spin system in two dimensions

The large N limit of the O(N) Heisenberg spin system in two dimensions (a lattice version of the non-linear σ-model) is analysed by the collective field technique. A compact expression for the mass gap and the β-function is obtained for arbitrary but fixed gN. The strong and weak coupling limits of this expression correctly reproduce the known results.     

Differential cross sections for in the CM energy range from 2.0 to 3.1 GeV

Exclusive production of proton-antiproton pairs by two photon scattering at CM energies between 2.0 GeV and 3.1 GeV has been measured with the TASSO detector at the e⁺e⁻ storage ring PETRA. The angular distribution is flat within the accepted CM angular range |cos Θ^*|0.7. The integrated cross section (|cos Θ^*|0.6) drops from about 4 nb at 2 GeV to less than 0.5 nb above 3 GeV. For the two-photon production of the η_c(2984) and its subsequent decay into proton-antiproton the upper limit

Full-size image

(95% CL) is found.     

Hydrodynamical approach to the electron-positron annihilation into hadrons

The problem is reconsidered and it stressed that viscosity must be taken into account. This makes superfluous introduction of an “initial hadronic volume” V_o ～ m_π^?1 which in the e⁺e^? case can hardly be physically motivated. The viscosity becomes the single source of dissipation. Rough estimate of multiplicity is presented. Further, black body electromagnetic radiation from the hot hadronic clump turns out to be essential. It leads to an increase of energy spent on neutral component.     

Inclusive Jψ production in e+e− annihilation in the energy range from 4.0 to 5.0 GeV

We report on inclusive production of $\text{J}\text{ψ}$ (3.1)-mesons observed in e⁺e^?-annihilation in the energy range $\text{s}\text{= 4.0–5.0}\text{GeV}$. After substraction of the radiative tail of the ψ(3.7) direct production of the $\text{J}\text{ψ}$ (3.1) is found to be in the order of 0.1% of the total hadronic cross section. No enhancements are seen at $\text{s}\text{= 4.03}\text{GeV}$ and 4.4 GeV. The level is in agreement with expectations from violation of the Zweig-rule.     

A total energy trigger at large angles used in a calorimetric study of 150 GeV and 300 GeV pion and proton interactions on hydrogen

Hard hadronic scattering was studied by selecting 150 GeV and 300 GeV π^?p and pp events with large energy in a 240 cell calorimeter covering 452 to 1352 in the c.m.s. polar angle and the full 2π azimuth. A downstream calorimeter measured the remaining energy flow at smaller angles. For large energy deposited in the segmented calorimeter the proton induced cross section drops below the pion induced cross section, as expected in a constituent scattering picture. However, neither a simple energy scaling of the cross section nor a dominant jet structure of the events is observed. No evidence was found for recently proposed higher-twist mechanisms leading to events     

Charged pion production in e+e− annihilation at 14, 22 and 34 GeV CM energy

The inclusive production of π^± mesons in e⁺e^? annihilation has been measured at c.m. energies of 14, 22 and 34 GeV for pion momenta between 0.3 ans 10 GeV/c. The fraction of pions among the charged hadrons is above 90% at 0.4 GeV/c and decreases to about 50% at high momenta. The scaled cross sections ($\text{s}\text{β}$) $\text{d}\text{σ}\text{d}\text{x}$ at 14, 22 and 34 GeV as well as the 5.2 GeV data from DASP have a rather similar x dependence. After integration over the x range from 0.2 to 0.6 the cross sections indicate a monotonic decrease with increasing centre-of-mass energy.     

Inclusive properties of the ee annihilation into hadrons

The reaction e⁺e⁻ → hadrons is described on the basis of an hadronic structure for the photon. The structure functions of the inclusive reaction e⁺e⁻ → h + anything describe then the parton constitution of the photon in the scaling limit. Various types of couplings and models are considered (global couplings with vector mesons, fundamental photon-parton-antiparton couplings with formation of jets or fans). Precise shapes for the inclusive spectra and multiplicity distributions are deduced. Detailed comparisons with hadronic collisions A + B → h + anything are proposed in the fragmentation, the phase space boundary and the pionisation regions which could determine the nature of the partons and their interactions.     

A positron annihilation study of recovery of alpha-Zr from electron irradiation damage

Electron irradiation damage and its thermally-activated recovery has been studied in α-Zr by positron annihilation spectroscopy. The samples were irradiated with 1.5 MeV electrons at a nominal temperature of 295 K. The Doppler broadening technique was used and the results are reported in terms of peak (S) and wing (W) lineshape parameters. Recovery processes are evident over the range 300–670 K for S and from 300 to 600 K for W.     

A study of trimuon events in 280 GeV muon interactions

In 280 GeV μ⁺ iron interactions the inelastic production of muon pairs has been observed in excess of QED processes. For energies greater than 20 GeV deposited in the target calorimeter the interactions are found to be mainly hadronic. Cross sections are presented for this process in the mass range 1?2.5 GeV/c² and in the kinematic regions covered by the apparatus acceptance. The data are in good agreement with a photon-gluon fusion model for charmed particle production.     

Transverse momentum and angular distributions of hadrons in e+e− jets from QCD

Hadron jets in e⁺e^? annihilation will broaden at high energies due to gluon bremsstrahlung. With nonperturbative p_T effects dying out rapidly, the basic features of hadron jets can be calculated in perturbation theory. We examine the p_T distribution of secondarily produced hadrons. This is uniquely connected with the deviation from the 1 + cos²θ dependence of single particle inclusive distributions. We discuss what can be learned about the gluon fragmentation given the p_T and/or angular distributions. A sum rule is derived which establishes a relationship between the average p_T² and α_S.     

Inclusive production of vector and tensor mesons in antiproton-proton annihilation and non-annihilation interactions at 9.1 GeV/c

Cross sections have been determined for the inclusive production of vector $\text{(?}{}^0\text{, ω,}\text{K}{}^1\text{)}$ and tensor (f, A₂^±) mesons in $\text{p}\text{p}$ reactions at 9.1 GeV/c for both annihilation and non-annihilation processes. Distributions in the Feynman variable x and transverse momentum squared, p_T², have been examined for the ?⁰, ω and f mesons. The slopes for p_T² appear to be exponential and decrease with increasing particle mass for both annihilation and non-annihilation reactions, furthermore the slopes have consistently higher values for non-annihilation reactions. Comparisons with other data indicate that the ratio ?⁰/π^? is independent of antiproton momentum in annihilation processes.