Antiproton-neutron interactions at 100 GeV/c

From an exposure of the 30-inch deuterium filled bubble chamber to a 100 GeV/c antiproton-enriched beam at FNAL, we have calculated the topological cross sections for antiproton-neutron interactions with three or more charged particles in the final state. A comparison of our data with pn data at the same momentum allows us to estimate the annihilation contribution to each multiplicity, and hence calculate the average value, and width, of the annihilation multiplicity distribution. Our results are consistent with those from $\text{p}\text{p}$ data at 100 GeV/c, but depart from the trend of lower-energy $\text{p}\text{p}$ data.     

Off-shell NN annihilation studied in π+p interactions at 8 and 16 GeV/c

Interactions in which the baryon is emitted forwards in the c.m.s. are studied in 8 and 16 GeV/cπ⁺p collisions. These interactions are interpreted as representing baryon exchange. The properties of such off-shell $\text{N}$N annihilation events are studied. It is found that the multiplicity distribution of the multi-pion system as a function of the effective mass for events with |u_pp| < 1 GeV² is the same as for real $\text{N}\text{N}$ annihilations.     

Rapidity density distributions in antiproton-proton collisions

Data on the density of charged particles in rapidity space for annihilation and non-annihilation p?p interactions at 7.3 and 12 GeV/c are reported. It is shown that the central rapidity density for non-annihilation processes is a simple linear function of $\text{ln}\text{(}\text{s}\text{)}$ from these low energies up to p?p collider energies ($\text{s}\text{=540}\text{GeV}$). Significant differences in density distributions for p?p and e^?e⁺ annihilations at comparable energies are found.     

Comparison of the reactions π− p → p + X and pp → p + X at 205 GeVc

Characteristics of the reactions π^? p → p + X and pp → p + X are compared at $\text{205}\text{GeV}\text{c}$. In the lower multiplicity final states significant differences are observed in the spectrum of M², the mass-squared of the produced system X. However, the inclusive reactions show remarkable similarities in the distribution of momentum transfer to the recoil proton and in the dependence on M² of the average charged multiplicity of X. Triple-Regge theory with PPP or PRR terms is found to correctly predict the ratio of the inclusive cross sections for 30 ? M² ? 120 GeV².     

Universal multiplicity formula

Thermodynamic reasoning is used to derive a universal multiplicity formula for particle production in high energy collisions. Among the results are the equality of πp, pp and γp multiplicity, the prediction of a slow decrease in deep inelastic multiplicity when Q² increases, and the prediction of an s${}^{\mathrm{<mtext>3</mtext><mtext>8</mtext>}}$ dependence of hadronic multiplicity in e⁺ ? e^? annihilation.     

Some information from nucleon-antinucleon annihilation at rest: e+e− annihilation,hadronic fragmentation and deep inelastic structure functions

The experimental spectra of charged pions in $\text{N}\text{N}$ annihilation at rest are described in a model of quasi-two-body decays. The same model predicts the π⁰, ? and ω spectra. We apply a previous calculation to determine in the vector-dominance model, the pions spectra in e⁺e^? annihilation at the same energy. The $\text{N}\text{N}$ system is then used as a heavy hadron in order to describe, in a model-independent way: (i) the projectile fragmentation part in inclusive reactions; (ii) the valence part of the deep inelastic structure function.     

Multiplicities of secondary hadrons produced in vp and vp charged current interactions

In an experiment with the hydrogen bubble chamber BEBC at CERN multiplicities of hadrons produced in νp and $\text{v}\text{p}$ interactions have been investigated. Results are presented on the multiplicities of charged hadrons and neutral pions, forward and backward multiplicities of charged hadrons and correlations between forward and backward multiplicities. Comparisons are made with hadronic reactions and e⁺e^? annihilation. In the framework of the quark-parton model the data imply similar charged multiplicities for the fragments of a u- and a d-quark, and a larger multiplicities for the fragments of a uu- than for a ud-diquark. The correlation data suggest independent fragmentation of the quark and diquark for hadronic masses above ～ 7 GeV and local charge compensation within an event.     

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.     

Scaling violation favouring high multiplicity events at 540 GeV CMS energy

New data are presented on the charged multiplicity distribution for non single-diffractive events produced in pp? interactions at a CM energy $\text{s}\text{= 540}\text{GeV}$. The distribution in the full pseudorapidity range is compared with data from the ISR. Using the scaling variable $\text{z =}\text{n}\text{〈n〉}$ a change of shape is observed. The effect is manifested as an increase from 2% to 6% in the proportion of high multiplicity (z > 2) events. For the central pseudorapidity range, |η| ? 1.5, scaling is approximately valid up to $\text{s}\text{= 540}\text{GeV}$.     

Comment on CP violation in B0-B0 mixing

We note that in the six-quark model the CP violating dilepton asymmetry in semileptonic B⁰-$\text{B}$⁰ decays can be significant only if the non-zero value of the charm quark mass plays an important role in the B⁰-$\text{B}$⁰ width or mass transition matrix elements. The annihilation diagram, which has been proposed as a source of the difference between the charged and neutral D meson lifetimes, is considered. We show that this diagram does not contribute to the B⁰-$\text{B}$⁰ width transition matrix element because of a helicity mismatch.     

A scaling test in π− p semi-inclusive reactions

The scaling properties of the semi-inclusive reactions π^?p → π^?+(n?1) charged + neutrals at 7.5 and 21 GeV/c are analysed. The distributions of the h-functions on the x-variable for π^? particles indicate the presence of a limited scaling. The choosing of a certain value for the reduced charged multiplicity $\text{n}\text{〈n〉}$ is pointed out.     

Threshold properties of electroproduction and annihilation

The threshold relation for deep-inelastic electroproduction that was suggested by Drell and Yan and by West is not a general property of softened field theories. However, for individual Feynman graphs of certain perturbation-expansion models it is valid in the form of an inequality. This is shown for every graph in φ³ theory, and for certain simple graphs when fields and particles with spin are considered, provided that the fields to which the electromagnetic current couples have the same spin as the target particle. The structure functions F₂(ω) and $\text{F}{}_2\text{(ω)}$ for electroproduction and electron-positron annihilation are both expected to behave like |ω ? 1 |^p at ω = 1, with the same power p for each but not necessarily the same coefficient. The behaviour of $\text{F}{}_2\text{(ω)}$ at ω = 0 is investigated and is found to result in finite multiplicity in the annihilation process at infinite energy.     

Multiplicity of charged particles π− interactions on nuclei at 40 GeV/c

Multiparticle production in π^?-nucleus interactions at 40 GeV/c (Fifth Joint CERN-Serpukhov Experiment) has been studied using a spark-chamber technique at the Serpukhov accelerator. The mean multiplicities, the pseudorapidity distributions and the dispersion of the multiplicity distributions of charged particles produced on C, Al, Cu and Pb targets are presented. The data have been analysed, both subtracting and including secondary protons with p < 1 GeV/c. In the region of pseudorapidity η > 3.4 the average multiplicity is nearly independent of the size ($\text{ν}$) of the target nucleus, while it increases for η < 3.4. In the forward direction (η > 4) the mean multiplicity on nuclei is smaller than the mean multiplicity on hydrogen. The dependence upon $\text{ν}$ in the target fragmentation region is stronger when the emitted protons are included in the pseudorapidity distributions of the secondary particles. The dispersion of the multiplicity distributions for the different nuclear targets versus the mean multiplicity shows the same slope as found by the world statistics on hydrogen and by other experiments on nuclei at different energies. The results are compared with the predictions of the coherent tube model and with the soft hadron-nucleus collision model.     

Charged particle multiplicities in 100 GeV/cpp interactions

Results are presented on the topological cross sections obtained for antiproton-proton interactions from an exposure of the Fermilab 30-inch bubble chamber to a 100 GeV/c negative beam enriched in $\text{p}$'s. The $\text{p}$p inelastic cross section is found to be σ_inel = 34.6 ± 0.4 mb, and the average inelastic charged particle multiplicity to be 〈n〉 = 6.74 ± 0.05.     

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.     

Photon and neutral pion distributions in 60 and 200 A GeV16O+nucleus and proton+nucleus reactions

Transverse momentum (p_T) distributions of inclusive photons and neutral pions at midrapidity are measured with a lead glass calorimeter in $\text{60}\text{and}\text{200 A}\text{GeV}{}^{16}\text{O}\text{+}\text{nucleus and proton}\text{+}\text{nucleus reactions}$. The variation of the average transverse momentum is investigated as function of centrality, determined by measurements of the remaining energy of the projectile and the charged particle multiplicity. For small values of the entropy, deduced from the multiplicity density, an increase in average p_T is observed levelling off for larger values of entropy. The target-mass and energy dependence of π⁰ p_T distributions are presented.     

Charged particle multiplicity distributions for 32 GeV/c K±p and pp interactions and for 50 GeV/c π±p interactions

Topological cross sections are presented for K⁺p, K^?p and $\text{p}\text{p}$ interations at 32 GeV/c and for π⁺p and π^?p interactions at 50 GeV/c observed in the 4.5 m Mirabelle hydrogen bubble chamber at Serpukhov. Parameters characterizing the behaviour of the multiplicity distributions, namely 〈n_c〉, D and f₂ and the normalized moments are given. The dependence of these parameters on the energy and the nature of the beam particle is discussed. The multiplicity distributions obtained cannot be described by a single function in the KNO variables.     

Inclusive strange particle production in π+p interactions at 16 GeV/c

The production of $\text{K}{}_{\mathrm{S}}{}^0\text{, Λ}\text{and}\text{Λ}$ is measured in π⁺p reactions at 16 GeV/c. The total strange particle cross section is found to be 4.0 ± 0.3 mb, about 20% of the inelastic cross section. Cross sections for single strange particles and for strange particle pairs are determined, both inclusively and as functions of the charged multiplicity. Relative production rates for different strange particle combinations are compared with the prediction of the isospin statistical model. Inclusive spectra for single particles are studied and it is found the K_S⁰ are produced mostly in the forward hemisphere, most probably by fragmentation of the incident pion into $\text{K}\text{K}\text{π}$. The Λ are mostly backwards, probably deriving from fragmentation of the proton into ΛK pairs. The $\text{Λ}$ tend to be produced forwards, but evidence is found for central $\text{Λ}\text{Λ}$ production. Distributions in rapidity of the Λ particles from π⁺p interactions are compared in terms of the factorisation hypothesis. Results are given on the Λ transversal polarisation.     

General features of the pp interaction at 12 GeV/c

Simple inclusive cross sections for $\text{p}\text{p}$ interactions at 12 GeV/c are given. The data cover prong cross sections, V⁰ production and resonances. Separation has been made into annihilation and non-annihilation modes. Some implications of the data are discussed. It is pointed out that the ratios of cross sections for $\text{?}{}^0\text{π}{}^{\mathrm{?}}$ production are independent of incident antiproton momentum in $\text{p}\text{p}$ annihilation processes, and that data at the highest available pp energies (ISR) tend to the same value.