QCD predictions for γγ annihilation to baryons

QCD predictions for large-momentum transfer cross sections of the type $\text{γγ →}\text{B}\text{B}\text{′}$ are given, for B and B′ any members of the baryon octet or decuplet, and all possible helicity combinations for photons and baryons.     

Study of J/Ψ three-body decays involving baryons and a pseudoscalar meson in the diquark model

The J/Ψ decay into a baryon pair and a pseudoscalar meson is computed, for some channels, in lowest order in perturbative QCD, modeling the baryon with a quark-diquark system. We use a set of parameters that has been proposed by some authors in order to fit the proton magnetic form factor G _M ^P, the angular distribution of protons in the processes γγ → pp?, γp → γp and the width of η_c → γγ.     

Photoproduction of μ pairs and large-pT particles in QCD

We calculate cross sections for $\text{γ}\text{N}\text{→ μ}\text{μ}\text{X}\text{, γ}\text{N}\text{→ (}\text{jet)X and}\text{γ}\text{N}\text{→ π}{}^{\mathrm{+}}\text{X}$ using the distribution functions for quarks in the photon predicted by QCD. The Drell-Yan contribution to the μ-pair cross section is masked by the Bethe-Heitler process in the region where it is interesting. However, the characteristic cross section for photoproduction of large-p_T particles, which is predicted by QCD, is measurable.     

Heavy-quark production by hadrons: Gluon jet fragmentation versus fusion

We show that at $\text{p}\text{p}$ collider energies heavy quarks are dominantly produced by the fragmentation of gluon jets into $\text{Q}\text{Q}$ with Q = c,b. This is because the underlying gg → gg jet cross section exceeds the fusion process $\text{gg → Q}\text{Q}$ by over two orders of magnitude. We compute the perturbative contribution to the gluon fragmentation from 2 → 3 processes such as gg $\text{→ gQ}\text{Q}$. We point out the observable consequences for single-lepton production and same-opposite charge dileptons. In particular, the observed production of dileptons with large p_T and low effective mass is explained.     

A possible description of baryon dynamics in dual and gauge theories

We present an attempt to generalize to baryons a framework recently proposed in order to unify gauge, dual and Regge-Gribov theories of mesons. We find it necessary to depart from the $\text{1}\text{N}{}_{\mathrm{<mtext>colour</mtext>}}$ expansion of quantum chromodynamics (QCD) and to replace it by a more general definition of a “dual” approximation of QCD, based on the zero-width limit. Theoretical and phenomenological consequences of the scheme are derived. For N_colour = 3, the baryon resembles a Y shaped string; three families of new “baryonium” bound states are predicted and rough estimates of intercepts and slopes of the associated Regge trajectories are given. A new type of Zweig-like selection rule is found to hold in leading order and its violations through higher-order topologies are discussed. Duality diagrams for baryons are ambiguous unless implemented with extra lines indicating the flow of certain colour indices. Duality between scattering and annihilation channels is found in B$\text{B}$ scattering and its consequences are discussed. Some justification is given for the quark counting rule for total cross sections. Finally, implications of our scheme for the Regge-Gribov calculus in processes involving baryons are discussed.     

Calculation of the γγ → ϱ0ϱ0 cross section at high energies

The processes with the cross sections not decreasing with energy become important at high energies. The simplest processes of this kind are γγ → V_i⁰V_j⁰ where V⁰ = ?⁰, ω, ?, ….. We calculate their cross sections in the high-energy small angle region s ? |t| ? μ². The cross section γγ → ?⁰?⁰ at high energies (s ? 10 GeV²) exceeds those of γγ → ππ, ?⁺?^? considerably. At $\text{s ? 10}{}^4\text{GeV}{}^2$ (this is the characteristic energy for the VLEPP and SLC colliders) and $\text{|t| ? 2}\text{GeV}{}^2$, the ratio $\text{(}\text{d}\text{σ/}\text{d}\text{t)(γγ → ?}{}^0\text{?}{}^0\text{)/(}\text{d}\text{σ/}\text{d}\text{t)(γγ → μ}{}^{\mathrm{+}}\text{μ}{}^{\mathrm{?}}\text{) ? 70}$.     

Polarization of gluon jets in photon-photon scattering

We show that the linear polarization of a gluon emerging from the reaction $\text{e}\text{+}\text{e}\text{→}\text{e}\text{+}\text{e}\text{+}\text{g}\text{+}\text{g}$ is large - on the order of 20%. This polarization arises from the process γ + γ → quark loop → g + g, which is expected to dominate the two gluon jet cross section. The polarization can be used to test quantum chromodynamics (QCD), even if the gluon jets cannot be distinguished clearly from the background of quark jets. If the QCD prediction is accepted, our result can be used to enhance the signal of gluon jets, thereby aiding in the study of their properties.     

SU(6) symmetry breaking effects in deep inelastic scattering

The fact that the N and Δ states of the $\text{56}$ baryons are not degenerate in mass is shown to imply that the deep inelastic scattering ratio F_2n(x)/F_2p(x) should approach $\text{1}\text{4}$ as x → 1. The rate of approach is predicted to be approximatel linear in x. The possibility of observing analogous effects in other large momentum transfer processes is also discussed.     

QCD predictions for beauty production in π p and pp collisions

The total cross sections for beauty production in πp, pp and $\text{p}$p collisions are calculated within perturbative QCD. It turns out that the cross sections are around several nanobarns at presently available energies. For the future $\text{p}$p colliders, the total cross section reaches several millibarns.     

Angular distributions and structure functions from two-jet events at the CERN SPS pp collider

The two-jet cross section measured in the UA1 apparatus at the CERN $\text{p}\text{p}$ Collider has been analysed in terms of the centre-of-mass scattering angle θ and the scaled longitudinal parton momenta x₁ and x₂. The angular distribution dσ/d cos σ rises rapidly as cos → 1, independent of x₂ and x₂, as expected in vector gluon theories (QCD). The differential cross section in x₁ and x₂ is consistent with factorization and provides a measurement of the proton structure function $\text{F(x) = G(x) +}\text{4}\text{9}\text{[Q(x) +}\text{Q}\text{(x)]}$ at values of the four-momentum transfer squared, -t? ≈ 2000 GeV². Over the range x = 0.10?0.80 the structure function shows an exponential x dependence and may be parametrized by the form F(x) = 6.2 exp (?9.5x).     

Remark on baryonic decays of B mesons

We point out that B mesons might possess significant baryonic decay modes like B → Λ_c$\text{N}$. Invoking a simple-minded spectator ansatz for B decays we estimate BR(B → Λ_c$\text{N}$+X) ≈ 2–13% while exclusive two-body channels might reach values of a few percent. Observation of such transitions could yield valuable information on the dynamics of weak decays and maybe even on charm baryons. The search for bottom baryons would, however, be made more difficult by a sizeable baryonic branching ratio of bottom mesons.     

Momentum transfer distributions of some diffractive enhancements in K−p interactions at 14.3 GeV/c

We discuss the structure of the momentum transfer distributions for the diffractive dissociation processes p → nπ⁺, p → Δ⁺⁺π^? and $\text{K}{}^{\mathrm{?}}\text{→}\text{K}{}_{890}{}^{10}\text{π}{}^{\mathrm{?}}$. In the near-threshold mass region a clear break of slope is found around t′KK ～ 0.25 GeV² for the two baryonic channels, whereas no comparable structure is seen for the mesonic system. The $\text{K}\text{→}\text{K}{}^1\text{π}$ differential cross section exhibits a nearly exponential behaviour up to t′_pp ～ 0.6 GeV², falling over three orders of magnitude. The slope variations and breaks are strongly correlated both to the mass region considered and to the decay angle of the fragmentation system.     

Elastic antiproton-proton photoproduction between threshold and 4.8 GeV

The cross section for the process $\text{γ}\text{p}\text{→}\text{p}\text{pp}$ has been measured from threshold up to 4.8 GeV using a tagged photon beam and a multiparticle spectrometer which detected all final state particles. The production cross section rises rapidly from threshold to a constant value of 35 nb. No evidence is found in the mass spectra for the production of narrow meson resonances decaying into $\text{p}\text{p}$.     

Production and signature of intermediate vector bosons

The front-back asymmetry of outgoing muons in the inclusive reaction $\text{p}\text{p}\text{→ Z(→ μ}{}^{\mathrm{+}}\text{μ}{}^{\mathrm{?}}\text{)+}$ anything is calculated in the framework of the Drell-Yan model. We get very general expressions for the front-back asymmetry and the differential cross section in terms of the weak coupling constants and the parton distributions. Results for W^± production and proton-proton collisions are also given. Numerical estimates are made using various parton distributions and the Weinberg-Salam model for definiteness. We comment on the predictions of gauge theories that accommodate the absence of parity violating effects in atomic physics. We also give a new estimate of the inclusive cross sections $\text{p}\text{p}$ or pp → Z(→ μ⁺μ^?) or W^±(→ μ^±ν_μ) + anything. The effects of asymptotic freedom in the frontback asymmetries and the total cross sectons are investigated. We reanalyze results for the purely leptonic reaction e⁺e^? → γ, Z → μ⁺μ^?.     

Peripheral pn production and decay angular distributions in the reaction π−p → (pn)p at 12 GeV/c incident momentum

The reaction $\text{π}{}^{\mathrm{?}}\text{p}\text{→ (}\text{p}\text{n}\text{)}\text{p}{}_{\mathrm{s}}$, where p_s is a slow proton, was measured at 12 GeV/c incident momentum with the CERN-OMEGA spectrometer. Both antiproton and proton were identified uniquely by electronics information. We obtained 1844 events with four-momentum Transfer squared in the range 0.13 ? |t| ? 0.33 GeV² and with invariant masses $\text{M(}\text{p}\text{n}\text{)}$ up to 2.5 GeV. The corresponding cross section in this t range is determined to be σ = 4 ± 0.4 μb. Extrapolating the differential cross section over the whole t range assuming dσ/dt ≈ exp(5.3t) we estimate a cross section of σ = 9.3 ± 2.0 μb. Comparison with data on $\text{π}{}^{\mathrm{?}}\text{p}\text{→ (}\text{p}\text{p}\text{)}\text{n}{}_{\mathrm{s}}$ (where n_s is a slow neutron) in the same t range shows that the $\text{(}\text{p}\text{n}\text{)}\text{p}{}_{\mathrm{s}}\text{and}\text{(}\text{p}\text{p}\text{)}\text{n}{}_{\mathrm{s}}$ cross sections have approximately the same magnitude.     

On the QCD perturbative predictions for the signal ofW± production in hadronic collisions

Evidence for the intermediate bosons in high energy pp and p?p collisions as signal in the cross section of large p_T charged lepton pp, $\text{p}\text{p}\text{→}\text{W}{}^{\mathrm{\pm }}\text{+}\text{X}$, W^±→?^±ν_? is considered for CM energy range $\text{s}\text{=100?800}\text{GeV}$. Besides the usual Drell-Yan term which gives a very sharp peak in the lepton p_T distribution, the first order QCD contribution is included thus producing the intermediate boson with transverse momentum and smearing the lepton distribution. Scaling violation of the structure functions is incorporated and compared with the case when it is absent.     

Rise of proton proton total cross section and inclusive spectra

The origin of the rise of p-p total cross section (σ_t(pp)) is investigated by making use of the inclusive sum rule. The contribution to the rise of σ_t(pp) from the development of sharp peak near the kinematical boundary in the process p+p→p+ “anything” is almost completely canceled out by the decrease of the cross section in other x-region between s=45 (GeV/c)² and s=2820 (GeV/c)². Then the net contribution to the rise of σ_t(pp) from the process p+p→p+ “anything” is very likely to be zero. The true origin of the rise of σ_t(pp) is found to be the increase of inclusive cross sections at x ? 0 between PS and ISR energies. The contribution from the process p+p→π+ “anything” at x ? 0 to the rise of σ_t(pp) is estimated to be 3.2 mb, that from the process p+p→K + “anything”, 0.71 mb and that from the process p+p→$\text{p}$ “anything”, 0.62 mb. According to our conclusion we expect that all total cross sections will rise with energy at high energy.     

Hadronic production of charm via flavour excitation

We present a calculation of the contribution of flavour excitation diagrams to the hadronic production of open charm. The main new ingredients in the calculation are: (i) a proper treatment of the QCD evolution of the input charm sea distribution, with constraints from the existing charm structure function data; (ii) use of the available charm transverse momentum data to fix the $\text{t}\text{?}{}_{\mathrm{<mtext>min</mtext>}}$ cutoff which regulates the $\text{t}\text{?}\text{? 0}$ divergence in the diagrams. We are then able to make a stable calculation of the resulting charm cross section. The flavour excitation contribution turns out to be an order of magnitude larger than for fusion. As a result the observed magnitudes of the charm cross section at accelerator and ISR energies are satisfactorily reproduced, thus eliminating a long standing difficulty of the perturbative QCD approach to open charm production. Furthermore, we calculate the longitudinal and transverse spectra of charmed hadrons using a simple recombination model. We show that the existing ISR data on the production of fast Λ_c are well, and naturally, reproduced by this approach. Qualitative predictions for bottom production are also discussed.     

Next-to-leading order QCD corrections to bg→tW− at the CERN Large Hadron Collider

The next-to-leading order QCD corrections to the Standard Model process of single top production, bg→tW⁻, for the CERN Large Hadron Collider with $\text{s}\text{=14}$ TeV have been calculated. For renormalization and factorization scales μ=μ₀ (μ₀=m_t+m_W), the NLO hadronic cross section is ∼42 pb, while ∼26.5 pb for tree level. The NLO QCD corrections can enhance the cross section by a factor from 1.4 to 1.7 for μ₀/2<μ<2μ₀.     

Cross section of ion excitation in ion-ion collision

The “effective Feynman diagram” technique introduced in a previous paper is used to express the cross section of ion excitation in ion-ion collisions $\text{(A + B → A}{}^1\text{+ B)}$ in terms of the corresponding photon resonance absorption $\text{(hv + A → A}{}^1\text{)}$ and Thomson-scattering (hv + B → hv + B) cross sections. The result is checked for the process He⁺ + H(1s) → He⁺ + H(2p) with experiment and very good agreement is obtained.