Positive particle production in the fragmentation region at the CERN ISR

Cross sections for the production of positive pions, kaons and protons in proton-proton collisions at the CERN ISR have been measured. These measurements extend to transverse momenta p_T of 2.5 GeV and span the range in $\text{x = 2p}{}_{\mathrm{<mtext>L</mtext>}}\text{/}\text{s}$ between 0.3 and 0.8 For transverse momenta larger than ～ 1 GeV the cross sections show an increase relative to low-energy data, but are consistent with scaling within the energy range measured here, $\text{31 <}\text{s}\text{< 63}\text{GeV}$.     

First determination of the proton electromagnetic form factors at the threshold of the time-like region

From the measurement of $\text{B}\text{e}{}^{\mathrm{+}}\text{e}{}^{\mathrm{?}}\text{=}\text{Γ(}\text{p}\text{p}\text{→}\text{e}{}^{\mathrm{+}}\text{e}{}^{\mathrm{?}}\text{)}\text{Γ}\text{p}\text{p}\text{→total}\text{= (3.2 ± 10}{}^{\mathrm{?7}}\text{)}$, obtained in an experiment at CERN with antiprotons at rest, a value of the proton electromagnetic form factors at the threshold of the time-like region is derived: |G_E| = |G_M| = 0.51 ± 0.08 at q² = -3.52 (GeV/c)².     

Deep-inelastic electroproduction of neutrons in the proton fragmentation region

Experiments at HERA looking for deep-inelastic electroproduction of neutrons in the proton fragmentation region are in progress. They are aimed to measure the pion structure function at small Bjorken x. The important condition for such a study is to establish under what kinematical conditions the dominance of the pion-pole graph in the process is guaranteed. We analyse other sources of the leading neutron, in order to figure out the kinematical region where the one-pion exchange dominates.     

Deep-inelastic electroproduction of neutrons in the proton fragmentation region

Experiments at HERA looking for deep-inelastic electroproduction of neutrons in the proton fragmentation region are in progress. They are aimed to measure the pion structure function at small Bjorken x. The important condition for such a study is to establish under what kinematical conditions the dominance of the pion-pole graph in the process is guaranteed. We analyse other sources of the leading neutron, in order to figure out the kinematical region where the one-pion exchange dominates.     

Experimental tests of limiting fragmentation at the ISR

We present direct tests of the hypothesis of limiting fragmentation from an experiment at the CERN Intersecting Storage Rings at centre-of-mass energies between 31 and 53 GeV. Single-particle inclusive distributions and partial multiplicity distributions are observed for the case in which the energy of one beam is fixed while varying the energy of the other beam. Within cones around the beam, limiting fragmentation is shown to be valid.     

Lambda polarization in the K− fragmentation region

Results on Λ polarization in the inclusive reaction K^?p→Λ + X at 12 and 16 GeV/c for 0.6<x<1.0, are presented. These results, obtained with the CERN Omega Spectrometer, show that the polarization is important at large x and increases with p_t over the covered range 0<p_t<1.2 GeV/c. The average polarization for 31 857 lambdas with x>0.6 is P_Λ = 0.35 ± 0.02, along the direction $\text{K}{}^{\mathrm{?}}\text{×}\text{Λ}$. The polarization can be expressed as P(x, p_t) = (0.66±0.03)p_t independent of x in the range covered by the experiment.     

Spectroscopy and Regge trajectories of heavy quarkonia in the relativistic quark model

The mass spectra of charmonia and bottomonia are calculated in the framework of the relativistic quark model up to high orbital and radial excitations. The Regge trajectories of heavy quarkonia are constructed both in the (J,M ²) and (n _r ,M ²) planes, where J is the total angular momentum and nr is the radial quantum number. All daughter trajectories turn out to be almost linear and parallel, while parent trajectories exhibit some nonlinearity. Such nonlinearity occurs only in the vicinity of ground states and few lowest excitations and is more pronounced for bottomonia, while it is only marginal for charmonia. The obtained results are compared with available experimental data, and a possible interpretation of the new charmonium-like states above open charm production threshold is discussed.     

Magnitude of Regge cut contributions in the triple-Regge region

Starting from the reggeon calculus, the various possibilities of absorptive pomeron cut corrections in the triple-Regge region are considered. For the case of pp → pX, we estimate their importance at present day energies. We conclude that at highest ISR energies, pomeron cuts of the eikonal type are not enough, and enhanced diagrams with at least one additional triple-pomeron coupling need be included.     

Regge phenomenology of inclusive spectra in the central region

In the light of new data from the ISR, initial steps are taken towards the Regge analysis of inclusive spectra in the central region. It is shown that some features in the data necessitate the introduction of a further singularity in addition to the Pomeron and the meson trajectories ? - f - ω - A₂. The resulting model yields many predictions via duality and factorisation which can easily be tested at ISR and Batavia energies.     

Couplings of the rho meson in a holographic dual of QCD with Regge trajectories

The couplings g_ρHH of the ρ meson with a scalar meson H are calculated in a holographic dual of QCD in which the Regge trajectories for the mesons are manifest. In contrast to the conclusion in general AdS/QCD models, the resulting couplings grow linearly with the quantum number of excited H; thus they are far from universal. This non-universality seems to result from the disappearance of an explicit cutoff in the holographic dimension in this model. Correspondingly, the ρ-dominance for the electromagnetic form factors of H does not hold any more, even in an apparent sign-alternating manner. With these couplings at hand, the asymptotic behavior of the form factors can easily be calculated. The form factor exhibits the 1/Q^(2Δ-2) behavior, which is in accordance with the scaling behavior of the fixed-angle scattering amplitude based on the AdS/CFT correspondence. It is also pointed out that the asymptotic behavior can be matched to the results of perturbative QCD, if the conformal dimension Δ of the operator is replaced by the combination τ+L of the meson. PACS  11.25.Tq; 12.40.Vv; 14.40.Cs     

Production of high transverse momentum particles in p-p-collisions in the central region at the CERN ISR

The inclusive production al all charged particles of transverse momentum p_T between 1.5 and 4.4 GeV/c at centre of mass angles 90° and 59.4° from p-p-collisions with √s = 44 and 53 GeV has been measured. No strong energy dependence is observed for these transverse momenta.     

Inclusive photo- and electroproduction of pions in the triple Regge region

We develop a Regge pole expansion including spin for inclusive photo- and electroproduction of pions in the photon fragmentation region and see to what extent the available data at intermediate energies can be explained in terms of Regge poles alone. It is shown that a pure Regge pole model is not adequate, although some qualitative features are reproduced.     

Measurement of the polarization in the forward peak of π−p→K0λ at 5 GeV/c

The π^?p→K⁰λ polarization has been measured at 5 GeV/c in the range 0<?t<1.4 (GeV/c)². The polarization is small for ?t?0.4 (GeV/c)², becoming negative at the higher values of ?t.     

Electroproduction of π+ mesons in the resonance region

Results on the reaction ep→e′nπ⁺ are presented in the mass range 1.355 ?W ?1.775 GeV at q₂=1GeV² and in the range 1.415 ? W ? 1.595 GeV at q²=0.6 GeV². From the angular distribution of the π⁺ meson the polarization terms σ_u + ?σ_L, σ_p and σ_I have been determined in the range of production angles 0 <θ_π⁺ ?63°     

A measurement of the transverse momenta of partons,and of jet fragmentation as a function of √s in p-p collisions

A large solid-angle apparatus consisting of a superconducting solenoid magnet, cylindrical drift chambers and two arrays of lead-glass counters was used to examine particles associated with a high transverse momentum trigger in p-p collisions with three √s values at the CERN ISR. The trigger was given by energy deposition in lead-glass arrays centred at 90°. The trigger transverse momentum range covered was 3 < $\text{p}{}_{\mathrm{<mtext>T\; trig</mtext>}}\text{< 11}\text{GeV}\text{c}$. Results are given for p_out for both individual charged particles, and also for the sum of charged particle momenta in the hemisphere opposite to the trigger. Mean values are then deduced for the parton transverse momentum k_T, and for the jet fragmentation momentum j_T.     

A measurement of single electrons,electron pairs,and associated phenomena,in proton-proton collisions at the CERN ISR

Measurements of single-electron production in proton-proton collisions at the CERN ISR are presented for five centre-of-mass energies √s = 23.5, 30.6, 44.8, 52.7, and 62.4 GeV. The invariant cross sections for single electrons with transverse momenta of 0.60 to 4.7 GeV/c are given. Measurements of electron-positron pairs and measurements of charged hadrons produced in association with the single electrons, are also reported.     

Significance of the fragmentation region in ultrarelativistic heavy-ion collisions

We present measurements of the pseudorapidity distribution of primary charged particles produced in Au+Au collisions at three energies, sqrt[s(NN)]=19.6, 130, and 200 GeV, for a range of collision centrali-ties. The distribution narrows for more central collisions and excess particles are produced at high pseudorapidity in peripheral collisions. For a given centrality, however, the distributions are found to scale with energy according to the "limiting fragmentation" hypothesis. The universal fragmentation region described by this scaling grows in pseudorapidity with increasing collision energy, extending well away from the beam rapidity and covering more than half of the pseudorapidity range over which particles are produced. This approach to a universal limiting curve appears to be a dominant feature of the pseudorapidity distribution and therefore of the total particle production in these collisions.     

Peripheral dynamics of inclusive reactions in the fragmentation region

Peripheral dynamics is studied for the limiting fragmentation of protons and pions. The calculated distributions are discussed and compared with experimental data.     

On the recombination mechanism of quarks into a baryon in proton fragmentation

The similarity and difference between our quark cascade model with recombination mechanism and Van Hove's quark fragmentation-recombination model are discussed. Van Hove's fragmentation-recombination model is extended to the model which describesx-dependence of the hadron spectra as well as the baryon multiplicities by using our diffusion equation. The recombination probability in Van Hove's model can be related with the recombination factor λ′ in our diffusion equation. Thex-dependence of the hadron spectra causes another restriction on the recombination probability in Van Hove's model. The inclusive spectra of mesons, proton andΔ ⁺⁺ in proton fragmentation and baryon multiplicities except∑ ^? multiplicity are explained by both our model with recombination mechanism and the model with recombination mechanism a la Van Hove. But the ration(∑ ^?)/n(∑ ^+;) may not be explained by naive quark-parton model with recombination mechanism without considering quark spin.