Measurement of <Emphasis Type="Italic">K</Emphasis><Superscript> + </Superscript><Emphasis Type="Italic">K</Emphasis><Superscript>-</Superscript> production in two-photon collisions in the resonant-mass region

K ⁺ K ^- production in two-photon collisions has been studied using a large data sample of 67 fb^-1 accumulated with the Belle detector at the KEKB asymmetric e ⁺ e ^- collider. We have measured the cross section for the process for center-of-mass energies between 1.4 and 2.4 GeV, and found three new resonant structures in the energy region between 1.6 and 2.4 GeV. The angular differential cross sections have also been measured.Received: 30 September 2003, Published online: 18 December 2003     

Measurement and QCD analysis of neutral and charged current cross sections at HERA

The inclusive e⁺p single and double differential cross sections for neutral and charged current processes are measured with the H1 detector at HERA. The data were taken in 1999 and 2000 at a centre-of-mass energy of and correspond to an integrated luminosity of 65.2 pb^-1. The cross sections are measured in the range of four-momentum transfer squared Q² between 100 and and Bjorken x between 0.0013 and 0.65. The neutral current analysis for the new e⁺p data and the earlier e^-p data taken in 1998 and 1999 is extended to small energies of the scattered electron and therefore to higher values of inelasticity y, allowing a determination of the longitudinal structure function F_L at high Q² ( ). A new measurement of the structure function is obtained using the new e⁺p and previously published neutral current cross section data at high Q². These data together with H1 low Q² precision data are further used to perform new next-to-leading order QCD analyses in the framework of the Standard Model to extract flavour separated parton distributions in the proton.Arrival of the final proofs: 11 July 2003     

Measurement of inclusive jet cross sections in photoproduction at HERA

Inclusive jet cross sections are measured in photoproduction at HERA using the H1 detector. The data sample of events in the kinematic range of photon virtualities and photon-proton centre-of-mass energies represents an integrated luminosity of . Jets are defined using the inclusive algorithm. Single- and multi-differential cross sections are measured as functions of jet transverse energy E_T ^jet and pseudorapidity in the domain and . The cross sections are found to be in good agreement with next-to-leading order perturbative QCD calculations corrected for fragmentation and underlying event effects. The cross section differential in E_T ^jet, which varies by six orders of magnitude over the measured range, is compared with similar distributions from colliders at equal and higher energies.Received: 24 February 2003, Revised: 26 May 2003, Published online: 11 July 2003     

Developing a generalized diffraction model for elastic pd scattering at intermediate energies

A generalization of the Glauber-Sitenko diffraction model that includes the spin dependence of NN amplitudes, the D-wave of the deuteron, and the charge exchange effects is constructed for elastic pd scattering at intermediate energies. The developed model was used to analyze differential cross sections and some spin observables (analyzing powers) at the incident proton energies T _p = 1 GeV, 440 and 250 MeV. It was shown that predictions of the generalized diffraction model agree both with the experimental data and with the exact Faddeev calculations at low transfer momenta.     

Fragmentation cross sections of16O at 60 and 200 GeV/nucleon

We used CR39 plastic nuclear track detectors (C₁₂H₁₈O₇) in combination with automatic track measurement to determine total charge changing and partial cross sections for the production of fragments of chargeZ=6 andZ=7 in collisions of¹⁶O beam nuclei at energies of 60 GeV/nucleon and 200 GeV/nucleon in targets H, C, CR39, CH₂, Al, Cu, Ag and Pb. Total charge changing cross sections due to the process of electromagnetic dissociation are calculated based on a theoretical model and found to be consistent with total and partial electromagnetic dissociation cross sections derived from this experiment. The energy dependence of pure nuclear fragmentation is investigated.     

Measurement of prompt photons with associated jets in photoproduction at HERA

The photoproduction of prompt photons, together with an accompanying jet, has been studied in ep collisions at a centre-of-mass energy of 318 GeV with the ZEUS detector at HERA using an integrated luminosity of 77 pb^-1. Cross sections were measured for the transverse energy of the photon and the jet larger than 5 and 6 GeV, respectively. The differential γ+jet cross sections were reconstructed as functions of the transverse energy, pseudorapidity and x_γ ^obs, the fraction of the incoming photon momentum taken by the photon-jet system. Predictions based on leading-logarithm parton-shower Monte Carlo models and next-to-leading-order (NLO) QCD generally underestimate the cross sections for the transverse energies of prompt photons below 7 GeV, while the k_T-factorisation QCD calculation agrees with the data better. When the minimum transverse energy of prompt photons is increased to 7 GeV, both NLO QCD and the k_T-factorisation calculations are in good agreement with the data.     

Measurement of diffractive photoproduction of vector mesons at large momentum transfer at HERA

Elastic and proton–dissociative photoproduction of , and vector mesons (, , respectively) have been measured in interactions at HERA up to GeV, where t is the four-momentum transfer squared at the photon–vector–meson vertex. The analysis is based on a data sample in which photoproduction reactions were tagged by detection of the scattered positron in a special-purpose calorimeter. This limits the photon virtuality, , to values less than 0.01 GeV, and selects a average center-of-mass energy of = 94 GeV. Results for the differential cross sections, , for , and mesons are presented and compared to the results of recent QCD calculations. Results are also presented for the t-dependence of the pion-pair invariant-mass distribution in the mass region and of the spin-density matrix elements determined from the decay-angle distributions. The Pomeron trajectory has been derived from measurements of the W dependence of the elastic differential cross sections for both and mesons. Received: 16 October 1999 / Revised version: 17 January 2000 / Published online: 6 April 2000     

Deeply virtual Compton scattering off nuclei

We consider the hard leptoproduction of a photon off nuclei up to spin-1. As a new result we present here the general azimuthal angular dependence of the differential cross section for a spin-1 target. Its twist-two Fourier coefficients of the interference and squared deeply virtual Compton scattering amplitude are evaluated in leading order approximation of perturbation theory in terms of generalized parton distributions, while the pure Bethe-Heitler cross section is exactly calculated in terms of electromagnetic form factors. Relying on a simple model for the nucleon generalized parton distribution H, which describes the existing DVCS data for a proton target, we estimate the size of unpolarized cross sections, beam and longitudinal target spin as well as unpolarized charge asymmetries for the present fixed target experiments with nuclei. These estimates are confronted with preliminary HERMES data for deuterium and neon.Received: 1 October 2003, Published online: 3 December 2003     

Antiproton-proton cross sections at 200 and 900 GeV c.m. energy

Data on antiproton-proton cross sections at the c.m. energies 200 and 900 GeV are presented. The data were obtained at the CERN antiproton-proton Collider operated in a new pulsed mode in which the same beams were accelerated and decelerated between beam energies of 450 and 100 GeV. The properties of the machine determine the ratio of the luminosities at the two energies to about 1% and thus an accurate measurement of the ratioR of the inelastic cross sections could be made. We findR (=σ ⁹⁰⁰/σ ²⁰⁰)=1.20±0.01±0.02, where the first error is statistical and the second systematic. Interpolating existing data to estimateσ _ine1(200 GeV) this measurement ofR leads toσ _ine1(900 GeV)=50.3+0.4+1.0 mb. Using an extrapolated value ofσ _e1/σ _tot we estimate the total cross section at 900 GeV to be 65.3±0.7±1.5 mb. Both the inelastic and total cross sections are compatible with a ln² s dependence. Comparisons are made with different fits to the total cross section energy dependence.     

A measurement of the photonuclear interactions of 180 GeV muons in iron

The energy spectrum and the cross section of photonuclear interactions of 180 GeV muons in iron were measured at the CERN SPS using prototype modules of the ATLAS hadron calorimeter. The differential cross section for a muon fractional energy loss was measured in the range 0.1&lt;v&lt;1. The integrated cross section is cm²g^-1 in agreement with the theoretical prediction of cm²g^-1. The best adjustment of the data to the theory is achieved for the value of of the photon-nucleon cross section for photons with energies in the range from 18 to 180 GeV. Received: 22 January 2003 / Published online: 5 May 2003     

Formation of close-to-target products in reactions induced by <Superscript>12</Superscript>C ions on tin isotopes at the energy of 2.2 GeV per nucleon

Cross sections for charge-exchange reactions induced by the interaction between ¹²C ions of energy E_{¹² C} = 2.2E_{^{12} C} = 2.2 GeV per nucleon and tin targets enriched in the isotopes ^118,120,124Sn were measured by the induced-activity method. The cross sections for products whose charge numbers were in excess of the target charge number (Sb and Te) were determined. The shape of the isotope distribution of Sb products was indicative of the evaporative character of neutron emission in the formation of final-state products. The dependence of cross sections for charge-exchange reactions on the nucleonic composition of the target was considered. The contribution of electromagnetic excitation to the cross section for the reaction ¹²⁴Sn(¹²C, x)¹²⁴Sn was estimated.     

Cross sections and asymmetries for the reaction from threshold to 1 GeV

Total cross sections, differential cross sections and asymmetries for the reaction from threshold to 1 GeV have been measured. The outgoing π⁰ was detected by a 4π neutral meson spectrometer. Our data are compared with the corresponding np→NNπ^± reactions. The isoscalar partial cross sections are extracted from the relevant total cross sections. They are significant throughout the whole energy range. Below the Δ-region, energy-integrated differential cross sections show a large anisotropy difference between the neutral and charged pion channels, respectively. A partial-wave fit shows that the initial T = 0 state is dominated by the ³D₁ wave in this energy region. Finally, predictions of phenomenological models give reasonable good account of the measured observables but cannot reproduce the sign of the asymmetries.     

Measurement of D0, D+, Ds+ and D*+ production in fixed target 920?GeV proton–nucleus collisions

The inclusive production cross sections of the charmed mesons D⁰,D⁺,D_s ⁺ and D^*+ have been measured in interactions of 920 GeV protons on C, Ti, and W targets with the HERA-B detector at the HERA storage ring. Differential cross sections as a function of transverse momentum and Feynman’s x variable are given for the central rapidity region and for transverse momenta up to p_T=3.5 GeV/c. The atomic mass number dependence and the leading to non-leading particle production asymmetries are presented as well. PACS 13.85.Ni; 24.85.+p; 13.20.Fc     

Comparison of K−p Topological Cross Sections at 32 and 33.8 GeV/c with Lower Energy Data

The K⁻p experiments at 32.1 GeV/c and 33.8 GeV/c in the Mirabelle bubble chamber are reviewed and the resulting topological cross sections are compared to lower energy data with beam momenta between 4.2 and 16 GeV/c. Some quantities characterizing the multiplicity distributions are compiled for these data and their energy dependence is compared to results from pp experiments. Studying the scaling behavior of the K⁻p multiplicity distributions, “quasi scaling” is observed for data with p_Lab ≧ 8.25 GeV/c.     

A precise determination of the τ-mass

The energy dependence of the cross sections for e⁺e^? → e^±(μ^±) + 1 charged track has been measured for centre of mass energies between 3.60 and 4.40 GeV. The pair production of the τ-lepton is observed at all energies and the τ-mass is determined to be 1.787_?0.018^+0.010 GeV from a fit to the energy dependence of the cross section.     

η production in nuclei by protons at Tp≦ 1 GeV

The reactionpA →η X has been measured on⁶Li, C and Cu targets at a proton energy of 0.9 GeV at the SATURNE accelerator. The doubly differential cross sections at T_p=0.9 GeV together with data at T_p=1 GeV, previously presented [1], are analysed in the frame of a recent folding model [3].     

An experimental test of exchange degeneracy in the hyperchange exchange reactions π+p→K+Σ+and K−→π−Σ+

For the first time, the line reversed reactions π⁺p→K⁺Σ⁺and K^?p→π^?Σ⁺ have been studied in the same apparatus. We present the differential cross sections and polarizations over a large t range and at two momenta, 7.0 and 10.1 GeV/c. The differential cross sections as a function of t are shown for the first time to cross over. Going from the lower to the higher momentum, the differences in cross section between the two reactions diminish at low |t| by about a factor 2. We find large polarizations of opposite sign for the two reactions. The momentum dependence, presented in the form of α_eff(t) for the t range 0 to ?2 (GeV/c)², is compared with the expectations from the K¹?K⁷ trajectory.     

Energy dependence of backward π−d elastic scattering in the 1–2 GeV region

Differential cross sections for backward π^?d elastic scattering (?1 ≦ cos θ_c.m ≦ ?0.98) have been measured at fourteen momenta from 0.98 to 1.76 GeV/c and at 2.45 GeV/c. Energy dependence of the cross section exibits a new wide structure at √s ≈ 2.9 GeV. Possible mechanisms of the reaction accounting for this structure are presented. Experimental data are compared with theoretical calculations.     

Charmonium production in deep inelastic scattering at HERA

The electroproduction of and mesons is studied in elastic, quasi-elastic and inclusive reactions for four momentum transfers and photon-proton centre of mass energies GeV. The data were taken with the H1 detector at the electron proton collider HERA in the years 1995 to 1997. The total virtual photon-proton cross section for elastic production is measured as a function of and W. The dependence of the production rates on the square of the momentum transfer from the proton (t) is extracted. Decay angular distributions are analysed and the ratio of the longitudinal and transverse cross sections is derived. The ratio of the cross sections for quasi-elastic and meson production is measured as a function of . The results are discussed in terms of theoretical models based upon perturbative QCD. Differential cross sections for inclusive and inelastic production of mesons are determined and predictions within two theoretical frameworks are compared with the data, the non-relativistic QCD factorization approach including colour octet and colour singlet contributions, and the model of Soft Colour Interactions. Received: 10 March 1999 / Published online: 8 September 1999