On the reactions p + p↦p + Λ + K+ and p + p↦p + Σ0 + K+ near thresholds

The cross-sections for the reactions of the strange production p + p ↦ p + Λ + K⁺ and p + p ↦ p + Σ⁰ + K⁺ near thresholds of the final states pΛK⁺ and pΣ⁰K⁺ are calculated in the effective Lagrangian approach. Our approach is based on the dominant contribution of the one-pion exchange and strong interaction of the colliding protons in the initial state. The theoretical values of the cross-sections agree reasonably well with the experimental data. The polarization properties of the Λ- and Σ⁰-hyperons are discussed.     

On polarization of strange baryons in reactions p + p↦p + Λ0 + K+ and p + p↦p + Σ0 + K+ near thresholds

Polarization properties of strange baryons produced in pp reactions, p + p↦p + Λ⁰ + K⁺ and p + p↦p + Σ⁰ + K⁺, near thresholds of the final states pΛ⁰K⁺ and pΣ⁰K⁺ are analysed relative to polarizations of colliding protons. The cross-sections for pp reactions are calculated within the effective Lagrangian approach accounting for strong pp rescattering in the initial state of colliding protons with a dominant contribution of the one-pion exchange and strong final-state interaction of daughter hadrons (Eur. Phys. J. A 9, 425 (2000)). Received: 22 October 2001 / Accepted: 14 November 2001     

Annihilation of + \bar p + p → e + + e ? + π0 and + \bar p + p → γ + π0 through an ω-Meson intermediate state

The s-channel annihilation of a proton and an antiproton into a neutral pion and a real or virtual photon followed by lepton pair emission is studied. Such a mechanism is expected to play a role at moderate values of the total energy $ \sqrt s $ , when the pion is emitted in the angular region around 90° in the center-of-mass system. A fair comparison with the existing data is obtained taking scattering and annihilation channels into account. The cross section is calculated and numerical results are given in the kinematical range accessible in the PANDA experiment at FAIR.     

The p + p → π+ + d reaction close to threshold at COSY

Differential and total cross sections of the p + p → π⁺ + d reaction close to threshold were measured employing a magnetic spectrograph with track reconstruction, a very thin liquid hydrogen target and an accelerated proton beam with high phase space density. The data resolve a previous discrepancy between the n + p → π⁰ + d and the π⁺ + d → 2p reaction close to threshold indicating that isospin symmetry may be broken in the s-wave part of the cross section.     

A study ofK + p elastic scattering and reactionK + p→K + pπ+π− at 70 GeV/c

Results are presented onK ⁺ p elastic scattering and on the reactionK ⁺ p→K ⁺ pπ⁺π^? at 70 GeV/c. For the elastic channel, we measured the total ((2.29±0.04)mb) and differentialdσ/dt cross sections. The reactionK ⁺ p→K ⁺ pπ⁺π^? has a total cross section of (470±23) μb and is shown to be dominated by diffractive dissociation processes. The contributions of the quasi-two-body channels $$K^ + p \to K*^0 (890)\Delta ^{ + + } (1,236)$$ and $$K^ + p \to K*^0 (1,430)\Delta ^{ + + } (1,236)$$ and of the Double-Pomeron Exchange (DPE) processes are estimated.     

Measurements of π+p,K+p and pp elastic scattering)

The paper presents the results on differential cross sections for elastic scattering of 7⁺-, K⁺-mesons and protons on protons in the 4-momentum transfer squared range 0·08 ¦t¦ 1·0 (GeV/c)² and incident particle momentum of 29 and 43 GeV/c for pions and kaons and 29, 43, 50 and 65 GeV/c for protons. The measurements were taken with the spectrometer Sigma, installed in the positive beam of the IHEP accelerator.Presented by F. A. Yotch at the Symposium on Hadron-Hadron Scattering at High Energies, Liblice, Czechoslovakia, June 16–21, 1975.The authors would like to express their gratitude to A. A.Logunov, Yu. D.Prokoshkin, L. D.Soloviev and V. A.Yarba for their support of this experiment. We are indebted to CERN Administration for giving us a permission to use a part of equipment of the CIBS spectrometer and to W.Kienzle for useful discussions.     

Final-state interactions and repulsive Coulomb effects ind+3He→3H+p+p reaction

Differential cross sections of the reactiond+³He³H+p+p have been measured atE _d =23.083 MeV in two different kinematical configurations. A gas target was used in order to obtain absolute differential cross sections and two E–E telescopes allowed a very good identification of the various particles coming from thed+³He reaction. The role of the finalstate interactions and repulsive Coulomb effects appears rather distinctly.     

Measurement of PV asymmetry in +p→d+γ and ■+d→n+p

The measurement of parity-violating (PV) observables in few-nucleon system can shed light on our current understanding of the weak interaction between nucleons.Theoretical models describe the nucleonnucleon weak interaction at low energies use a series of undetermined parameters.Two parity violating measurements have been considered: the capture of polarized slow neutrons on hydrogen (n + p → d + γ) at Los Alamos National Laboratory for first phase and Oka Ridge National Laboratory for second phase and the helicity dependence of the deuteron photodisintegration cross section using circularly polarized photons (γ + d → n + p) at Shanghai Institute of Applied Physics.The goal of both experiments is to constraint the weak meson-nucleon couplings to a precision of 1 ×10-8 .The introduction of both experiments is presented.     

Spin structure of the “forward” charge-exchange reaction n + p → p + n and deuteron charge-exchange breakup d + p → (pp) + n

The spin structure of the nucleon charge-exchange process n + p → p + n is investigated. Analysis shows that the spin-dependent part of the differential cross section of the process n + p → p + n at zero angle, which is proportional to the differential cross section of the deuteron charge-exchange breakup d + p → (pp) + n in the “forward” direction, plays the predominant role in the wide range of neutron momenta.     

Photoproduction of J/ψ in non-single-diffractive p+p collisions

Significant enhancements of J/ψ production at very low transverse momenta were recently observed by the ALICE and STAR collaborations in peripheral hadronic A+A collisions. The anomalous excess points to coherent photon-nucleus interactions in violent hadronic heavy-ion collisions, which were conventionally studied only in ultra-peripheral collisions. Assuming that the coherent photoproduction is the underlying mechanism responsible for the excess observed in peripheral A+A collisions, its contribution in p+p collisions with nuclear overlap, i.e. nonsingle-diffractive collisions, is of particular interest. In this paper, we perform a calculation of exclusive J/ψ photoproduction in non-single-diffractive p+p collisions at the RHIC and LHC energies based on the pQCD motivated parametrization using the world-wide experimental data, which could be further employed to improve the precision of the phenomenological calculations for photoproduction in A+A collisions. The differential rapidity and transverse momentum distributions of J/ψ from photoproduction are presented. In comparison with the J/ψ production from hadronic interactions, we find that the contribution of photoproduction is negligible.     

Study of theK + K − π+ π− system centrally produced in the reactions π+ p→π+(K + K − π+ π−)p andpp→p(K + K − π+ π−)p at 85 GeV/c

The reactions π⁺ p→π⁺(K ⁺ K ^? π⁺ π^? p andpp→p(K ⁺ K ^? π⁺ π^?)p where the (K ⁺ K ^? π⁺ π^?) system is centrally produced have been studied at 85 GeV/c. 48% of the final state proceeds through single or double vector meson resonant production i.e.,K ^*0(890) (37%), ? (4%),ρ ⁰ (7%). Evidence is found for associatedK ^*0 (890) \(\bar K\) ^*o (890) production (6.4±1.1%) with a cross section ten times higher than that found for associated ? ? production in the same experiment.     

n + p → d + γ in effective field theory

The radiative capture process n + p → d + γ provides clear evidence for meson exchange currents in nuclear physics. We compute this process at low energies using a recently developed power counting for the effective field theory that describes nucleon-nucleon interactions. The leading order contribution to this process comes from the photon coupling to the nucleon magnetic moments. At subleading order there are other contributions. Among these are graphs where the photon couples directly to pions, i.e. meson exchange currents. These diagrams are divergent and require the presence of a local four-nucleon-one-photon counterterm. The coefficient of this operator is determined by the measured cross section, σ^expt = 334.2±0.5 mb, for incident neutrons with speed |v| = 2200 m/s.     

Forward-backward multiplicity correlations in σ+ p,K + p andpp collisions at 250 GeV/c

Forward-backward multiplicity correlations in σ⁺,K ⁺ p andpp collisions at 250 GeV/c ( \(\sqrt s \) =22 GeV) are given for all charges and for the different charge combinations. The correlations are found to be caused predominantly by centrally produced particles. It is demonstrated that this result is an agreement with observations at the ISR and the CERNp \(\bar p\) -Collider. The results are compared to expectations from LUND, DPM and FRITIOF Monte Carlo models and a geometrical picture relating correlations in hadron-hadron collisions toe ⁺ e ^? data in terms of impact parameters is tested.     

Higher order bose-einstein correlations in π+p and K+p collisions at 250 GeV/c

Bose-Einstein correlations up to fourth order are presented at $\sqrt s = 22GeV$ . Genuine third-order correlations are observed. The experimental data are compared with predictions from a quantum statistical approach of radiation from a partially coherent source and with the FRITIOF model.     

Strange and non-strange baryon production in π+ p andK + p interactions at 250 GeV/c

We present data on the production of the baryons Λ, \(\bar \Lambda \) ,p and of the baryon resonances Σ^*+ (1385) and Δ⁺⁺ (1232) inK ⁺ p and π⁺ p interactions at 250 GeV/c. Results are given on total and semi-inclusive cross sections, Feynman-x spectra, transverse momentum distributions and Λ polarization. The data are compared with measurements at lower energies, with deep inclastic lepton nucleon data and with predictions of quark-parton models. The models underestimate Λ production in the central c.m. region, a feature also seen in recent heavy-ion data. This failure can be cured in JETSET 6.3 by adjustment of the di-quark break-up probability.     

\bar K K and\bar p p off-shell annihilations fromK − +p → Λ + pions at 4.2 GeV/c

We have investigated the properties of off-shell \(\bar K\) K and \(\bar p\) p annihilations into pions by using the interactionsK ^? p → Λ + pions at 4.2 GeV/c. The properties considered are multiplicities, hadronic temperatures and angular distributions. These properties appear more akin to those of \(\bar p\) p annihilations in flight than to that of \(\bar p\) p annihilation at rest despite the fact that the annihilation energy is small.     

Parton rescattering effect on particle production in ultra-relativistic p+p collisions

The parton rescattering effect on the charged particle production in ultra-relativistic p+p collisions is studied by the parton and hadron cascade model PACIAE, based on PYTHIA. We have calculated charged particle pseudorapidity density at mid-rapidity and the pseudorapidity distribution in inelastic and non-single diffractive p+p collisions at $\sqrt{s}=200$ , 900, 5500, and 14000 GeV with the PYTHIA and PACIAE models. The calculated results for $\sqrt{s}=900$  GeV are well compared with the ALICE data. Comparing the PYTHIA results (without parton rescattering) with the PACIAE results (with parton rescattering), it turned out that the parton rescattering may play an important role and this effect increases with increasing CMS energy.     

A study of double pomeron exchange inπ + p andK + p interactions at 250 GeV/c

Using the ARGUS detector at thee ⁺ e ^– storage ring DORIS II at DESY, we have measured the inclusive production ofD ⁰,D ⁺ andD ^*(2010)⁺ mesons inB decays and in nonresonante ⁺ e ^– annihilation around 10.6 GeV. The inclusive branching ratios forB decays toD ⁰,D ⁺ andD ^*+ mesons are found to be (52.2±8.2±3.5)%, (27.2±6.3±3.5)% and (34.8±6.0±3.5)% respectively. Thus,D ⁰ andD ⁺ production account for about 70% of the charm produced inB decays, neglectingbu contributions to the total width. The production cross sections and momentum spectra for continuume ⁺ e ^– annihilation are also presented.Supported by the German Bundesministerium für Forschung und Technologie, under contract number 054DO51P     

Photoproduction of π + p pairs on nuclei

The photoproduction of pion-nucleon pairs on nuclei was analyzed. The contributions of both nucleonic and isobar configurations in the ground state of nuclei were taken into account. The cross section for the photoproduction of pion-proton pairs in the reactions ¹⁶O(??, ?? ⁺ p)¹⁵C and ¹²C(??, ?? ⁺ p)¹¹Be were calculated.     

光子-核子散射的双谱函数和γ+p→p+π++π-非弹性截面

本文将带区近似法推广到光子-核子散射过程。由t道弹性么正条件导出了光子-核子散射的带区谱函数和s道散射振幅的吸收部分,由此计算了光生π介子的非弹性截面,并与实验作了比较。