The neutron/proton ratio of fast nucleon emission in antiproton annihilation on nuclei

The measurement of fast protons and neutrons emitted after antiproton annihilation at rest on²³⁸U and⁶³Cu reveals a large neutron/proton ratioR. Its value for⁶³Cu is larger than expected from the conventional model of intranuclear pion rescattering. A value ofR essentially constant over the whole range of mass number, from¹²C up to²³⁸U, is also announced by the experimentalists. It is shown that, on the contrary, the conventional scheme predicts a regular increase ofR with mass number. Alternative explanations of the effect are looked for. Within the usual scheme, an excess of negative pions, leading to more emitted neutrons, is not compatible with final pion multiplicities. The influence of meson resonances on the neutron/proton ratio is considered, as well as the possible occurrence of annihilations on two nucleons. They cannot warrant an increase ofR at low mass targets sufficient to explain a constant value over the whole range of target masses.     

Cross-sections of large-angle hadron production in proton– and pion–nucleus interactions IV: copper nuclei and beam momenta from ±3 GeV/c to ±15 GeV/c

We report on double-differential inclusive cross-sections of the production of secondary protons, charged pions, and deuterons, in the interactions with a 5% λ _abs thick stationary copper target, of proton and pion beams with momentum from ±3 GeV/c to ±15 GeV/c. Results are given for secondary particles with production angles 20°<θ<125°. The inclusive pion production cross-sections are compared to those on beryllium and tantalum, published by us recently.     

Spin dependence of inclusive reactions from proton-proton collisions at 7.9 GeV/c

The spin dependence of inclusive proton and pion production by 7.9 GeV/c protons has been measured using a polarized proton target, for nominal values of x = p_L^cm/p_max^cm = 0.7 in the transverse momentum range 0.4 GeV/c <pp_t < 1.2 GeV/c, and for p_t = 0.4 GeV/c in the range 0.1 < x < 0.96. The results indicate a positive asymmetry of +5% over this kinematic region, which corresponds to fragmentation of the unpolarized proton.     

Nucleons produced in inelastic electron scattering with a deuterium target

We have measured at ?k² = 0.6 (GeV/c)² and W = 2.3 GeV the inclusive electroproduction cross sections for final-state neutrons and protons from a deuterium target. By comparison with previous data from a proton target, we present cross sections for inclusive nucleon production from neutrons which show great similarity to those from protons. There is evidence that ?⁰ production is present with essentially the same strength as with a proton target.     

Cross-sections of large-angle hadron production in proton– and pion–nucleus interactions VII: tin nuclei and beam momenta from ±3 GeV/c to ±15 GeV/c

We report on double-differential inclusive cross-sections of the production of secondary protons, charged pions, and deuterons, in the interactions with a 5% λ _int thick stationary tin target, of proton and pion beams with momentum from ±3 GeV/c to ±15 GeV/c. Results are given for secondary particles with production angles 20^○<θ<125^○. Cross-sections on tin nuclei are compared with cross-sections on beryllium, carbon, copper, tantalum and lead nuclei.     

Charged pion production in 70 GeV/cK + p interactions

Inclusive charged pion production is studied in an exposure of BEBC, filled with hydrogen, to an incidentK ⁺ beam of 70 GeV/c. Total cross sections for pion production and inclusive longitudinal and transverse momentum distributions of π^?'s and of positive particles are presented and compared with data at lower energies. Earlier evidence for scaling in the fragmentation regions is confirmed. The central region π^? cross section increases proportionally top _LAB ^?1/4 ; positive particles show almost no energy dependence atx=0. Particle ratios π⁺/π^? are studied as a function ofx andy ^* and a comparison with 70 GeV/cK ^? p data is made. Analysis of structure functions for (ππ) pairs and of particle production associated with π^± triggers at large |x| in the context of quark/parton models, provides qualitative evidence for the diquark-quark structure of the proton.     

Left–right asymmetry for pion and kaon production in the semi-inclusive deep-inelastic scattering process

We analyze the left–right asymmetry in the semi-inclusive deep-inelastic scattering (SIDIS) process without introducing any weighting functions. With the current theoretical understanding, we find that the Sivers effect plays a key role in our analysis. We use the latest parametrization of the Sivers and fragmentation functions to reanalyze the π ^± production process and find that the results are sensitive to the parametrization. We also extend our calculation on the K ^± production, which can help us know more about the Sivers distribution of the sea quarks and the unfavored fragmentation processes. HERMES kinematics with a proton target, COMPASS kinematics with a proton, deuteron, and neutron target (the information on the neutron target can be effectively extracted from the ³He target), and JLab kinematics (both 6 GeV and 12 GeV) with a proton and neutron target are considered in our paper.     

Cross sections of large-angle hadron production in proton– and pion–nucleus interactions III: tantalum nuclei and beam momenta from ±3 GeV/c to ±15 GeV/c

We report on double-differential inclusive cross sections of the production of secondary protons, charged pions, and deuterons, in the interactions with a 5% λ _abs thick stationary tantalum target, of proton and pion beams with momentum from ±3 GeV/c to ±15 GeV/c. Results are given for secondary particles with production angles 20°<θ<125°. They are of particular relevance for the optimization of the design parameters of the proton driver of a neutrino factory.     

Measurement of polarized target asymmetry on γn→π−p around the second resonance region

The polarized target asymmetry for γn→π^?p was measured over the second resonance region from 0.55 to 0.9 GeV at pion c.m. angles between 60° and 120°. A double-arm spectrometer was used with a deuterated butanol target to detect both the pion and the proton, thus considerably improving the data quality. Including the new data in the amplitude analysis, the radiative decay widths of three resonances were determined more accurately than before. The results are compared with various quark models.     

Cross-sections of large-angle hadron production in proton- and pion-nucleus interactions I: beryllium nuclei and beam momenta of +8.9 GeV/c and −8.0 GeV/c

We report on double-differential inclusive cross-sections of the production of secondary protons, deuterons, and charged pions and kaons, in the interactions with a 5% λ _abs thick stationary beryllium target, of a +8.9 GeV/c proton and pion beam, and a −8.0 GeV/c pion beam. Results are given for secondary particles with production angles 20^○<θ<125^○. On leave of absence at Ecole Polytechnique Fédérale, Lausanne, Switzerland.     

Can we get deeper inside the pion at the LHC?

We propose a measurement of leading neutrons spectra at LHC in order to extract inclusive π ⁺ p and π ⁺ π ⁺ cross-sections with high p _T jets production. The cross-sections for these processes are simulated with the use of parton distributions in hadrons. In this work we estimate the possibility to extract parton distributions in the pion from the data on these cross-sections and also search for signatures of fundamental differences in the pion and proton structure.     

Cross-sections of large-angle hadron production in proton–and pion–nucleus interactions V: lead nuclei and beam momenta from ±3 GeV/c to ±15 GeV/c

We report on double-differential inclusive cross-sections of the production of secondary protons, charged pions, and deuterons, in the interactions with a 5% λ _int thick stationary lead target, of proton and pion beams with momentum from ±3 GeV/c to ±15 GeV/c. Results are given for secondary particles with production angles 20°<θ<125°. Cross-sections on lead nuclei are compared with cross-sections on beryllium, copper, and tantalum nuclei.     

Inclusive particle production in π− n interactions at high energies

Results on inclusive particle production in π^? n interactions at 21, 205 and 360 GeV/c are presented. The invariant cross sections in both neutron fragmentation and central regions are found to be equal within errors to the corresponding cross sections for π^? p collisions and exhibit the same energy dependence. A strong energy dependence of the invariant cross section ratios of negative and positive pions is observed. There is also an indication of transverse momentum dependence of these ratios. The η^? correlations in the neutron fragmentation region show little variation with energy and are in agreement with the predictions of the naive quark recombination scheme.     

Single spin asymmetry in inclusive pion production,Collins effect and the string model

We calculated the single spin asymmetry in the inclusive pion production in the fragmentation region of transversely polarized proton-proton collisions. We generated the asymmetry at the level of fragmentation function (Collins effect) by the Lund coloured string mechanism. We compared our results to the presently available experimental data. We obtained a qualitative agreement with the data after assuming that the transverse polarizations of the u and the d quarks in the proton are +1 and ? 1, respectively, at x_B=1.     

Multi-meson exchange in non-Abelian gauge theories

We find a new sum rule for the residue of the J = 0 fixed pole in Compton scattering. The sum rule applies to any target and links the residue to a calculable set of contributions from the resonance region. We discuss proton, neutron, deutron and pion targets and the possibility of discriminating from previous models. The relationship with the parton model is noted and the feasibility of measuring pion photoabsorption cross sections is discussed.     

Cross-sections of large-angle hadron production in proton– and pion–nucleus interactions VI: carbon nuclei and beam momenta from ±3 GeV/c to ±15 GeV/c

We report on double-differential inclusive cross-sections of the production of secondary protons, charged pions, and deuterons, in the interactions with a 5% λ _int thick stationary carbon target, of proton and pion beams with momentum from ±3 GeV/c to ±15 GeV/c. Results are given for secondary particles with production angles 20°<θ<125°. Cross-sections on carbon nuclei are compared with cross-sections on beryllium, copper, tantalum and lead nuclei.     

SU(2) Flavor Asymmetry of the Proton Sea in Chiral Effective Theory

We refine the computation of the d? ? ū flavor asymmetry in the proton sea with a complementary effort to reveal the dynamics of pion exchange in high-energy processes. In particular, we discuss the efficacy of pion exchange models to simultaneously describe leading neutron electroproduction at HERA along with the d? ? ū flavor asymmetry in the proton. A detailed \({\chi^{2}}\) analysis of the ZEUS and H1 data, when combined with constraints on the pion flux from Drell-Yan data, allows regions of applicability of one-pion exchange to be delineated. Based on the fit results, we also address a possible estimate for leading proton structure functions in upcoming tagged deep-inelastic scattering experiments at Jefferson Lab on the deuteron with forward protons.     

Proton and neutron contributions to the charge longitudinal response

The charge longitudinal response of nuclei, as measured by inclusive inelastic electron scattering, is investigated in the semiclassical RPA framework. The proton and neutron contributions to the total response are explicitly separated out. It is found that a sizable neutron ejection can be induced by RPA correlations, particularly at low momentum and energy transfer. A comparison of our theory with the experimental data is presented, also in the case of asymmetric nuclei (N ≠ Z). In particular, the differences in the neutron contributions between ³⁰Ca and ⁴⁸Ca are discussed.