Inclusive Pion Production Research Articles

Energy dependence of the single spin asymmetries in inclusive pion production processes

Recent data from the E925 Collaboration at Brookheaven National Laboratory show a significant energy dependence of the single-spin left-right asymmetry in inclusive hadron production in hadron-hadron collisions. We analyze the experimental results and show that the observed energy dependence can be reproduced naturally in the picture proposed in a previous Letter. We fix all the parameters at the Fermilab E704 energy and calculate the asymmetry at the BNL E925 energy. We compare the results with the data and make predictions for experiments at even higher energies.

Transverse single spin asymmetries in Drell-Yan processes

Recently, it has been shown, contrary to previous beliefs, that the k_T distribution of quarks in a transversely polarized proton can be asymmetric. This ``Sivers effect'' had already been used to explain transverse single spin asymmetries (SSA) observed in inclusive pion production, p(transv. polarized) p --> pion + X and p-bar(transv. polarized) p --> pion + X. In such channels, however, other mechanisms, like the ``Collins effect'' (a k_T asymmetric fragmentation of a transversely polarized quark into pions), may generate SSA. The Sivers asymmetry is used here to compute SSA in Drell-Yan processes; in this case, by considering the differential cross-section in the lepton-pair invariant mass, rapidity and transverse momentum, other mechanisms which may originate SSA cannot contribute. Estimates for RHIC experiments are given.

STUDIES IN RAPIDITY AND pT-SPECTRA OF PIONS IN HIGH ENERGY NN, NA AND AA COLLISIONS: A COMPREHENSIVE APPROACH

The present paper aims at testing a very simple approach to interpret the characteristics of inclusive production of pions in high energy NA and AA collisions by a somewhat in-depth analysis of the same for NN interactions; and also at reporting here thus some interesting observations made on the nature of rapidity and transverse momentum spectra of the produced pions. And this approach is built upon a newly offered master formula holding the key for converting the results of high energy nucleon–nucleon (NN) collision to the corresponding observables on differential and inclusive cross-sections for both nucleon–nucleus and nucleus–nucleus (heavy ion) collisions in a generalized form. The proposed formulae, used in a somewhat phenomenological way, can provide modestly reliable parametrization of data in the broad range of collision energy and the varied range of projectile-target combinations. This opens up the possibility of understanding in a quite unified manner the large amount of data on the rapidity and transverse momentum spectra in a wide range of interactions and energies starting right from ISR, rather Bevelac, to the relativistic heavy ion collisions (RHIC) via the various collider scales of energy. The agreements between the data and calculations, in most cases, are quite satisfactory both qualitatively and quantitatively. While highlighting this success, the limitation of the approach has also been pointed out in the end as clearly and categorically as possible.

Inclusive soft pion production from 12.3 and17.5 GeV/cprotons on Be, Cu, and Au

Differential cross-sections are presented for the inclusive production of charged pions in the momentum range 0.1 to 1.2 GeV/c in interactions of 12.3 and 17.5 GeV/c protons with Be, Cu, and Au targets. The measurements were made by Experiment 910 at the Alternating Gradient Synchrotron in Brookhaven National Laboratory. The cross-sections are presented as a function of pion total momentum and production polar angle $\theta$ with respect to the beam.

Neutrino anomaly and ν-nucleus interactions

A review of various calculations of the inclusive quasi-elastic reactions and pion production processes in neutrino reactions for various nuclei at intermediate energies relevant to solar, atmospheric and accelerator neutrinos is presented

Single spin asymmetries in $p\uparrow p \rightarrow \pi X$ and $\bar{p} \uparrow p \rightarrow \pi X$

We study the inclusive production of charged and neutral pions in the reactions $p \uparrow p \rightarrow \pi X$ and $\bar{p} \uparrow p \rightarrow \pi X$ in the framework of single spin asymmetries. We propose a two components model where production of pions occurs both by recombination of the constituents present in the initial state and by fragmentation of quarks in the final state. Taking the Thomas precession mechanism in the recombination component into account, we obtain a good description of the experimentally observed single spin asymmetries. We show that the observed single spin asymmetries are consistent with the measured spin alignment in the polarized proton as measured by HERMES and SMC.

Analyzing powers in inclusive pion production at high energy and nucleon spin structure

Analyzing powers in inclusive pion production at high energy and nucleon spin structure

ANALYZING POWERS IN INCLUSIVE PION PRODUCTION AT HIGH ENERGY AND THE NUCLEON SPIN STRUCTURE

Analyzing powers in inclusive pion production in high energy transversely polarized proton–proton collisions are studied theoretically in the framework of the quark recombination model. Calculations by assuming the SU(6) spin-flavor symmetry for the nucleon structure disagree with the experiments. We solve this difficulty by taking into account the realistic spin distribution functions of the nucleon, which differs from the SU(6) expectation at large x, with a perturbative QCD constraint on the ratio of the unpolarized valence distributions, u/d→5 as x→ 1. We also discuss the kaon spin asymmetry and find AN(K+)=-AN(K0) in the polarized proton–proton collisions at large x F .

Inclusive production of neutral pions in hadronic Z decays

A measurement of the inclusive production of pi0 mesons in hadronic Z decays is presented and compared to Monte Carlo model predictions. The analysis is based on approximately 2 million hadronic events recorded with the ALEPH detector at LEP at a centre-of-mass energy of sqrt(s) = 91.2 GeV. Neutral pions are reconstructed using photons from conversion pairs and photons measured in the electromagnetic calorimeter. The inclusive pi0 momentum spectrum is measured in the range from 0.025 < x(p) = p/p(beam) < 1 to be 4.80 +/- 0.07(stat) +/- 0.31(sys). The differential inclusive pi0 cross section has also been measured as a function of transverse momentum with respect to the event plane (p_T^in and p_T^out_T).

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 xB=1.

Asymmetry in inclusive pion production.

On the basis of the mechanism proposed for one-spin asymmetries in inclusive hadron production we specify an $x$--dependence of asymmetries in inclusive processes of pion production. The main role in generation of this asymmetry belongs to the orbital angular momentum ofquark-antiquark cloud in internal structure of constituent quarks. The $x$--dependence of asymmetries in the charged pion production at large $x$ reflects the corresponding dependence of constituent quark polarization in the polarized proton.

Single spin asymmetry for p↑ p → πX in perturbative QCD

Within the QCD-improved parton model and assuming the factorization theorem to hold in the helicity basis and for higher twist contributions, we show how nonzero single spin asymmetries in hadron-hadron high energy and moderately large p T inclusive processes can be obtained, even in massless perturbative QCD, provided the quark intrinsic motion is taken into account. A simple model is constructed which reproduces the main features of the data on the single spin asymmetry observed in inclusive pion production in p p collisions.

Comments on polarization asymmetry measurements

In this report some results on the one-spin asymmetryy, obtained by the FNAL E581/E704 Collaboration for inclusive pion production at 200 GeV/c by a polarized beam, are discussed. It is argued that the presented data, mainly x F -dependences, cannot be interpreted in the sense adopted by the authors.

Inclusive charged pion production in hadron-nucleus interactions at 100 and 320 GeV/c

An experiment has been performed with the Fermilab 30-inch bubble chamber and Downstream Particle Identifier to study inclusive charged pion production in the high energy interactions of π±,K+,p and\(\bar p\) with thin foils of magnesium, silver and gold. The laboratory rapidity and transverse momentum distributions are presented separately for π+ and π− production. Comparisons are made with data from hadron-proton interactions and theA dependence of the cross sections in the different kinematic regions is discussed. We investigate the dependence of the cross sections on the number of observed protons ejected from the nucleus. By using our π−A data from two different beam energies, we study the energy dependence of these spectra. Comparisons are made with the VENUS string model Monte Carlo.

Neutron-induced particle production in the cumulative and noncumulative regions at intermediate energies

The first systematic measurements of neutron-induced inclusive production of protons, deuterons, tritons and charged pions on carbon, copper and bismuth in the bombarding energy range of 300–580 MeV and in the angular interval from 51° to 165° have been analyzed in the framework of the cascade-exciton model. The role of single-particle scattering, the effects of rescattering, the pre-equilibrium emission and “coalescence” mechanism in particle production in the cumulative (i.e., kinematically forbidden for quasi-free intranuclear projectile-nucleon collisions) and noncumulative regions are discussed. A weak sensitivity of the inclusive distributions to the specific reaction mechanisms and a need of correlation and polarization measurements are noted.

Inclusive production of charged pions, kaons and protons in υ(4S) decays

Using the detector ARGUS at thee + e − storage ring DORIS II, we have investigated inclusive momentum spectra of charged pions, kaons, and protons from decays of the υ(4S) meson. The kaon spectra have been measured in two independent ways, by coherently exploiting the detector's particle identification capabilities, and by detecting decays in-flight. The extracted mean multiplicities for charged hadrons are 7.17±0.05±0.14 pions, 1.56±0.03±0.05 kaons and 0.110±0.010±0.007 protons per υ(4S) decay, where pions and protons fromK and Δ decays have been subtracted.

Left-right asymmetry and orbiting valence quarks in polarized protons and antiprotons

It is shown that the asymmetry observed in the recent single-spin large-x F inclusive pion production experiments at high-energies should be considered as a strong indication for the existence of orbiting valence quarks in polarized protons and antiprotons. The underlying physical picture in which orbiting valence quarks give rise to flavor-currents is discussed. The close connection between these currents and the measured quantities — in particular baryon's magnetic moment and the abovementioned asymmetry — is pointed out.

Pion production in nuclear collisions

The production of pions in nuclear collisions is analyzed in terms of a microscopic reaction model, where the free energy of the entrance channel is transferred to the final channel through the coupling of the relative motion to the internal excitation of N*-resonances. Such a model allows quite naturally for a consistent analysis of the exclusive and the inclusive production of pions. It turns out that the pionic fusion cross section is determined predominantly by the spectroscopic parentage between the initial target projectile combination and the final nucleus, whereas the inclusive part is dominated by the energy dependence of the phase space factor, i.e. by the number of the degrees of freedom which are relevant in a given kinematical situation. This model is applied to the analysis of available experimental data from threshold to the Δ(1232)-region. A consistent analysis of both the inclusive and the exclusive part of the pion spectrum is presented.

Measurement of the inclusive production of neutral pions and charged particles on the Z 0 resonance

We present a study of the inclusive production of neutral pions and charged particles from 112 000 hadronic Z 0 decays. The measured inclusive momentum distributions can be reproduced by parton shower Monte Carlo programs and also by an analytical QCD calculation. Comparing our results to e +e − data between √ s = 9 and 91 GeV, we findfind that the evolution of the spectra with center of mass energy is consistent with the QCD predictions.

Inclusive (p, ?0) reactions atE lab=200 MeV

The inclusive production of neutral pions has been studied with a proton beam atE lab =200 MeV. The twoγ rays from theπ 0 decay were detected by means of a setup of ten Pb-glass Cherenkov detectors. Measurements on several targets (C, Al, Ni, Y,118Sn,124Sn, Pb, U) have been made to investigate theA-dependence. A fit of the total experimental cross sections is obtained with a relationσ tot incl =10.3×A 0.83 μb. Comparison with (p, π±) reactions is presented.