Inclusive Pion Production Research Articles

Testing the process dependence of the Sivers function via hadron distributions inside a jet

We study the process dependence of the Sivers function by considering the impact of color-gauge invariant initial and final state interactions on transverse spin asymmetries in proton–proton scattering reactions within the framework of the transverse momentum dependent (TMD), generalized parton model. To this aim, we consider the azimuthal distribution of leading pions inside a fragmenting jet as well as single inclusive jet asymmetry in polarized proton–proton collisions. In contrast to single inclusive pion production, in both cases we can isolate the Sivers contribution and thereby study its process dependence. The predictions for the Sivers asymmetry obtained with and without inclusion of color gauge factors are comparable in size but with opposite signs. We conclude that both processes represent unique opportunities to discriminate among the two approaches and test the universality properties of the Sivers function in hadronic scattering reactions.

THE MESON PRODUCTION IN PROTON–PROTON COLLISIONS IN NEXT-TO-LEADING ORDER AND INFRARED RENORMALONS

In this paper, we investigate the next-to-leading order contribution of the higher-twist Feynman diagrams to the large-pT inclusive pion production cross-section in proton–proton collisions and present the general formulae for the higher-twist differential cross-sections in the case of the running coupling and frozen coupling approaches. We compared the resummed next-to-leading order higher-twist cross-sections with the ones obtained in the framework of the frozen coupling approach and leading-twist cross-section. The structure of infrared renormalon singularities of the higher-twist subprocess cross-section and its resummed expression (the Borel sum) are found. It is shown that the resummed result depends on the choice of the meson wave functions used in the calculations. We discuss the phenomenological consequences of possible higher-twist contributions to the meson production in proton–proton collisions in next-to-leading order at RHIC.

Validation of Geant4 hadronic physics models at intermediate energies

GEANT4 provides a number of physics models at intermediate energies (corresponding to incident momenta in the range 1-20 GeV/c). Recently, these models have been validated with existing data from a number of experiments: (a) inclusive proton and neutron production with a variety of beams (π−, π+, p) at different energies between 1 and 9 GeV/c on a number of nuclear targets (from beryllium to uranium); (2) inclusive pion/kaon/proton production from 14.6 GeV/c proton beams on nuclear targets (from beryllium to gold); (3) inclusive pion production from pion beams between 3-13 GeV/c on a number of nuclear targets (from beryllium to lead). The results of simulation/data comparison for different GEANT4 models are discussed in the context of validating the models and determining their usage in physics lists for high energy application. Due to the increasing number of validations becoming available, and the requirement that they be done at regular intervals corresponding to the GEANT4 release schedule, automated methods of validation are being developed.

Sivers asymmetries for inclusive pion and kaon production in deep-inelastic scattering

We calculate the Sivers distribution functions induced by the final-state interaction due to one-gluon exchange in diquark models of a nucleon structure, treating the cases of scalar and axial-vector diquarks with both dipole and Gaussian form factors. We use these distribution functions to calculate the Sivers single-spin asymmetries for inclusive pion and kaon production in deep-inelastic scattering. We compare our calculations with the results of HERMES and COMPASS, finding good agreement for ${\ensuremath{\pi}}^{+}$ production at HERMES, and qualitative agreement for ${\ensuremath{\pi}}^{0}$ and ${K}^{+}$ production. Our predictions for pion and kaon production at COMPASS could be probed with increased statistics. The successful comparison of our calculations with the HERMES data constitutes prima facie evidence that the quarks in the nucleon have some orbital angular momentum in the infinite-momentum frame.

Infrared renormalons and single meson production in proton-proton collisions

In this article, we investigate the contribution of the higher-twist Feynman diagrams to the large-${p}_{T}$ inclusive pion production cross section in proton-proton collisions and present the general formulas for the higher-twist differential cross sections in the case of the running coupling and frozen coupling approaches. The structure of infrared renormalon singularities of the higher-twist subprocess cross section and the resummed expression (the Borel sum) for it are found. We compared the resummed higher-twist cross sections with the ones obtained in the framework of the frozen coupling approach and leading-twist cross section. We obtain, that ratio $R=({\ensuremath{\Sigma}}_{{\ensuremath{\pi}}^{+}}^{\mathrm{HT}}{)}^{\mathrm{res}}/({\ensuremath{\Sigma}}_{{\ensuremath{\pi}}^{+}}^{\mathrm{HT}}{)}^{0}$, for all values of the transverse momentum ${p}_{T}$ of the pion identically equivalent to ratio $r=({\ensuremath{\Delta}}_{\ensuremath{\pi}}^{\mathrm{HT}}{)}^{\mathrm{res}}/({\ensuremath{\Delta}}_{\ensuremath{\pi}}^{\mathrm{HT}}{)}^{0}$. It is shown that the resummed result depends on the choice of the meson wave functions used in calculation. Phenomenological effects of the obtained results are discussed.

EPS09 — A new generation of NLO and LO nuclear parton distribution functions

We present a next-to-leading order (NLO) global DGLAP analysis of nuclear parton distribution functions (nPDFs) and their uncertainties. Carrying out an NLO nPDF analysis for the first time with three different types of experimental input -- deep inelastic $\ell$+A scattering, Drell-Yan dilepton production in p+$A$ collisions, and inclusive pion production in d+Au and p+p collisions at RHIC -- we find that these data can well be described in a conventional collinear factorization framework. Although the pion production has not been traditionally included in the global analyses, we find that the shape of the nuclear modification factor $R_{\rm dAu}$ of the pion $p_T$-spectrum at midrapidity retains sensitivity to the gluon distributions, providing evidence for shadowing and EMC-effect in the nuclear gluons. We use the Hessian method to quantify the nPDF uncertainties which originate from the uncertainties in the data. In this method the sensitivity of $\chi^2$ to the variations of the fitting parameters is mapped out to orthogonal error sets which provide a user-friendly way to calculate how the nPDF uncertainties propagate to any factorizable nuclear cross-section. The obtained NLO and LO nPDFs and the corresponding error sets are collected in our new release called {\ttfamily EPS09}. These results should find applications in precision analyses of the signatures and properties of QCD matter at the LHC and RHIC.

Soft-fermion-pole contribution to single-spin asymmetry for pion production in pp collisions

We study the single transverse spin asymmetry for the inclusive pion production in the nucleon–nucleon collision, p↑p→πX, based on the twist-3 mechanism in the collinear factorization. We derive the soft-fermion-pole (SFP) contribution to the twist-3 single-spin-dependent cross section associated with the twist-3 quark–gluon correlation functions in the polarized nucleon. We find that the SFP can give rise to a large effect to the asymmetry AN owing to the large partonic hard cross sections with the large color factor, if the SFP function has a similar magnitude as the soft-gluon-pole (SGP) function, in spite of the absence of the “derivative term” for the SFP function unlike for the SGP function.

Electromagnetic and hadron calorimeters in the MIPP experiment

The purpose of the MIPP experiment is to study the inclusive production of photons, pions, kaons, and nucleons in π, K, and p interactions on various targets using beams from the Main Injector at Fermilab. The function of the calorimeters is to measure the production of forward-going neutrons and photons. The electromagnetic calorimeter consists of 10 lead plates interspersed with proportional chambers. It was followed by the hadron calorimeter with 64 steel plates interspersed with scintillator. The data presented were collected with a variety of targets and beam momenta from 5 to 120 GeV/ c. The energy calibration of both calorimeters with electrons, pions, kaons, and protons is discussed. The resolution for electrons was found to be 0.27 / E , and for hadrons the resolution was 0.554 / E with a constant term of 2.6%. The performance of the calorimeters was tested on a neutron sample.

Erratum: Pion production by protons on a thin beryllium target at 6.4, 12.3, and 17.5 GeV/cincident proton momenta [Phys. Rev. C 77, 015209 (2008)

An analysis of inclusive pion production in proton-beryllium collisions at 6.4, 12.3, and 17.5 GeV/c proton beam momentum has been performed. The data were taken by Experiment 910 at the Alternating Gradient Synchrotron at the Brookhaven National Laboratory. The differential $\pi^+$ and $\pi^-$ production cross sections ($d^2\sigma/dpd\Omega$) are measured up to 400 mRad in $\theta_{\pi}$ and up to 6 GeV/c in $p_{\pi}$. The measured cross section is fit with a Sanford-Wang parameterization.

Pion production by protons on a thin beryllium target at 6.4, 12.3, and 17.5 GeV/cincident proton momenta

An analysis of inclusive pion production in proton-beryllium collisions at 6.4, 12.3, and 17.5 GeV/c proton beam momentum has been performed. The data were taken by Experiment 910 at the Alternating Gradient Synchrotron at the Brookhaven National Laboratory. The differential {pi}{sup +} and {pi}{sup -} production cross sections (d{sup 2}{sigma}/dpd{omega}) were measured up to 400 mrad in {theta}{sub {pi}} and up to 6 GeV/c in p{sub {pi}}. The measured cross section was fit with a Sanford-Wang parametrization.

Inclusive pion production by pions on nuclei and determination of root-mean-square radii of proton and neutron distributions

A brief nonanalytic survey of data available in the literature for parameters that characterize nuclear sizes is given, and the potentials of some methods for determining these sizes are compared. Attention is given primarily to determining nuclear sizes in experiments that study pion-nucleus interaction. For pointlike protons and neutrons, values of parameters that describe the radial dependences of their densities according to the Fermi distribution are presented in a tabular form. The method proposed previously at the Institute of Theoretical and Experimental Physics (ITEP, Moscow) for determining nuclear sizes on the basis of measuring differential cross sections for π∓ + A → πforw± + X processes in the kinematical region where the recorded interaction event occurs on a single proton (neutron) of nucleus A, the presence of the remaining nucleons manifesting itself in shadowing effects, is described, and examples of the application of this method are given.

Single transverse-spin asymmetry in very forward and very backward neutral particle production for polarized proton collisions at [formula omitted

In the 2001–2002 running period of the Relativistic Heavy Ion Collider (RHIC), transversely polarized protons were accelerated to 100 GeV for the first time, with collisions at s=200 GeV. We present results from this run for single transverse-spin asymmetries for inclusive production of neutral pions, photons and neutrons of the energy region 20–100 GeV for forward and backward production for angles between 0.3 mrad and 2.2 mrad with respect to the polarized proton direction. An asymmetry of AN=(−0.090±0.006±0.009)×(1.0−0.24+0.47) was observed for forward neutron production, where the errors are statistical and systematic, and the scale error is from the beam polarization uncertainty. The forward photon and π0, and backward neutron, photon, and π0 asymmetries were consistent with zero. The large neutron asymmetry indicates a strong interference between a spin–flip amplitude, such as one pion exchange which dominates lower energy neutron production, and remaining spin–non-flip amplitudes such as reggeon exchange.

Gluon recombination in high parton density QCD: Inclusive pion production

We argue that the collinear factorization of the fragmentation functions in high energy hadron and nuclei collisions breaks down at transverse momenta ${k}_{T}\ensuremath{\lesssim}{Q}_{s}/g$ due to high parton densities in the colliding hadrons and/or nuclei. We calculate, at next-to-leading order in projectile parton density and to all orders in target parton density, the double-inclusive cross-section for production of a pair of gluons in the scalar ${J}^{PC}={0}^{++}$ channel. Using the low energy theorems of QCD we find the inclusive cross-section for $\ensuremath{\pi}$-meson production.

Inclusive production of charged pions in p + C collisions at 158 GeV/c beam momentum

The production of charged pions in minimum bias p+C interactions is studied using a sample of 377000 inelastic events obtained with the NA49 detector at the CERN SPS at 158 GeV/c beam momentum. The data cover a phase space area ranging from 0 to 1.8 GeV/c in transverse momentum and from -0.1 to 0.5 in Feynman xF. Inclusive invariant cross sections are given on a grid of 270 bins per charge, thus offering for the first time a dense coverage of the projectile hemisphere and of the cross-over region into the target fragmentation zone.

Experimental data on the single-spin asymmetry and their interpretations by the chromomagnetic string model

An attempt to interpret the various existing experimental data on the single-spin asymmetries in inclusive pion production by polarized proton and antiproton beams is made. As the basis of analysis, the chromomagnetic string model is used. A whole measured kinematic region is covered. The successes and failures of such an approach are outlined. The possible improvements of the model are discussed.

Inclusive production of charged pions in p+p collisions at 158 GeV/c beam momentum

New results on the production of charged pions in p+p interactions are presented. The data come from a sample of 4.8 million inelastic events obtained with the NA49 detector at the CERN SPS at 158 GeV/c beam momentum. Pions are identified by energy loss measurement in a large TPC tracking system which covers a major fraction of the production phase space. Inclusive invariant cross sections are given on a grid of nearly 300 bins per charge over intervals from 0 to 2 GeV/c in transverse momentum and from 0 to 0.85 in Feynman x. The results are compared to existing data in overlapping energy ranges.

General features of single-spin asymmetry in inclusive pion production in fixed-target experiments

The results of various experiments that measured a single-spin asymmetry in inclusive pion production are analyzed in the energy range between 13 and 200 GeV. The experimental fact that the single-spin asymmetry begins increasing at one universal value of the pion energy in the c.m. frame is established.

Parton intrinsic motion in inclusive particle production: unpolarized cross sections, single spin asymmetries, and the Sivers effect

The relevance of intrinsic (or primordial) transverse momentum of partons in the inclusive production of particles at high energy and moderately large ${p}_{T}$ has been known for a long time, beginning with Drell-Yan and diphoton processes, and continuing with photon and meson production in hadronic collisions. In view of its renewed interest in the context of polarized processes and single spin asymmetries we perform, in the framework of perturbative QCD with the inclusion of spin and ${\mathbit{k}}_{\ensuremath{\perp}}$ effects, a detailed analysis of several such processes in different kinematical situations. We show that the inclusion of these effects leads, at the level of accuracy reachable in this approach, to an overall satisfactory agreement between theoretical predictions and experimental unpolarized data, thus giving support to the study of spin effects and single spin asymmetries within the same scheme. We present results for transverse single spin asymmetries, generated by the so-called Sivers effect, in inclusive pion and photon production in proton-proton collisions. We compare our results with the available experimental data and with previous results obtained using simplified versions of this approach.

Searches for single-spin asymmetry in the inclusive production of neutral pions in the central region at a proton beam energy of 70 GeV

Results are presented that were obtained by measuring single-spin asymmetry in the inclusive production of neutral pions in the reaction p+p ↑→ π0+X at xF≈0. A beam of 70-GeV protons was extracted directly from the vacuum chamber of the accelerator by means of a bent single crystal. For transverse momenta in the range 1.0<pT<3.0 GeV/c, the single-spin asymmetry independently measured by two detectors is zero within the errors. This result is in agreement with Fermilab data obtained at 200 GeV, but it is at odds with CERN data measured at 24 GeV.

Indications of suppressed high [formula omitted] hadron production in nucleus–nucleus collisions at CERN-SPS

Inclusive pion production at high transverse momenta (pT≳2 GeV/c) in nucleus–nucleus (A+A) collisions at CERN-SPS (sNN≈20 GeV) is revisited and systematically compared to all existing proton–proton data in the same range of center-of-mass energies. The ratio of A+A to p + p pion cross-sections (nuclear modification factor) for central Pb + Pb, Pb + Au and S + Au reactions does not show a strong enhancement as a function of pT as previously found, but is consistent with scaling with the number of nucleon–nucleon (NN) collisions. Neutral pion yields per NN collision in head-on Pb + Pb reactions are suppressed, whereas peripheral yields are enhanced. These results together indicate that some amount of “jet quenching” may already be present in central heavy-ion reactions at sNN≈20 GeV.