Charged Pion Production Research Articles

New determination of the production cross section for γ rays in the Galaxy

The flux of $\gamma$ rays is measured with unprecedented accuracy by the $\textit{Fermi}$ Large Area Telescope from 100 MeV to almost 1 TeV. In the future, the Cherenkov Telescope Array will have the capability to measure photons up to 100 TeV. To accurately interpret this data, precise predictions of the production processes, specifically the cross section for the production of photons from the interaction of cosmic-ray protons and helium with atoms of the ISM, are necessary. In this study, we determine new analytical functions describing the Lorentz-invariant cross section for $\gamma$-ray production in hadronic collisions. We utilize the limited total cross section data for $\pi^0$ production channels and supplement this information by drawing on our previous analyses of charged pion production to infer missing details. In this context, we highlight the need for new data on $\pi^0$ production. Our predictions include the cross sections for all production channels that contribute down to the 0.5% level of the final cross section, namely $\eta$, $K^+$, $K^-$, $K^0_S$, and $K^0_L$ mesons as well as $\Lambda$, $\Sigma$, and $\Xi$ baryons. We determine the total differential cross section $d\sigma(p+p\rightarrow \gamma+X)/dE_{\gamma}$ from 10 MeV to 100 TeV with an uncertainty of 10% below 10 GeV of $\gamma$-ray energies, increasing to 20% at the TeV energies. We provide numerical tables and a script for the community to access our energy-differential cross sections, which are provided for incident proton (nuclei) energies from 0.1 to $10^7$ GeV (GeV/n).

Assessing the theory-data tension in neutrino-induced charged pion production: The effect of final-state nucleon distortion

Pion production on nuclei constitutes a significant part of the total cross section in experiments involving few-GeV neutrinos. Combined analyses of data on deuterium and heavier nuclei points to tensions between the bubble-chamber data and the data of the $\mathrm{MINER}\ensuremath{\nu}\mathrm{A}$ experiment, which are often ascribed to unspecified nuclear effects. In experimental analysis use is made of approximate treatments of nuclear dynamics, usually in a Fermi gas approach with classical treatments of the reaction mechanism, and fits are often performed by simply rescaling cross sections. To understand the origin of these tensions, check the validity of approximations, and to further advance the description of neutrino pion production on nuclei, a microscopic quantum mechanical framework is needed to compute nuclear matrix elements. We use the local approximation to the relativistic distorted wave impulse approximation to calculate the nuclear matrix elements. We include the distortion of wave functions of the final-state nucleon in a real energy-dependent potential. We compare results with and without distortion. To perform this comparison under conditions relevant to neutrino experiments, we compute cross sections for the $\mathrm{MINER}\ensuremath{\nu}\mathrm{A}$ and T2K charged-pion production datasets. The inclusion of nucleon distortion leads to a reduction of the cross section up to 10%, but to no significant change in shape of the flux-averaged cross sections. Results with and without distortion compare favorably to experimental data, with the exception of the low-${Q}^{2}$ $\mathrm{MINER}\ensuremath{\nu}\mathrm{A}$ ${\ensuremath{\pi}}^{+}$ data. We point out that hydrogen target data from BEBC is also overpredicted at low ${Q}^{2}$, and the data-model discrepancy is similar in shape and magnitude as what is found in comparison to $\mathrm{MINER}\ensuremath{\nu}\mathrm{A}$ data. Including nucleon distortion alone cannot explain the overprediction of low-${Q}^{2}$ cross sections measured by $\mathrm{MINER}\ensuremath{\nu}\mathrm{A}$. The similar overprediction of BEBC data on hydrogen means that it is impossible to ascribe this discrepancy solely to a nuclear effect. Axial form factors might not be constrained in a satisfactory way by the Argonne and Brookhaven National Laboratories (ANL/BNL) data alone. Axial couplings and their ${Q}^{2}$ dependence should ideally be derived from more precise data on hydrogen and deuterium. Nuclear matrix elements should be tested with e.g., electron scattering data for which nucleon level physics is better constrained.

Results on system size dependence of strangeness production in the CERN SPS energy range from NA61/SHINE

NA61/SHINE is a multipurpose fixed-target facility at the CERN Super Proton Synchrotron. The main goals of the NA61/SHINE strong interactions program are to discover the critical point of strongly interacting matter and study the properties of the onset of deconfinement. To reach these goals, hadron production measurements are performed in the form of a two-dimensional scan by varying collision energy and system size. The Collaboration has recently finished data acquisition for its original program on strong interactions, accumulating broad data samples on hadron production in various systems in the SPS energy range. In this contribution, the NA61/SHINE results on identified charged kaon and pion production in p+p, Be+Be and Ar+Sc collisions at the SPS energy range (√SNN = 5.1 - 17.3 GeV) are presented. The NA61/SHINE measurements of small and intermediate-mass ion collisions establish an interesting system size dependence, showing a rapid change of hadron production properties that starts when moving from Be+Be to Ar+Sc system. In particular, Ar+Sc is the smallest system for which a significant enhancement of K+/π+ ratio with respect to p+p collisions is observed. Obtained energy and system size dependence of the measured charged hadron multiplicities are compared with available world data and various theoretical models.

Longitudinal double helicity asymmetry $A_{LL}$ from direct photon, jet and charged pion production in polarized $\vec{p}+\vec{p}$ collisions

Understanding the proton spin composition from the quarks and gluons spin polarization and their motion is important to test various kinds of sum rules and nonperturbative properties of hadrons. At the Relativistic Heavy Ion Collider (RHIC), we collide longitudinally polarized proton beams and measure the double helicity asymmetry A_{LL}ALL, which is an important physical quantity for extracting the polarized parton distribution functions (PDFs) of the proton. Direct photon, jet and charged pion production are good channels to probe the gluon spin polarization inside the proton, with the ability to probe also the sign of the gluon spin. Direct photon production is the theoretically ``cleanest’’ channel, with little fragmentation contribution, but limited by statistics. On the other hand, jet and charged pion production have more statistics, but include more hard processes and hadronization effects. I will present the recent measurements of direct photon, jet and charged pion A_{LL}ALLs at PHENIX and show their complementary roles in extracting the gluon spin.

Hadron production with collinearly-improved unintegrated gluon distributions in high energy proton-proton collisions * *Supported by the National Natural Science Foundation of China (12165004, 12061141008, 11975005), Guizhou Provincial Science and Technology Projects ([2019]5103, [2019]5653), the Education Department of Guizhou Province (KY[2021]131), the National Key Research and Development Program of China (2018YFE0104700, 2018YFE01014800)

The collinearly-improved Balitsky-Kovchegov (ciBK) equation evolved unintegrated gluon distribution (UGD) is used for the first time to study hadron production in high energy proton-proton collisions in order to improve the predictive power of the Color Glass Condensate effective theory. We show that the ciBK equation evolved UGD provides a relatively better description of LHC data on the transverse momentum and integrated multiplicity distributions of charged hadron and neutral pion production for several collision energies compared with the running coupling Balitsky-Kovchegov (rcBK) equation evolved UGD. This is because the ciBK evolved UGD has a sharper transverse momentum distribution than the rcBK UGD. The impact of running coupling prescriptions on hadron production is studied, and it is found that the parent dipole and smallest dipole running coupling prescriptions provide similar depictions of the data. Moreover, the scale dependence of the fragmentation function is investigated by taking three typical values of scale. We find that the differences resulting from the scale dependence of the fragmentation function can be fully absorbed into the normalization factor, which lumps higher order corrections.

Charged pion production from Au + Au collisions at [formula omitted] GeV in the relativistic Vlasov-Uehling-Uhlenbeck model

Using the isospin-dependent relativistic Vlasov-Uehling-Uhlenbeck (RVUU) model, we study charged pion (π±) production in Au+Au collisions at sNN= 2.4 GeV. By fitting the density dependence of the Δ resonance production cross section in nuclear medium to reproduce the experimental π± multiplicities measured by the HADES Collaboration, we obtain a good description of the rapidity distributions and transverse momentum spectra of π± in collisions at various centralities. Some shortcomings in the description of π± production may indicate the need for including the strong potential on π± in RVUU, which is at present absent. We also calculate the proton rapidity distribution in the most central collisions and compare with the coalescence invariant proton rapidity distribution extracted from preliminary HADES data.

Measurement of charged-pion production in deep-inelastic scattering off nuclei with the CLAS detector

Background: Energetic quarks in nuclear deep-inelastic scattering propagate through the nuclear medium. Processes that are believed to occur inside nuclei include quark energy loss through medium-stimulated gluon bremsstrahlung and intranuclear interactions of forming hadrons. More data are required to gain a more complete understanding of these effects. Purpose: To test the theoretical models of parton transport and hadron formation, we compared their predictions for the nuclear and kinematic dependence of pion production in nuclei. Methods: We have measured charged-pion production in semi-inclusive deep-inelastic scattering off D, C, Fe, and Pb using the CLAS detector and the CEBAF 5.014-GeV electron beam. We report results on the nuclear-to-deuterium multiplicity ratio for π+ and π− as a function of energy transfer, four-momentum transfer, and pion energy fraction or transverse momentum—the first three-dimensional study of its kind. Results: The π+ multiplicity ratio is found to depend strongly on the pion fractional energy z and reaches minimum values of 0.67±0.03, 0.43±0.02, and 0.27±0.01 for the C, Fe, and Pb targets, respectively. The z dependencies of the multiplicity ratios for π+ and π− are equal within uncertainties for C and Fe targets but show differences at the level of 10% for the Pb-target data. The results are qualitatively described by the GiBUU transport model, as well as with a model based on hadron absorption, but are in tension with calculations based on nuclear fragmentation functions. Conclusions: These precise results will strongly constrain the kinematic and flavor dependence of nuclear effects in hadron production, probing an unexplored kinematic region. They will help to reveal how the nucleus reacts to a fast quark, thereby shedding light on its color structure and transport properties and on the mechanisms of the hadronization process.Received 25 September 2021Accepted 23 December 2021DOI:https://doi.org/10.1103/PhysRevC.105.015201©2022 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasColor confinementDeep inelastic scatteringLepton induced nuclear reactionsParticle interactionsParticle productionQuantum chromodynamicsStrong interactionNuclear PhysicsParticles & Fields

Charged pion, kaon, proton and antiproton production in large collision systems

The main goal of PHENIX expirement, located at Relativistic Heavy-ion collider, is the investigation of quark-gluon plasma (QGP). One of the aspects of the QGP study is describing the process of its hadronization. Very important contribution to understanding of hadronization process was given by discovering of anomaly large ratio of protons production to pions production (ρ/π) in Au+Au collisions in comparison to the same ratio in proton-proton collisions. This effect was called baryon puzzle and was explained in a frame of recombination model of hadronization.Although charged hadrons production has been previously studied in elementary proton-proton collisions and symmetric Au+Au collisions, it has never been investigated before in the large asymmetric collisions systems (such as Cu+Au) or the collisions of large deformed nuclei (U+U). The study of such large collisions systems allows to study features of baryon and meson production versus collision geometry and system size.

Bjorken variable and scale dependence of quark transport coefficient in semi-inclusive lepton production of hadron off nuclei

Nuclear modification of hadron production in deep inelastic lepton-nucleus scattering can be applied to study the parton propagation mechanism in cold nuclear matter. By means of the analytic parameterization of quenching weight based on BDMPS formalism with the target nuclear geometry effect, the leading-order computations for hadron multiplicity ratios are performed with comparison to the HERMES charged pions production data on the quarks hadronization occurring outside the nucleus. The relation is discovered between quark transport coefficient and the measurable kinematic variables in deep inelastic scattering. Four models are proposed on the quark transport coefficient. The constant model, the power-law model and the double power-law model can be ruled out because of the experimental fact that the transverse momentum broadening increases as a function of the photon virtuality $$Q^{2}$$ . The quark transport coefficient is determined as a function of the Bjorken variable x and scale $$Q^2$$ . The trend of quark transport coefficient in respect of Bjorken variable x and scale $$Q^2$$ is qualitatively in partial agreement with HERMES experimental data on transverse momentum broadening. It is hoped that our effort is conducive to understanding of jet quenching phenomenon in relativistic heavy ion collisions.

Weighted [formula omitted] asymmetry from pretzelosity in SIDIS at electron ion colliders

We investigate the transverse momentum weighted azimuthal asymmetry with a sin⁡(3ϕh−ϕS) modulation in electroproduction of charged pion production off the transversely polarized proton using the weighted function as W=QT3sin⁡(3ϕh−ϕS)/(6M2Mh), with QT=|PhT|/z, and PhT the transverse momentum of the produced pion. The weighted asymmetry is contributed by the product of the second transverse-moment of the pretzelosity distribution function and the first transverse-moment of the Collins function. Using the extracted result for the proton pretzelosity and the available parametrization for the pion Collins function, we numerically predict the weighted sin⁡(3ϕh−ϕS) asymmetry for charged pion production at electron ion colliders (EICs). One can find that the weighted asymmetries for the π+ production in SIDIS process are positive, while those for the π− production are negative in the kinematics regions of EICs. We emphasize the importance of the planned high luminosity EICs in the aspect of constraining pretzelosity in the near future.

Neutral pion reconstruction using machine learning in the experiment at 〈E ν〉 6 GeV

This paper presents a novel neutral-pion reconstruction that takes advantage of the machine learning technique of semantic segmentation using MINERvA data collected between 2013–2017, with an average neutrino energy of 6 GeV. Semantic segmentation improves the purity of neutral pion reconstruction from two γs from 70.7 ± 0.9% to 89.3 ± 0.7% and improves the efficiency of the reconstruction by approximately 40%. We demonstrate our method in a charged current neutral pion production analysis where a single neutral pion is reconstructed. This technique is applicable to modern tracking calorimeters, such as the new generation of liquid-argon time projection chambers, exposed to neutrino beams with 〈E ν〉 between 1–10 GeV. In such experiments it can facilitate the identification of ionization hits which are associated with electromagnetic showers, thereby enabling improved reconstruction of charged-current νe events arising from νμ → νe appearance.

Measurement of single-spin asymmetry for charged pions in the SPASCHARM experiment at U70 accelerator

The SPASCHARM experiment at U70 aims an exploration of a fundamental problem in modern particle physics, the role of spin in strong interactions. At present, the first physics data have been accumulated at a negative 28 GeV beam, interacting with a frozen polarized proton target. The SPASCHARM wide-aperture spectrometer can detect both charged and neutral particles in the large solid angle with 2π azimuthal coverage in the fragmentation region of beam-particles. It covers the kinematic region of non-perturbative quantum chromodynamics (QCD), where the theoretical predictions are difficult and unreliable due to the full strength quark confinement at low and medium momentum transfers. In this report, the current status of the experiment is presented. The algorithm for reconstructing charged tracks is discussed along with its results on real data and the comparison with the Monte Carlo (MC) simulations. Based on a real track reconstruction, the statistical errors for the measurements of single-spin asymmetries in inclusive charged pion production are estimated. The data analysis is in progress.

QCD resummation on single hadron transverse momentum distribution with the thrust axis

We derive the transverse momentum dependent (TMD) factorization and resummation formula of the unpolarized transverse momentum distribution (jT) for the single hadron production with the thrust axis in an electron-positron collision. Two different kinematic regions are considered, including small transverse momentum limit jT « Q, and joint transverse momentum and threshold limit jT « Q(1 − zh) « Q, where Q and zh are the hard scattering energy and the observed hadron momentum fraction. Using effective theory methods, we resum logarithms ln(Q/jT) and ln(1 − zh) to all orders. In the end, we present the differential cross sections and Gaussian widths calculated for the inclusive charged pion production and find that our results are consistent with the measurements reported by the Belle collaboration.

Charged-pion production in mathbf {Au+Au} collisions at sqrt{mathbf {s}_{mathbf {NN}}} = 2.4~{mathbf {GeV}}

We present high-statistic data on charged-pion emission from Au + Au collisions at sqrt{s_{mathrm{NN}}} = 2.4~hbox {GeV} (corresponding to E_{beam} = 1.23~hbox {A GeV}) in four centrality classes in the range 0–40% of the most central collisions. The data are analyzed as a function of transverse momentum, transverse mass, rapidity, and polar angle. Pion multiplicity per participating nucleon decreases moderately with increasing centrality. The polar angular distributions are found to be non-isotropic even for the most central event class. Our results on pion multiplicity fit well into the general trend of the available world data, but undershoot by 2.5~sigma data from the FOPI experiment measured at slightly lower beam energy. We compare our data to state-of-the-art transport model calculations (PHSD, IQMD, PHQMD, GiBUU and SMASH) and find substantial differences between the measurement and the results of these calculations.

Initial nuclear effects in the improved HIJING code and the production of charged pions, kaons and (anti)protons at STAR BES

The improved Heavy Ion Jet Interaction Generator (HIJING) code is introduced to explore possible initial nuclear effects on the bulk observables of charged pions, kaons and (anti)protons observed in Au+Au collisions at sNN=7.7, 11.5, 19.6, 27 and 39 GeV. The standard HIJING code is extended by (i) different baryon production mechanisms, and (ii) Regge collective cascade recipe. We find that the centrality dependence of the identified particle multiplicity dN/dy at mid-rapidity is quite sensitive to Regge cascading. The overall contribution of baryon production mechanism is shown to enhance the centrality dependence of the mixed particle ratios, K±/π± and p±/π± at <Npart><200 (which corresponds to 20%−100% centrality), especially at higher collision energy. It turns out that the bulk data are shown to be more consistent with HIJING (plus a suitable hadron rescattering code) employing both an advanced popcorn baryon production mechanism and Regge initial scatterings.

Measurement of the muon neutrino charged-current single π+ production on hydrocarbon using the T2K off-axis near detector ND280

We report the measurements of the single and double differential cross section of muon neutrino charged-current interactions on carbon with a single positively charged pion in the final state at the T2K off-axis near detector using 5.56×1020 protons on target. The analysis uses data control samples for the background subtraction and the cross section signal, defined as a single negatively charged muon and a single positively charged pion exiting from the target nucleus, is extracted using an unfolding method. The model-dependent cross section, integrated over the T2K off-axis neutrino beam spectrum peaking at 0.6 GeV, is measured to be σ=(11.76±0.44(stat)±2.39(syst))×10−40 cm2 nucleon−1. Various differential cross sections are measured, including the first measurement of the Adler angles for single charged pion production in neutrino interactions with heavy nuclei target.11 MoreReceived 11 September 2019Revised 12 December 2019DOI:https://doi.org/10.1103/PhysRevD.101.012007Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasParticle interactionsParticles & Fields

Near-threshold incoherent pion photoproduction on the deuteron with final-state interaction effects

Incoherent pion photoproduction on the deuteron γd→πNN is investigated in the energy region Eγthr≤Eγ≤ 160 MeV. The model applied contains the amplitudes of the impulse approximation as well as the NN and πN rescattering in the final state. For the elementary γN→πN amplitude, the unitary isobar MAID-2007 model is used. This model is parameterized in terms of invariant amplitudes and allows one to give a more reliable description of the threshold region. The half-off-shell NN and πN scattering amplitudes are obtained from separable representations of realistic NN and πN interactions, respectively. For the first time, numerical results for the linear photon asymmetry Σ, vector T11 and tensor T2M (M=0,1,2) deuteron spin asymmetries for the reactions γd→π−pp, γd→π+nn, and γd→π0np are presented. In addition, results for the unpolarized differential and total cross sections are given. We found that the influence of NN rescattering is moderate in both charged-and neutral-pion production channels, whereas πN rescattering is almost negligible in the charged-pion production channels which is not the case in neutral-pion production since a noticeable contribution is obtained. The calculated results for unpolarized differential and total cross sections are compared with the available experimental data and other theoretical models, and a satisfactory agreement is obtained.

Tuning the genie pion production model with MINERvA data

Faced with unresolved tensions between neutrino interaction measurements at few-GeV neutrino energies, current experiments are forced to accept large systematic uncertainties to cover discrepancies between their data and model predictions. In this paper, the widely used pion production model in GENIE is compared to four MINERvA charged current pion production measurements using NUISANCE. Tunings, ie, adjustments of model parameters, to help match GENIE to MINERvA and older bubble chamber data are presented here. We find that scattering off nuclear targets as measured in MINERvA is not in good agreement with scattering off nucleon (hydrogen or deuterium) targets in the bubble chamber data. An additional ad hoc correction for the low-$Q^2$ region, where collective effects are expected to be large, is also presented. While these tunings and corrections improve the agreement of GENIE with the data, the modeling is imperfect. The development of these tunings within the NUISANCE frameworkallows for straightforward extensions to other neutrino event generators and models, and allows omitting and including new data sets as they become available.

Addendum to “Muon-neutrino-induced charged-current pion production on nuclei”

This short paper is an addendum to a recent publication on charged current neutrino-induced pion production (Phys.\ Rev.\ C96 (2017) no.1, 015503). It presents comparisons of pion production cross sections measured at the T2K near detector for a CH target.

Collision centrality dependencies of charged pion production in 12C+ 181 Ta collisions at 4.2 A GeV/c

The collision centrality dependencies of the average kinematical characteristics of the negative and positive pions, produced in [Formula: see text] collisions at [Formula: see text], were investigated. The ratio [Formula: see text] proved to be [Formula: see text], [Formula: see text] and [Formula: see text] in the peripheral, semicentral, and central [Formula: see text] collision events, respectively, decreasing noticeably with increasing collision centrality. The suppression (decrease) of the ratio [Formula: see text] was observed in the semicentral and central [Formula: see text] collisions as compared to the ratio [Formula: see text], estimated using the simple model for [Formula: see text] collision system. The ratio [Formula: see text] estimated using the simple model agreed well with the corresponding ratio [Formula: see text], estimated for [Formula: see text] collisions at [Formula: see text] based on the Wounded Nucleon Model (WNM). Comparison of the emission angle as well as momentum distributions of the charged pions in the peripheral and central [Formula: see text] collisions revealed the significant decrease of the fraction of the relatively fast charged pions (with smaller emission angles) and increase of the fraction of the relatively slow charged pions (with larger emission angles) with an increase in collision centrality. The results of the present analysis can be useful for analysis of the centrality dependence of the charged pion production in heavy ion collisions at high energies.