Charged Pion Production Research Articles

Peripheral, Ultrarelativistic Production of Particles in Heavy Ion Collisions

The cross sections for the production of two-pions in ultraperipheral ultrarelativistic heavy ion collisions, calculated in the impact parameter Equivalent Photon Approximation (EPA), are presented. Differential distributions in impact parameter, dipion invariant mass, single pion and dipion rapidity, pion transverse momentum and pion pseudorapidity are shown. The $\gamma \gamma \to \pi^+ \pi^-$ subprocess constitutes a background to the $A A \to A \rho^0 (\to \pi^+ \pi^-) A$ process, initiated by emission of a photon by one of colliding nuclei. Only a part of the dipion invariant mass distribution associated with the $\gamma\gamma$-collisions can be visible as the cross section for the $A A \to A \rho^0 A$ reaction is very large. Differential distributions for two $\rho^0$ meson production in exclusive ultraperipheral, ultrarelativistic collisions via a double scattering mechanism are presented. The cross section for $\gamma A \to \rho^0 A$ is parametrized based on a calculation from the literature. Smearing of $\rho^0$ masses is taken into account. The results of calculations are compared to experimental data obtained at RHIC and to the contribution of the two-photon mechanism. The double scattering mechanism populates larger $\rho^0 \rho^0$ invariant masses and larger rapidity distances between the two $\rho^0$ mesons compared to the $\gamma \gamma$ fusion. It gives a significant contribution to the $A A \to A A \pi^+ \pi^- \pi^+ \pi^-$ reaction. Some observables related to charged pions are presented. The results of our calculation are compared with the STAR collaboration results for four charged pion production. While the shape in invariant mass of the four-pion system is very similar to the measured one, the predicted cross section constitutes only 20 \% of the measured one. \end{abstract}

Measurement of A LL and cross section of high p T charged π meson production for constraining ΔG at PHENIX

PHENIX at RHIC measured invariant differential cross section and double helicity asymmetry ALL of high pT charged pions production in polarized p + p collision at √s = 200 GeV. Interpretations of preliminary results regarding constraining gluon helicity distribution are discussed.

Study of the production of charged pions, kaons, and protons in pPb collisions at sqrt(sNN) = 5.02 TeV

Spectra of identified charged hadrons are measured in pPb collisions with the CMS detector at the LHC at sqrt(sNN) = 5.02 TeV. Charged pions, kaons, and protons in the transverse-momentum range pt approximately 0.1-1.7 GeV and laboratory rapidity abs(y) < 1 are identified via their energy loss in the silicon tracker. The average pt increases with particle mass and the charged multiplicity of the event. The increase of the average pt with charged multiplicity is greater for heavier hadrons. Comparisons to Monte Carlo event generators reveal that EPOS LHC, which incorporates additional hydrodynamic evolution of the created system, is able to reproduce most of the data features, unlike HIJING and AMPT. The pt spectra and integrated yields are also compared to those measured in pp and PbPb collisions at various energies. The average transverse momentum and particle ratio measurements indicate that particle production at LHC energies is strongly correlated with event particle multiplicity.

Negative Charged Pion Production on a Deuteron by Quasi-Real Photons

Experimental differential cross sections of photoproduction of negative pions on a deuteron have been obtained as functions of the polar angle of emission of π– mesons. A comparison is made of the measured cross sections with the results of calculations in a model that takes account the interaction in the final state of the reaction.

Beam spin asymmetries of charged and neutral pion production in semi-inclusive DIS

We present a study on the beam single spin asymmetries $A_{LU}^{\sin\phi_h}$ of $\pi^+$, $\pi^-$ and $\pi^0$ production in semi-inclusive deep inelastic scattering process, by considering Collins effect and the $g^\perp D_1$ term simultaneously. We calculate the twist-3 distributions $e(x, \bm k_T^2)$ and $g^\perp(x,\bm k_T^2)$ for the valence quarks inside the proton in a spectator model. We consider two different options for the form of diquark propagator, as well as two different choices for the model parameters in the calculation. Using the model results, we estimate the beam spin asymmetries $A_{LU}^{\sin\phi_h}$ for the charged and neutral pions and compare the results with the measurement from the HERMES Collaboration. We also make predictions on the asymmetries at CLAS with a $5.5 \,\textrm{GeV}$ beam using the same model results. It is found that different choices for the diquark propagator will not only lead to different expressions for the distribution functions, but also result in different sizes of the asymmetries. Our study also shows that, although the spectator model calculation can describe the asymmetries for certain pion production in some kinematic regions, it seems difficult to explain the asymmetries of pion production for all three pions in a consistent way from the current versions.

Precision Measurement of Charged Pion and Kaon Differential Cross Sections ine+e−Annihilation ats=10.52 GeV

Measurements of inclusive differential cross sections for charged pion and kaon production in e+ e- annihilation have been carried out at a center-of-mass energy of sqrt[s]=10.52 GeV. The measurements were performed with the Belle detector at the KEKB e+ e- collider using a data sample containing 113×10(6) e+ e- → qq events, where q={u,d,s,c}. We present charge-integrated differential cross sections dσ(h±)/dz for h±={π±,K±} as a function of the relative hadron energy z=2E(h)/sqrt[s] from 0.2 to 0.98. The combined statistical and systematic uncertainties for π± (K±) are 4% (4%) at z∼0.6 and 15% (24%) at z∼0.9. The cross sections are the first measurements of the z dependence of pion and kaon production for z>0.7 as well as the first precision cross section measurements at a center-of-mass energy far below the Z0 resonance used by the experiments at LEP and SLC.

Production of pions, kaons and protons at high pT in sNN=2.76TeV Pb–Pb collisions

In this work we report on the production of charged pions, kaons, and (anti) protons in pp and Pb-Pb collisions at sqrt{s_NN}= 2.76 TeV for 3 < pT < 20 GeV/c. The evolution of the nuclear modification factor, RAA, with collision centrality and transverse momentum is discussed.

Pion production in the MiniBooNE experiment

Background: Charged current pion production gives information on the axial formfactors of nucleon resonances. It also introduces a noticeable background to quasi-elastic measurements on nuclear targets. Purpose: Understand pion production in neutrino interactions with nucleons and the reaction mechanism in nuclei. Method: The Giessen Boltzmann--Uehling--Uhlenbeck (GiBUU) model is used for an investigation of neutrino-nucleus reactions. Results: Theoretical results for integrated and differential cross sections for the MiniBooNE neutrino flux are compared to the data. Two sets of pion production data on elementary targets are used to obtain limits for the neutrino-nucleus reactions. Conclusions: The MiniBooNE pion production data are consistent with the BNL elementary data if a small flux renormalization is performed while the ANL input data lead to significantly too low cross sections. A final determination of in-medium effects requires new data on elementary (p,D) targets.

Cross sections of large-angle hadron production in proton-nucleus and pion-nucleus interactions

We report on double-differential inclusive cross sections of the production of secondary protons and charged pions (in interactions with thin stationary targets made of Be, C, Cu, Sn, Ta, and Pb) of proton and pion beams with momentum from ±3 to ±15 GeV/c.

System-size and centrality dependence of charged kaon and pion production in nucleus-nucleus collisions at 40AGeV and 158AGeV beam energy

Measurements of charged pion and kaon production are presented in centrality selected Pb+Pb collisions at 40A GeV and 158A GeV beam energy as well as in semi-central C+C and Si+Si interactions at 40A GeV. Transverse mass spectra, rapidity spectra and total yields are determined as a function of centrality. The system-size and centrality dependence of relative strangeness production in nucleus-nucleus collisions at 40A GeV and 158A GeV beam energy are derived from the data presented here and published data for C+C and Si+Si collisions at 158A GeV beam energy. At both energies a steep increase with centrality is observed for small systems followed by a weak rise or even saturation for higher centralities. This behavior is compared to calculations using transport models (UrQMD and HSD), a percolation model and the core-corona approach.

Study of the inclusive production of charged pions, kaons, and protons in pp collisions at $\sqrt{s} = 0.9, 2.76,\mbox{ and }7~\mbox{TeV}$

Spectra of identified charged hadrons are measured in pp collisions at the LHC for sqrt(s) = 0.9, 2.76, and 7 TeV. Charged pions, kaons, and protons in the transverse-momentum range pt approximately 0.1-1.7 GeV and for rapidities abs(y) < 1 are identified via their energy loss in the CMS silicon tracker. The average pt increases rapidly with the mass of the hadron and the event charged-particle multiplicity, independently of the center-of-mass energy. The fully corrected pt spectra and integrated yields are compared to various tunes of the PYTHIA6 and PYTHIA8 event generators.

Probing Nuclear Symmetry Energy with the Sub-threshold Pion Production

Within the framework of the semiclassical Boltzmann—Uehling—Uhlenbeck transport model, we investigate the effects of symmetry energy on the sub-threshold pion using the isospin MDI interaction with the stiff and soft symmetry energies in the central collision of 48Ca+48Ca at the incident beam energies of 100, 150, 200, 250 and 300 MeV/nucleon. We find that the ratio of π−/π+ of sub-threshold charged pion production is greatly sensitive to the symmetry energy, particularly around 100 MeV/nucleon energies. Large sensitivity of sub-threshold charged pion production to nuclear symmetry energy may reduce uncertainties of probing nuclear symmetry energy via heavy-ion collision.

Superscaling predictions for neutrino-induced charged-current charged pion production at MiniBooNE

Superscaling approximation (SuSA) predictions to neutrino-induced charged-current charged pion production in the Δ-resonance region are explored under MiniBooNE experimental conditions. The results obtained within SuSA for the flux-averaged double-differential cross sections of the π+ production for the νμ+CH2 reaction as a function of the muon kinetic energy and of the scattering angle, the cross sections averaged over the angle, the total cross section for the π+ production, as well as CC1π+ to CCQE cross section ratio are compared with the corresponding MiniBooNE experimental data. The SuSA predictions are in good agreement with data on neutrino flux average cross sections, but a somewhat different dependence on the neutrino energy is predicted than the one resulting from the experimental analysis.

Cross-sections of large-angle hadron production in proton– and pion–nucleus interactions VIII: aluminium 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 aluminium 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 aluminium nuclei are compared with cross-sections on beryllium, carbon, copper, tin, tantalum and lead nuclei.

Beam-Target Double-Spin AsymmetryALTin Charged Pion Production from Deep Inelastic Scattering on a Transversely PolarizedHe3Target at1.4&lt;Q2&lt;2.7 GeV2

We report the first measurement of the double-spin asymmetry A{LT} for charged pion electroproduction in semi-inclusive deep-inelastic electron scattering on a transversely polarized {3}He target. The kinematics focused on the valence quark region, 0.16<x<0.35 with 1.4<Q{2}<2.7 GeV{2}. The corresponding neutron A{LT} asymmetries were extracted from the measured {3}He asymmetries and proton over {3}He cross section ratios using the effective polarization approximation. These new data probe the transverse momentum dependent parton distribution function g{1T}{q} and therefore provide access to quark spin-orbit correlations. Our results indicate a positive azimuthal asymmetry for π{-} production on {3}He and the neutron, while our π{+} asymmetries are consistent with zero.

Longitudinal spin physics results from COMPASS

The COMPASS experiment at the CERN SPS has a broad physics program focused on the nucleon spin structure and hadron spectroscopy, using muon and hadron beams, respectively. Results from the COMPASS on the inclusive longitudinal double spin asymmetries A1d,p measured in deep-inelastic polarized muon scattering off the polarized 6LiD and NH3 targets are presented. The new proton data cover the range Q2>1(GeV2/c), 0.004<x<0.7 and improve the statistical precision of g1p(x) by factor of two at x<0.02 compared to previous measurements. The spin-dependent non-singlet function g1NS(x,Q2) extracted from the data allows to evaluate the isovector quark density Δq3(x,Q2) and check the Bjorken sum rule prediction. The helicity distributions for the three lightest quark and antiquark flavours extracted from the measured double spin asymmetries for production of charged pions and kaons in semi-inclusive deep-inelastic scattering are also presented and discussed. The gluon polarization in the nucleon was determined using open charm production or high transverse-momentum hadron pairs production in polarized muon scattering off longitudinally polarized 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% nuclear interaction length thick stationary tin target, of proton and pion beams with momentum from \pm3 GeV/c to \pm15 GeV/c. Results are given for secondary particles with production angles between 20 and 125 degrees. Cross-sections on tin nuclei are compared with cross-sections on beryllium, carbon, copper, tantalum and lead nuclei.

Multifractality in charged pion production at a few GeV/n

The multifractal analysis of charged pion produced in 16O–AgBr interactions at 2.1 AGeV and 24Mg–AgBr interactions at 4.5 AGeV has been investigated using the Takagi moment method in pseudo-rapidity space. The generalized fractal dimensions Dq are determined for these two interactions for different orders of moment. Experimental data reflects multifractal geometry in the multipion production process. From the knowledge of the generalized fractal dimensions Dq, the multifractal specific heat has also been evaluated for these data. A detailed comparison is presented with the results obtained from 12C–AgBr and 28Si–AgBr interactions at 4.5 AGeV/c, 28Si–AgBr interactions at 14.5 A GeV/c, 16O–AgBr interactions 60 AGeV and 32S–AgBr interactions 200 AGeV from the recent literatures.

Geant4 hadronic cascade models analysis of proton and charged pion transverse momentum spectra fromp+Cu and Pb collisions at 3, 8, and 15 GeV/c

Geant4 has an abundant set of physics models that handle the diverse interaction of particles with matter across a wide energy range. However, there are also many well established reaction codes currently used in the same fields where Geant4 is applied. One such code is the Ultra-relativistic Quantum Molecular Dynamics (UrQMD) model. In order to take advantage of the UrQMD code, we create a tool to enable comparisons among UrQMD and Geant4 hadronic models. This tool allows a user to process the output file of UrQMD through Geant4 toolkit, while at the same time, can choose among different Geant4 hadronic model generators. As an example, the UrQMD model is compared with the HARP-CDP experimental data and with the Binary and FRITIOF generators, in the framework of Geant4. It is shown that the UrQMD model can better reproduce charged pion production for p+Cu and Pb interactions at 3, 8 and 15 GeV/c, and is a good candidate for Geant4 hadronic models.

Extension of the Liège intranuclear cascade model at incident energies between 2 and 12 GeV. Aspects of pion production

Abstract The validity of the standard version of the Liege Intra-Nuclear Cascade (INCL4) model, which has been shown to be quite successful for the description of spallation reactions, is limited to an upper incident energy of ∼2 GeV, because inelastic elementary processes are restricted to the excitation and de-excitation of the Delta resonance. In this paper, the INCL4 model is extended to higher incident energy by including other inelastic elementary collisions. However, excitation of heavier baryonic resonances is replaced by direct multipion production in elementary nucleon–nucleon and pion–nucleon collisions. The predictions of the modified model for production of charged pions by proton and pion beams off nuclei are compared with experimental data of the HARP Collaboration for beam energies between 2 and 12 GeV. The apparent duality between the approach based on excitation of numerous baryonic resonances and our approach is briefly discussed.