Charged Pion Production Research Articles

Nuclear geometry effect and transport coefficient in semi-inclusive lepton-production of hadrons off nuclei

Hadron production in semi-inclusive deep-inelastic scattering of leptons from nuclei is an ideal tool to determine and constrain the transport coefficient in cold nuclear matter. The leading-order computations for hadron multiplicity ratios are performed by means of the SW quenching weights and the analytic parameterizations of quenching weights based on BDMPS formalism. The theoretical results are compared to the HERMES positively charged pions production data with the quarks hadronization occurring outside the nucleus. With considering the nuclear geometry effect on hadron production, our predictions are in good agreement with the experimental measurements. The extracted transport parameter from the global fit is shown to be qˆ=0.74±0.03 GeV2/fm for the SW quenching weight without the finite energy corrections. As for the analytic parameterization of BDMPS quenching weight without the quark energy E dependence, the computed transport coefficient is qˆ=0.20±0.02 GeV2/fm. It is found that the nuclear geometry effect has a significant impact on the transport coefficient in cold nuclear matter. It is necessary to consider the detailed nuclear geometry in studying the semi-inclusive hadron production in deep inelastic scattering on nuclear targets.

Pion production in high-energy neutrino reactions with nuclei

[Background] A quantitative understanding of neutrino interactions with nuclei is needed for precision era neutrino long baseline experiments (MINOS, NOvA, DUNE) which all use nuclear targets. Pion production is the dominant reaction channel at the energies of these experiments. [Purpose] Investigate the influence of nuclear effects on neutrino-induced pion production cross sections and compare predictions for pion-production with available data. [Method] The Giessen Boltzmann--Uehling--Uhlenbeck (GiBUU) model is used for the description of all incohrent channels in neutrino-nucleus reactions. [Results] Differential cross sections for charged and neutral pion production for the MINER$\nu$A neutrino and antineutrino flux are calculated. An estimate for the coherent cross section is obtained from a comparison of data with theoretical results. The invariant mass ($W$) distribution of the $\Delta$ resonances produced is analyzed. [Conclusions] Final state interactions affect the pion kinetic energy spectra significantly. The data for charged pion production at MINER$\nu$A are compatible with the results of calculations using elementary data taken from an old Argonne National Laboratory experiment. Remaining differences can be attributed to coherent production; the data for antineutrino induced neutral pion production, where no coherent contribution is present, are reproduced quite well. In contrast, the MiniBooNE data, taken at a lower energy, are consistently higher than the theoretical description. The analysis of $W$-distributions shows that experimental cuts on this quantity lead to shape distortions for nuclear targets.

Charged-to-neutral correlation at forward rapidity in Au + Au collisions atsNN=200GeV

Event-by-event fluctuations of the ratio of inclusive charged to photon multiplicities at forward rapidity in Au+Au collision at $\sqrt{s_{NN}}$=200 GeV have been studied. Dominant contribution to such fluctuations is expected to come from correlated production of charged and neutral pions. We search for evidences of dynamical fluctuations of different physical origins. Observables constructed out of moments of multiplicities are used as measures of fluctuations. Mixed events and model calculations are used as baselines. Results are compared to the dynamical net-charge fluctuations measured in the same acceptance. A non-zero statistically significant signal of dynamical fluctuations is observed in excess to the model prediction when charged particles and photons are measured in the same acceptance. We find that, unlike dynamical net-charge fluctuation, charge-neutral fluctuation is not dominated by correlation due to particle decay. Results are compared to the expectations based on the generic production mechanism of pions due to isospin symmetry, for which no significant (<1%) deviation is observed.

Tsallis Statistical Interpretation of Transverse Momentum Spectra in High-EnergypA Collisions

In Tsallis statistics, we investigate charged pion and proton production forpCu andpPb interactions at 3, 8, and 15 GeV/c. Two versions of Tsallis distribution are implemented in a multisource thermal model. A comparison with experimental data of the HARP-CDP group shows that they both can reproduce the transverse momentum spectra, but the improved form gives a better description. It is also found that the difference betweenqandq′is small when the temperatureT = T′for the same incident momentum and angular interval, and the value ofqis greater thanq′in most cases.

Transverse Single-Spin Asymmetries in Proton-Proton Collisions Within Collinear Factorization

We provide a new analysis within collinear factorization of transverse single-spin asymmetries (TSSAs) in high transverse momentum charged and neutral pion production in pp collisions at the Relativistic Heavy Ion Collider (RHIC). This study incorporates the so-called twist-3 fragmentation term and shows that one can describe RHIC data through this mechanism. Moreover, by fixing other non-perturbative inputs through extractions of transverse momentum dependent functions in e+e- → h1h2X and semi-inclusive deep-inelastic scattering (SIDIS), we provide for the first time a consistency between certain spin/azimuthal asymmetries in all three reactions (i.e., pp, e+e-, and SIDIS).

ANin proton-proton collisions and the role of twist-3 fragmentation

We review and give an update on the current status of what causes transverse single-spin asymme- tries (TSSAs) in semi-inclusive processes where a single hadron is detected in the final state, especially those involving proton-proton (pp) collisions. In particular, we provide a new analysis within collinear factorization of TSSAs in high transverse momentum charged and neutral pion production in ppcollisions at the Relativistic Heavy Ion Collider (RHIC). This study incorporates the so-called twist-3 fragmentation term and shows that one can describe RHIC data through this mechanism. Moreover, by fixing other non-perturbative inputs through extractions of transverse momentum dependent functions in e + e − → h1h2X and semi-inclusive deep-inelastic scattering (SIDIS), we provide for the first time a consistency between certain spin/azimuthal asymmetries in all three reactions (i.e., pp, e + e − , and SIDIS).

ANin inclusive lepton-proton collisions: TMD and twist-3 approaches

We consider the inclusive production of hadrons in lepton-nucleon scattering. For a transversely polarized nucleon this reaction shows a left-right azimuthal asymmetry, which we compute this asymmetry in both TMD and in twist-3 collinear factorization formalisms. All non-perturbative parton correlators of the calculation are fixed through information from other hard processes. Our results for the left-right asymmetry agree in sign with recent data for charged pion production from the HERMES Collaboration and from Jefferson Lab. We discuss similarities and differences of two formalisms.

First measurement of neutrino and antineutrino coherent charged pion production on argon.

We report on the first cross section measurements for charged current coherent pion production by neutrinos and antineutrinos on argon. These measurements are performed using the ArgoNeuT detector exposed to the NuMI beam at Fermilab. The cross sections are measured to be 2.6(-1.0)(+1.2)(stat)(-0.4)(+0.3)(syst)×10(-38) cm(2)/Ar for neutrinos at a mean energy of 9.6 GeV and 5.5(-2.1)(+2.6)(stat)(-0.7)(+0.6)(syst)×10(-39) cm(2)/Ar for antineutrinos at a mean energy of 3.6 GeV.

Measurement of Coherent Production ofπ±in Neutrino and Antineutrino Beams on Carbon fromEνof 1.5 to 20 GeV

Neutrino-induced coherent charged pion production on nuclei νμA→μ(±)π(∓)A is a rare, inelastic interaction in which a small squared four-momentum |t| is transferred to the recoil nucleus, leaving it intact in the reaction. In the scintillator tracker of MINERvA, we remove events with evidence of particles from nuclear breakup and reconstruct |t| from the final-state pion and muon. We select low |t| events to isolate a sample rich in coherent candidates. By selecting low |t| events, we produce a model-independent measurement of the differential cross section for coherent scattering of neutrinos and antineutrinos on carbon. We find poor agreement with the predicted kinematics in neutrino generators used by current oscillation experiments.

Measurement of “pretzelosity” asymmetry of charged pion production in semi-inclusive deep inelastic scattering on a polarizedHe3target

An experiment to measure single-spin asymmetries in semi-inclusive production of charged pions in deep-inelastic scattering on a transversely polarized $^3$He target was performed at Jefferson Lab in the kinematic region of $0.16<x<0.35$ and $1.4<Q^2<2.7$ ${\rm GeV^2}$. The pretzelosity asymmetries on $^3$He, which can be expressed as the convolution of the $h^\perp_{1T}$ transverse momentum dependent distribution functions and the Collins fragmentation functions in the leading order, were measured for the first time. Using the effective polarization approximation, we extracted the corresponding neutron asymmetries from the measured $^3$He asymmetries and cross-section ratios between the proton and $^3$He. Our results show that for both $\pi^{\pm}$ on $^3$He and on the neutron the pretzelosity asymmetries are consistent with zero within experimental uncertainties.

Left-right spin asymmetry inℓN↑→hX

We consider the inclusive production of hadrons in lepton-nucleon scattering. For a transversely polarized nucleon this reaction shows a left-right azimuthal asymmetry, which we compute in twist-3 collinear factorization at leading order in perturbation theory. All non-perturbative parton correlators of the calculation are fixed through information from other hard processes. Our results for the left-right asymmetry agree in sign with recent data for charged pion production from the HERMES Collaboration and from Jefferson Lab. However, the magnitude of the computed asymmetries tends to be larger than the data. Potential reasons for this outcome are identified. We also give predictions for future experiments and highlight in particular the unique opportunities at an Electron Ion Collider.

Production of light flavour hadrons at intermediate and high pT in pp, p–Pb and Pb–Pb collisions measured with ALICE

Abstract Light flavour transverse momentum spectra at intermediate and high p T provide an important baseline for the measurement of perturbative QCD processes in pp, for the evaluation of initial state effects in p–Pb, and for investigating the suppression from parton energy loss in Pb–Pb collisions. The measurement of the nuclear modification factor R pPb for inclusive charged particles is extended up to 50 GeV/ c in p T compared to our previous measurement and remains consistent with unity up the largest momenta. Results on R pPb of charged pions, kaons and protons that cover up to 14 GeV/ c in p T are presented and compared to R pPb of inclusive charged particles. On the production of charged pions, kaons, and protons up to p T = 20 GeV / c in Pb–Pb collisions final results for R AA are presented.

Measurement of hadron composition in charged jets from pp collisions with the ALICE experiment

We report the first measurement of charged pion, kaon and (anti-)proton production in jets from hadron colliders. The measurement was carried out with the ALICE detector using $2\times10^8$ minimum bias pp collisions at a centre-of-mass energy of $\sqrt{s}=7$ TeV at the LHC. We present the $\pi$, K and p transverse momentum ($p_\textrm{T}$) spectra, as well as the spectra of the reduced momentum (${z^\textrm{ch}\equiv p_\textrm{T}^\textrm{track}/p_\textrm{T, jet}^\textrm{ch}}$), in charged jets of $p_\textrm{T}$ between 5--20 $\textrm{GeV}/c$. The measurement is compared to Monte Carlo calculations.

Measurement of charged pion production yields off the NuMI target

The fixed-target MIPP experiment, Fermilab E907, was designed to measure the production of hadrons from the collisions of hadrons of momenta ranging from 5 to 120 GeV/c on a variety of nuclei. These data will generally improve the simulation of particle detectors and predictions of particle beam fluxes at accelerators. The spectrometer momentum resolution is between 3 and 4%, and particle identification is performed for particles ranging between 0.3 and 80 GeV/c using $dE/dx$, time-of-flight and Cherenkov radiation measurements. MIPP collected $1.42 \times10^6$ events of 120 GeV Main Injector protons striking a target used in the NuMI facility at Fermilab. The data have been analyzed and we present here charged pion yields per proton-on-target determined in bins of longitudinal and transverse momentum between 0.5 and 80 GeV/c, with combined statistical and systematic relative uncertainties between 5 and 10%.

Production of charged pions, kaons and protons at large transverse momenta in pp and Pb–Pb collisions at [formula omitted

Transverse momentum spectra of π±, K± and p(p¯) up to pT=20 GeV/c at mid-rapidity in pp, peripheral (60–80%) and central (0–5%) Pb–Pb collisions at sNN=2.76 TeV have been measured using the ALICE detector at the Large Hadron Collider. The proton-to-pion and the kaon-to-pion ratios both show a distinct peak at pT≈3 GeV/c in central Pb–Pb collisions. Below the peak, pT<3 GeV/c, both ratios are in good agreement with hydrodynamical calculations, suggesting that the peak itself is dominantly the result of radial flow rather than anomalous hadronization processes. For pT>10 GeV/c particle ratios in pp and Pb–Pb collisions are in agreement and the nuclear modification factors for π±, K± and p(p¯) indicate that, within the systematic and statistical uncertainties, the suppression is the same. This suggests that the chemical composition of leading particles from jets in the medium is similar to that of vacuum jets.

Towards an explanation of transverse single-spin asymmetries in proton-proton collisions: The role of fragmentation in collinear factorization

We study the transverse single-spin asymmetry for single-hadron production in proton-proton collisions within the framework of collinear twist-3 factorization in quantum chromodynamics. By taking into account the contribution due to parton fragmentation, we obtain a very good description of all high transverse-momentum data for neutral and charged pion production from the Relativistic Heavy Ion Collider. Our study may provide the crucial step toward a final solution to the long-standing problem of what causes transverse single-spin asymmetries in hadronic collisions within quantum chromodynamics. We show for the first time that it is possible to simultaneously describe spin/azimuthal asymmetries in proton-proton collisions, semi-inclusive deep-inelastic scattering, and electron-positron annihilation by using collinear twist-3 factorization in the first process along with transverse-momentum-dependent functions extracted from the latter two reactions.

Forward–backward multiplicity correlation in high-energy nucleus–nucleus interactions at a few AGeV/c

We have presented a systematic study of two-particle rapidity correlations in terms of investigating the dynamical fluctuation observable in the forward–backward pseudo-rapidity windows by analyzing the experimental data of interactions at 4.5 AGeV/c, interactions at 4.1 AGeV/c, and interactions at 4.5 AGeV/c. The experimental results have been compared with the results obtained from the analysis of event sample simulated (MC-RAND) by generating random numbers and also with the analysis of events generated by the UrQMD and AMPT model. Our study confirms the presence of strong short-range correlations among the produced particles in the forward and the backward pseudo-rapidity region. The analysis of the simple Monte Carlo-simulated (MC-RAND) events signifies that the observed correlations are not due to mere statistics only; explanation of such correlations can be attributed to the presence of dynamical fluctuations during the production of charged pions. Comparisons of the experimental results with the results obtained from analyzing the UrQMD data sample indicate that the UrQMD model cannot reproduce the experimental findings. The AMPT model also cannot explain the experimental results satisfactorily. Comparisons of our experimental results with the results obtained from the analysis of higher energy emulsion data and with the results of the RHIC data have also been presented.

Study of the production of charged pions, kaons, and protons in pPb collisions at [Formula: see text]5.02[Formula: see text

Spectra of identified charged hadrons are measured in pPb collisions with the CMS detector at the LHC at sqrt{s_{NN}} =5.02,text {TeV} . Charged pions, kaons, and protons in the transverse-momentum range p_{mathrm {T}} approx 0.1–1.7{,text {GeV/}c} and laboratory rapidity |y | < 1 are identified via their energy loss in the silicon tracker. The average p_{mathrm {T}} increases with particle mass and the charged multiplicity of the event. The increase of the average p_{mathrm {T}} 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 p_{mathrm {T}} 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.

System-size dependence of charged kaon and pion production in nucleus-nucleus collisions at beam energies of 40A GeV and 158A GeV

We present the system size (centrality) dependence of the mean transverse mass, of the K/π ratio, and the width of the rapidity distributions. Except for the latter a steep increase with centrality is observed for small systems followed by a weak rise or even saturation for higher centralities at both energies. This behavior is compared to calculations using transport models (UrQMD and HSD), a percolation model and the core-corona approach.

Double-scattering mechanism in the exclusiveAA→AAρ0ρ0reaction in ultrarelativistic collisions

We calculate, for the first time, differential distributions for double $\rho^0$ meson production in exclusive ultraperipheral, ultrarelativistic collisions via a double scattering mechanism. The calculations are done in impact parameter space. The cross section for $\gamma A \to \rho^0 A$ is parametrized based on an existing calculation. Smearing of $\rho^0$ masses is taken into account. The results of our calculations are compared at the RHIC energy to the contribution of the two-photon mechanism discussed previously in the literature. The cross section for the double scattering mechanism is found to be an order of magnitude larger at $M_{\rho \rho} <$ 2 GeV and more than two orders of magnitude at $M_{\rho \rho} >$ 3 GeV, than that for the photon-photon mechanism. Compared to the two-photon mechanism the double scattering mechanism populates somewhat larger $\rho^0 \rho^0$ invariant masses and larger rapidity distances between the two $\rho^0$ mesons and gives a significant contribution to the $A A \to A A \pi^+ \pi^- \pi^+ \pi^-$ reaction. Some observables related to charged pions are presented too. We compare the results of our calculation with the STAR collaboration results on 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. We discuss a possibility of identifying the double scattering mechanism at the LHC.