Momentum Distributions Of Pions Research Articles

Tau polarization effects in ντ/ν¯τ -tungsten interactions at the LHC energies

Recent studies have demonstrated that the tau produced in charged current neutrino deeply inelastic interactions at the GeV-TeV neutrino energy range is not fully polarized. In this paper we investigate the impact of the tau polarization on the pions generated in its decay. In particular, we consider tau neutrino-tungsten interactions at the LHC energies and estimate the associated pion momentum, energy, and angular distributions. The contribution of the F5 is also investigated. Our results indicate that the pion properties are sensitive to the tau polarization state as well as to the magnitude of F5. Published by the American Physical Society 2024

Extensive/Nonextensive Statistics for pT Distributions of Various Charged Particles Produced in p + p and A + A Collisions in a Wide Range of Energies

A comprehensive review on various experimental parametrizations proposed to fit the transverse momentum distributions of charged pions, kaons, and protons produced at energies ranging between 7.7 GeV and 2.76 TeV is introduced. We present a systematic study for their statistical fits to the extensive Maxwell–Boltzmann (MB) and nonextensive statistics (generic axiomatic statistics and the Tsallis one as a special case). The inconsistency that the MB approach is to be utilized in characterizing the chemical freezeout, while the Tsallis approach determining the kinetic freezeout is discussed. The resulting energy dependence of the different fit parameters largely varies with the particle species and the degree of (non)extensivity. This manifests itself in that the Tsallis nonextensive approach seems to work well for p + p, rather than for A + A collisions. Nevertheless, discussing the deeper physical insights of nonextensive statistical approaches is not targeted, drawing a complete picture of the utilization of the Tsallis statistics in modeling the transverse momentum distributions of several charged particles produced at a wide range of energies and, accordingly, presenting a criticism or a support of the relevant works. This may be considered as the main advantage of this review.

Investigating pi ^{-} production in central ^{7}text {Be}+^{9}text {Be} and ^{40}text {Ar}+ ^{45}text {Sc} collisions at CERN SPS energies with PYTHIA8/Angantyr

We study pion production in proton–proton (pp) and in central ^{7}Be + ^{9}Be and ^{40}text {Ar}+ ^{45}text {Sc} collisions at CERN super proton synchrotron (SPS) energies within the Angantyr model, whose pp dynamics are modeled by PYTHIA 8.303 event generator. We have tuned the parameters of the default multi-partonic interaction (MPI) mechanism in PYTHIA 8.303 to describe simultaneously the measured rapidity and transverse momentum distributions of pions in inelastic pp-collisions in the beam momentum range from 20 to 158 GeV/c. We explore the influence of the standard Lund fragmentation and thermal string models, on the pi ^{-} observables, mainly from light(er) ion beams at CERN SPS energies. The role of primary hadron rescattering (HadSc) is also discussed. We find that the PYTHIA 8.303/Angantyr model employing both pp-tuned and thermal-string model with HadSc is able to reproduce the observed pi ^{-} yields in the light(er) ion beams at the whole CERN SPS energies.

Machine-learning-based identification for initial clustering structure in relativistic heavy-ion collisions

$\alpha$-clustering structure is a significant topic in light nuclei. A Bayesian convolutional neural network (BCNN) is applied to classify initial non-clustered and clustered configurations, namely Woods-Saxon distribution and three-$\alpha$ triangular (four-$\alpha$ tetrahedral) structure for $^{12}$C ($^{16}$O), from heavy-ion collision events generated within a multi-phase transport (AMPT) model. Azimuthal angle and transverse momentum distributions of charged pions are taken as inputs to train the classifier. On multiple-event basis, the overall classification accuracy can reach $95\%$ for $^{12}$C/$^{16}$O + $^{197}$Au events at $\sqrt{S_{NN}} =$ 200 GeV. With proper constructions of samples, the predicted deviations on mixed samples with different proportions of both configurations could be within $5\%$. In addition, setting a simple confidence threshold can further improve the predictions on the mixed dataset. Our results indicate promising and extensive possibilities of application of machine-learning-based techniques to real data and some other problems in physics of heavy-ion collisions.

Quantum entanglement and thermal behavior in charged-current weak interactions

We show that quantum entanglement between causally separated regions of a nucleon in antineutrino-nucleon scattering manifests itself as a thermal component in the resulting pion momentum distribution. For antineutrino scattering coherently from the (carbon) nucleus as a whole, this thermal component is absent, as expected by our quantum entanglement thermalization proposition. These phenomena, which have been observed in proton-proton collisions at the Large Hadron Collider, and in electromagnetic deep inelastic scattering, are now for the first time shown to exist in electroweak interactions as well.

Long-range azimuthal correlations for partially coherent pion emission in proton-proton collisions

In this paper, we investigate the influence of coherent pion emission on long-range azimuthal correlations in relativistic proton-proton collisions. We study the pion momentum distribution for a coherent source with both transverse and Bjorken longitudinal expansions, and calculate the two-particle correlation function C(Δη,Δϕ). A “ridge” structure is observed in the correlation function C(Δη,Δϕ) of the coherent pion emission, whether the coherent source is expanding or static. The onset of this long-range azimuthal correlation can be traced back to the asymmetric initial transverse profile of the coherent source, owing to the interference in coherent emission. We further construct a partially coherent pion-emitting source by incorporating a chaotic emission component. From the experimental data of the two-pion Hanbury-Brown-Twiss correlations in pp collisions at s=7 TeV, we extract a coherent fraction of pion emission, which increases with increasing charged-particle multiplicity, as an input of the partially coherent source model. The ridge structure is observed in the correlation function C(Δη,Δϕ) for the partially coherent source. The correlation becomes stronger at higher multiplicities because of the larger degrees of coherence. The results in this work are meaningful for fully understanding the collectivity in the small system of pp collisions.

About Transverse Momentum Distributions of Negative Pions in p12C and π–12C Collisions at High Energies

Collision centrality dependences of the transverse momentum distributions of negative pions produced in p12C and p−12C collisions at 9.9 and 40 GeV/c, respectively, are investigated. The shapes and widths of the normalized transverse momentum distributions, as well as the average values of the transverse momentum of the negative pions, do not depend within the uncertainties on the collision centrality in p12C and п−12C collisions at 9.9 and 40 GeV/c in experiment, which is confirmed by the modified FRITIOF model calculations and minimum X2 fits of the experimental spectra with the two- and three-temperature Hagedorn model functions. Modified FRITIOF model calculations underestimate the average values of transverse momenta of the negative pions in experiment and do not reproduce the tail of the experimental transverse momentum distributions of the negative pions in both collision types. It is obtained that the transverse momentum distributions of the negative pions exhibit two temperature (two-slope) shapes in peripheral and central p12C collisions at 9.9 GeV/c in agreement with the early works on nucleus-nucleus collisions at incident energies of the order of a few GeV/c. However, the transverse momentum distributions of the negative pions in peripheral and central p−12C collisions at 40 GeV/c can be described well assuming the three temperature (three-slope) shapes of these spectra.

Transverse Momentum Distributions of Charged Hadrons Produced in He12C Collisions at 4.2A GeV/c

We study the trend of transverse momentum (pT) and maximum transverse momentum (pTmax) distributions of pions and protons in He12C-interactions at 4.2A GeV/c. A comparison between theoretical results, from Cascade model (Dubna version), and experimental results, provided by the 2-m propane bubble chamber of JINR, Dubna, is made. Different regions in terms of the trend of pT distributions of the particles are identified: a region where the pT is greater than 0.375 GeV/c is termed as region-III. This region has a maximum value of pT$$\sim $$ 1 and 1.5 GeV/c, respectively, for π -mesons and protons. Here, the protons affect the pT distribution one order more than the mesons and the experimental and Cascade results disagree with each other. In addition, the number of particles detected in the experiments is less than the model, in the region-III. This aimed to establish a correlation between the production of the maxim pT and high-pT region and to comprehend the dynamics of the production of particles with high momentum distribution.

Analysis of transverse momentum distributions of charged particles produced in CC interactions at 4.2 A GeV/c

In this paper, the transverse momentum and maximum transverse momentum distributions of protons and pions produced in an event for CC collisions at 4.2 A GeV/c have been analyzed. This analysis is based on experimental data obtained from 2 m propane bubble chamber at Joint Institute for Nuclear Research, Dubna, Russia and simulation data obtained from Dubna cascade code. We observed three disparate zones for the transverse momentum distribution of the produced particles. The third zone where transverse momentum is greater than 0.375 GeV/c is restricted only for pions with transverse momentum approximately equal to 1 GeV/c, and for protons the restricted value of [Formula: see text] is [Formula: see text][Formula: see text]1.5 GeV/c. So contribution of pions to this region is less and decreases sharply than the contribution of protons. The results of cascade model are not fully compatible with the experimental results in the third [Formula: see text] region, as this region contains less number of particles for model data as compared with experimental data but is compatible in the case of [Formula: see text].

Transverse Momentum Distributions of Pions, Kaons and Protons in p − p Interactions at 2.76 TeV

The spectra and particle yield ratios of π±, K± meson, protons and anti-protons in proton-proton (p − p) interactions at $$ \sqrt{s}=2.76 $$ TeV are presented. CRMC generators: EPOS-LHC, EPOS1.99 and QGSJETII-04, are used for simulations and the results are compared with LHC-CMS experimental data. The particles are identified in the transverse momentum range of pT ≈ 0.1 − 1.7 GeV/c and absolute rapidity, ∣y∣ < 1. In simulation, same cuts in pT and y are used as in the experiment. The EPOS1.99 model predicts the data well as compared to the other two models, which predict in some of the pT regions only. The different models used could not effectively describe the experimental data in all pT range.

Quantum Monte Carlo formalism for dynamical pions and nucleons

In most simulations of nonrelativistic nuclear systems, the wave functions found solving the many-body Schr\"odinger equations describe the quantum-mechanical amplitudes of the nucleonic degrees of freedom. In those simulations the pionic contributions are encoded in nuclear potentials and electroweak currents, and they determine the low-momentum behavior. In this work we present an alternative quantum Monte Carlo formalism in which both relativistic pions and nonrelativistic nucleons are explicitly included in the quantum-mechanical states of the system. We report the renormalization of the nucleon mass as a function of the momentum cutoff, an Euclidean time density correlation function that deals with the short-time nucleon diffusion, and the pion cloud density and momentum distributions. In the two-nucleon sector we show that the interaction of two static nucleons at large distances reduces to the one-pion exchange potential, and we fit the low-energy constants of the contact interactions to reproduce the binding energy of the deuteron and two neutrons in finite volumes. We show that the method can be readily applied to light-nuclei.

Pion transverse-momentum spectrum and elliptic anisotropy of partially coherent source

In this letter, we study the pion momentum distribution of a coherent source and investigate the influences of coherent emission on the pion transverse-momentum (pT) spectrum and elliptic anisotropy. With a partially coherent source, constructed by a conventional viscous hydrodynamics model (chaotic part) and a parameterized expanding coherent source model, we reproduce the pion pT spectrum and elliptic anisotropy coefficient v2(pT) in the peripheral Pb–Pb collisions at sNN=2.76 TeV. It is found that the influences of coherent emission on the pion pT spectrum and v2(pT) are related to the initial size and shape of the coherent source, largely due to the interference effect. However, the effect of source dynamical evolution on coherent emission is relatively small. The results of the partially coherent source with 33% coherent emission and 67% chaotic emission are consistent with the experimental measurements of the pion pT spectrum, v2(pT), and especially four-pion Bose–Einstein correlations.

Rapidity dependence of charged pion production at relativistic energies using Tsallis statistics

Transverse momentum distributions of charged pions produced in Au+Au collisions at 62.4GeV, 130GeV, 200GeV, Cu+Cu and d+Au collisions at 200GeV, p+p collisions at 62.4 and 200GeV and Pb+Pb collisions at 17.3GeV are studied using the Tsallis distribution as a parametrization. The non-extensivity parameter and Tsallis volume increase with energy, while the Tsallis temperature shows a decrease at higher energies. Using BRAHMS $ p_T$ spectra obtained in Au+Au collisions at 62.4GeV and 200GeV, Tsallis fit parameters are obtained on a very wide rapidity range. Results are compared with p+p and Cu+Cu data and changes of Tsallis parameters with rapidity and energy are investigated. We found that non-extensivity parameter q shows a decrease from midrapidity to forward rapidities for all the studied systems. Tsallis volume, V , increases with the system size from p+p, Cu+Cu to Au+Au, both in central rapidity region and at forward rapidities. The values of temperatures increase with rapidity, but the $ T/\cosh(y)$ ratio is constant as a function of rapidity.

Revealing the source of the radial flow patterns in proton–proton collisions using hard probes

In this work, we propose a tool to reveal the origin of the collective-like phenomena observed in proton–proton collisions. We exploit the fundamental difference between the underlying mechanisms, color reconnection and hydrodynamics, which produce radial flow patterns in Pythia 8 and Epos 3, respectively. Specifically, we proceed by examining the strength of the coupling between the soft and hard components which, by construction, is larger in Pythia 8 than in Epos 3. We study the transverse momentum () distributions of charged pions, kaons and (anti) protons in inelastic pp collisions at TeV produced at mid-rapidity. Specific selections are made on an event-by-event basis as a function of the charged particle multiplicity and the transverse momentum of the leading jet () reconstructed using the FastJet algorithm at mid-pseudorapidity (). From our studies, quantitative and qualitative differences between Pythia 8 and Epos 3 are found in the spectra when (for a given multiplicity class) the leading jet is increased. In addition, we show that for low-multiplicity events the presence of jets can produce radial flow-like behavior. Motivated by our findings, we propose to perform a similar analysis using experimental data from RHIC and LHC.

Effects of ρ-meson width on pion distributions in heavy-ion collisions

The influence of the finite width of ρ meson on the pion momentum distribution is studied quantitatively in the framework of the S-matrix approach combined with a blast-wave model to describe particle emissions from an expanding fireball. We find that the proper treatment of resonances which accounts for their production dynamics encoded in data for partial wave scattering amplitudes can substantially modify spectra of daughter particles originating in their two body decays. In particular, it results in an enhancement of the low-pT pions from the decays of ρ mesons which improves the quantitative description of the pion spectra in heavy ion collisions obtained by the ALICE collaboration at the LHC energy.

Event-shape engineering for inclusive spectra and elliptic flow in Pb-Pb collisions atsNN=2.76TeV

We report on results obtained with the Event Shape Engineering technique applied to Pb-Pb collisions at $\sqrt{s_\rm{NN}}=2.76$ TeV. By selecting events in the same centrality interval, but with very different average flow, different initial state conditions can be studied. We find the effect of the event-shape selection on the elliptic flow coefficient $v_2$ to be almost independent of transverse momentum $p_\rm{T}$, as expected if this effect is due to fluctuations in the initial geometry of the system. Charged hadron, pion, kaon, and proton transverse momentum distributions are found to be harder in events with higher-than-average elliptic flow, indicating an interplay between radial and elliptic flow.

Forward hadron production in ultra-peripheral proton–heavy-ion collisions at the LHC and RHIC

We discuss hadron production in the forward rapidity region in ultraperipheral proton-lead collisions at the LHC and proton-gold collisions at RHIC. Our discussion is based on the Monte Carlo simulations of the interactions of virtual photons emitted by a fast moving nucleus with a proton beam. We simulate the virtual photon flux with the STARLIGHT event generator and then particle production with the SOPHIA, DPMJET, and PYTHIA event generators. We show the rapidity distributions of charged and neutral particles, and the momentum distributions of neutral pions and neutrons at forward rapidities. According to the Monte Carlo simulations, we find large cross sections of ultraperipheral collisions for particle production especially in the very forward region, leading to substantial background contributions to investigations of collective nuclear effects and spin physics. Finally we can distinguish between proton-nucleus inelastic interactions and ultraperipheral collisions with additional requirements of either of the charged particles at midrapidity and a certain level of activities at negative forward rapidity.

Observables in ultrarelativistic heavy-ion collisions from two different transport approaches for the same initial conditions

For nucleus-nucleus collisions at Relativistic-Heavy-Ion Collider (RHIC) energies we calculate observables in two conceptually transport theories, i.e. the n-body molecular dynamical model RSP and in the Parton-Hadron-String-Dynamics (PHSD), starting out from the same distribution of the initial energy density at the quark gluon plasma (QGP) formation time. The RSP is based on the Nambu Jona-Lasinio (NJL) Lagrangian whereas in PHSD the partons are described by the dynamical quasi-particle model (DQPM). Despite of the very different description of the parton properties, their interactions and of the hadronization in both approaches the final transverse momentum distributions of pions and kaons are rather similar. Thus it will be difficult to conclude from the final experimenal data on the details of the initial plasma properties.

Observation of Λ(4)H Hyperhydrogen by Decay-Pion Spectroscopy in Electron Scattering.

At the Mainz Microtron MAMI, the first high-resolution pion spectroscopy from decays of strange systems was performed by electron scattering off a (9)Be target in order to study the Λ binding energy of light hypernuclei. Positively charged kaons were detected by a short-orbit spectrometer with a broad momentum acceptance at 0° forward angles with respect to the beam, efficiently tagging the production of strangeness in the target nucleus. Coincidentally, negatively charged decay pions were detected by two independent high-resolution spectrometers. About 10(3) pionic weak decays of hyperfragments and hyperons were observed. The pion momentum distribution shows a monochromatic peak at pπ≈133 MeV/c, corresponding to the unique signature for the two-body decay of hyperhydrogen Λ(4)H→(4)He+π(-), stopped inside the target. Its Λ binding energy was determined to be BΛ=2.12±0.01 (stat)±0.09 (syst)MeV with respect to the (3)H+Λ mass.

Production of π/K/p from intermediate to high pT in pp, p–Pb and Pb–Pb collisions measured by ALICE

In this work the results on the transverse momentum distributions ($\sim0.3<p_{\rm T}<15$ GeV/$c$) of charged pions, kaons and (anti)protons, measured in $\rm pp$ and $\rm Pb-Pb$ collisions at $\sqrt{s_{\rm NN}}=2.76$ TeV and in $\rm p-Pb$ collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV, are presented. The evolution of the spectral shapes and particle ratios with multiplicity is shown and the similarities among the different systems are discussed.