Charged Pion Multiplicity Research Articles

Negatively Charged Pion Multiplicity Analysis in Hadron-Hadron and Hadron-Nucleus Collisions at Momenta of 1-400 GeV/c

Data on the mean multiplicity of negative pion produced in minimum bias proton-proton, proton-neutron and proton-nucleus interactions as well as central nucleus-nucleus interactions at momenta of I .4-400 GeV/c per nucleon have been compared within the framework of a modified I-RITIOF model [1]. [2].The results for neutron-neutron and nucleon-nucleon interactions were then constructed. The dependence of the mean pion multiplicity in proton-nucleus and central nuclear collisions are studied as a function of the collision energy and the nucleus mass number. The model shows good agreement for pi -mesons, as shown in several comparisons in refs

Study of charged particles produced in the 84Kr + nuclear emulsion interactions at 1 GeV per nucleon

Abstract The main focus of this article is to study the characteristics of charged pions and their correlation with shower particles emitted in the interaction of 84Kr + emulsion at 1 A GeV. Author have also studied the dependence of the average multiplicity of charged pions and shower particles with projectile mass. In this study author observed that the average multiplicity of charged pions and shower particles showing the linear dependency on the projectile mass.

Symmetry energy investigation with pion production from Sn+Sn systems

In the past two decades, pions created in the high density regions of heavy ion collisions have been predicted to be sensitive at high densities to the symmetry energy term in the nuclear equation of state, a property that is key to our understanding of neutron stars. In a new experiment designed to study the symmetry energy, the multiplicities of negatively and positively charged pions have been measured with high accuracy for central 132Sn+124Sn, 112Sn+124Sn, and 108Sn+112Sn collisions at E/A=270 MeV with the SπRIT Time Projection Chamber. While individual pion multiplicities are measured to 4% accuracy, those of the charged pion multiplicity ratios are measured to 2% accuracy. We compare these data to predictions from seven major transport models. The calculations reproduce qualitatively the dependence of the multiplicities and their ratios on the total neutron and proton number in the colliding systems. However, the predictions of the transport models from different codes differ too much to allow extraction of reliable constraints on the symmetry energy from the data. This finding may explain previous contradictory conclusions on symmetry energy constraints obtained from pion data in Au+Au system. These new results call for still better understanding of the differences among transport codes, and new observables that are more sensitive to the density dependence of the symmetry energy.

Stopping of protons in pA collisions at SPS and NICA energies in analytical hydrodynamic model and in SMASH event generator

Our study is motivated by the first experimental results on pion production and stopping obtained in pA collisions in E910 experiment at BNL. The effect of stopping is the deceleration of an incident high energy proton traversing the target nucleus. It appears due to the energy losses relevant to the production of secondary particles in the inelastic interactions with nucleons.A hydrodynamic effective model of stopping is proposed that is based on the consideration of the nuclear matter as a liquid and by the introduction of an effective stopping force acting on a fast-moving proton. With this force, we obtain a differential equation that describes the relativistic motion of a proton in a nucleus. Calculations in the framework of this analytical model are performed for the correlation between the mean multiplicity of charged pions and a number of binary collisions.

First measurement of ν¯μ and νμ charged-current inclusive interactions on water using a nuclear emulsion detector

This paper reports the track multiplicity and kinematics of muons, charged pions, and protons from charged-current inclusive $\bar{\nu}_{\mu}$ and $\nu_{\mu}$ interactions on a water target, measured using a nuclear emulsion detector in the NINJA experiment. A 3-kg water target was exposed to the T2K antineutrino-enhanced beam with a mean energy of 1.3 GeV. Owing to the high-granularity of the nuclear emulsion, protons with momenta down to 200 MeV/$c$ from the neutrino-water interactions were detected. We find good agreement between the observed data and model predictions for all kinematic distributions other than the number of charged pions. These results demonstrate the capability of measurements with nuclear emulsion to improve neutrino interaction models.

Study of relativistic charged particles production in 84Kr36 emulsion interactions ∼1GeV per nucleon with wounded nucleon model

The experimental results on the multiplicity and probability distribution of the emitted charged pions [Formula: see text] in the interactions of [Formula: see text]Kr[Formula: see text] projectile at around 1[Formula: see text]GeV per nucleon with nuclear emulsion targets are reported. In this work, we have employed a wounded nucleon model (WNM) to calculate the total number of wounded nucleons [Formula: see text] and the total number of interactions [Formula: see text]. The dependence of average multiplicities of produced relativistic charged particles on the calculated wounded nucleons and total interactions are investigated. The obtained results revealed that the average multiplicity of [Formula: see text] is dependent on the projectile and target mass number. The calculated values of the total number of wounded nucleons and the total numbers of interactions show a strong dependence on the mass of the colliding nuclei. The emission rate of the mean multiplicity of [Formula: see text] and [Formula: see text] linearly increases with increasing the total number of wounded nucleons and interactions.

Multiplicity dependence of light nuclei production at LHC energies in the canonical statistical model

The statistical model with exact conservation of baryon number, electric charge, and strangeness – the Canonical Statistical Model (CSM) – is used to analyze the dependence of yields of light nuclei at midrapidity on charged pion multiplicity at the LHC. The CSM calculations are performed assuming baryon-symmetric matter, using the recently developed Thermal-FIST package. The light nuclei-to-proton yield ratios show a monotonic increase with charged pion multiplicity, with a saturation at the corresponding grand-canonical values in the high-multiplicity limit, in good qualitative agreement with the experimental data measured by the ALICE collaboration in pp and Pb–Pb collisions at different centralities and energies. Comparison with experimental data at low multiplicities shows that exact conservation of charges across more than one unit of rapidity and/or a chemical freeze-out temperature which decreases with the charged pion multiplicity improves agreement with the data.

News on mean pion multiplicity from NA61/SHINE

NA61/SHINE is a large acceptance fixed target experiment at the CERN SPS which studies final hadronic states in interactions between various particles and nuclei [1]. The main topic of this contribution are preliminary results for mean negatively charged pion multiplicities 〈π−〉 from central Ar+Sc and Be+Be collisions. The data were taken recently by the NA61/SHINE collaboration for a wide range of beam momenta. Measured rapidity distributions [see formula in PDF] were extrapolated to unmeasured regions to obtain total multiplicities 〈π−〉 A new scheme to calculate the mean number of wounded nucleons 〈W〉 utilizing the EPOS MC model is described. Using data from other experiments, a comparison of [see formula in PDF]for different collisions and beam momenta is discussed.

Constraining the density dependence of the symmetry energy using the multiplicity and average pT ratios of charged pions

The charged pion multiplicity ratio in intermediate-energy heavy-ion collisions, a probe of the density dependence of symmetry energy above the saturation point, has been proven in a previous study to be extremely sensitive to the strength of the isovector $\mathrm{\ensuremath{\Delta}}(1232)$ potential in nuclear matter. As there is no knowledge, either from theory or experiment, about the magnitude of this quantity, the extraction of constraints on the slope of the symmetry energy at saturation by using exclusively the mentioned observable is hindered at present. It is shown that, by including the ratio of average ${p}_{T}$ of charged pions $\ensuremath{\langle}{p}_{T}^{({\ensuremath{\pi}}^{+})}\ensuremath{\rangle}/\ensuremath{\langle}{p}_{T}^{({\ensuremath{\pi}}^{\ensuremath{-}})}\ensuremath{\rangle}$ in the list of fitted observables, the noted problem can be circumvented. A realistic description of this observable requires accounting for the interaction of pions with the dense nuclear matter environment by the incorporation of the so-called $S$-wave and $P$-wave pion optical potentials. This is performed within the framework of a quantum molecular dynamics transport model that enforces the conservation of the total energy of the system. It is shown that constraints on the slope of the symmetry energy at saturation density and the strength of the $\mathrm{\ensuremath{\Delta}}$(1232) potential can be simultaneously extracted. A symmetry energy with a value of the slope parameter $L>50$ MeV is favored, at $1\ensuremath{\sigma}$ confidence level, from a comparison with published FOPI experimental data. A precise constraint will require experimental data more accurate than presently available, particularly for the charged pion multiplicity ratio, and better knowledge of the density and momentum dependence of the pion potential for the whole range of these two variables probed in intermediate-energy heavy-ion collisions.

Direct detection of antihydrogen atoms using a BGO crystal

The ASACUSA collaboration has developed a detector consisting of a large size BGO crystal to detect an atomic antihydrogen beam, and performed the direct detection of antihydrogen atoms. Energy spectra from antihydrogen annihilation on the BGO crystal are discussed in comparison to simulation results from the GEANT4 toolkit. Background mainly originating from cosmic rays were strongly suppressed by analyzing the energy deposited in the BGO and requiring a multiplicity of charged pions. Thus antihydrogen events were identified.

Consistency check of charged hadron multiplicities and fragmentation functions in SIDIS

We derived the conditions on certain combinations of integrals of the fragmentation functions of pion using HERMES data of the sum for the charged pion multiplicities from semi-inclusive deep-inelastic scattering (SIDIS) off the deuteron target. In our derivation the nucleon parton distribution functions (PDFs) are assumed to be isospin SU(2) symmetric. Similar conditions have also been obtained for the fragmentation functions (FFs) of kaon by the sum of charged kaon multiplicities as well. We have chosen several FFs to study the impact of those conditions we have derived. Among those FFs, only that produced in the nonlocal chiral-quark model (NL$\chi$QM) constantly satisfy the conditions. Furthermore, the ratios of the strange PDFs $S(x)$ and the nonstrange PDFs $Q(x,Q^2)$ extracted from the charged pion and kaon multiplicities differ from each other significantly. Finally, we demonstrate that the HERMES pion multiplicity data is unlikely to be compatible with the two widely-used PDFs, namely CTEQ6M and NNPDF3.0.

The impact of energy conservation in transport models on the π−/π+ multiplicity ratio in heavy-ion collisions and the symmetry energy

The charged pion multiplicity ratio in intermediate energy central heavy-ion collisions has been proposed as a suitable observable to constrain the high density dependence of the isovector part of the equation of state. A comparison of various transport model predictions with existing experimental data has led, however, to contradictory results. Using an upgraded version of the Tübingen QMD transport model, which allows the conservation of energy at a local or global level by accounting for the potential energy of hadrons in two-body collisions and leading thus to particle production threshold shifts, we demonstrate that compatible constraints for the symmetry energy stiffness can be extracted from pion multiplicity and elliptic flow observables. However, pion multiplicities and ratios are proven to be highly sensitive to the yet unknown isovector part of the in-medium Δ(1232) potential which hinders, at present, the extraction of meaningful information on the high density dependence of the symmetry energy. A solution to this problem together with the inclusion of contributions presently neglected, such as in-medium pion potentials and retardation effects, are needed for a final verdict on this topic.

Multiplicity–rapidity–impact parameter correlation in pion–xenon interactions at intermediate energies

We study the correlation among impact parameter, multiplicity and longitudinal rapidity of neutral and charged pions, protons and neutrons produced in the interactions of charged pions with xenon nuclei at momenta of 2.34, 3.5, 9 and 30GeV/c. The correlation is investigated using a JAM modeling code.

Microcanonical hadron production inppcollisions

We apply a microcanonical statistical model to investigate hadron production in $pp$ collisions. The parameters of the model are the energy $E$ and the volume $V$ of the system, which we determine via fitting the average multiplicity of charged pions, protons, and antiprotons in $pp$ collisions at different collision energies. We then make predictions of mean multiplicities and mean transverse momenta of all identified hadrons. Our predictions on nonstrange hadrons are in good agreement with the data, the mean transverse momenta of strange hadron as well. However, the mean multiplicities of strange hadrons are overpredicted. This agrees with canonical and grand-canonical studies, where a strange suppression factor is needed. We also investigate the influence of event-by-event fluctuations of the $E$ parameter.

Evidence of multifractality and constant specific heat in hadronic collisions at high energies

We analyzed the experimental data on the charged pion multiplicity distribution in p-AgBr interactions at 200 GeV/c and ${\ensuremath{\pi}}^{\ensuremath{-}}\ensuremath{-}\mathrm{AgBr}$ interactions at 200 and 350 GeV/c in terms of multifractals. We calculate the values of generalized dimension ${D}_{q}$ for $q=2,$ 3, 4, and 5 with the help of the method proposed by Takagi. Also from the knowledge of ${D}_{q},$ the multifractal specific heat is calculated for different sets of interactions. It has been observed that the value of specific heat is more or less constant over the entire range of energies. This observation supports the constant specific heat approximation model and suggests that this parameter may come out as an essential characteristic of the hadron-hadron and hadron-nucleus interactions.

Multiplicity of charged and neutral pions in deep-inelastic scattering of 27.5 GeV positrons on hydrogen

Measurements of the individual multiplicities of pi+, pi- and pi0 produced in the deep-inelastic scattering of 27.5 GeV positrons on hydrogen are presented. The average charged pion multiplicity is the same as for neutral pions, up to approximately z= 0.7, where z is the fraction of the energy transferred in the scattering process carried by the pion. This result (below z= 0.7) is consistent with isospin invariance. The total energy fraction associated with charged and neutral pions is 0.51 +/- 0.01 (stat.) +/- 0.08 (syst.) and 0.26 +/- 0.01 (stat.) +/- 0.04 (syst.), respectively. For fixed z, the measured multiplicities depend on both the negative squared four momentum transfer Q^2 and the Bjorken variable x. The observed dependence on Q^2 agrees qualitatively with the expected behaviour based on NLO-QCD evolution, while the dependence on x is consistent with that of previous data after corrections have been made for the expected Q^2-dependence.

Geometrical effects in antiproton annihilation on nuclei

The importance of geometrical effects in the A dependence of many observables regarding antiproton annihilation on nuclei is expected on theoretical grounds. The cases of the charged pion multiplicity and of the frequency of the so-called single nucleon events are examined. In the first case, the respective roles of surface diffuseness, partial nuclear opacity, and pion absorption mechanism are examined. The possibility of extracting from comparison with experiment the average location of the annihilation site is critically discussed. The obtained values are in agreement with current theoretical estimates.

Event-by-event fluctuations in heavy ion collisions and the QCD critical point

The event-by-event fluctuations of suitably chosen observables in heavy ion collisions at SPS, RHIC and LHC can tell us about the thermodynamic properties of the hadronic system at freeze-out. By studying these fluctuations as a function of varying control parameters, it is possible to learn much about the phase diagram of QCD. As a timely example, we stress the methods by which present experiments at the CERN SPS can locate the second-order critical endpoint of the first-order transition between quark-gluon plasma and hadron matter. Those event-by-event signatures which are characteristic of freeze-out in the vicinity of the critical point will exhibit nonmonotonic dependence on control parameters. We focus on observables constructed from the multiplicity and transverse momenta of charged pions. We first consider how the event-by-event fluctuations of such observables are affected by Bose-Einstein correlations, by resonances which decay after freeze-out and by fluctuations in the transverse flow velocity. We compare our thermodynamic predictions for such noncritical event-by-event fluctuations with NA49 data, finding broad agreement. We then focus on effects due to thermal contact between the observed pions and a heat bath with a given (possibly singular) specific heat, and due to the direct coupling between the critical fluctuations of the sigma field and the observed pions. We also discuss the effect of the pions produced in the decay of sigma particles just above threshold after freeze-out on the inclusive pion spectrum and on multiplicity fluctuations. We estimate the size of these nonmonotonic effects which appear near the critical point, including restrictions imposed by finite size and finite time, and conclude that they should be easily observable.

The Bose-Einstein effect and joint WW decay

The influence of the Bose–Einstein interference effect on the joint WW hadronic decay is discussed. It is shown that the weight method incorporating this effect into Monte Carlo generators produces in a natural way an excess of average multiplicity as compared to the independent decay of two W bosons. The quantitative results for the average multiplicity and momentum distribution of charged pions, obtained with a simple parametrization of weights compatible with the observed shape of the “Bose–Einstein ratio”, agree well with the existing data.

Equation of state of hadronic matter and electromagnetic radiation from relativistic heavy ion collisions

We study the radiation of thermal photons and dileptons likely to be produced in relativistic heavy ion collisions. We find that the thermal photon multiplicity scales with the charged pion multiplicity as $dN_{ch}/dy)^\alpha$ with $\alpha\sim 1.2$ for a transversely expanding system, contrary to the general belief of a quadratic dependence. The scaling is shown to be valid, both for real and virtual photons. The coefficient of proportionality at a given energy may help us identify the appropriate equation of state of hot hadronic matter produced in such collisions.