Charged Particle Spectra Research Articles

Collective properties of hadrons in comparison of models prediction in pp collisions at 7 TeV

Analysis of the spectra of unidentified charged particles obtained by the CMS experiment in proton–proton collisions is reported in comparison with the simulation results of PYTHIA8.24 and EPOS-LHC models. The spectra obtained by the experiment were normalized to all non-single-diffractive (NSD) events using corrections for trigger and selection efficiency, acceptance, and branching ratios. The transverse-momentum (pT) spectra of the charged particles are measured in twelve equal bins of pseudorapidity (η) from 0.0 to 2.4 for pT from 0.1 to 2 GeV/c. The PYTHIA model reproduces the experimental data well in all bins of η especially in the region of high pT while the EPOS model predicts well in the intermediate pT regions. The intermediate regions where the EPOS model predicts well, broadens with increasing η.We used the Blast-wave model with Boltzmann–Gibbs statistics to study collective properties of the hadronic matter and for better comparison of the models’ prediction with the experimental data while determining the values of kinetic freeze-out temperature (T0) and transverse flow velocity (βT) for data and models. The values of T0 decrease with increasing η for data as well as for both the models. The transverse flow velocity has no clear trend with increasing η but a run through shows an increasing trend in the case of the data and the PYTHIA model but a decreasing trend in the case of the EPOS model. The multiplicity parameter N0 increases with increasing η and its values obtained by the fit function for the PYTHIA are closer to the ones obtained for data than the EPOS. It is concluded that none of the models completely describes the data in all bins of η over the entire pT range but the PYTHIA has better prediction than the EPOS model because the former has implied flow-like effects and formation of color string resulting from multiple hard sub-collisions between final and initial partons (color reconnection) from independent hard scatterings due to which the model predicts the data well.

Using Z Boson Events to Study Parton-Medium Interactions in Pb-Pb Collisions.

The spectra measurements of charged hadrons produced in the shower of a parton originating in the same hard scattering with a leptonically decaying Z boson are reported in lead-lead nuclei (Pb-Pb) and proton-proton (pp) collisions at a nucleon-nucleon center-of-mass energy of 5.02TeV. Both Pb-Pb and pp data sets are recorded by the CMS experiment at the LHC and correspond to an integrated luminosity of 1.7 nb^{-1} and 320 pb^{-1}, respectively. Hadronic collision data with one reconstructed Z boson candidate with the transverse momentum p_{T}>30 GeV/c are analyzed. The Z boson constrains the initial energy and direction of the associated parton. In heavy ion events, azimuthal angular distributions of charged hadrons with respect to the direction of a Z boson are sensitive to modifications of the in-medium parton shower and medium response. compared to reference data from pp interactions, the results for central Pb-Pb collisions indicate a modification of the angular correlations. The measurements of the fragmentation functions and p_{T} spectra of charged particles in Z boson events, which are sensitive to medium modifications of the parton shower longitudinal structure, are also reported. Significant modifications in central Pb-Pb events compared to the pp reference data are also found for these observables.

Repulsive black holes and higher-derivatives

In two-derivative theories of gravity coupled to matter, charged black holes are self-attractive at large distances, with the force vanishing at zero temperature. However, in the presence of massless scalar fields and four-derivative corrections, zero-temperature black holes no longer need to obey the no-force condition. In this paper, we show how to calculate the long-range force between such black holes. We develop an efficient method for computing the higher-derivative corrections to the scalar charges when the theory has a shift symmetry, and compute the resulting force in a variety of examples. We find that higher-derivative corrected black holes may be self-attractive or self-repulsive, depending on the value of the Wilson coefficients and the VEVs of scalar moduli. Indeed, we find black hole solutions which are both superextremal and self-attractive. Furthermore, we present examples where no choice of higher-derivative coefficients allows for self-repulsive black hole states in all directions in charge space. This suggests that, unlike the Weak Gravity Conjecture, which may be satisfied by the black hole spectrum alone, the Repulsive Force Conjecture requires additional constraints on the spectrum of charged particles.

PACIAE 2.2.1: An updated issue of the parton and hadron cascade model PACIAE 2.2

The parton and hadron cascade model PACIAE 2.2 (cf. Yan et al. (2018) [11]) has been upgraded to the new issue of PACIAE 2.2.1 with the chiral magnetic effect (CME). The charge correlation parameter, γss and γos, which is typically used to “detect” the CME, is calculated by PACIAE 2.2.1 in Au+Au and Pb+Pb collisions, and the result is consistent with the STAR and ALICE data. As an example, PACIAE 2.2.1 model is employed to mimic the pseudorapidity distribution (dNch/dη) and transverse momentum spectra (pT) of charged particles in non-central Au+Au collisions at RHIC energy and Pb+Pb collisions at LHC energy. The chiral magnetic effect is found to partly affect the final-state basic observables in relativistic nuclear collisions. By this new issue a more realistic dynamical evolution of relativistic nuclear collisions can be depicted. Program summaryProgram Title: PACIAE version 2.2.1CPC Library link to program files:https://doi.org/10.17632/w3g68dj4d9.3Code Ocean capsule:https://codeocean.com/capsule/3695338Licensing provisions: CC By 4.0Programming language: FORTRAN 77 or GFORTRANJournal reference of previous version: Comput. Phys. Comm. 224 (2018) 417Does the new version supersede the previous version?: No.Reasons for the new version: In order that PACIAE 2.2.1 model is now able to simulate the CME-related physics and a more realistic dynamical evolution scenario in the relativistic nucleus-nucleus collisions.Summary of revisions: In PACIAE 2.2.1 model the chiral magnetic effect is introduced. The CME-induced charge separation mechanism [7] into the initial partonic states is artificially added by switching py values for a fraction f of the downward moving partons with those of the corresponding upward moving antipartons.Nature of problem: PACIAE is based on PYTHIA, where it has no any mechanisms to generate the chiral magnetic effect (CME). The CME is a novel transport phenomenon arising from the interaction between quantum anomalies and strong magnetic fields in the ultra-relativistic nuclear collisions. Charge separation is an important consequence of the CME. In order to depict the CME, the corresponding upgrade about introducing a global charge separation scheme into the initial partonic states is highly required.Solution method: The global CME-induced charge separation mechanism [7] into the initial partonic states is introduced by switching py values for a fraction f of the downward moving partons with those of the corresponding upward moving antipartons.Additional comments including restrictions and unusual features: PACIAE 2.2.1 has three versions of PACIAE 2.2.1a, 2.2.1b, and 2.2.1c. PACIAE 2.2.1a is for the elementary collision (here no upgraded from PACIAE 2.2a). PACIAE 2.2.1b and PACIAE 2.2.1c are for the nucleus-nucleus collision of A + A with input file of usu.dat. PACIAE 2.2.1b and PACIAE 2.2.1c are similar in the physical contents but are different in the topological structure [8].•Using the attached input file of usux.dat to run 1000 events for the s = 200 GeV Non Single Diffractive pp collision by PACIAE 2.2.1a takes ≈0.5 min.•Using the attached input file of usu.dat to run 10 events for the 35%-45% non-central Au+Au collisions at sNN = 200 GeV by PACIAE 2.2.1b takes ≈6 min.•Using the attached input file of usu.dat to run 10 events for the 35%-45% non-central Au+Au collisions at sNN = 200 GeV by PACIAE 2.2.1c takes ≈8 min.

Fractionally charged BPS particles in M-string on 3D orbifolds

In this paper, we study the M-string realization of chiral [Formula: see text]-super-conformal field theory in 6 dimensions and its orbifold compactification down to three-dimensional (3D). We analyze its fractionally charged BPS particle spectrum in connection with effective 3D Chern–Simons gauge theory and the supersymmetric fractional quantum Hall effect in [Formula: see text] dimensions. We construct the set of underlying fractionally charged BPS particles in the ground state of the compactified M string and find that it contains 144 BPS states that are generated by four basic quasi-particles (two bosonic-like and two fermionic like) and their CPT conjugate. Two representations of the gauge bosons and the gauginos as condensates of the basic quasiparticles are found and explicit realizations are also given. Other features concerning generalizations are also discussed.

Radiation from a charge drifting along a cylindrical channel

Radiation of a charged particle moving in a cylindrical channel with elastic walls is studied. We assume that the particle in the channel is in free motion, periodically colliding with the channel wall. Explicit expressions for the spectrum and angular distribution of radiation are obtained. These results can be used to calculate the spectrum and radiation intensity of charged particles in carbon nanotubes of relatively great diameter. The emission spectrum is essentially a bremsstrahlung one, however, periodic collisions of the particle with the wall lead to coherent amplification of radiation at frequencies that are multiples of the collision frequency. If a beam of particles is channeled, then the multiple spectral lines merge into a continuous spectrum.

Application of machine learning in the determination of impact parameter in the Sn132+Sn124 system

Background: $^{132}$Sn+$^{124}$Sn collisions at the beam energy of 270 MeV$/$nucleon have been performed at the Radioactive Isotope Beam Factory (RIBF) in RIKEN to investigate the nuclear equation of state. Reconstructing impact parameter is one of the important tasks in the experiment as it relates to many observables. Purpose: In this work, we employ three commonly used algorithms in machine learning, the artificial neural network (ANN), the convolutional neural network (CNN) and the light gradient boosting machine (LightGBM), to determine impact parameter by analyzing either the charged particles spectra or several features simulated with events from the ultra-relativistic quantum molecular dynamics (UrQMD) model. Method: To closely imitate experimental data and investigate the generalizability of the trained machine learning algorithms, incompressibility of nuclear equation of state and the in-medium nucleon-nucleon cross sections are varied in the UrQMD model to generate the training data. Results: The mean absolute error $\Delta b$ between the true and the predicted impact parameter is smaller than 0.45 fm if training and testing sets are sampled from the UrQMD model with the same parameter set. However, if training and testing sets are sampled with different parameter sets, $\Delta b$ would increase to 0.8 fm. Conclusion: The generalizability of the trained machine learning algorithms suggests that these machine learning algorithms can be used reliably to reconstruct impact parameter in experiment.

Medium effects of charged particles in Xe+Xe collisions at s NN = 5.44 TeV using modified Tsallis distribution

We present a systematic study of transverse momentum [Formula: see text] spectra of charged particles in [Formula: see text] and Xe[Formula: see text]Xe collisions at [Formula: see text] TeV. The published data of invariant yields of charged particles as a function of [Formula: see text] is taken from ALICE at LHC in the mid-pseudorapidity region [Formula: see text]. The modified form of Tsallis distribution is used here to analyze the [Formula: see text] spectra of charged particles. The power law of Tsallis/Hagedorn form gives very good description of the charged particle spectra in [Formula: see text] collisions within a [Formula: see text] range of 0.15 GeV/[Formula: see text] to 50 GeV/[Formula: see text]. When we go from [Formula: see text] collisions to heavy-ion (Xe[Formula: see text]Xe) collisions, the original form of Tsallis/Hagedorn distribution is not able to describe the [Formula: see text] spectra of charged particles properly. This may be occurred due to the medium effects or the final state effects. Here we discuss two types of medium effects of charged particles in Xe[Formula: see text]Xe collisions, one is the transverse flow in the low to intermediate [Formula: see text] region ([Formula: see text] GeV/[Formula: see text]) and the other is the energy loss in the high [Formula: see text] region ([Formula: see text] GeV/[Formula: see text]), using the modified Tsallis distribution.

Wide-range tracking and LET-spectra of energetic light and heavy charged particles

We developed a highly-selective technique to measure the energy loss and linear-energy-transfer (LET) spectra of energetic charged particles in high-resolution and over a large collection of particle-event types. Precise and wide-range spectral and tracking measurements were performed with a single semiconductor pixel detector. The quantum-counting sensitivity, high-granularity and per-pixel spectrometric response of the Timepix ASIC chip enable the detailed spectral-tracking registration of single charged particles across the detector semiconductor sensor. Both the deposited energy along the particle trajectory (energy loss) and the path length of the particle track across the semiconductor sensor are precisely measured for each particle. This allows for the determination of the particle LET in silicon in high accuracy and over a wide-range of energies, particle types and directions. The tracking and energy loss response together with the resolving power at the particle-event level make it possible to selectively provide LET distributions of the light and heavy charged particle components in mixed-radiation and omnidirectional fields. This technique applies to energetic (E > 10 MeV/u) charged particles generating tracks greater than the pixel size and incident at non-perpendicular direction (>20∘) to the sensor plane. The technique applies also to electrons of energy above few MeV as well as highly energetic and minimum-ionizing-particles (MIPs). We make use of existing and in part newly collected data at well-defined radiation fields with proton and light ion beam accelerators. Flexible measurements, ease of deployment and online response are possible by the use of compact readout electronics such as the miniaturized radiation camera MiniPix (size < 8 cm, weight < 50 g) operable by any PC. Results are given for protons and light ions (He, C) of selected energies above 10 MeV/u and directions (2π FoV). We include also electrons (20 MeV). Selective and detailed LET spectra are produced over a wide range (10−1 to 102 keV/μm) in silicon.

Inelasticity resulting from rapidity spectra analysis

In this work we study the pseudorapidity spectra of charged particles produced in proton + proton and proton + antiproton interactions in a wide energy range using the non-extensive Tsallis approach. We evaluate the inelasticity coefficients of the discussed reactions which remain approximately independent of the collision energy.

Examining the event-shape-dependent modifications to charged-particle transverse momentum spectra and elliptic flow in p -Pb collisions at energies available at the CERN Large Hadron Collider

Purported signatures of collective dynamics in small systems like proton-proton (pp) or proton-nucleus (p-A) collisions still lack unambiguous understanding. Despite the qualitative and/or quantitative agreement of the data to hydrodynamic models, it has remained unclear whether the harmonic flows in small systems relate to the common physical picture of hydrodynamic collectivity driven by the initial geometry. In the present work, we aim to address this issue by invoking a novel concept of Event Shape Engineering (ESE), which has been leveraged to get some control of the initial geometry in high-energy heavy-ion collisions. We utilise ESE by constructing a reference flow vector, $q_{2}$ that allows to characterise an event based on it's ellipticity. Applying this technique on a data set, simulated from a 3+1D viscous hydrodynamic model EPOS3, we study the event-shape dependent modifications to some of the bulk properties like, inclusive transverse momentum ($p_{T}$) spectra and $p_{T}$-differential $v_{2}$ for p-Pb collisions at 5.02 TeV. Selecting events on the basis of different magnitudes of reference flow vector $q_{2}$, we observe a hint of event-shape induced modifications of $v_{2}$ as a function of $p_{T}$ but, the inclusive $p_{T}$-spectra of charged particles seem to be insensitive to this event-shape selection.

Mass spectra and incident energy resolved spectra after collisions of hydrocarbon ions with fusion-plasma tungsten thin films

We have performed surface-induced dissociation studies of small deuterated hydrocarbon cations i.e. CDx+ with x=2-4, colliding with two types of tungsten-coated surfaces, in the incident energy range between Ein = 0 eV approximately, up to Ein = 100 eV. A 34 nm thick W layer deposited on stainless steel using the Thermionic Vacuum Arc (TVA) method and a small sample of a tile cut from ASDEX-Upgrade tiles, consisting of PlasmaSprayed (PS) tungsten on carbon, are exposed to ion flux in these experiments. A double-focussing reverse geometry BE mass spectrometer, is used under ultra high vacuum conditions. Mass spectra of secondary charged particles are recorded via time-of-flight mass analyser. For comparison, we have performed equivalent study on polished stainless steel under experimental status explained in Section 2 below. At very low energies i.e. below 10 eV, only surface reflected projectiles are seen, whereas most of them are neutralized by surface micro charges. We observed that the fragmentation pattern of the small molecular ions at a given energy is strongly dependent on the surface. The roughness of both of the said thin films and their reflectivity for the projectile ion beam is studied by analysis of the ion yields of the reaction products

Radiation Belts during a Magnetic Field Reversal

An axisymmetric model is used to study changes in the shape of the Earth’s radiation belts and energy spectra of charged particles in them during a geomagnetic field reversal. Regions of stable existence of radiation belts are obtained analytically by generalizing the Stormer theory to the case of an axisymmetric quadrupole. An reversal scenario is proposed in which it is shown that a gradual reduction of radiation belts can occur with a decrease in the dipole component of the modern geomagnetic field. The spatial and energy distributions of the flux density of protons and electrons are obtained, which made it possible to determine the maximum dose rate of radiation on various magnetic shells during the reversal process.

Systematic investigation of the particle spectra in heavy-ion collisions at the Large Hadron Collider

We investigate the charged particle spectra produced in the heavy-ion collisions at nine centralities from different systems, i.e. [Formula: see text] at [Formula: see text] TeV and 5.02 TeV as well as [Formula: see text] at [Formula: see text] TeV, at Large Hadron Collider (LHC) using one empirical formula inspired by the stationary solution of the Fokker-Planck equation, dubbed as the generalized Fokker-Planck solution (GFPS). Our results show that the GFPS can reproduce the experimental particle spectrum up to transverse momentum [Formula: see text] about 45 GeV/c with the maximum discrepancy 30% covering 10 orders of magnitude. The discrepancy between the data and the results from the GFPS decreases to 15% when the maximum of the charged particle transverse momentum is cut to 20 GeV/c. We confirmed that the Tsallis distribution derived from the non-extensive statistics, which can reproduce the particle spectra produced in small collision systems, such as [Formula: see text], up to few hundreds GeV/c, can only apply to systematically study the particle spectra up to 8 GeV/c in [Formula: see text] collisions at LHC, as pointed out in the study of identified particle spectra in [Formula: see text] collisions at [Formula: see text] TeV. A brief discussion on GFPS is also given.

Event multiplicity, transverse momentum and energy dependence of charged particle production, and system thermodynamics in pp collisions at the Large Hadron Collider

In the present work, we study the recent collision energy and multiplicity dependence of the charged particle transverse momentum spectra as measured by the ALICE collaboration in pp collisions at and 13 TeV using the non-extensive Tsallis distribution and the Boltzmann–Gibbs blast wave (BGBW) model. A thermodynamically consistent form of the Tsallis distribution is used to extract the kinetic freeze-out parameters from the transverse momentum spectra of charged particles at mid-rapidity. In addition, a comprehensive study of fitting range dependence of transverse momentum spectra on the freeze-out parameters is done using Tsallis statistics. The applicability of BGBW model is verified by fitting the transverse momentum spectra of the bulk part (∼2.5 GeV/c) for both 5.02 and 13 TeV energies and also in different multiplicity classes. The radial flow, is almost independent of collision energy and multiplicity whereas the behavior of kinetic freeze-out temperature significantly depends on multiplicity classes. It is found that the Tsallis distribution generally leads to a better description for the complete transverse momentum spectra whereas the BGBW model explains the bulk part of the system.

Charged-particle spectra from μ− capture on Al

Published data on the emission of charged particles following nuclear muon capture are extremely limited. In addition to its interest as a probe of the nuclear response, these data are important for the design of some current searches for lepton flavor violation. This work presents momentum spectra of protons and deuterons following $\mu^{-}$ capture in aluminum. It is the first measurement of a muon capture process performed with a tracking spectrometer. A precision of better than 10% over the momentum range of 100--190 MeV/c for protons is obtained; for deuterons of 145--250 MeV/c the precision is better than 20%. The observed partial yield of protons with emission momenta above 80 MeV/c (kinetic energy 3.4 MeV) is $0.0322\pm0.0007(\text{stat})\pm0.0022(\text{syst})$ per capture, and for deuterons above 130 MeV/c (4.5 MeV) it is $0.0122\pm0.0009(\text{stat})\pm0.0006(\text{syst})$. Extrapolating to total yields gives $0.045\pm0.001(\text{stat})\pm0.003(\text{syst}) \pm 0.001(\text{extrapolation})$ per capture for protons and $0.018\pm0.001(\text{stat})\pm0.001(\text{syst})\pm 0.002(\text{extrapolation})$ for deuterons, which are the most precise measurements of these quantities to date.

Nuclear system size scan for freeze-out properties in relativistic heavy-ion collisions by using a multiphase transport model

A system size scan program was recently proposed for the STAR experiments at the Relativistic Heavy Ion Collider(RHIC). In this study, we employ a multiphase transport (AMPT) model for considering the bulk properties at the freeze-out stage for $\mathrm{^{10}B+^{10}B}$, $\mathrm{^{12}C+^{12}C}$, $\mathrm{^{16}O+^{16}O}$, $\mathrm{^{20}Ne+^{20}Ne}$, $\mathrm{^{40}Ca+^{40}Ca}$, $\mathrm{^{96}Zr+^{96}Zr}$, and $\mathrm{^{197}Au+^{197}Au}$ collisions at RHIC energies $\sqrt{s_{NN}}$ of 200, 20, and 7.7 GeV. The results for $\mathrm{^{197}Au+^{197}Au}$ collisions are comparable with those of previous experimental STAR data. The transverse momentum $p_{T}$ spectra of charged particles ($\pi^{\pm}$, $K^{\pm}$, $p$, and $\bar{p}$) at the kinetic freeze-out stage, based on a blast-wave model, are also discussed. In addition, we use a statistical thermal model to extract the parameters at the chemical freeze-out stage, which agree with those from other thermal model calculations. It was found that there is a competitive relationship between the kinetic freeze-out parameter $T_{kin}$ and the radial expansion velocity $\beta_{T}$, which also agrees with the STAR or ALICE results. We found that the chemical freeze-out strangeness potential $\mu_{s}$ remains constant in all collision systems and that the fireball radius $R$ is dominated by $\left\langle \mathrm{N_{Part}}\right\rangle$, which can be well fitted by a function of $a \left\langle \mathrm{N_{Part}}\right\rangle^{b}$ with $b \approx 1/3$. In addition, we calculated the nuclear modification factors for different collision systems with respect to the $ \mathrm{{}^{10}B} + \mathrm{{}^{10}B}$ system, and found that they present a gradual suppression within a higher $p_{T}$ range from small to large systems.

Transverse Momentum and Pseudorapidity Dependence of Particle Production in Xe–Xe Collision at sNN=5.44 TeV

Through the collision-system configuration, the Tsallis statistics is combined with a multisource thermal model. The improved model is used to investigate the transverse momentum and pseudorapidity of particles produced in Xe–Xe collisions at sNN=5.44 TeV. We discuss detailedly the thermodynamic properties, which are taken from the transverse momentum pT distributions of π, K, and p for different centralities. The pseudorapidity η spectra of charged particles for different centralities are described consistently in the model. And, the model result can estimate intuitively the longitudinal configuration of the collision system.

Initial, effective, and kinetic freeze-out temperatures from transverse momentum spectra in high-energy proton(deuteron)–nucleus and nucleus–nucleus collisions

The transverse momentum spectra of charged particles produced in proton(deuteron)-nucleus and nucleus-nucleus collisions at high energies are analyzed by the Hagedorn thermal model and the standard distribution in terms of multi-component. The experimental data measured in central and peripheral gold-gold (Au-Au) and deuteron-gold ($d$-Au) collisions by the PHENIX Collaboration at the Relativistic Heavy Ion Collider (RHIC), as well as in central and peripheral lead-lead (Pb-Pb) and proton-lead ($p$-Pb) collisions by the ALICE Collaboration at the Large Hadron Collider (LHC) are fitted by the two models. The initial, effective, and kinetic freeze-out temperatures are then extracted from the fitting to the transverse momentum spectra. It is shown that the initial temperature is larger than the effective temperature, and the effective temperature is larger than the kinetic freeze-out temperature. The three types of temperatures in central collisions are comparable with those in peripheral collisions, and those at the LHC are comparable with those at the RHIC.

Continuous spectra of light charged particles from interaction of 30 MeV energy protons with cooper

This paper presents the experimental double-differential and integral cross sections of reactions (p,xp), and (p,xα) on natCu nucleus. The experiment with the protons, accelerated to energy of 30.0 MeV was performed at the isochronous cyclotron of Institute of Nuclear Physics (Kazakhstan). We investigated the adequacy of the theoretical models in explaining the measured experimental data and contributions of direct, preequilibrium and compound processes in the formation of the cross sections were determined. We assert that the traditional frameworks are valid for the description of the experimental data.