Primary Charged Particles Research Articles

An Extensive Analysis of Tsallis Statistics: π±, K± Mesons, and pp¯ Baryon in Inelastic pp Collisions

This study explores the inelastic doubly differential transverse momentum spectra of the primary charged particles, (π++π−), (K++K−) and (pp¯), as a function of observables associated with underlying event (UE) at s=13TeV. The particle production is measured on the basis of different angular regions like toward, transverse and away, elucidated with respect to the direction of leading particle of an event. To study the thermal freeze-out parameters, the non-extensive Tsallis distribution function is used to extract the temperature Teff and chemical potential μ, which provide a basis to explain the QCD matter. The Tsallis distribution function describes transverse momentum spectra in pseudorapidity region of |η|<0.8. It is observed that effective temperature Teff changes from away to towards and forward region.

Observation of strangeness enhancement with charmed mesons in high-multiplicity pPb collisions at sNN=8.16 TeV

The production of prompt Ds+ and D+ mesons is measured by the LHCb experiment in proton-lead (pPb) collisions in both the forward (1.5<y*<4.0) and backward (−5.0<y*<−2.5) rapidity regions at a nucleon-nucleon center-of-mass energy of sNN=8.16 TeV. The nuclear modification factors of both Ds+ and D+ mesons are determined as a function of transverse momentum, pT, and rapidity. In addition, the Ds+ to D+ cross section ratio is measured as a function of the primary charged particle multiplicity in the event. An enhanced Ds+ to D+ production in high-multiplicity events is observed for the whole measured pT range, in particular at low pT and backward rapidity, where the significance exceeds six standard deviations. This constitutes the first observation of strangeness enhancement in charm quark hadronization in high-multiplicity pPb collisions. The results are also qualitatively consistent with the presence of quark coalescence as an additional charm quark hadronization mechanism in high-multiplicity proton-lead collisions. © 2024 CERN, for the LHCb Collaboration 2024 CERN

Multiplicity and event-scale dependent flow and jet fragmentation in pp collisions at s\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\sqrt{s} $$\\end{document} = 13 TeV and in p–Pb collisions at sNN\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\sqrt{s_{\ extrm{NN}}} $$\\end{document} = 5.02 TeV

Long- and short-range correlations for pairs of charged particles are studied via two-particle angular correlations in pp collisions at s\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\sqrt{s} $$\\end{document} = 13 TeV and p–Pb collisions at sNN\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\sqrt{s_{\ extrm{NN}}} $$\\end{document} = 5.02 TeV. The correlation functions are measured as a function of relative azimuthal angle ∆φ and pseudorapidity separation ∆η for pairs of primary charged particles within the pseudorapidity interval |η| < 0.9 and the transverse-momentum interval 1 < pT< 4 GeV/c. Flow coefficients are extracted for the long-range correlations (1.6 < |∆η| < 1.8) in various high-multiplicity event classes using the low-multiplicity template fit method. The method is used to subtract the enhanced yield of away-side jet fragments in high-multiplicity events. These results show decreasing flow signals toward lower multiplicity events. Furthermore, the flow coefficients for events with hard probes, such as jets or leading particles, do not exhibit any significant changes compared to those obtained from high-multiplicity events without any specific event selection criteria. The results are compared with hydrodynamic-model calculations, and it is found that a better understanding of the initial conditions is necessary to describe the results, particularly for low-multiplicity events.

Multiplicity dependence of charged-particle production in pp, p–Pb, Xe–Xe and Pb–Pb collisions at the LHC

Multiplicity (Nch) distributions and transverse momentum (pT) spectra of inclusive primary charged particles in the kinematic range of |η|<0.8 and 0.15 GeV/c<pT<10 GeV/c are reported for pp, p–Pb, Xe–Xe and Pb–Pb collisions at centre-of-mass energies per nucleon pair ranging from sNN=2.76 TeV up to 13 TeV. A sequential two-dimensional unfolding procedure is used to extract the correlation between the transverse momentum of primary charged particles and the charged-particle multiplicity of the corresponding collision. This correlation sharply characterises important features of the final state of a collision and, therefore, can be used as a stringent test of theoretical models. The multiplicity distributions as well as the mean and standard deviation derived from the pT spectra are compared to state-of-the-art model predictions. Providing these fundamental observables of bulk particle production consistently across a wide range of collision energies and system sizes can serve as an important input for tuning Monte Carlo event generators.

Charged Particle Pseudorapidity Distributions Measured with the STAR EPD

In 2018, in preparation for the Beam Energy Scan II, the STAR detector was upgraded with the Event Plane Detector (EPD). The instrument enhanced STAR’s capabilities in centrality determination for fluctuation measurements, event plane resolution for flow measurements, and in triggering overall. Due to its fine radial granularity, it can also be utilized to measure pseudorapidity distributions of the produced charged primary particles, in EPD’s pseudorapidity coverage of 2.15&lt;|η|&lt;5.09. As such a measurement cannot be done directly, the response of the detector to the primary particles has to be understood well. The detector response matrix was determined via Monte Carlo simulations, and corrected charged particle pseudorapidity distributions were obtained in Au + Au collisions at the center of mass collision energies sNN = 19.6 and 27.0 GeV using an iterative unfolding procedure. Several systematic checks of the method were also done.

Optimizing the Parton Showers in PYTHIA8 for Xe–Xe collision at 5.44 TeV

We present the doubly differential invariant yield of primary charged particles [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text], [Formula: see text] in Xe–Xe collisions at [Formula: see text] = 5.44 TeV, as a function of [Formula: see text] in kinematic region of [Formula: see text] and for the pseudorapidity interval of [Formula: see text] by using PYTHIA8 tuned to different Parton Showers like Simple Showers (Time-Like, Space-Like), DIRE and VINCIA Showers. The predictions of hard and soft QCD processes of Parton Showers are then compared with the ALICE data at different centrality classes of 0–5%, 50–60% and 70–80%. The observed deviations are connected with the kinematics involved and are mostly due to the color coherence and soft gluon emission from parton pairs. As PYTHIA8 does not take into account the Cronin effect, thus the deviation at low [Formula: see text] is due to Cronin effect. The nuclear modification factor is constructed and it is observed that the signal is less than unity or suppression is seen which is coming from Parton Showers.

Single proton LET characterization with the Timepix detector and artificial intelligence for advanced proton therapy treatment planning

Objective. Protons have advantageous dose distributions and are increasingly used in cancer therapy. At the depth of the Bragg peak range, protons produce a mixed radiation field consisting of low- and high-linear energy transfer (LET) components, the latter of which is characterized by an increased ionization density on the microscopic scale associated with increased biological effectiveness. Prediction of the yield and LET of primary and secondary charged particles at a certain depth in the patient is performed by Monte Carlo simulations but is difficult to verify experimentally. Approach. Here, the results of measurements performed with Timepix detector in the mixed radiation field produced by a therapeutic proton beam in water are presented and compared to Monte Carlo simulations. The unique capability of the detector to perform high-resolution single particle tracking and identification enhanced by artificial intelligence allowed to resolve the particle type and measure the deposited energy of each particle comprising the mixed radiation field. Based on the collected data, biologically important physics parameters, the LET of single protons and dose-averaged LET, were computed. Main results. An accuracy over 95% was achieved for proton recognition with a developed neural network model. For recognized protons, the measured LET spectra generally agree with the results of Monte Carlo simulations. The mean difference between dose-averaged LET values obtained from measurements and simulations is 17%. We observed a broad spectrum of LET values ranging from a fraction of keV μm−1 to about 10 keV μm−1 for most of the measurements performed in the mixed radiation fields. Significance. It has been demonstrated that the introduced measurement method provides experimental data for validation of LETD or LET spectra in any treatment planning system. The simplicity and accessibility of the presented methodology make it easy to be translated into a clinical routine in any proton therapy facility.

Simulation Studies of Track-Based Analysis of Charged Particles in Symmetric Hadron–Hadron Collisions at 7 TeV

This manuscript presents a simulation study of a track-based analysis of the multiplicity distributions of the primary charged particle compared to experimental measurements in symmetric hadron–hadron collisions acquiring maximum energy for the new particle production. The data are compared to the simulations of EPOS, PYTHIA8, Sibyll, and QGSJET under the same conditions. The event generators in the current study are simple parton-based models that incorporate the Reggie–Gribov theory. The latter is a field theory based on the QCD that uses the mechanism of multiple parton interactions. It has been found that the PYTHIA8 model chases the data well in most of the distributions but depends on the momentum and the requirement of charged particles in a given track, due to its feature-like color reshuffling of quarks and gluons through the color re-connection modes and initial and final state radiations by incorporating the parton showers. The EPOS model could also reproduce some spectral regions and presents a good comparison after the PYTHIA8. All the other models could not produce most of the spectra except for the limited region, which also depends on the analysis’s cuts. Besides the model’s prediction, we used Tsallis–Pareto and Hagedorn functions to fit the aforementioned spectra of the charged particles. The fit is applied to the data and models, and their results are compared. We extract the temperature parameter T01 (effective temperature (Teff)) from the Tsallis–Pareto-kind function and T02 (kinetic freezeout temperature) from the Hagedorn function. The temperatures are affected by pT as well Nch cuts.

Measuring Particle Production Using Tracklets

The purpose of the study was to access the particle production. Tracklets was adopted to measure the relationship between centrality ranged from outermost (70–80%) to central (0–5%) collisions and the primary charged-particle density at = 2. 76 TeV. It reveals that the dependence of centrality and that measured at lower collision energies ( < 2.76 TeV) are similar.

Study of Vertex Finding and Multiplicity Determination in Au-Au Collisions using the sPHENIX MVTX

This project investigated a simulated Au-Au collision data sheet under sPHENIX environment, with 10 events in total. The sPHENIX’s MVTX will be assembled in three cylindrical layers with the main geometrical parameters listed in Table 1. Finally, we can conclude that for this Au-Au collision simulation events, nearly all the detected hits are due to primary charged particles, which made abandoning “remote” layers cannot improve the found Z coordinates resolution.

The antinucleus annihilation reconstruction algorithm of the GAPS experiment

The General AntiParticle Spectrometer (GAPS) is an Antarctic balloon-borne detector designed to measure low-energy cosmic antinuclei (<0.25GeV/n), with a specific focus on antideuterons, as a distinctive signal from dark matter annihilation or decay in the Galactic halo. The instrument consists of a tracker, made up of ten planes of lithium-drifted Silicon Si(Li) detectors, surrounded by a plastic scintillator Time-of-Flight system. GAPS uses a novel particle identification method based on exotic atom capture and decay with the emission of pions, protons, and atomic X-rays from a common annihilation vertex.An important ingredient for the antinuclei identification is the reconstruction of the “annihilation star” topology. A custom antinucleus annihilation reconstruction algorithm, called the “star-finding” algorithm, was developed to reconstruct the annihilation star fully, determining the annihilation vertex position and reconstructing the tracks of the primary and secondary charged particles. The reconstruction algorithm and its performances were studied on simulated data obtained with the Geant4-based GAPS simulation software, which fully reproduced the detector geometry. This custom algorithm was found to have better performance in the vertex resolution and reconstruction efficiency compared with a standard Hough-3D algorithm.

Penningionization processes involving cold Rydberg alkali metal atoms

This paper investigates the Penning ionization (PI) processes in cold gas media of alkali atoms. The PI autoionization widths of atomic pairs show a drastic dependence (by orders of magnitude) on the orbital quantum numbers of Rydberg atoms involved in a long-range dipole-dipole interaction. The nontrivial dependence of the PI efficiency on the size of colliding particles was considered, with a particular accent to the applications in the research of cold matter created in the experiments with magneto-optical traps. We have analytically described the optimal, highly asymmetric configurations of atomic Rydberg pairs, which lead to an explosive intensification (by several orders of magnitude) of a free-electron escaping due to PI. The excited states of atoms in the optimal pairs turn out to have a strong difference in atomic shell sizes. The optimal pairs’ properties may be favorable for the generation of primary (seeding) charged particles when a cold Rydberg medium evolves into a cold plasma. Within the framework of the semiclassical approach, we have obtained universal analytical formulas containing two adjustable parameters and present here their values in tabulated form, which allows estimating the PI rate constants for various pairs of alkali metal atoms.

Multiparton interactions in pp collisions from machine learning-based regression

Multi-Parton Interactions (MPI) in pp collisions have attracted the attention of the heavy-ion community since they can help to elucidate the origin of collective-like effects discovered in small collision systems at the LHC. In this work, we report that in PYTHIA 8.244, the charged-particle production in events with a large number of MPI (${\rm N}_{\rm mpi}$) normalized to that obtained in minimum-bias pp collisions shows interesting features. After the normalization to the corresponding $\langle {\rm N}_{\rm mpi} \rangle$, the ratios as a function of $p_{\rm T}$ exhibit a bump at $p_{\rm T}\approx3$ GeV/$c$; and for higher $p_{\rm T}$ ($>8$ GeV/$c$), the ratios are independent of ${\rm N}_{\rm mpi}$. While the size of the bump increases with increasing ${\rm N}_{\rm mpi}$, the behavior at high $p_{\rm T}$ is expected from the "binary scaling" (parton-parton interactions), which holds given the absence of any parton-energy loss mechanism in PYTHIA. The bump at intermediate $p_{\rm T}$ is reminiscent of the Cronin effect observed for the nuclear modification factor in p--Pb collisions. In order to unveil these effects in data, we propose a strategy to construct an event classifier sensitive to MPI using Machine Learning-based regression. The study is conducted using TMVA, and the regression is performed with Boosted Decision Trees (BDT). Event properties like forward charged-particle multiplicity, transverse spherocity and the average transverse momentum ($\langle p_{\rm T} \rangle$) are used for training. The kinematic cuts are defined in accordance with the ALICE detector capabilities. In addition, we also report that if we apply the trained BDT on existing (${\rm INEL}>0$) pp data, i.e. events with at least one primary charged-particle within $|\eta|<1$, the average number of MPI in pp collisions at $\sqrt{s}=5.02$ and 13 TeV are 3.76$\pm1.01$ and 4.65$\pm1.01$, respectively.

Radiation stability and reliability of Cu–ZnO/P3OT hybrid heterostructures under swift heavy ion irradiations

Hybrid heterostructures (HH's) were prepared by depositing conducting poly (3-octylthiophene) (P3OT) polymer and Cu-doped zinc oxide (Cu–ZnO) composites films onto indium-doped tin oxide (ITO) substrate using an ultra-sonication cast technique. The weight percentage (wt%) of Cu–ZnO was varied such as 3 wt% and 5 wt% for heterostructure studies. In the HH's, P3OT works as hole-transporting and an electron donor (i.e. hole acceptor) material, while the Cu–ZnO was used as an electron-transporting and hole donor (i.e. electron acceptor) material. The radiation stability and reliability of HH's was studied by performing in-situ current-voltage (I–V) measurements during swift heavy ion (SHI) irradiation by 80 MeV O6+ and 120 MeV Ag9+ ions at increasing ion fluences. Additionally, the in-situ capacitance-voltage (C–V) measurements at frequencies of 1 MHz and 5 MHz were also performed under both the ion irradiations as a function of ion fluences. It was observed that the SHI irradiation-induced secondary charged particles are mainly responsible for modifying the heterostructures properties by depositing energy in the hybrid layer, interfacial region, and ITO substrate. The modification mostly occurs in terms of irradiation-induced various types of defects at the interface of heterostructures. However, after irradiation, minor/insignificant changes in the I–V and C–V characteristics were observed reflecting the radiation stability and reliability of HH's. Therefore, this study may emerge out to be very fascinating for an in-depth understanding of the interaction processes exchanged by primary and secondary charged particles besides the possible applications in radiation harsh environment of such hybrid materials.

The Optimal Pair of Rydberg Alkali-Metal Atoms in the Nonsymmetric Penning Ionization Processes

Features of Penning ionization in cold gaseous media of Rydberg alkali-metal atoms have been investigated. In contrast to the hydrogen atom, the corresponding autoionization widths exhibit a strong (by orders of magnitude) dependence on the orbital quantum numbers of the atoms involved in the long-range dipole–dipole interaction. An important feature of Penning ionization is the nontrivial dependence of its efficiency on the Rydberg particle size. For all types of alkali-metal atoms, the optimal highly nonsymmetric configurations of Rydberg pairs have been found that lead to the explosive (by several orders of magnitude) intensification of the free electron formation by means of the Penning ionization processes. This property makes Penning ionization an important means of forming primary charged particles during the cold Rydberg plasma formation. The numerical data for pairs of potassium atoms are reported that demonstrate a significant effect of the Forster resonance on the values of the Penning ionization rate constants.

Another Approach to Track Reconstruction: Cluster Analysis

A novel combination of data analysis techniques is introduced for the reconstruction of primary charged particles and of daughters of photon conversions, created in high energy collisions. Instead of performing a classical trajectory building or an image transformation, efficient use of both local and global information is undertaken while keeping competing choices open. The measured hits in silicon-based tracking detectors are clustered with the help of a k-medians clustering. It proceeds by alternating between the hit-to-track assignment and the track-fit update steps, until convergence. The clustering is complemented with the possibility of adding new track hypotheses or removing unnecessary ones. A simplified model of a silicon tracker is employed to test the performance of the proposed method, showing good efficiency and purity characteristics.

Color reconnection as a possible mechanism of intermittency in the emission spectra of charged particles in PYTHIA-generated high-multiplicity pp collisions at energies available at the CERN Large Hadron Collider

Nonstatistical fluctuation in pseudorapidity ($\ensuremath{\eta}$), azimuthal ($\ensuremath{\phi}$), and pseudorapidity-azimuthal ($\ensuremath{\eta}\text{--}\ensuremath{\phi}$) distribution spectra of primary particles of PYTHIA Monash (default) generated $pp$ events at $\sqrt{s}=2.76$, 7, and 13 TeV have been studied using the scaled factorial moment technique. A weak intermittent type of emission could be realized for minimum-bias (MB) $pp$ events in $\ensuremath{\chi}(\ensuremath{\eta}\text{--}\ensuremath{\phi})$ space and a much stronger intermittency could be observed in high-multiplicity (HM) $pp$ events in all $\ensuremath{\chi}(\ensuremath{\eta})$, $\ensuremath{\chi}(\ensuremath{\phi})$, and $\ensuremath{\chi}(\ensuremath{\eta}\text{--}\ensuremath{\phi})$ spaces at all the studied energies. For HM $pp$ events, at a particular energy, the intermittency index ${\ensuremath{\alpha}}_{q}$ is found to be largest in two-dimensional $\ensuremath{\chi}(\ensuremath{\eta}\text{--}\ensuremath{\phi})$ space and least in $\ensuremath{\chi}(\ensuremath{\eta})$ space, and no center of mass energy dependence of ${\ensuremath{\alpha}}_{q}$ could be observed. The anomalous dimensions ${d}_{q}$ are observed to be increased with the order of the moment $q$, suggesting a multifractal nature of the emission spectra of various studied events. While, the coefficient ${\ensuremath{\lambda}}_{q}$ is found to decrease monotonically with the order of the moment $q$ for two-dimensional analysis of MB $pp$ events as well as for one-dimensional analysis of HM $pp$ events, a clear minimum in ${\ensuremath{\lambda}}_{q}$ values could be observed from the two-dimensional HM $pp$ data analysis. For PYTHIA Monash generated sets of data, the strength of the intermittency is found to vary significantly with the variation of the strength of the color reconnection (CR) parameter, i.e., reconnection range RR, for $\mathrm{RR}=0.0$, 1.8 and 3.0, thereby, establishing a strong connection between the CR mechanism and the observed intermittent type of emission of primary charged particles of the studied high-multiplicity $pp$ events.

Energy and system dependence of nuclear modification factors of inclusive charged particles and identified light hadrons measured in p–Pb, Xe–Xe and Pb–Pb collisions with ALICE

We report recent ALICE results on primary charged particle and neutral meson production in pp, p–Pb, Pb–Pb and Xe–Xe collisions at LHC energies. In this article, measurements of the nuclear modification factors RAA of primary charged particles and of light neutral mesons in Pb–Pb, in Xe–Xe and in p–Pb collisions in a wide pT range and different centrality classes are discussed. We compare the nuclear modification factors obtained for different collision systems as a function of transverse momentum, collision centrality as well as charged particle multiplicity (dNch/dη). We also present comparison of experimental results to model calculations.

ALICE results on system-size dependence of charged-particle multiplicity density in p–Pb, Pb–Pb and Xe–Xe collisions

Particle production at LHC energies involves the interplay of hard (perturbative) and soft (non-perturbative) QCD processes. Global observables, such as the charged-particle multiplicity, are related to the initial geometry and the energy density produced in the collision. They are important to characterise relativistic heavy-ion collisions and to constrain model calculations. The LHC produced Xenon–Xenon collisions for the first time in October 2017. New results on the primary charged-particle pseudorapidity density, and its pseudorapidity and centrality dependence are presented for this lighter and deformed nucleus, and compared to measurements obtained for lead ions. New results will also be presented for p-Pb collisions at the highest energy of 8.16 TeV, as part of an overview of all the measurements at LHC Run 1 and 2 energies. These studies allow us to investigate the evolution of particle production with energy and system size and to compare models based on various particle production mechanisms and different initial conditions.

Оптимальная пара ридберговских атомов щелочных металлов в несимметричных пеннинговских процессах ионизации

Penning ionization (PI) processes for cold Rydberg alkali metal atoms are investigated. Contrary to the reference case of a hydrogen atom, the corresponding autoionization widths demonstrate a sharp dependence (by orders of magnitude) on the orbital quantum numbers of the atoms exposed to long-range dipole-dipole interaction. An important feature of PI is the nontrivial dependence of its efficiency on the size of Rydberg particles. For all types of alkali atoms, the existence of optimal Rydberg pairs has been demonstrated (highly asymmetric configurations of Rydberg pairs), which lead to an explosive intensification (by several orders of magnitude) of the formation of free electrons due to PI processes. This property makes PI an important source of the formation of primary charged particles during the formation of cold Rydberg plasma. The presented numerical data for potassium atomic pairs demonstrate a significant effect of the Förster resonance on the values of PI rate constants.