Spectra In Pp Collisions Research Articles

Statistical Thermal Model for Particle Production in pp Collisions at RHIC and LHC Energies

In this paper, an improved multi-source thermal model is used to analyze the transverse momentum spectra in pp collisions at high energies, ranging from sNN = 62.4 GeV to 7 TeV. Via a detailed comparison between the model results and experimental data at RHIC and LHC energies, the thermodynamic properties of particle production are decided. It is shown that the excitation factors of emission sources depend linearly on lnsNN in the framework. Based on the variation regularity of the source excitation factors, transverse momentum spectra are predicted in pp collisions at higher energies; potential future pp colliders operating at sNN = 33 and 100 TeV.

Constituent quark number scaling from strange hadron spectra in pp collisions at TeV * * Supported by National Natural Science Foundation of China (11575100), and by Shandong Province Natural Science Foundation(ZR2019YQ06, ZR2019MA053), and by A Project of Shandong Province Higher Educational Science and Technology Program (J18KA228)

We show that the spectra of and at midrapidity in the inelastic events in collisions at 13 TeV exhibit a constituent quark number scaling property, which is a clear signal of quark combination mechanism at hadronization. We use a quark combination model with equal velocity combination approximation to systematically study the production of identified hadrons in collisions at = 13 TeV. The midrapidity spectra for protons, , , , and in the inelastic events are simultaneously fitted by the model. The multiplicity dependence of the yields of these hadrons are also well understood. The strong dependence of the ratio is well explained by the model, which further suggests that the production of two hadrons with similar masses is determined by their quark content at hadronization. The spectra of strange hadrons at midrapidity in different multiplicity classes in collisions at 13 TeV are predicted for further tests of the model. The midrapidity spectra of soft ( GeV/c) strange quarks and up/down quarks at hadronization in collisions at 13 TeV are extracted.

Nuclear modification factor of D0 mesons in PbPb collisions at [formula omitted

The transverse momentum (pT) spectrum of prompt D0 mesons and their antiparticles has been measured via the hadronic decay channels D0→K−π+ and D‾0→K+π− in pp and PbPb collisions at a centre-of-mass energy of 5.02 TeV per nucleon pair with the CMS detector at the LHC. The measurement is performed in the D0 meson pT range of 2–100GeV/c and in the rapidity range of |y|<1. The pp (PbPb) dataset used for this analysis corresponds to an integrated luminosity of 27.4 pb−1 (530 μb−1 ). The measured D0 meson pT spectrum in pp collisions is well described by perturbative QCD calculations. The nuclear modification factor, comparing D0 meson yields in PbPb and pp collisions, was extracted for both minimum-bias and the 10% most central PbPb interactions. For central events, the D0 meson yield in the PbPb collisions is suppressed by a factor of 5–6 compared to the pp reference in the pT range of 6–10GeV/c. For D0 mesons in the high-pT range of 60–100GeV/c, a significantly smaller suppression is observed. The results are also compared to theoretical calculations.

Universal scaling of strange particle pT spectra in pp collisions

As a complementary study to that performed on the transverse momentum ($p_{\rm T}$) spectra of charged pions, kaons and protons in proton-proton (pp) collisions at LHC energies 0.9, 2.76 and 7 TeV, we present a scaling behaviour in the $p_{\rm T}$ spectra of strange particles ($K_{S}^{0}$, $\rm \Lambda$, $\rm \Xi$ and $\phi$) at these three energies. This scaling behaviour is exhibited when the spectra are expressed in a suitable scaling variable $z=p_{\rm T}/K$, where the scaling parameter $K$ is determined by the quality factor method and increases with the center of mass energy ($\sqrt{s}$). The rates at which $K$ increases with $\mathrm{ln}\sqrt{s}$ for these strange particles are found to be identical within errors. In the framework of the colour string percolation model, we argue that these strange particles are produced through the decay of clusters that are formed by the colour strings overlapping. We observe that the strange mesons and baryons are produced from clusters with different size distributions, while the strange mesons (baryons) $K_{S}^{0}$ and $\phi$ ($\rm \Lambda$ and $\rm \Xi$) originate from clusters with the same size distributions. The cluster's size distributions for strange mesons are more dispersed than those for strange baryons. The scaling behaviour of the $p_{\rm T}$ spectra for these strange particles can be explained by the colour string percolation model in a quantitative way.

LHC-ALICE実験√s = 5.02TeV pp衝突におけるジェット横運動量スペクトル測定

LHC-ALICE実験√s = 5.02TeV pp衝突におけるジェット横運動量スペクトル測定

Neutral meson production in pp, p–Pb and Pb–Pb collisions with ALICE at the LHC

The ALICE experiment is mainly devoted to the study of QGP expected to be created in heavy-ion collisions at the LHC. In the early stage of such collisions, partons can be scattered and photons can be produced in energetic hard processes. High energy partons will interact with the QGP, and from the measurement of the particles originated from the parton fragmentation in vacuum, one can infer transport properties of the QGP. Therefore, study of high-pT hadrons production is important to constrain the properties of the hot and dense medium. The strong suppression of the high-pT hadrons in heavy-ion collisions has been explained by the energy loss of the partons in medium and it can be investigated experimentally via the nuclear modification factor of hadrons.ALICE measured neutral mesons (π0 and η) at mid-rapidity in a wide pT range in pp, p-Pb and Pb-Pb collisions. Neutral mesons are reconstructed via complementary methods, using the electromagnetic calorimeters, PHOS and EMCal, and by the central tracking system, identifying photons converted to e+e− pairs in the material of the inner barrel detectors (ITS and TPC). Measurement of neutral meson spectra in pp collisions at s=0.9,2.76,7 and 8 TeV provides valuable comparison data for pQCD calculations and allows to study scaling properties of hadron production at the LHC energies. The study of neutral mesons production in p-Pb collisions helps to disentangle initial and final state effects on the suppression itself. The latest results of neutral meson measurement in pp, p-Pb and Pb-Pb collisions will be shown in this paper.

Transverse momentum spectra and the nuclear modification factor of charged particles with ALICE

The observed suppression of particle production at high transverse momentum in nucleus-nucleus collisions at high energies is an effect of the energy loss of partons as they propagate through the hot and dense deconfined QCD medium. The measurement of transverse momentum spectra of primary charged particles in Pb–Pb collisions and the comparison to the measurement in pp collisions are important to study the properties of the deconfined medium. In 2015, pp and Pb–Pb collisions have been recorded at the LHC at the energy of = 5.02 TeV. The inclusive charged particle production is measured with the ALICE detector in the pseudo-rapidity range |η| < 0.8 and in the transverse momentum range 0.15 < pT < 40 GeV/c. The spectra in Pb–Pb, determined for several centrality intervals, are compared to the reference spectrum in pp collisions by calculating the nuclear modification factor RAA. The data are compared to measurements at the lower collision energy of 2.76 TeV and to model predictions.

Production of light nuclei and anti-nuclei inppand Pb-Pb collisions at energies available at the CERN Large Hadron Collider

The production of (anti-)deuteron and (anti-)$^{3}$He nuclei in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV has been studied using the ALICE detector at the LHC. The spectra exhibit a significant hardening with increasing centrality. Combined blast-wave fits of several particles support the interpretation that this behavior is caused by an increase of radial flow. The integrated particle yields are discussed in the context of coalescence and thermal-statistical model expectations. The particle ratios, $^3$He/d and $^3$He/p, in Pb-Pb collisions are found to be in agreement with a common chemical freeze-out temperature of $T_{\rm chem} \approx 156$ MeV. These ratios do not vary with centrality which is in agreement with the thermal-statistical model. In a coalescence approach, it excludes models in which nucleus production is proportional to the particle multiplicity and favors those in which it is proportional to the particle density instead. In addition, the observation of 31 anti-tritons in Pb-Pb collisions is reported. For comparison, the deuteron spectrum in pp collisions at $\sqrt{s} = 7$ TeV is also presented. While the p/$\pi$ ratio is similar in pp and Pb-Pb collisions, the d/p ratio in pp collisions is found to be lower by a factor of 2.2 than in Pb-Pb collisions.

Role of the pion electromagnetic form factor in theΔ(1232)→γ*Ntimelike transition

The $\Delta(1232) \to \gamma^\ast N$ magnetic dipole form factor ($G_M^\ast$) is described here within a new covariant model that combines the valence quark core together with the pion cloud contributions. The pion cloud term is parameterized by two terms: one connected to the pion electromagnetic form factor, the other to the photon interaction with intermediate baryon states. The model can be used in studies of pp and heavy ion collisions. In the timelike region this new model improves the results obtained with a constant form factor model fixed at its value at zero momentum transfer. At the same time, and in contrast to the Iachello model, this new model predicts a peak for the transition form factor at the expected position, i.e. at the $\rho$ mass pole. We calculate the decay of the $\Delta \to \gamma N$ transition, the Dalitz decay ($\Delta \to e^+ e^- N$), and the $\Delta$ mass distribution function. The impact of the model on dilepton spectra in pp collisions is also discussed.

Parton energy loss in the mini quark–gluon plasma and jet quenching in proton–proton collisions

We evaluate the medium suppression of light hadron spectra in pp collisions at RHIC and LHC energies in the scenario with formation of a mini quark–gluon plasma. We find a significant suppression effect. For pT ∼10 GeV we obtained the reduction of the spectra by ∼[20–30, 25–35, 30–40]% at TeV. We also discuss how this phenomenon may change the predictions for the nuclear modification factors for AA and pA collisions.

Strangeness production in ALICE

The ALICE experiment at the LHC has measured the production of strange and multi-strange hadrons both in Pb–Pb and pp collisions at unprecedented beam energies. Transverse momentum spectra at mid-rapidity for K0S mesons, Λ, and Ω− baryons and their anti-particles in Pb–Pb collisions at TeV are presented in different centrality intervals. Particles are reconstructed via their weak decay topologies into charged particles only over a wide momentum range, exploiting the tracking and particle identification capabilities of the ALICE detector. The corresponding production yields are compared with those observed in pp collisions and lower energy heavy-ion reactions. In particular, results on baryon-to-meson ratio, strangeness enhancements, elliptic flow and nuclear modification factors are discussed. The comparison of strange particle spectra in pp collisions at TeV with PYTHIA Perugia-2011 predictions is also presented.

Search for heavy resonances in the W/Z-tagged dijet mass spectrum in pp collisions at 7 TeV

A search has been made for massive resonances decaying into a quark and a vector boson, qW or qZ, or a pair of vector bosons, WW, WZ, or ZZ, where each vector boson decays to hadronic final states. This search is based on a data sample corresponding to an integrated luminosity of 5.0 fb−1 of proton–proton collisions collected in the CMS experiment at the LHC in 2011 at a center-of-mass energy of 7 TeV. For sufficiently heavy resonances the decay products of each vector boson are merged into a single jet, and the event effectively has a dijet topology. The background from QCD dijet events is reduced using recently developed techniques that resolve jet substructure. A 95% CL lower limit is set on the mass of excited quark resonances decaying into qW (qZ) at 2.38 TeV (2.15 TeV) and upper limits are set on the cross section for resonances decaying to qW, qZ, WW, WZ, or ZZ final states.

Feynman scaling violation on baryon spectra in pp collisions at LHC and cosmic ray energies

A significant asymmetry in baryon/antibaryon yields in the central region of high energy collisions is observed when the initial state has nonzero baryon charge. This asymmetry is connected with the possibility of baryon charge diffusion in rapidity space. Such a diffusion should decrease the baryon charge in the fragmentation region and translate into the corresponding decrease of the multiplicity of leading baryons. As a result, a new mechanism for Feynman scaling violation in the fragmentation region is obtained. Another numerically more significant reason for the Feynman scaling violation comes from the fact that the average number of cut Pomerons increases with initial energy. We present the quantitative predictions of the Quark-Gluon String Model for the Feynman scaling violation at LHC energies and at even higher energies that can be important for cosmic ray physics.

Feynman Scaling Violation on Baryon Spectra in pp Collisions at LHC and Cosmic Ray Energies

Feynman Scaling Violation on Baryon Spectra in pp Collisions at LHC and Cosmic Ray Energies

Light-flavour hadron production in pp and Pb–Pb collisions in the ALICE experiment at the LHC

Nuclear matter under extreme conditions of temperature and density can be investigated in ultrarelativistic heavy-ion collisions. The measurement of transverse momentum (p T ) distributions and yields of identified particles is a fundamental step in understanding collective and thermal properties of the matter produced in such collisions. At intermediate transverse momentum, it allows for testing the “recombination models” where hadrons could be formed by the coalescence of quarks from a deconfined quark-gluon plasma (QGP). At higher transverse momenta, particle spectra allow one to investigate the mechanism of parton energy loss in the hot and dense hadronic medium. The measurement of spectra in pp collisions not only provides the baseline for the heavy-ion data but also allows for the tuning and optimization of QCD-inspired models. The latest ALICE results on identified and inclusive light-flavour charged particles in pp collisions at √s = 0.9, 2.76 and 7 TeV and Pb-Pb collisions at √s NN = 2.76 TeV is reviewed. p T spectra, yields and ratios in pp as a function of the collision energy is shown and compared to previous experiments and Monte Carlo predictions. Recent Pb–Pb results in different centrality intervals is presented and compared to √s NN = 200 GeV Au–Au collisions at RHIC. Comparison with predictions from thermal and hydrodynamic models is also discussed.

Search for narrow resonances in dilepton mass spectra in pp collisions at [formula omitted

A search for narrow, high-mass resonances decaying to electron or muon pairs has been performed using pp collision data collected at s=7TeV by the CMS experiment in 2011. The data sample corresponds to an integrated luminosity of approximately 5 fb−1. The event yields observed in the signal regions are consistent with predictions of the standard model backgrounds, and upper limits on the cross section times branching fraction for a resonance decaying to dileptons are extracted from a shape analysis of the dilepton invariant mass distribution. The resulting mass limits at 95% confidence level are 2330 GeV for the Z′ in the Sequential Standard Model, 2000 GeV for the superstring-inspired Zψ′ resonance, 890 (540) GeV for the Stueckelberg extension ZSt′ with the mass parameter ϵ=0.06 (0.04), and 2140 (1810) GeV for Kaluza–Klein gravitons with the coupling parameter k/M¯Pl of 0.10 (0.05). These limits are the most stringent to date.

ROLE OF GLUONS IN SOFT AND SEMI-HARD MULTIPLE HADRON PRODUCTION IN pp COLLISIONS AT LHC

Hadron inclusive spectra in pp collisions are analyzed within the modified quark–gluon string model including both the longitudinal and transverse motion of quarks in the proton in the wide region of initial energies. The self-consistent analysis shows that the experimental data on the inclusive spectra of light hadrons like pions and kaons at ISR energies can be satisfactorily described at transverse momenta not larger than 1–2 GeV /c. We discuss some difficulties to apply this model at energies above the ISR and suggest to include the distribution of gluons in the proton unintegrated over the internal transverse momentum. It leads to an increase in the inclusive spectra of hadrons and allows us to extend the satisfactory description of the data in the central rapidity region at energies higher than ISR.

Identified particles in pp and Pb–Pb collisions at LHC energies with the ALICE detector

The ALICE experiment has been taking data since 2009, with proton and lead beams. In this paper, the different particle identification techniques used by the experiment are briefly reviewed. The current results on identified particle spectra in pp collisions at and 7 TeV, and in Pb–Pb collisions at are summarized. In particular, the energy dependence of the spectral shapes and particle ratios in pp collisions is discussed and the results are compared to previous experiments and commonly used Monte Carlo models. The baryon/meson ratio Λ/K0S is studied in Pb–Pb collisions as a function of transverse momentum and centrality, and it is compared to previous results. The evolution of the particle spectra in Pb–Pb with collision centrality is compared to measurements at lower energies and discussed in the context of thermal and hydrodynamical models.

On saturation of charged hadron production in pp collisions at LHC

First results on charged hadron transverse momentum spectra in pp collisions obtained by the CMS Collaboration at the LHC are analyzed in the z-scaling approach. These LHC data confirm z-scaling. The saturation regime of the scaling function ψ(z) observed in pp and interactions at lower energies GeV is verified. The saturation of ψ(z) for charged hadrons is found down to a value of z ≃ 0.05 at the highest energy GeV currently reached by the colliders. A microscopic scenario of hadron production is discussed in connection with the search for new signatures of phase transitions in hadron matter. Constituent energy loss and its dependences on the transverse momentum and collision energy are estimated. We suggest that the beam energy scan program in the saturation region at the LHC could be of interest.

Scaling and multiplicity dependence of [formula omitted] spectra in pp collisions at [formula omitted

With the experimental data from STAR on the multiplicity dependence of the transverse momentum spectra of charged particles in pp collisions at s N N = 200 GeV , we investigate the scaling property of the spectra in those collisions. Using the scaling functions of pion and proton obtained in studying spectra in Au + Au and d + Au collisions, we describe the charged particle p T spectra in pp collisions as a superposition of those from pion and proton. Species contents are obtained and p / π ratio is given as a function of p T for events with some given charged multiplicities.