Average Transverse Mass Research Articles

Two-particle Bose-Einstein correlations and their Lévy parameters in PbPb collisions at sNN=5.02 TeV

Two-particle Bose–Einstein momentum correlation functions are studied for charged-hadron pairs in lead-lead collisions at a center-of-mass energy per nucleon pair of sNN=5.02TeV. The data sample, containing 4.27×109 minimum bias events corresponding to an integrated luminosity of 0.607 nb−1, was collected by the CMS experiment in 2018. The experimental results are discussed in terms of a Lévy-type source distribution. The parameters of this distribution are extracted as functions of particle pair average transverse mass and collision centrality. These parameters include the Lévy index or shape parameter α, the Lévy scale parameter R, and the correlation strength parameter λ. The source shape, characterized by α, is found to be neither Cauchy nor Gaussian, implying the need for a full Lévy analysis. Similarly to what was previously found for systems characterized by Gaussian source radii, a hydrodynamical scaling is observed for the Lévy R parameter. The λ parameter is studied in terms of the core-halo model. ©2024 CERN, for the CMS Collaboration 2024 CERN

Pion Interferometry with Lévy-Stable Sources in sNN = 200 GeV Au + Au Collisions at STAR

Measurements of femtoscopic correlations in high-energy heavy-ion collisions are used to unravel the space–time structure of the particle-emitting source (the quark–gluon plasma). Recent results indicate that the pion pair source exhibits a power law behavior and can be described well by a Lévy distribution. In this study, Lévy fits were applied to the measured one-dimensional two-pion correlation functions in Au + Au collisions at sNN = 200 GeV. The three extracted source parameters are the Lévy scale parameter, R, which relates to the size of the source; the correlation strength parameter, λ; and the Lévy exponent, α, which characterizes the power law tail of the source. In this paper, we report the current status of the analysis of the extracted Lévy source parameters and present their dependence on average transverse mass, mT, and on centrality.

Event-by-event investigation of the two-particle source function in [formula omitted] TeV PbPb collisions with EPOS

The investigation of the two-particle source function in lead-lead collisions simulated by the EPOS model at a center of mass energy per nucleon pair of sNN=2.76 TeV is presented. The two-particle source functions are reconstructed directly on an event-by-event basis for pions, kaons and protons separately, using the final stage of EPOS. A Lévy source shape is observed for all three particle species in the individual events, deviating significantly from a Gaussian shape. The source parameters are extracted as functions of collision centrality and pair average transverse mass (mT). The Lévy exponent is found to be ordered accordingly to particle mass. The Lévy scale parameter is found to scale for all particle species with mT according to Gaussian hydrodynamic predictions; however, there is no mT-scaling found across these species. In case of pions, the effects of the decay products and hadronic rescattering are also investigated. The Lévy exponent is decreased when decay products are also included in the analysis. Without hadronic rescattering and decay products, the source shape is close to a Gaussian.

Lévy-stable two-pion Bose-Einstein correlations in sNN=200 GeV Au+Au collisions

We present a detailed measurement of charged two-pion correlation functions in 0%-30% centrality $\sqrt{s_{_{NN}}}=200$ GeV Au$+$Au collisions by the PHENIX experiment at the Relativistic Heavy Ion Collider. The data are well described by Bose-Einstein correlation functions stemming from L\'evy-stable source distributions. Using a fine transverse momentum binning, we extract the correlation strength parameter $\lambda$, the L\'evy index of stability $\alpha$ and the L\'evy length scale parameter $R$ as a function of average transverse mass of the pair $m_T$. We find that the positively and the negatively charged pion pairs yield consistent results, and their correlation functions are represented, within uncertainties, by the same L\'evy-stable source functions. The $\lambda(m_T)$ measurements indicate a decrease of the strength of the correlations at low $m_T$. The L\'evy length scale parameter $R(m_T)$ decreases with increasing $m_T$, following a hydrodynamically predicted type of scaling behavior. The values of the L\'evy index of stability $\alpha$ are found to be significantly lower than the Gaussian case of $\alpha=2$, but also significantly larger than the conjectured value that may characterize the critical point of a second-order quark-hadron phase transition.

Lévy Femtoscopy with PHENIX at RHIC

In this paper we present the measurement of charged pion two-particle femtoscopic correlation functions in s N N = 200 GeV Au + Au collisions in 31 average transverse mass bins, separately for positive and negative pion pairs. Lévy-shaped source distributions yield a statistically acceptable description of the measured correlation functions, with three physical parameters: correlation strength parameter λ , Lévy index α and Lévy scale parameter R. The transverse mass dependence of these Lévy parameters is then investigated. Their physical interpretation is also discussed, and the appearance of a new scaling variable is observed.

Identified particle production and freeze-out properties in heavy-ion collisions at RHIC Beam Energy Scan program

The first phase of Beam Energy Scan (BES) program at the Relativistic Heavy-Ion Collider (RHIC) was started in the year 2010 with the aim to study the several aspects of the quantum chromodynamics (QCD) phase diagram. The Solenoidal Tracker At RHIC (STAR) detector has taken data at $\sqrt{s_{NN}} = $ 7.7, 11.5, 19.6, 27, and 39 GeV in Au+Au collisions in the years 2010 and 2011 as part of the BES programme. For these beam energies, we present the results on the particle yields, average transverse mass and particle ratios for identified particles in mid-rapidity ($|y|$ < 0.1). The measured particle ratios have been used to study the chemical freeze-out dynamics within the framework of a statistical model.

Identified hadron production from the RHIC beam energy scan

A current focus at the RHIC is the beam energy scan to study the QCD phase diagram—temperature (T) versus baryon chemical potential (μB). The STAR experiment has collected data for Au+Au collisions at 7.7, 11.5 and 39 GeV in the year 2010. We present midrapidity results on rapidity density, average transverse mass and particle ratios for identified hadrons from the STAR experiment. Collision dynamics are studied in the framework of chemical and kinetic freeze-out conditions.

Results from the STAR Beam Energy Scan Program

The main aim of the beam energy scan (BES) program at the Relativistic Heavy-Ion Collider (RHIC) is to explore the quantum chromodynamics (QCD) phase diagram. The specific physics goal is to search for the phase boundary and the QCD critical point. We present results from Au+Au collisions at various energies collected in the BES program by the Solenoidal Tracker At RHIC (STAR) experiment. First results on transverse momentum ( p T ) spectra, d N / d y , and average transverse mass ( 〈 m T 〉 ) for identified hadrons produced at mid-rapidity for s N N = 7.7 GeV are presented. Centrality dependence of d N / d y and 〈 p T 〉 are also discussed and compared to corresponding data from other energies. In addition, first results on charged hadron directed ( v 1 ) and elliptic flow ( v 2 ) for s N N = 7.7 , 11.5 and 39 GeV are presented. New results on event-by-event fluctuations (particle ratio, net-proton and net-charge higher moments) are presented for s N N = 39 GeV .

Centrality dependence of proton and antiproton spectra in Pb+Pb collisions at40AGeV and158AGeV measured at the CERN Super Proton Synchrotron

The yields of (anti)protons were measured by the NA49 Collaboration in centrality-selected Pb + Pb collisions at 40A and 158A GeV. Particle identification was obtained in the laboratory momentum range from 5 to 63 GeV/c by measuring the energy loss dE/dx in the time projection chamber detector gas. The corresponding rapidity coverage extends 1.6 units from midrapidity into the forward hemisphere. Transverse-mass spectra, the rapidity dependences of the average transverse mass, and rapidity density distributions were studied as a function of collision centrality. The values of the average transverse mass as well as the midrapidity yields of protons normalized to the number of wounded nucleons show only modest centrality dependences. In contrast, the shape of the rapidity distribution changes significantly with collision centrality, especially at 40A GeV. The experimental results are compared to calculations of the hadron-string dynamics and the ultrarelativistic quantum-molecular-dynamics transport models.5 MoreReceived 10 September 2010DOI:https://doi.org/10.1103/PhysRevC.83.014901© 2011 The American Physical Society

Indication of a coexisting phase of quarks and hadrons in nucleus-nucleus collisions

The variation of average transverse mass of identified hadrons with charge multiplicity have been studied for AGS, SPS and RHIC energies. The observation of a plateau in the average transverse mass for multiplicities corresponding to SPS energies is attributed to the formation of a co-existence phase of quark gluon plasma and hadrons. A subsequent rise for RHIC energies may indicate a deconfined phase in the initial state. Several possibilities which can affect the average transverse mass are discussed. Constraints on the initial temperature and thermalization time have been put from the various experimental data available at SPS energies.

A Quark Model for Baryon Production at Low Transverse Momentum

AbstractA quark model for baryon production at low pT is obtained as generalization of the quark‐antiquark fusion model. The quark transverse momenta are taken into account using an average transverse mass of the quarks. This leads to the incorporation of both quark fusion and quark recombination into one model. The model is able to describe qualitative features of the reactions pp → (Δ, ¯Δ, ∑+, ∑−) + X at 12 and 24 GeV/c.

Transverse-Momentum Limitation in the One-Dimensional Gas Model

A strict application of the assumptions of the pion rapidity-gas model of multiproduction, together with simple kinematics, imply a connection between the coupling strength $C$ and the average transverse mass ${\overline{\ensuremath{\mu}}}_{T}$, which is $C\ensuremath{\lesssim}\frac{M}{{\overline{\ensuremath{\mu}}}_{T}}$, with $M$ a typical leading particle mass. The most important consequence is that if $C$ is large, as it is experimentally, ${\overline{\ensuremath{\mu}}}_{T}$ must be small, and thus a strong transverse-momentum limitation need not be introduced as a separate assumption. Furthermore $C$ is limited to order 1 (which incidentally means that there must be a critical coupling constant in the multiperipheral model). Experimentally $C$ appears to be near its maximal value. We indicate that there is a kind of model in which this arises automatically.

Multiplicities in lepton-hadron processes

The average multiplicity in deep inelastic electro- and neutrinoproduction at large ω( ω∼ s/ Q 2 + 1) is related in Feynman's version of the parton model to the average multiplicities in high-energy electron-positron annihilation and hadron-hadron scattering. The relation is: 〈n(s, Q 2)〉 eP,ν P ∼ C e + e − ln( Q 2 M 1⊥ 2 ) + C h ln(ω − 1) , where C e + e − and C h are, respectively, the coefficients of ln( s/ M 1⊥ 2) in the multiplicities from e +-e − and P-P in to hadrons, and M 1⊥ is an average transverse mass.