Dependence Of Particle Production Research Articles

Particle balance in a steady state plasma in a dipole magnetic field

Detailed experiments and modeling are performed to investigate spatial (r and θ) dependence of particle production (Z), loss (Lp) and retention (Z − Lp) rates in a steady state plasma in a dipole magnetic field. A mathematical model is developed that solves the particle balance equation, considering generation through ionization, losses through diffusion and recombination, and by taking into account the measured values of plasma parameters and dipole fields in space. Depending upon the pressure p and angle θ, Z is found to peak ∼r = (3 – 6) × 10−2 m from the center of the magnet and decreases downstream, whereas Lp steadily increases toward the chamber wall. Particle balance (Z = Lp) is realized either at a single point in space or over a wider region, and can be tuned by varying p, whereas Z − Lp is found to be a maximum at an optimum pressure (∼1.0 mTorr). Results indicate that while the diffusion is primarily classical (∼1/B2), the recombination coefficient scales as ∼1/B0.5, as a result of its implicit dependence on the magnetic field through the electron temperature. The ionization coefficient is rather high and approximately uniform until ∼0.02 Tesla, and thereafter decreases linearly at lower fields.

Latest predictions from the EbyE NLO EKRT model

We present the latest results from the NLO pQCD + saturation + viscous hydrodynamics (EbyE NLO EKRT) model. The parameters in the EKRT saturation model are fixed by the charged hadron multiplicity in the 0-5 % 2.76 TeV Pb+Pb collisions. The s, A and centrality dependence of the initial particle production follows then from the QCD dynamics of the model. This allows us to predict the s and A dependence of the particle production. We show that our results are in an excellent agreement with the low-pT data from 2.76 TeV and 5.02 TeV Pb+Pb collisions at the LHC as well as with the data from the 200 GeV Au+Au collisions at RHIC. In particular, we study the centrality dependences of hadronic multiplicities, flow coefficients, and various flow correlations. Furthermore, the nuclear mass number dependence of the initial particle production and hydrodynamic evolution can be tested in the 5.44 TeV Xe+Xe collisions at the LHC. To this end, we show our predictions for charged particle multiplicities, and in particular, show how the deformations of the Xe nuclei reflect into the flow coefficients.

A comment on generalized Schwinger effect

A spatially homogeneous, time-dependent, electric field can produce charged particle pairs from the vacuum. When the electric field is constant, the mean number of pairs which are produced depends on the electric field and the coupling constant in a non-analytic manner, showing that this result cannot be obtained from the standard perturbation theory of quantum electrodynamics. When the electric field varies with time and vanishes asymptotically, the result may depend on the coupling constant either analytically or non-analytically. We investigate the nature of this dependence in several specific contexts. We show that the dependence of particle production on coupling constant is non-analytic for a class of time-dependent electric fields, with the leading order non-analytic behaviour being controlled by a specific parameter which can be identified. We also demonstrate that, for another class of electric fields, which vary rapidly, the dependence of particle production on coupling constant is analytic. Finally, we describe what happens to these results when we go beyond the leading order, using some specific examples.

Ratios of strange hadrons to pions in collisions of large and small nuclei

The dependence of particle production on the size of the colliding nuclei is analyzed in terms of the thermal model using the canonical ensemble. The concept of strangeness correlation in clusters of sub-volume V_c is used to account for the suppression of strangeness. A systematic analysis is presented of the predictions of the thermal model for particle production in collisions of small nuclei. The pattern of the maxima of strange-particles-to-pion ratios as a function of beam energy is quite special, as they do not occur at the same beam energy and are sensitive to the system size. In particular, the Lambda /pi ^+ ratio shows a clear maximum even for small systems while the maximum in the K^+/pi ^+ ratio is less pronounced in small systems.

Centrality dependence of particle production inp−Pbcollisions atsNN=5.02TeV

We report measurements of the primary charged particle pseudorapidity density and transverse momentum distributions in p-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV, and investigate their correlation with experimental observables sensitive to the centrality of the collision. Centrality classes are defined using different event activity estimators, i.e. charged particle multiplicities measured in three disjunct pseudorapidity regions as well as the energy measured at beam rapidity (zero-degree). The procedures to determine the centrality, quantified by the number of participants ($N_{\rm part}$), or the number of nucleon-nucleon binary collisions ($N_{\rm coll}$), are described. We show that, in contrast to Pb-Pb collisions, in p-Pb collisions large multiplicity fluctuations together with the small range of participants available, generate a dynamical bias in centrality classes based on particle multiplicity. We propose to use the zero-degree energy, which we expect not to introduce a dynamical bias, as an alternative event-centrality estimator. Based on zero-degree energy centrality classes, the $N_{\rm part}$ dependence of particle production is studied. Under the assumption that the multiplicity measured in the Pb-going rapidity region scales with the number of Pb-participants, an approximate independence of the multiplicity per participating nucleon measured at mid-rapitity of the number of participating nucleons is observed. Furthermore, at high-$p_{\rm T}$ the p-Pb spectra are found to be consistent with the pp spectra scaled by $N_{\rm coll}$ for all centrality classes. Our results represent valuable input for the study of the event activity dependence of hard probes in p-Pb collision and, hence, help to establish baselines for the interpretation of the Pb-Pb data.

Jets, bulk matter, and their interaction in heavy ion collisions at several TeV

We discuss a theoretical scheme that accounts for bulk matter, jets, and the interaction between the two. The aim is a complete description of particle production at all transverse momentum (${p}_{t}$) scales. In this picture, the hard initial scatterings result in mainly longitudinal flux tubes, with transversely moving pieces carrying the ${p}_{t}$ of the partons from hard scatterings. These flux tubes constitute eventually both bulk matter (which thermalizes and flows) and jets. We introduce a criterion based on parton energy loss to decide whether a given string segment contributes to the bulk or leaves the matter to end up as a jet of hadrons. Essentially low ${p}_{t}$ segments from inside the volume will constitute the bulk, high ${p}_{t}$ segments (or segments very close to the surface) contribute to the jets. The latter ones appear after the usual flux tube breaking via q-qbar production (Schwinger mechanism). Interesting is the transition region: Intermediate ${p}_{t}$ segments produced inside the matter close to the surface but having enough energy to escape, are supposed to pick up q-qbar pairs from the thermal matter rather than creating them via the Schwinger mechanism. This represents a communication between jets and the flowing bulk matter (fluid-jet interaction). Also very important is the interaction between jet hadrons and the soft hadrons from the fluid freeze-out. We employ this picture to investigate Pb-Pb collisions at 2.76 TeV. We discuss the centrality and ${p}_{t}$ dependence of particle production and long-range dihadron correlations at small and large ${p}_{t}$.

Wounded Constituents

The concept of the "wounded" hadronic constituents is formulated. Preliminary estimates indicate that it may help to understand the transverse mass dependence of particle production in hadron-nucleus and nucleus-nucleus collisions.

Probing Longitudinal Dynamics at RHIC

Particle production of charged hadrons in Au+Au collisions at \(\sqrt {s_{NN} } = 200\) GeV bas been studied as a function of rapidity by the BRAHMS Collaboration at RHIC. Selected recent results are presented with emphasis on longitudinal dynamics of particle production. The rapidity dependence of particle production imposes more stringent constraints on theoretical models describing dynamics of nuclear matter created by high-energy heavy ion collisions.

Resonances at RHIC

In this report, we discuss the measurement of the hadronic decay modes of resonances in relativistic heavy-ion collisions, emphasizing on RHIC results. The study of resonances can provide: (1) the yield and spectra of more particles with different properties to study whether the system is in thermal equilibrium; (2) an independent probe of the time evolution of the source from chemical to kinetic freeze-out and detailed information on hadronic interaction at later stage; (3) the study of medium effects at a late stage of the collisions; (4) a measurement of flavour and baryon/meson dependence of particle production at intermediate pT (>2 GeV/c).

High pT inclusive charged hadron spectra from Au+Au collisions at [formula omitted] GeV

The STAR Collaboration presents new measurements of inclusive charged hadron distributions for p T < 12 GeV/c from Au+Au collisions at S N N = 200 . Charged hadron suppression at high p T is similar in shape and magnitude at all centralities to that observed previously at S N N = 130 for p T < 6 GeV/c. The ratio of spectra from central and peripheral Au+Au collisions shows that hadron suppression is approximately constant within 6 < p T < 12 GeV/c. The ratios of charged hadron spectra at the two beam energies show a 15–20% increase in yield at low p T . At high p T , the ratios show a larger increase that agrees well with pQCD calculations of the S N N dependence of particle production in Au+Au collisions.

Dependence of particle production in high energy heavy ion collisions on the nuclear equation of state

The total pion production cross section in central high energy heavy ion collisions depends strongly on the nuclear equation of state. This fact can be used to detect phase transitions from normal nuclear matter into abnormal superdense states (density isomers).