Reaction Plane Determination Research Articles

Development of Detector Control System (DCS) for forward hadron calorimeters in the BM@N and the MPD experiments

The BM@N and the MPD experiments at NICA facility (Dubna, Russia) will use the forward hadron calorimeters (FHCal) for centrality and reaction plane determination in the heavy ion collisions. The FHCal is a modular lead/scintillator sampling calorimeter with longitudinal segmentation. The light from each longitudinal section in module is detected with one silicon photomultiplier (MPPC) with sensitive area of 3x3mm2. In total, the FHCal at the BM@N experiment has 438 readout channels, while two MPD calorimeter arms have 616 readout channels. This article shows the DCS design with hardware and software development for these calorimeters. The DCS will be used to control and correct the bias voltages with temperatures of MPPCs. An integration into the main DCS systems for both experiments are discussed.

New forward hadron calorimeter for centrality and reaction plane determination at BM@N heavy ion experiments

It is proposed to replace existing Zero Degree Calorimeter of the BM@N setup at the Nuclotron (JINR) by a new forward hadron calorimeter for the measurement of the collision centrality and reaction plane orientation in heavy ions experiments. This calorimeter with transverse and longitudinal segmentation will be assembled from modules presently constructed for FHCal MPD and PSD CBM. The proposed design of the new calorimeter, simulation results for centrality and reaction plane determination by the new calorimeter, as well as radiation doses in the calorimeter simulated by FLUKA are discussed. The performance of hadron calorimeter supermodule studied at CERN is shown.

The very forward hadron calorimeter PSD for the future CBM@FAIR experiment

The Projectile Spectator Detector (PSD) of the CBM experiment at the future FAIR facility is a compensating lead-scintillator calorimeter designed to measure the energy distribution of the forward going projectile nucleons and nuclei fragments (reaction spectators) produced close to the beam rapidity. The detector performance for the centrality and reaction plane determination is reviewed based on Monte-Carlo simulations of gold-gold collisions by means of four different heavy-ion event generators. The PSD energy resolution and the linearity of the response measured at CERN PS for the PSD supermodule consisting of 9 modules are presented. Predictions of the calorimeter radiation conditions at CBM and response measurement of one PSD module equipped with neutron irradiated MPPCs used for the light read out are discussed.

Performance study of the anisotropic flow and reaction plane reconstruction in the CBM experiment

The Projectile Spectator Detector (PSD) is a subsystem of the CBM experiment at the future FAIR facility designed to determine centrality and reaction plane orientation in the heavy-ion collisions. It will be done by measurement of the energy distribution of the heavy nucleons and nuclei fragments emitted close to the beam rapidity in forward direction. For the anticipated beam energies of FAIR SIS100 and SIS300 accelerators, different event generators (iQMD, UrQMD, DCM-QGSM, LA-QGSM and HSD) were used for the study of directed and elliptic proton flow in Au+Au collisions. Produced particles were transported with the GEANT4 Monte-Carlo using the CBM detector geometry. Performance of the reaction plane determination is shown for different PSD setups to demonstrate effects of the detector granularity and magnetic field. Simulation results are compared with the FOPI, AGS E877, E895 and STAR experimental data.

Azimuthal anisotropy (v2) of high-pT π0 and direct γ in Au+Au collisions at = 200 GeV

Preliminary results from the STAR collaboration of the azimuthal anisotropy (v2) of π0 and direct photon (γdir) at high transverse momentum (pT) from Au+Au collisions at center-of-mass energy = 200 GeV are presented. A shower-shape analysis is used to select a sample free of direct photons (π0) and a sample rich in direct photons γrich. The relative contribution of background in the γrich sample is determined assuming no associated charged particles nearby γdir. The v2 of direct photons (vγdir2) at mid-rapidity (|ηγdir| < 1) and high pT (8 < pγdirT < 16 GeV/c) is extracted from those of π0 and neutral particles measured in the same kinematic range. In mid-central Au+Au collisions (10–40%), the v2 of π0 (vπ02(pT)) and charged particles (vch2(pT)) are found to be ~ 0.12 and nearly independent of pT. The measured vγdir2(pT) is positive finite and systematically smaller than that of π0 and charged particles by a factor of ~ 3. Although the large vπ02 at such high pT might be partially due to the path-length dependence of energy loss, the non-zero value of vγdir2 indicates a bias of the reaction plane determination due to the presence of jets in the events. Systematic studies are currently in progress.

Reaction plane determination by means of the ALICE zero degree calorimeters

A possible way to estimate the reaction plane of the ion-ion collision is to measure the sideward deflection of the spectator neutrons. In the ALICE experiment this kind of measurement can be performed by means of the two neutron zero degree calorimeters (ZN), which are located at opposite sides with respect to the beam intersection point (IP). In fact the ZN calorimeters, thanks to their segmentation in four towers, are position sensitive devices. Concerning their localizing capability, a spatial resolution of ∼3 mm has been measured for a 100 GeV/c hadron beam. This performance will be used to reconstruct, event by event, the centroid coordinate of the spectator neutron spot on the ZN front-face, which is sensitive to the directed flow (“bounce off”) of spectator neutrons. The measurement of the centroid will therefore allow to reconstruct the 1st-order event plane azimuth. A simulation is performed in order to estimate the dependence of the event plane resolution on the magnitude of the directed flow v1 of the spectator neutrons and on the neutron multiplicity (event centrality). In particular, it will be shown that the event plane resolution is not dominated by the smearing on the centroid measurement, but by the smearing due to the transverse lead beam divergence at the IP. Finally a possible tool to select events with small lead beam divergence at IP is discussed, using the information coming from both the ZN calorimeters.

Fluid dynamics as a diagnostic tool for heavy-ion collisions

Ultra-relativistic heavy-ion collisions at an energy are studied in a three-dimensional fluid dynamical model. The results of a hydrodynamical evolution using the PIC-method are shown. The importance and diagnostic value of a proper reaction plane determination is emphasized, and the time development of collective observables is presented.

Disappearance of Collective Rotation in Heavy Ion Collisions11The project supported partly by National Natural Science Foundation of China

A theoretical analysis of collective rotation is performed in heavy ion collisions below 100 MeV/nucleon in the quantum molecular dynamics approach. Both methods are contributed to this analysis, one is based on the shapes of azimuthal distribution, and the other is based on the numerical semiclassical calculation of rotation. The collective rotation becomes weaker with the increasing of beam energy, and tends to fade out at a certain beam energy. The impact parameter dependence of collective motion is also discussed. In connection with recent experiments, theoretical results and experimental data are compared by taking into account the fluctuation of experimental reaction plane determination.

Collective motion of reverse-reaction system in the intermediate-energy domain via the quantum-molecular-dynamics approach.

Collective motion for the reverse reaction system $^{40}\mathrm{Ar}$${+}^{27}$Al below 100 MeV/nucleon is studied via the quantum-molecular-dynamics approach. The azimuthal distribution of nucleons and the semiquantitative calculation of rotational observables contribute to the analysis of collective rotation. The collective rotation becomes weaker with increasing beam energy, and fades out at a higher energy. Quantitative comparison between calculation and data is also performed by taking into account the fluctuation of experimental reaction plane determination.

Collective flow by the azimuthal correlation of projectile fragments in relativistic heavy-ion collisions.

An analysis that does not require the determination of reaction plane on an event-by-event basis, and involves only azimuthal correlation function of the projectile fragment pairs, has been employed to measure the collective flow of nuclear matter. Using this technique, we study the flow of projectile fragments of charge Z\ensuremath{\ge}2 produced in $^{197}\mathrm{Au}$ induced-emulsion reactions at 10.6A GeV. The collective flow is observed to be the most pronounced in semicentral collisions. The results are compared with those of $^{28}\mathrm{Si}$ at 14.5A GeV, $^{238}\mathrm{U}$ at 0.96A GeV, $^{84}\mathrm{Kr}$ at 1.52A GeV, and $^{56}\mathrm{Fe}$ at 1.7A GeV.

Rotational behavior in intermediate energy heavy ion collisions.

The rotational behavior together with in-plane collective flow for the intermediate energy $^{40}\mathrm{Ar}$${+}^{27}$Al reaction is investigated by analyzing the rapidity-dependent azimuthal distributions with the Boltzmann-Uehling-Uhlenbeck (BUU) model. The azimuthal distributions are fitted by a Legendre polynomial expansion up to the second order. By incorporating the uncertainties in the experimental reaction plane determination into our calculations, quantitative agreement between the calculations and data is obtained. It is found that the rotational behavior at midrapidity depends strongly on the impact parameter. Information about the in-plane collective flow is also extracted from the azimuthal distributions. Both the rotational behavior and the in-plane collective flow depend strongly on the in-medium nucleon-nucleon cross section and nuclear equation of state.

Multiplicity dependence of azimuthal distributions for 36Ar+197Au collisions at E/A=35 MeV.

Collisions between $^{36}\mathrm{Ar}$ projectile and $^{197}\mathrm{Au}$ target nuclei at E/A=35 MeV have been studied with the Michigan State University Miniball, a 4\ensuremath{\pi} phoswich array with a low detection threshold. Azimuthal distributions of charged particles with respect to the reaction plane are determined via the transverse-momentum-tensor method. Dependence on the kinetic energy of the emitted particles, the collision geometry, and the associated charged particle multiplicity is investigated. Corrections for the intrinsic resolution of the experimental reaction plane determination are applied. Scaling implied by the coalescence model is explored and the data are compared to the results of microscopic calculations within the Boltzmann-Uehling-Uhlenbeck theory.

Some collective aspects in Au+Au collisions at E/ A = 150 and 400 MeV

Abstract We present some preliminary results concerning collective aspects in Au+Au collisions studied with the FOPI detector in GSI-Darmstadt. We mainly depict here the method and results of azimuthal distributions relative to the reaction plane as a function of the centrality and the charge Z of the fragments. Accuracy on the reaction plane determination is also given.

Inversion of collective matter flow and equation of state

The multidetector array Mur + Tonneau has been used to perform a 4π detection of charged particles and fragments emitted in reactions at energies ranging from 25 to 95 MeV/u. The collective transverse momentum in the reaction plane (sidewards flow parameter) is observed to strongly vary as a function of impact parameter and incident energy. The measured values have to be corrected for the effects due to the error on the reaction plane determination and to the detector limitations. Those limitations caused by the method itself are more important than those caused by the detector. The flow value changes from negative values (negative scattering at low energies) to positive values (compression, at high energies). The inversion (or balance) energy is in the range 50–100 MeV/u, depending on the system and impact parameter value. Comparisons between experimental data and theoretical values are shown for the system 40Ar+27Al. These studies (BUU, Landau-Vlasov, QMD) show that the flow, and especially the inversion energy, is sensitive to the nucleon-nucleon cross section σNN in medium. The data indicate that a momentum dependent effective interaction should be used. Then, the flow value is not much sensitive to the incompressibility modulus K, but possibly in peripheral collisions. Additionnal observables should be used. The azimuthal distribution of mid-rapidity particles indicates a rotation-like behaviour of the interaction region.

Reaction plane determination using azimuthal correlations.

We present a new technique for the determination of the reaction plane in heavy-ion reactions at incident energies ranging from the Fermi energy up to \ensuremath{\approxeq}100 MeV/nucleon. Our technique exploits the azimuthal correlation between light particles and the reaction plane. For illustrative purposes, azimuthal distributions of particles with respect to the reaction plane are extracted from data taken by the Michigan State University 4\ensuremath{\pi} array for 35 MeV/nucleon Ar+V collisions. The influences of momentum conservation and detection biases on the reaction plane determination are discussed, and the accuracy of the new technique is evaluated.

Reaction plane determination for 36Ar+197Au collisions at E/A=35 MeV.

Collisions between $^{36}\mathrm{Ar}$ projectile and $^{197}\mathrm{Au}$ target nuclei at E/A=35 MeV have been studied with a 4\ensuremath{\pi} phoswich array with a low detection threshold. Azimuthal distributions of light-charged particles and intermediate-mass fragments are extracted with respect to reaction planes determined from fission fragments or from the emission patterns of coincident light particles and intermediate-mass fragments. The internal consistency and sensitivity to particle detection thresholds are explored for the various techniques of reaction plane determination. For the present reaction, the reaction plane can be determined with comparable accuracy from the distribution of fission fragments as from the orientation of the major axis of the transverse momentum tensor constructed from the emitted light particles and intermediate-mass fragments. Monte Carlo calculations are performed illustrating the sensitivity of the transverse momentum tensor method to the azimuthal anisotropy of the single-particle distributions and the convergence of this method as a function of particle multiplicity. The extraction of experimental uncertainties in the determination of the reaction plane is discussed.