12C Collisions Research Articles

The multichannel experimental and theoretical study of the 12C(18O,18F)12B single charge exchange reaction mechanism

The study of a network of nuclear reactions populated in the 18O + 12C collision is the main topic of the present paper. It was performed to test nuclear structure and reaction theories in describing the full reaction mechanism occurring in the (18O, 18F) single charge exchange nuclear reaction. From the experimental side, an 18O beam was produced at 275 MeV incident energy by the K800 superconducting cyclotron and the MAGNEX magnetic spectrometer was used at the Laboratori Nazionali del Sud of the Istituto Nazionale di Fisica Nucleare to momentum analyse the ejectiles produced in the nuclear reactions within the same experimental setup. From the theoretical side, the proposed approach consists of analysing the whole network of nuclear reactions in the framework of a unique comprehensive and coherent theoretical calculation. This holistic approach, applied both to the experimental and theoretical analysis, is the main feature and novelty of the work presented here.

Stellar limits on scalars from electron-nucleus bremsstrahlung

We revisit stellar energy-loss bounds on the Yukawa couplings g B,L of baryophilic and leptophilic scalars ϕ. The white-dwarf luminosity function yields g B ≲ 7 × 10-13 and g L ≲ 4 × 10-16, based on bremsstrahlung from 12C and 16O collisions with electrons. In models with a Higgs portal, this also implies a bound on the scalar-Higgs mixing angle sinθ ≲ 2 × 10-10. Our new bounds apply for mϕ ≲ 1 keV and are among the most restrictive ones, whereas for mϕ ≲ 0.5 eV, long-range force measurements dominate. Besides a detailed calculation of the bremsstrahlung rate for degenerate and semi-relativistic electrons, we prove with a simple argument that non-relativistic bremsstrahlung by the heavy partner is suppressed relative to that by the light one by their squared-mass ratio. This large reduction was overlooked in previous much stronger bounds on g B. In an appendix, we provide fitting formulas (few percent precision) for the bremsstrahlung emission of baryophilic and leptophilic scalars as well as axions for white-dwarf conditions, i.e., degenerate, semi-relativistic electrons and ion-ion correlations in the “liquid” phase.

Multi-channel experimental and theoretical approach to study the 12C(18O,18F)12B single charge exchange reaction

The broad network of nuclear reactions populated in the 18O + 12C collision was studied to test the capability of state-of-art nuclear structure and reaction theories to describe both the direct and sequential components of the (18O, 18F) single charge exchange nuclear reaction. The experiment was performed using the 18O beam at 275 MeV incident energy produced by the K800 superconducting cyclotron and the MAGNEX magnetic spectrometer at the Laboratori Nazionali del Sud of the Istituto Nazionale di Fisica Nucleare. A unique comprehensive and coherent theoretical calculation, able to describe the whole network of direct reactions, is the approach proposed for the first time to analyse this large set of experimental data. This holistic approach, applied both to the experimental and theoretical analysis, is the main feature and novelty of the work here presented.

High event rate analysis technique for the dual-axis duo-lateral position-sensitive silicon detectors of FAUST

The dual-axis duo-lateral (DADL) position-sensitive silicon detector was developed to obtain precise position and energy information for detected charged particles. The Forward Array Using Silicon Technology (FAUST) is currently equipped with 68 DADL detectors backed by CsI(Tl) scintillators for the study of charged particle correlations in heavy-ion collisions where precise position and energy information is essential. When conventional signal processing electronics were used for the DADL detectors, a position dependence of the measured energy as well as distortions in the calculated particle positions were observed. In previous work, waveforms from the detector after preamplification were studied to better understand the features that give rise to these distortions; therein, a waveform analysis technique was developed to improve the energy resolution and linearity in position reconstruction. However, the reading and writing of waveforms for an entire detector array limits data collection rates and adds significant burden in data storage and analysis speed. In this work, the integrators of a Struck SIS3316 ADC were utilized to process 228Th source data to develop and optimize a new analysis method that captures the benefits of the waveform analysis technique while circumventing the waveform writing requirement. This integrator method – capable of 59keV (FWHM) energy resolution – was used in the collection of 35 MeV/nucleon 28Si + 12C collision data using FAUST to investigate exotic decays of highly excited highly deformed nuclei. In this data, a position resolution of 0.4mm (FWHM) was obtained for 25MeV α-particles; for α-particles near this energy that originate from 8Be ground state decays, a 8Be ground state width of 30keV (FWHM) was obtained. The impact of the energy-dependent DADL position resolution emergent from electronic noise on the quality of excited state measurement was modeled and compared to the experimental data.

About Transverse Momentum Distributions of Negative Pions in p12C and π–12C Collisions at High Energies

Collision centrality dependences of the transverse momentum distributions of negative pions produced in p12C and p−12C collisions at 9.9 and 40 GeV/c, respectively, are investigated. The shapes and widths of the normalized transverse momentum distributions, as well as the average values of the transverse momentum of the negative pions, do not depend within the uncertainties on the collision centrality in p12C and п−12C collisions at 9.9 and 40 GeV/c in experiment, which is confirmed by the modified FRITIOF model calculations and minimum X2 fits of the experimental spectra with the two- and three-temperature Hagedorn model functions. Modified FRITIOF model calculations underestimate the average values of transverse momenta of the negative pions in experiment and do not reproduce the tail of the experimental transverse momentum distributions of the negative pions in both collision types. It is obtained that the transverse momentum distributions of the negative pions exhibit two temperature (two-slope) shapes in peripheral and central p12C collisions at 9.9 GeV/c in agreement with the early works on nucleus-nucleus collisions at incident energies of the order of a few GeV/c. However, the transverse momentum distributions of the negative pions in peripheral and central p−12C collisions at 40 GeV/c can be described well assuming the three temperature (three-slope) shapes of these spectra.

A novel visage of molecular resonances in 12C + 12C

Resonances observed in the 12C + 12C collisions are studied by the molecular model. Firstly, normal-modes analysis made around the equilibrium equator-equator touching configuration gives a basic insight into dynamics of the system. The quantum numbers of the states also indicate rotational motions of the constituent 12C nuclei, which relate the normal modes to the corresponding inelastic 12C + 12C channels. Next, low-lying 11 states are taken up as bases, and Coriolis coupling has been diagonalized. Many excited states are obtained with intermediate widths, which is just in accord with the experimental observation. For example, the second and third excited states have characteristic feature as low-lying mutual 2+ excitation with the spin vectors of 12C nuclei along the molecular z′-axis. Those states appear very close to the molecular ground state with the higher spin of ΔJ = 2, to form a bunch. Resultant excitation functions are surprisingly in good agreement with the experiments, which lights up a new physical picture of molecular structures of the high-spin 12C + 12C resonances.

Laser-assisted proton collision on light nuclei at moderate energies

AbstractWe present a non-relativistic analytic quantum mechanical model to calculate angular differential cross-sections for laser-assisted proton nucleon scattering on a Woods–Saxon optical potential where the nth-order photon absorption is taken into account simultaneously. With this novel description we can integrate two well-established fields, namely low-energy nuclear physics and multi-photon processes together. As a physical example we calculate cross-sections for proton–12C collision at 49 MeV in the laboratory frame in various realistic laser fields. We consider optical Ti:sapphire and X-ray lasers with intensities which are available in existing laser facilities or in the future ELI or X-FEL.

12C + 12C resonances by a molecular model

Resonances observed in the 12C + 12C collisions are studied with a molecular model. At high spins J = 12–16, a stable dinuclear configuration is found to be an equator- equator touching one as is obtained in the 28Si + 28Si system. With K-quantum number being specified as rotation-vibration model, normal modes have been solved around the equilibrium, firstly. Furthermore, Coriolis coupling has been investigated by diagonalization among low- lying normal-mode states with K = 0 and K-excitation. It is found that the Coriolis coupling introduces about 30% of K-mixing into the K = 0 molecular ground states of J = 12–16. The analyses of the angular momentum coupling show up a dominance of the lowest L in the inelastic channel of the molecular ground state newly obtained. Thus alignments appear strongly in the inelastic channel, which is in agreement with the explanation by the band crossing model. Discussion is given on "why disalignments appear in the 28Si + 28Si system, in contrast to the above results".

Spectral temperatures of Δ0(1232) resonances produced in p 12C and d 12C collisions at 4.2 GeV/c per nucleon

Spectral temperatures of Δ0(1232) resonances produced in p 12C and d 12C collisions at 4.2 GeV/c per nucleon

On spectral temperatures of negative pions produced in d 12C, 4He12C, and 12C12C collisions at 4.2 A GeV/c

The experimental transverse momentum distributions of negative pions produced in d 12C, 4He12C, and 12C12C collisions at 4.2 A GeV/c were analyzed in the framework of Hagedorn Thermodynamic Model. The spectral temperatures of π − mesons as well as their relative contributions to the total multiplicity of π − mesons were extracted from fitting the p t spectra by two-temperature Hagedorn function. The results were compared systematically with the earlier results obtained from analysis of non-invariant center-of-mass energy spectra of negative pions produced in the analyzed collisions.

Comparison of characteristics of Δ0(1232) produced in p 12C and d 12C collisions at 4.2 A GeV/c

Comparison of characteristics of Δ0(1232) produced in p 12C and d 12C collisions at 4.2 A GeV/c

Centrality in Relativistic Nuclear Collisions and the Random Matrix Approach

Using the random matrix approach, results for nearest-neighbor distributions obtained from experimental data on 12C + 12C collisions at 4.2 A GeV/c and simulations produced with the aid of an ultra-relativistic quantum molecular dynamics model are studied. Comparison reveals that the observed changes in the nearest-neighbor distributions for different multiplicities can be associated with the onset of a region of central collisions.

Production of Δ0(1232)-resonances in p + 12C collisions at a momentum of 4.2 GeV/c

The production of Δ 0(1232)-resonances in p + 12C collisions at 4.2 GeV/c was investigated with 4π acceptance. The masses and widths of the resonances were obtained from ananalysis of foreground and background invariant-mass distributions of pπ − pairs obtained using an angular criterion. The fraction of charged π −-mesons coming from the Δ 0(1232) decay was estimated and compared to those obtained in earlier analyses. The momentum, transverse momentum, kinetic energy, rapidity, and emission angle distributions as well as the invariant cross-sections of Δ 0(1232)-resonances werere constructed in the laboratory frame. The freeze-out temperature of theΔ 0(1232)-resonances produced in p + 12C collisions was estimated and compared to the freeze-out temperatures obtained using different methods for Δ(1232)-resonances produced in other experiments with different sets of colliding nuclei at various incident energies.

Measurement of charged pions in 12C + 12C collisions at 1 A GeV and 2 A GeV with HADES

We present the results of a study of charged pion production in 12C + 12C collisions at incident beam energies of 1A GeV and 2A GeV using the HADES spectrometer at GSI. The main emphasis of the HADES program is on the dielectron signal from the early phase of the collision. Here, however, we discuss the data with respect to the emission of charged hadrons, specifically the production of pi+- mesons, which are related to neutral pions representing a dominant contribution to the dielectron yield. We have performed the first large-angular range measurement of the distribution of pi+- mesons for the 12C + 12C collision system covering a fairly large rapidity interval. The pion yields, transverse-mass and angular distributions are compared with calculations done within a transport model, as well as with existing data from other experiments. The anisotropy of pion production is systematically analyzed.

Dielectron spectroscopy at 1-2 AGeV with HADES⋆

The HADES spectrometer at GSI (Darmstadt) is investigating the e + e - pair production in p+p, p+A and A+A collisions. In this contribution we would like to highlight the physics motivations and the experiments performed so far, focusing mainly on the first results coming from 12C + 12C collisions at 1 and 2AGeV, and on preliminary results from p+p/d+p collisions at 1.25AGeV.

Measurement of the di-electron mass spectrum in 12C+ 12C collisions at 2 AGeV by HADES

The physics program of the High Acceptance Di-Electron Spectrometer HADES at GSI is largely motivated by the aim to study medium modifications of hadrons predicted by many theoretical approaches, as well as by the need to shed light on the still unexplained results of the former DLS experiment. In this contribution the HADES experiment is outlined and first results obtained in 12C+12C collisions at 2 AGeV are presented.

Isotopic Scaling and the Symmetry Energy in Spectator Fragmentation

Isotopic effects in the fragmentation of excited target residues following collisions of 12C on (112,124)Sn at incident energies of 300 and 600 MeV per nucleon were studied with the INDRA 4pi detector. The measured yield ratios for light particles and fragments with atomic number Z < or = 5 obey the exponential law of isotopic scaling. The deduced scaling parameters decrease strongly with increasing centrality to values smaller than 50% of those obtained for the peripheral event groups. Symmetry-term coefficients, deduced from these data within the statistical description of isotopic scaling, are near gamma = 25 MeV for peripheral and gamma < 15 MeV for central collisions.

Probing of in-medium hadron structure with HADES

The High Acceptance DiElectron Spectrometer (HADES) has been recently commissioned at GSI Darmstadt. It has been designed to study hadron properties inside nuclear matter via measurements of dielectron decays in proton, pion and heavy ion induced reactions in 1−2 AGeV energy range. We report first preliminary results on invariant masses of e+e− pairs measured in 12C + 12C collisions at E=2 AGeV and compare them to simulations based on UrQMD transport model. In summary we present and discuss planned experiments.

Thermal multifragmentation of hot nuclei and liquid-fog phase transition

Multiple emission of intermediate-mass fragments (IMF) in the collisions of protons (up to 8.1 GeV), 4He (4 and 14.6 GeV), and 12C (22.4 GeV) on Au has been studied with the 4π setup FASA. In all the cases, thermal multifragmentation of the hot and diluted target spectator takes place. The fragment multiplicity and charge distributions are well described by the combined model including the modified intranuclear cascade followed by the statistical multibody decay of the hot system. IMF-IMF-correlation study supports this picture, giving a very short time scale of the process (≤70 fm/c). This decay process can be interpreted as the first-order nuclear “liquid-fog” phase transition inside the spinodal region. The evolution of the mechanism of thermal multifragmentation with increasing projectile mass was investigated. The onset of the radial collective flow was observed for heavier projectiles. The analysis reveals information on the fragment space distribution inside the breakup volume: heavier IMFs are formed predominantly in the interior of the fragmenting nucleus possibly due to the density gradient.

Modified Glauber model for the total reaction cross-section of 12C + 12C collisions

Glauber's theory has been adopted to calculate the total heavy-ion reaction cross-sections at high energies. At relatively low energies, Glauber's total reaction cross-section has been modified in order to take into account the Coulomb field effect and is called modified Glauber model I. In addition to the Coulomb field effect, the nuclear effect has also been taken into account in the Glauber model and is called modified Glauber model II. An analytical expression for the transparency function for heavy-ion reactions, involving the nuclear densities of the colliding ions and the nucleon-nucleon cross- section, has been obtained within the framework of the modified Glauber models I and II. The transparency and the total reaction cross-sections of the 12C + 12C collisions are calculated at different bombarding energies. The obtained results are in good agreement with the experimental data and with previous theoretical calculations.