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Mid-Rapidity Emission and N/Z Ratios in 58Ni+58Ni Collisions at 52 AMeV

This study examines mid-rapidity emission during heavy-ion collisions at intermediate energies, specifically focusing on 58Ni+58Ni at 52 AMeV. We analyze source reconstruction, free nucleon multiplicities, and the neutron-to-proton (N/Z) ratio of complete nuclear matter. The results reveal progressive neutron enrichment of mid-rapidity source nuclear matter with respect to centrality. By utilizing multisource fitting techniques, we provide insights into neutron dynamics and nuclear composition, highlighting the importance of detecting neutron multiplicities for precision measurements of N/Z ratios.

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Mid-Rapidity Emission and N/Z Ratios in 58Ni+58Ni Collisions at 52 AMeV

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  1. N/Z OF MID-RAPIDITY AND QUASI-PROJECTILE EMISSION IN 58Ni+58Ni AT 52 AMeV TOPICS IN HEAVY ION COLLISIONS 03 • D. Thériault, A. Vallée, L. Gingras, Y. Larochelle, René Roy, L. Beaulieu, • F. Grenier, F. Lemieux, J. Moisan, C. St-Pierre, S. Turbide • Université Laval, Québec • - INDRA Collaboration, France • - Sherry Yennello’s Group, Texas A&M Univesity OUTLINE • Mid-rapidity emission in heavy ion collisions at intermediate energies • Source reconstruction • Free nucleon multiplicities • Neutron/proton ratio of complete nuclear matter: MRS and QP • Conclusion

  2. HEAVY ION COLLISIONS AT INTERMEDIATE ENERGIES (20-100 AMeV) BINARY DISSIPATIVE REACTIONS Target Projectile MRS QT E* QP E* MRS: L. Gingras et al., Phys. Rev. C 65, 061604(2002)

  3. NEUTRON ENRICHMENT AT MID-RAPIDITY? AS A FUNCTION OF CENTRALITY: - N/Z OF COMPLETE MRS NUCLEAR MATTER - N/Z OF COMPLETE QP NUCLEAR MATTER COMPLETE NUCLEAR MATTER = BOUND PARTICLES (A≥2) + FREE PROTONS + FREE NEUTRONS VELOCITY RECONSTRUCTION 58NI + 58NI 52 AMeV INDRA MULTISOURCE FIT 58NI + 58NI 52 AMeV INDRA MULTISOURCE FIT 36Ar + 58NI 50 AMeV HERACLES

  4. 58Ni + 58Ni 52 AMeV Isotopic resolution Z≤4 Charity evaporation attractor line 5≤Z≤24 N/Z of system (1.07) Z≥25 INDRA AT GANIL, FRANCE Plastics (phoswichs) Ionisation chambers Silicons CsI (Tl)

  5. SOURCES SELECTION (A≥2) QP QT MRS Vrel VQT 2 cm/ns Vres BEAM DIRECTION • Dividing Vrel forward distribution by backward distribution, • probability tables are built for backward distribution QP attribution. • Probability tables are usedevent by event for backward distribution QP attribution.

  6. BOUND NUCLEONS IN MRS (A≥2) 58Ni + 58Ni at 52 AMeV QP MRS Neutrons Protons ------ Neutrons Protons ------ SMR Graphs exclude free nucleons and QP residue

  7. FREE NUCLEONS • Great overlap in velocity distributions • - Multisource fit technique is used Laboratory frame: Avec: where Es is the kinetic energy of a nucleon at rest in a source frame moving at Vs and θ is the detection angle Each source (QP,QC,SMR) has 4 parameters to fit: T(temperature), VS(velocity), BC(Coulomb barrier) and N (multiplicity).

  8. Free protons energy spectras 58Ni + 58Ni at 52 AMeV ….. MRS ---- QP QC TOTAL QP MRS

  9. FREE NEUTRONS IN 36Ar + 58Ni AT 50 AMeV HERACLES Multidetector, Université Laval, + neutron detectors Cyclotron Institute, Texas A&M University. 105O 60O 120O 45O Heracles Array BEAM TARGET 150O 135O 75O 90O Neutron detectors BC-501

  10. FREE NEUTRONS ENERGY SPECTRAS 36Ar + 58Ni 50 AMeV ….. ---- QT MRS TOTAL MRS QT

  11. LINK BETWEEN 36Ar+58Ni AND 58Ni+58Ni FOR FREE NEUTRONS THE LINK IS EXCITATION ENERGY PER NUCLEON FOR QT IN (36Ar+58Ni) AND QP IN (58Ni+58Ni). IS USED RELATION :QP 58Ni+ 58Ni 52 AMeV :QP 40Ar+27Al 40 AMeV # #G. Lanzano et al., Nucl. Phys. A683, 566(2001)

  12. N/Z RATIOS (QP AND MRS) 58Ni+58Ni 52 AMeV --------- N/Z=1.07 N/Z MRS N/Z QP

  13. CONCLUSION - Progressive neutron enrichment (with centrality) of MRS nuclear matter. • N/Z ratio of the complete MRS nuclear material reaches a value higher • than the initial system’s one (1.07) and that of the QP which decreases • around 1. • An experiment detecting neutron multiplicities and charged particles • in the same setup would greatly improve precision on MRS N/Z • measurement.

  14. PROJECTILE RECONSTRUCTED MASS AND CHARGE 58Ni+58Ni 52 AMeV Neutron nb. Proton nb. Neutron nb. N/Z=1.07

  15. MISSING NEUTRONS TO RECOVER PROJECTILE N/Z (1.07) * BUU simulations (b=3fm - 4.5 fm) (neutronMRS 58Ni+58Ni / neutronMRS 36Ar+58Ni = 1.86) Neutron nb.

  16. N/Z RATIOS (QP AND SMR) IN 58Ni+58Ni AT 52 AMeV WITH CORRECTION FOR FREE NEUTRONS IN SMR N/Z MRS N/Z QP ------- N/Z=1.07

  17. ETL HYPOTHESIS FOR NEUTRON MULTIPLICITIES

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