- Mid-rapidity emission in heavy ion Mid-rapidity emission in heavy ion collisions at intermediate energiescollisions at intermediate energies- Source reconstructionSource reconstruction- Free nucleon multiplicities Free nucleon multiplicities - Neutron/proton ratio of complete nuclear matter: MRS and QPNeutron/proton ratio of complete nuclear matter: MRS and QP- ConclusionConclusion

-D. Thériault, A. Vallée, L. Gingras, Y. Larochelle, René Roy, L. Beaulieu, D. Thériault, A. Vallée, L. Gingras, Y. Larochelle, René Roy, L. Beaulieu, F. Grenier, F. Lemieux, J. Moisan, C. St-Pierre, S. Turbide F. Grenier, F. Lemieux, J. Moisan, C. St-Pierre, S. Turbide Université Laval, QuébecUniversité Laval, Québec

- INDRA Collaboration, France- INDRA Collaboration, France

- Sherry Yennello’s Group, Texas A&M Univesity- Sherry Yennello’s Group, Texas A&M Univesity

HEAVY ION COLLISIONS AT INTERMEDIATE ENERGIES (20-100 AMeV)HEAVY ION COLLISIONS AT INTERMEDIATE ENERGIES (20-100 AMeV)BINARY DISSIPATIVE REACTIONSBINARY DISSIPATIVE REACTIONS

QP E*QT E*MRS

ProjectileTarget

MRS: L. Gingras et al., Phys. Rev. C 65, 061604(2002)

AS A FUNCTION OF CENTRALITY:AS A FUNCTION OF CENTRALITY:

- - N/ZN/Z OF OF COMPLETE MRSCOMPLETE MRS NUCLEAR MATTER NUCLEAR MATTER

- - N/ZN/Z OF OF COMPLETE QPCOMPLETE QP NUCLEAR MATTER NUCLEAR MATTER

NEUTRON ENRICHMENT AT MID-RAPIDITY?NEUTRON ENRICHMENT AT MID-RAPIDITY?

COMPLETE NUCLEAR MATTERCOMPLETE NUCLEAR MATTER

==BOUND PARTICLES (ABOUND PARTICLES (A≥2) ≥2)

++FREE PROTONSFREE PROTONS

++FREE NEUTRONSFREE NEUTRONS

VELOCITY RECONSTRUCTION58NI + 58NI 52 AMeV INDRA

MULTISOURCE FIT58NI + 58NI 52 AMeV INDRA

MULTISOURCE FIT36Ar + 58NI 50 AMeV HERACLES

5858Ni + Ni + 5858Ni 52 AMeVNi 52 AMeV

INDRA AT GANIL, FRANCEINDRA AT GANIL, FRANCE

Ionisation chambers

Plastics (phoswichs)

Silicons

CsI (Tl)

Isotopic resolution Z≤4Charity evaporation attractor line 5≤Z≤24N/Z of system (1.07) Z≥25

SOURCES SELECTIONSOURCES SELECTION

Vrel

BEAM DIRECTION

VresVQT 2 cm/ns

QT MRS QP

(A≥2)

- Dividing Vrel Dividing Vrel forward distribution forward distribution by by backward distribution, , probabilityprobability tables are built for tables are built for backward distribution QP QP attribution. attribution.

- Probability tables are usedProbability tables are used event by event for event by event for backward distribution QP attribution. QP attribution.

BOUND NUCLEONS IN MRS (A≥2)BOUND NUCLEONS IN MRS (A≥2)

SMR

Graphs exclude free nucleons and QP residueGraphs exclude free nucleons and QP residue

MRSMRSQPQP

5858Ni + Ni + 5858Ni at 52 AMeVNi at 52 AMeV

NeutronsProtons

------ NeutronsProtons

------

FREE NUCLEONSFREE NUCLEONS

- Great overlap in velocity distributionsGreat overlap in velocity distributions

- Multisource fit technique is usedMultisource fit technique is used

TBcEeBcET

NvolumedEd

Nd /)()(2/3)(2)(

2

TBcEeBcET

NsurfacedEd

Nd /)()(24)(

2

'22/1

'

2EE

dEd

Nd

ElabE

labdEd

Nd

Laboratory frame:

Avec: SSlablab EEEEE cos2/12/12'

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).

Free protons energy spectras Free protons energy spectras 5858Ni + Ni + 5858Ni at 52 AMeVNi at 52 AMeV

---- QP ….. QC TOTALMRS

QPMRS

FREE NEUTRONS IN FREE NEUTRONS IN 3636Ar + Ar + 5858Ni AT 50 AMeVNi AT 50 AMeV

HERACLES Multidetector, Université Laval, + neutron detectorsHERACLES Multidetector, Université Laval, + neutron detectorsCyclotron Institute, Texas A&M University.Cyclotron Institute, Texas A&M University.

45O

60O105O

120O

75O

90O

135O

150O

BEAM

Neutron detectors BC-501Neutron detectors BC-501

TARGET

Heracles Array

FREE NEUTRONS ENERGY SPECTRAS FREE NEUTRONS ENERGY SPECTRAS 3636Ar + Ar + 5858Ni 50 AMeVNi 50 AMeV

---- QT ….. MRS TOTAL

MRS

QT

LINK BETWEEN LINK BETWEEN 3636Ar+Ar+5858Ni AND Ni AND 5858Ni+Ni+5858Ni FOR FREE NEUTRONSNi FOR FREE NEUTRONS

proj

resproj

Z

ZZCQP

A

E *

THE LINK IS EXCITATION ENERGYTHE LINK IS EXCITATION ENERGY PER NUCLEON FOR QT IN PER NUCLEON FOR QT IN ((3636Ar+Ar+5858Ni) AND QP IN (Ni) AND QP IN (5858Ni+Ni+5858Ni).Ni).

RELATIONRELATION IS USEDIS USED

:QP 58Ni+ 58Ni 52 AMeV:QP 40Ar+27Al 40 AMeV #

#G. Lanzano et al., Nucl. Phys. A683, 566(2001)

N/Z RATIOS (QP AND MRS) N/Z RATIOS (QP AND MRS) 5858NiNi+58+58Ni 52 AMeVNi 52 AMeV

N/Z MRS N/Z QP --------- N/Z=1.07

CONCLUSIONCONCLUSION

- N/Z ratio of the complete MRS nuclear material reaches a value higher 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 than the initial system’s one (1.07) and that of the QP which decreases around 1.around 1.

- An experiment detecting neutron multiplicities and charged particlesAn experiment detecting neutron multiplicities and charged particles in the same setup would greatly improve precision on MRS N/Z in the same setup would greatly improve precision on MRS N/Z measurement.measurement.

- Progressive neutron enrichment (with centrality) of MRS nuclear matter. Progressive neutron enrichment (with centrality) of MRS nuclear matter.

PROJECTILE RECONSTRUCTED MASS AND CHARGE PROJECTILE RECONSTRUCTED MASS AND CHARGE 5858NiNi+58+58Ni 52 AMeVNi 52 AMeV

Proton nb. Neutron nb. Neutron nb. N/Z=1.07

MISSING NEUTRONS TO RECOVER PROJECTILE N/Z (1.07)MISSING NEUTRONS TO RECOVER PROJECTILE N/Z (1.07)

Neutron nb. * BUU simulations (b=3fm - 4.5 fm)

(neutronMRS 58Ni+58Ni / neutronMRS

36Ar+58Ni = 1.86)

N/Z RATIOS (QP AND SMR) IN N/Z RATIOS (QP AND SMR) IN 5858NiNi+58+58Ni AT 52 AMeVNi AT 52 AMeVWITH CORRECTION FOR FREE NEUTRONS IN SMRWITH CORRECTION FOR FREE NEUTRONS IN SMR

N/Z MRS N/Z QP ------- N/Z=1.07

ETL HYPOTHESIS FOR NEUTRON MULTIPLICITIES