Investigation of the freeze-out configuration in the 197 Au Au reaction at 23 AMeV Rafał Najman for CHIMERA collaboration M. Smoluchowski Institute of Physics Jagiellonian University The theoretical analysis of properties of superheavy nuclei do not predict any long living nuclei with compact shapes beyond the island of stability (N ~ 184, Z ~ 114).

Search for superheavy nuclei M. Warda, Int. J. of Mod. Phys. E 16,452 (2007) Liquid drop model with shell corrections and Hartree – Fock – Bogoliubov theory with the Gogny D1S force calculations have shown that metastable islands of nuclear bubbles can exist for nuclei in the range A= K. Dietrich, K.Pomorski Phys. Rev. Lett. 80, 37 (1998) J. Decharge et al. Nucl. Phys.A 716, 55 (2003 )‏  The energy of the toroidal minimum decrease relatively to the potential energy of the spherical configuration with increase of the mass of the system  For Z>140, the global minimum of potential energy corresponds to the toroidal shape

BUU simulations for central collisions of Au + Au A.Sochocka et al., Int. J. Mod. Phys. E17, 190 (2008) Calculations predict that a threshold energy for toroidal freeze-out configuration is at about 23 MeV / nucleon

Results of ImQMD simulation Time evolution of 238 U U at Ecm=3570 MeV and b=0 fm E = 30 AMeV Time evolution of quadrupole moment for 238 U U Tian et al., Phys. Rev. C77, (2008)‏ 4 Flat shape Prolate spheroid E = 5.4 – 7.4 AMeV

Formation the toroidal-shapes configurations can be observed in binary droplet collision at high velocity 5 V=3.89 m/s Phys.Rev.E 80, Macroscopic droplet collisions V=9.1 m/s

CHIMERA – Charged Heavy Ion Mass and Energy Resolving Array CHIMERAs advantage: 1192 telescopes: Si and CsI Low detection threshold - 1MeV/A Covering almost 94% of 4  Z and A identification 17 rings 687 telescopes on 9 wheels

ΔE-E technique

Time of Flight Techinique

TLF well defined events PLF IVS Fission fragments from PLF decay Global properties of experimental data from 197 Au+ 197 Au reaction at 23 AMeV

N frag ≥ 5 Multiplicity distribution for well defined events Z frag > 2Z frag > 9 N frag = 3 N frag = 4 N frag ≥

Shape analysis δ parameter measures the shape of the events in momenta space. Z frag > 9

Shape analysis A, B, C, D - plane parameters Δ2 parameter measures the flatness of the events in velocity space. For toroids it is much smaller than for sphere or bubble.

Observables distributions One can see that for both observables the biggest difference between experimental distribution and model predictions is observed for the Ball 8V 0, and Bubble 8V 0 configurations. In contrast to that, the experimental data seem to be more consistent with the simulations assuming toroidal freeze-out configurations. Flat events conditions:

Location of toroidal events on the ϴ plane vs ϴ flow plane

Efficiency factor: EF is: Very low for spherical freeze-out configurations in respect to the corresponding values for toroidal configuration For QMD calculations is strongly dependent on the ϴ plane range For experimental data the value of the EF is about 50% for events located in the reaction plane (ϴ plane > 75 0 ) Is reduced by factor 2 for events perpendicular to the reaction EF values for experimental data are very close to the model predictions for toroidal configurations. This observation may indicate the formation of toroidal/flat freeze-out configuration created in the Au + Au collisions at 23 MeV/nucleon. Efficiency factor – ratio of number of events fulfilling the selection conditions to the total number of events with 5 heavy fragments Flat events conditions:

In order to get additional evidence to support the hypothesis that toroidal objects are created, the behavior of other observables was investigated: mass standard deviations of fragments, relative angles of fragment pairs, mean velocities of fragments as a function of their mass relative velocities of fragments pairs Other observables

AA standard deviation of masses for flat events with 5 fragments

New observables: For V ij distributions the mean values for class of events located outside the reaction plane are smaller in comparison to the case of events located in the reaction plane. This observation may be used as an indication that for events located outside the reaction plane freeze-out configuration is more extended in comparison with that for events located inside reaction plane. Outside reaction plane θ flow > 20 θ plane < 75 θ flow > 20 θ plane > 75 θ flow < 20 θ plane < 75 θ flow < 20 θ plane > 75 Inside reaction plane region dominated noncentral collisions Outside reaction plane V ij is mean value of relative velocities for flat events with 5 fragments Other observables region where observation of toroidal freeze-out configuration is expected

Road Map 1.Search for toroidal freeze-out configurations in events with smaller number of fragments (3 and 4) 2.Isotopic identification of light fragments ( 3 ≤ Z ≤ 9 ) 3.Investigation of isotopic composition of IVS

Summary and outlook The experimental data for well defined events have been shown. The experimental data are compared with ETNA and QMD model predictions. Efficiency factor is used as indication of formation of exotic freeze-out configuration. Comparison between experimental data and model predictions may indicate the formation of flat/toroidal nuclear system. Distribution of v ij indicates that toroidal freeze-out configuration may be created outside reaction plane Additional analysis of experimental data

Breakup Collaboration F.Amorini1,2, L.Auditore3, A.Bubak4, T.Cap5, G.Cardella6, E. De Filippo6, E.Geraci2,6, L.Grassi2,6, A.Grzeszczuk4, E.La Guidara7, J.Han1, D.loria3, S.Kowalski4, T.Kozik8, G.Lanzalone1,9, I.Lombardo2,9, Z.Majka8, R.Najman8, N.G.Nicolis10, A.Pagano6, E.Piasecki11, S.Pirrone6, R.Płaneta8, G. Politi2,6, F.Rizzo1,2, P.Russotto1,2, K.Siwek-Wilczyńska5, I.Skwira-Chalot5, A.Sochocka12, A.Trifirò3, M.Trimarchi3, J.Wilczyński13, G.Verde6, W.Zipper4 1) INFN, Laboratori Nazionali del Sud, Catania, Italy 2) Dipartimento di Fisica e Astronomia Universitá di Catania, Catania, Italy 3) Dipartimento di Fisica Universitá di Messina and INFN Gruppo Collegato di Messina, Italy 4) Institute of Physics,University of Silesia, Katowice, Poland 5) Faculty of Physics,University of Warsaw, Warsaw, Poland 6)INFN,Sezione di Catania, Italy 7)Centro Siciliano di Fisica Nucleare e Struttura della materia 8) M.Smoluchowski Institute of Physics, Jagiellonian University, Kraków, Poland 9)Università Kore, Enna,Italy 10)Department of Physics, The University of Ioannina,Ioannina,Greece 11) Heavy IonLaboratory,University of Warsaw, Warsaw, Poland 12) Department of Physics, Astronomy and Applied Informatics, Jagiellonian University, Kraków, Poland 13) A.SołtanInstitute for Nuclear Studies,Świerk, Poland

Reconstruction results

Estimation of collision centrality One can see on this plot that noncentral events are located at small θ flow angles (> 20 degree) and big θ plane angles (< 75 degree). As an impact parameter estimator for experimental data we used total transverse momentum

CHIMERA – Charged Heavy Ion Mass and Energy Resolving Array

E- particle energy [MeV] calculated from: E=a L · Channel desilpg + b L m- ion mass [u] R – distance from target to detector [cm] t 0 – time offset calculated for each detector [ns] α= 3·T / d T- cyclotron period [ns] d- distance between two beam bursts [channels] For calibration data the following 8-parametres function is fitted: ToF Techinique

b) Klasteryzacja QMD – model dynamiczny Zimne fragmenty LAB Kod GEMINI Rozpad gorących frgmentów i przyśpiesznie w polu kulombowskim Czas [ fm/c ] CM detektor QMD + GEMINI Nukleony są przedstawione w formie paczek falowych o stałej szerokości w czasie - układ ewoluuje zgodnie z równaniem Hamiltona.

ETNA – Expecting Toroidal Nuclear Agglomeration + GEMINI kod A CN = A T + A P Z CN = Z T + Z P - minus nukleony emitowane w początkowej fazie (preequilibrium) reakcji A CN = A T + A P Z CN = Z T + Z P - minus nukleony emitowane w początkowej fazie (preequilibrium) reakcji Losowanie fragmentów: Rozkład Gaussa = Z tot / N N =5 – liczba fragmentow Losowanie fragmentów: Rozkład Gaussa = Z tot / N N =5 – liczba fragmentow Wszystkie fragmenty są umieszczane w konfiguracji “wymrożenia” w kształcie kuli, bańki i toroidu warunek przekrywania: R ij > R i + R j + 2fm Wszystkie fragmenty są umieszczane w konfiguracji “wymrożenia” w kształcie kuli, bańki i toroidu warunek przekrywania: R ij > R i + R j + 2fm Uwzględnienie niecentralnych kolizji dla zadanego parametru zderzenia b Uwzględnienie niecentralnych kolizji dla zadanego parametru zderzenia b E ava = E CM + Q – E COULOMB - dostępna energia Podział dostępnej energii: E ava = E* + E th = NaT 2 +3/2k(N-1)T ; zakladając równą temperaturę, N – liczba fragmentów Dynamiczny kod GEMINI:  rozpad wzbudzonych fragmentów  przyśpieszanie w polu kulombowskim Dynamiczny kod GEMINI:  rozpad wzbudzonych fragmentów  przyśpieszanie w polu kulombowskim Detekcja cząstek w detektorze CHIMERA ,   numer detektora   rand,  rand Próg energetyczny E thr = 1 MeV/A Próg energetyczny E thr = 1 MeV/A  Z FWHM = 1 ch.u. A=2.08* Z ( przewidywania kodu GEMINI )  Z FWHM = 1 ch.u. A=2.08* Z ( przewidywania kodu GEMINI ) Opisuje rozpad obiektu tworzonego w fazie wymrażania. Obiekt taki tworzy się po emisji nukleonów przedrównowagowych z systemu złożonego, który powstaje w wyniku połączenie się jądra wiązki z jądrem tarczy.

Definition of sphericity and coplanarity where p (n) i is the i-th Cartesian momentum component of the n-th particle, and is the n-th fragment momentum vector. The diagonalization of the momentum tensor gives the eigenvalues: ti, (t1 < t2 < t3). From the cartesian components of fragment Z  5 momenta in the centre of mass may construct the tensor