Giovanni Casini Istituto Nazionale di Fisica Nucleare Sezione di Firenze SUMMARY. Some Physics at the Fermi regime.

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1 Fast emission processes in peripheral heavy ion reactions and their impact on reaction dynamics Giovanni Casini Istituto Nazionale di Fisica Nucleare Sezione di Firenze SUMMARY Some Physics at the Fermi regime Experimental info Event classes vs. impact parameter Midvelocity emissions and Evaporation Energetics of the systems Conclusions KEMER -- NUFRA09 sept 28-oct collaboration 1

2 Midvelocity (MIDV) Emissions: many experimental evidences LCP from Ni+C,Au at 34.5 AMeV Many experiments report about MIDV emissions of LCP, neutrons and IMF at FERMI ENERGIES Au C Toke et al. PRL75(95)2920 Gingras et al. PRC65(02)061604R LCP Piantelli et al PRC74(06) Yanez PRC68(03)011602R NbNb 38AMeV Ni+NI at 30AMeV NbNb 23AMeV IMF Milazzo et al. P Lett. B09(01)204 2 Hudan et al PRC 71(05)054604

3 Reaction Dynamics, a naïve (useful) sketch neck physics fast emissions nuclear surfaces low densities and isospin drift (Esym) high energy densities chemical-thermal eq. partial reabsorption of the neck matter, excitation of QP,QT fluctuactions of QP,QT variables nuclear shape Coulomb Related emissions Angular momentum excitation of QP,QT Emission Hierarchies evaporation Slower QP,QT decay 3 EAL,EPAX issues n-rich n-poor evaporation

4 Reaction Dynamics, a naïve (useful) sketch neck physics fast emissions nuclear surfaces low densities and e.g. see talks isospin drift (Esym) Paolo Russotto high energy densities Romualdo DeSouza chemical-thermal eq. Hermann Wolter fast aligned fission isospin effects shape fluctuations Coulomb Related emissions Angular momentum excitation of QP,QT Emission Hierarchies evaporation MULTIFGRAMENTATION 4 of QP and/or QT

5 Reaction Dynamics, a naïve (useful) sketch We concentrate on: midv charactectistics QP decay Some details on: statistical concepts for MIDV emissions, Excitation process of QP, QT evaporation 5

6 Experimental Setup The Fiasco conceptual sketch M.Bini et al., NIMA 515 (2003) 497 GAS DETECTORS THE FIASCO SETUP SI SI Telescopes specific for binary collisions detection of both QP,QT tools for LCP,IMF precise velocity measurements Phoswich Scintillators QP beam IMF,LCP QT Experiments at LNS INFN CATANIA Nb+93Nb at 17, 23, 30, 38 AMeV 116 Sn+116Sn at 23, 30, 38 AMeV 93 Nb+116Sn at 23, 30, 38 AMeV 93 (in direct and reverse kinematics) 6

7 FIASCO: a composite Setup for semi-peripheral collisions A suitable apparatus for HEAVY fragments: detection of QP (fast, close to 0o) and QT (even slow and emitted around 90o) A large-acceptance array for LIGHT ejectiles: LCP and IMF identification and velocity (momentum) determination QP QT QP-QT coincident detection with very low E-threshold ( 0.1AMeV ) MEASURED ejectiles: QP,QT, p,d,t, alphas, IMF with 3<Z<10 (not isotopes) 7

8 The market of the ordering parameters In dissipative collisions there is the possibility to follow the evolution of a given variable as a function of the impact paratameter. search for GOOD ordering parameters (OP) SOME EXAMPLES from the MARKET Plagnol et al. INDRA Coll. PRC61(00) uses Etrans12 b relation: YES Planeta et al. CHIMERA Coll PRC77(08) uses (Vzmax/Vproj)CM b relation: YES Theriault et al. TexasA&M PRC74(06) uses (Zproj-ZQP) Theriault et al. INDRA Coll PRC71(05) uses (Zproj-ZQP) b relation: NO Manduci et al. INDRA Coll NP A811(08)93 uses Mtot vs. Etottrans b relation: NO Milazzo et al. Multics-Medea Coll NP A703(02)466 uses VQP and Mimf cuts b relation: YES but not explicit In many cases one checks the goodness of a given OP by using a suitable model including evaporation and detection filter. (e.g. QMD+GEMINI, DIT+GEMINI, BNV+SMM, CoMDII+evap...) NEED to follow the results with b; cross-checks of different experimental results 8

9 The selected ordering parameter b vs. TKEL TKEL = Ediss= Ecm- (µvrel2 /2) Sn+Sn QMD CHIMERA code Under the hypothesis of two-body kinematics TKEL ( or Ediss) also used by other groups Nb+Nb E.Galichet at al. INDRA Coll PRC 79(09) Sn+Sn Experimental Suggested also in recent theoretical papers J.Rizzo et al NP A806(06)79 Nb+Nb 35,50 AMeV S.Piantelli et al. Phys. Rev. C 74 (2006)

10 The selected ordering parameter b vs. TKEL TKEL = Ediss= Ecm- (µvrel2 /2) Sn+Sn QMD CHIMERA code Nb+Nb Under the hypothesis of two-body kinematics IMPORTANT: Sn+Sn Experimental Nb+Nb S.Piantelli et al. Phys. Rev. C 74 (2006) even at Fermi energies TKEL remains a good event selector (but TKEL E*QP+E*QT!) Consequence: all the QP,QT observables should scale in a reasonable way with TKEL 10

11 The reaction pattern EXP ALPHA TKEL=600 MeV MC Piantelli et al., PRC 74 (2006) THE EVAPORATION CONTRIBUTION A well defined Coulomb Ring at forward angles in the QP system: evaporation from fully independent QP and QT, far from each other. Emission pattern at forward angles reproduced with statistical decay of excited and rotating QP at saturation density. 11

12 The reaction pattern EXP ALPHA TKEL=600 MeV MC Piantelli et al., PRC 74 (2006) THE MIDV CONTRIBUTION An abundant production of particles and fragments at MIDV, extending even at forward angles in the QP reference frame MIDV emissions are not compatible with standard emission from two hot spherical nuclei HOW TO SEPARATE THE TWO PARTS? 12

13 Disentangling the contributions 38AMeV 93 STEP 0: MC simulations with 'white' emission in phase-space to estimate the efficiency; then correct the measured yield QP QT STEP 1: global balances of CHARGE and CM-ENERGY for the forward emisphere in SCM profiting of the symmetry of the reaction find: ZTOTforw ECMTOTforw then CM deduce total free neutron multiplicity statistical STEP 2: take the measured emissions forward in QP frame and deduce the total evaporation yield assuming angular distributions given by statistical model. Share neutrons with hypothses on N/Z of MIDV source STEP 3: using kinetic energies, yields and Q-values estimate the excitation energy competing to QP STEP 4: by subtraction of the EVAP component from total quantities, find the mass, charge and energy of the MIDV region A.Mangiarotti et al., PRL 93 (2004) S.Piantelli midvelocity 13 et al., PRC 74 (2006)

14 Mass and energy balances After the separation of the two components one can study the properties of the QP (QT) sources and the MIDVEL source. 38AMeV 93 WE OBSERVE THE FOLLOWING: Proportionality between TKEL and the excitation energy of QP b QP average energy density <4MeV/u; the QP is moderately hot (at least in semiperipheral collisions) CALORIMETRIC METHOD 20 Almost equal energy sharing : E*QP E*mid S.Piantelli 400 MeV et al., PRC 74 (2006) Large amount of energy is deposited in the contact region: does the system enter into the multifragmentation regime? 14 A.Mangiarotti et al., PRL 93 (2004)

15 A hot decaying QP 38AMeV 93 GOOD AGREEMENT with STATISTICAL EVAPORATION from excited nuclei (GEMINI R.J.Charity et al., NPA 483 (1988) 371) LIGHT PARTICLES MULTIPLICITIES for GIVEN TKEL (i.e. GIVEN QP Excitation Energy) NOTE: no evidence for QP multifragmentation in these more peripheral collisions Exp. QP evaporation GEMINI Arrhenius PLOTS: EXP slopes and abundancies are well reproduced by GEMINI 15 S.Piantelli et al., Phys. Rev. C 74 (2006) 34609

16 More details on... A) QP decay and mass correlations B) midvelocity region physics 16

17 QP decay and mass correlations At low energies, when no MIDV is present, the excitation of QP and QT is (mainly) due to exchanges of nucleons in the common mean-field Nucleon Exchange Model various versions started by J.Randrup) There is a tendency from non-equilibrium (short times, peripheral reactions) to equilibrium partition between the fragments (long times, central collisions): the whole nuclear system goes towards thermal equilibrium (witnessed by equal Temperatures for QP,QT) EXAMPLES of these studies Ge+Ho at 8.5 AMeV Kwiatkovski PRC41(1990)958 Sn+Mo at 14 AMeV Casini PRL78(1997)828 17

18 QP decay and mass correlations S.Piantelli et al., Phys. Rev. C 78 (2008) At Fermi energies, the presence of MIDV alters this scenario: how does the heating of QP and QT proceed in presence of MIDV emission and neck phenomena? This is the first example study at this energy Need of an asymmetric mass system Sn+Nb, both kinematics (reverse and direct). Thus we can follow the evolution of the QP in two cases when it comes from Nb and when it comes from Sn. DIRECT KINEMATICS Nb-like P QP QT T vqpcm vcm Pv=vQTCM /(vqtcm +vqpcm) =0.445 EXIT CHANNEL case 1 : mass ratio equal to the entrance mass ratio vqtcm 18

19 QP decay and mass correlations S.Piantelli et al., Phys. Rev. C 78 (2008) At Fermi energies, the presence of MIDV alters this scenario: how does the heating of QP and QT proceed in presence of MIDV emission and neck phenomena? This is the first example study Need of an asymmetric mass system Sn+Nb, both kinematics (reverse and direct). Thus we can follow the evolution of the QP in two cases when it comes from Nb and when it comes from Sn. DIRECT KINEMATICS Nb-like P QP QT T vqpcm vcm Pv=vQTCM /(vqtcm +vqpcm) =0.5 EXIT CHANNEL case 2 : mass ratio equal 0.5, symmetric primary masses vqtcm 19

20 QP decay and mass correlations S.Piantelli et al., Phys. Rev. C 78 (2008) At Fermi energies, the presence of MIDV alters this scenario: how does the heating of QP and QT proceed in presence of MIDV emission and neck phenomena? This is the first example study Need of an asymmetric mass system Sn+Nb, both kinematics (reverse and direct). Thus we can follow the evolution of the QP in two cases when it comes from Nb and when it comes from Sn. REVERSE KINEMATICS Sn-like QP P QT vqpcm T vcm Pv=vQTCM /(vqtcm +vqpcm) =0.5 EXIT CHANNEL case 2 bis : mass ratio equal 0.5, symmetric primary masses vqtcm 20

21 QP decay and mass correlations S.Piantelli et al., Phys. Rev. C 78 (2008) direct and reverse kin QP DATA MANY ASPECTS the effect of MIDV emissions the effect of evaporation charge the non-equilibrium when QP and QT reseparate (the history does matter) PRIMARY CHARGES in REV. and DIR. kin. are equal: stringent test for the procedure as we are looking 21 at the same system (the MIDV emissions are equal)

22 QP decay and mass correlations S.Piantelli et al., Phys. Rev. C 78 (2008) direct and reverse kin QP DATA MANY ASPECTS the effect of MIDV emission the effect of evaporation charge Look at the most populated exit channel masses i.e. QP Sn-like for reverse kinematics (Pv=0.555) 22

23 QP decay and mass correlations S.Piantelli et al., Phys. Rev. C 78 (2008) direct and reverse kin QP DATA MANY ASPECTS the effect of MIDV emission the effect of evaporation charge Look at the most populated exit channel masses i.e. QP Nb-like for direct kinematics (Pv=0.445) 23

24 QP decay and mass correlations S.Piantelli et al., Phys. Rev. C 78 (2008) charge direct and reverse kin QP DATA Look at the central masses i.e. QP Nb-like equal to Sn-like (Pv=0.5) MANY ASPECTS the non-equilibrium when QP and QT reseparate (the history does matter) Comparing the two kinematics one sees a strong difference in the decay of QP coming from light-nb with respect to QP coming from heavy-sn 24

25 QP decay vs. TKEL Sn Nb EXIT CHANNEL with the same initial mass ratio Pv=0.555 for SnNb Pv=0.445 for NbSn 25

26 QP decay vs. TKEL EXIT CHANNEL selecting equal primary final sizes Pv=0.500 for SnNb Pv=0.500 for NbSn 26

27 QP decay vs. TKEL EXIT CHANNEL selecting equal primary final sizes Pv=0.500 for SnNb Pv=0.500 for NbSn At all energy losses one finds strong correlation between evaporated charges and reaction path of the QP 27

28 QP excitation vs. TKEL QP DIRECT KIN. INITIAL MASS RATIO REVERSE KIN. INITIAL MASS RATIO QP QP has the same Excitation Energy By the CALORIMETRIC METHOD we reconstruct the Excitation Energy of the QP for different Pv values, for each bin of TKEL 28

29 QP excitation vs. TKEL QP DIRECT KIN. EQUAL MASSES QP HIGH EXCITATION QP REVERSE KIN. EQUAL MASSES QP LOW EXCITATION the excitation energy per nucleon is not the same: namely, the entire system has not the same temperature A possible explanation is that part of the very hot MIDV region is re-absorbed by the two interacting nuclei. The nucleus which takes larger part of this region gains a 29 'surplus' of excitation and then evaporates more particles.

30 The properties of the Midv emission high neutron content for bound species S.Piantelli et al., Phys. Rev. C 74 (06) Hydrogen isotopes: strong neutron enrichment in the MIDV component with respect to N/Z for evaporated hydrogen from QP (and well reproduced by standard stastical model) EXP TOTAL MIDVEL EXP QP evap NiNi at 52 6 He (Green line: Gemini) also IMF are n-rich! Helium Thèriault INDRA COLL PRC71(2005) 30 QP Z=15 phospor

31 The properties of the Midv emission high neutron content for bound species S.Piantelli et al., Phys. Rev. C 74 (06) EXP TOTAL MIDVEL Hydrogen isotopes: strong neutron enrichment in the MIDV component with respect to N/Z for evaporated hydrogen from QP (and well reproduced by standard stastical model) EXP QP evap SnNi at 35 MIDV QP-region also IMF are n-rich! yield ratios (Green line: Gemini) Berillium parallel VIMF Planeta CHIMERA COLL PRC77(2008)

32 Midvel Source Physics EXP Nb+Nb 38AMeV We now consider two well measured variables, the N/Z of hydrogen (N/Z)H and the yield ratio of protons and alphas Yp/Y CHECK with other data available in the literature 32

33 Midvel Source Physics EXP Nb+Nb 38AMeV The various independent data are consistent and confirm different features for QP and MIDV emissions PLEASE, CAUTION!: the comparison is not straightforward; it is mostly obtained by using pictures and by comparing the various impact-parameter scales. 33

34 Midvel Source Physics OBSERVATIONS: high energy densities; abundancy of IMF; unusual isospin content; it seems we are far from binary-step decay of hot nuclei (à la GEMINI) HYPOTHESES: low barion densities can be reached; enough time to approach a (local) chemical and thermal equilibrium ( fm/c) Indications of a initial rapid thermalization of a participant zone: NIMROD people for Zn+Ni,Mo,Au 26,35,47AMeV Wang PRC72(05)024603, NIMROD people for Ar112Sn 40,55AMeV Wang PRC75(07) LASSA people for Sn+Sn isotopes 50AMeV Tsang PRL92(04) LASSA people for Cd+Mo 50AMeV PRC71(05) many theoretical dynamical predictions QUESTION: Can statistical concepts still be applyied to the decay of a (small) transient system which forms in the interaction region (a mutifragment source)? Approach used also by LASSA people; Xu PRC65(02)061602R for semiperiph. and central collisions of 114Cd+92Mo at 50AMeV. We used the Statistical Multifragmentation Model (SMM) looking for a source responsible of the measured MIDV emissions 34 SMM: Botvina & Mishustin EPJA30(06)121 and ref. therein

35 Midvel Source Physics What source for SMM? Caution on its size, its isospin and its energy density. More doubts than for sources formed in central collisions. Moreover, estimates are affected by free neutron indetermination and by the fact that what one sees as MIDV emission is only a part of the source which can be partially 'reabsorbed' by the QP-QT THEREFORE we run the code in a wide (reasonable) grid of values for A,Z (i.e. N/Z) and looking for the parameters which reproduce the data in terms of (N/Z)H and of Yp/Y within 20 The barion density was taken /6 according to other results for central sources (but this parameter is not so effective) 35

36 Midvel Source Physics G.Casini et al submitted to PRC 2009 SMM RESULTS We found some triples (A,Z,E) for the source which reasonably reproduce the behavior of the MIDV ejectiles, namely the 'anomalous' values of proton to alpha ratios and n-enrichment of hydrogen. Moreover, the same code in the 'liquid' low-excitation regime can reproduce (as Gemini does) the QP decay 36

37 Midvel Source Physics RESULTS: features of the possible MIDV source SOURCE Thermal Excitation Lower limit: 4 AMeV Upper limit: 9 AMeV, close to the energy in the n-n reference system SMM results: indication for high excitations (6-8 MeV) with a slight increase with increasing TKEL conclusions: the observed results are indeed compatible with a strongly excited source other authors see the same, e.g.: Wang PRC72(05) Xu PRC65(02)061602R 37

38 Midvel Source Physics RESULTS: features of the possible MIDV source SOURCE SIZE A Lower limit: mass corresponding to the observed MIDV emitted charge Upper limit: twice the lower limit SMM results: there is no indication for a trend in source size QP Conclusions: the size of the source weakly affects the break-up fragments at MIDV (high excitation) The same observation made by Hudan PRC71(05) pag.1 38

39 Midvel Source Physics RESULTS: features of the possible MIDV source SOURCE ISOSPIN N/Z Lower limit: N/Z=0.9 Upper limit: N/Z=2.0 SMM results: the average N/Z of the source increases with TKEL. There is indication for a nenrichment of the source with respect to the entrance asymmetry (N/Z=1.268) conclusions: isospin drift seems to play a role in determining the observed chemistry at MIDV. 39

40 Neutron drift into neck zone? The subject is intensely debated (e.g. isospin drift in dilute matter?) The present work, within a model, can only suggest a n-enrichment of the MIDV matter for rather peripheral collisions 'YES' PARTY Theriault PRC71(2005) Ni+Ni at 52AMeV Theriault PRC74(2006) Zn+Zn at 45AMeV 'MIDDLE' PARTY Xu PRC62(2000)031603R 114 Cd+92Mo Nickel Zinc MIDV in semicentral collisions is more n-deficient with respect to MIDV in central collisions or it is more excited 'NO' PARTY Sobotka et al. PRC62(2000)031603R 129Xe+120Sn neutron + INDRA data For semicentral collisions they conclude no net n-enrichment 40

41 Conclusions For semiperipheral collisions we measured and separated MIDV emissions from the QP-QT decay. While QP-QT emission is consistent with evaporation equilibrated source at normal density, this is not true for MIDV from an Correlation between evaporation and size of primary QP/QT (after MIDV emissions) is observed. This could be due to the different reabsorption of the hot neck matter by the two main nuclei. The high energy densities reached in the contact region overcome the 'threshold' for multifragmentation Some observed MIDV properties can be explained by the multifragmentation of a hot diluted system brought by the fast dynamics into the instability region Within SMM, it results that the 'small' MIDV source is more neutron rich than the original matter Further programs can benefit of exotic beams in extending the studies to a wider domain of isospin Charge and mass idenitification capability (is and) will be an important issue. FAZIA is a project in this direction, designed to work also at the 41 rather low energies of future RIB facilities (SPES, Spiral2).

42 Persepectives FAZIA Si-Si-CsI Telescopes with specially selected Si-crystals Fully digital analysis of signals 42

43 Persepectives FAZIA For semiperipheral impacts we measured and separated the MIDV emissions from the QP evaporation. QP (QT) emission is consistent with evaporation from an equilibrated source at normal density while this is not the case for MIDV Correlations between evaporation and size of primary QP/QT (after MIDV emissions) are observed. They can be qualitatively explained by the partial reabsorption of the hot MIDV zone by one of the main nuclei. The high energy densities reached in the contact region overcome the 'threshold' for multifragmentation Some observed MIDV properties can be explained by the multifragmentation of a hot diluted system brought by the fast dynamics into the instability region Within SMM, it results that the 'small' MIDV source is more neutron rich than the original matter Further programs can benefit of exotic beams extending the studies to a wider domain of isospin (of sufficient energy) in The detector capability to give Z,A for the ejectiles is and will be an important issue. FAZIA is a project in this direction, designed to work also at the rather low energies of future RIB facilities (SPES, Spiral2). 43

44 Energy balances for the QP and the midvelocity region The same Excitation energies can be view as a function of relative parameters TKEL/Ecm or b/bgr 38AMeV 93 Plagnol INDRA XeSn@39 Toke XeBi@29 Galichet INDRA NiNi@52 Xu LASSA CdMo@50 We investigate up to very peripheral collisions Estimate of relative variables allow easier (important) comparisons with other experiments 44

45 QP decay: correlations with mass ratio 45