E. De Filippo (INFN Catania)

for the REVERSE / ISOSPIN collaboration

Time sequence and isoscaling in neck fragmentation

Time sequence and isoscaling in neck fragmentation

Fragments production in peripheral collisions: isospin dependence in neck formation

The Reverse experiment with CHIMERA detector

Characterization of dynamical emitted light fragments in ternary events: time scale and time sequence

Comparison with BNV calculations

Isoscaling in “neck” fragmentation ?

CONCLUSIONS AND OUTLOOK (Chimera upgrading)

Pisa, February 24-26 2005

Fragments can have several origin: they can be emitted sequentially from (eventually equilibrated) projectile-like or target-like source or promptly (dynamical emission) during the first stage of the reaction.

At the Fermi energy, in binary dissipative collisions, an emission component of fragments and light particles is centered between quasi-projectile and quasi-target-velocity.

Evolution of the density contour plot at 6 fm in the reaction 124Sn + 64Ni at 35 A.MeV: the formation of a neck-like structure brought after 100-160 fm/c to a ternary event with the appearance of dynamical emitted IMFs. V. Baran et al. Nucl. Phys. A730 (2004) 329

Neck fragmentation and isospin degree of freedom

2)()0,(),( IEIEIE sym A

ZNI

Asymmetry

Looking for a constraint to the density dependence of EOS asymmetry term

Depending upon the shape of symmetry potential around 0 neutron/proton diffusion effects and a neutron enrichment of the neck region could be induced (isospin fractionation).

NEUTRONS

PROTONSAsy-soft

Asy-stiff

Nuc

l Phy

s. A

703,

603

(20

02)

124Sn I=0.2

The CHIMERA detector and Reverse experiment

1192 Si-CsI(Tl) Telescopes

1m

1°

30°

TARGET

176°

BeamREVERSE Experiment: 688 Telescopes, forward part.

2002/2003- CHIMERA-Isospin 1192 telescopes

REVERSE Experiment: 688 Telescopes, forward part.

2002/2003- CHIMERA-Isospin 1192 telescopes

Experimental Methods:

E(Si)-E(CsI(tl)): CHARGE, ISOTOPES

E(Si) –TOF(Si) VELOCITY - MASS

PULSE SHAPE in CsI(Tl) p,d,t,3He,4He,.6,7,..Li,… Zlight<5

124Sn + 64Ni,27Al 112Sn + 58Ni

1°

30°

35 A.MeV

TERNARY EVENTS SELECTIONTERNARY EVENTS SELECTION

To get insight the different mechanisms of IMFs production we have selected in the Vpar-Charge bi-dimensional plot three regions where PLFs, TLFs and IMFs can be easily separated:

beamnii

totPp

P

P

,1.

p/pbeam> 0.6

Z1+Z2+Z3 ~ ZTOTPLF

TLFIMF

BASIC CHARACTERISTICS OF SELECTED EVENTS

Parallel velocity distribution for Z=4,6,12,18 IMFs in coincidence with projectile-like fragment (PLF) and target-like fragment in ternary events. BNV

IMFs mechanism production: REDUCED VELOCITY PLOT*IMFs mechanism production: REDUCED VELOCITY PLOT*

TLF PLF

Vr1Vr2

IMF

We have constructed event-by-event the relative velocity of IMF respect to TLF (ry) and of IMF respect to the PLF (rx).

Relative velocities were normalized to the relative velocity for a Coulomb repulsion between fragments of charge Z1,Z2 (Vviola)

CE*2 3.7755.0

3/12

3/11

21

AA

ZZEC

Plotting the two reduced relative velocity (rx) versus (ry) in a bi-dimensional plot different scenarios can be disentangle: for example sequential decay from PLF (TLF) should be represented by a distribution

around rx=1 (ry=1).

On the contrary simultaneous values of rx and ry larger than one can support a non-statistical origin for these fragments.

*E. De Filippo, A. Pagano, J. Wilczyński et al. (Isospin collaboration), to be published Phys. Rev. C

Events close to diagonal correspond to a prompt ternary division while those approaching a ratio ~ 1 correspond to a sequential

emission from PLF or TLF respectively.

Prompt

12

3

21

3

1 40 fm/c

2 80 fm/c

3 120 fm/c

Points are calculated in a simple kinematical simulation assuming that IMFs separate from projectile (square) or from target (circle) after a time interval of 40, 80 and 120 fm/c elapsed from the primary binary separation of the projectile from the target at t=0.

Points are calculated in a simple kinematical simulation assuming that IMFs separate from projectile (square) or from target (circle) after a time interval of 40, 80 and 120 fm/c elapsed from the primary binary separation of the projectile from the target at t=0.

Results of BNV transport model for IMFs emission probability from neck region for different impact parameters (V. Baran et al. Nucl. Phys. A730 329, 2004).

REDUCED VELOCITY PLOTS: REDUCED VELOCITY PLOTS:

BNV

Note: BNV model accounts only for the “prompt” component of IMF’s

ISOSCALING FROM THE RATIO OF ISOTOPE YIELDSISOSCALING FROM THE RATIO OF ISOTOPE YIELDS

M.B. Tsang et al. Phys. Rev. C64, 054615

R21= Y2(N,Z)/Y1(N,Z) =

C exp(N + Z)

For two systems having a different isospin asimmetry, the ratio of isotope yields with Z protons and N neutrons obtained from sistem 2 (neutron rich) and system 1 (neutron poor) has been found to follow a significative scaling (exponential dependence) where and are scaling parameters.

112Sn+112Sn and 124Sn+124Sn

50 A.MeV (MSU data)

E. Geraci et al., Nucl. Phys. A732 (2004) 173

A signal of phase transition: A signal of phase transition: Isospin distillationIsospin distillation

03.003.1

01.063.0ˆ

02.056.1ˆ

C

p

n

0.02-0.47

0.010.44

900

081

1

2

1

2

.ˆ

.ˆ

TPTP

TPTPp

TPTP

TPTPn

AZ

AZ

AN

AN

values channelEntrance

Neutron enrichment in the gas phase

Zp

Nn

Z

p

p

N

n

n

NiSn

NiSn CCZNY

ZNYZNR

ˆˆ),(

),(),(

,

,

,

,

1

2

1

221

58112

64124

Isoscaling in central collisions Isoscaling in central collisions

112Sn+58Ni and 124Sn+64Ni at 35 AMeV Central collisionsCHIMERA-REVERSE experiment

Gating the reduced plot for light IMFs:Gating the reduced plot for light IMFs:

ISOSCALING OF ISOTOPIC DISTRIBUTIONS

ISOSCALING OF ISOTOPIC DISTRIBUTIONS

We have started a study upon isoscaling signal for peripheral collisions and neck fragmentations. Infact also if isoscaling relation can be derived assuming chemical and thermal equilibrium, this is not a necessary condition to observe this signal.

For the IMFs sequential emission from projectile-like source a nice fit is observed with =0.61 and =-0.61 parameter’s values.

For the IMFs sequential emission from projectile-like source a nice fit is observed with =0.61 and =-0.61 parameter’s values.

exp(-0.61*Z)exp(-0.61*Z)

exp(0.61*N)exp(0.61*N)

For the neck region the isoscaling signal seems to be yet present also if the quality of the exp(N) fit is poor, especially for heavier IMFs.

This study can be interesting for the future prosecution of data analysis because isoscaling parameters could be sensitive to the density dependence of EOS as shown by dynamical calculations.

Prel

imin

ary

data

exp(0.53*N) exp(-0.40*Z)

CHIMERAPS-UPGRADING (2005-2006)

Method: rise time measurement for Pulse shape application

Present threshold for charge identification 10 A.MeV

mass(*)

(*) charge for particle stopped in silicon detector is reconstructed by EPAX formula

Charge

Charge and mass for light Ions

IDENTIFICATION IN CHIMERA

124Sn+64Ni 35 A.MeV

CFD90% Stop TAC

RiseTime ~ Stop-Start

Si PA Amp SplitCFD30% Start TAC

QDC

ET

TDC

Standard ‘’CHIMERA LINE’’

upgrading

Results: charge identification up Z 15

With ~ 4 MeV/A energy threshold for particle stopped in silicon detector

a

+ TOF

A, Z

40Ar+12C 20 A.MeV

We have studied with the forward part of the CHIMERA detector the 124Sn + 64Ni and 112Sn + 58Ni at 35 A.MeV. Fragments produced in semi-peripheral ternary reactions have been investigated. The analysis method gives the possibility to evaluate the

time scale of the process. Comparison, for light IMFs ions, with BNV calculations supports the scenario of dynamical production of IMFs in the overlapping zone (neck) between target and projectile nuclei.

Conclusions and OutlookConclusions and Outlook

Isospin effects, in particular of isoscaling signal are under study. Sistematic evaluation of isoscaling parameters with proper source selection are important quantities for testing symmetry energy density dependence of EOS in asymmetric nuclear matter.

The Chimera detector will be upgrated and the combination of pulse-shape analysis and time-of-flight measurements in Silicon detectors will increase the capability of fragment identification in mass and charge: this is important not only for the prosecution of the isospin physics studies with stable beams but of course also for future planning of experiments with exotic beams.

The Chimera detector will be upgrated and the combination of pulse-shape analysis and time-of-flight measurements in Silicon detectors will increase the capability of fragment identification in mass and charge: this is important not only for the prosecution of the isospin physics studies with stable beams but of course also for future planning of experiments with exotic beams.

The REVERSE – ISOSPIN COLLABORATION

INFN, Sezione di Catania and Dipartimento di Fisica e Astronomia, Università di Catania, Italy INFN, Sezione di Milano and Instituto di Fisica Cosmica, CNR, Milano,Italy INFN, Laboratori Nazionali del Sud and Dipartimento di Fisica e Astronomia, Università di Catania, Italy INFN, Gruppo Collegato di Messina and Dipartimento di Fisica, Università di Messina, Italy INFN, Sezione di Milano and Dipartimento di Fisica Università di Milano, Italy Institute for Physics and Nuclear Engineering, Bucharest, Romania Institute of Physics, University of Silesia, Katowice, Poland M. Smoluchowski Institute of Physics, Jagellonian University, Cracow, Poland Institute de Physique Nucl´eaire, IN2P3-CNRS and Université Paris-Sud, Orsay, France LPC, ENSI Caen and Université de Caen, France INFN, Sezione di Bologna and Dipartimento di Fisica, Università di Bologna, Italy Saha Institute of Nuclear Physics, Kolkata, India GANIL, CEA, IN2P3-CNRS, Caen, France, H. Niewodniczanski Institute of Nuclear Physics, Cracow, Poland DAPNIA/SPhN,CEA-Saclay, France IPN, IN2P3-CNRS and Université Claude Bernard, Lyon, France Institute of Modern Physics, Lanzhou, China Institute of Experimental Physics, Warsaw University, Warsaw, Poland INFN, Sezione Napoli and Dipartimento di Fisica, Università di Napoli Institute for Nuclear Studies, Swierk/Warsaw, Poland