Physics Case and Theory Working Group

 

According to the large variety of subjects presented in the SPIRAL2 Letter of Intent, a ‘Physics Cases and Theory’ working group has been formed at the very beginning of the PARIS collaboration. Its primary goal is to coherently highlight the fundamental physics issues to be addressed by the new device. This is quite a challenge having in mind the diversity of interests at PARIS – including giant dipole resonance structural properties as well as molecular-like nuclear states and reaction dynamics from barrier energies up to the multifragmentation regime (1). The ‘Physics Cases and Theory’ group is aimed to constitute the natural 'bridge' between theory and experiment. "Which physics point can be brought to light with the resolution realistically achievable in experiment?" is an example of the questions to be answered by the working team. Its implication for defining the strategy to be adopted in future proposals appears thus straight.

In the course of its first half-year of operation, the contacts established with the theoreticians involved already at the time of the preparation of the Letter of Intent, but also with a few others, have been strengthened. While triggering these discussions, the group succeeded in creating a smooth synergy between the various goals and requests expressed within the collaboration. A summary of this first working stage has been presented at the PARIS meeting held in Cracow in May 2007.

In a second stage, the vivid interest manifested by several teams to join the collaboration raised the question about enlarging even more the ambitious physics program of PARIS. Topics related to exotic structural effects (super-deformation, shell gaps at the drip lines) as well as subjects of importance in astrophysics have seriously been envisaged as ‘new’ PARIS physics cases (2). In addition to the primary goal of using PARIS at the radioactive SPIRAL2 facility, the installation of the γ-array at the secondary target position of the S3 spectrometer – profiting from very intense stable LINAG beams - has been estimated as very promising as well. The ‘Physics Cases and Theory’ working group invests much effort in finding the best compromise for matching an as wide as possible range of physics and pays special attention on the specific constraints inherent to the various topics. The outcome of preliminary thoughts has been presented in May 2008 at the PARIS meeting in York. The list of requirements established by the group has been summarized in a single table. This compilation constitutes a crucial input for the other PARIS working groups, namely those dealing with simulations, electronics and mechanics.

List of requirements related to the different physics cases to be addressed at PARIS

Physics

Case

Recoil mass

v/c

[%]

Eg range [MeV]

DEg/Eg

[%]

DEsum/Esum

[%]

DMg

W

coverage

DT

[ns]

Ancillaries

Comments

Jacobi transition

40-150

<10

0.1-30

4

<5

4

2p-4p

<1

AGATA

HI det.

High eff.

Beam rej.

Shape Phase Diagram

160-180

<10

0.1-30

6

<5

4

2p-4p

<1

HI det.

High eff.

Differential method

Beam rej.

Hot GDR in n-rich nuclei

120-140

<11

0.1-30

6

<8

4

2p-4p

<1

HI det.

Beam re.

Isospin mixing

60-100

<7

5-30

6

-

-

4p

<1

HI det.

High eff.

Beam rej.

Reaction dynamics

160-220

<7

0.1-25

6-8

<8

4

2p

<1

n-det.

FF det.

Complex coupling

Collectivity vs. multi- fragmentation

120-200

<8

5-30

5

-

-

2p

<1

LCP det.

HI det.

Complex coupling

Radiative capture

20-30

<3

1-30

<4

5

-

4p

<1

HI det.

High eff.

Multiple Coulex

40-60

<7

2-6

5

-

-

2p

<5

AGATA

CD det.

Complex coupling

Astrophysics

16-90

0.1

0.1-6

6

5

-

4p

<1

Outer PARIS shell as active shield

High eff.

Back-ground

Shell structure at intermediate energies (SISSI/LISE)

16-40

20-40

0.5-4

 

3

-

-

 

3p

 

<<1

 

 

SPEG or VAMOS

 

High eff.

Low Ibeam

g-g coinc

Shell structure at low energies (separator part of S3)

30-150

10-15

0.3-3

3

-

-

3p

<<1

Spectrometer  part of S3

 

High eff.

Low Ibeam

g-g coinc

Relativistic Coulex

40-60

50-60

1-4

4

-

1

Forward 3p

<<1

AGATA

HI analyzer

Ang. Distr.

Lorentz boost

 

In line with the above, the group is nowadays investigating how accurately a given physics point can be probed with the resolution to be foreseen in experiment. This study is progressively deepened thanks to the fast progress of the ‘Simulations’ working group. It recently led to concrete propositions for the key experiments to be run at the different stages of the development of the device.

As priority flagship experiments, two reactions among the early physics cases of the Letter of Intent (Jacobi transition and radiative capture) have already been chosen, and the most relevant system concerned with the new PARIS topics is presently under discussion.

 

(1) Seven physics cases have been presented in the SPIRAL2 Letter of Intent. They are:

- Jacobi shape transitions (A.Maj, J.Dudek)

- Shape phase diagrams with the GDR differential method (A.Maj, I.Mazumdar)

- Hot GDR studies in neutron-rich nuclei (D.R.Chakrabarty, M.Kmiecik)

- Isospin mixing at finite temperature (M.Kicinska-Habior)

- Onset of multifragmentation and GDR (J.P.Wieleczko)

- Reaction dynamics around the barrier by means of γ–ray measurements (C.Schmitt, O.Dorvaux)

- Heavy-ion radiative capture (S.Courtin, D.Jenkins)

 

(2) Five more topics are seriously envisaged to be added to the early PARIS physics cases list, encompassing:

- Multiple (normal) Coulex (P.Napiorkowski, F.Azaiez, A.Maj)

- Shell structure at intermediate beam energies (Z.Dombradi, F.Azaiez)

- Nuclear astrophysics (S.Harisopulos)

- Relativistic Coulex (P.Bednarczyk)

- Shell structure with PARIS@S3 (F. Azaiez)