DIRECT REACTIONS WITH MUST and FUTURE with MUST2 and SPIRAL2 D. Beaumel, IPNO XV eme Colloque GANIL Giens, May 2006
Direct reactions using the recoil particle Method Exotic Beam + light target (CH2,CD2) Detect the target- like ejectile (E,!) LAB (E*,! CM ) Radioactive beam CH 2 CD 2 inelastic SPEG CATS1 CATS2 Stripping (d,p) The MUST array Cooling 8 Telescopes Connectors surface: 6x6cm 2 DS Strip 60X+60Y (300 µm) Si(Li) 3mm CsI Pickup reactions (p,d),(d, 6 Li), Good angular and E resolution Nice angular distributions! Bound and unbound states on the same footing Detectors Preamplifiers Need large angular coverage Thin targets of light nuclei 10 4-10 5 pps beams for transfer
(p,p ) reaction on neutron-rich oxygens Study the neutron magic number evolution with a neutron-sensitive probe (p,p ) ~50 MeV/A : protons interact 3 times more with neutrons of the nucleus M n /M p ratio of neutron/proton transition matrix elts P.G. Thirolf et al. PLB485(2000)16 22 O : Strong increase of the 2 + energy for the 22 O nucleus Decrease of the B(E2) Importance of the N=14 subshell closure? Exp QRPA Monte-Carlo Shell-Model
22 O(p,p ) reaction measured at SPEG 22 O Beam, 46 MeV/u 1200 pps MUST telescopes CATS2 3.2 (2) MeV CH 2 target
Analysis and results 2 kinds of OM analysis p h e n o m e n o l o g i c a l " DWBA calculations using v i b r. f o r m f a c t o r s " g l o b a l p o t e n t i a l s KD Folding microscopic " Microscopic form factors (continuum HFB +QRPA) " Microscopic optical potential - Folding model : CDM3Y6 interaction (Imaginary part : Koning&Delaroche) - Cross-check with JLM #$ p constrained with B(E2)
(M p from coulex experiments) results for M n /M p 20 O 22 O More balanced contributions of protons and neutrons to the 2+ in 22 O higher 2+ energy Strong N=14 shell-closure M i c r o P h e n o E.Becheva,Y. Blumenfeld, E. Khan, et al., PRL 2006
The light neutron rich nuclei 16 B 13 Be 10 Li 7 He 9 He 5 H 7 H 4 n Drip-line and beyond experimentally accessible Structures in core+xn, 1n and 2n haloes Molecular states ab initio calculations tractable
Results of GFMC calculations From R. Roth (S. Pieper, private comm.)
The light neutron rich nuclei 16 B 13 Be 10 Li 7 He 9 He 5 H 7 H 4 n Drip-line and beyond experimentally accessible Structures in core+xn, 1n and 2n haloes Molecular states ab initio calculations tractable
Search for Tetraneutron at SPIRAL/GANIL RI Beams : new opportunities for studying multineutron systems?? Prepared clusters in light neutron-rich nuclei (Ikeda) observable using simple reaction Recently : 14 Be Break-up experiment @ GANIL (F.M.Marques et al. PRC(2002)) 10 Be 6 events compatible with a bound 4 n! E p /E n in neutron counters
Predictions for tetraneutron UNBOUND! Attempts to bind the tetraneutron Slight changes of 2-body forces modify 3-body forces Add 4-body (T=2) I show that it does not seem possible to change modern nuclear Hamiltonians to bind tetraneutron without destroying many other successful predictions of those Hamiltonians. This means that, should a recent experimental claim of a bound tetraneutron be confirmed, our understanding of nuclear forces will have to be significantly changed S. C. Pieper, PRL 90, June 2003 it is pointed out that from the theoretical perspective the two-body nucleon-nucleon force cannot by itself bind four neutrons, even if it can bind a dineutron. A very strong phenomenological four-nucleon (4N) force is needed in order to bind the tetraneutron. Such a 4N force, if it existed, would bind 4 He by about 100 MeV N.K. Timofeyuk, J.Phys, January 2003
Our alternative approach to B.U. reactions % 8 He very neutron rich large Overlap < 8 He % & 4n > (d, 6 Li) well known! transfer reaction : large Overlap < 6 Li 4 He & d> ' cross section ~ few mb/sr mb/sr 12 C(d, 6 Li) 8 Be E = 9.5 MeV/u Missing mass measurement : ' Energy of the states ' Bound and resonant states on the same footing! CM H.H.Gutbrod et al., Nucl. Phys (1971)
Setup of E465s at G3-SPEG d( 8 He, 6 Li) SiLi MUST 65 µm Si Dubna Delivered by SPIRAL Si MUST 8 He beam @15.8MeV/u (~2.5.10 4 pps) CATS1 4 n 6 Li CD 2 Target 1.65 mg.cm -2 CATS2 Plastic (x2)
Results 8 He(d, 6 Li)4n Neutron gated Bound Unbound Nombre de coups 4 n Pure 5-body FSI (nn_nn) 12 C E.Rich, Ph.D thesis E CM CM (4n) MeV No evidence for a bound tetraneutron correlations between the 4 neutrons
Parity inversion in N=7 isotones E b (MeV) 2 Inversion of 2s 1/2 et 1p 1/2 shells 15 O 14 N 13 C 12 B 11 Be 10 Li 9 He? 0 11 Be(d, 3 He) 10 Li with MUST -2-4 -6-8 -10 1/2 + N=7 isotones Counts S n 2s 1/2 neutron S.P.state -12-14 1/2-8 7 6 5 4 3 Z How about 9 He? E CM (MeV) S. Pita, PhD thesis, IPN Orsay
Previous 9 He results 9 Be( 14 C, 14 O) 9 He H.G. Bolen et al. PPNP 42(1999) Proposed 9 He level scheme ) M = 40.94 MeV 5.25 [4.30] [5/2 + ] 2.42 [3/2 -,1/2 + ] 9 Be(( -,( + ) 9 He K.K. Seth et al. PRL 58(1987) ) M = 40.8 MeV GS: +1.27 0.0 9 He 1/2-8 He+n H.G. Bolen et al. PPNP 42(1999)17-26 But evidence of an l=0 GS from ( 11 Be, 8 He+n) Chen et al., PLB 505 (2001) Study of 8 He(d,p) 9 He E. Tryggestad et al.
Experimental setup: 8 He(d,p) 8 He BEAM Plastic detectors
Parity inversion in 9 He
The Array Collaboration: IPNO,SPhN/Saclay,GANIL M U S T 2 : a m a j o r u p g r a d e o f M U S T I n c r e a s e a n g u l a r c o v e r a g e " B e t t e r e f f i c i e n c y " Measure several reactions in one shot Increase granularity (multiparticle events) New electronics to handle the increase of channels 10cm DSSD 128+128 300µm Si(Li) 4.5mm CsI(PD) 4cm ASICs 16 channels E and T
- PLAN -BASICS -Exp. Method. Inv Kinematics MUST II -MUST II. Geometry -MATE (ASIC).Signals process.slow Control -Data Acquisition. Trigger. Dead-Time - WHO 36 MUVI 2.3K parameters 16 ADC14 bits Slow Control I2C 2 MHz 288 Energy Spectra 150 KeV Threshold 40 KeV FWHM % 288 Time Spectra 500 psec FWHM
ANALYSE (SUITE) : Analyse des spectres à poursuivre : 4n, 3n, 2n Autres données à etudier : 9 He, 8 He, 7 He, 7 H = Informations sur interaction nn AMELIORATIONS SOUHAITEES : Intensité du faisceau (?) Cible mince deutérium pure (?) MUST II
Outlook Broad Physics program for Direct Reactions with MUST2! Shell evolution through 1-nucleon transfer reactions e.g. 68 Ni(d,p)! Astrophysics, e.g. 60 Fe(d,p)! 60 Fe(n,!)! 2-nucleon transfer reactions "d-transfer for neutron-proton pairing in N=Z nuclei "2p- and 2n-transfer: detailed spectroscopy very far from stability! Helium induced reactions - cryogenic target developed different selectivity Ex: (", 3 He) alternative to (d,p)! Pygmy resonances (in proton-rich nuclei), GMR studies! etc
Near future (2007 ): + TIARA BT Det ExoGam TIARA VAMOS First application : study of np pairing in N=Z nuclei
New generation arrays for DR studies From SISSI/SPIRAL to Light ions (!Ar) * Heavier ions (Fission fragments) Lower Incident energies * slight shift of (E,!) plots H i g h l y d e s i r a b l e i m p r o v e m e n t s : Increase particle-gamma coincidence efficiency I m p r o v e P I D o f l o w e n e r g y p a r t i c l e s Improve capability of multi-reaction studies (e.g. (dp)(d,n)) I n t e g r a t e n e w l i g h t - i o n t a r g e t s
Existing concept: EXL Si+Si(Li)+CsI To be installed at NESR ESPA (EXL Silicon Particle Array) EGPA (EXL Gamma and Particle Array) R&D @ IPNO
SPIRAL2 Erecoil (MeV) E recoil (MeV) 100 10 1 Si/CsI - Tracking Si DE-E Si - PSD Si - TOF 132 Sn(p, p) E=740 MeV/u, E* = 0 MeV 18 C(", ") E=400 MeV/u, E* = 0 MeV 18 C(p, p') E=400 MeV/u, E* = 25 MeV 196 Pb(", "') E=400 MeV/u, E* = 15 MeV 196 Pb( 3 He, t) E=400 MeV/u, E* = 0 MeV 12 Be( 3 He, t) E=400 MeV/u, E* = 0 MeV 22 C(p, d) E=15 MeV/u, E* = 0 MeV 132 Sn(d, p) E=15 MeV/u, E* = 0 MeV 0.1 20 40 60 80 100 120 140 160!! lab (deg) recoil (deg)
Working Group on new generation particle+gamma arrays for DR studies starting point : Discussion group @ SPIRAL2 Reactions Workshop (Oct 2005) Scope : " Design a new (particle+gamma) array " Setup a collaboration Timescales : design: ~2 years, build: 3-4 years Autum 2006 : LoI for GANIL Synergies with : " Reaction dynamics (FAZIA) " Gamma calorimeters Next meeting : June 26-27 th in Daresbury -- Join!