Two-Proton Halo Structure

Transcription

1 DREB 2012, Pisa, Italia Breakup Reactions of Ne to Study its Motivation: Nuclear Structure of Ne & Astrophysics Impact Experimental Methods: Knockout Reactions & Coulomb Dissociation Results: Proton Knockout and Inelastic Breakup on a C Target Ingredients to the 2p-Removal Cross Section Ne 3-Body/Coulomb Spectra Summary & Outlook Two-Proton Halo Structure Felix Wamers 1,2, Justyna Marganiec 2,3 for the R 3 B collaboration 1 Institut für TU Darmstadt 2 Kernreaktionen u. Nukl. GSI 3 Extreme Matter GSI Felix Wamers, TU Darmstadt DREB 2012, Pisa, 28 th of March

2 The Ne Nucleus - Why is it interesting? Ne is a proton-dripline nucleus, with strong indications of having a 2p halo Zhukov & Thompson, PRC 52 (1995) 3505 Ne O p p Ne O + 2p, a borromean 3-body system (p-p and 16 F are unbound) S 2p = 950 kev T 1/2 = ms (β + to F) Groundstate J π =1/2 - ; no bound exc. states Is there a 2p-halo? Is there 50% s- or p-wave content in the valence protons? 1p 3/2 1s 1/2 Neutrons 2s 1/2 1p 1/2 1d 5/2 1p 1/2 1p 3/2 1s 1/2 Protons Shell model view of the Ne ground-state? Grigorenko et al., PRC 71 (2005) (R). 3-body cluster model: s 2 content 48%. Geithner&Neff et al., PRL 101 (2008) Q-radius measurement + FMD: 42% s 2. Tanaka et al., PRC 82 (2010) Reaction cross-sections: Long tail in Ne matter density, dominant s 2 configuration. Oishi et al., PRC 82 (2010) body model: s 2 content %. Felix Wamers, TU Darmstadt DREB 2012, Pisa, 28 th of March

3 O(2p,γ) Ne in Nuclear Astrophysics: X-ray Bursts, rp-process, Neutron Stars Cataclysmic binary systems (X-ray bursts): rp-process Görres et al., PRC 51 (1995) 392 CNO cycle: 14 N(p,γ) O(β - ) N(p,a) O is a waiting point for CNO-cycle breakup: Heavier elements: O(α,γ) 19 Ne(p,γ) Alternative (rp): O(2p,γ) Ne(β - ) F(p,γ) Mg 20 Mg 21 Mg 22 Mg 23 Mg 24 Na 18 Na 19 Na 20 Na 21 Na 22 Na 23 Ne 16 Ne Ne 18 Ne 19 Ne 20 Ne 21 Ne 22 Proton Number Z rp-process νp-process p-process s-process O 13 F O 14 F 16 O F O 16 F 18 O F 19 O 18 F 20 O 19 F 21 O 20 N 12 N 13 N 14 N N 16 N N 18 N 19 C 11 C 12 C 13 C 14 C C 16 C C 18 r-process B 10 B 11 B 12 B 13 B 14 B B 16 B Fusion up to iron Neutron number N The reaction rate can be enhanced by a few orders of magnitude by taking into account the three-body continuum states. Grigorenko et al., PLB 641 (2006) 254 Felix Wamers, TU Darmstadt DREB 2012, Pisa, 28 th of March

4 The S318 Experiment: Coulomb Dissociation of Ne Lead Target: Ne(γ,2p) O O + p + p Ne Ne* O p p virtual photons O p p p O Projectile nat Pb Pb-Target p Ne Excitation energy spectrum virtual photon theory ( γ, ) σ PD 2 p detailed balance theorem Cross section for reverse reaction: radiative capture on O(2p,γ) But also: Ne nuclear-structure Felix Wamers, TU Darmstadt DREB 2012, Pisa, 28 th of March

5 The S318 Experiment: Nuclear Inelastic Excitation of Ne Inelastic / Diffractive Scattering Ne Ne* O p p Projectile nat C O p p C-Target p p O - (Nuclear) inelastic excitation O+p+p final channel - Ne relative-energy spectrum - Competition/Interference with EM (Coulomb) excitation - Estimation (and subtraction) of nucl. background of the Pb target - Source of contamination for the 1p knockout channel Felix Wamers, TU Darmstadt DREB 2012, Pisa, 28 th of March

6 The S318 Experiment: One-proton Knockout from Ne One-proton Knockout Ne p 16 F* O p p nat C O p p O Proton Internal Momentum r 16 p proton = p r ( F ) Projectile C-Target One-proton knockout O+p final channel - 16 F relative energy spectrum - Knocked-out proton s internal momentum distribution via momentum of 16 F Glauber-type reaction model Angular momentum of knocked-out proton s 2 /d 2 configuration mixture in Ne Felix Wamers, TU Darmstadt DREB 2012, Pisa, 28 th of March

7 The S318 Experiment at GSI Production of Radioactive Ne Beams Ion sources: 20 Ne Linear Accelerator UNILAC: AMeV SIS Synchrotron SIS: AMeV Thick Be-Target ESR FRS Fragment Separator: Select Ne Bρ = p Q A βγ Z Experimental Halls Cave C, R 3 B/LAND setup: 500 AMeV Felix Wamers, TU Darmstadt DREB 2012, Pisa, 28 th of March

8 The S318 Experiment: 500 AMeV Ne beams R 3 B/LAND << FRS Cave C >> ToF distance: ~ m Beam from FRS Active slit ROLU Scintillator POS γ-rays + Protons Dipole magnet ALADIN 0 Neutrons Fibre, GFI Veto ToF-wall LAND Scintillators S2, S8 Position-sensitive PIN diodes, PSP Target TGT Crystal Ball, XB Si-strip SST Drift chambers PDC Protons TFW 16.7 Fragments ToF walls (scint.) NTF Beam detectors: (Crystal Ball: (DSSSD box: Aladin: Fragment arm: Proton arm: (LAND: Tracking & ID of incoming Ne beam 4π NaI shell, γ-rays and recoil protons) Tracking & ID of recoil protons) Dipole magnet to deflect fragments and protons Fibre detectors and a small ToF Wall Drift Chambers and a large ToF Wall Large-Area Neutron Detector) Felix Wamers, TU Darmstadt DREB 2012, Pisa, 28 th of March

9 Selection of Reaction Channels One-Proton Knockout from Ne Ne ~ 500 AMeV: C Target Identification of oxygen mass O 14 O 13 O Ne(C,X) 16 F O + p Tracking of fragments and protons Proton-multiplicity distribution 0 1 = 1p-knockout Mass and Momentum of Fragment Momenta and Multiplicity of Protons 2 = inelastic exc. Felix Wamers, TU Darmstadt DREB 2012, Pisa, 28 th of March

10 One-Proton Knockout from Ne 16 F Excitation Energy 16 F* Invariant Mass (P µ P µ ) E rel ( O+p) m2 + m1m2γ 1γ cos ( 1 β β ) ( m ) E rel = m 2 ϑ + m 1,2 1 2 Grigorenko, PRC 71 (2005) (R). Exclusive selection of knockout from halo -states possible Felix Wamers, TU Darmstadt DREB 2012, Pisa, 28 th of March

11 Halo -Proton Knockout from Ne 16 F (= O+p) Transverse Momentum x-projection: w(s 2 ) ~ 38% y-projection: w(s 2 ) ~ 42% s-wave d-wave total s-wave d-wave total Glauber-type calculation (MOMDIS) Bertulani et al., CPC 5 (2006) 372 x and y projections equivalent Different results reflect systematic uncertainty of the measurement s-wave content of ~41% in the Ne halo (weighted average) Indication of a moderate halo character of Ne Good agreement with most theoretical predictions Felix Wamers, TU Darmstadt DREB 2012, Pisa, 28 th of March

12 2-proton-removal cross section Partial cross sections, spectrosc. strength Ne(Target,X) 16 F O + X Calculations (MOMDIS), C. Bertulani CH 2 : 213 ± 5 mb C: 1 ± 4 mb (H: 48 ± 3 mb) Pb: 483 ± 30 mb σ σ + σ + σ 2 p ko _ 2 p ko _1p inel. Estimate for 1p-efficiency: 87% Single-particle cross sections: σ s = 52.7 mb σ d = 34.1 mb 41% s-wave content from 16 F mom.: σ calc = 0.41*σ s *σ d = mb Spectroscopic Strength : Percentage of halo knockout: 67% Corresponds to 71 mb. S = σ exp /σ calc = 1.7 Diffractive part still to be subtracted Felix Wamers, TU Darmstadt DREB 2012, Pisa, 28 th of March

13 Ne Breakup on Carbon: Experimental Response for Protons Proton Trigger Efficiency: 100 % within statistical error Proton Drift Chamber Efficiency: 1p: (87.0 +/- 0.5)% 2p: (75.6 +/- 0.9)% G3 Simulations with R3BRoot: 1- and 2-proton acceptance Felix Wamers, TU Darmstadt DREB 2012, Pisa, 28 th of March

14 3-Body Dissociation of Ne: Reconstruction of the 3-Body rel. Energy Tracking of 2p events after breakup on Pb or C targets J. Marganiec Felix Wamers, TU Darmstadt DREB 2012, Pisa, 28 th of March

15 3-Body Dissociation of Ne: Comparison of Different Targets J. Marganiec J. Marganiec Felix Wamers, TU Darmstadt DREB 2012, Pisa, 28 th of March 2012

16 3-Body Dissociation of Ne: Total Excitation on Pb 140 mb from knockout J. Marganiec Felix Wamers, TU Darmstadt DREB 2012, Pisa, 28 th of March

17 3-Body Dissociation of Ne: Coulomb Excitation on Pb J. Marganiec Felix Wamers, TU Darmstadt DREB 2012, Pisa, 28 th of March 2012

18 Coulomb Dissociation of Ne: O+p+p 3-Body Correlation Analysis J. Marganiec Felix Wamers, TU Darmstadt DREB 2012, Pisa, 28 th of March

19 Coulomb Dissociation of Ne: O+p+p 3-Body Correlations Exp. Sensitivity: Comparison of data to 100% s and 100% d-wave calculations J. Marganiec L. Grigorenko et al. Felix Wamers, TU Darmstadt DREB 2012, Pisa, 28 th of March

20 Summary & Outlook Summary - S318 experiment: Study of Ne in inverse kinematics - Carbon-induced proton knockout O+p - Carbon-induced inelastic excitation O+2p - Pb-induced Coulomb excitation O+2p - Preliminary Results: - Structure of Ne studied via 16 F transverse momentum after knockout A moderate s 2 content in the two Ne valence protons of ~ 40% is found - Analysis of partial cross sections in progress - Ne differential Coul.-Diss. Cross section determined - Recalculation into photodiss. and radiative-capture x.s. ongoing - Analysis of 3-body correlation observables promising for sufficient exp. sensitivity to determine s 2 /d 2 content in Ne g.s. halo. Felix Wamers, TU Darmstadt DREB 2012, Pisa, 28 th of March

21 Summary & Outlook Outlook - Near Future: - Finalise efficiency, acceptance and resolution for proton detection - Spectroscopic factors of Ne halo protons from partial cross sections - O* gamma rays simulations for XB response - Further Plans: - s/d ratio from shape of 16 F relative energy - Detailed understanding of higher excitation region in 16 F - Analysis of the (p,2p) quasi-free knockout channels - Work on theory: QFS reaction codes (C. Bertulani) Recent QFS experiments at LAND/R 3 B: -Talks by Alina Movsesyan - Posters by Leyla Atar, Matthias Holl, and Valerii Panin Felix Wamers, TU Darmstadt DREB 2012, Pisa, 28 th of March

22 Acknowledgements Thomas Aumann, Leonid Chulkov Leonid Grigorenko ( Ne structure) Michael Heil, Justyna Marganiec, Ralf Plag, Haik Simon, Carlos Bertulani (Reaction Theory), and the whole R 3 B collaboration. Thanks for your attention! Felix Wamers, TU Darmstadt DREB 2012, Pisa, 28 th of March