Seeking the Purported Magic Number N32 with HighPrecision

Seeking the Purported Magic Number N=32 with High-Precision Mass Spectrometry Susanne Kreim November 4 th 2011 Overview Physics Aims Technical Novelties skreim@cern. ch

Physics Interest Z=20 N=32 M. Bissell, et al. , `Spins, moments, and charge radii beyond 48 Ca', INTC-P-313 (2011) G. Audi and M. Wang, private communication (2011) skreim@cern. ch

Structural Evolution Ø Evolution of shell strength ü Disappearing of magic numbers, appearing of new shell or sub-shell closures O. Sorlin, M. -G. Porquet, Porgr. Part. Nucl. Phys. 61, 602 (2008) ü Island of inversion at N=20: „intruding“ pf orbitals had to be included in calculations Ø Ordering of shell occupation from binding energies ü Low uncertainty needed because of small relative effect R. B. Cakirli et al. , PRL 102, 082501 (2009) ü Exacting test for nuclear models skreim@cern. ch

Sub-Shell Closure at N=32, 34? Ø Evidence for N=32 shell gap but not for N=34 ü Behavior of E(21+) energies in n-rich Ca isotopes H. L. Crawford et al. , PRC 82, 014311 (2010) N=32 Isotones ü Behavior of E(21+) energy of n-rich Ti isotopes S. N. Liddick et al. , PRC 70, 064303 (2004) B. Fornal et al. , PRC 70, 064304 (2004) ü Behavior of E(21+) energy of n-rich Cr isotopes J. I. Prisciandaro et al. , Phys. Lett. B 510, 17 (2001) Ø Theoretical predictions ü Shell gaps for N=32 and N=34 within shell-model calculations M. Honma et al. , PRC 65, 061301(R) (2002) ü BMF calculations confirm N=32 but negate N=34 T. Rodríguez et al. , PRL 99, 062501 (2007) S. N. Liddick et al. , PRC 70, 064303 (2004) skreim@cern. ch

Three-Body Forces Ø Pairing gaps reproduced ü ü Include NN and 3 N forces on the microscopic level Example: n-rich Ca isotopes full calculation needed Strong evidence for N=32 and N=34 shell gaps Pairing gap accessible via mass measurements N=28 shell closure N=32, N=34 shell gaps J. Menendez and A. Schwenk, private communication (2011) skreim@cern. ch

Current Performance of ISOLTRAP Ø Accuracy ≈ 1· 10 -8 achievable via frequency measurement to extract wanted mass Ø Half-life ≈ 60 ms Production yield ≈ few 100 ions per second Efficiency ≈ 1% Resolving power for isobar separation ≈ 105 Contamination ratio ≈ 104: 1 plus ≈ 103: 1 Resolving power for isomer separation ≈ 107 Time-of-flight detection via “Ramsey method” Ø Ø Ø M. Mukherjee et al. , Eur. Phys. J. D 22, 53 (2008) skreim@cern. ch

MR-To. F Measurement Mode Advantages: ü few 10 ms vs. few 100 ms measurement time → lower half-life ü high repetition rate → lower yield Disadvantage: üSeparation limit ~200, 000 üLess precise but well within limit of physic‘s case Alternative: üUse in stacking mode → higher contamination ratio R. N. Wolf et al. , Hyp. Int. 199, 115 (2011) skreim@cern. ch

Beam Time Requests Nuclei Shifts Target Ion Source 52 -54 Ca 6 UCx RILIS 52 -55 Sc 8 UCx RILIS 58 -60 Cr 6 YO or UCx RILIS Ø Half-lives between 50 ms and 10 s ü Ø Mass uncertainty between 200 -700 ke. V ü Ø 1 case only extrapolated 4 cases only extrapolated Yield between 100 and 104 ions/µC ü measured and extrapolated, already demonstrated at ISOLTRAP Ø MR-To. F mass separator calibration 0. 3 shifts per A → 3 additional shifts Ø MR-To. F measurement mode → 4 additional shifts skreim@cern. ch

Outlook Ø Measurements on atomic Sc in 2012 ? not accessible via in-trap decay ü 52 Sc test case for ongoing UV break-up studies ü 55 Sc only accessible with direct MR-To. F measurement ü Laser-ionization scheme could be enhanced ü Ø 52, 55 Sc Measurements on Cr in 2014 ? ü Feasible with laser-ionization scheme skreim@cern. ch

The ISOLTRAP Collaboration . . . with support from our newly established collaboration with theory group of Achim Schwenk: Thank you! skreim@cern. ch

Three-Body Forces Ø Current limitations for medium-mass nuclei ü Theoretical approaches based on phenomenology ü Extrapolations to n-rich nuclei suffer from large divergence ü 3 N forces not included Ø Chiral Effective Field Theory ü low-energy approach to QCD ü Include NN and 3 N forces on the microscopic level ü Test nuclear forces also for exotic nuclei: example O dripline Ø 3 N forces for SM calculations ü 2 valence, 1 core particle → (effective) TBME ü 1 valence, 2 core particles → effective SPE T. Ostuka et al. , PRL 105, 032501 (2010) skreim@cern. ch

N-Rich Ca Isotopes Ø Pairing gaps reproduced ü 3 rd order MBPT + 3 N forces + pfg 9/2 space ü Strong evidence for N=32 and N=34 shell gaps ü Pairing gap accessible via mass measurements N=28 shell closure N=32, N=34 shell gaps J. Menendez and A. Schwenk, private communication (2011) skreim@cern. ch