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PROGRESS ON M1 RESEARCH

PROGRESS ON M1 RESEARCH. Norbert Pietralla , TU Darmstadt. Thanks to organizers and influential contributions of Aldo C.! Outline Motivation N ew experimental techniques and approaches Relativistic M1-projectile COULEX: V ls in exotic nuclei ( 85 Br )

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PROGRESS ON M1 RESEARCH

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  1. PROGRESS ON M1 RESEARCH Norbert Pietralla, TU Darmstadt • Thankstoorganizersandinfluentialcontributionsof Aldo C.! • Outline • Motivation • New experimental techniquesandapproaches • Relativistic M1-projectile COULEX: Vls in exoticnuclei (85Br) • M1-precision measurements: towardsnuclearchargecurrents (6Li) • M1-scissors mode: Howwidedoesit „open“? (156Gd) • Summary

  2. Motivation • Magneticdipole (M1) transitionsare sensitive to • transitionchargecurrents (orbital) • transitionalspinmotion (spin-flip) • andyieldinformationon • proton/neutron-structureofnuclearstates • localspin-orbit splitting • i.e., dynamicsofeffectivedegreesoffreedomin thevalence-space g B E

  3. Tensor force, spin-orbit splitting, andevolutionofshellstructure • T. Otsuka et al. Quest forlocalmeasurementofVls

  4. Unique experimental signatureofVls? Spin-flip M1 transitions: direct observation of spin-orbit splitting 1p1/2 j< = l-1/2 Unique signature! 1p (l=1) B(M1;j<j>)  1 N2 j> = l+1/2 1p3/2

  5. Experimental challengeof fast M1 transitions in exoticnuclei 1+T=1of32S at 8.124 MeV (,‘) at HIS (Duke Univ.) • Strong M1 transitions [B(M1)  1 N2] aretypicallyvery fast [~ fs] • M1 from (in)directlifetimemeasurements (DSAM) difficult • Classicaltechniques • electronscattering • photonscattering • etc. • not applicabletoexoticnuclei • Need newapproach ! N.P. et al., NIM A 483, 556 (2002).  Relativistic M1-projectile COULEX

  6. Unique experimental signatureofp1/2? 0.47(5) N2 ??? 0.68(10) N2 89Y 85Br 87Rb Relativistic Coulomb excitation reactions athigh v/c large M1 matrix elements significantly contribute to total COULEX yield c(E2)  (1/)2 c(M1) – independent Possible at GSI Relativistic beam energies  50-70 % PreSPEC-AGATA need precise Doppler correction and reduce Doppler broadening Huge Doppler spread in -ray spectrum

  7. PreSPEC-AGATA @ GSI Schematic Setup Gamma-ray detection 2012: HPGe array using pulse- -2014 shape analysis and -ray tracking techniques (AGATA) BaF&LaBr scintillators (HECTOR+) picturefrom C. Domingo-Pardo et al., NIM A 694, 297-312 (2012) FRS (GSI, Darmstadt) particle selection: Bρ-ΔE-Bρ Particle identification: TPC tracking detectors ToF measurement Energy-loss measurement LYCCA (D.Rudolph, M.Bentley, P.Reiter et al.) Outgoing particle tracking and identification: Z identification via E-ΔE Mass identification via E-ToF

  8. PreSPEC-AGATA in Operation March 2014 Hector LYCCA AGATA FRS Beam 85Br 300 MeV/u ~2 104pps > 99% pure

  9. Experimental Challenges Beam fromaccelerator (or in-flightseparator) Nuclearreaction in a fixedtarget Excitedreactionproductsleavethetarget (flightdirectionchanges) Emission of Doppler-shiftedγ-radiation Need γ-energy in therestframeoftheemittingnucleus (Doppler-correction) Need thetracksofparticleandγ-ray Spectroscopicresolutiondepends onaccuratetrackreconstructionofboth, γ-rayandparticle!

  10. PreSPEC-AGATA Commissioning 2012:Coulomb Excitationof80Kr on Gold Coulomb excitationof80Kr FWHM 2% data: M.Reese (TU Darmstadt) forPreSPEC

  11. PreSPEC-AGATA Commissioning, 2012 Coulomb excitationof80Kr Secondaryfragmentationof80Kr data: M.Reese (TU Darmstadt) forPreSPEC

  12. M1 characterofthe1191-keV -ray • E2 and M1 X-sectionshavedifferent energydependence • c(E2)  (1/)2 • c(M1) – independent 85Br • Measure c at two energies 200 MeV/u, 300 MeV/u • Deduce |δ|fromratioc(300MeV/u) /c(200MeV/u) Example using same strengths as in stable 87Kr: B(M1;1/2-3/2-) =0.58 N2 B(E2;1/2-3/2-)≈1 Wu c(300MeV/u) /c(202MeV/u) = 0.87

  13. Two-Target Solution(TU Darmstadt) Idea: 2 targets. First targetthickenoughtoslow down beam from 300 to 200 MeV/u at thesecondtarget. All information in onemeasurement! • Working principle: • Lifetimeofexcitedstate ~50 fs. • Decayhappensdirectly after excitation. • Decaypositionequaltoexitationposition • Twopeaks will appear due to different detectionangles (Doppler-effect) • Excitation in firsttargethappens at high energy (300 MeV/u) • Exitation in secondtargethappens at lowerenergy (200 MeV/u) • Peaks geometricallyseparatedby Doppler-correction Reminder: Doppler effect

  14. Two-Target Solution: Simulations Simulated Peak shapes (Doppler-correctedEnergy vs. detection angle): • Pro‘s: • one beam energy • one FRS setting • same conditionsforbothenergies • thicktarget • increasedexcitation prob. • betterpeaktobackgroundratio • Con‘s: • thicktarget • increased angular straggling • increasedenergystraggling • increadedvelocityuncertainty

  15. First data on Relativistic M1-Projectile COULEX 85Br on Au Mar.2014 online spectra, 5 h, no Doppler corr. ~ 5% of total data data: M. Reese, C. Stahl, M. Lettmann (TU Darmstadt)

  16. ExpectedData: RealisticSimulation efficiencyfromperformancecommissioning backgroundfromfirstdata on 85Br datatakingfinished April 2014 data-analysis time: est. 2 yrs resultingsensitivity: B(M1) = 0.6(2) N2 > 90% M1 Simulation Doppler-correction on downstream-target Excitingnewwayformeasuringspin-orbit splittingofexoticnuclei at FAIR ! ThankstoPreSPEC-, AGATA-collaborations, andM.Reese, C.Stahl, M.Lettmann et al.

  17. M1 from orbital currents: Scissors Modehere: E2 / M1 competition M1 scissors mode: “How wide does it open?” TRM: N.LoIudice, F.Palumbo; IBM: F. Iachello; RPA: A.Faessler; SR: J. Ginocchio;…

  18. M1 scissorsmode: Photon scattering! • Scissorsmode • Classically: currentloop •  magneticexcitation: M1 N.P. et al., PRC 58, 184 (1998). E2 M1 NuclearScissorsMode A.Richter, Darmstadt, 1983

  19. Scissors mode of 156Gd in polarized -beam TU Darmstadt-NRF program @ HIS N.P. et al., PRL 88, 012502 (2002). N.P. et al., NIM A 483, 556 (2002). … data: T. Beck (TU Darmstadt) Weller et al.,Prog. Part. Nucl. Phys. 62 (2009) 257

  20. Multipole mixing ratio polarization plane  02 data: T. Beck (TU Darmstadt)

  21. Estimate for E2-strength of scissors band Alaga Rule: (good K quantum number) E2 M1 expect in 2+sc 2+1transition

  22. First evidence for transition? M1 E2 Peak isforsure not a gstransition! (from angular distribution)

  23. 3rd topic:6Li as Benchmark forab-initioNuclearStructureTheory Nuclear Quasideuteron-Configurations: A.F.Lisetskiy et al., Phys. Rev. C 60, 064310 (1999).

  24. S-DALINAC at TU Darmstadtworld-wideunique in EFT – energyregime Recirculating superconducting LINAC Niobium cavities, LHe cooled @ 2 K, 3 GHz cw e-beams, < 130 MeV,  60 A

  25. 6Li as Benchmark forab-initioTheory 3562 0+,T=1 parity forbidden M1 2185 3+,T=0 1474 4He + 2H 1+,T=0 0+ T=0 1+ T=0 6Li • Exp.: ΓM1=8.16(19) eV (from (e,e‘)) • S. Pastore et al., PRC 87 (2013):chiralcurrentscontributesignificantlytoΓM1 • GFMC withone-body EM currentoperator at leadingorder (impulseapproximation): 6.90(2) eV • GFMC with additional two-body meson-exchange currentsupto N3LO (χEFT): 8.41(3) eV L. Cohen and R. Tobin, Nucl. Phys. 14(1959) W.C. Barber et al., Phys. Rev. 120 (1960) E.C. Booth and K.A. Wright, Nucl. Phys. 35 (1962) W.C Barber et al., Phys. Rev. 41 (1963) S.J. Skorka et al., Phys. Rev. 47 (1963) W.L. Creten et al., Nucl. Phys. A120 (1968) F. Eigenbrod, Z. Phys. 228 (1969) V.K. Rasmussen and C.P. Swann, Phys. Rev. 183 (1969) J.C. Bergstrom et al., Nucl. Phys. A251 (1975)

  26. Principleof (Relative) Self Absorption1 1 F. R. Metzger, Prog. in Nucl. Phys. 7 (1959) 53; N.P. et al., PRC (1994). Use scatterer made of absorber material as „high-resolution detector“. scatterer scatterer calibrationtarget calibrationtarget Self Absorption: Decrease of Scattered Photons because of Resonant Absorption

  27. Determination ofGround-State Transition Width andBranching Ratio totheGround State • calculateRasfunctionof • selfabsorptionRexpdeterminedexperimentally • comparisongivesground-statetransitionwidth • 0  B(M1) • relative measurement: systematicssuppressed • sub-1% precisionbecomesfeasible

  28. Self Absorption Measurement on 6Li(Ch.Romig, TU Darmstadt, PhDthesis, 2014 in preparation) • scatterer: 5 g Li2CO3 (enrichedto 95% in 6Li) • calibrationtarget: 4.2 g 11B (sandwiched) • absorber: 10 g Li2CO3 (enrichedto 95% in 6Li) • endpoint energy: 7.1 MeV • 7 days w/o absorber • 8 days w/ absorber S-DALINAC data 2013 R = 0.5178 ± 0.0015 (0.3% relative uncertainty) 0 ? Staytuned… Ch.Romig, TU Darmstadt, 2014 HIS-2/ELI-NP will providethisprecisionforexcitations 2 ordersof magn. weaker !

  29. Summary and Outlook Progress on M1 Research • New experimental technologyandmethods (scientificopportunitiesfornuclearshellmodel) • „AvailabilityFrontier“ (Relativistic M1-projectile COULEX, local Vls in radioactiveexoticnuclei) • „SensitivityFrontier“ (intensepolarized-raybeams, weakchannels: strong physics) • „Precision Frontier“ (high countrates, newmethods)

  30. i 1 1 2 2 Source Electron Source 130 MeV Electron LINAC Photon Experiments 10 MeV Injector: Photon Scattering / Photofission < 30 MeV Tagger: Photodesintegration / Photon Scattering S-DALINAC at TU Darmstadt Thanksto • State of Hesse • TU Darmstadt • DFG

  31. Bremsstrahlung-Site

  32. Parityquantumnumber for J=1 states • Elasticscatteringdistribution not isotropicaboutincidentpolarization plane. • Nointensityalongoscillatingdipolevector • Azimuthalrotationby 90oforM1 and E1 distributions • Observable onlyforlinearlypolarized beam N.Pietralla, H.R. Weller et al., NIM A 483 (2002) 556.

  33. 1. AvailabilityFrontier • Current NRF measurementsrequire gramm-size targets (~ 1022-21nuclei) • Requiredby • crosssections (~ eV b) • detectionefficiency (~ 10%), • availableluminosity (numberoftargetnucleitimes-rayflux) • resonablylong beam times (orderofdays) • Rare p-processnuclei (106Cd,130Ba,156Dy,174Hf) ~ 0.1% ab., enriched material at ~$1,000/mg • Long-livedradioactive isotopes(10Be,182Hf,250Cm) T1/2 > ~10,000 yrs. 51 morenuclideswouldbecomeaccessibleto NRF A varietyofscientificquestionscouldbeanswered.

  34. 2. SensitivityFrontier • Search forweaksignals sensitive tothephysicsunderstudy • Oneexample: Rotational Moment of Inertia oftheScissors Mode • Other examples: • decaybranchingsinto sensitive channels • searchforpredictedpygmyquadrupoleresonance (PQR) • measurementofdecay E2/M1 multipole mixingratios • measurementofparity-mixing matrixelement in 20Ne • tobecontinued… 156Gd @ HIS Data: J.Beller, TU Darmstadt

  35. 3. Precision Frontier N. Pietralla et al., PRC 58, 184 (1998) • High Intensity = High countrates smallstatisticaluncertainties • addressunresolvedquestionsthatcannotbeansweredtodaybecauseofuncertainties • e.g., scalingofscissorsmodewithdeformation • evolutionof K-mixing in octupole-vibrationalbandsofdeformednuclei • the „unknownunknown“… 1+ 2+ • High Intensityenablesnewapproaches • e.g.  NuclearSelf Absorption

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