Lifetime measurement of the 6.791 MeV state in 15 O

1. Lifetime measurement of the 6.791 MeV state in 15O Naomi Galinski SFU, Department of Physics, Burnaby BC TRIUMF, Vancouver BC CAWONAPS, 10 December 2010 Recipient of a DOC-FFORTE-fellowship of the Austrian Academy of Sciences at the Institute of SFU

2. Globular clusters: Oldest known/visible objects in our galaxy Compact groups of 100,000 - 1 million stars 1980: 16-20 Gyr Now: 10-15 Gyr Age of the universe: WMAP  13.7±0.2 Gyr Globular clusters can’t be older than the universe Motivation 1) Primordial gas cloud 2) Globular clusters form first L. Krauss and B. Chaboyer, Science 299, 65 (2003) 3) Galactic disk forms 4) Globular clusters occupy galactic halo

3. Age determination of globular clusters: Correlation between luminosity at MS turnoff point & age globular cluster CNO cycle dominates energy production at end of MS lifetime 14N(p, γ)15Ois the slowest reaction Reaction rate uncertainty could change globular cluster age by 0.5-1 Gyr Motivation Red giant branch (He->C) MS turnoff point Main sequence (MS) branch (H->He) Luminosity Temperature

4. Need to know 14N(p, γ)15Oreaction rate at low (stellar) energies E0 30 keV (for T = 0.02 GK) Past experiments only go down to ECM = 70 keV Energy below low-energy limit of direct γ ray measurements Need to extrapolate down to low energies using R-matrix analysis of S-factor The 14N(p, γ)15Oreaction Formicola et al., Phys. Let. B 591, 61-68 (2004)

5. S-factor of 14N(p,)15O reaction R-matrix fits to the 14N(p,)15O 6.79 MeV transition. Review article: Solar fusion cross sections II, the pp chain and CNO cycles, arXiv:1004.2318v3 [nucl-ex] 10 Oct 2010 Total S-factor of the 14N(p,)15Oreaction with contributions of different transitions to states of 15O. Angulo et al., Nucl. Phys. A 690, 755-768 (2001) • Largest remaining uncertainty in reaction rate is due to width, , of 6.791 MeV state • This will constrain the R-matrix fit • Obtain width from lifetime:  = ℏ / 

6. Previous measurements • Results marginally disagree • Only one group, Bertone et al., has claimed central value • This value is not generally accepted

7. Doppler Shift Attenuation Method (DSAM) 3He + Au  ejectile Au  15O 16O E(t)=max (0)=max E(t)=0 (t)=0 • In DSAM an excited recoil populated by a reaction decays as it slows down in a heavy foil • The Doppler shifted energy of  rays emitted from a recoil traveling with reduced velocity (t)=v(t)/c is given by: Simulated lineshapes for different lifetimes. These are fit to the data to determine the lifetime of the excited state.

8. DSAM and 6.791 MeV lifetime 3He + Au Au 15O  E(t)=max (0)=max E(t)=0 (t)=0  3He 16O 15O • Lower  limit of DSAM ~1 fs •  of 6.791 MeV state ~1 fs • For accuracy need to know stopping powers • Electronic stopping power better known • Nuclear stopping not known so well • Previous measurements low recoil velocity (≤0.0016) • Nuclear stopping region • 14N+p →γ+15O • We had higher recoil velocity (≤0.055) • Used inverse kinematic reaction • 3He+16O→α+15O

9. Experiment TRIUMF ISAC II: • Stable beam of 16O at 50 MeV (1st run) and 35 MeV (2nd run) • 3He was implanted in a Au and Zr target foil. • We used the Doppler shift lifetime (DSL) chamber, a target chamber specifically designed for DSAM experiments. • The  rays were detected using a GeTIGRESS detector on a single mount

10. Experimental setup 15O   • 3He+16O→α+15O E Si detector (100 μm and 25 μm) Vacuum chamber E Si detector (500 μm) 16O beam 16O Au/Zr foil (25 μm) Implanted 3He (6×1017 atoms/cm2) TIGRESS detector at 0° Collimator

11. Doppler Shift Lifetime chamber

12.  ray spectrum Full energy peak Single escape peak Double escape peak 5239.9 keV 15O 5183 keV 15O Doppler shifted 6176.3 keV 15O Doppler shifted 511 keV 6791 keV 15O Doppler shifted 937 keV 18F 3He(16O,p) 1369 keV 24Mg 12C(16O,4He) keV Fig. Add back spectra of  rays using the Zr foil

13. Si detector particle ID spectrum Light charged particles from 3He + 16O → x + X Heavier ejectiles dE [Ch]  (15O) 3He (scat) p (18F) E [Ch] Fig. Si 2D spectrum from Zr foil. It is the energy deposited in the dE Si detector vs. the energy deposited in the E Si detector. Ejectiles can be identified this way.

14.  ray spectrum gated on  Ungated spectrum Spectrum gated on  particles Au foil 2nd run Zr foil 2nd run Au foil 1st run Figures: Doppler shifted 6.791 MeV  ray peak for the 1st and 2nd experiment using either Au or Zr target foils.

15. Lifetime fit of 6.791 MeV state from the first experiment PRELIMINARY Lifetime = fs Sky Sjue

16. Work in progress • Analysis of 1st data set: • Refine calibration of  ray energy to get correct addback spectra • Need to know centroid with precision within 1 keV • Analysis of 2nd data set: • Check GEANT4 simulation of kinematics of alpha particles • Get lifetime of 6.791 MeV state from: • lineshape analysis from Au foil data • lineshape analysis from Zr foil data • centroid shift analysis from Au and Zr data

17. Collaborators: B. Davids1, S. Sjue1, T.K. Alexander, G.C. Ball1, R. Churchman1, D.S. Cross1,2, H. Dare3, M. Djongolov1, H. Al Falou1, P. Finlay4, J.S. Forster5, A. Garnsworthy1, G. Hackman1, U. Hager1, D. Howell2, M. Jones6,R. Kanungo7, R. Kshetri1, K.G. Leach4, J.R. Leslie8, L. Martin1, J.N. Orce1, C. Pearson1, A.A. Phillips4, E. Rand4, S. Reeve1,2, G. Ruprecht1, M.A. Schumaker4, C. Svensson4, S. Triambak1, M. Walter1, S. Williams1, J. Wong4 1TRIUMF, Vancouver, BC, Canada 2Dept. of Phys., Simon Fraser University, Burnaby, BC, Canada 3Dept. of Phys., University of Surrey, Guildford, UK 4Dept. of Phys., University of Guelph, Guelph, ON, Canada 5Dept. of Phys., Université de Montréal, QC, Canada 6Dept. of Phys., University of Liverpool, Liverpool, UK 7Astr. and Phys. Dept., St. Mary’s University, Halifax, NS, Canada 8Dept. of Phys., Queen’s University, Kingston, ON, Canada Receipient of a DOC-FFORTE-fellowship of the Austrian Academy of Sciences at the Institute of SFU

18. Simulation  ejectile 15O recoil Reaction kinematics Intrinsic lineshape of high energy  rays of the TIGRESS detector Beam and target characteristics Angular detection efficiency of the  ray detector • Stopping power and straggling of recoil as a function of time in the target Sky Sjue

19. Stopping mechanisms for recoils • Nuclear stopping: (<0.005) • Collisions between atoms • Large energy loss • Changes direction of nuclei • Electronic stopping: (≥0.02) • Long range collisions with e- • Small energy transfer • Small deflection of nuclei

20. Reactions to measure lifetime • 14N(p,γ)15O • Direct kinematics • 15O has <0.0016 • Nuclear stopping region • 3He (16O,)15O* • Higher Q-value • Inverse kinematic reaction • 15O has <0.055 • Electronic stopping region • Cleaner signal with coincidence detection of  • We did previous measurements with 3He implanted foils

21. Globular cluster age uncertainties • Age estimated to be between 10 - 15 Gyrs • Biggest uncertainties comes fromderiving distances to globular clusters • Stellar evolution input parameters that can significantly affect age estimates: • Oxygen abundance [O/Fe] • Treatment of convection within stars • Helium abundance • 14N+p→15O+ reaction rate • Helium diffusion • Transformations from theoretical temps and luminosities to observed colors and magnitudes • Biggest effect of the nuclear reactions is 14N+p→15O+ • Accounts for 0.5 - 1 Gyrs variation in ages

22. S factor -> luminosity -> cluster age Degl’Innocenti et al., Phys. Let. B 590, 13-20 (2004)