1. Tracking Background GRETINA Software Working Group Meeting September 21-22, 2012, NSCL MSU I-Yang Lee Lawrence Berkeley National Laboratory

2. Outline  Tracking principle  Status and results  Future developments Sept. 21, 2012GRETINA SWG2

3. July 21, 2008UCB-UT Summer School3  -ray interactions  In a detector with dimension comparable to the attenuation length, a gamma-ray will interact several times before it is fully absorbed (full energy) or escape (partial energy) Examples in a Ge detector: 0.05 MeV : photo absorption 1.0 MeV : several Compton scatterings + photo absorption (full energy) or escape (partial energy) 10.0 MeV : pair production + absorption of both 511 (full energy) or escape of 1 or 2 511 (partial energy)

4. July 21, 2008UCB-UT Summer School4 Multiple interactions  Example : 1.332 MeV in 8  9 cm tapered Ge detector ̶ Compton scatterings, escape ̶ Compton scatterings, photo absorb ̶ No interaction

5. July 21, 2008UCB-UT Summer School5 What is tracking  Use the position and energy of each of the interaction points determined by signal decomposition  Use properties of  -ray interactions.  Determine the  -ray scattering sequence –Sum only the interactions belonging to a gamma ray, resolve multiple gamma rays. –The position of the first interaction – Doppler correction

6. July 21, 2008UCB-UT Summer School6 Tracking principle Source location and interaction points are known 1)Assume full energy is deposited 2) Start tracking from the source E  = E e1 + E e2 + E e3 For N! possible permutations, check interaction points for Compton scattering condition: Select the sequence with the minimum  2 <  2 max  correct scattering sequence  rejects partial energy event  reject gamma rays with wrong direction N=5 E e1 E e2 E e3 θ1θ1 θ2θ2 source EE E’ 

7. July 21, 2008UCB-UT Summer School7 Tracking issues  Computing time  N!. Cut off large N events, or better algorithm  Finite position and energy resolutions. Trade-off efficiency vs. P/T depending on experimental requirements 4 ! = 24 8 ! = 40,320 12! = 479,001,600

8. July 21, 2008UCB-UT Summer School8 Tracking algorithm Any two points with  <  p are grouped into the same cluster 1)Group interaction into clusters 2)Tracking each cluster  multiple  -ray hitting the detector

9. July 21, 2008UCB-UT Summer School9 Tracking algorithm INPUT Position and Energy of Interactions From Signal Decomposition Cluster Identification Based on Angular Separation Tracking Clusters Using Compton and Pair-production Formulae GoodAddSplitBad OUTPUT Gamma Rays Reconstructed Energy, Interaction Points, and Scattering Sequence Split-Add Split Clusters  Use 3-D position of interactions  Determine principle axes of cluster moment  Split cluster perpendicular to the axes Principle axis Split Add

10. Tracking improvements  Selectively add back single hit events  Improve  2 cuts  Speed up tracking by early termination  Improve cluster creation and splitting  Using  -ray angular distribution and range  Coupling with signal decomposition Sept. 21, 2012GRETINA SWG10

11. Future improvement Use physical properties of clusters in additional to geometrical information:  Number of interaction as a function of energy  Energy distribution of interactions  Use learning algorithms Sept. 21, 2012GRETINA SWG11 Improve cluster creation and splitting

12. July 21, 2008UCB-UT Summer School12 Future improvement  Angular distribution information  Range information However, These are probabilistic formulae Using  -ray angular distribution and range

13. Future improvement  Receive several possible decomposition results for a given event.  Use tracking to determine the best set of interactions. (e.g. 1 point vs. 2 closely spaced points). Sept. 21, 2012GRETINA SWG13 Coupling with signal decomposition

14. Cave 4C set up 5-module setup at Cave4C 88-Inch cyclotron

15. Number of interactions Fusion 40 Ar + 122 Sn Excitation of 197 Au No. of interactions / event

16. Tracking results  Event with 17 interaction points given by decomposition.  Tracking constructed 4 good gamma rays from 13 points. /global/data1x/gretina/Cave4CApr11/Run056/Global.dat 2 nd event

17. Effect of ignoring single hit Alpha = 10°, ≥ 2 interaction/cluster, all FOM  Include 1-hit event if r < r (E) will recover 90% peak counts

18. MSU configuration MSU18

19. Effect of include 1-hit event Clustering Track with 1-hit Track no 1-hit 133 Ba  Include 1-hit event if r < r (E)

20. 60 Co tracking Crystal P/T = 0.24 Clustering 0.40 Tracking no 1-hit 0.55 MSU20 Tracking cut at 79% efficiency

21. GRETINA v.s. Gammasphere MSU21 Tracking + 1 hit z-cut (eff. = 92%) Gammasphere Normalized to 1408 keV 152 Eu

22. Experiments at NSCL [rad] in GRETINA energy [keV] (laboratory frame) Doppler-reconstructed gamma-ray spectrum for 3-6 interactions in GRETINA for 28 Si γ rays of 28 Si at v/c = 0.38 in GRETINA FWHM: 1% 28 Si from 36 Ar fragmentation

23. Tracked 28 Si spectrum MSU23 2 + area Crystal21836 Clustering27149 Tracking20755

24. 64 Ge from 65 Ge Tracked with 1 hit E  (1 keV/ ch) Crystal 8/22/2012e2524

25. 64 Ge crystal Total projection 8/22/2012e2525 Gate 677 keV Gate 902 keV

26. 64 Ge track Total projection Gate 677 keV Gate 902 keV 8/22/2012e2526

27. Summary  Current version of tracking algorithm performed as expected based on a position resolution about 2- 2.5 mm RMS, 1% energy resolution at v/c=0.4.  Many opportunities exist for further improvements. Sept. 21, 2012GRETINA SWG27