1. A new Si recoil tracking detector for the R 3 B experiment at GSI Nick Ashwood The University of Birmingham

2. Outline  Motivation  Suppression of spectroscopic factors  Quasi-free scattering  Current work  GSI and current experimental set-up  Future plans  Upgrade for FAIR and R 3 B  New detectors  The new Si tracking detector  The R 3 BRoot simulation package  Design considerations  Physics simulations  Mechanical design and electronics  Further work

3. Shell structure

4. Modification of shell structure  Unlike atomic shell structure, the nuclear shell model is under a potential of it’s own making.  Choice of potential alters magic numbers. Solution of the Schrodinger equation determines energy levels of the states and hence the magic numbers.

5. Modification by the tensor force  Tensor force first introduced by Yukawa through exchange of  mesons.  Spin orbit partners attract each other.  Similarly “anti-partners” repel each other. T Otsuka et al. PRL 105, 032501 (2010)

6. Direct Reactions R Lemmon private communication

7. Spectroscopic factors  Nuclear structure can be determined for the differential cross-section of the reaction for a give state.  Important quantity is to measure is the spectroscopic factor.  The spectroscopic factor describes how close the state is to being a pure shell model state.  Controversy over whether spectroscopic gives true indication of orbit occupancy.  Measurements only in asymptotic region.

8. Spectroscopic factor controversy  Many arguments over whether spectroscopic factors are a “good” measurement of shell structure.  Direct reactions only measure at the periphery of the nucleus where the measurements are biased towards 100% occupancy of the state.  A better measurement would be relative spectroscopic factors or ANC’s Possible way round this is to use high energy direct reactions which can probe deeply bound states i.e. QFS Removal of weakly bound nucleons result in no reduction of spectroscopic factor A Gade et al. PRC 77 044306 (2008)

9. Quasi-free scattering  QFS takes place at high energies ~ 1 GeV/nucleon.  (p,2p), (p,pn), (p,p  )  (e,e’p)  Set kinematic conditions so that nucleons come out back to back c.f. elastic scattering  Detect complete spectroscopy in inverse kinematics  Allows final state interactions to be measured

10. GSI Helmholtz Centre

11. Reactions with Relativistic Radioactive Beams (R 3 B) A/Z Z 11 Be 10 Be 8 Li M Barr private communication, J Taylor PhD thesis

12. Facility for Antiproton and Ion Research (FAIR)

13. R 3 B experiment  Located on the high energy branch of FAIR at GSI.  Detection of all reaction channels.  Study of nuclear and astro-physical reactions  Main reactions of interest are quasi-free scattering reactions with hydrogen target  (p,2p), (p,pn), (p,p  ), etc J Taylor PhD thesis

14. Initial Design  Main requirements were for high resolution for momentum and energy  Good intrinsic energy resolution  High resolution spectroscopy in both energy and position  High granularity  At least 2 layers were required to track particle.  Also gives E-  E particle identification  Detector designed for QFS but needs large angular coverage able to cope with other reaction requirements  e.g. elastic scattering, coulex, etc.

15. Initial Design  First layer 2.5 cm from beam axis  100  m thick  2 x 10 cm  Second layer 10 cm from beam axis  300  m thick  4 x 10 cm  Simulations done in the R 3 BSim package  Full energy of the protons detected using a “perfect” calorimeter  CALIFA energies not included

16. Simulation Development R 3 BSim developed by the USC and Daresbury – Based on Geant4 + ROOT 2 geometries of calorimeter 2 geometries of tracker ALADIN, LAND, ToF Wall, etc – Working (p,2p) event generator – Existing analysis code R 3 BROOT developed at GSI – Based on ROOT + Geant3/4 + FLUKA 2 geometries of calorimeter 1 geometry of tracker ALADIN, LAND, ToF Wall, etc – No (p,2p) event generator implemented – No analysis code

17. Simulations of Elastic Scattering  Elastic scattering event generator written for R 3 BRoot  Compare well with R 3 BSim simulations Pitch (cm) CALIFA E(  ) (%) R 3 BRoot  Esep (MeV) R 3 BSim  Esep (MeV) 0.134.84.1 0.114.64 0.0512.2 0.050.52.22.1 0.010.50.60.5

18. Efficiency  Efficiency of detecting two protons from (p,2p) events  As energies increase get more forward focusing of protons  If end cap included get ~ 90% efficiency

19. Design constraints  Must detect protons at most forward angles  Inner layer as thin as possible  At least 3 layers  Strip redundancy  Inner layer as close to target as possible  Accurate determination of reaction vertex  Distance to outer layers large as possible  No shielding between detector and target

20. The two designs Barrel Detector Geometry  3 layers of Si strip detectors  Orthogonal strips  58, 109 and 119 mm from beam axis  2 end cap detectors  300 and 350 mm from target position  Easy analysis of positions  Asics chips positioned at forward angles

21. The two designs Lampshade Detector Geometry 3 layers of Si strip detectors – Stereoscopic strips – 69 mm (14 o ), 194 mm (33 o ) and 196 mm (33 o ) from beam axis at zero position – 9.8 mm gap between layer 2 and 3 All electronics can be placed before target Analysis of positions more difficult  3 layers of Si strip detectors  Stereoscopic strips  69 (14 o ), 194 (33 o ) and 196 (33 o ) mm from beam axis at zero position  9.8 mm gap between layers 2 and 3  All electronics can be placed before target  Analysis of positions more difficult and loss of efficiency

22. Comparison of Resolutions Barrel Detector Lampshade Detector  Resolution is almost the same for both detectors  Given the advantage of the lampshade detector design, this will be the detector geometry we went for

23. Lampshade resolutions with CALIFA  Separation energy calculated by Si + CsI energies.  Background from protons punching through CALIFA.  Gate on highest energy CsI energies to cut out background   Esep = 2.8 MeV  Eff(m>=2) = 71%

24. Background Contribution  Energy profile of particle 1 does not look like detected energies, whereas particle 2 does  Detected energies dominated by CsI energy peak at 0.15 GeV  Proton punch through ~320 MeV  Recovery of events needed or extend CALIFA crystals

25. Detection of protons and gammas 12 C(p,2p) 11 B*(5 MeV) 11 B in ground state 11 B in 5 MeV state  Reduction in background due to thicker CsI crystals  Broad peak is unresolved triplet  Cascade through 2 MeV state  Gate on gamma energies in CALIFA

26. Detection of protons and gammas 12 C(p,2p) 11 B*(5 MeV) CALIFA barrel only CALIFA + perfect end-cap  CALIFA barrel low in efficiency but collects full energy  End-cap technology yet to be decided

27. Detection of protons and gammas 12 C(p,2p) 11 B*(5 MeV) CALIFA barrel CALIFA end-cap  Gammas pushed forward in reaction  Mostly detected in end-cap

28. “Lampshade” design  The inner detector module (green) has 6 detector modules, each with 2 silicon wafers  The outer detectors (blue) are formed from 2 layers of 12 detector modules, each with 3 silicon wafers  Manufacturing masks are shared between one of the outer and inner detector modules slices to reduce costs. View from beam direction 3 rd layer 300  m 2 nd layer 300  m 1 st layer 100  m

29. Outer and Inner silicon modules Silicon Design  Strips are stereoscopic rather than perpendicular strips  Reduced capacitance due to non-metalization  Diamond shaped pixels  50  m pitch  Inner layer  Max distance from beam axis = 69 mm  Tilt angle = 14 o  Outer layers  Max distance from beam axis = 194/196 mm  Tilt angle = 33 o

30. Mechanical Design Si Tracker Cryogenics CALIFA Target Vacuum chamber Si Tracker

31. R3B Slow Control To R3B DAQ

32. Further Work  Implementation of full tracking and analysis code  Prototyping of Si starts in April  Call for tender put out in October  ASICS design is set and manufacturing has started  Full detector should be in place by mid 2014  GLAD moved to cave C this year  New tracking detector coupled to CALIFA demonstrator in 2014  Full experiment at FAIR in 2017  Design of next generation tracker

33. Collaboration And the R 3 B collaboration