Experimental Study of Hypernuclei with Heavy Ion Beams at GSI: HypHI Collaboration

1. Study of Hypernuclei with Heavy Ion Beams (HypHI) at GSI - Experimental design and performance test of the detector system –Shizu Minami　Universtät Mainz, Germanyon behalf of HypHI collaboration • Introduction • Phase 0 experiment • Experimental apparatus • Monte Carlo simulation • Performance test of detectors • Summary

2. Introduction • Study of hypernuclei with Heavy Ion Beams • Production of hypernuclei in flight • Measurement of life time and decay property • Magnetic moment • Rare Isotopebeam • High probability to produce proton-rich or neutron-rich hypernuclei • Heavy Ion collision • Only way to produce hypernuclei with S < -2

3. L • Hypernuclei produced in beam fragment • Hyperon(s) produced at participant region coalesce with a beam fragment • Experimental study at Dubna with 3.7 A GeV 4He and 3.0 A GeV 6Li deduced production cross section of 4LH ~ 0.3mb, however small statistics. S. Avramenko, et, al, Nucl. Phys. A547 (1992) 95c • The cross section obtained in the Dubna’s experiment was reproduced by the theoretical calculation based on the coalescence model. M. Wakai, H.Bando and M. Sano Phys. Rev. C38 (1988) 748, M. Sano and M. Wakai, Prog of Theor Phys. Suppl. 117 (1994) 99 L

4. Phase 0 experiment • Purpose • To establish experimental method • To investigate the mechanism of hypernucleus-production at beam fragment region • Observable • Production cross sections and lifetimes of 3LH, 4LH and 5LHe. • Polarization of 5LHe

5. Signal: 4H ->  BG: BG: • Method • 6Li beam with 2 A GeV in kinetic energy ( Eth for N+NL+K+N~1.6GeV) • Measurement of decayed particles from mesonic decay mode. 3LH  3He +p- 4LH  4He + p- 5LHe  4He + p + p- • Reconstruction of secondary vertex (~20cm in average behind target) • Invariant mass • Background • p+ 3He/4He : request secondary vertex behind target • L+ 3He/4He : reject events with 3He/4He at the detector just after target

6. Experimental apparatus Dipole magnet : 0.7 T 1.4m depth Target: 12C with 8g/cm2 TR0: primary vertex, DE TR1,TR2 : decay vertex TOF walls :Time of flight, DE, Position

7. Development • Scintillating fibre detector • DE measurement at TR0 H7260 (32ch multi-anode PMT by HAMAMATSU) SCSF-78M -.83D. NON S-type by Kuraray Diameter is 0.83mm with 2 clads Monte Carlo simulation TR0 TR1 TR2 DE at TR0 by BG DE at TR0 by signal • Secondary vertex trigger 　　　1000 ch  　Logic module (VUPROM1) based on FPGA/DSP

8. Development • TOF walls • p- trigger by ALADIN TOF wall • a (z=2 ) trigger by TOF+ wall : 2.5 x 4.5 x 100 cm3 Time over threshold • Logic module (VUPROM1) based on FPGA/DSP • Fast trigger (<500ns) with No. of channels >1000ch ( Secondary vertex & time over threshold) • TDC for the scintillating fibre detectors with 2.5 ns granularity VUPROM1 developed by GSI EE VME 6U 256 LVDS I/O by High Density connector (VHDCI) Fast Programmable Logic Device Xilinx Virtex-4 (max. clock freq. 400MHZ)

9. Monte Carlo Simulation Tools: Geant4 and Ultra Relastivistic Quantum Molecular Dynamics calculations(UrQMD) Purpose: Optimize detector setup, Background study, Trigger study

10. s=0.27mm s=4.3mm Secondary Vertex resolution Momentum resolution p-: s=8.3MeV/c a: s=310 MeV/c

11. Condition • Production cross section of 4LH s is 0.1mb • Branching ratio to p-+a is 0.5 • Coalescence factor of 4LH production is 0.01 • Nuclear reaction at target is 1 barn Expected Yields 2.6 x 103 / week 6Li beam with intensity of 107/sec. 12C target with 8g/cm2 • Invariant mass spectrum of 4LH with background

12. Table 3 Efficiency and reduction factor of the each trigger condition. • MC simulation for Trigger rate • The beam intensity of 107/sec • 40% of the beam expected to interact at the target. • Full function of the trigger 0.017%, trigger rate is expected to be 0.7kHz. • This value fulfills the requirement by the DAQ system which expected to accept up to 3kHz.

13. Perfomance test of detectors • TOF+ prototype ( Sep. 2007 ) • Time of flight vs DE - 2 A GeV Ni beam scattered by C target DE Time of flight DE • Time over threshold　for He trigger DE Time over threshold measured by Logic module ~ He> 2.5ns 7ch

14. Scintillating fibre detector • DE spectra by proton, He, Li and Be and their cluster sizes • TDC by the logic module

15. Summary Monte Carlo simulation to design a detecotor setup of HypHI phase 0 experiment have been performed of the case of 4LH. Secondary vertex and invariant mass resolution have been investigated. The way to distinguish signal from background have been studied. The resulting invariant mass spectra shows enough significance of signal to background. The yields of reconstructed 4LH events is expected to be 2.6 x 103 / week. Trigger rate have been studied by MC siimulations and obtained results fulfils the requirement by the DAQ system. Tests of proto-type detectors showed expected performance.

16. Scintillating fibre detector

17. Scintillating fibre detector

18. Momentum resolution D =0. 31MeV/c =8.3MeV/c

19. Efficiency of signal and reducton of background • Each layer TR1,TR2 and TOF walls have 2hits • Secondary vertex by TR1 and TR2 • Tracking with TR0,TR1,TR2 and TOF walls. PID by dE at TOF • Remove events with Free L • Remove events with alpha at TR0

20. Typical Tracks by a hypernucleus decay Negative pion from hypernucleus decay make a track which don’t across the target. The track can be identified by following procedure. Identify hit by particles come from the target. Veto the signals identified by 1st step. Reconstruct tracks with surviving signals after applying the veto.

21. Particles come from the target List up combination of TR1 and TR2 comes from target.

22. Negative pion track crossing the decay volume TR1N & (TR2M or TR2M+1 or ………..TR2L) On this stage, I think we don’t need good resolution, we can reduce channels by making OR of several channels before coming to this stage.

23. Algorithm