1. 1 Pion beam tracker for HADES Jerzy Pietraszko CBM Collaboration Meeting, March 9-13, 2009, GSI, Darmstadt

2. 2 Omega production in  +A in‘99 spectacular effects predicted…

3. 3 π beam at GSI  π experiments planned from the very beginning of the HADES  The Pion Beam Facility available at GSI since 1998 Q doublet defines acceptance  = 2.3 msr Momenta up to 2.8 GeV/c,  p/p = 8% Beam spot at the HADES focal point: 3σ x – 2.0 cm, 3σ y – 1.8 cm H1, H2 & H3 for beam momentum reconstruction (fiber arrays) exclusive measurements  p/p = 0.3% 7.5 o dispersive plane Number of pions at the HADES target (extrapolated to SCL of SIS)

4. 4 Beam transport in HADES beam line - MIRKO beam momentum = 1.0 GeV/c + 0.0 % beam momentum = 1.0 GeV/c + 1.0 % beam momentum = 1.0 GeV/c + 2.0 % beam momentum = 1.0 GeV/c - 2.0 %beam momentum = 1.0 GeV/c - 1.0 % MIRKO – beam optics and beam transport Used at GSI for setting up the accelerator and beam transport. 90% - 95% of beam particles

5. 5 Beam detectors for pion experiment  Background reaction rejection LH2 Target: entrance window diameter 15 mm, LH2 cell diameter 25 mm A beam detector in front of the LH2 target with diameter of the active area of 15 mm used in LVL1 trigger. 25mm 15mm LH2 Target measured pion beam profile

6. 6 Beam detectors for pion experiment  Background reaction rejection Position sensitive, fast detector, directly in front of the target. Included in the LVL1 trigger. Selecting beam particles which hit the target. 5 single crystalline diamonds available: 300  m, size 3.5mm x 3.5mm and 500  m, size 4.7mm x 4.7mm. Three different metalization schemes but only one (Ti/Pt/Au) shows stable operation, no or small "upcharge" effect. Long term test needed. Factor of 10 thinner than Hodoscopes, multiple scattering factor 3 smaller. 10mm x 10mm will be available this year. Time resolution: expected below 50 ps (signal/noise ratio), measured: about 120 ps Efficiency: close to 100 %. Readout electronics: rise time ~1.2 ns and signal base-width ~10ns) – important for high rates and time structure of the beam monitoring.

7. 7 Main tasks for beam detectors  Momentum determination of beam particles Detectors have to be installed in the dispersive plane, fast, position sensitive, radiation hard (10 7 /s/cm 2 ), readout integrated into HADES readout system. Active area: minimum 8cm(x-dir) x 6cm(y-dir). Hodoscopes, used for this purpose. Multiple scattering is a disadvantage. A silicon micro-strip detector. Dedicated readout integrated into HADES system. Operated in vacuum. A Silicon strip from Micron Semiconductors (used at HERMES) Size: 9.9 x 9.9 cm 2 300  m thick 128 strips per side with a pitch of 758  m position resolution: 222  m

8. 8 Towards a successful, high intensity pion experiment (  − rate 10 6 /s)  Needed preparations: Diamond detector in front of the target included in the LVL1 trigger. Optimized the beam transport scheme in order to reduce the beam spot. The beam tracking detectors installed in the vacuum with readout system integrated into the HADES DAQ.  Test run ("machine experiment") with the following aims: SQL at SIS, very high extraction efficiency from SIS (close to 100 %). Perfect micro-spill structure of the beam, monitored by our fast diamond detectors. Position sensitive (silicon) detector located in front of the target and a diamond detector to measure precisely the beam spot and tails of the beam at the target point. Few days of running time to see the stability of the SIS operation at the SQL.  Go for a physics, few-week-long run...

9. 9 backup slides

10. 10 backup slides

11. 11 Beam transport in HADES beam line - MIRKO  MIRKO – beam optics and beam transport Used at GSI for setting up the accelerator and beam transport. 7.5 o 3m Dispersive Plane

12. 12 Beam quality – beam emittance, intro  Beam emittance – the area of the emittance ellipse Quantity that characterizes the effective phase volume of a beam distribution x, x' – where x – position, x' – transverse angle The emittance ellipse has a constant area throughout the length of the system if the forces are linear. x x' x  Multiple scattering Beam detectors in the beam line causes an increase in x'. x' Smaller influence at the focus

13. 13 Main tasks for beam detectors and LVL1 trigger  Background reaction rejection – offline analysis How (Can we ?) to separate two following types of reactions:  Background reaction: beam particle + (carbon, stainless steel)  Measured process: beam particle + target nucleus e + e − spectroscopy, inclusive measurement Source of background reaction located around the target Distance to the target: > 1 cm in x,y Lepton momenta > 100 MeV/c – whole invariant mass spectrum  offline background rejection extremely difficult !!!  Example: Nb/Be target, vertex reconstruction based on e + e − pairs Nb Be - reconstructed from GEANT - reconstracted from tracking invMass > 600 MeV/c whole invMass range

14. 14 Multiple scattering measured with HADES  Apr07 run, p+p at 3.5 GeV Pion hodoscopes in the beam line, 17 m upstream of the target. ROLU detector located 1 m upstream of the target. 26 mm wide window in ROLU. ROLU/Veto ratio - with pion hodoscope in beam 0.333M/55M ROLU/Veto ratio - without pion hodoscope in beam 0.023M/56M  a "beam halo" increased by about a factor of 16 !!!  Consequences: –huge radiation load for detectors (RICH), LVL1 trigger based on META multiplicity very sensitive, DAQ saturated with background reactions. Veto detectorTargetROLU 26 mmPion hodoscope Beam direction 35 mm diamond detector

15. 15 Targets for pion experiment The influence of the thickness of the medium in radiation lengths on the omega shape. target for pion target for proton Ideal tracking, 3 mm target diameter  the main contribution comes from the spectrometer !!! Negligible effect from Be target omega from Geant reconstructed omega

16. 16 Omega production in  A p e+e- < 300 MeV/c  - p bound  n  e + e - n  „at rest”: mass modifications in  0  e+ e- 208 Pb -- HADES W.Schoen et al. Acta Phys.PolB27(1996)2959 M.Effenberger et al. Nucl-th/9901039 in‘99 spectacular effects predicted…

17. 17 exclusive inclusive π+A, p+A and ρ/ω production * Dielectron production (HSD) –p + Nb, π + Nb –results form HSD model (upper row) –after HADES filter acceptance (0.35) efficiency (0.25) How to increase the prod. prob. –beam energy 3.5  4.0 GeV  increase 20 %  decrease in acceptance 3%  more decays outside 5 % * Based on HSD model: parameterization of NN, πN experimental cross-sections combined with OBE and LSM models and hadronic transport. HSD after HADES filter HSD model

18. 18 ω decays inside/outside the nucleus Omega production and decay –radial vs. long. coordinate –p+Nb at 3.5 GeV –π+Nb at 1.17 GeV Omega decays inside the nucleus –p+Nb  3.5 GeV – 42% inside 4.0 GeV – 40% inside –π+Nb  1.17 GeV - 70% inside e+ e- R(A=100)  5.5 fm 0.1ρ o 0.9ρ o production decay