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A First Analysis of the 3 He Test Beamtime

A First Analysis of the 3 He Test Beamtime. CB Meeting Mainz, March 9, 2010. Patricia Aguar Bartolomé Alexander Mushkarenkov. Physics Motivations. Experimental verification of the GDH sum rule on the neutron (measurement of a total inclusive helicity dependent cross section)

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A First Analysis of the 3 He Test Beamtime

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  1. A First Analysis of the 3He Test Beamtime CB Meeting Mainz, March 9, 2010 Patricia Aguar Bartolomé Alexander Mushkarenkov

  2. Physics Motivations Experimental verification of the GDH sum rule on the neutron (measurement of a total inclusive helicity dependent cross section) Helicity dependent cross section on some (Np)p channels Polarised 3He is the best substitute of a polarised free neutron =>First double polarisation experiment on 3He !! in the test, measured photon range was [200-800 MeV]

  3. Setup • Cell transport system • worked fine. • Minimal loss of • polarisation during • transport. • Setup for the cell • polarisation • measurement worked • well.

  4. Experimental Conditions • 2 different MAMI energies (855, 525 MeV) with circularly polarised (≈ 80%) electrons • 3He gas target 20 cm long at ~ 4 bar • Open hadronic trigger (inclusive measurement) (CB.or.TAPS): CB M1 – Ethr ~ 20 MeV TAPS M1 – Ethr ~ 40 MeV with Cherenkov on-line Veto

  5. Beamtime in July 2009 241 h • Approx. 380 hours of beamtime Ee- = 855MeV => 110 h of data on tape Ee- = 525MeV => 115 h of data on tape Tagg. eff. =>16 h • Exchange of the cell two times per day (30 - 60 minutes) • More than 1/3 of the beam time “lost” for several different problems (Acqu, MAMI, …)

  6. Polarised Total Inclusive Cross Section for 855 MeV Runs A. Fix Model for g3He p X • APROX. 110 HOURS OF • BEAMTIME • NO EVENT SELECTION • ONLY TRUE - RANDOM • SUBTRACTION for the • tagger TDCs 1) Target relaxation time ≈ 4 h. 2) Large beam halo induced huge background in our detector. MAIN LIMITING FACTORS

  7. Beam Halo Problem Eg = 855 MeV Eg = 525 MeV LESS BACKGROUND FROM BEAM HALO AT 525 MeV

  8. Polarised Total Inclusive Cross Section only for CB Events – 855 MeV ONLY CB or CB.AND.TAPS TRIGGERS

  9. Polarised Total Inclusive Cross Section only for TAPS M1 Events - 855 MeV • Count Rate • TAPS trigger ≈ CB trigger. • Error bars as large as • before. ONLY TAPS (WITHOUT CB) TRIGGER

  10. Polarised Total Inclusive Cross Section for CB+Cuts - 855 MeV ONLY CB or CB.AND.TAPS TRIGGERS • CB events rejected • when all clusters • satisfied the conditions: • Ecluster < 50 MeV. AND. • q<300 or q>1400 (NEGLIGIBLE LOSS OF EFFICIENCY ) ERROR BARS DECREASED BY 1.5

  11. Monte Carlo Detection & Geometrical Efficiency Simulation – 525 MeV Efficiency for pp-≈ 90 - 95 % Efficiency for np0≈ 100 % SIMULATED REACTIONS ON THE FREE NEUTRON (quasi-free generation in GEANT4 did not work) In a first approximation, TAPS (without CB) events can be neglected for the evaluation of a total inclusive cross section (small correction factor)

  12. Polarised Total Inclusive Cross Section for CB - 525 MeV Runs A. Fix Model for g3He p X ONLY CB or CB.AND.TAPS TRIGGERS • APROX. 110 HOURS OF BEAMTIME • NO EVENT SELECTION • ONLY TRUE - RANDOM SUBTRACTION for the tagger TDCs • LONGER TARGET RELAXATION TIME (10-15 hours) • REDUCED BEAM HALO ERROR BARS SIGNIFICANTLY REDUCED

  13. Polarised Total Inclusive Cross Section for CB+Cuts - 525 MeV ONLY CB or CB.AND.TAPS TRIGGERS A. Fix Model for g3He p X • CB events rejected • when all clusters • satisfied the conditions: • Ecluster < 50 MeV. AND. • q<300 or q>1400 (NEGLIGIBLE LOSS OF EFFICIENCY ) No efficiency correction applied (points will slightly decrease, especially below 300 MeV)

  14. Next Analysis Steps • Improved CB energy cuts. • Analysis of TAPS (without CB) events. • Separation between npo and pp- using the MWPCs information. • Evaluation of the detection efficiency.

  15. Conclusions Despite several problems (ACQU, PID, Beam halo...) a good result was obtained from the test, especially at 525 MeV. With improved beam and/or trigger conditions (lead wall in front of CB, most upstream crystals out of CB trigger, harder trigger,...) luminosity can be improved by a factor 2 to 10. We have proved that a polarised gas 3He target can be used for the check of the GDH sum rule on the neutron. As a by-product, the g0 polarisability of the neutron can also be determined. The helicity dependence of some partial channels (np0, npopo, nh) can also be measured (determination of the resonance properties). Advantage with respect to the polarised deuterated butanol target: no need to detect the recoil neutron to identify these partial channels (effects due to polarised protons are small).

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