1. TRIUMF: differential cross sections at 20 – 68 MeV → Roman Tacik PSI: 1. Analyzing powers of scattering at 45 – 90 MeV 2. Total SCX cross sections at 40 – 250 MeV Measurements of Total π - -p Charge Exchange Cross Sections at Low Energies Pion-nucleon scattering at low energies Johannes Breitschopf, Physikalisches Institut Universität Tübingen Aim: Reliable data base for π p scattering below 100 MeV σ-term πNN coupling constant strong isospin breaking

2. A_y at PSI with LEPS Analyzing power measurement at PSI: Principle Background suppression: Active polarized target Background suppression: Active polarized target  TT  Beam ±p Polarized Proton Target  Detector +-+-

3. Active target Active polarized target B. van den Brandt et al., NIM A446 (2000) BC 800 lightguide quarz- adapter scintillator PM 800mm,  12mm 18 mm 5 mm Helmholtz coils targetcell / mixing chamber  wave- guide light- guide beam 3 He/ 4 He 4 He

4. Background suppression Active polarized target for background suppression π + scattering at T π = 68.6 MeV, θ cm = 81.3° Focal plane spectrum 1. without constraint 2.-4. with increasing size of active target signal.

5. Results A_y pi+ Wieser et al., PRC54 (1995)LEPS/PSI Phys. Lett. B588 (2004) 155 KH80 SAID FA02 +p+p

6. LEPS/PSI Phys. Lett. B588 (2004) 155 KH80 SAID FA02 J. D. Patterson et al., Pys. Rev. C66 (2002) 025207 -p-p

7. Total SCX cross section Total cross section for π - p →π 0 n (SCX) Δ-resonance region Low energy region

8. Test of isospin breaking π p elastic scatteringSCX

9. Principle of Measurement Principle of experiment 4π scintillation detector I0I0 I =I 0 e -ασ π- π- neutrals: SCX π - p  π 0 n π- π- π- π- beam definition counters TargetTarget ← 20 cm → ← 10 cm → → ← 2 mm 7mm → ←

10. Data acqusition? Data acquisition CH 2 58 270 414 pions 57 768 918 pions seen in box neutrals 58 270 414 - 57 768 918 = 501 223 neutrals transmission 0.991398(12) DAQ: All parameters (TDC, ADC, FADC) event-by-event (total of 3.5 TB) Typical example:

11. i = C, CH 2 0 = empty target α = target thickness Typical target dimensions:3.5 cm x 4.0 cm x 7.6 mm (CH2) 3.5 cm x 4.0 cm x 4.5 mm (C)

12. Detector and corrections Modeling of the detector in GEANT3 Corrections: GEANT 3 and 4 detection of neutrals: γ’s (5.5%), n’s (2%), π 0 -Dalitz (1.2%) muons In addition π - – capture randoms efficiencies

13. Corretions_all Corrections for detection of neutrals GEANT3 πE3 πM1

14. Preliminary results from πM1 channel

15. Percent deviation from SAID FA02

16. Comparison with other data and predictions

17. Percent deviation from SAID FA02 in comparison with other data

18. Summary1 1. @PSI: Analyzing powers 45 – 90 MeV R. Meier, M. Cröni et al.,Phys. Lett. B588 (2004) 155 Summary and outlook I No strong deviations from KH80 or SAID FA02. Experimental data tend to be below predictions at the lowest energies. Similar findings for @TRIUMF J. D. Patterson et al., Phys. Rev. C66 (2002) 025207

19. πE3 channel: 40 – 80 MeV Of particular interest for isospin breaking Summary2 Summary and outlook II 2.SCX @PSI: Total SCX cross sections Transmission on CH 2 and C in event mode (3.5 TB) πM1 channel: 60 – 250 MeV, ~ 2% statistical error ~ 1 – 2% systematical error Findings (preliminary): Confirms Bugg et al. data About 3% above Friedman et al. data Excellent agreement with SAID SM95/FA02 Below KH80 up to 170 MeV Analysis in progress

20. Collaboration R. Meier, M. Cröni, R. Bilger, J. Breitschopf, H. Clement, H. Denz, J. Pätzold, G. J. Wagner Physikalisches Institut, Univ. Tübingen, Tübingen, Germany B. van den Brandt, P. Hautle, J. A. Konter, S. Mango Paul Scherrer Institut, Villigen, Switzerland G. J. Hofman, M. Pavan TRIUMF, Vancouver, British Columbia, Canada J. Comfort Arizona State University, Tempe, Arizona, USA K. Föhl School of Physics, Univ. of Edinburgh, UK E. Friedman Racah Inst. of Physics, The Hebrew University, Jerusalem, Israel Analyzing powers J. Breitschopf, M. Bauer, H. Clement, M. Cröni, H. Denz, R. Meier, G.J. Wagner Physikalisches Institut, Univ. Tübingen, Tübingen, Germany E. Friedman Racah Inst. of Physics, The Hebrew University, Jerusalem, Israel E. Gibson California State University, Sacramento, USA Supported by BMBF (06Tü9871) and DFG (European Gradudate School Basel – Tübingen) SCX