1. Yasser Maghrbi Graduiertenkolleg, Todtmoos 2007
Meson photoproduction off 7Li
Yasser Maghrbi Graduiertenkolleg, Todtmoos 2007

2. Summary 1 - Motivations - η photoproduction - Use of 7Li
2 - Experimental setup
3 - Current status of analysis
- Coherent photoproduction
- Preliminary cross section calculation
4 - Conclusions and outlook

3. Motivations : η photoproduction

4. Motivations : η photoproduction

5. Motivations : Use of 7Li coherent photoproduction : γ + A → η + A
- Study of S11(1535)
- Search for eta-mesic nuclei
→ 7Li : - Good conditions (Spin and Isospin ≠0, ..)
- High form factor
7Li : Next candidate After 3He

6. Motivations : Use of 7Li σ(3He)coherent = 0.4 μb σ(7Li)coherent = ??
Form Factor (~coherent photoproduction)
σ(3He)coherent = 0.4 μb σ(7Li)coherent = ??

7. Motivations : Use of 7Li total cross-section at low energy
Quasi-free cross-sections →region closer to heavy nuclei

8. Motivations : Use 7Li double pion channel : σ-meson in-medium behavior
σ→ππ ► if σ produced and detected : M(σ)= M(ππ)
Models : Mass(σ) if Density
→ becomes degenerate with its chiral partner :
the pion, at large density
→ Expect shift in Invariant mass distributions towards small values for π0π0 but not for π0π+/-
Mass comparison between the channels π0π0 & π0π+/-

9. Experimental setup

10. Analysis : coherent photoprod. for η→γγ
We expect to have small coherent production due to form factor
Missing energy :
No clear signature of coherent production was found

11. Analysis : total cross-section

12. Analysis : detectors efficiency
Goal : Detection efficiency → independent from the way that η are produced inside the nucleus (several processes)
→ to simulate all processes : η generated isotropically with
2 degrees of freedom (kinetic energy, polar angle)
Ekinectic (MeV) theta (°)

13. Analysis : Cross-section calculation Removing the background
cross section for quasi-free (3 detected particles) → fitting invariant mass
cross section for coherent (2 detected particles) → almost background free

14. Analysis : Cross-section calculation Removing the background
cross section normalized to A2/3
Before After

15. Analysis : cross sections comparison
Calcium Deuterium Lithium

16. Conclusion and outlook
- No clear signature of eta coherent production in the channel η → γ γ
- First cross section in good agreement with predictions.
In progress :
- Differential cross sections
- Channel η →π0π0π0
In the future :
- Double pion channel

17. Yasser Maghrbi Graduiertenkolleg, Todtmoos 2007
Any question?
Yasser Maghrbi Graduiertenkolleg, Todtmoos 2007

18. HAPPY BIRTHDAY Marlon Horras (the Basel team)