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

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

Motivations : η photoproduction

Motivations : η photoproduction

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

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 = ??

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

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+/-

Experimental setup

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

Analysis : total cross-section

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 (°)

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

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

Analysis : cross sections comparison Calcium Deuterium Lithium

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

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

HAPPY BIRTHDAY Marlon Horras (the Basel team)