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Impact of the Delta (1232) resonance on neutral pion photoproduction in chiral perturbation theory

We present an ongoing project to assess the importance of D-waves and the $Δ(1232)$ resonance for descriptions of neutral pion photoproduction in Heavy Baryon Chiral Perturbation Theory. This research has been motivated by data published by the A2 and CB-TAPS collaborations at MAMI [1]. This data has reached unprecedented levels of accuracy from threshold through to the $Δ$ resonance. Accompanying the experimental work, there has also been a series of publications studying the theory that show that, to go beyond an energy of $E_γ=170$ MeV, it is necessary to include other aspects, in particular the $Δ(1232)$ as a degree of freedom [2] and possibly higher partial waves [3].