A final state interaction model of resonance photoproduction

Transcription

1 A final state interaction model of resonance photoproduction HASPECT week Kraków May 30 - June 1, 2016 Łukasz Bibrzycki Pedagogical University of Cracow 1 / 24

2 1. Resonances dynamically created in the final state (and others) 2. What can we describe? 3. Major obstacles 4. Which processes observable in JLab experiments may be interesting in context of the FSI model? 5. No conclusions yet 2 / 24

3 Resonances dynamically created in the nal state meaning of the term Quantum mechanical meaning of the scattering process interaction region OK, but what happens in the bulb (interaction region)? 3 / 24

4 In some theories we are able to express the S- matrix in terms of systematic expansion using microscopic degrees of freedom QED We can perturbatively expand the scattering amplitude to any (practically doable) order, thus improving the accuracy of prediction 4 / 24

5 The same applies to pqcd and electroeweak model of Weinberg and Salam In nonperturbative regime of QCD there s no systematic expansion of that kind 5 / 24

6 Although we can draw a diagram like it does not represent a term of convergent perturbative expansion of the ππ production amplitude on the nucleon. It isn t useless however in fact it represents the dominant (1PE) mechanism of the ππ production This in turn enables the derivation of the elastic ππ amplitude 6 / 24

7 The problem is this particular diagram describes the dominant contribution only to: particular reaction for particular kinematics If we took a very similar diagram...it does not represent the dominant part of the πη production amplitude 7 / 24

8 ...Leap forward 8 / 24

9 So, how can we know that such diagram is relevant for resonance photoproduction?...let s make a step back 9 / 24

10 As it is impossible to use perturbation theory in hadron physics at low and moderate energies we construct amplitudes using general principles of: Lorentz invariance Unitarity Analyticity Crossing symmetry Other symmetries 10 / 24

11 One can observe a duality among crossing related amplitudes: Namely, that for given kinematics only some of them can be dominant In particular Low energy regime is dominated by s-channel amplitudes High energy regime is dominated by t-channel exchange amplitudes 11 / 24

12 The s-channel for meson-meson and meson-baryon (also photon-meson and photon-baryon) scattering is dominated by the resonant intermediate states: 12 / 24

13 Now assume that we photoproduce a 3 particle system consisting of nucleon and 2 (pseudoscalar) mesons Final state emerges due to t-channel exchange Conclusion: 2 meson states produced by new Jlab experiments are ideally fit for description by FSI model Meson-meson FSI are dominated by the s- channel intermediate resonant states 13 / 24

14 Caveats: Production of π+π-, K+K-, π+π-π 0 at small 4- momentum transfers is dominated by pomeron exchange Drell process Final state dominated by I=1/2 and I=3/2 byryonic resonances 14 / 24

15 What can we describe? Structure of the production amplitude Born amplitude Rescattering amplitude Where: A mn photoproduction amplitude of the meson pair mn, V mn - Born amplitude, t FSI -rescattering amplitude 15 / 24

16 Catalogue of amplitudes Born amplitudes ππ S-wave P-wave D-wave F-wave FSI amplitudes (Based on GKPY parametrisation up to 1.5 GeV) ππ I=0 I=1 I=2 S-wave P-wave + +* + D-wave S-wave * FSI model is not dominant 16 / 24

17 Catalogue of amplitudes Born amplitudes KK S-wave P-wave D-wave F-wave FSI amplitudes KK I=0 I=1 S-wave + + P-wave +* + D-wave + - F-wave + - * FSI model is not dominant 17 / 24

18 Catalogue of amplitudes πη (I=1) S-wave P-wave D-wave F-wave Remarks Born amplitudes Easily extendable to πη channel FSI amplitudes +* For M πη 1 GeV * model (by Leśniak and Furman) includes channels πη and KK, in principle it covers a 0 (1450) but due to other open channels its use beyond 1 GeV is problematic We are also able to calculate the contribution of the Drell background to ππ photoproduction amplitude in practically any partial wave 18 / 24

19 Applications of our amplitudes ππ S-wave 19 / 24

20 Applications of our amplitudes ππ D-wave 20 / 24

21 Applications of our amplitudes πη S-wave 21 / 24

22 Major obstacles Can we neglect the baryon resonance production in the direct channel and other contributions? Isovector πη and KK FSI amplitudes difficult to extend beyond 1 GeV due to the lack of data a 0 (1450) branching fractions to πη, ωππ, a 0 (980)ππ unknown 22 / 24

23 Which processes observable in JLab experiments may be interesting in context of the FSI model? Photoproduction of all pseudoscalar pair channels: ππ, πη, πη, KK, ηη, η η,... Photoproduction of 3 pseudoscalars (πππ, KKπ, ππη,...) with nucleon in the final state especially if experiment is able to isolate resonant final states like f 0 (980)Δ(1232) There were indications of such enhancement in old CLAS data (was this trace pursued?) 23 / 24

24 At present we do not describe the γp f0(980)δ(1232) πππn reaction but our amplitudes are easily extendable to that case Thank you 24 / 24