Future Spin Observable Measurements at PANDA

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1 Future Spin Observable Measurements at PANDA Walter Ikegami Andersson Uppsala University on behalf of the PANDA collaboration Swedish Nuclear Physics Meeting October 27-28, 2016 Chalmers University of Technology Gothenburg, Sweden 1 / 11

2 Outline 1 PANDA Detector at FAIR 2 Spin Observables - Polarisation in ΞΞ - Polarisation in ΩΩ 3 Previous results 4 Outlook 2 / 11

3 PANDA Detector Target- and forward spectrometer provide a near 4π coverage Antiproton p beam 1.5 p p 15 GeV/c High resolution measurement and PID HESR Startup phase - L cm 2 s 1 HESR High Luminosity mode - L cm 2 s 1 3 / 11

4 Spin Observables in pp Y Y Density matrix formalism ρ = 1 2j 2j + 1 I + 2j 2j + 1 L=1 L M= L I = Tr(T ρt ), T Ψ i = Ψ f Q L Mr L M pp ΛΛ Manifests in angular distributions At PANDA, unpolarised beam and target: Polarisation Spin Correlation I(cos θ p ) 1 4π (1 + αp y cos θ p ) 4 / 11

5 Polarisation in ΞΞ Consider decays: Ξ Λπ, Λ πp Three polarisation parameters: r 1 1, r 1 0, r 1 1 Directly related to P x, P y, P z. Two are zero due to symmetry: P x = P z = 0 Joint angular distribution depends on I(θ Λ, φ Λ, θ p, φ p ) Choosing a frame such that φ Λ = 0 and integrating over θ Λ, the angular distribution is: I(θ p, φ p ) = 1 ( 1 + α Λ α Ξ cos θ p + π ) 4π 4 α ΛP sin θ p (β Ξ sin φ p γ Ξ cos φ p ) Erik Thomé, Elisabetta Perotti, Uppsala University pp Ξ Ξ + Λ Λ π π + π p p π + 5 / 11

6 Polarisation in ΩΩ Consider decays: Ω ΛK, Λ πp Fifteen polarisation parameters: rm L, L = 1, 2, 3, M = L,..., L Eight are zero due to symmetry The angular distribution of the first decay Ω ΛK is: pp Ω Ω + Λ Λ π p K K + p π + I(θ Λ, φ Λ ) = 1 4π [ (1 3 cos2 θ Λ )r sin2 θ Λ cos 2φr sin 2θ Λ cos φr α sin θ Λ(8 15r 1 1 sin φ Λ r 3 1(3 + 5 cos 2θ Λ sin φ Λ ) + 30(3r 3 2 sin 2φ Λ sin 2θ Λ + 6r 3 3 sin 3φ sin 2 θ Λ ))] Erik Thomé, Elisabetta Perotti, Uppsala University 6 / 11

7 Polarisation in ΩΩ Three polarisation parameters r0 2, r 1 2, r 2 2 are extracted with the following expectation values: cos 2 θ Λ = cos θ Λ sin θ Λ cos φ Λ = π 2π 0 0 = 1 15 (5 2 3r0 2 ) π 2π 0 0 I(θ Λ, φ Λ ) cos 2 θ Λ sin θ Λ dθ Λ dφ Λ I(θ Λ, φ Λ ) cos θ Λ sin θ Λ cos φ Λ sin θ Λ dθ Λ dφ Λ sin 2 θ Λ sin 2 φ Λ = = r π 2π 0 0 I(θ Λ, φ Λ ) sin 2 θ Λ sin 2 φ Λ sin θ Λ dθ Λ dφ Λ = 1 15 (5 + 3r r 2 2 ) Erik Thomé, Elisabetta Perotti, Uppsala University 7 / 11

8 Polarisation in ΩΩ When considering the Λ πp decay and integrating over the θ Λ, φ Λ angles: I(θ p, φ p ) = 1 4π (1 + α Ωα Λ cos θ p ( ) 3 + α Λ 5 r r 1 3 (β Ω cos φ p + γ Ω sin φ p ) sin θ p ) Extract remaining polarisation parameters with following expectation values: ( ) 2 10 r 1 1 (15 cos θ Λ 1) sin φ p = + r πα Λ γ Ω r 1 3 = 4 10 (3 cos θ Λ 1) sin φ p πα Λ γ Ω r 2 3 = 1024 sin φ Λ cos φ p 3π 2 α Λ γ Ω ( 1 r 3 3 = sin φ Λ cos φ Λ sin φ p + 2 ) 6r r πα Λ β Ω 8 / 11

9 Previous results Using a simplified Monte Carlo framework: p p (GeV/c) Reaction σ (µb) Eff (%) Decay BR (%) Rate 1.64 pp ΛΛ Λ pπ s pp Ξ + Ξ 2 20 Ξ Λπ s pp Ω + Ω 0.002* 30 Ω ΛK 68 4 h pp Λ c Λ c 0.1* 30 Λ c Λπ d 1 All measurements are exclusive! Erik Thomé, PhD thesis, Uppsala University Sophie Grape, PhD thesis, Uppsala University 9 / 11

10 Cross section prediction During first two years of data taking: 80 days beam time to X(3872) scan X(3872) scan operate at p p = 7.0 GeV/c Above production threshold of ΩΩ and ΞΞ Theoretical prediction shows: Cross section of ΩΩ larger at 7.0 than 12.0 GeV/c Cross section of ΞΞ smaller A.B Kaidalov, P.E. Volkovitsky Z. Phys C 63, (1994) 10 / 11

11 Outlook New ongoing simulation studies: Study pp ΛΛ, pp ΞΞ and pp ΩΩ channels Improved software (PANDAroot): - Realistic detector description - New software tools for track reconstruction and PID Different energy regimes: GeV/c, higher cross sections GeV/c, lower cross sections Study relevant background channels Two papers are foreseen: Journal paper on PANDA starting program Paper on Spin Observable measurements in pp ΩΩ 11 / 11