Measurement of the double polarisation observable G with the - PowerPoint PPT Presentation

Measurement of the double polarisation observable G with the Crystal Barrel Experiment @ ELSA Marcus Grüner for the CBELSA/TAPS Collaboration Supported by SFB/TR 16 Helmholtz-Institut für Strahlen- und Kernphysik der Uni Bonn

Content • baryon spectroscopy • the Crystal Barrel/TAPS experiment @ ELSA • polarisation observables • data analysis • results • summary Marcus Grüner 13/06/11 2

baryon spectrosopy Marcus Grüner 13/06/11 3

Crystal Barrel/TAPS @ ELSA radiator target tagging system polarised target flux monitor Crystal Barrel calorimeter gas Č erenkov detector MiniTAPS calorimeter Marcus Grüner 13/06/11 4

Crystal Barrel/TAPS @ ELSA radiator target tagging system polarised target flux monitor Crystal Barrel calorimeter gas Č erenkov detector Marcus Grüner 13/06/11 5

Crystal Barrel/TAPS @ ELSA radiator target tagging system polarised target flux monitor Crystal Barrel calorimeter gas Č erenkov detector MiniTAPS calorimeter Marcus Grüner 13/06/11 6

Crystal Barrel/TAPS @ ELSA radiator target tagging system polarised target flux monitor Crystal Barrel calorimeter gas Č erenkov detector MiniTAPS calorimeter Marcus Grüner 13/06/11 7

Crystal Barrel/TAPS @ ELSA radiator target tagging system polarised target flux monitor Crystal Barrel calorimeter gas Č erenkov detector MiniTAPS calorimeter Marcus Grüner 13/06/11 8

Crystal Barrel/TAPS @ ELSA radiator target forward detector:  90 CsI(Tl) crystals  coverage 12° - 30° in θ ● photomultiplier readout delivers trigger signal ● charge identification by 180 plastic scintillators tagging system flux monitor Crystal Barrel calorimeter:  1230 CsI(Tl) crystals  angular coverage 30° - 156° in θ  high detection efficiency for photons  scintillating fibre detector for charge identification of reaction products Marcus Grüner 13/06/11 9

Crystal Barrel/TAPS @ ELSA radiator target Mini Taps calorimeter:  216 BaF crystals  coverage 1° - 12° in θ  trigger information for small θ tagging system flux monitor Marcus Grüner 13/06/11 10

The „complete” experiment A complete model independent partial wave analysis demands: • and 3 single polarisation observables • 4 properly chosen double polarisation observables [Chiang, Tabakin, Phys. Rev C55 (1997)] Crystal Barrel/TAPS @ ELSA: Photon Polarisation Target Polarisation X Y Z  unpolarised - T - - linear H (-P) -G circular - F - -E Marcus Grüner 13/06/11 11

Event selection for cuts on raw data: • multiplicity: 3 hits in the calorimeters • charge: 1x charged 2x neutral • time • coplanarity: • colinearity: • proton missing mass • meson mass meson mass[MeV] missing mass[MeV] Marcus Grüner 13/06/11 12

The observables and G longitudinally polarised protons • Target material butanol • contribution of reactions on protons bound in (C,O) Marcus Grüner 13/06/11 13

Meson Asymmetries p  p  0    E = 1066 MeV Marcus Grüner 13/06/11 14

Beam asymmetry 0   p  p   E = 1050 MeV Bonn-Gatchina PWA A.Thiel CB/TAPS @ ELSA SAID-Analysis D.Elsner CBELSA/TAPS MAID-Analysis GRAAL (O. Bartalini, Eur. Phys. J A26, 399 (2005)) Marcus Grüner 13/06/11 15

0   Beam asymmetry in p  p   = 110° MAID without (1400) A.Thiel CB/TAPS @ ELSA without (1520) without (1680) Marcus Grüner 13/06/11 16

0   Observable G in p  p   = 110° G MAID Without (1440) A.Thiel CB/TAPS @ ELSA without (1520) without (1680) Marcus Grüner 13/06/11 17

Observable G in G E = 1050 MeV G E = 950 MeV Bonn-Gatchina PWA A.Thiel CB/TAPS @ ELSA SAID-Analysis MAID-Analysis Marcus Grüner 13/06/11 18

summary • Polarisation observables are necessary to describe the nucleon excitation spectrum by a partial wave analysis without ambiguities. • With the Crystal Barrel/TAPS setup @ ELSA it is possible to measure single and double polarisation observables in different reaction channels. • These measured datasets provide new constraints for the partial wave analysis. supported by SFB/TR 16 Marcus Grüner 13/06/11 19

The Dilution Factor Marcus Grüner 13/06/11 20

and photoproduction  ,    N    N   N  N  N  N • The nucleon excitation spectrum has overlapping resonances. • For a complete description of the spectrum with a partial wave analysis, it is necessary to measure polarisation observables. Marcus Grüner 13/06/11 21

Production of linearily polarised photons • with a goniometer different bremsstrahl radiators can be positioned in the beam with high accuracy • coherent scattering of the beam on a diamond cristal creates polarisation degrees of up to 65% • photons are tagged in energy by a tagging spectrometer system Marcus Grüner 13/06/11 22

main detector components Crystal Barrel calorimeter:  1230 CsI(Tl) crystals  angular coverage 30° - 156° in θ  high detection efficiency for photons  scintillating fibre detector for charge identification of reaction products forward detektor:  90 CsI(Tl) crystals  angular coverage 12° - 30° in θ ● photomultiplier readout delivers Mini-Taps calorimeter: trigger signal  216 BaFl crystals ● charge identification by 180 plastic  coverage 1° - 12° in θ scintillators  trigger information for small θ Marcus Grüner 13/06/11 23