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

▶
measurement of the double polarisation observable g with
SMART_READER_LITE
LIVE PREVIEW

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

Jan 27, 2024 208 likes •460 views

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

slide-1
SLIDE 1

Measurement of the double polarisation observable G with the Crystal Barrel Experiment @ ELSA

Marcus Grüner

for the CBELSA/TAPS Collaboration

Helmholtz-Institut für Strahlen- und Kernphysik der Uni Bonn Supported by SFB/TR 16

slide-2
SLIDE 2

13/06/11 Marcus Grüner

2

Content

  • baryon spectroscopy
  • the Crystal Barrel/TAPS experiment @ ELSA
  • polarisation observables
  • data analysis
  • results
  • summary
slide-3
SLIDE 3

13/06/11 Marcus Grüner

3

baryon spectrosopy

slide-4
SLIDE 4

13/06/11 Marcus Grüner

4

radiator target tagging system polarised target Crystal Barrel calorimeter gas Čerenkov detector flux monitor MiniTAPS calorimeter

Crystal Barrel/TAPS @ ELSA

slide-5
SLIDE 5

13/06/11 Marcus Grüner

5

radiator target tagging system polarised target Crystal Barrel calorimeter gas Čerenkov detector flux monitor

Crystal Barrel/TAPS @ ELSA

slide-6
SLIDE 6

13/06/11 Marcus Grüner

6

radiator target tagging system polarised target Crystal Barrel calorimeter gas Čerenkov detector flux monitor MiniTAPS calorimeter

Crystal Barrel/TAPS @ ELSA

slide-7
SLIDE 7

13/06/11 Marcus Grüner

7

Crystal Barrel/TAPS @ ELSA

radiator target tagging system polarised target Crystal Barrel calorimeter gas Čerenkov detector flux monitor MiniTAPS calorimeter

slide-8
SLIDE 8

13/06/11 Marcus Grüner

8

radiator target tagging system polarised target Crystal Barrel calorimeter gas Čerenkov detector flux monitor MiniTAPS calorimeter

Crystal Barrel/TAPS @ ELSA

slide-9
SLIDE 9

13/06/11 Marcus Grüner

9

radiator target 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 forward detector:

 90 CsI(Tl) crystals  coverage 12° - 30° in θ

  • photomultiplier readout delivers

trigger signal

  • charge identification by 180

plastic scintillators

Crystal Barrel/TAPS @ ELSA

slide-10
SLIDE 10

13/06/11 Marcus Grüner

10

radiator target tagging system flux monitor Mini Taps calorimeter:

 216 BaF crystals  coverage 1° - 12° in θ trigger information for small θ

Crystal Barrel/TAPS @ ELSA

slide-11
SLIDE 11

13/06/11 Marcus Grüner

11

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
slide-12
SLIDE 12

13/06/11 Marcus Grüner

12

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]

slide-13
SLIDE 13

13/06/11 Marcus Grüner

13

The observables and G

longitudinally polarised protons

  • Target material butanol
  • contribution of reactions on protons bound in (C,O)
slide-14
SLIDE 14

13/06/11 Marcus Grüner

14

Meson Asymmetries

   pp0

E = 1066 MeV

slide-15
SLIDE 15

13/06/11 Marcus Grüner

15

Beam asymmetry

Bonn-Gatchina PWA SAID-Analysis MAID-Analysis A.Thiel CB/TAPS @ ELSA D.Elsner CBELSA/TAPS GRAAL (O. Bartalini, Eur. Phys. J A26, 399 (2005))

   pp

E = 1050 MeV

slide-16
SLIDE 16

13/06/11 Marcus Grüner

16

Beam asymmetry in

A.Thiel CB/TAPS @ ELSA

   pp

= 110°

MAID without (1400) without (1520) without (1680)

slide-17
SLIDE 17

13/06/11 Marcus Grüner

17

Observable G in

   pp

A.Thiel CB/TAPS @ ELSA

G = 110°

MAID Without (1440) without (1520) without (1680)

slide-18
SLIDE 18

13/06/11 Marcus Grüner

18

Observable G in

A.Thiel CB/TAPS @ ELSA

E = 1050 MeV G G

Bonn-Gatchina PWA SAID-Analysis MAID-Analysis

E = 950 MeV

slide-19
SLIDE 19

13/06/11 Marcus Grüner

19

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

slide-20
SLIDE 20

13/06/11 Marcus Grüner

20

The Dilution Factor

slide-21
SLIDE 21

13/06/11 Marcus Grüner

21

and photoproduction

  • 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.

N  N

,  N

N  N

 N

slide-22
SLIDE 22

13/06/11 Marcus Grüner

22

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
slide-23
SLIDE 23

13/06/11 Marcus Grüner

23

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

trigger signal

  • charge identification by 180 plastic

scintillators Mini-Taps calorimeter:

 216 BaFl crystals  coverage 1° - 12° in θ trigger information for small θ