2
play

2 Outline Short Motivation Experimental Setup Polarization - PowerPoint PPT Presentation

Apr 26, 2023 •415 likes •727 views

Polarization Observables T and F in Single 0 and -Photoproduction off Quasi-Free Nucleons Thomas Strub, Basel Group, A2 Collaboration University of Basel 30th May 2014 A 2 Outline Short Motivation Experimental Setup Polarization

  1. Polarization Observables T and F in Single π 0 and η -Photoproduction off Quasi-Free Nucleons Thomas Strub, Basel Group, A2 Collaboration University of Basel 30th May 2014 A 2

  2. Outline Short Motivation Experimental Setup Polarization Observables Analysis Methods Selected Results Conclusion Outline 1 Short Motivation 2 Experimental Setup 3 Polarization Observables 4 Analysis Methods 5 Selected Results 6 Conclusion Polarization Observables T and F Thomas Strub, Basel Group, A2 Collaboration

  3. Outline Short Motivation Experimental Setup Polarization Observables Analysis Methods Selected Results Conclusion Motivation Problem ◮ Nucleons’ excitation spectrum is a complicated overlap of many short lived, broad resonances ◮ Cannot be understood from differential cross sections alone Polarization observables from meson photoproduction ◮ Probing spin degrees of freedom ◮ Need 8 carefully chosen observables for complete experiment ◮ Need high precision measurements Proton and neutron channel ◮ Probe isospin degree of freedom ◮ Isospin decomposition into A V 3 , A IV , A IS for π photoproduction � 1 � 2 � 2 � 1 AV 3 + A ( γ p → π 0 p ) = + AV 3 + A ( γ p → π + n ) = − � AIV − AIS � � AIV − AIS � 3 3 3 3 � 1 � 2 � 2 � 1 A ( γ n → π 0 n ) = + AV 3 − AV 3 + � AIV + AIS � � AIV + AIS � A ( γ n → π − p ) = + 3 3 3 3 ◮ At least one measurement off the neutron needed. Polarization Observables T and F Thomas Strub, Basel Group, A2 Collaboration

  4. Outline Short Motivation Experimental Setup Polarization Observables Analysis Methods Selected Results Conclusion Motivation Mass [ MeV/c 2 ] Special case η N(I=1/2) � (I=3/2) D 13 (1700) F 15 (1680) D 33 (1700) D 15 (1675) ◮ Isospin I = I z = 0. S 11 (1650) S 31 (1620) 1600 P 33 (1600) S 11 (1535) ◮ No isospin changing current ( A V 3 = 0) D 13 (1520) P 11 (1440) 1400 A ( γ p → η p ) = A IS + A IV P 33 (1232) 1200 � A ( γ n → η n ) = A IS − A IV Notation : 1000 ⇒ only N ∗ resonances contribute L 2I2J ; L=0(S),1(P),2(D),... P 11 (939) = � � � � � ◮ Recent results show a narrow structure arround 1670 MeV Photoproduction off the neutron ◮ Neutron bound in nucleus = ⇒ quasi free neutron ◮ Correct treatment of Fermi motion ◮ Comparision of free and quasi free proton data Polarization Observables T and F Thomas Strub, Basel Group, A2 Collaboration

  5. Outline Short Motivation Experimental Setup Polarization Observables Analysis Methods Selected Results Conclusion Experimental Setup Experimental Setup Polarization Observables T and F Thomas Strub, Basel Group, A2 Collaboration

  6. Outline Short Motivation Experimental Setup Polarization Observables Analysis Methods Selected Results Conclusion MAinzer MIcrotron High quality electron beam ◮ Energy up to 1.5 GeV ◮ Intensity up to 100 µ A ◮ Polarization ≈ 80 % Bremsstrahlungs photons ◮ 1/ E γ distribution ◮ Photon polarization: Olsen maximum function 1 Polarization degree 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0 200 400 600 800 1000 1200 1400 Photon Energy Polarization Observables T and F Thomas Strub, Basel Group, A2 Collaboration

  7. Outline Short Motivation Experimental Setup Polarization Observables Analysis Methods Selected Results Conclusion Crystal Ball/TAPS @ MAMI CB ◮ PID ◮ MPWC ◮ NaI crystals TAPS ◮ BaF2/PWO crystals ◮ Veto wall = ⇒ Almost 4 π acceptance Polarization Observables T and F Thomas Strub, Basel Group, A2 Collaboration

  8. Outline Short Motivation Experimental Setup Polarization Observables Analysis Methods Selected Results Conclusion Polarization Observables Polarization Observables Polarization Observables T and F Thomas Strub, Basel Group, A2 Collaboration

  9. Outline Short Motivation Experimental Setup Polarization Observables Analysis Methods Selected Results Conclusion Definition of T and F (experimental approach) T and F are defined by d σ ↑ ( φ ′ ) − d σ ↓ ( φ ′ ) 1 T cos ( φ ′ ) = d σ ↑ ( φ ′ ) + d σ ↓ ( φ ′ ) , P T P γ where ( ↑ , ↓ ) denotes the target polarization state, d σ − ( φ ) − d σ + ( φ ) 1 F cos ( φ ) = d σ − ( φ ) + d σ + ( φ ) , P T P γ where (+ , − ) denotes the photon helicity state. ◮ φ = Angle between target Here, F = F ( E , θ ) , T = T ( E , θ ) , P T = P T ( t ) polarization vector and and P γ = P γ ( E γ , P B ( t )) production plane ◮ φ ′ = Angle between target ◮ Symmetric contributions cancel in the polarization vector and normal to production plane numerator ◮ Denominator equals unpolarized d σ Polarization Observables T and F Thomas Strub, Basel Group, A2 Collaboration

  10. Outline Short Motivation Experimental Setup Polarization Observables Analysis Methods Selected Results Conclusion Methods to extract T and F ◮ Target: D-butanol ( C 4 D 9 OD ), only deuterons are polarized. ◮ Carbon/oxygen contribution vanish in numerator ◮ Two methods can be used: ◮ 1. Normalize with deuterium target d σ − DB ( φ ) − d σ + DB ( φ ) 1 A cos ( φ ) = d σ − D ( φ ) + d σ + P T P γ D ( φ ) = ⇒ Needs flux and efficiency correction of count rates. ◮ 2. Normalize with D-butanol target DB ( φ ) − dN + dN − DB ( φ ) 1 A cos ( φ ) = · d dN − DB ( φ ) + dN + P T P γ DB ( φ ) = ⇒ No need for flux and efficiency correction, but dilution factor d , i.e., d = 1 + d σ 0 C d σ 0 DB Polarization Observables T and F Thomas Strub, Basel Group, A2 Collaboration

  11. Outline Short Motivation Experimental Setup Polarization Observables Analysis Methods Selected Results Conclusion Analysis Methods Analysis Methods Polarization Observables T and F Thomas Strub, Basel Group, A2 Collaboration

  12. Outline Short Motivation Experimental Setup Polarization Observables Analysis Methods Selected Results Conclusion Event selection ◮ Event selection ◮ Full exclusive on proton (neutron as spectator) → π 0 + p ( n ) γ + d − → 2 γ + p ( n ) 2 neutral, 1 charged − γ + d − → η + p ( n ) → 2 γ + p ( n ) 2 neutral, 1 charged − → 3 π 0 + p ( n ) γ + d − → η + p ( n ) − → 6 γ + p ( n ) 6 neutral, 1 charged − ◮ Full exclusive on neutron (proton as spectator) → π 0 + n ( p ) γ + d − → 2 γ + n ( p ) 3 neutral, 0 charged − γ + d − → η + n ( p ) → 2 γ + n ( p ) 3 neutral, 0 charged − → 3 π 0 + p ( n ) γ + d − → η + n ( p ) − → 6 γ + n ( p ) 7 neutral, 0 charged − ◮ Determination of the neutron candidate by χ 2 -test. ◮ Invariant mass cut on all 3 π 0 from η → 6 γ decay. Polarization Observables T and F Thomas Strub, Basel Group, A2 Collaboration

  13. Outline Short Motivation Experimental Setup Polarization Observables Analysis Methods Selected Results Conclusion Applied Cuts All cuts are determined from LD 2 target for all θ and energy bins. ◮ Coplanarity cut ∆ φ = 180 ◦ − | φ meson − φ recoil | ◮ Invariant mass cut meson | − m theo. ∆ m meson = | P µ meson ◮ Missing mass cut meson | − m theo ∆ MM = | P µ γ + P µ nucleon − P µ nucleon Polarization Observables T and F Thomas Strub, Basel Group, A2 Collaboration

  14. Outline Short Motivation Experimental Setup Polarization Observables Analysis Methods Selected Results Conclusion Reconstruction of Kinematics Transfer kinematics into CM frame ◮ Fermi momentmum from deuterium (carbon/oxygen) targed = ⇒ Initial state not determined ◮ Reconstruction of nucleons fermi momentum from final state, i.e., solve P µ γ + P µ nucleon = P µ meson + P µ recoil for P µ nucleon . ◮ Have enough information to reconstruct Fermi momentum of nucleon. Polarization Observables T and F Thomas Strub, Basel Group, A2 Collaboration

  15. Outline Short Motivation Experimental Setup Polarization Observables Analysis Methods Selected Results Conclusion Dilution Factor ◮ Determination of the dilution factor from missing mass spectra 1 1 1 1 1 0.9 0.9 TOMultiPad_Dummy_0 0.9 TOMultiPad_Dummy_1 0.9 TOMultiPad_Dummy_2 0.9 TOMultiPad_Dummy_3 Entries 0 Entries 0 Entries 0 Entries 0 Mean 0 Mean 0 Mean 0 Mean 0 0.8 0.8 RMS 0 0.8 RMS 0 0.8 RMS 0 0.8 RMS 0 0.7 0.7 0.7 0.7 0.7 0.6 0.6 0.6 0.6 0.6 0.5 0.5 0.5 0.5 0.5 0.4 0.4 0.4 0.4 0.4 0.3 0.3 0.3 0.3 0.3 counts [a.u.] 0.2 0.2 0.2 0.2 0.2 0.1 0.1 0.1 0.1 0.1 0 0 1 0 1 0 1 0 1 0.9 TOMultiPad_Dummy_4 TOMultiPad_Dummy_5 TOMultiPad_Dummy_6 TOMultiPad_Dummy_7 0.9 0.9 0.9 0.9 Entries 0 Entries 0 Entries 0 Entries 0 Mean 0 Mean 0 Mean 0 Mean 0 0.8 0.8 RMS 0 0.8 RMS 0 0.8 RMS 0 0.8 RMS 0 0.7 0.7 0.7 0.7 0.7 0.6 0.6 0.6 0.6 0.6 0.5 0.5 0.5 0.5 0.5 0.4 0.4 0.4 0.4 0.4 0.3 0.3 0.3 0.3 0.3 0.2 0.2 0.2 0.2 0.2 0.1 0.1 0.1 0.1 0.1 0 0 0 0 0 -200 0 -200 0 -200 0 -200 0 200 η MM -p [MeV] ◮ Carbon + x Deuterium = Sum ≈ D-butanol ◮ Dilution factor d = 1 + � MMcut ∆ MM carbon / � MMcut ∆ MM deuterium Polarization Observables T and F Thomas Strub, Basel Group, A2 Collaboration

  16. Outline Short Motivation Experimental Setup Polarization Observables Analysis Methods Selected Results Conclusion Selected Results Selected Results (preliminary) Polarization Observables T and F Thomas Strub, Basel Group, A2 Collaboration

Recommend

More recommend