1 / 24

Adam J. Sarty Saint Mary’s University

Measurement of the Coulomb quadrupole amplitude in the γ * p → Δ (1232) reaction in the low momentum transfer region (E08-010). Adam J. Sarty Saint Mary’s University. representing David Anez (SMU & Dalhousie U., PhD student) Doug Higinbotham (Jefferson Lab) Shalev Gilad (MIT)

montana
Download Presentation

Adam J. Sarty Saint Mary’s University

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Measurement of the Coulomb quadrupole amplitude in the γ*p→Δ(1232) reaction in the low momentum transfer region (E08-010) Adam J. Sarty Saint Mary’s University representing David Anez(SMU & Dalhousie U., PhD student) Doug Higinbotham(Jefferson Lab) ShalevGilad(MIT) Nikos Sparveris(spokesperson Emeritus!) Experiment proposal spear-headed by Nikos 2 years ago … he has handed it over for us to complete!

  2. E08-010: A short/little few-day “N D” Experiment! • Currently Scheduled to Run for 6 days: • April 3-8, 2011 • “squeezed” in between and “SRC” (E07-006) and “x>2” (E08-014) experiments. • The focus on low Q2 allows the high rates / short run • Personnel from this experiment will clearly be linked into the other two experiments. • Let me now overview the physics goals of the experiment, and give a few of the particulars.(Start with a general review …)

  3. * p0 D(1232) p p Where/How the Physicscomes in: * : EM Multipolarity of transition (Electric, Magnetic, Scalar) (Dipole, Quadrupole, etc.) Vertex #1 : Nucleon Structure model enters here: * + p   (CQM or “pion cloud” Bag Model, etc.) Vertex #2 : (1232) Model for decay PLUS 0p reaction Dynamics Lp value for nomenclature of transition amplitude determined here.

  4. * p0 D(1232) p p Where/How the Physicscomes in: * : EM Multipolarity of transition (Electric, Magnetic, Scalar) (Dipole, Quadrupole, etc.) Vertex #1 : Nucleon Structure model enters here: * + p   (CQM or “pion cloud” Bag Model, etc.) Vertex #2 : (1232) Model for decay PLUS 0p reaction Dynamics Lp value for nomenclature of transition amplitude determined here. NOTE: any full model for the reaction hasto deal with separating the desiredResonant excitation from “Other Processes”)

  5. Understanding the Nomenclature: #1 – the incident photonWhat “kind” (MULTIPOLE) of Photon can Excite p  ? * + p  (1232) ( Lgp ½+ = 3/2+ ) • Conserve Parity: Final p is +, so … pinitial= (pg)(pproton) = (pg)(+) = + • So photon’s parity is Even. • Recalling Parity of EM Multipoles: • Electric: EL = (-1)L • Magnetic: ML = (-1)L+1 • Scalar (or Coulomb): CL = (-1)L • So… Lgp= 1+  M1 (magnetic dipole) OR Lgp= 2+  E2, C2 (quadrupole)

  6. Understanding the Nomenclature: #2 – the N final stateEnsuring the intermediate state was (or could be!) resonance of interest - we’re interested here in the (1232) (1232)  p + p0 Jp= 3/2+ [ (½+ 0- )s l] So, Constraints on l: (the relative angular momentum of the pp0 pair in Final State) • Can have: l+ ½ = 3/2 (i.e. l = 1)orl– ½ = 3/2 (i.e. l = 2) • MUST conserve Parity: final p = + pfinal= (pp)(pproton) (-1)l = (+)(-) (-1)l + = (-1) l +1… so: l = ODD  l = 1 Sp = ½+

  7. Understanding the Nomenclature: #3 – The final labeling Joining the Photon and N angular momentum constraints(focusing still on (1232) resonance) • The full Multipole label for a specific *N  N transition amplitude carries information about the constraints on the initial virtual-photon  final pion-nucleon angular momentum …

  8. Understanding the Nomenclature: #3 – The final labeling Joining the Photon and N angular momentum constraints (focusing still on (1232) resonance) • The full Multipole label for a specific *N  N transition amplitude carries information about the constraints on the initial virtual-photon  final pion-nucleon angular momentum …Example:The dominant “Spherical” (single-quark spin-flip) transition amplitude is labeled M1+ l = 1 Magnetic photon(must be M1) J = l+ 1

  9. Understanding the Nomenclature: #3 – The final labeling Joining the Photon and N angular momentum constraints (focusing still on (1232) resonance) • The full Multipole label for a specific *N  N transition amplitude carries information about the constraints on the initial virtual-photon  final pion-nucleon angular momentum …Example:The dominant “Spherical” (single-quark spin-flip) transition amplitude is labeled M1+ and the smaller “Deformed” (quadrupole) transitions; E1+and S1+ (with E meaning “electric” and S “scalar” photon) The “S” can also be written “L” (“longitudinal”) – related by a kinematic factor to amplitudes written with “S” l = 1 Magnetic photon(must be M1) J = l+ 1

  10. Goal of these kind of “N D” Experiments:Quantify “non-spherical” Components of Nucleon wf Talking with a CQM view of a nucleon wave-function: • Dominant M1+ is a “spin-flip” transition;Nand D both “spherical”…L=0 between 3 quarks • BUT, the Quadrupole transitions (E1+ , S1+ ) “sample” the “not L=0” parts of the wavefunctions. • Consider writing wavefunctions like so: then,we can view the quadrupoletx as…

  11. Goal of these kind of “N D” Experiments:Quantify “non-spherical” Components of Nucleon wf • These Quadrupole transitions thus give insight into small L=2 part of wf. Phys. Rev.C63, 63 (2000)

  12. Goal of these kind of “N D” Experiments:Quantify “non-spherical” Components of Nucleon wf • These Quadrupole transitions thus give insight into small L=2 part of wf. • Such L=2 parts arise from “colour hyperfine interactions” between quarksIF the assumption is a “one-body interaction”: Phys. Rev.C63, 63 (2000)

  13. Goal of these kind of “N D” Experiments:Quantify “non-spherical” Components of Nucleon wf • These Quadrupole transitions thus give insight into small L=2 part of wf. • BUTL=2 transitions can also arise via interactions with virtual exchanged pions (the “pion cloud”): Phys. Rev.C63, 63 (2000)

  14. Goal of THIS“N D” Experiment:FOCUS ON LOW Q2 WHERE PION CLOUD DOMINATES • At low momentum transfer: the Pion Cloud dominates the “structure” of wavefunctions • These pion dynamics dictate the long-range non-spherical structure of the nucleon … and that is where we focus.

  15. NOW: to p( e , e’ p )0Measurements 18 Response Functions:Each with their own Unique/Independentcombination of contributing Multipole transition amplitudes

  16. NOW: to p( e , e’ p )0Measurements 18 Response Functions:Each with their own Unique/Independentcombination of contributing Multipole transition amplitudes • No polarization required for these Responses (R’s) • L and T via cross-sections at fixed (W,Q2) but different v’s (“Rosenbluth”) • LT and TT via cross-sections at different Out-Of-Plane angles  • We will extract just RLT (by left/right measurements) – and s0 – since LT term isvery sensitive to size of L1+ (see next slide…)

  17. NOW: to p( e , e’ p )0Measurements 18 Response Functions:Each with their own Unique/Independentcombination of contributing Multipole transition amplitudes For Example: decomp of 5 R’s (Drechsel & Tiator)

  18. Status of World Data at Low Q2(2 years old…from proposal)EMR ~ E2/M1 ratio CMR ~ C2/M1 ratio

  19. Status of World Data at Low Q2(2 years old…from proposal)EMR ~ E2/M1 ratio CMR ~ C2/M1 ratio We focus on getting CMR values in this region

  20. Where our Planned Results Fit(2 years old…from proposal)focus on: CMR ~ C2/M1 ratio at lowest Q2

  21. Where our Planned Results Fit(2 years old…from proposal)focus on: CMR ~ C2/M1 ratio at lowest Q2 • Q2 = 0.040 (GeV/c)2 • New lowest CMR value • θe = 12.5° • Q2 = 0.125 (GeV/c)2 • Validate previous measurements • Q2 = 0.090 (GeV/c)2 • Bridge previous measurements

  22. Step back to look at what weactually will measure:

  23. Finish with a Step back to look at what weactually will measure: Q2 = 0.040 GeV2 s0 LT Theta-pq W Q2 = 0.090 GeV2 s0 LT Theta-pq W

  24. Finish with a Step back to look at what weactually will measure: s0 LT W Theta-pq Q2 = 0.125 GeV2

More Related