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A Tale of Two (Toy) Models

A Tale of Two (Toy) Models. CERN Courier: July, 2007 Harry Lee, Dan Carman, Reinhard Schumacher, MM Two possible pictures of how spin is transferred from virtual photon to the L. Carman, MM: photon to u-quark; through s-sbar spin correlation to L . Schumacher: directly from photon

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A Tale of Two (Toy) Models

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  1. A Tale of Two (Toy) Models CERN Courier: July, 2007 Harry Lee, Dan Carman, Reinhard Schumacher, MM Two possible pictures of how spin is transferred from virtual photon to the L. Carman, MM: photon to u-quark; through s-sbar spin correlation to L. Schumacher: directly from photon to s-sbar to L. Problem: both consistent with data! How (else) to distinguish models?

  2. Quark Pair Creation • Quark-pair creation: “kernel” of exclusive production • What field couples to the q-q current? u d S L ss produced From flux-tube s u s u K+ ss produced from photon K+ s u d L

  3. Using Exclusive Production to Study Quark Pair Creation • Lund model: successful phenomenology for hadron production; e.g. in e+e- reactions • color flux-tube broken by qq production • production rate depends on constituent quark mass • : : ~ 1 : 1 : 0.2 • Vector meson dominance: photon fluctuates into a virtual qq meson • production rate depends on quark charge • : : ~ 1: 0.25 : 0.25 ss ss uu uu dd dd

  4. Distinguish ModelsStudy ratios of s s : dd : uu • Measure ratios: K+L : p+n : p0p K+ p0 p+ s d u n p L s u d 0.2 : 1 : 1 Ratio : exponential in quark mass

  5. Distinguish Models • Measure ratios: K+L : p+n : p0p K+ L n p s d u s p+ p0 d u 1 : 1 : 4 Ratio : proportional to (charge)2

  6. 90k 420k 540k 480k • Missing Mass • 2-body final state (n) p+a P (p0)a ~0 84k 350k 910k forward f Lab Angle g backward

  7. 50k 150k 45k 5k K+ Missing Mass (L) K+a “Fake” plots mis-identified protons mis-identified pions forward f Lab Angle g backward

  8. Limits of the “quark model” ? Can the Lund model work in the limit of single qq pair production? • recent analysis of a Hall C p+(n) production experiment • Kaskulov, Gallmeister, Mosel; arXiv:0804.1834v4 [hep-ph] • model was developed to explain Rosenbluth separated exclusive electro-production of p+(n) asLdescribed well as t-channel exchange asTdescribed well as “quark-scattering followed by string-breaking” with Lund model parameters • model also works for un-separated data

  9. Exclusive np+: sum of two processes sT: DIS via LUND model sL: t-channel exchange u d d photon probes meson structure n photon couples to quark d u p+ t-channel no form factor: q2 independent form factor falls with q2

  10. Analysis goals and plans • Model-independent goal • measure ratio of p+n : p0p : K+L cross-sections • proportional to uu : dd : ss rate • Extend Kaskulov, Gallmeister, Mosel model • extend to dd and ss production • Analysis plan • identify final states (done) • decide on binning ( high/low bins for W, q2, t ) • tune PYTHIA/JETSET (fitting and MC generator) • Study single quark-pair creation

  11. An interesting observation …. For forward-going protons (qLAB < 200) : only recoil meson is the r0 ??

  12. And the winner is …. crude accepance correction done; kaon decay not corrected Ratio: K+L : p+n : p0p 0.23 : 0.88 : 1.12 errors ~ 20% ??

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