Exclusive Production RatiosMac Mestayer, Kijun Park, Christian Weiss

What are we measuring?– ratios of cross-sections for 2-body (baryon-

meson) final states: e.g. +n vs. 0p vs. K+– i.e. ratios of processes in which only one

pair is produced :

What can we learn by measuring them?– kinematic domain in which the dominant

interacting currents are quarks, not hadrons– how the color flux-tube is broken.

Sept. 26, 2009 Hadron Spectroscopy Meeting Mac Mestayer 1

uu dd ssqq

Quark Pair Creation• Quark-pair creation: “kernel” of exclusive production• What field couples to the q-q current?

su

sud

K+

su

K+

udS

ss producedFrom flux-tube

ss produced from photon

Sept. 26, 2009 Mac Mestayer 2Hadron Spectroscopy Meeting

Using Exclusive Production to Study Quark Pair Creation

uu dd ss

uu dd ss

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Limits of the “quark model” ?

Can the Lund model work in the limit of single qq pair production?– recent analysis of a Hall C +(n) production

experiment • Kaskulov, Gallmeister, Mosel; arXiv:0804.1834v4

[hep-ph]

– model was developed to explain Rosenbluth separated exclusive electro-production of +(n)

L described well as t-channel exchange

T described well as “quark-scattering followed by string-breaking” with Lund model parameters

– model also works for un-separated dataSept. 26, 2009 Mac Mestayer 4Hadron Spectroscopy Meeting

Exclusive n+: sum of two processes

t-channel

form factor falls with q2

du

+

nudd

photon couplesto quark

photon probesmeson structure

no form factor: q2 independent

T: DIS via LUND model L: t-channel exchange

Sept. 26, 2009 Mac Mestayer 5Hadron Spectroscopy Meeting

Analysis goals and plans

• Model-independent goal– measure ratio of +n : 0p : K+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

Sept. 26, 2009 Mac Mestayer 6Hadron Spectroscopy Meeting

() +

“Fake” plots

mis-identified protons

mis-identified pions

K+ Missing Mass

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forward Lab Angle backward

P (0)

(n) +

forward Lab Angle backward

Missing Mass2-body final state

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Sept. 26, 2009 Mac Mestayer 15Hadron Spectroscopy Meeting

Conclusions

• Yield ratios show simple phenomenology• Statistics look good• Analysis work to be done:

– rad. corrections, phase-space factors, background subtractions

• Decide on binning• Develop event generator for K+

– t-channel exchange + LUND-type model

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Lund model value: 0.2

Ratio ofnormalized yields : K+ / + n

W = 1.9 GeV

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Ratio ofnormalized yields : K+ / + n

W = 2 GeVLund model value: 0.2

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Lund model value: 0.2

Ratio ofnormalized yields : K+ / + n

W = 2.2GeV