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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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