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Proton, Pion and Kaon Transparency Measurements
• Overview of existing (& new kaon!) transparency data
Questions:• A-dependent analysis – any improvements needed?• What transparency data is needed from 12 GeV?
Rolf EntINT/SeattleOctober 27, 2009
Total Hadron-Nucleus Cross Sections
Hadron– Nucleustotal cross section
Fit to
K
pp_
Hadron momentum60, 200, 250 GeV/c
< 1 interpreted as due to the strongly interacting nature of the probe A. S. Carroll et al. Phys. Lett 80B 319
(1979)
= 0.72 – 0.78, for p, , k
Traditional nuclear physics calculations (Glauber calculations) predict transparency to be nearly energy independent.
T
1.0
5.0Energy (GeV)
Ingredients
• h-N cross-section
• Glauber multiple scattering approximation
• Correlations & Final-State Interaction effects
hN
Physics of Nuclei: Color Transparency
From fundamental considerations (quantum mechanics, relativity, nature of the strong interaction) it is predicted (Brodsky, Mueller) that fast protons scattered from the nucleus will have decreased final state interactions
QCD
A(e,e’h), h = hadron
Search for Color Transparency in Quasi-free
A(e,e’p) Scattering
Constant value line fits give good description:2/df = 1
Conventional Nuclear Physics Calculation by Pandharipande et al. (dashed) also gives good description
No sign of CT yet
A-dependence Studies
1) Fit to = Aa
or T = A-1
2) Classical attenuation model with effective cross section eff
independent of
Search for Color Transparency in Quasi-free
A(e,e’p) Scattering
Fit to = Aa
= constant = 0.75
Close to proton-nucleus total cross section data! But slightly higher than 0.72-0.73 from free proton-nucleus data.
Tp’ [MeV}
Search for Color Transparency in Quasi-free
A(e,e’p) ScatteringAnalyzed in terms of an effective cross section with classical attenuation model follows general energy dependence from free N-N scattering, but at reduced values
A(e,e’+) Missing Mass Spectra
Dashed line: two-pion thresholdGreen: simulated multi-pion yield (following phase space)Solid line: Used cut in transparency analysis (but similar results with a two-pion threshold cut)
Physics of Nuclei: Pion Transparency
|
A(e,e’+)
With CT
W/O CT
Physics of Nuclei: Pion Transparency
|
A(e,e’+)
Red: low- points
Without Color Transparency
With Color Transparency
Physics of Nuclei: Color Transparency
Total pion-nucleus cross section slowly disappears, or … pion escape probability increases Color Transparency Unique possibility to map out at 12 GeV (up to Q2 = 10)
such that one can directly see QCD at Work
Total pion-nucleus cross section slowly disappears, or … pion escape probability increases Color Transparency?
A(e,e’+)
6 7 8 9 10
Physics of Nuclei: Color Transparency A(e,e’+)
Total pion-nucleus cross section slowly disappears, or … pion escape probability increases Color Transparency Unique possibility to map out at 12 GeV (up to Q2 = 10)
such that one can directly see QCD at Work
Total pion-nucleus cross section slowly disappears, or … pion escape probability increases Color Transparency?
Projections for 12 GeV
Physics of Nuclei: Kaon Transparency
Transparency w.r.t. to hydrogen (BUT…)
Preliminary
Physics of Nuclei: Kaon Transparency
Transparency better defined w.r.t. to deuterium, as and peaks close
Preliminary
Physics of Nuclei: Kaon Transparency
Carroll et al.
~ 0.78
A(e,e’K+) data point
to = 0.85-0.90
Preliminary
Physics of Nuclei: Hadron Transparency
(Pion data fit too high in this plot!)
Compare with free hadron-nucleon cross sections:NN ~ 40 mBN ~ 24 mBKN ~ 20 mBAll are lower (artefact of Glauber?) but follow general energy dependence
Preliminary
p
K
Preliminary
Physics of Nuclei: Color Transparency
AGSA(p,2p)
Glauber calculation
Pp (GeV/c)5.1 7.3 9.62.9
Results inconsistent with CT only. But can be explained by including additional mechanisms such as nuclear filtering or charm resonance states.
The A(e,e’p) measurements will
extend up to ~10 GeV/c proton momentum,
beyond the peak of the rise in transparency found
in the BNL A(p,2p) experiments.
Physics of Nuclei: Color Transparency
A(e,e’+) at 12 GeV(at fixed coherence length)
12 GeV
