Transcript "Proton, Pion and Kaon Transparency Measurements"

Proton, Pion and Kaon Transparency
Measurements
Rolf Ent
INT/Seattle
October 27, 2009
• Overview of existing (& new kaon!) transparency data
Questions:
• A-dependent analysis – any improvements needed?
• What transparency data is needed from 12 GeV?
Total Hadron-Nucleus Cross Sections
K
a
p
p
_
p
Hadron– Nucleus
total cross section
Fit to
Hadron momentum
60, 200, 250 GeV/c
a = 0.72 – 0.78, for p, p, k
a < 1 interpreted as due to the
strongly interacting nature of the
probe
A. S. Carroll et al. Phys. Lett 80B 319 (1979)
Physics of Nuclei: Color Transparency
Traditional nuclear physics calculations (Glauber calculations)
predict transparency to be nearly energy independent.
1.0
Ingredients
A(e,e’h), h = hadron
• s
h-N cross-section
hN
• Glauber multiple
scattering approximation
T
Energy (GeV)
QCD
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
5.0
• Correlations & Final-State
Interaction effects
Search for Color Transparency in
Quasi-free A(e,e’p) Scattering
Constant value line fits give good description:
c2/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 s = soAa
or T = Aa-1
2) Classical attenuation
model with effective
cross section seff
independent of r
Search for Color Transparency in
Quasi-free A(e,e’p) Scattering
Fit to s = soAa
a
a = constant = 0.75
Close to proton-nucleus
total cross section data!
But slightly higher than
0.72-0.73 from free
proton-nucleus data.
Search for Color Transparency in
Quasi-free A(e,e’p) Scattering
Analyzed in terms of
an effective cross
section with classical
attenuation model 
follows general energy
dependence from free
N-N scattering, but at
reduced values
Tp’ [MeV} 
A(e,e’p+) Missing Mass Spectra
Dashed line: two-pion threshold
Green: 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’p+)
With CT
W/O CT
|
Physics of Nuclei: Pion Transparency
A(e,e’p+)
Red: low-e points
|
Physics of Nuclei: Color Transparency
A(e,e’p+)
Without Color Transparency
Total pion-nucleus cross section slowly disappears, or …
pion escape probability increases  Color Transparency?
Transparency
 Unique possibility to map out at 12 GeV (up to Q2 = 10)
such that one can directly see QCD at Work
Physics of Nuclei: Color Transparency
A(e,e’p+)
Projections for 12 GeV
6
7
8
9
10
Total pion-nucleus cross section slowly disappears, or …
pion escape probability increases  Color Transparency?
Transparency
 Unique possibility to map out at 12 GeV (up to Q2 = 10)
such that one can directly see QCD at Work
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 L and S peaks close
Preliminary
Physics of Nuclei: Kaon Transparency
Preliminary
A(e,e’K+)
data point to
a = 0.85-0.90
Carroll et al.
a ~ 0.78
Physics of Nuclei: Hadron Transparency
Preliminary
Compare with free
hadron-nucleon cross
sections:
NN ~ 40 mB
pN ~ 24 mB
KN ~ 20 mB
All are lower
(artefact of Glauber?)
 but follow general
energy dependence
(Pion data fit too
high in this plot!)
K
Preliminary
p
p
Physics of Nuclei: Color Transparency
Results inconsistent with CT only.
But can be explained by including
additional mechanisms such as
nuclear filtering or charm
resonance states.
AGS
A(p,2p)
Glauber
calculation
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.
2.9
5.1
7.3
9.6
Pp (GeV/c)
Physics of Nuclei: Color Transparency
A(e,e’r+) at 12 GeV
(at fixed coherence length)
12 GeV