Transcript Nuclei at Short Distance Scale Ronald Ransome Piscataway, NJ

Nuclei at Short Distance Scale
Ronald Ransome
Rutgers, The State University of New Jersey
Piscataway, NJ
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Some unanswered questions
 How


is the nucleon affected by the nuclear medium?
Change in quark distributions
Change in nucleon size and shape
 How
do we get from quarks and gluons to nucleons
and mesons?


At what distance scale does this occur?
What are the signatures?
 What

is the short-range behavior of the nuclear force?
Nature of the force in cold, dense nuclear matter
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Experimental approaches
 In
medium form factors using polarization transfer
 Elastic form factors of light nuclei
 Deuteron photo-disintegration
 Inclusive cross section measurements
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In medium form factors
 Question
– can the effects of the nuclear environment
on the nucleon structure be “summarized” in a change
to the form factor?
 Of interest for many years, but difficult to approach
experimentally and theoretically
 Measurements on 4He show standard calculations are
inadequate, QMC model of form factor modification
seems to improve calculations
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In medium form factors
E03-104 ran in Oct. 2006, will check both
increase at Q2 =1.6 and make improved induced
polarization measurement.
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Axial form factor
K. Tsushima, et al.,
PRC 70, 038501, (2004)
QMC model also
predicts substantional
modification of the axial
form factor with a 10%
change at low Q2
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Axial form factor
 QMC
model also predicts a 5% difference between
carbon and lead
 First measurements of this will be done by the
MINERnA experiment at FNAL
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Future needs
 The
only nucleus explored in detail have been 2H, and
4He


Would like to have high statistics measurements on 3H, 3He,
and some heavier nuclei, such as 12C or 16O
Requires continued running at lower energies
 High
intensity neutrino beams offer many new
opportunities
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Deuteron form factors
 As
the smallest nucleus, the deuteron is a key to
understanding short range behavior
 Elastic form factors at high Q2 are sensitive to models
of the short range correlations
 Good statistics at high Q2 requires the 12 GeV upgrade
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Deuteron form factors
Projected data for 12 GeV beam
For elastic ed, ds = sM (A+B tan2(q/2)),
Calculation of B has most model dependence
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Deuteron Photo-disintegration
 Both
polarization and cross section measurements have
given indications of the transition from the nucleonmeson regime to the quark-gluon regime
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Deuteron photo-disintegration
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Deuteron Photo-disintegration
Measurements can be
extended to larger
angles and momentum
transfer with 12 GeV
upgrade
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3He(g,pp)n
of 3He through pp pair can be
compared photo-disintegration of pn pair in deuteron
 Measurements made at CLAS (PRC 70, 064003,
2004), will continue with JLab experiment 03-005,
which will make measurements in the coming year
(Congress willing)
 Photo-disintegration
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Short Range Correlations
 Short
range correlations give a picture at the highest
densities.
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Short Range Correlations
A(e,e’)X, A = 3He, 4He,
12C, 56Fe
K. Egiyan, et al, (CLAS), PRC 68:014313,2003;
PRL 96, 082501,2006.
Measured Composition ( %)
1N state
2N SRC
3N SRC
2H
96 ± 0.7
4.0 ± 0.7
---
3He
92 ± 1.6
8.0 ± 1.6
0.18 ± 0.06
4He
86 ± 3.3
15.4 ± 3.3
0.42 ± 0.14
12C
80 ± 4.1
19.3 ± 4.1
0.55 ± 0.18
56Fe
76 ± 4.7
23.0 ± 4.7
0.79 ± 0.25
M. Strikman “Jefferson Lab may have directly
observed short-range nucleon correlations,
with densities similar to those at the heart of a
neutron star.” (CERN Courier 11/2005)
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Future work
 Search
for short range correlations needs higher beam
energies to explore higher x regime
 JLab proposal 12-06-105 will explore up to x=3
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Summary of existing progress
 Good
progress in determining the nature of the
transition from nucleon-meson regime to quark-meson
regime
 Polarization has been a key tool, but experimentally
difficult to pursue to much higher Q2
 Good progress in determining short-range correlations
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Future
 In
medium form factor measurements need to be done
on more nuclei with good statistics


Needs beam time at < 5 GeV on many nuclei
Neutrino beams would add significant new information
of deuteron, 3He needs higher
beam energies to continue studies
 Form factors of deuteron need 12 GeV to explore high
Q2 region
 Light nuclei form factors, esp. 3H, still could be greatly
improved
 Photo-disintegration
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Conclusions
 Still
work to be done with lower energy beams
 JLab upgrade will allow more efficient exploration of
the short range nature of the nuclear force
 Neutrino beams will provide a useful new tool
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Thanks
 Thanks
to Rolf Ent, Ron Gilman, Makis Petratros,
Steffen Strauch, Elaine Schulte, and Wally
Melnitchouk for help with this talk
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