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Short-range NN interactions:
Experimental Past and Future
Nadia Fomin
University of Tennessee
April 12th, 2017
Electron scattering is a great tool for studying subatomic structure:
unlike a proton, it cannot be absorbed by the nucleus
resolution varies with momentum transfer, allowing us to probe
the entire volume of the nucleus
Choosing an Appropriate Microscope
q
1
"for his pioneering studies of electron
scattering in atomic nuclei and for his
thereby achieved discoveries
concerning the structure of the
nucleons"
R. Hofstadter
Nobel Prize 1961
Collisions – Measured Cross sections
M
Qx
QMMW
qqQ
EE
2
2
'
2
222
2222
θ
dΩ
dN
flux F
electrons of energy E dFNdN )(
Number of scattering centersTarget
scattered
electrons of energy E’
Thomas
Jefferson
National
Accelerator
Facility
A B C
Electron
Source
Linacs
Experimental Halls
D
now with an 11 GeV beam
High momentum tails in A(e,e’p)
• E89-004: Measure of 3He(e,e’p)d
• Measured far into high momentum
tail: Cross section is ~5-10x
expectation
Difficulty
• High momentum pair can come from
SRC (initial state)
OR
• Final State Interactions (FSI) and
Meson Exchange Contributions (MEC)
“slow” nucleons “fast” nucleons
p p p p
A(e,e’p)
2H(e,e’p) Mainz
PRC 78 054001 (2008)
E =0.855 GeV
θ = 45o
E’=0.657 GeV
Q2=0.33 GeV2
x=0.88
Unfortunately: FSI, MECs
overwhelm the high momentum
nucleons
2N SRC3N SRC
Nucleon
momentum
distribution in 12C
High momentum nucleons
- Short Range Correlations
Try inclusive scattering!
Select kinematics such that
the initial nucleon
momentum > kf
2N SRC3N SRC
High momentum nucleons
- Short Range Correlations
22*
1
22
)(),('
kMpMMArg
ArgEkSdEkddEd
d
AA
iei
QE
||
22
2
)(2
)()(
1),(
y
np
kdkkn
qyMNZdd
dyF
Ok for A=2
Deuterium
Fomin et al, PRL 108 (2012)
2N SRC3N SRC
C. Ciofi degli Atti and S.
Simula, Phys. Rev. C 53
(1996).
Nucleon
momentum
distribution in 12C
High momentum nucleons
- Short Range Correlations
2N SRC3N SRC
C. Ciofi degli Atti and S.
Simula, Phys. Rev. C 53
(1996).
P>kfermi
Nucleon
momentum
distribution in 12C
High momentum nucleons
- Short Range Correlations
Mean
field
High
momentum
from SRCs
Short Range Correlations• To experimentally probe SRCs, must be in the high-momentum region (x>1)
• To measure the relative probability of
finding a correlation, ratios of heavy to light
nuclei are taken
• In the high momentum region, FSIs are
thought to be confined to the SRCs and
therefore, cancel in the cross section ratios
)(2
2 AaA D
A
1.4<x<2 => 2 nucleon correlation
2.4<x<3 => 3 nucleon correlation
• L. L. Frankfurt and M. I. Strikman, Phys.
Rept. 76, 215(1981).
• J. Arrington, D. Higinbotham, G. Rosner, and
M. Sargsian (2011), arXiv:1104.1196
• L. L. Frankfurt, M. I. Strikman, D. B. Day, and
M. Sargsian, Phys. Rev. C 48, 2451 (1993).
• L. L. Frankfurt and M. I. Strikman, Phys.
Rept. 160, 235 (1988).
• C. C. degli Atti and S. Simula, Phys. Lett. B
325, 276 (1994).
• C. C. degli Atti and S. Simula, Phys. Rev. C
53, 1689 (1996).
A
j
jj QxAaj
AQx1
22 ),()(1
),(
),()(2
2
22 QxAaA
....),()(3
2
33 QxAaA
Before my time
A
j
jj QxAaj
AQx1
22 ),()(1
),(
),()(2
2
22 QxAaA
....),()(3
2
33 QxAaA
1.4<x<2 => 2 nucleon correlation
2.4<x<3 => 3 nucleon correlation
Previous measurements
Egiyan et al, Phys.Rev.C68, 2003
No observation of scaling for
Q2<1.4 GeV2
1.4<x<2 => 2 nucleon correlation
2.4<x<3 => 3 nucleon correlation
Test scaling in x and Q2
3He
12C
3He
12C
W
MW
M
Mq 22 41
2
22
αi represents the light cone nuclear momentum fraction carried by the
constituent nucleon𝜶𝒊 =
𝒑𝒊−𝒑𝑨−/𝑨
SRC
EMC
J.Seely, et al., PRL 103, 202301 (2009)
Enter 9Be
N. Fomin et al, PRL 108 (2012)
a2
-1
O. Hen, et al, PRC 85, 047301 (2012)
L. Weinstein, et al., PRL 106, 052301 (2011)
J. Seely, et al., PRL103, 202301 (2009)
N. Fomin, et al., PRL 108, 092052 (2012)
JA, A. Daniel, D. Day, N. Fomin, D.
Gaskell, P. Solvignon, PRC 86, 065204
(2012)
• Goal was a measurement of the lepton-nucleon
cross section at high Q2
• To achieve statistical precision in a
reasonable amount of time, an iron target
was used, on the assumption that
meaning
Discovery of the EMC effect
12/
/
D
A A
)()()( 222 xNFxZFxF npA
e-
e-
MA
M*A-1
DIS
W2≥(Mn+Mπ)2
)(2
1)(
)]()([2
1)(
21
2
1
xFx
xF
xqxqexF iii
Shadowing
Anti-Shadowing
(pion excess)Fermi motion effects
EMC region
)()()( 222 xNFxZFxF npA
Nuclear dependence of the
structure functions discovered
30+ years ago by the European
Muon Collaboration (EMC effect)
The EMC effect
Nucleon structure functions are
modified by the nuclear medium
Depletion of high-x quarks for
A>2 nuclei is not expected or
understood
Measurements before 2004
• NMC – extraction of F2n/F2
p
• BCDMS -- 50 < Q2 < 200 (GeV2)
• HERMES – first measurement on 3He
• SLAC E139 – most precise large
x data
• Q2 independent
• Universal shape
• Magnitude approximately
scales with density
Nucleon structure is modified in the nuclear medium
or
Nuclear structure is modified due to hadronic effects
Models of the EMC effect
• Dynamical rescaling
• Nucleon ‘swelling’
• Multiquark clusters (6q, 9q ‘bags’)
• More detailed binding calculations
•Fermi motion + binding
• N-N correlations
• Nuclear pions
Nuclear Dependence of the EMC effect
Quark distributions are modified in
nuclei
Modification scales with A
ratio evaluated at x=0.6
ratio evaluated at x=0.6
4He
4He
Precision results on light
nuclei from JLab E03-103
•C/D and 4He/D ratios – no
isoscalar correction necessary
•Consistent with SLAC results, but
much higher precision at high x
PhD theses: J. Seely, A. Daniel
•Fit the slope of the ratios for
0.35<x<0.7:
• Compare across nuclei
dx
dREMC
J.Seely, A. Daniel, et al., PRL103, 202301 (2009)
SRC
EMC
J.Seely, et al., PRL 103, 202301 (2009)
Enter 9Be
N. Fomin et al, PRL 108 (2012)
a2
-1
O. Hen, et al, PRC 85, 047301 (2012)
L. Weinstein, et al., PRL 106, 052301 (2011)
J. Seely, et al., PRL103, 202301 (2009)
N. Fomin, et al., PRL 108, 092052 (2012)
JA, A. Daniel, D. Day, N. Fomin, D.
Gaskell, P. Solvignon, PRC 86, 065204
(2012)
2N knockout experiments establish NP dominance
R. Subedi et al., Science
320, 1476 (2008)
R. Shneor et al.,
PRL 99, 072501 (2007)
• Knockout high-initial-
momentum proton, look for
correlated nucleon partner.
• For 300 < Pmiss < 600 MeV/c all
nucleons are part of 2N-SRC
pairs: 90% np, 5% pp (nn)
2N knockout experiments establish NP dominance
R. Subedi et al., Science
320, 1476 (2008)
R. Shneor et al.,
PRL 99, 072501 (2007)
9.5 ± 2 %
96 ± 23 %
NP dominance
R. Subedi et al., Science
320, 1476 (2008)
R. Shneor et al.,
PRL 99, 072501 (2007)9.5 ± 2 %
96 ± 23
%
also Ciofi and Alvioli PRL 100, 162503 (2008)Sargsian, Abrahamyan, Strikman, Frankfurt PR C71 044615 (2005)
Slide courtesy O. Hen
Data mining using CLAS NP dominance continues for heavy nuclei
Assuming scattering off 2N-SRC pairs:
• (e,e’p) is sensitive to np and pp pairs
• (e,e’pp) is sensitive to pp pairs alone
=> (e,e’pp)/(e,e’p) ratio is sensitive to the np/pp
ratio
Coming very soon: [A=3 Measurements]
• Quasielastic electron scattering with 3H and 3He
• Study isospin dependence of 2N and 3N correlations
• Test calculations of FSI for well-understood nuclei
• EMC effect on A=3 nuclei
More nucleons in a correlation
1.4<x<2 => 2 nucleon correlation
2.4<x<3 => 3 nucleon correlation
A
j
jj QxAaj
AQx1
22 ),()(1
),(
),()(2
2
22 QxAaA
....),()(3
2
33 QxAaA
2N SRC3N SRC
3N correlations (x>2 inclusive scattering)
K. Egiyan et al, PRL96, 082501 (2006) <Q2> (GeV2): CLAS: 1.6 E02-019: 2.7
Jlab E12-06-105
&& E12-10-008• short-range nuclear structure
- Isospin dependence
- A-dependence
• Super-fast quarks
Jlab E12-06-105
&& E12-10-008• short-range nuclear structure
- Isospin dependence
- A-dependence
• Super-fast quarks
Summary
• SRCs and EMC effect have been under the
microscope for many decades – 6GeV era at
Jlab has yielded interesting data
• 12 GeV experiments continue the search
• Upcoming experiments in Halls A/C
Study short range correlations in 3He/3H
Map out nuclear dependencies of clustering
Study how quark distributions are modified in nuclei over
free nucleons
• New results in the next few years!