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Short-Range Correlation Studies at JLab:
Recent Results and Upcoming Experiments
Nadia Fomin
University of Tennessee
June 21st, 2017
2017 Annual User Group Meeting1
2N SRC3N SRC
Nucleon
momentum
distribution in 12C
High momentum nucleons - Short Range Correlations
• Two nucleons with inter-
nucleon distance < size of
nucleon
• Hard core interaction low
CM momentum; high relative
momenta2
• Scaling of x>1 cross sections
relative to the deuteron
--implies high momentum tail is a
result of short-range correlations
• NP dominance of short-range pairs
--tensor interaction
• No trivial (A or density)
dependence for SRC behavior or
EMC effect
--from high-precision light nuclei
data
• Suggestive correlation between
EMC effect and SRC plateaus
What have we learned from 6GeV era?
3
Choosing an Appropriate Microscope
q
1
4
x=Ax=1
x=1
1<x<2 is combination of 2-body and 1*-body contributions; 3+ body
effect assumed to be small
(*=Fermi-smeared)Log-ish(xBj )
5
x=Ax=1
x=1
1<x<2 is combination of 2-body and 1*-body contributions; 3+ body
effect assumed to be small
(*=Fermi-smeared)Log-ish(xBj )
?
6
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 7
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
8
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 and we’re
probing 2-body physics
9
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
10
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
A
j
jj QxAaj
AQx1
22 ),()(1
),(
),()(2
2
22 QxAaA
....),()(3
2
33 QxAaA
QE
Jlab E02-019
11
Before my time
A
j
jj QxAaj
AQx1
22 ),()(1
),(
),()(2
2
22 QxAaA
....),()(3
2
33 QxAaA
• Moderate Q2 data from SLAC
• Originally analyzed in the y-scaling
picture
12
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
13
E02-019: 2N correlations in A/D ratios
<Q2>=2.7 GeV2Fomin et al, PRL 108 (2012)
Jlab E02-019 14
Test scaling in x and Q2
3He
12C
3He
12C
W
MW
M
Mq 22 41
2
22
15
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)
16
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 %
17
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)
18
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
2N correlations
Have not solved the nuclear
dependence
20
Linear relationship with EMC effect
•Fit the slope of the ratios for 0.3<x<0.7:
dx
dREMC
J.Seely, A. Daniel, et al., PRL103, 202301 (2009) 21
Upcoming experiments
• Tritium program in Hall A – First DIS measurements on 3H
– First x > 1 measurements on 3H; isospin and 3N-SRCs sensitivity
– Detailed extraction of proton, neutron momentum distributions
– High precision determination of the charge radius difference
• Inclusive program in Hall C
– Short-range nuclear structure
• Isospin dependence
• A-dependence (new nuclei)
– Super-fast quarks
– Precision EMC ratios on new nuclei
22
JLab Tritium Target
• Thin Al windows
– Beam entrance: 0.010”
– Beam exit: 0.011”
– Side windows: 0.018”
– 25 cm long cell at ~200 psi T2 gas
– Vacuum isolation window
• Tritium cell filled and sealed at Savannah River National Lab
– Pressure: accuracy to <1%,
– Purity: 99.9% T2 gas, main contaminant is D2
– 12.32 y half-life: after 1 year ~5% of 3H decayed to 3He
• Administrative current limit: 20 mA23
JLab 3He & 3H Measurements
E12-06-118: Marathon d/u ratios from 3H(e,e’)/3He(e,e’) DIS measurements E12-11-112: x>1 scattering: isospin structure of short-range correlations E12-14-011: Proton/neutron momentum distributions in 3H (3He)E12-14-009: elastic: 3H – 3He charge radius difference [3H “neutron skin”]
Thermo-mechanical design of a static gas target for electron accelerators B. Brajuskovic et al., NIM A 729 (2013) 469
Relatively small amount of tritium (~1kC) in a cell machined from single block of Al
24
Use inclusive scattering (high statistics, small FSI); gain isospin sensitivity
through target isospin structure
s 3H/3
s 3He/3
=(2pn +1nn) /3
(2pn +1pp) /3=1.0
Simple estimates for 2N-SRC
Isospin independent Full n-p dominance (no T=1)
Few body calculations [M. Sargisan, Wiringa/Peiper (GFMC)] predict n-p
dominance, but with sizeable contribution from T=1 pairs
40% difference between full isosinglet dominance and isospin independent
Goal is to measure 3He/3H ratio in 2N-SRC region with 1.5% precision
Extract R(T=1/T=0) to ±4%
Factor of two improvement over previous
triple-coincidence, with smaller FSI
Isospin structure of 2N-SRCs (JLab E12-11-112)
25
3He(e,e’p)/3H(e,e’p)
arXiv:1409.1717
JLab E12-14-011 Proton and Neutron Momentum Distributions in A = 3 Asymmetric Nuclei
3He/3H ratio for proton knockout n/p ratio in 3H No neutron detection
required
np-dominance at high-Pm
implies n/p ratio 1
n/p at low Pm enhanced
Spokespeople: L. Weinstein, O.Hen, W. Boeglin, S. Gilad
Map out difference between proton and neutron distribution up to (and slightly beyond) Fermi momentum
26
Jlab E12-06-105 && E12-10-008 in Hall C
• short-range nuclear structure
- Isospin dependence
- A-dependence
• Super-fast quarks
• EMC effect across nuclei
27
Jlab E12-06-105 && E12-10-008 in Hall C
• short-range nuclear structure
- Isospin dependence
- A-dependence
• Super-fast quarks
• EMC effect across nuclei
28
• Light nuclei for nuclear structure
studies
• Heavier nuclear for approximate
N/Z scan
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
29
3N correlations (x>2 inclusive scattering)
K. Egiyan et al, PRL96, 082501 (2006) <Q2> (GeV2): CLAS: 1.6 E02-019: 2.7
30
Have we actually seen 3N SRC in ratios?
31
3N correlations
32
3N correlations – isospin dependence
• 5% normalization uncertainty not shown – will likely improve
33
Can we see a second plateau?
Deuteron: smeared SRC similar to 2H
(A/D is ~flat) until x>1.8
3He: cross section of stationary 3N-SRC
begins to fall off closer to x=2.6. Sets in
EARLIER at high Q2
34
3N correlation measurements – 3H/3He
Momentum-isospin correlations for 3N-SRCs
p3 = p1 + p2
p1 = p2 = p3
extremely large momentum
“Star configuration”
(a) yields R(3He/3H) ≈ 1.4 if configuration is isospin-independent, as does (b)
(a) yields R(3He/3H) ≈ 3.0 if nucleon #3 is always the doubly-occurring nucleon
(a) yields R(3He/3H) ≈ 0.3 if nucleon #3 is always the singly-occurring nucleon
“Linear
configuration”
R≠1.4 implies isospin dependence AND
non-symmetric momentum sharing35
3N correlation measurements – Hall C
1H
2H
3He
4He
6,7Li
9Be
10,11B
12C
27Al
40*,48Ca
48Ti
54Fe
58,64Ni
64*Cu
108*Ag
119*Sn
197*Au
232Th
36
3N correlations – are we there yet? Is
there accessible
α3N_MIN=1.6
Where does 2N contribution become negligible?
Calculation by M. Sargsian37
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
Continue to probe correlation with EMC effect
• New results in the next few years! 38
In-Medium Nucleon Structure Functions[E11-107: O. Hen, L.B. Weinstein, S. Gilad, S.A. Wood]
• DIS scattering from nucleon in
deuterium
• Tag high-momentum struck nucleons
by detecting backward “spectator”
nucleon in Large-Angle Detector
aS = (ES - pSZ ) /mS
R ~
F2
tag
ge
d/F
2u
nta
gg
ed
Projected uncertainties
S. Jeschonnek and J.W. Van Orden, Phys. Rev. C 81, 014008 (2010) and
Phys. Rev. C 78, 014007 (2008); M.M. Sargsian, Phys. Rev. C82, 014612 (2010)
?
• Compare proton knock-
out from dense and thin
nuclei: 4He(e,e′p)3H and 2H(e,e′p)n
• Modern, rigorous 2H(e,e’p)n calculations
show reaction-dynamics
effects and FSI will
change the ratio at most
8%
• QMC model predicts 30%
deviation from free
nucleon at large virtuality
In-Medium Nucleon Form Factors[E11-002: E. Brash, G. M. Huber, R. Ransom, S. Strauch]
What have we learned from 6GeV era?
--Scaling of x>1 cross sections relative to the deuteron
--implies high momentum tail is a result of short-range correlations
--NP dominance of short-range pairs
-- tensor interaction
--No trivial (A or density) dependence for SRC behavior or EMC effect
-- from high-precision light nuclei data
--Suggestive correlation between EMC effect and SRC plateaus
How do we know this?
--slides explaining measurements
What’s coming up: Tritium for isospin dependence and to compare to
calculations, Hall C for further mapping out nuclear dependence.
Why not more correlations?
--3N stuff, upcoming attempts to measure
Internal Monologue
41
