The Hall A Tritium target program
John Arrington
Argonne National Lab
Joint Hall A & C Summer
Collaboration Meeting
Newport News, VA
July 17,2015
Outline
 The JLab tritium target
– Details from Roy Holt, David Meekins
 Planned three-nucleon experiments
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Deep inelastic scattering [F2n/F2p, (EMC effect)]
Inclusive QE at x > 1 [short-range correlations]
3H,3He(e,e’p)
[n,p momentum distributions]
Elastic scattering
[form factors, charge radii]
Tritium Targets at Electron Accelerators
Lab
Year
Quantity
(kCi)
Thickness
(g/cm2)
Current
(mA)
Current x
thickness
(mA-g/cm2)
Stanford
1963
25
0.8
0.5
0.4
MIT-Bates
1982
180
0.3
20
6.0
Saskatoon
1985
3
0.02
30
0.6
Saclay
1985
10
1.1
10
11.0
JLab
(2016)
1
0.08
25
2.0
Sufficient for detailed inclusive and QE studies of elastic and
quasielastic scattering at low-to-moderate Q2, and high-Q2 DIS
when coupled with high energy and large acceptance (BigBite)
JLab Luminosity ~ 2.6 x 1036 nuclei/cm2/s
Target technical reports (2012-2014)
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Jefferson Lab Tritium Target Cell, D. Meekins, November 28, 2014
Activation of a Tritium Target Cell, G. Kharashvili , June 25, 2014
A Tritium Gas Target for Jefferson Lab, R. J. Holt et al, April 8, 2014.
Thermomechanical Design of a Static Gas Target for Electron Accelerators, B. Brajuskovic et al.,
NIM A 729 (2013) 469.
Absorption Risks for a Tritium Gas Target at Jefferson Lab, R. J. Holt, August 13, 2013.
Beam-Induced and Tritium-Assisted Embrittlement of the Target Cell at JLab, R. E. Ricker (NIST),
R. J. Holt, D. Meekins, B. Somerday (Sandia), March 4, 2013.
Activation Analysis of a Tritium Target Cell for Jefferson Lab, R. J. Holt, D. Meekins, Oct. 23, 2012.
Tritium Inhalation Risks for a Tritium Gas Target at Jefferson Lab, R. J. Holt, October 10, 2012.
Tritium Permeability of the Al Target Cell, R. J. Holt, R. E. Ricker (NIST), D. Meekins, July 10, 2012.
(orTritium
a DOETarget,
lab) T. O’Connor, March 29, 2012.
Scattering Chamber Isolation for the JLab
Hydrogen Getter System for the JLab Tritium Target, T. O’Connor, W. Korsch, February 16, 2012.
Tritium Gas Target Safety Operations Algorithm for Jefferson Lab, R. J. Holt, February 2, 2012.
Tritium Gas Target Hazard Analysis for Jefferson Lab, E. Beise et al, January 18, 2012.
Analysis of a Tritium Target Release at Jefferson Lab, B. Napier (PNNL), R. J. Holt, January 10, 2012.
Don’t try this at home!
Next review: September
Task force: R. J. Holt, A. Katramatou, W. Korsch, D. Meekins, T. O’Connor, G. Petratos, R. Ransome,
J. Singh, P. Solvignon, B. Wojtsekhowki
Design Authority and Project Manager: Dave Meekins
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: 25 mA
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”]
(PR12-15-007: 3H charge and magnetic form factors at high Q2)
Relatively small amount of tritium (~1kC) in a cell machined from single block of Al
Thermo-mechanical design of a static gas target for electron accelerators
B. Brajuskovic et al., NIM A 729 (2013) 469
1) MARATHON: F2n/F2p, d(x)/u(x) as x  1
Several predictions based on simple assumptions about symmetries in proton
SU(6)-symmetric wave function of the proton in the quark model (spin up):
– u and d quarks identical
– N and D degenerate in mass
– d/u = 1/2, F2n/F2p = 2/3
SU(6) symmetry is broken: N-D Mass Splitting
– Mechanism produces mass splitting between S=1 and S=0 diquark spectator.
– symmetric states are raised, antisymmetric states are lowered (~300 MeV).
– S=1 suppressed => d/u = 0, F2n/F2p = 1/4, for x -> 1
pQCD: helicity conservation (qp) => d/u =2/(9+1) = 1/5, F2n/F2p = 3/7 for x -> 1
Dyson-Schwinger Eq.: Contains finite size S=0 and S=1 diquarks
– d/u = 0.28, F2n/F2p = 0.49
PDF predictions at large-x
Nucleon Model
F2n/F2p
d/u
Du/u
Dd/d
A1n
A1p
SU(6)
2/3
1/2
2/3
-1/3
0
5/9
Valence Quark
1/4
0
1
-1/3
1
1
DSE contact
interaction
DSE realistic
interaction
pQCD
0.41
0.18
0.88
-1/3
0.38
0.83
0.49
0.28
0.65
-0.26
0.17
0.59
3/7
1/5
1
1
1
1
Neutron Structure Function
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Proton structure function:
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Neutron structure function (isospin symmetry):
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Ratio:
CJ12: J. Owens et al, PRD 87 (2013) 094012
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Focus on high x:
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2 experiments to push to larger x, reduce extrap.
JLab12 experiments to reduce model dependence
– 3H/3He: 3H target and existing spectrometers
– Deuteron: radial TPC and CLAS12
– Proton : PVDIS on proton with SOLID
JA, W. Melnitchouk, J. Rubin, PRL 108 (2012) 252001
From three-body nuclei to the quarks
JLab E12-06-118: G. Petratos, R. Holt, R. Ransome, J. Gomez
• Mirror symmetry of A=3 nuclei
– Extract F2n/F2p from ratio of measured
3He/3H structure functions
R = Ratio of “EMC ratios” for 3He and 3H
Most systematic, theory uncertainties cancel
Relies only on difference in nuclear effects
• Calculated to 1.5%
High-x data from Jlab12 will provide
benchmark data for hadron structure
EMC effect:
A-dependence
SLAC E139
– Most precise large-x data
– Nuclei from A=4 to 197
Conclusions
– Universal x-dependence
– Magnitude varies
• Scales with A (~A-1/3)
• Scales with density
J. Gomez, et al., PRD49, 4349 (1994)
Importance of light nuclei
1) Mass vs. density dependence
4He is low mass, higher density
9Be is higher mass, low density
3He is low mass, low density (no data)
2) Constrain 2H – free nucleon difference
 JLab E03-013: JA and D. Gaskell
Marathon can provide measurement of
EMC effect in ‘isoscalar’ A=3 nucleus
2) Short-Range Correlations
n(k) [fm3]
N-N interaction
Hard interaction at short range
Nucleon momentum
distribution in 12C
Mean field
part
k [GeV/c]
Inclusive scattering at large x
e’
e
q
Nucleus
A
e-p elastic scattering: x = 1
Quasielastic scattering x  1
Motion of nucleon in the nucleus
broadens the peak
Low energy transfer region (x>1)
suppresses inelastic backgrounds
x=1: e-p
elastic peak
JA, et al., PRL 82 (2001) 2056
Inclusive scattering at large x
e’
e
q
Nucleus
A
Quasielastic scattering x  1
Motion of nucleon in the nucleus
broadens the peak
By examining region of low energy
super-elastic
transferx=1:
(x>1),
suppress
inelastic
region,
x>1
e-p
backgrounds
elastic peak
Inclusive scattering at large x
e’
e
QE
q
Nucleus
A
Quasielastic scattering x  1
Motion of nucleon in the nucleus
broadens the peak
By examining region of low energy
super-elastic
transferx=1:
(x>1),
suppress
inelastic
region,
x>1
e-p
backgrounds
elastic peak
High momentum tails should yield
constant ratio if SRC-dominated
N. Fomin, et al., PRL 108 (2012) 092052
SRC evidence: A/D ratios
QE
Ratio of cross sections shows a
(Q2-independent) plateau above
x ≈ 1.5, as expected in SRC picture
High momentum tails should yield
constant ratio if SRC-dominated
N. Fomin, et al., PRL 108 (2012) 092052
n(k) [fm-3]
Short-Range Correlations and x > 1
Nucleon momentum
distribution in 12C
Short-range
N-N effect
k [GeV/c]
N. Fomin, et al., PRL 108 (2012) 092052
Drawbacks:
• Can’t reconstruct initial momentum event-by-event
• Can’t separate e-p and e-n scattering
Isospin structure of 2N-SRCs
Two-nucleon knockout: 12C(e,e’pN), 4He(e,e’pN), A(e,e’pp)
• Reconstruct initial high momentum proton
• Look for fast spectator nucleon from SRC in opposite direction
• Find spectator ~100% of the time, neutron >90% of the time
• Fraction of pp pairs increases with initial nucleon momentum
R. Subedi, et al., Science 320, 1476 (2008)
I. Korover, et al., PRL 113, 022501 (2014)
O. Hen, et al., Science 346, 6209 (2014)
R. Schiavilla, et al., PRL 98, 132501 (2007)
12C(e,e’pN):
90% of observed pairs are
pn; tensor force  isosinglet dominance
R(T=1/T=0) = 208%
Drawbacks:
• Limited statistics (low cross sections)
• Large final-state interactions
Isospin structure of 2N-SRCs (JLab E12-11-112)
P. Solvignon, J. Arrington, D. Day, D. Higinbotham
Use inclusive scattering (high statistics, small FSI); gain isospin sensitivity
through target isospin structure
Simple estimates for 2N-SRC
Isospin independent
Full n-p dominance (no T=1)
s
s
3
3
H
He
/3
/3
=
(2 pn + 1nn) /3
= 1.0
(2 pn + 1pp) /3
 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
Momentum-isospin correlations for 3N-SRCs
“Linear configuration”
p3 = p1 + p2
extremely large momentum
“Star configuration”
p1 = p2 = p3
(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
R≠1.4 implies isospin dependence AND
non-symmetric momentum sharing
21
21
3) 3He(e,e’p)/3H(e,e’p)
JLab E12-14-011 Proton and Neutron Momentum Distributions in A = 3 Asymmetric Nuclei
L. Weinstein, O.Hen, W. Boeglin, S. Gilad
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
Map out difference between proton and neutron
distribution up to (and slightly beyond) Fermi momentum
arXiv:1409.1717
Charge radii: 3He and 3H(e,e’p)
L. Meyers, JA, D. Higinbotham
1.5 PAC days
One-time opportunity for 3H at JLab
Precise theoretical calculations of <r2rms>3H, <r2rms>3He
Experimental results: large uncertainties, discrepancies
GFMC
EFT
SACLAY
BATES
Atomic
<r2rms>3H
1.77(1)
1.756(6)
<r2rms>3He
1.97(1)
1.962(4)
1.76(9)
1.68(3)
--------
1.96(3)
1.97(3)
1.959(4)
DRRMS = 0.20(10)
DRRMS = 0.19(04)
With new tritium target and JLab Luminosity, we aim to improve
precision on DRRMS by factor 3-5 over SACLAY results
Summary
 Experiments with 3H at JLab can provide:
• 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
 Textbook physics experiments – benchmark data
 Polarized triton target and experiments should be evaluated
Polarized tritium target?
 Safe: chemically contained by Li3H, low beam currents ~100 nA
 New possible experiments
– Bjorken sum rule from polarized electron scattering from
polarized 3H and 3He
– Medium modification of GEp/GMp of bound proton: single and
double arm experiments
– EMC effect on polarized proton in a nucleus: g1p and nuclear
structure known very well
– ….