The Hall A Tritium target program

John ArringtonArgonne National Lab

Joint Hall A & C Summer Collaboration Meeting

Newport News, VAJuly 17,2015

Outline

The JLab tritium target– Details from Roy Holt, David Meekins

Planned three-nucleon experiments– 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

(A)

Current x thickness

(A-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

JLab Luminosity ~ 2.6 x 1036 nuclei/cm2/s

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)

Target technical reports (2012-2014) 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. Scattering Chamber Isolation for the JLab Tritium Target, T. O’Connor, March 29, 2012. 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.

Task force: R. J. Holt, A. Katramatou, W. Korsch, D. Meekins, T. O’Connor, G. Petratos, R. Ransome, J. Singh, P. Solvignon, B. Wojtsekhowki

Don’t try this at home!(or a DOE lab)

Next review: September

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 A

JLab 3He & 3H MeasurementsE12-06-118: 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)

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

1) MARATHON: F2n/F2p, d(x)/u(x) as x 1

SU(6)-symmetric wave function of the proton in the quark model (spin up):

– u and d quarks identical– N and degenerate in mass– d/u = 1/2, F2

n/F2p = 2/3

SU(6) symmetry is broken: N- 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, F2

n/F2p = 1/4, for x -> 1

pQCD: helicity conservation (qp) => d/u =2/(9+1) = 1/5, F2n/F2

p = 3/7 for x -> 1

Dyson-Schwinger Eq.: Contains finite size S=0 and S=1 diquarks– d/u = 0.28, F2

n/F2p = 0.49

Several predictions based on simple assumptions about symmetries in proton

PDF predictions at large-x

Nucleon Model F2n/F2

p d/u u/u d/d A1n A1

p

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

0.41 0.18 0.88 -1/3 0.38 0.83

DSE realistic interaction

0.49 0.28 0.65 -0.26 0.17 0.59

pQCD 3/7 1/5 1 1 1 1

Neutron Structure Function

CJ12: J. Owens et al, PRD 87 (2013) 094012

JA, W. Melnitchouk, J. Rubin, PRL 108 (2012) 252001

Proton structure function:

Neutron structure function (isospin symmetry):

Ratio:

Focus on high x:

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

From three-body nuclei to the quarks

• Mirror symmetry of A=3 nuclei

– Extract F2n/F2

p 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

JLab E12-06-118: G. Petratos, R. Holt, R. Ransome, J. Gomez

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)

1) Mass vs. density dependence4He is low mass, higher density9Be is higher mass, low density3He is low mass, low density (no data)

Importance of light nuclei

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

Hard interaction at short rangeN-N interaction

Mean fieldpart

n(k

) [f

m-

3 ]

k [GeV/c]

2) Short-Range Correlations

Nucleon momentum distribution in 12C

Inclusive scattering at large x

e

e’

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-pelastic peak

JA, et al., PRL 82 (2001) 2056

Inclusive scattering at large x

Quasielastic scattering x 1

Motion of nucleon in the nucleus broadens the peak

By examining region of low energy transfer (x>1), suppress inelastic backgrounds

x=1: e-pelastic peak

super-elastic region, x>1

e

e’

Nucleus A

Inclusive scattering at large x

e

e’

Nucleus A

Quasielastic scattering x 1

Motion of nucleon in the nucleus broadens the peak

By examining region of low energy transfer (x>1), suppress inelastic backgrounds

x=1: e-pelastic peak High momentum tails should yield

constant ratio if SRC-dominated

QE

N. Fomin, et al., PRL 108 (2012) 092052

super-elastic region, x>1

SRC evidence: A/D ratios

High momentum tails should yield constant ratio if SRC-dominated

QE

N. Fomin, et al., PRL 108 (2012) 092052

Ratio of cross sections shows a (Q2-independent) plateau above x ≈ 1.5, as expected in SRC picture

n(k

) [f

m-3]

k [GeV/c]

Short-Range Correlations and x > 1

Nucleon momentum distribution in 12C

N. Fomin, et al., PRL 108 (2012) 092052

Short-rangeN-N effect

Drawbacks:•Can’t reconstruct initial momentum event-by-event •Can’t separate e-p and e-n scattering

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

Isospin structure of 2N-SRCs

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)

np pairs

pp pairs

Drawbacks:•Limited statistics (low cross sections)•Large final-state interactions

12C(e,e’pN): 90% of observed pairs are pn; tensor force isosinglet dominance

R(T=1/T=0) = 208%

Use inclusive scattering (high statistics, small FSI); gain isospin sensitivity through target isospin structure

Simple estimates for 2N-SRCIsospin 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) P. Solvignon, J. Arrington, D. Day, D. Higinbotham

2121

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 sharing

3) 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 3HNo neutron detection required

np-dominance at high-Pm implies n/p ratio 1

n/p at low Pm enhanced

L. Weinstein, O.Hen, W. Boeglin, S. Gilad

Map out difference between proton and neutron distribution up to (and slightly beyond) Fermi momentum

Charge radii: 3He and 3H(e,e’p)

RRMS = 0.20(10)

With new tritium target and JLab Luminosity, we aim to improve precision on RRMS by factor 3-5 over SACLAY results

One-time opportunity for 3H at JLabPrecise theoretical calculations of <r2

rms>3H, <r2rms>3He

Experimental results: large uncertainties, discrepancies

<r2rms>3H <r2

rms>3He

GFMC 1.77(1) 1.97(1)EFT 1.756(6) 1.962(4)SACLAY 1.76(9) 1.96(3)BATES 1.68(3) 1.97(3)Atomic -------- 1.959(4)

RRMS = 0.19(04)

L. Meyers, JA, D. Higinbotham1.5 PAC days

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– ….