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 –Deep inelastic scattering [F2n/F2p, (EMC effect)] –Inclusive QE at x > 1 [short-range correlations] – 3 H, 3 He(e,e’p) [n,p momentum distributions] –Elastic scattering [form factors, charge radii]

Tritium Targets at Electron Accelerators LabYearQuantity (kCi) Thickness (g/cm 2 ) Current (  A) Current x thickness (  A-g/cm 2 ) Stanford MIT-Bates Saskatoon Saclay JLab(2016) JLab Luminosity ~ 2.6 x nuclei/cm 2 /s Sufficient for detailed inclusive and QE studies of elastic and quasielastic scattering at low-to-moderate Q 2, and high-Q 2 DIS when coupled with high energy and large acceptance (BigBite)

Target technical reports ( )  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,  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,  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,  Activation Analysis of a Tritium Target Cell for Jefferson Lab, R. J. Holt, D. Meekins, Oct. 23,  Tritium Inhalation Risks for a Tritium Gas Target at Jefferson Lab, R. J. Holt, October 10,  Tritium Permeability of the Al Target Cell, R. J. Holt, R. E. Ricker (NIST), D. Meekins, July 10,  Scattering Chamber Isolation for the JLab Tritium Target, T. O’Connor, March 29,  Hydrogen Getter System for the JLab Tritium Target, T. O’Connor, W. Korsch, February 16,  Tritium Gas Target Safety Operations Algorithm for Jefferson Lab, R. J. Holt, February 2,  Tritium Gas Target Hazard Analysis for Jefferson Lab, E. Beise et al, January 18,  Analysis of a Tritium Target Release at Jefferson Lab, B. Napier (PNNL), R. J. Holt, January 10, 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 T 2 gas –Vacuum isolation window  Tritium cell filled and sealed at Savannah River National Lab –Pressure: accuracy to <1%, –Purity: 99.9% T 2 gas, main contaminant is D 2 –12.32 y half-life: after 1 year ~5% of 3 H decayed to 3 He  Administrative current limit: 25  A

JLab 3 He & 3 H Measurements E : Marathon d/u ratios from 3 H(e,e’)/ 3 He(e,e’) DIS measurements E : x>1 scattering: isospin structure of short-range correlations E : Proton/neutron momentum distributions in 3H (3He) E : elastic: 3 H – 3 He charge radius difference [ 3 H “neutron skin”] (PR : 3 H charge and magnetic form factors at high Q 2 ) 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: F 2n /F 2p, 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, F 2 n /F 2 p = 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, F 2 n /F 2 p = 1/4, for x -> 1 pQCD: helicity conservation (q  p) => d/u =2/(9+1) = 1/5, F 2 n /F 2 p = 3/7 for x -> 1 Dyson-Schwinger Eq.: Contains finite size S=0 and S=1 diquarks –d/u = 0.28, F 2 n /F 2 p = 0.49 Several predictions based on simple assumptions about symmetries in proton

PDF predictions at large-x Nucleon ModelF 2 n /F 2 p d/u  u/u  d/d A1nA1n A1pA1p SU(6)2/31/22/3-1/305/9 Valence Quark1/401-1/311 DSE contact interaction / DSE realistic interaction pQCD3/71/51111

Neutron Structure Function CJ12: J. Owens et al, PRD 87 (2013) JA, W. Melnitchouk, J. Rubin, PRL 108 (2012)  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 – 3 H/ 3 He: 3 H 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 F 2 n /F 2 p from ratio of measured 3 He/ 3 H structure functions R = Ratio of “EMC ratios” for 3 He and 3 H 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 E : 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 dependence 4 He is low mass, higher density 9 Be is higher mass, low density 3 He is low mass, low density (no data) Importance of light nuclei 2) Constrain 2 H – 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 range N-N interaction Mean field part n(k) [fm - 3 ] k [GeV/c] 2) Short-Range Correlations Nucleon momentum distribution in 12 C

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-p elastic 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-p elastic 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-p elastic peak High momentum tails should yield constant ratio if SRC-dominated QE N. Fomin, et al., PRL 108 (2012) 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) Ratio of cross sections shows a (Q 2 -independent) plateau above x ≈ 1.5, as expected in SRC picture

n(k) [fm -3 ] k [GeV/c] Short-Range Correlations and x > 1 Nucleon momentum distribution in 12 C N. Fomin, et al., PRL 108 (2012) Short-range N-N effect Drawbacks: Can’t reconstruct initial momentum event-by-event Can’t separate e-p and e-n scattering

Two-nucleon knockout: 12 C(e,e’pN), 4 He(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, (2014) O. Hen, et al., Science 346, 6209 (2014) R. Schiavilla, et al., PRL 98, (2007) np pairs pp pairs Drawbacks: Limited statistics (low cross sections) Large final-state interactions 12 C(e,e’pN): 90% of observed pairs are pn; tensor force  isosinglet dominance R(T=1/T=0) = 20  8%

Use inclusive scattering (high statistics, small FSI); gain isospin sensitivity through target isospin structure Simple estimates for 2N-SRC Isospin independentFull 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 3 He/ 3 H 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 E ) P. Solvignon, J. Arrington, D. Day, D. Higinbotham

21 Momentum-isospin correlations for 3N-SRCs p 3 = p 1 + p 2 p 1 = p 2 = p 3 extremely large momentum “Star configuration” (a) yields R( 3 He/ 3 H) ≈ 1.4 if configuration is isospin-independent, as does (b) (a) yields R( 3 He/ 3 H) ≈ 3.0 if nucleon #3 is always the doubly-occurring nucleon (a) yields R( 3 He/ 3 H) ≈ 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) 3 He(e,e’p)/ 3 H(e,e’p) arXiv: JLab E Proton and Neutron Momentum Distributions in A = 3 Asymmetric Nuclei 3 He/ 3 H ratio for proton knockout  n/p ratio in 3 H  No neutron detection required np-dominance at high-P m implies n/p ratio  1 n/p at low P m 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: 3 He and 3 H(e,e’p)  R RMS = 0.20(10) With new tritium target and JLab Luminosity, we aim to improve precision on  R RMS by factor 3-5 over SACLAY results One-time opportunity for 3 H at JLab Precise theoretical calculations of 3H, 3He Experimental results: large uncertainties, discrepancies 3H 3He GFMC1.77(1)1.97(1)  EFT 1.756(6)1.962(4) SACLAY1.76(9)1.96(3) BATES1.68(3)1.97(3) Atomic (4)  R RMS = 0.19(04) L. Meyers, JA, D. Higinbotham 1.5 PAC days

Summary  Experiments with 3 H at JLab can provide: First DIS measurements on 3 H First x > 1 measurements on 3 H; 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 Li 3 H, low beam currents ~100 nA  New possible experiments –Bjorken sum rule from polarized electron scattering from polarized 3 H and 3 He –Medium modification of G Ep /G Mp of bound proton: single and double arm experiments –EMC effect on polarized proton in a nucleus: g 1 p and nuclear structure known very well –….