EMC Effect: Isospin dependence and PVDIS

Transcription

1 EMC Effect: Isospin dependence and PVDIS Ian Cloët Argonne National Laboratory Quantitative challenges in EMC and SRC Research and Data-Mining Massachusetts Institute of Technology 2 5 December 216

2 The EMC effect In the early 8s physicists at CERN thought that nucleon structure studies using DIS could be enhanced (by a factor A) using nuclear targets The European Muon Collaboration (EMC) conducted DIS experiments on an iron target F 2 Fe /F 2 D J. J. Aubert et al., Phys. Lett. B 123, 275 (1983) Fe EMC effect expectation before EMC experiment Experiment (Gomez et al., Phys. Rev. D 49, 4348 (1994).) x The results are in complete disagreement with the calculations... We are not aware of any published detailed prediction presently available which can explain behavior of these data. Measurement of the EMC effect created a new paradigm regarding QCD and nuclear structure more than 3 years after discovery a broad consensus on explanation is lacking what is certain: valence quarks in nucleus carry less momentum than in a nucleon One of the most important nuclear structure discoveries since advent of QCD understanding its origin is critical for a QCD based description of nuclei table of contents Quantitative challenges in EMC and SRC 2 5 December / 17

3 Understanding the EMC effect The puzzle posed by the EMC effect will only be solved by conducting new experiments that expose novel aspects of the EMC effect Measurements should help distinguish between explanations of EMC effect e.g. whether all nucleons are modified by the medium or only those in SRCs Important examples are: EMC effect in polarized structure functions flavour dependence of EMC effect JLab DIS experiment on 4 Ca & 48 Ca sensitive to flavour dependence but to truely access flavour dependence PVDIS must play a pivotal role EMC ratios Q 2 = 5 GeV 2 ρ =.16 fm 3 I. Sick and D. Day, Phys. Lett. B 274, 16 (1992). EMC effect Polarized EMC effect EMC ratios Z/N = 82/126 (lead) F 2A /F 2D d A /d f u A /u f Q 2 = 5 GeV x x table of contents Quantitative challenges in EMC and SRC 2 5 December / 17

4 Nucleons in Nuclei Nuclei are extremely dense: proton rms radius is rp ' 5 fm, corresponds hard sphere rp ' 1.1 fm ideal packing gives ρ '.13 fm 3 ; nuclear matter density is ρ '.16 fm 3 2% of nucleon volume inside other nucleons nucleon centers 2 fm apart Natural to expect that nucleon properties are modified by nuclear medium even at the mean-field level in contrast to traditional nuclear physics 2 π b ρ1 (b) [fm 1 ] For realistic charge distribution 25% of proton charge at distances r > 1 fm 1.5 proton neutron 1..5 Understanding validity of two viewpoints.5 1. remains key challenge for nuclear physics b [fm] a new paradigm or deep insights into colour confinement in QCD table of contents Quantitative challenges in EMC and SRC 2 5 December / 17

5 Nucleons in Nuclei Nuclei are extremely dense: proton rms radius is r p 5 fm, corresponds hard sphere r p 1.1 fm ideal packing gives ρ.13 fm 3 ; nuclear matter density is ρ.16 fm 3 2% of nucleon volume inside other nucleons nucleon centers 2 fm apart For realistic charge distribution 25% of proton charge at distances r > 1 fm Natural to expect that nucleon properties are modified by nuclear medium even at the mean-field level in contrast to traditional nuclear physics Understanding validity of two viewpoints remains key challenge for nuclear physics ρ(r) [fm 3 ] 2 π b ρ1(b) [fm 1 ] He AV18+UX ideal packing limit r [fm] proton neutron b [fm] a new paradigm or deep insights into colour confinement in QCD table of contents Quantitative challenges in EMC and SRC 2 5 December / 17

6 Quarks, Nuclei and the NJL model Continuum QCD integrate out gluons 1 m 2 g Θ(Λ2 k 2 ) this is just a modern interpretation of the Nambu Jona-Lasinio (NJL) model model is a Lagrangian based covariant QFT, exhibits dynamical chiral symmetry breaking & quark confinement; elements can be QCD motivated via the DSEs Quark confinement is implemented via proper-time regularization quark propagator: [/p m + iε] 1 Z(p 2 )[/p M + iε] 1 wave function renormalization vanishes at quark mass-shell: Z(p 2 = M 2 ) = confinement is critical for our description of nuclei and nuclear matter 1 π α eff(k 2 ) NJL DSEs ω =.6 S. x. Qin et al., Phys. Rev. C 84, 4222 (211) k [GeV] M(p) [GeV] NJL DSEs p [GeV] table of contents Quantitative challenges in EMC and SRC 2 5 December / 17

7 Nucleons in the Nuclear Medium For nuclei, we find that quarks bind together into colour singlet nucleons however contrary to traditional nuclear physics approaches these quarks feel the presence of the nuclear environment as a consequence bound nucleons are modified by the nuclear medium Modification of the bound nucleon wave function by the nuclear medium is a natural consequence of quark level approaches to nuclear structure For a proton in nuclear matter find Dirac & charge radii each increase by about 8%; Pauli & magnetic radii by 4% F2p () decreases; however F2p /2MN largely constant µp almost constant 1. free current NM current empirical F1p(Q2).6 (ρb =.16 fm 3 ) Q2 [GeV2] table of contents Quantitative challenges in EMC and SRC 2 5 December / 17

8 Nucleons in the Nuclear Medium F1p(Q 2 ) For nuclei, we find that quarks bind together into colour singlet nucleons however contrary to traditional nuclear physics approaches these quarks feel the presence of the nuclear environment as a consequence bound nucleons are modified by the nuclear medium Modification of the bound nucleon wave function by the nuclear medium is a natural consequence of quark level approaches to nuclear structure For a proton in nuclear matter find Dirac & charge radii each increase by about 8%; Pauli & magnetic radii by 4% F 2p () decreases; however F 2p /2M N largely constant µ p almost constant free current NM current (ρb=.16 fm 3 ) empirical Q 2 [GeV 2 ] F2p(Q 2 ) free current NM current (ρb=.16 fm 3 ) empirical Q 2 [GeV 2 ] table of contents Quantitative challenges in EMC and SRC 2 5 December / 17

9 EMC effect in light nuclei [J. Seely et al., PRL 13, 2231 (29)] EMC effect determined by local density 9 Be consistent with our mean-field approach table of contents Quantitative challenges in EMC and SRC 2 5 December / 17

10 Isovector EMC Effect? Why should we expect a (large) isovector EMC effect? Consider the Bethe Weizsäcker mass formula E B = a V A a S A 2/3 Z 2 a C A a (A 2 Z) 2 1/3 A ± δ(a, Z) A a V = a S = 17.8 a C =.711 a A = 23.7 a P = 11.8 [J. W. Rohlf (1994)] There is a trivial isovector EMC effect from: N Z = u A d A non-trivial effect must remain after isoscalarity correction to have a flavour dependent EMC effect f ISO A (x) = A 2 F 2p + F 2n Z F 2p + N F 2n table of contents Quantitative challenges in EMC and SRC 2 5 December / 17

11 NJL at Finite Density Finite density (mean-field) Lagrangian: qq interaction in σ, ω, ρ channels L = ψ q (i M V q ) ψ q + L I Fundamental physics mean fields couple to the quarks in nucleons Masses [GeV] ρ [fm 3 ] M Ms Ma MN EB/A [MeV] Z/N = Z/N =.1 Z/N =.2 Z/N =.5 Z/N = ρ [fm 3 ] Quark propagator: S(k) 1 = /k M + iε S q (k) 1 = /k M /V q + iε Hadronization + mean field = effective potential V u(d) = ω ± ρ, ω = 6 G ω (ρ p + ρ n ), ρ = 2 G ρ (ρ p ρ n ) G ω Z = N saturation & G ρ symmetry energy table of contents Quantitative challenges in EMC and SRC 2 5 December / 17

12 SRCs shift momentum from n to p therefore opposite to mean-field medium modification from SRCs needs to compensate for this table of contents Quantitative challenges in EMC and SRC 2 5 December / 17 Flavour dependence of EMC effect [ICC, W. Bentz and A. W. Thomas, Phys. Rev. Lett. 12, (29)] Z/N = 26/3 (Iron) Z/N = 82/126 (Lead) 1.1 EMC ratios EMC ratios 1.9 R γ Fe R γ Pb d A /d f.7 d A /d f u A /u f Q 2 = 5. GeV 2.6 u A /u f Q 2 = 5. GeV x x Find that EMC effect is basically a result of binding at the quark level for N > Z nuclei, d-quarks feel more repulsion than u-quarks: V d > V u therefore u quarks are more bound than d quarks Find isovector mean-field shifts momentum from u-quarks to d-quarks p + ( p + q(x) = p + V + q p + V + x V q + ) p + V +

13 SRCs shift momentum from n to p therefore opposite to mean-field medium modification from SRCs needs to compensate for this table of contents Quantitative challenges in EMC and SRC 2 5 December / 17 Flavour dependence of EMC effect EMC ratios [ICC, W. Bentz and A. W. Thomas, Phys. Rev. Lett. 12, (29)] 1.2 Z/N = 2/28 (calcium-48) Z/N = 82/126 (Lead) 1.1 F 2A /F 2D R γ Pb d A /d f.7 d A /d f u A /u f Q 2 = 5 GeV 2.6 u A /u f Q 2 = 5. GeV x EMC ratios x Find that EMC effect is basically a result of binding at the quark level for N > Z nuclei, d-quarks feel more repulsion than u-quarks: V d > V u therefore u quarks are more bound than d quarks Find isovector mean-field shifts momentum from u-quarks to d-quarks p + ( p + q(x) = p + V + q p + V + x V q + ) p + V +

14 Weak mixing angle and the NuTeV anomaly sin 2 θ W MS APV(Cs) Standard Model Completed Experiments Future Experiments SLAC E158 NuTeV Fermilab 21 press release: The predicted value was The value we found was.2277, a difference of.5. It might not sound like much, but the room full of physicists fell silent when we first revealed the result Møller [JLab] Qweak [JLab] PV-DIS [JLab] Z-pole D CDF Q (GeV) 99.75% probability that the neutrinos are not behaving like other particles... only 1 in 4 chance that our measurement is consistent with prediction NuTeV: sin 2 θ W =.2277 ±.13(stat) ±.9(syst) [G. P. Zeller et al. Phys. Rev. Lett. 88, 9182 (22)] Standard Model: sin 2 θ W =.2227 ±.4 3σ = NuTeV anomaly Huge amount of experimental & theoretical interest [6+ citations] Evidence for physics beyond the Standard Model? No widely accepted complete explanation table of contents Quantitative challenges in EMC and SRC 2 5 December / 17

15 Paschos-Wolfenstein ratio Paschos-Wolfenstein ratio motivated the NuTeV study: R P W = σν NC A σ ν NC A σcc ν A σ ν CC A xa q A = ( ) ( 9 sin2 θ W xa u 1 A ) 9 sin2 θ W xa d x A d A +x A s A 1 3 x A u A A +x A s A fraction of target momentum carried by valence quarks of flavor q For an isoscalar target u A d A and if s A u A + d A R P W = 1 2 sin2 θ W + R P W ; R P W = ( sin2 θ W ) xa u A x A d A x A s A x A u A +x A d A R P W well constrained = excellent way to measure weak mixing angle NuTeV result for R P W is smaller than Standard Model value Studies suggest that largest contributions to R P W maybe: strange quarks charge symmetry violation (CSV) = u p d n, d p u n nuclear effects NuTeV target was 69 tons of steel? = non-trivial nuclear corrections table of contents Quantitative challenges in EMC and SRC 2 5 December / 17

16 sin 2 θ W MS A Reassessment of the NuTeV anomaly Standard Model Experiments [Bentz, ICC et. al, PLB 693, 462 (21)] APV(Cs) SLAC E158 NuTeV NuTeV + EMC + CSV + strangeness }{{} Standard Model corrections Z-pole D CDF Q (GeV) Paschos-Wolfenstein ratio motivated NuTeV study: R P W = σν A NC σcc ν A σ ν A NC σ ν A CC N Z = 1 2 sin2 θ W NuTeV: sin 2 θ W =.2277 ±.13(stat) ±.9(syst) + ( sin2 θ W ) x u A x d A x u A +x d A [Zeller et al. PRL. 88, 9182 (22)] Standard Model: sin 2 θ W =.2227 ±.4 3σ = NuTeV anomaly Using NuTeV functionals: sin 2 θ W =.2221 ±.13(stat) ±.2(syst) Corrections from the EMC effect ( 1.5 σ) and charge symmetry violation ( 1.5 σ) brings NuTeV result into agreement with the Standard Model consistent with mean-field expectation momentum shifted from u to d quarks table of contents Quantitative challenges in EMC and SRC 2 5 December / 17

17 New insights from Parity-Violating DIS PVDIS can test this explanation for the NuTeV anomaly & provide much needed new insight into the EMC effect X l l γ X A + l l Z X 2 A γ Z interference gives non-zero asymmetry; in Bjorken limit: A P V = σ R σ L = G F Q 2 ] σ R + σ L 4 1 (1 y)2 [a 2 (x) + 2 α em 1 + (1 y) 2 a 3(x) a 2 (x) = 2 g e A F γz 2 F γ 2 6 u+ + 3 d + 4 u + + d + 4 sin2 θ W a 3 (x) = 2 g e V x F γz 3 F γ 2 3 ( 1 4 sin 2 θ W ) 2 u + d 4 u + + d + Parton model expressions [ ] F γ 2, F γz 2 = x [ e 2 q, 2 e q g q q V ] (q + q) F γz 3 = 2 q e q g q A (q q) g q V = ±1 2 2 e q sin 2 θ W g q A = ±1 2 table of contents Quantitative challenges in EMC and SRC 2 5 December / 17

18 Isovector Effects in Nuclei [ICC, W. Bentz and A. W. Thomas, Phys. Rev. Lett. 19, (212)] 1.1 Z/N = 26/3 (iron) 1.1 Z/N = 82/126 (lead) a2(xa) 1.9 Q 2 = 5 GeV 2 a 2 a naive 2 9 a2(xa) 5 4 sin2 θ W Q 2 = 5 GeV a 2 a naive sin2 θ W x A PVDIS γ Z interference: a 2 (x) = 2 g e A F γz 2 (x) F γ 2 (x) N Z sin2 θ W x A u + A (x) d+ A (x) u + A (x) + d+ A (x) Deviation from naive expectation: momentum shifted from u to d quarks F γz 2 (x) has markedly different flavour dependence compared with F γ 2 (x) a measurement of both enables an extraction of u(x) and d(x) separately Proposal to measure a 2 (x) of 48 Ca was deferred twice... table of contents Quantitative challenges in EMC and SRC 2 5 December / 17

19 Isovector Effects in Nuclei [ICC, W. Bentz and A. W. Thomas, Phys. Rev. Lett. 19, (212)] 1.1 Z/N = 2/28 (calcium-48) 1.1 Z/N = 82/126 (lead) a2(xa) 1.9 Q 2 = 5 GeV 2 a 2 a naive 2 9 a2(xa) 5 4 sin2 θ W Q 2 = 5 GeV a 2 a naive sin2 θ W x A PVDIS γ Z interference: a 2 (x) = 2 g e A F γz 2 (x) F γ 2 (x) N Z sin2 θ W x A u + A (x) d+ A (x) u + A (x) + d+ A (x) Deviation from naive expectation: momentum shifted from u to d quarks F γz 2 (x) has markedly different flavour dependence compared with F γ 2 (x) a measurement of both enables an extraction of u(x) and d(x) separately Proposal to measure a 2 (x) of 48 Ca was deferred twice... table of contents Quantitative challenges in EMC and SRC 2 5 December / 17

20 Anti-Quarks & Gluons in Nuclei [ICC, W. Bentz and A. W. Thomas, Phys. Rev. Lett. 19, (212)].25 Z/N = 1 (carbon).25 Z/N = 82/126 (lead).2.2 a3(xa).15.1 a 3 a naive.5 3 ( ) 9 Q 2 = 5 GeV sin 2 θ W x A PVDIS γ Z interference: a 3 (x) = 2 g e V x F γz 3 (x) F γ 2 (x) a3(xa).15.1 a 3 a naive.5 3 ( ) 9 Q 2 = 5 GeV sin 2 θ W x A N Z 9 ( 1 4 sin 2 )u A θ (x) + d A (x) W 5 u + A (x) + d+ A (x) a 3 (x) is a sensitive measure of anti-quarks in nucleons and nuclei Under DGLAP the numerator evolves as a non-singlet independent of the gluons whereas denominator evolution involves the gluon PDF given a large Q 2 lever arm a 3 (x) can help constrain the gluon PDF this is a key goal of Jefferson Lab and a future EIC table of contents Quantitative challenges in EMC and SRC 2 5 December / 17

21 Anti-Quarks & Gluons in Nuclei a3(xa) Z/N = 1 (carbon).1 a 3 a naive.5 3 ( ) 9 Q 2 = 5 GeV sin 2 θ W x A PVDIS γ Z interference: a 3 (x) = 2 g e V [ICC, W. Bentz and A. W. Thomas, Phys. Rev. Lett. 19, (212)] x F γz 3 (x) F γ 2 (x) Gluon EMC ratio g A (x) g (x) Z/N = 1 (carbon) I. Sick and D. Day, Phys. Lett. B 274, 16 (1992) N Z 9 ( 1 4 sin 2 )u A θ (x) + d A (x) W 5 u + A (x) + d+ A (x) a 3 (x) is a sensitive measure of anti-quarks in nucleons and nuclei x Q 2 = 5. GeV 2 Under DGLAP the numerator evolves as a non-singlet independent of the gluons whereas denominator evolution involves the gluon PDF given a large Q 2 lever arm a 3 (x) can help constrain the gluon PDF this is a key goal of Jefferson Lab and a future EIC table of contents Quantitative challenges in EMC and SRC 2 5 December / 17

22 Conclusion Need new experiments that provide clean access to new aspects of the EMC effect PVDIS experiment on 48 Ca deferred twice would provide critical information on the flavour dependence of the EMC effect NuTeV anomaly can be explained by an isovector EMC effect & CSV To make progress with the JLab PAC on approving experiments to help solve the EMC effect it is essential to identify at most a handful of must do experiments EMC ratios SL( q ) Z/N = 2/28 (calcium-48) F 2A /F 2D d A /d f u A /u f Q 2 = 5 GeV x free current Hartree.4 free current RPA 12 C current RPA Coulomb Sum Rule another key.2 NM current RPA Pb experiment C experiment C GFMC observable to shed light on medium modification q [GeV] table of contents Quantitative challenges in EMC and SRC 2 5 December /

23 Backup Slides table of contents Quantitative challenges in EMC and SRC 2 5 December / 17

24 The NuTeV experiment Paschos-Wolfenstein ratio was not directly measured: R P W = σν NC σ ν NC σ ν CC σ ν CC = R ν = σν NC σ ν CC, R ν σ ν NC = σ ν ; R P W = Rν r R ν CC 1 r NuTeV measured: R ν NuTeV =.3916(7) & R ν NuTeV =.45(16) Corrections to R ν( ν) result from the presence of heavy quarks in the sea, the production of heavy quarks in the target, higher order terms in the cross section, and any isovector component of the light quarks in the target. In particular, in the case where a final-state charm quark is produced from a d or s quark in the nucleon, there are large... [G. P. Zeller et al., arxiv:hep-ex/1159] NuTeV then performed a sophisticated Monte-Carlo analysis using constraints from the Paschos-Wolfenstein ratio table of contents Quantitative challenges in EMC and SRC 2 5 December / 17

25 CSB Correction to NuTeV Two sources of charge symmetry breaking (CSB) corrections quark mass differences: δm = m d m u 4 MeV quark charge differences: e 2 u e 2 d [QED splitting/qed evolution of PDFs] CSB correction to Paschos-Wolfenstein ratio: R CSB P W ( ) 1 7 x u 3 sin2 A θ x d A W ( ) 1 x u A +x d A sin2 θ x δu x δd W x u p +x d p δd (x) = d p (x) u n (x) δu (x) = u p (x) d n (x) Mass differences what do we expect? Consider deuteron: deuteron u u d proton + d d u neutron therefore since: m u < m d = x u A < x d A e 2 u > e 2 d = u-quarks lose momentum faster than d-quarks to γ-field Expect CSB corrections reduce NuTeV discrepancy with Standard Model table of contents Quantitative challenges in EMC and SRC 2 5 December / 17

26 Quasi-elastic scattering Quasi-elastic scattering is used to study nucleon properties in a nucleus: q 2 = ω 2 q 2 l k θ k q A 1 A The cross-section for this process reads d 2 [ ( σ q 4 q 2 dω dω = σ Mott q 4 R L(ω, q ) + 2 q 2 + θ ) ] tan2 R T (ω, q ) 2 response functions are accessed via Rosenbluth separation In the DIS regime Q 2, ω x = Q 2 /(2 M N ω) = constant response functions are proportional to the structure functions F 1 (x, Q 2 ) and F 2 (x, Q 2 ) table of contents Quantitative challenges in EMC and SRC 2 5 December / 17

27 Quasi-elastic scattering Quasi-elastic scattering is used to study nucleon properties in a nucleus: q 2 = ω 2 q 2 l k θ k q N N p p The cross-section for this process reads dσ dω = σ Mott [ G τ E (Q 2 ) + G 2 M (Q 2 ) ] response functions are accessed via Rosenbluth separation In the DIS regime Q 2, ω x = Q 2 /(2 M N ω) = constant response functions are proportional to the structure functions F 1 (x, Q 2 ) and F 2 (x, Q 2 ) table of contents Quantitative challenges in EMC and SRC 2 5 December / 17

28 Quasi-elastic scattering Quasi-elastic scattering is used to study nucleon properties in a nucleus: q 2 = ω 2 q 2 A l P q γ θ l F 2 (x, Q 2 ) P X X The cross-section for this process reads dσ dx dq 2 = 2π [( α2 e x Q (1 + y) 2) ] F 2 (x, Q 2 ) y 2 F L (x, Q 2 ) response functions are accessed via Rosenbluth separation In the DIS regime Q 2, ω x = Q 2 /(2 M N ω) = constant response functions are proportional to the structure functions F 1 (x, Q 2 ) and F 2 (x, Q 2 ) table of contents Quantitative challenges in EMC and SRC 2 5 December / 17

29 Coulomb Sum Rule The Coulomb Sum Rule reads S L ( q ) = q ω + dω R L(ω, q ) G 2 E (Q2 ) G 2 E = Z G 2 Ep(Q 2 ) + N G 2 En(Q 2 ) Non-relativistic expectation as q becomes large S L ( q p F ) 1 CSR counts number of charge carriers The CSR was first measured at MIT Bates in 198 then at Saclay in 1984 both experiments observed significant quenching of the CSR Two plausible explanations: 1) nucleon structure is modified in the nuclear medium; 2) experiment/analysis is flawed e.g. Coulomb corrections A number of influential physicists have argued very strongly for the latter table of contents Quantitative challenges in EMC and SRC 2 5 December / 17

30 Coulomb Sum Rule Today No new data on the CSR since SLAC data from early 199s The quenching of the CSR has become one of the most contentious observations in all of nuclear physics Experiment E5-11 was performed at Jefferson Lab in 25 should settle controversy of CSR quenching once and for all publication of results expected soon State-of-the-art traditional nuclear physics (GFMC) calculations find no quenching [A. Lovato et al., PRL 111, no. 9, 9251 (213)] table of contents Quantitative challenges in EMC and SRC 2 5 December / 17

31 Longitudinal Response Function In nuclear matter response function given by = R L (ω, q) = 2 Z π ρ B Im Π L (ω, q) + σ, ω, ρ Longitudinal polarization Π L is obtained by solving a Dyson equation We consider two cases: (1) the electromagnetic current is that if a free nucleon; (2) the current is modified by the nuclear medium The in-medium nucleon current causes a sizeable quenching of the longitudinal response driver of this effect is modification of the proton Dirac form factor Nucleon RPA correlations play almost no role for q.7 GeV RL(ω, q)/z [GeV 1 ] free current Hartree free current RPA NM current Hartree NM current RPA 28 Pb experiment q =.5 GeV q = GeV ω [GeV] table of contents Quantitative challenges in EMC and SRC 2 5 December / 17

32 Coulomb Sum Rule S L ( q ) = q ω + dω R L(ω, q ) G 2 E (Q2 ) G 2 E = Z G 2 Ep(Q 2 ) + N G 2 En(Q 2 ) Recall that the non-relativistic expectation is unity for q p F GFMC 12 C results are consistent with this expectation SL( q ) [ICC, W. Bentz and A. W. Thomas, Phys. Rev. Lett (216)] 1..6 free current Hartree.4 free current RPA 12 C current RPA.2 NM current RPA Pb experiment 12 C experiment 12 C GFMC q [GeV] For a free nucleon current find relativistic corrections of 2% at q 1 GeV in the non-relativistic limit our CSR result does saturate at unity An in-medium nucleon current induces a further 2% correction to the CSR good agreement with exisiting 28 Pb data although this data is contested Our 12 C result is in stark contrast to the corresponding GFMC prediction forthcoming Jefferson Lab should break this impasse table of contents Quantitative challenges in EMC and SRC 2 5 December / 17