EMC Effect: Isospin dependence and PVDIS Ian Clot Argonne National - PowerPoint PPT Presentation

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 2016

The EMC effect In the early 80s physicists at CERN 56 Fe 1 . 2 thought that nucleon structure 1 . 1 studies using DIS could be enhanced 1 2 /F D 2 (by a factor A ) using nuclear targets F Fe 0 . 9 The European Muon Collaboration 0 . 8 EMC effect (EMC) conducted DIS experiments 0 . 7 expectation before EMC experiment Experiment (Gomez et al. , Phys. Rev. D 49 , 4348 (1994).) on an iron target 0 . 6 0 0 . 2 0 . 4 0 . 6 0 . 8 1 J. J. Aubert et al. , Phys. Lett. B 123 , 275 (1983) 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 30 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 2016 2 / 17

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 40 Ca & 48 Ca sensitive to flavour dependence but to truely access flavour dependence PVDIS must play a pivotal role I. Sick and D. Day, Phys. Lett. B 274, 16 (1992). Z/N = 82 / 126 (lead) 1 . 2 EMC effect 1 . 1 Polarized EMC effect 1 . 1 1 EMC ratios EMC ratios 1 0 . 9 0 . 9 0 . 8 0 . 8 F 2 A /F 2 D 0 . 7 0 . 7 Q 2 = 5 GeV 2 d A /d f Q 2 = 5 GeV 2 ρ = 0.16 fm − 3 u A /u f 0 . 6 0 . 6 0 0 . 2 0 . 4 0 . 6 0 . 8 1 0 0 . 2 0 . 4 0 . 6 0 . 8 1 x x table of contents Quantitative challenges in EMC and SRC 2–5 December 2016 3 / 17

Nucleons in Nuclei Nuclei are extremely dense: proton rms radius is r p ≃ 0 . 85 fm, corresponds hard sphere r p ≃ 1 . 10 fm ideal packing gives ρ ≃ 0 . 13 fm − 3 ; nuclear matter density is ρ ≃ 0 . 16 fm − 3 20% of nucleon volume inside other nucleons – nucleon centers ∼ 2 fm apart For realistic charge distribution 25% of 1 . 5 proton proton charge at distances r > 1 fm neutron Natural to expect that nucleon 2 π b ρ 1 ( b ) [fm − 1 ] 1 . 0 properties are modified by nuclear medium – even at the mean-field level 0 . 5 in contrast to traditional nuclear physics 0 Understanding validity of two viewpoints 0 0 . 5 1 . 0 1 . 5 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 2016 4 / 17 Weinberg’s Third Law of Progress in Theoretical Physics:

Nucleons in Nuclei Nuclei are extremely dense: 4 He – AV18+UX proton rms radius is r p ≃ 0 . 85 fm, 0 . 15 ideal packing limit ρ ( r ) [fm − 3 ] corresponds hard sphere r p ≃ 1 . 10 fm 0 . 10 ideal packing gives ρ ≃ 0 . 13 fm − 3 ; nuclear matter density is ρ ≃ 0 . 16 fm − 3 0 . 05 20% of nucleon volume inside other nucleons – nucleon centers ∼ 2 fm apart 0 0 0 . 5 1 . 0 1 . 5 2 . 0 2 . 5 3 . 0 r [fm] For realistic charge distribution 25% of 1 . 5 proton proton charge at distances r > 1 fm neutron Natural to expect that nucleon 2 π b ρ 1 ( b ) [fm − 1 ] 1 . 0 properties are modified by nuclear medium – even at the mean-field level 0 . 5 in contrast to traditional nuclear physics 0 Understanding validity of two viewpoints 0 0 . 5 1 . 0 1 . 5 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 2016 4 / 17 Weinberg’s Third Law of Progress in Theoretical Physics:

Quarks, Nuclei and the NJL model “integrate out gluons” 1 g Θ(Λ 2 − k 2 ) Continuum QCD ➞ m 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 p − m + iε ] − 1 Z ( p 2 )[ / p − M + iε ] − 1 [ / quark propagator: ➞ wave function renormalization vanishes at quark mass-shell: Z ( p 2 = M 2 ) = 0 confinement is critical for our description of nuclei and nuclear matter 9 NJL NJL 0 . 4 8 DSEs – ω = 0 . 6 DSEs 7 M ( p ) [GeV] S. x. Qin et al. , Phys. Rev. C 84 , 042202 (2011) 0 . 3 π α eff ( k 2 ) 6 5 0 . 2 4 1 3 0 . 1 2 1 0 0 0 0 . 5 1 . 0 1 . 5 2 . 0 0 0 . 5 1 . 0 1 . 5 2 . 0 p [GeV] k [GeV] table of contents Quantitative challenges in EMC and SRC 2–5 December 2016 5 / 17

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% F 2 p (0) decreases; however F 2 p / 2 M N largely constant – µ p almost constant 1 . 0 free current 0 . 8 NM current ( ρ B =0 . 16 fm − 3 ) empirical F 1 p ( Q 2 ) 0 . 6 0 . 4 0 . 2 0 0 0 . 5 1 . 0 1 . 5 2 Q 2 [GeV 2 ] table of contents Quantitative challenges in EMC and SRC 2–5 December 2016 6 / 17

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% F 2 p (0) decreases; however F 2 p / 2 M N largely constant – µ p almost constant 1 . 0 1 . 8 free current free current 1 . 6 0 . 8 NM current ( ρ B =0 . 16 fm − 3 ) NM current ( ρ B =0 . 16 fm − 3 ) 1 . 4 empirical empirical 1 . 2 F 1 p ( Q 2 ) F 2 p ( Q 2 ) 0 . 6 1 . 0 0 . 8 0 . 4 0 . 6 0 . 4 0 . 2 0 . 2 0 0 0 0 . 5 1 . 0 1 . 5 2 0 0 . 5 1 . 0 1 . 5 2 Q 2 [GeV 2 ] Q 2 [GeV 2 ] table of contents Quantitative challenges in EMC and SRC 2–5 December 2016 6 / 17

EMC effect in light nuclei [J. Seely et al. , PRL 103 , 202301 (2009)] 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 2016 7 / 17

Isovector EMC Effect? Why should we expect a (large) isovector EMC effect? Consider the Bethe–Weizsäcker mass formula Z 2 ( A − 2 Z ) 2 E B = a V A − a S A 2 / 3 − a C A 1 / 3 − a A ± δ ( A, Z ) A a V = 15 . 75 a S = 17 . 8 a C = 0 . 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 ( x ) = A F 2 p + F 2 n f ISO A 2 Z F 2 p + N F 2 n table of contents Quantitative challenges in EMC and SRC 2–5 December 2016 8 / 17

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 1 . 2 12 M M a 8 1 . 0 M s M N Masses [GeV] 4 E B /A [MeV] 0 . 8 0 0 . 6 − 4 Z /N = 0 0 . 4 − 8 Z/N = 0 . 1 Z/N = 0 . 2 0 . 2 − 12 Z/N = 0 . 5 Z/N = 1 − 16 0 0 0 . 1 0 . 2 0 . 3 0 . 4 0 . 5 0 . 6 0 0 . 1 0 . 2 0 . 3 0 . 4 0 . 5 ρ [fm − 3 ] ρ [fm − 3 ] S ( k ) − 1 = / k − M + iε ➞ S q ( k ) − 1 = / k − M ∗ − / Quark propagator: V q + iε Hadronization + mean–field = ⇒ effective potential V u ( d ) = ω 0 ± ρ 0 , ω 0 = 6 G ω ( ρ p + ρ n ) , ρ 0 = 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 2016 9 / 17