Models of the EMC effect 1+3 Models of the EMC Effect G. A. Miller, U. W. Outline • Requirements • Nuclear binding (nucleons only) does not explain EMC effect • Add pions does not explain DY • Nucleon is modified • 3 models and consequences • Nuclear σL Experiments EMC – “Everyone’s Model is Cool (1985) A F 2 F 2 Binding effect new-light nuclei, high x 1 some models 01x uncool Drell-Yan- No one’s model is cool Explain both EMC and DY Requirements -Goals • Model describes free distributions • Good support and satisfy positivity • Consistency with nuclear properties • Describe deep inelastic and di-muon production data • Predict new phenomena Smith, Miller Walecka model Pb Binding fails Binding causes no EMC effect Explanation • Hugenholz van Hove theorem nuclear + - stability implies (in rest frame) P =P =MA + • P =A(MN -8 MeV) + • average nucleon p =MN-8 MeV Pions fail // • It’s easy to explain one or the other • Intrinsic structure of nucleon is changed • Need models! Single nucleon modification by nuclei • Does it make sense? • Neutron in nucleus is modified, lifetime changed from 17 minutes to forever • Binding changes energy denominator, suppresses pe ν component • Change energy denominator change wave fun • Strong fields polarize nucleons- analog of Stark effect, induces dipole moment of atom • Nuclei: no direction - monopole polarization Nucleon in medium- 3 models Nuclear matter External fields QMC, CISMM: based on nuclear saturation properties Nuclei modify nucleons: models 1. QMC- quarks in nucleons exchange mesons with nuclear medium - P 2. CISM- quarks in nucleons exchange infinite pairs of pions, vector mesons with nuclear medium -P 3. Suppression of point-like-configurations –D All three well-grounded in QCD MUST BE THERE All three poorly evaluated now Seeing definitive evidence for any would be very interesting - big effects needed Quark Meson Coupling Model –Guichon,Thomas,Saito Nuclear matter External fields σ, ω Effect of the coupling to the (constant) external fields q σ : mq → mq − gσσ (attraction) q ω : Eq → Eq + gωω (repulsion) ⎛ f (r) ⎞ iEqt ⎜ ⎟ Quark field ψ q (x) = e ⎜ r ⎟χ1/ 2 ⎝iσ.rˆ g(r)⎠ f(r) scalar field effect g(r) 5 Spin experiments examine LoC g • 1n , g1p in nuclei Bentz, Cloet Thomas • other ways to enhance EMC? Spin DPP Quark energy levels in π field Consequences • Twist-2 structure functions at low scale Λ • QCD evolution to higher Q2 • Sum rules, support and positivity • Gluon’s carry 30 % momentum at Λ=600 MeV UV cutoff • Distributions calculated in rest frame and infinite momentum frame Computed distribution functions, DPP Results –Nuclear Matter Smith-Miller Medium modified Free DIS DY Smith Miller 2003 Polarization transfer in 4He(e,e’p) Nucleon form factors in medium-Strauch Nucleon in medium- 3 models Nuclear matter External fields QMC, CISMM: both enhance lower components! Closer look needed! Lower components LoC • LoC account for QF2/F1 • LoC gives non-spherical shape of proton • Medium modifies LoC • Medium modifies shape Suppression of Point Like Configurations- Frankfurt, Strikman PLC has NO int. with medium energy denominator increased EMC ratio Medium modified form factors Frank, Jennings, Miller PRC54,920 Nuclear modification of σL • Nuclear pions modify σL • Nuclear mesons modify σL • Model of coherent effects, gluons Coherent Pions in the proton and σL x Pions from nuclear LF wave fun DY OK OPE σ (L) enhanced (coherent) Miller 2001 How to get nuclear LF wave fun ? Machleidt Miller PionsPions andand thethe EMCEMC effecteffect Why pions?Why pions? TooToo many many pions pionsbadbad Some allowed Some allowed More mesons? GAM,SJB,MK (00) σ(L): rule out meson model, learn nuclear glue Summary • Nuclear binding (nucleons only) does not explain EMC effect • Add pions does not explain DY • Nucleon is modified • 3 models, form factor is modified • Nuclear σL to reveal nuclear glue Remainder are spares EMC effect A bag in matter A F2 F2 Nuclear matter External fields σ, 1 01x Effect of the coupling to the (constant) external fields q σ : mq → mq − gσσ (attraction) q ω : Eq → Eq + gωω (repulsion) (NB: here is a chiral invariant) QCDQCD viewview of Nucleus?Nucleus? • Earliest lattice calculations Hamiltonian, strong coupling limit confinement, flux string, color singlet clusters leading order: inert nucleons sit interactions: string break meson exchange model SCQCD of nuclei, GAM quark, gluon effects PRC39,1563 hard to find, but vital Chiral instanton soliton Sea!! • nucleons in nuclei (Smith & M ’03,04) σ (L) π + gluons Enhancing EMC-spin independent Melnitchouk Sargsian Strikman Ratio bound to free F2 3 models 3 models3 models.