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