Observation of quark-hadron duality in gamma*-p helicity cross sections

Combining data on unpolarized and polarized inclusive proton structure functions, we perform the first detailed study of quark-hadron duality in individual helicity-1/2 and 3/2 virtual photoproduction cross sections. We find that duality is realized more clearly in the helicity-1/2 channel, with duality violating corrections < 10% over the entire nucleon resonance region, while larger, < 20% corrections are found in the helicity-3/2 sector. The results are in general agreement with quark model expectations, and suggest that data above the Delta resonance region may be used to constrain both spin-averaged and spin-dependent parton distributions.Comment: 15 pages, 5 figure

Medium Modifications from 4He(e,e'p)3H

Polarization transfer in quasi-elastic nucleon knockout is sensitive to the properties of the nucleon in the nuclear medium, including possible modification of the nucleon form factor and/or spinor. In our recently completed experiment E03-104 at Jefferson Lab we measured the proton recoil polarization in the 4He(e,e'p)3H reaction at a Q^2 of 0.8 (GeV/c)^2 and 1.3 (GeV/c)^2 with unprecedented precision. These data complement earlier data between 0.4 and 2.6 (GeV/c)^2 from both Mainz and Jefferson Lab. The measured ratio of polarization-transfer coefficients differs from a fully relativistic calculation, favoring either the inclusion of a medium modification of the proton form factors predicted by a quark-meson coupling model or strong charge-exchange final-state interactions. The measured induced polarizations agree well with the fully relativistic calculation and indicate that these strong final-state interactions may not be applicable.Comment: 7 pages, 3 figures. Based on invited talk presented by S. Strauch at "Sixth International Conference on Perspectives in Hadronic Physics", ICTP, Trieste, May 12-16, 200

Svojstva hadrona u jezgrama

Nucleon properties are modified in the nuclear medium. To understand these modifications and their origin is a central issue in nuclear physics. For example, a wide variety of QCD-based models, including quark-meson coupling and chiral-quark soliton models, predict that the nuclear constituents change properties with increasing density. These changes are predicted to lead to observable changes in the nucleon structure functions and electromagnetic form factors. We present results from a series of recent experiments at MAMI and Jefferson Lab, which measured the proton recoil polarization in the 4He (e,e′p )3H reaction to test these predictions. These results, with the most precise data at Q2 = 0.8 (GeV/c)2 and at 1.3 (GeV/c)2 from E03-104, put strong constraints on available model calculations, such that below Q2 = 1.3 (GeV/c)2 the measured ratios of polarization-transfer are successfully described in a fully relativistic calculation when including a medium modification of the proton form factors or, alternatively, by strong charge-exchange final-state interactions. We also discuss possible extensions of these studies with measurements of the 4He(e,e′p )3H and 2H(e,e′p )n reactions as well as with the neutron knockout in 4He(e,e′n )3He.Svojstva nukleona mijenjaju se u jezgrama. Razumijevanje tih promjena i njihovih uzroka je središnje pitanje nuklearne fizike. Na primjer, niz modela zasnovanih na QCD, uključivši vezanje kvark-mezon i solitonske modele kiralnih kvarkova, predviđaju da sastavnice jezgri mijenjaju svojstva s povećanjem gustoće. Predviđa se da te promjene vode na promjene nukleonskih strukturnih funkcija i elektromagnetskih faktora oblika koji se mogu opažati. Opisujemo ishode niza nedavnih mjerenja u MAMI i Jefferson Lab-u u kojima se mjerila odbojna polarizacija protona u reakciji 4He(~e, e′~p ) 3H radi provjera navedenih predviđanja. Ti ishodi, zajedno s najtočnijim podacima na Q2 = 0.8 (GeV/c) 2 i na 1.3 (GeV/c) 2 iz mjerenja E03-104, postavljaju jaka ograničenja na modelske račune. Tako ispod Q2 = 1.3 (GeV/c) 2 , izmjereni omjeri prijenosa polarizacije uspješno opisuju relativistički računi kada se uključe promjene protonskih faktora oblika u jezgri, ili, kao inačica, snažna izmjena naboja u međudjelovanju u konačnom stanju. Raspravljamo također proširenje tih studija na mjerenja 4He(~e, e′~p ) 3H i 2H(~e, e′~p )n reakcija te na izbijanje neutrona u 4He(~e, e′~n ) 3He reakciji

Precise Extraction of the Induced Polarization in the He-4(e,e(l)(p)over-right-arrow)H-3 Reaction

We measured with unprecedented precision the induced polarization P-y in He-4(e, e(l)(p) over right arrow)H-3 at Q(2) = 0.8 and 1.3 (GeV/c)(2). The induced polarization is indicative of reaction-mechanism effects beyond the impulse approximation. Our results are in agreement with a relativistic distorted-wave impulse approximation calculation but are overestimated by a calculation with strong charge-exchange effects. Our data are used to constrain the strength of the spin-independent charge-exchange term in the latter calculation