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

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

Rapid Liana Colonization along a Secondary Forest Chronosequence

Lianas (woody vines) can have profound effects on tree recruitment, growth, survival, and diversity in tropical forests. However, the dynamics of liana colonization soon after land abandonment are poorly understood, and thus it is unknown whether lianas alter tree regeneration early in succession. We examined the liana community in 43 forests that ranged from 1 to 31 yr old in central Panama to determine how fast lianas colonize young forests and how the liana community changes with forest succession. We found that lianas reached high densities early in succession, commonly exceeding 1000 stems/ha within the first 5 yr of forest regeneration. Lianas also increased rapidly during early succession in terms of basal area but did not show evidence of saturation within the 30 yr of our chronosequence. The relative contribution of lianas to total woody plant community in terms of basal area and density increased rapidly and reached a saturation point within 5 yr (basal area) to 15 yr (density) after land abandonment. Our data demonstrate that lianas recruit early and in high density in tropical forest regeneration, and thus lianas may have a large effect on the way in which secondary forests develop both early and throughout succession

New developments in the statistical approach of parton distributions

We recall how parton distributions are constructed in a statistical physical picture of the nucleon. The chiral properties of QCD lead to strong relations between quarks and antiquarks distributions and the importance of the Pauli exclusion principle is also emphasized. A global next-to-leading order QCD analysis of unpolarized and polarized deep-inelastic scattering data allows to determine a small number of free parameters. Some predictions are compared to recent experimental results and we discuss the prospects of this physical framework.Comment: 10 pages, 12 figures. Invited talk presented at the " Corfu Summer Institute on EPP,CORFU2005, Corfu, Greece, September 4-26, 2005. To be published in Journal of Physics, Conference Series (2006

Distribution, Abundance, and Biomass Estimates for Primates within Kahuzi-Biega Lowlands and Adjacent Forest in Eastern DRC

Africa’s tropical forests have been subjected to alarming rates of forest clearing in the last two decades. Baseline data are critical to understanding the impacts of large-scale habitat loss and fragmentation. This report describes the distribution and relative abundance of anthropoid primates in 1994–95 within and adjacent to Kahuzi-Biega National Park lowland sector, eastern Democratic Republic of Congo. This is a region for which few empirical data exists. Density and biomass estimates derived from transect sampling are discussed for both adjacent settlement and remote sampling zones where minimum biomass estimates are 436 kg/km2 and 663 kg/km2, respectively. With the exception of red colobus Procolobus badius in sampling zone KB 4, hunting pressures do not appear to have been excessive. The owl-faced guenon Cercopithecus hamlyni is widely distributed and relatively abundant throughout the survey areas

Measurement of Double-Polarization Asymmetries in the Quasielastic ³→He (→e, e\u27 d) Process

We present a precise measurement of double-polarization asymmetries in the ³→He (→e, e\u27 d) reaction. This particular process is a uniquely sensitive probe of hadron dynamics in 3He and the structure of the underlying electromagnetic currents. The measurements have been performed in and around quasielastic kinematics at Q2 = 0.25(GeV/c)2 for missing momenta up to 270 MeV/c. The asymmetries are in fair agreement with the state-of-the-art calculations in terms of their functional dependencies on pm and ω, but are systematically offset. Beyond the region of the quasielastic peak, the discrepancies become even more pronounced. Thus, our measurements have been able to reveal deficiencies in the most sophisticated calculations of the three-body nuclear system, and indicate that further refinement in the treatment of their two-and/or three-body dynamics is required

Rosenbluth Separation of the πᵒ Electroproduction Cross Section

We present deeply virtual πᵒ electroproduction cross-section measurements at xB = 0.36 and three different Q2 values ranging from 1.5 to 2 GeV2, obtained from Jefferson Lab Hall A experiment E07-007. The Rosenbluth technique is used to separate the longitudinal and transverse responses. Results demonstrate that the cross section is dominated by its transverse component and, thus, is far from the asymptotic limit predicted by perturbative quantum chromodynamics. Nonetheless, an indication of a nonzero longitudinal contribution is provided by the measured interference term σLT. Results are compared with several models based on the leading-twist approach of generalized parton distributions (GPDs). In particular, a fair agreement is obtained with models in which the scattering amplitude includes convolution terms of chiral-odd (transversity) GPDs of the nucleon with the twist-3 pion distribution amplitude. This experiment, together with previous extensive unseparated measurements, provides strong support to the exciting idea that transversity GPDs can be accessed via neutral pion electroproduction in the high-Q2 regime