119292449
Nuclear physics with a medium-energy Electron-Ion Collider
A polarized ep/eA collider (Electron-Ion Collider, or EIC) with variable center-of-mass energy √s ∼ 20–70 GeV and luminosity ∼1034 cm−2 s−1 would be uniquely suited to address several outstanding questions of Quantum Chromodynamics (QCD) and the microscopic structure of hadrons and nuclei: i) the three-dimensional structure of the nucleon in QCD (sea quark and gluon spatial distributions, orbital motion, polarization, correlations); ii) the fundamental color fields in nuclei (nuclear parton densities, shadowing, coherence effects, color transparency); iii) the conversion of color charge to hadrons (fragmentation, parton propagation through matter, in-medium jets). We briefly review the conceptual aspects of these questions and the measurements that would address them, emphasizing the qualitatively new information that could be obtained with the collider. Such a medium-energy EIC could be realized at Jefferson Lab after the 12GeV Upgrade (MEIC), or at Brookhaven National Lab as the low-energy stage of eRHIC.
119400238
Modelling power corrections to the Bjorken sum rule for the neutrino structure function F1
Direct measurements of the structure functions Fνp1 and Fνn1 at a neutrino factory would allow for an accurate extraction of αs from the Q2-dependence of the Bjorken sum rule, complementing that based on the Gross–Llewellyn-Smith sum rule for F3. We estimate the power (1/Q2-) corrections to the Bjorken sum rule in the instanton vacuum model. For the reduced matrix element of the flavour-nonsinglet twist-4 operator ūgμνγνγ5u − (u → d) we obtain a value of 0.18 GeV2, in good agreement with the QCD sum rule calculations of Braun and Kolesnichenko. Our result allows one to reduce the theoretical error in the determination of αs.
16508900
Pion cloud and sea quark flavor asymmetry in the impact parameter representation
We study large-distance contributions to the nucleon parton densities in the transverse coordinate (impact parameter) representation based on generalized parton distributions (GPDs). Chiral dynamics generates a distinct component of the partonic structure, located at momentum fractions x ~ 0, and the universal large-distance pion cloud at b > b_core -- could naturally account for the x-dependence of the measured asymmetry.
118372228
Transverse target spin asymmetry in inclusive DIS with two-photon exchange
We study the transverse target spin dependence of the cross section for inclusive electron-nucleon scattering with unpolarized beam. Such dependence is absent in the one-photon exchange approximation (Christ-Lee theorem) and arises only in higher orders of the QED expansion, from the interference of one-photon and absorptive two-photon exchange amplitudes as well as from real photon emission (bremsstrahlung). We demonstrate that the transverse spin-dependent two-photon exchange cross section is free of QED infrared and collinear divergences. We argue that in DIS kinematics the transverse spin dependence should be governed by a 'partonlike' mechanism in which the two-photon exchange couples mainly to a single quark. We calculate the normal spin asymmetry in an approximation where the dominant contribution arises from quark-helicity flip due to interactions with nonperturbative vacuum fields (constituent quark picture) and is proportional to the quark transversity distribution in the nucleon. Such helicity-flip processes are not significantly Sudakov-suppressed if the infrared scale for gluon emission in the photon-quark subprocess is of the order of the chiral symmetry breaking scale, {mu}{sub chiral}{sup 2}>>{lambda}{sub QCD}{sup 2}. We estimate the asymmetry in the kinematics of the planned Jefferson Lab Hall A experiment to be of the order 10{sup -4}, with different sign formore » proton and neutron. We also comment on the spin dependence in the limit of soft high-energy scattering.« less
15375029
SMALL-x PHYSICS: From HERA to LHC and Beyond
▪ Abstract We summarize the lessons learned from studies of hard scattering processes in high-energy electron-proton collisions at HERA and antiproton-proton collisions at the Tevatron, with the ai...
16801030
Polarized antiquark flavor asymmetry in Drell–Yan pair production
Abstract. We investigate the role of the flavor asymmetry of the nucleon's polarized antiquark distributions in Drell–Yan lepton pair production in polarized nucleon–nucleon collisions at HERA (fixed–target) and RHIC energies. It is shown that the large polarized antiquark flavor asymmetry predicted by model calculations in the large–$N_c$ limit (chiral quark–soliton model) has a dramatic effect on the double spin asymmetries in high mass lepton pair production, as well as on the single spin asymmetries in lepton pair production through $W^\pm$–bosons at $M^2 = M_W^2$.
22188300
Differences between mean-field dynamics and N-particle quantum dynamics as a signature of entanglement.
A Bose-Einstein condensate in a tilted double-well potential under the influence of time-periodic potential differences is investigated in the regime where the mean-field (Gross-Pitaevskii) dynamics become chaotic. For some parameters near stable regions, even averaging over several condensate oscillations does not remove the differences between mean-field and N-particle results. While introducing decoherence via piecewise deterministic processes reduces those differences, they are due to the emergence of mesoscopic entangled states in the chaotic regime.