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[en] Polarized electron beams have played an important role in scattering experiments at moderate to high beam energies. Historically, these experiments have been primarily targeted at studying hadronic structure - from the quark contribution to the spin structure of protons and neutrons, to nucleon elastic form factors, as well as contributions to these elastic form factors from (strange) sea quarks. Other experiments have aimed to place constraints on new physics beyond the Standard Model. For most experiments, knowledge of the magnitude of the electron beam polarization has not been a limiting systematic uncertainty, with only moderately precise beam polarimetry requirements. However, a new generation of experiments will require extremely precise measurements of the beam polarization, significantly better than 1%. This article will review standard electron beam polarimetry techniques and possible future technologies, with an emphasis on the ever-improving precision that is being driven by the requirements of electron scattering experiments.
[en] The transverse momentum spectra of hadrons produced in high energy collisions can be decomposed into two components: the exponential ('thermal') and the power ('hard') ones. Recently, the H1 Collaboration has discovered that the relative strength of these two components in Deep Inelastic Scattering (DIS) depends drastically upon the global structure of the event - namely, the exponential component is absent in the diffractive events characterized by a rapidity gap. We discuss the possible origin of this effect and speculate that it is linked to confinement. Specifically, we argue that the thermal component is due to the effective event horizon introduced by the confining string, in analogy to the Hawking-Unruh effect. In diffractive events, the t-channel exchange is color-singlet and there is no fragmenting string - so the thermal component is absent. The slope of the soft component of the hadron spectrum in this picture is determined by the saturation momentum that drives the deceleration in the color field, and thus the Hawking-Unruh temperature. We analyze the data on non-diffractive pp collisions and find that the slope of the thermal component of the hadron spectrum is indeed proportional to the saturation momentum
[en] Here, the development of the chiral dynamics based description of nuclear electroweak currents is reviewed. Gerald E. (Gerry) Brown’s role in basing theoretical nuclear physics on chiral Lagrangians is emphasized. Illustrative examples of the successful description of electroweak observables of light nuclei obtained from chiral effective field theory are presented.
[en] Relativistic Dirac coupled channel analyses using optical potential model are performed for the 800 MeV proton inelastic scatterings from 26Mg and the results are compared with those from several other axially symmetric deformed nuclei for the systematic Dirac analyses. Employing scalar-vector model, scalar and time-like vector optical potentials in Lorentz covariant form are calculated phenomenologically by solving Dirac coupled channel equations using sequential iteration method. Dirac equations are reduced to second-order differential equations to obtain Schroedinger equivalent effective central and spin-orbit optical potentials and it is found that the heavier deformed nucleus has the larger effective central potential strength. Using the first-order rotational collective model to describe the low-lying excited states of ground state rotational band in the deformed nuclei, deformation parameters for the excited states are calculated and it is observed that the lighter deformed nucleus has the larger deformation parameter for the lowest lying excited 2+ state at the 800 MeV proton inelastic scattering, indicating the stronger coupling to the ground state compared to that of heavier nucleus. (author)
[en] Several new gamma transitions were identified in 94Sr, 93Sr, 92Sr, 96Zr and 97Zr from the spontaneous fission of 252Cf. Excited states in 88,89,92,94,96Sr and 95,96,97,98Zr were reanalyzed and reorganized to propose the new two-phonon octupole vibrational states and bands. The spin and parity of 6+ are assigned to a 4034.5 keV state in 94Sr and 3576.4 keV state in 98Zr. These states are proposed as the two-phonon octupole vibrational states along with the 6+ states at 3483.4 keV in 96Zr, at 3786.0 keV in 92Sr and 3604.2 keV in 96Sr. The positive parity bands in 88,94,96Sr and 96,98Zr are the first two-phonon octupole vibrational bands based on a 6+ state assigned in spherical nuclei. It is thought that in 94,96Sr and 96,98Zr a 3- octupole vibrational phonon is weakly coupled to an one-phonon octupole vibrational band to make the two-phonon octupole vibrational band. Also, the high spin states of odd-A95Zr and 97Zr are interpreted to be generated by the neutron 2d5/2 hole and neutron 1g7/2 particle, respectively, weakly coupled to one- and two-phonon octupole vibrational bands of 96Zr. The high spin states of odd-A87Sr are interpreted to be caused by the neutron 1g9/2 hole weakly coupled to 3- and 5- states of 88Sr. New one- and two-POV bands in 95,97Zr and 87,89Sr are proposed, for the first time, in the present work. (author)
[en] A time-dependent approach to the scission process, i.e., to the transition from two fragments connected by a thin neck (deformation αi) to two separated fragments (deformation αf) is presented. This transition is supposed to take place in a very short time interval ΔT. Our approach follows the evolution from αi to αf of all occupied neutron states by solving numerically the two-dimensional time-dependent Schroedinger equation with time-dependent potential. Calculations are performed for mass divisions from AL = 70 to AL = 118(AL being the light fragment mass) taking into account all neutron states (Ω = 1/2, 3/2, …, 11/2) that are bound in 236U at αi. ΔT is taken as parameter having values from 0.25×10-22 to 6×10-22 s. The resulting scission neutron multiplicities νsc and primary fragments' excitation energies E*sc are compared with those obtained in the frame of the sudden approximation (ΔT = 0). As expected, shorter is the transition time more excited are the fragments and more neutrons are emitted, the sudden approximation being an upper limit. For ΔT = 10-22 which is a realistic value, the time dependent results are 20% below this limit. For transition times longer than 6×10-22 s the adiabatic limit is reached: No scission neutrons are emitted anymore and the excitation energy at αf is negligible. (author)
[en] Symmetry problems of the generator coordinate method (GCM) in intrinsic frame of a many-body system (nuclei) are considered. The appropriate generator functions and the corresponding GCM equations are derived. An important role of the symmetrization group in construction of Griffin–Hill–Wheeler (GHW) equations is emphasized. (author)
[en] The anharmonity in shape transitional nuclei, observed earlier, is studied and an alternative form is derived. The dichotomy of a constant anharmonicity along with a changing nuclear structure is resolved. The evolution of the collective nuclear structure from the spherical vibrator to the deformed rotor is studied through the variation of energy ratio R10/2(E10/E2) with R4/2, for Ba–Dy and for Dy–Hf(N<104) and R12/2. The role of the Z = 64 subshell and the N = 88–90 shape phase transition are illustrated in the Mallmann plot. The relative merits of the empirical formulae: rotation–vibration linearity model, the soft rotor formula and the power index formula are compared. (author)
[en] Dirac's equation states that an electron implies the existence of an antielectron with the same mass (more generally same arithmetic properties) and opposite charge (more generally opposite algebraic properties). Subsequent observation of antielectron validated this concept. This statement can be extended to all matter particles; observation of antiproton, antineutron, antideuton … is in complete agreement with this view. Recently antihypertriton was observed and 38 atoms of antihydrogen were trapped. This opens the path for use in precise testing of nature's fundamental symmetries. The symmetric properties of a matter particle and its mirror antimatter particle seem to be well established. Interactions operate on matter particles and antimatter particles as well. Conservation of matter parallels addition operating on positive and negative numbers. Without antimatter particles, interactions of the Standard Model (electromagnetism, strong interaction and weak interaction) cannot have the structure of group. Antimatter particles are characterized by negative baryonic number A or/and negative leptonic number L. Materialization and annihilation obey conservation of A and L (associated to all known interactions), explaining why from pure energy (A = 0, L = 0) one can only obtain a pair of matter particle antimatter particle — electron antielectron, proton and antiproton — via materialization where the mass of a pair of particle antiparticle gives back to pure energy with annihilation. These two mechanisms cannot change the difference in the number of matter particles and antimatter particles. Thus from pure energy only a perfectly symmetric (in number) universe could be generated as proposed by Dirac but observation showed that our universe is not symmetric, it is a matter universe which is nevertheless neutral. Fall of reflection symmetries shattered the prejudice that there is no way to define in an absolute way right and left or matter and antimatter. Experimental observation of CP violation aroused a great hope for explaining why our universe is not exactly matter antimatter symmetric. Sakharov stated that without the violation of baryonic number, it is not possible to obtain from pure energy a universe made of only matter. The fact that our universe is asymmetric (in number) but perfectly neutral, points toward the existence of a hypothetic interaction violating A and L but conserving all charges. This Matter Creation (MC) interaction creating either a pair of matter particles or antimatter particles (instead of a pair of particle antiparticle) would have a charge BAL = (A-L) and a neutral messenger Z*. Even if CP is conserved, MC would allow the creation of a number of matter particles not exactly equal to the number of antimatter particles. Our universe would then correspond to the remaining excess when all matter antimatter pairs have disappeared. Observation of matter nonconservation processes would be of great interest to falsify this speculation. In a plan with A and L as axes, pure energy is represented by the origin (A = 0, L = 0). A symmetric universe is also represented by (A = 0, L = 0) meaning that there are exactly the same number of baryons and antibaryons, and the same number of leptons and antileptons. Our present matter universe is instead represented by a point of the diagonal with A = L = present A value. This value is tiny relative to the number of gammas resulting from the annihilation of matter–antimatter particles. (author)