124338422
FIRST OBSERVATION OF A SNAKE DEPOLARIZING RESONANCE
Using a 104MeV stored polarized proton beam and a full Siberian snake, we recently found evidence for a so-called {open_quotes}snake{close_quotes} depolarizing resonance. A full Siberian snake forces the spin tune {nu}{sub s} to be a half integer. Thus, if the vertical betatron tune {nu}{sub y} is set near a quarter integer, then the {nu}{sub s}=n{plus_minus}2{nu}{sub y} second-order snake resonance can depolarize the beam. Indeed, with a full Siberian snake, we found a deep depolarization dip when {nu}{sub y} was equal to 4.756; moreover, when {nu}{sub y} was changed to 4.781, the deep dip disappeared and the polarization was preserved. {copyright} {ital 1997} {ital The American Physical Society}
28249891
Tolerance of imperfections in high-energy circular accelerators for polarized protons.
Realistic calculations show that imperfection-spin-resonance strengths {epsilon}{sub imp} can be corrected to {epsilon}{sub imp}{lt}1, at 20 TeV, Superconducting Super Collider (SSC) energy. Statistical analysis agrees well with the numerical calculation. The polarized proton must be accelerated through overlapping intrinsic and imperfection resonances. We found a correlation between the tolerable strengths of intrinsic and imperfection resonances {epsilon}{sub int} and {epsilon}{sub imp}, that is, at smaller {epsilon}{sub int}, the tolerable {epsilon}{sub imp} becomes larger, and vice versa. To obtain a larger tolerable {epsilon}{sub imp}, we suggest that the number of snakes should be chosen according to {ital N}{sub {ital S}}{ge}5{epsilon}{sub int}. When a large number of snakes is used in the accelerator, the tolerable deviation of the spin rotational angle from 180{degree} for each snake becomes more stringent. The error in the spin rotation angle gives rise to (1) an equivalent picket-fence imperfection resonance {epsilon}{sub imp}{sup eq} and (2) an energy-dependent spin tune {nu}{sub {ital s}}. Both of these effects may cause depolarization. Further, when the snake axis is not properly arranged, the spin tune deviates from half-integer. In this case, depolarization may arise from the snake resonances. Our analysis indicates that acceleration of polarized protons in the SSC is technically feasiblemore » if care is taken in constructing the snakes.« less
28227992
First test of the Siberian snake magnet arrangement to overcome depolarizing resonances in a circular accelerator.
We studied the G\ensuremath{\gamma}=2 imperfection depolarizing resonance at 108 MeV, both with and without a Siberian snake, by varying the resonance strength while storing beams of 104- and 120-MeV polarized protons at the Indiana University Cooler Ring. We used a cylindrically symmetric polarimeter to simultaneously study the effect of a depolarizing resonance on both the vertical and radial components of the polarization. AT 104 MeV we found that the Siberian snake eliminated the effect of the nearby G\ensuremath{\gamma}=2 depolarizing resonance.
118699188
Studies on the chromaticity correction and dynamic aperture of the AGS booster
Sextupole configurations with periodicity six and 24 are considered; the higher periodicity is selected on the basis of reduced emittance coupling between the horizontal and vertical motion. Results are given for proton and heavy ion acceleration cycles. The dynamic aperture from particle tracking is compared with the chaotic dynamic aperture. 6 refs., 8 figs., 2 tabs.
120385865
Is the momentum space optimally used with the FODO lattices
The available momentum space of a FODO lattice is determined by the maximum value of the dispersion function (δx=Dx ∂p/p). In a regular FODO lattice the dispersion function oscillates between its maximum and minimum values, which are always positive. The maximum value of the dispersion function in a FODO cell of a fixed length depends on the cell phase difference. An example of a new lattice, in which the dispersion function is lowered to half its value in the same FODO cell, is presented. The available momentum space in the new lattice is raised to twice that in the FODO lattice by allowing the dispersion function to oscillate between the same positive and negative values. The maxima of the dispersion function in the new lattice have half the value of those within the regular 90° cells.
35543062
Minimizing dispersion in flexible-momentum-compaction lattices.
Medium-energy accelerators are often confronted with problems during transition energy crossing, such as longitudinal microwave instability and nonlinear synchrotron motion. These problems can be avoided by an accelerator having a negative momentum-compaction factor. A modular method for designing a lattice with adjustable momentum-compaction factor is presented. The dispersion excursion of the basic flexible momentum compaction module can be minimized to less than the maximum dispersion of the focusing-defocusing (FODO) lattice containing the same FODO cells. The phase advance of the module can be adjusted to be an odd multiple of quarter betatron waves. We found that a lattice composed of such modules possesses excellent chromatic properties with excellent tunability, smaller systematic stop-band widths, and smaller sextupole distortion functions.
119235210
Template overlap method for massive jets
We introduce a new class of infrared safe jet observables, which we refer to as template overlaps, designed to filter targeted highly boosted particle decays from QCD jets and other background. Template overlaps are functional measures that quantify how well the energy flow of a physical jet matches the flow of a boosted partonic decay. Any region of the partonic phase space for the boosted decays defines a template. We will refer to the maximum functional overlap found this way as the template overlap. To illustrate the method, we test lowest-order templates designed to distinguish highly-boosted top and Higgs decays from backgrounds produced by event generators. For the functional overlap, we find good results with a simple construction based on a Gaussian in energy differences within angular regions surrounding the template partons. Although different event generators give different averages for our template overlaps, we find in each case excellent rejection power, especially when combined with cuts based on jet shapes. The template overlaps are capable of systematic improvement by including higher order corrections in the template phase space.
119173091
Order in a Spatially Anisotropic Triangular Antiferromagnet
The phase diagram of the spin-1/2 Heisenberg antiferromagnet on an anisotropic triangular lattice of weakly coupled chains is investigated using a renormalization group analysis which includes marginal couplings important for connecting to numerical studies of this model. In particular, the relative stability of incommensurate spiral spin density order and collinear antiferromagnetic order is studied. While incommensurate spiral order is found to exist over most of the phase diagram in the presence of a Dzyaloshinskii-Moriya (DM) interaction, at small interchain coupling and extremely weak DM coupling, collinear antiferromagnetic order can survive. The implications of the renormalization group analysis for numerical studies, many of which have found spin liquid-like behaviour, are discussed.
15011888
Effect on cosmic microwave background polarization of coupling of quintessence to pseudoscalar formed from the electromagnetic field and its dual.
We present the full set of power spectra of cosmic microwave background (CMB) temperature and polarization anisotropies due to the coupling between quintessence and pseudoscalar of electromagnetism. This coupling induces a rotation of the polarization plane of the CMB, thus resulting in a nonvanishing B mode and parity-violating TB and EB modes. Using the BOOMERANG data from the flight of 2003, we derive the most stringent constraint on the coupling strength. We find that in some cases the rotation-induced B mode can confuse the hunting for the gravitational lensing-induced B mode.
17587151
Nuclear Density-Dependent Effective Coupling Constants in the Mean-Field Theory
It is shown that the equation of state of nuclear matter can be determined within the mean-field theory of $\sigma \omega$ model provided only that the nucleon effective mass curve is given. We use a family of the possible nucleon effective mass curves that reproduce the empirical saturation point in the calculation of the nuclear binding energy curves in order to obtain density-dependent effective coupling constants. The resulting density-dependent coupling constants may be used to study a possible equation of state of nuclear system at high density or neutron matter. Within the constraints used in this paper to $M^*$ of nuclear matter at saturation point and zero density, neutron matter of large incompressibility is strongly bound at high density while soft neutron matter is weakly bound at low density. The study also exhibits the importance of surface vibration modes in the study of nuclear equation of state.
91854570
Effects of chiral symmetry restoration in nuclear medium