46 research outputs found
Strangeness Production at COSY
The paper gives an overview of strangeness-production experiments at the
Cooler Synchrotron COSY. Results on kaon-pair and phi meson production in pp,
pd and dd collisions, hyperon-production experiments and Lambda p final-state
interaction studies are presented.Comment: Proceedings of the 12th Int. Conf. on Meson-Nucleon Physics and the
Structure of the Nucleon (MENU2010) in Williamsburg (USA
Transverse-Longitudinal Coupling by Space Charge in Cyclotrons
A method is presented that enables to compute the parameters of matched beams
with space charge in cyclotrons with emphasis on the effect of the
transverse-longitudinal coupling. Equations describing the
transverse-longitudinal coupling and corresponding tune-shifts in first order
are derived for the model of an azimuthally symmetric cyclotron. The
eigenellipsoid of the beam is calculated and the transfer matrix is transformed
into block-diagonal form. The influence of the slope of the phase curve on the
transverse-longitudinal coupling is accounted for. The results are generalized
and numerical procedures for the case of an AVF cyclotron are presented. The
algorithm is applied to the PSI Injector II and Ring cyclotron and the results
are compared to TRANSPORT.Comment: 8 pages, 2 figure
A Geometrical Method of Decoupling
The computation of tunes and matched beam distributions are essential steps
in the analysis of circular accelerators. If certain symmetries - like midplane
symmetrie - are present, then it is possible to treat the betatron motion in
the horizontal, the vertical plane and (under certain circumstances) the
longitudinal motion separately using the well-known Courant-Snyder theory, or
to apply transformations that have been described previously as for instance
the method of Teng and Edwards. In a preceeding paper it has been shown that
this method requires a modification for the treatment of isochronous cyclotrons
with non-negligible space charge forces. Unfortunately the modification was
numerically not as stable as desired and it was still unclear, if the extension
would work for all thinkable cases. Hence a systematic derivation of a more
general treatment seemed advisable.
In a second paper the author suggested the use of real Dirac matrices as
basic tools to coupled linear optics and gave a straightforward recipe to
decouple positive definite Hamiltonians with imaginary eigenvalues. In this
article this method is generalized and simplified in order to formulate a
straightforward method to decouple Hamiltonian matrices with eigenvalues on the
real and the imaginary axis. It is shown that this algebraic decoupling is
closely related to a geometric "decoupling" by the orthogonalization of the
vectors , and , that were introduced with the
so-called "electromechanical equivalence". We present a structure-preserving
block-diagonalization of symplectic or Hamiltonian matrices, respectively. When
used iteratively, the decoupling algorithm can also be applied to n-dimensional
systems and requires iterations to converge to a given
precision.Comment: 13 pages, 1 figur
Race in an epigenetic time: thinking biology in the plural
The notion that biological memories of environmental experiences can be embedded in the human genome and even transmitted transgenerationally is increasingly relevant in the postgenomic world, particularly in molecular epigenetics, where the genome is conceptualized as porous to environmental signals. In this article I discuss the current rethinking of race in epigenetic rather than genetic terms, emphasizing some of its paradoxical implications, especially for public policy. I claim in particular that: (i) if sociologists want to investigate race in a postgenomic world they should pay more attention to this novel plastic and biosocial view of race; and (ii) there are no reasons to believe that an epigenetic view will extinguish race, or that soft-inheritance claims will produce a less exclusionary discourse than genetics (hard heredity). Quite the opposite, the ground for a re-racialization of social debates and the reinforcement of biological boundaries between groups are highlighted in the article
Collins and Sivers asymmetries in muonproduction of pions and kaons off transversely polarised protons
Measurements of the Collins and Sivers asymmetries for charged pions and charged and neutral kaons produced in semi-inclusive deep-inelastic scattering of high energy muons off transversely polarised protons are presented. The results were obtained using all the available COMPASS proton data, which were taken in the years 2007 and 2010. The Collins asymmetries exhibit in the valence region a non-zero signal for pions and there are hints of non-zero signal also for kaons. The Sivers asymmetries are found to be positive for positive pions and kaons and compatible with zero otherwise. © 2015
Counteracting Trapped Ion Effects in the HESR
Methods to counteract trapped ion effects in the High-Energy Storage
Ring HESR are studied in the present report. The circulating antiproton
beam ionizes the residual gas molecules of the UHV vacuum. The produced
ions are trapped in the negative potentential well of the antiproton
beam. Trapped ions can be extracted using either single isolated clearing
electrodes or continuous clearing electrodes. In addition resonant
transverse shaking of trapped ions and damping of coherent ion-beam
oscillations can be used in order to reduce the adverse effects of trapped
ions. In the region of dipole magnets the problem of trapped ions can be
mitigated by upgrading the UHV vacuum, i.e. by sputtering thin-film
NEG coatings onto the surfaces of the vacuum chamber and by using
heat jackets along the beam tubes. The highest clearing efficiencies in
dipole magnets can be achieved by extracting the trapped ions in the
vertical direction along the magnetic field lines. A distinctive feature
of the HESR ring is the internal PANDA target which deteriorates the
vacuum by a huge local pressure bump. Near the PANDA target continuous
clearing electrodes are necessary in order to counteract the high
production rate of trapped ions. In the region of the electron cooler (EC)
the optimum neutralization is reached if η = 1/γ2
e . Then, the azimuthal
cross-field drift velocity of the electrons is zero and the space-charge
potential is reduced. A stable neutralization with η = 1/γ2
e can be
achieved using the Ion-Cyclotron-Resonance (ICR) heating. The ICR
heating can be realized using the electrodes of the beam position monitors.
The RF can be tuned to be in resonance with the characteristic
cyclotron frequencies of the ion species in the magnetic field of the EC
solenoid
Ion Trapping in the High-Energy Storage Ring HESR
The problem of ion trapping in the high-energy storage ring HESR is
studied in the present report. Positive ions are trapped in the negative
potential well of the antiproton beam. The ions are produced by the
interaction between the antiproton beam and the residual gas. The adverse
effects of ion trapping like tune shifts, tune spreads and coherent
instabilities are reviewed. The ion production rate by ionization of the
residual gas molecules is estimated. The negative potential well and the
corresponding electric fields of the antiproton beam are evaluated in order
to study the transverse and longitudinal motion of the ions and the
accumulation in trapping pockets. The removal of ions can be achieved
using clearing electrodes and under certain conditions resonant transverse
beam shaking. Diagnostic tools and measurements of trapped ion
effects are sketched
Beam-target interaction and intrabeam scattering in the HESR ring : emittance, momentum resolution and luminosity
The beam-target interaction is studied with respect to the transverse and longitudinal emittance growth of the HESR antiproton beam. The transverse emittance growth caused by the small angle Coulomb scattering can be described analytically using the differential cross section of the Coulomb interaction. Similarly, the longitudinal emittance growth caused by the energy loss of the beam can be calculated using the differential cross section of the energy-loss distribution. It is shown that particles with energy losses near the maximum energy loss in a head-on collision with a target electron are lost due to momentum acceptance of the HESR ring. Taking a relative momentum acceptance of about into account yields an order of magnitude smaller growth rate of the mean square momentum deviation. The necessary cooling rates for the High Resolution mode and the High Luminosity mode are deduced assuming that the beam-target interaction is the dominant beam heating process. For comparison the effects of intrabeam scattering are estimated. For electron and stochastic cooling, analytic expressions are quoted in order to evaluate the momentum resolution and cooling rate. The potentialities of electron and stochastic cooling are discussed with respect to the achievable momentum resolution and beamtarget overlap. Beam loss rates and average luminosities are evaluated taking the total hadronic cross section, the restricted momentum acceptance of the HESR ring, the large angle Coulomb scattering and the Touschek effect into account