30,597 research outputs found
Electrodynamics at the Highest Energies
At very high energies, the bremsstrahlung and pair production cross sections
exhibit complex behavior due to the material in which the interactions occur.
The cross sections in dense media can be dramatically different than for
isolated atoms. This writeup discusses these in-medium effects, emphasizing how
the cross section has different energy and target density dependencies in
different regimes. Data from SLAC experiment E-146 will be presented to confirm
the energy and density scaling. Finally, QCD analogs of the electrodynamics
effects will be discussed.Comment: 10 pages with 7 figures. Invited talk presented at the Workshop on
Electromagnetic Probes of Fundamental Physics, Oct. 16-21, 2001, Erice, Ital
Localized Beampipe Heating due to Capture and Nuclear Excitation in Heavy Ion Colliders
At heavy ion colliders, two major sources of beam loss are expected to be
production, where the is bound to one of the nuclei, and
photonuclear excitation and decay via neutron emission. Both processes alter
the ions charged to mass ratio by well defined amounts, creating beams of
particles with altered magnetic rigidity. These beams will deposit their energy
in a localized region of the accelerator, causing localized heating, The size
of the target region depends on the collider optics. For medium and heavy ions,
at design luminosity at the Large Hadron Collider, local heating may be more
than an order of magnitude higher than expected. This could cause magnet
quenches if the local cooling is inadequate. The altered-rigidity beams will
also produce localized radiation damage. The beams could also be extracted and
used for fixed target experiments.Comment: Numerical Error fixed; to appear in NIM. 15 pages, no figure
ARIANNA: A radio detector array for cosmic neutrinos on the Ross Ice Shelf
ARIANNA (The Antarctic Ross Ice Shelf Antenna Neutrino Array) is a proposed
100 km^3 detector for ultra-high energy (above 10^17 eV) astrophysical
neutrinos. It will study the origins of ultra-high energy cosmic rays by
searching for the neutrinos produced when these cosmic rays interact with the
cosmic microwave background. Over 900 independently operating stations will
detect the coherent radio Cherenkov emission produced when astrophysical
neutrinos with energy above 10^17 eV interact in the Antarctic Ross Ice Shelf.
Each station will use 8 log periodic dipole antennas to look for short RF
pulses, with the most important frequencies between 80 MHz and 1 GHz. By
measuring the pulse polarization and frequency spectrum, the neutrino arrival
direction can be determined. In one year of operation, the full array should
observe a clear GZK neutrino signal, with different models predicting between 3
and 51 events, depending on the nuclear composition of the cosmic-rays and on
the cosmic evolution of their sources.Comment: 8 pages, presented at SORMA12. Many small improvements, per referee
comment
Ultra-peripheral collisions and hadronic structure
Ultra-peripheral collisions are the energy frontier for photon-mediated
interactions, reaching, at the Large Hadron Collider (LHC), center
of mass energies five to ten times higher than at HERA and reaching
energies higher than at LEP. Photoproduction of heavy quarkonium
and dijets in and collisions probes the gluon distribution in protons
at Bjorken- values down to , far smaller than can be
otherwise studied. In collisions, these reactions probe the gluon
distributions in heavy ions, down to values of a few . Although
more theoretical work is needed to nail down all of the uncertainties,
inclusion of these data in current parton distribution function fits would
greatly improve the accuracy of the gluon distributions at low Bjorken- and
low/moderate . High-statistics data probe the spatial
distribution of the interaction sites; the site distribution is given by the
Fourier transform of .
After introducing UPCs, this review presents recent measurements of dilepton
production and light-by-light scattering and recent data on proton and heavy
nuclei structure, emphasizing results presented at Quark Matter 2017 (QM2017).Comment: 8 pages, present at Quark Matter 2017 Final version, w/ 1 replaced
figure and a few new reference
Heavy ion beam loss mechanisms at an electron-ion collider
There are currently several proposals to build a high-luminosity electron-ion
collider, to study the spin structure of matter and measure parton densities in
heavy nuclei, and to search for gluon saturation and new phenomena like the
colored glass condensate. These measurements require operation with
heavy-nuclei. We calculate the cross-sections for two important processes that
will affect accelerator and detector operations: bound-free pair production,
and Coulomb excitation of the nuclei. Both of these reactions have large
cross-sections, 28-56 mb, which can lead to beam ion losses, produce beams of
particles with altered charge:mass ratio, and produce a large flux of neutrons
in zero degree calorimeters. The loss of beam particles limits the sustainable
electron-ion luminosity to levels of several times cm/s.Comment: 4 pages with 1 figur
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