arXiv subjects

Sabine Riemann

Publications and source records attributed to Sabine Riemann.

24 records · Page 2Linked to original sources

arXiv2011

A conventional positron source for International Linear Collider

A possible solution to realize a conventional positron source driven by a several-GeV electron beam for the International Linear Collider is proposed. A 300 Hz electron linac is employed to create positrons with stretching pulse length in order to cure target thermal load. ILC requires about 2600 bunches in a train which pulse length is 1 ms. Each pulse of the 300 Hz linac creates about 130 bunches, then 2600 bunches are created in 63 ms. Optimized parameters such as drive beam energy, beam size, and target thickness, are discussed assuming a L-band capture system to maximize the capture efficiency and to mitigate the target thermal load. A slow rotating tungsten disk is employed as positron generation target.

physics.acc-ph↗

arXiv2009

Undulator-Based Production of Polarized Positrons

Full exploitation of the physics potential of a future International Linear Collider will require the use of polarized electron and positron beams. Experiment E166 at the Stanford Linear Accelerator Center (SLAC) has demonstrated a scheme in which an electron beam passes through a helical undulator to generate photons (whose first-harmonic spectrum extended to 7.9MeV) with circular polarization, which are then converted in a thin target to generate longitudinally polarized positrons and electrons. The experiment was carried out with a one-meter-long, 400-period, pulsed helical undulator in the Final Focus Test Beam (FFTB) operated at 46.6GeV. Measurements of the positron polarization have been performed at five positron energies from 4.5 to 7.5MeV. In addition, the electron polarization has been determined at 6.7MeV, and the effect of operating the undulator with a ferrofluid was also investigated. To compare the measurements with expectations, detailed simulations were made with an upgraded version of Geant4 that includes the dominant polarization-dependent interactions of electrons, positrons, and photons with matter. The measurements agree with calculations, corresponding to 80% polarization for positrons near 6MeV and 90% for electrons near 7MeV.

physics.ins-det↗

arXiv2009

Frequency of Positron Helicity Reversal

The ILC baseline design for the positron source is based on a helical undulator and will deliver a positron beam with a polarization of 30% or more. In this contribution the need for fast reversal of the positron helicity is discussed.

physics.ins-det↗

arXiv2007

Radiation damage of the ILC positron source target

The radiation damage of the positron source target for the International Linear Collider (ILC) has been studied. The displacement damage in target material due to multi-MeV photons has been calculated by combining FLUKA simulations for secondary particle production, SPECTER data for neutron displacement cross-sections and the Lindhard model for estimations of displacement damage by ions. The radiation damage of a stationary Ti6Al4V target in units of displacements per atom (dpa) has been estimated for photons from an undulator with strength 0.92 and period 1.15 cm. The calculated damage is 7 dpa. Approximately 12.5% of displacement damage result from neutrons.

physics.acc-ph↗

arXiv2001

Search for exotic physics with four-fermion coupling at LEP

Preliminary results of measurements of fermion-pair production at LEP2 are used to derive limits on new physics phenomena. Combinations of the cross sections and asymmetrie of the 4 LEP collaborations are interpreted in terms four-fermion contact interactions, exchange of Z' and leptoquarks. Results on the search for extra dimensions are also presented.

hep-ex↗

arXiv1995

ZZ' Mixing and Radiative Corrections at LEP I

We present a method for a common treatment of $Z'$ exchange, QED corrections, and weak loops in $e^+ e^-$ annihilation. QED corrections are taken into account by convoluting a hard-scattering cross section containing $γ,\ Z,$ and $Z'$ exchange. Weak corrections and $ZZ'$ mixing are treated simultaneously by a generalization of weak form factors. Using the properly extended Standard Model program for the $Z$ line shape, ZFITTER, we perform and compare two different analyses of the 1990 LEP~I data in terms of theories based on the E$_6$-group and in terms of LR-symmetric models. From the LEP~I data alone, the $ZZ'$ mixing angle may be limited to $|θ_M| \le 0.01$ and the $Z'$ mass to $M_2 > 118$--148 GeV, depending on the model (95\%~CL).

hep-ph↗