5,246 research outputs found
Photon collimator system for the ILC Positron Source
High energy e+e- linear colliders are the next large scale project in
particle physics. They need intense sources to achieve the required luminosity.
In particular, the positron source must provide about 10E+14 positrons per
second. The positron source for the International Linear Collider (ILC) is
based on a helical undulator passed by the electron beam to create an intense
circularly polarized photon beam. With these photons a longitudinally polarized
positron beam is generated; the degree of polarization can be enhanced by
collimating the photon beam. However, the high photon beam intensity causes
huge thermal load in the collimator material. In this paper the thermal load in
the photon collimator is discussed and a flexible design solution is presented.Comment: 22 pages, 19 figures, 8 tables, cross-reference to table 4 fixe
Interference of Higgs boson resonances in mu^+ mu^- -> neutralino_i neutralino_j with longitudinal beam polarization
We study the interference of resonant Higgs boson exchange in neutralino
production in \mu^+ \mu^- annihilation with longitudinally polarized beams. We
use the energy distribution of the decay lepton in the process \neutralino_j
\to \ell^\pm \slepton^\mp to determine the polarization of the neutralinos. In
the CP conserving Minimal Supersymmetric Standard Model a non-vanishing
asymmetry in the lepton energy spectrum is caused by the interference of Higgs
boson exchange channels with different CP eigenvalues. The contribution of this
interference is large if the heavy neutral bosons H and A are nearly
degenerate. We show that the asymmetry can be used to determine the couplings
of the neutral Higgs bosons to the neutralinos. In particular, the asymmetry
allows to determine the relative phase of the couplings. We find large
asymmetries and cross sections for a set of reference scenarios with nearly
degenerate neutral Higgs bosons.Comment: 20 pages, 6 figures, minor typos corrected, to appear in Eur. Phys.
J.
Normal tau polarisation as a sensitive probe of CP violation in chargino decay
CP violation in the spin-spin correlations in chargino production and
subsequent two-body decay into a tau and a tau-sneutrino is studied at the ILC.
From the normal polarisation of the tau, an asymmetry is defined to test the
CP-violating phase of the higgsino mass parameter \mu. Asymmetries of more than
\pm70% are obtained, also in scenarios with heavy first and second generation
sfermions. Bounds on the statistical significances of the CP asymmetries are
estimated. As a result, the normal tau polarisation in the chargino decay is
one of the most sensitive probes to constrain or measure the phase \phi_\mu at
the ILC, motivating further detailed experimental studies.Comment: 20 pages, 10 figures, gzipped tar fil
Measurement of the H/A -> tau tau cross section and possible constraints on tan beta
The achievable precision of the cross section times branching ratio
measurement from the event rates is estimated for the MSSM H/A -> tau tau decay
in the associated production process gg -> b bbar H/A at large tan beta in CMS.
This work demonstrates that the above production and decay process exhibit a
large sensitivity to tan beta and thus add as a significant observable to a
global fit of the SUSY parameters. To illustrate this potential an example is
given concerning the achievable tan beta determination accuracy that could be
reached from the event rates and for a given set of SUSY parameters and
uncertainties
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