6,164 research outputs found
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
Model-independent constraints on spin observables
We discuss model-independent constraints on spin observables in exclusive and
inclusive reactions, with special attention to the case of photoproduction.Comment: 6 pages, 5 figures, Talk by J.-M. Richard at NSTAR 2009, IHEP,
Beijing (China), April 19-22, 2009, Proc. to appear in "Chinese Physics C
How light can the lightest neutralino be?
In this talk we summarize previous work on mass bounds of a light neutralino
in the Minimal Supersymmetric Standard Model. We show that without the GUT
relation between the gaugino mass parameters M_1 and M_2, the mass of the
lightest neutralino is essentially unconstrained by collider bounds and
precision observables. We conclude by considering also the astrophysics and
cosmology of a light neutralino.Comment: 6 pages, 3 figures, to appear in the proceedings of the 16th
International Symposium on Particles, Strings and Cosmology (PASCOS2010),
Valencia (Spain), July 19th - 23rd, 201
A T-odd asymmetry in neutralino production and decay
We study CP-violating effects in neutralino production and subsequent decay
within the Minimal Supersymmetric Standard Model with complex parameters M_1
and mu. The observable we propose is a T-odd asymmetry based on a triple
product in neutralino production e^+ e^- -> tilde{chi}^0_i tilde{chi}^0_2, i =
1,...,4, with subsequent leptonic three-body decay tilde{chi}^0_2 ->
tilde{chi}^0_1 l^+ l^-, l = e, mu, at an e^+ e^- linear collider with sqrt{s} =
500 GeV and polarised beams. We provide compact analytical formulae for the
cross section and the T-odd asymmetry taking into account the complete spin
correlations between production and decay. We give numerical predictions for
the cross section and the T-odd asymmetry. The asymmetry can go up to 10 %.Comment: 28 pages, LaTeX, 10 figures; v2: typos corrected, published versio
Physics Opportunities at mu+mu- Higgs Factories
We update theoretical studies of the physics opportunities presented by
mu+mu- Higgs factories. Interesting measurements of the Standard Model Higgs
decays into {\bar b}b, tau+tau- and WW* may be possible if the Higgs mass is
less than about 160 GeV, as preferred by the precision electroweak data, the
mass range being extended by varying appropriately the beam energy resolution.
A suitable value of the beam energy resolution would also enable the
uncertainty in the b-quark mass to be minimized, facilitating measurements of
parameters in the MSSM at such a first mu+mu- Higgs factory. These measurements
would be sensitive to radiative corrections to the Higgs-fermion-antifermion
decay vertices, which may violate CP. Radiative corrections in the MSSM may
also induce CP violation in Higgs-mass mixing, which can be probed via various
asymmetries measurable using polarized mu+mu- beams. In addition,
Higgs-chargino couplings may be probed at a second mu+mu- Higgs factory.Comment: Report of the Higgs factory working group of the ECFA-CERN study on
Neutrino Factory & Muon Storage Rings at CERN. 28 p
Organic aerosol and global climate modelling: a review
The present paper reviews existing knowledge with regard to Organic Aerosol (OA) of importance for global climate modelling and defines critical gaps needed to reduce the involved uncertainties. All pieces required for the representation of OA in a global climate model are sketched out with special attention to Secondary Organic Aerosol (SOA): The emission estimates of primary carbonaceous particles and SOA precursor gases are summarized. The up-to-date understanding of the chemical formation and transformation of condensable organic material is outlined. Knowledge on the hygroscopicity of OA and measurements of optical properties of the organic aerosol constituents are summarized. The mechanisms of interactions of OA with clouds and dry and wet removal processes parameterisations in global models are outlined. This information is synthesized to provide a continuous analysis of the flow from the emitted material to the atmosphere up to the point of the climate impact of the produced organic aerosol. The sources of uncertainties at each step of this process are highlighted as areas that require further studies
Momentum asymmetries as CP violating observables
Three body decays can exhibit CP violation that arises from interfering
diagrams with different orderings of the final state particles. We construct
several momentum asymmetry observables that are accessible in a hadron collider
environment where some of the final state particles are not reconstructed and
not all the kinematic information can be extracted. We discuss the
complications that arise from the different possible production mechanisms of
the decaying particle. Examples involving heavy neutralino decays in
supersymmetric theories and heavy Majorana neutrino decays in Type-I seesaw
models are examined.Comment: 20 pages, 9 figures. Clarifying comments and one reference added,
matches published versio
CP Phases in Correlated Production and Decay of Neutralinos in the Minimal Supersymmetric Standard Model
We investigate the associated production of neutralinos
accompanied by the neutralino
leptonic decay , taking into
account initial beam polarization and production-decay spin correlations in the
minimal supersymmetric standard model with general CP phases but without
generational mixing in the slepton sector. The stringent constraints from the
electron EDM on the CP phases are also included in the discussion. Initial beam
polarizations lead to three CP--even distributions and one CP--odd
distribution, which can be studied independently of the details of the
neutralino decays. We find that the production cross section and the branching
fractions of the leptonic neutralino decays are very sensitive to the CP
phases. In addition, the production--decay spin correlations lead to several
CP--even observables such as lepton invariant mass distribution, and lepton
angular distribution, and one interesting T--odd (CP--odd) triple product of
the initial electron momentum and two final lepton momenta, the size of which
might be large enough to be measured at the high--luminosity future
electron--positron collider or can play a complementary role in constraining
the CP phases with the EDM constraints.Comment: Revtex, 37 pages, 12 eps figure
Decays of the MSSM Higgs Bosons with Explicit CP Violation
We study Higgs boson decays in the minimal supersymmetric standard model
where the tree-level CP invariance of the Higgs potential is explicitly broken
by loop effects of soft CP-violating Yukawa interactions related to scalar
quarks of the third generation. The scalar-pseudoscalar mixing among two
neutral CP-even Higgs bosons and one CP-odd Higgs boson due to explicit CP
violation modifies their tree-level couplings to fermions, to the W^\pm and Z
bosons and to Higgs bosons themselves significantly. We analyze the
phenomenological impact of explicit CP violation on the branching ratios of the
neutral Higgs boson decays in detail and discuss how to directly confirm the
existence of explicit CP violation through \tau^+ \tau^- and t \bar{t} spin
correlations in the decays of the neutral Higgs bosons into a tau-lepton pair
and a top-quark pair.Comment: 28 pages, 10 figures, some references added and correcte
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