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r0.4     supersymmetry ( susy )  @xcite is among the most favoured and most studied extensions of the standard model ( sm ) and is capable of solving many of its problems .
one of its features is that the minimal supersymmetric standard model ( mssm ) provides a number of complex parameters which can serve as sources of cp violation .
they are conventionally chosen to be the higgsino mass parameter , @xmath7 , the @xmath8 and @xmath9 gaugino mass parameters , @xmath10 and @xmath11 , respectively , and the trilinear scalar coupling parameters , @xmath12 , of the third generation sfermions ( @xmath13 ) .
cp phases can give rise to cp - violating signals in collider experiments  @xcite , which have to be measured to determine or constrain the phases independently of measurements of electric dipole moments ( edm ) .
although also cp - even observables , such as masses or branching ratios , are sensitive to the cp phases , cp - odd observables are needed for direct evidence of cp violation .    in this report
neutralino pair production @xmath14 , for @xmath15 , and the subsequent leptonic two - body decay of one of the neutralinos @xmath1 followed by @xmath16 , for @xmath3 , at the ilc is studied  @xcite .
figure  [ shematic picture ] shows a schematic picture of the process .
the cp - sensitive spin correlations of the neutralino in its production process allow to probe the phase of the higgsino mass parameter @xmath17 and the gaugino parameter @xmath18  @xcite .    a full ild  @xcite detector simulation is performed in order to investigate in detail the prospects to measure cp - sensitive observables at the ilc .
all relevant sm background is taken into account , simulated with a realistic beam energy spectrum and beam backgrounds  @xcite .
in neutralino production , effects from cp - violating phases can only occur if two different neutralinos are produced .
cp asymmetries can then be defined with triple products of particle momenta . due to the spin correlation
the asymmetries show hints for cp phases already at tree level . for the process shown in fig .
[ shematic picture ] , a t - odd triple product of the beam and the final lepton momenta can be defined as  @xcite @xmath19 the corresponding asymmetry is @xmath20 where @xmath21 is the cross section for neutralino production and decay .
its sign depends on the charge of the leptons , which has to be tagged in the experimental analysis .    for the full simulation study
a benchmark scenario has been chosen such that the gaugino phase @xmath22 corresponds to a maximal cp asymmetry and the higgsino phase is zero , since it is strongly constrained by edm bounds .
the other parameters in the neutralino sector are @xmath23gev , @xmath24gev , @xmath25gev and @xmath26 .
this leads to the neutralino masses @xmath27 , @xmath28 , @xmath29 and @xmath30 , while the slepton masses are @xmath31 and @xmath32 . the neutralino pair production cross sections are calculated to be @xmath33 and @xmath34 , while the slepton pair production cross sections are @xmath35 and @xmath36 .
the slepton pair production is the main background , since there are two lightest neutralinos and two opposite - sign electrons or muons in the final state as in the case of the neutralino @xmath37 production .
furthermore , beam polarizations of @xmath38 have been chosen , which enhance slightly the susy cross section and the asymmetries , while the background from @xmath39- and chargino - pair production is suppressed . in this scenario
the cp asymmetries are @xmath40 and @xmath41 .
the ild is a concept under study for a multipurpose particle detector for the ilc .
it is designed for an excellent precision in momentum and energy measurement over a large solid angle .
a detailed description can be found in  @xcite . in the simulation all active elements and also cables , cooling systems , support structures and dead regions are taken into account  @xcite .
the radiation hard beam calorimeter is used to suppress background from @xmath42 events at low angles .
all relevant sm backgrounds and susy processes are generated using ` whizard `  @xcite .
a clean sample of signal events is needed in order to clearly measure the cp - violating effects in neutralino production .
otherwise the asymmetry will be reduced by the cp - even background events
. therefore , preselection cuts as listed in tab .
[ tab : preselectioncuts ] are applied to reject as much background as possible , while preserving good signal efficiency .
electrons and muons are identified using the _ particle flow _
approach  @xcite .
the cuts exploit the energy and angular distributions of the final state leptons , as well as the high missing transverse momentum @xmath43 due to the escaping neutralinos .
additional cuts on the total visible energy @xmath44 as well as on the invariant mass @xmath45 distributions further reduce the background contamination .
.preselection cuts , see ref .
@xcite for details.[tab : preselectioncuts ] [ cols= " < , < " , ]     it is remarkable that the moduli of the phases @xmath46 , @xmath47 can also be determined with high precision , using the cp - even observables alone .
however , only an inclusion of cp - odd asymmetries in the fit allows to resolve the sign ambiguities of the phases . without the cp - odd asymmetries in the fit
there is a twofold ambiguity , @xmath48 , and even fourfold if @xmath49 .
thus , the triple product asymmetries are not only a direct test of cp violation , but are also essential to determine the correct values of the phases .
the first full detector simulation study to measure susy cp phases at the ilc has been presented .
triple products of the final state lepton momenta in neutralino decays have been used as cp - odd observables .
realistic collider conditions have been simulated and all relevant sm backgrounds have been taken into account . a detailed cut flow analysis has been performed , including the development of a kinematic selection procedure that was used to obtain a very clean signal sample and to distinguish events from different neutralino decays . in the chosen benchmark scenario
the asymmetry could be measured with a relative precision of 10% with 500fb@xmath50 of data .
finally , the parameters of the neutralino mixing matrix have been fitted to cp - even and cp - odd observables and the complex phases could be determined with a precision of about 10% .
we would like to thank steve aplin , mikael berggren , jan engels , frank gaede , nina herder , jenny list , and mark thomson for very useful discussions and help with the detector simulations .
supersymmetric models provide many new complex phases which lead to cp violating effects in collider experiments . as an example , cp - sensitive triple product asymmetries in neutralino production @xmath0 and subsequent leptonic two - body decays @xmath1 , @xmath2 , for @xmath3 , 
 are studied within the minimal supersymmetric standard model . 
 a full ild detector simulation has been performed at a center of mass energy of @xmath4  gev , including the relevant standard model background processes , a realistic beam energy spectrum , beam backgrounds and a beam polarization of 80% and @xmath5 for the electron and positron beams , respectively . assuming an integrated luminosity of @xmath6 collected by the experiment and the performance of the current ild detector , a relative measurement accuracy of 10% for the cp - sensitive asymmetry can be achieved in the chosen scenario .