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Preliminary result presented @KAON09

Preliminary result presented @KAON09. Preliminary result presented @KAON09. Roadmap to a definitive result :. Reduce statistical error : Extend fit region down to 6 ns (at least )  hide a bad control of the background

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Preliminary result presented @KAON09

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  1. Preliminaryresultpresented @KAON09

  2. Preliminaryresultpresented @KAON09

  3. Roadmapto a definitive result : Reduce statisticalerror: Extendfitregiondown to 6 ns (at least)  hide a bad controlof the background Include 2004 data (0.7 fb-1 , smalleffectanyhow)  almostdone, needtotune some cuts, no big surprises Reduce systematics : Redotagsystematics  isactuallymuchsmaller ! New estimate ofnuclearinteractions  stillusing 2002. Not a big contribution, butmustbechecked Need some work. Connection withfitregion

  4. Tagsystematicswasevaluatedwrongly !!!!!! The variationof the slopewasdirectlyappliedto the resultobtainedwith the standard energythreshold. Instead, the analysisshouldhavebeenrepeated: in this way the effectismuchsmaller !!! We estimate that the tagefficiency can bereducedby at leastfactorof 2

  5. Fitregionhides a seriousproblem Fitveryunstable at smalltimes Assumeditdepends on the beam loss due to regeneration and nuclearinteraction on DC wall : Effect on propertimedistributionevaluatedanalytically: - beam loss on sphericalbeam pipe produce a step - cylindrical DC wallhas a complicatedeffect: at time t1one can feel or not the beam loss depending on kaonemission angle. Thishasalsotobeconvoluted withkaonangulardistribution. t1 New fitfunction: ( 1 – Ploss f(tdc/t*) ) + Plossnewparameter,tdcfixed

  6. New fitfunction far frombeingenough ! EitherPlossgoesvery high (expected 10-3 ÷ 10-4 ), eitherfBCKgoes up to 2 (was 0.74 in previousfit) Regeneration and nuclearinteractions background are reproducedverydifferently in MC at low and at high decaytimes. Needtofixitto data. This can also help re-estimating the nuclearinteractioncorrectiontotL. p+p-p0 background seems under control ?

  7. Up tonow the onlygoodvariabletoselectnuclearinteractionshasbeed the angle a :

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