Neutral kaon WG other activities

Neutral kaon WG other activities Volounteered Rapporteur: F. Bossi • Coherent KSregeneration • KL branching ratios • KL 00 and QCAL

Coherent KS regeneration M. AntonelliA. De Santis A. Di Domenico INFN Laboratori Nazionali di Frascati Physics Dept. University of Rome “La Sapienza” & INFN RM1 CP wg meeting 22 November 2002

Coherent regeneration Coherent regeneration occurs only in the strictly forward direction: This interference term is important for thin regenerators, i.e. when |rcoh| ~ |h±| as for the beam pipe and inner DC walls

Event selection Data sample : DST of 2001 and 2002 integrated luminosity: 340 pb-1 • Preliminary selection: • KS - sqrt(x2+y2) < 5 cm AND |z| < 10 cm • - |Minv - MK| < 5 MeV • KL -two track vertex inside a 40 cm radius sphere • - vertex inside 20 degree cone around extrapolated KL direction from PKs. • kinematic fit to improve KS KL vertex position • (the same as in interferometry study – M. Antonelli & A. Sibidanov)

Event selection Emiss (MeV) • | |PKL| - |Pp+p-| | < 5 MeV • |Emis + (Minv-MK0)| < 5 MeV Only scalar quantities used for the selection criteria in order to avoid distortion of angular distribution of the incoherent regeneration bkg. Minv (MeV)

q Regenerator PKL Background Pp+p- Beam pipe Resolution fixed incoherent regeneration q cut • Background evaluation: • angular distribution of incoherent • regeneration is assumed flat • (in solid angle) in the small q region • fit of incoherent regeneration • background and subtraction • cut q < 0.04 • Km3 background negligible • (checked with data) q (rad) DC inner wall Resolution fixed incoherent regeneration q cut q (rad)

signal + bkg bkg Background subtraction Incoherent regeneration bkg smeared according to MC and with data for q >qcut t / tS t / tS

Efficiency • Only relative variation of the efficiency are relevant. • (Normalization to through |h±|). • a preliminary MC study does not shows dramatic changes in the region of interest (M. Antonelli-A. Sibidanov): more accurate studies needed !

fit results Fit function: P(t) folded with MC resolution Beam pipe fit results: c2 = 27.6/15 |r| = (6.5 ±2.2) ·10-4 f = -1.05 ± 0.25 rad

fit results DC inner wall fit results: c2 = 14.0 / 15 |r| = (16.6 ± 6.6) ·10-4 f = -1.19 ± 0.27 rad

fit results DC inner wall Red curve: incoherent regeneration (only decay term) Black curve:coherent regeneration (decay and interference term)

fit result : phase DC inner wall The fit result is quite sensitive to the rcoh phase, due to the interference term

fit results: result stability vs q cut fit results as a function of the q cut parameter For comparison: horizontal lines are the Baldini-Michetti evaluations

Conclusion • Theoretical evaluations (Baldini-Michetti) compatible with • preliminary results • - more work to do on: • - Efficiency evaluation • - Refine Km3 and incoherent regeneration background • evaluation • - Complete analysis with full Kloe statistics

Our Christmas present to Paolo F. : We will measure absolute branching ratios

Status of the measurement of KL pln,p+p-branching ratios M. Antonelli, M. Dreucci, M. Moulson CP meeting 16-12-2002

Introduction • Problems in both measurements: • tag bias (common to all KL BR measurements) • tracking efficiency • Additional Problems KL p+p-: • momentum calibration • momentum resolution • ( semileptonic event selections • needs looser kinemtic cuts)

Tag bias Ks p+p-selection: Rt<10cm ;|z|<20 cm |m-mK|<5 MeV; |p*-p*K|<10 MeV e 63% • Main bias is expected from trigger • require trigger from ks pions: • clusters connected to fired trigger sector • no other cluster in “ks sectors” (avoid overlaps) • no splitted pion tracks (T2CL asso. quality) • + ks direction far from beam line (cos(q)>0.9) 39% 25% 20%

e KLtag 63% standard 39% Ks trigger 25% + overlaps 20% + tracks q. Ks dir. Tag bias: MC results Relative KS +- efficiency for various KL process KL p0p0p0 KL All KL p+p-p0 in FV KL en out FV Crash included KL mn +/- 1%

Tag bias: cont. • General : • Main KL decay mode can be measured with • “unbiased” tag. • Rare decays can be normalized to main one • Prospects: • a <1% biased tag available • compare with data (neutral vs charged Kltag) • for more studies we need good simulation of: • KL “shower”, fragments, • machine bkg. inclusion (soon)

Tracking efficiency Double tag method ( from KL p+p- analysis) Conditional efficiency N2/N1 from data KS p+p-

Data-MC comparison “Efficiency” dependence for about 20 variables (2000 data) just few examples efficiency definition = (# 2 tag events)/(# >0 tag events) DATA MC 0 206 MeV 0 206 MeV DATA MC

Data-MC comparison cont. No clear dependencies found DATA MC BUT Eff. vs <Hot rate>(Khz)

Kinematics Pmiss (MeV) Emiss (MeV)

QCAL infos and KL p0p0 search Caterina Bloise

QCAL infos and KL p0p0 search Can QCAL play any role in the KL p0p0search? Two items have been considered : background reduction knowledge of the distributions useful to separate signal and background 4-clusters sample ( last 115 pb-1 of the 2002 DAQ campaign) has been analyzed Results: QCAL is marginal for the background reduction QCAL-tagged background is crucial for the knowledge of the distributions of the 3p0 contamination.

QCAL infos and KL p0p0 search Likelihood Ratio - 4-clusters events (53.5 pb-1) Background selection: signal contamination evaluation Plot 1 : shape of the difference between events selected with DT  < 20 ns and those with DT  < 10 ns Plot 2 : shape of the difference between events selected with DT  < 10 ns and those with DT  < 5 ns Plot 3 : shape of the difference between events selected with DT  < 5 ns and those with DT  < 3 ns Black area : shape of the events selected requiring DT  < 3 ns 1 2 Events / 2. 3

QCAL infos and KL p0p0 search Likelihood Ratio - 4-clusters events (115 pb-1) Black histogram : Entire sample distribution Blue histogram : Event distribution without tagged sample by QCAL Events / 0.5 Background reduction is modest : 14884 events / ~66000  ~22% of the contamination is tagged by QCAL requiring at least one hit in time DT  < 5 ns

QCAL infos and KL p0p0 search Likelihood Ratio - 4-clusters events MC Events / 0.5 Black histogram : MC distribution for the entire background sample 15313 simulated events Red points : MC distribution for the QCAL tagged background - 3598 events

QCAL infos and KL p0p0 search Likelihood Ratio - 4-clusters events QCAL vs MC shape Events / 0.5 Black histogram : MC distribution for the entire background sample 15313 simulated events Red points : QCAL tagged background in 115 pb-1 - 14884 events

QCAL infos and KL p0p0 search Likelihood Ratio - 4-clusters events (115 pb-1) 4-clusters events (black points) 59794 collected in ~ 115 pb –1 Signal shape from MC 18208 simulated events Background shape from QCAL 14884 collected events Fit results : Signal (red histogram): 8570  220 ev Background: 51225  510 ev c2 : 459/356 Blue histogram is the sum of signal and background from fit results Events / 0.5

CONCLUSIONS The QCAL information is crucial for the knowledge of the background behaviour It is also important to increase its efficiency in order to achieve a better statistical accuracy on the interesting distributions

Neutral kaon WG other activities