1. Status report on analysis of BR(K S  p + p - p 0 ) A. Antonelli, M. Moulson, Second KLOE Physics Workshop, Otranto, 10-12 June 2002

2. Notes on the decay K S  p + p - p 0 Branching ratio not well measured at present: CPLEAR ’97 2.5 + 1.2 - 1.0 + 0.5 - 0.6 × 10 - 7 E621 ’96 4.8 +2.2 -1.6  1.1 × 10 - 7 PDG Avg. 3.2 + 1.2 - 1.0 × 10 - 7 Phenomenology & c PT2.4  0.7× 10 - 7 Part of amplitude is CP violating: L oddCP( p + p - p 0 ) I=0,2 = + 1Centrifugal barrier L evenCP( p + p - p 0 ) I=1,3 = - 1 Violates CP h +-0 = A[K S  ( p + p - p 0 ) CP - ]/A[K L  p + p - p 0 ] CP– component extracted by integration over Dalitz plot, traditionally in interference measurements BR[K S  ( p + p - p 0 ) I=1 ] ~ BR[K S  p 0 p 0 p 0 ] ~ 10 -9 Unlikely to be observed at KLOE

3. General analysis considerations 0.34 events produced per pb -1 : 58 events in 170 pb -1 with 100% efficiency Background rejection paramount: K L reconstruction needed for signal ID Use both K L crashes and vertices in DC No reliable K S tag using DC vertices available: New EVCL algorithm to include K S  p + p - p 0 events in ksl stream starting from K S Symmetric treatment of K L crash/vertex Not a tagged measurement in the usual KLOE sense Acceptable to rely on MC for most efficiencies: K L crash studied in K S  p + p - K S  p + p - additionally useful for normalization

4. Efficiency evaluation MC does a miserable job at simulating K L crash: Estimate K L crash efficiency from K S  p + p - events in data Useful mainly for estimating sensitivity For the actual BR measurement: Fundamental assumption: K L crash detection probability cancels from ratio Detection probability for K L vertex more likely to depend on K S decay mode, but ratio of efficiencies more amenable to simulation

5. Data and MC samples Data:All 2002 dk0 DST’s as of 5 Jun 2002  L dt, VLAB: 125.7 pb -1 46.0M total K L tags Useful control sample (downscaled 50×) MC kspppmp0, dedicated production Signal100K events MCall_phid, 10 M events BackgroundRuns 81-160 (2.4 M events, DBV-8) Runs 161-439 (7.6 M events, DBV-13) 1.42M total K L tags, effective  L dt  3.9 pb -1 Dedicated Ntuples made from DST’s and MC files DST Processing rate: ~0.6 pb -1 /CPU hour Volume of MC + data: 2.2 GB total

6. Control sample: K S  p + p - Unique vertex at origin, zero net charge: r xy < 5 cm, - 20 cm < z < 20 cm M - M K < 10 MeV, P - P K < 5 MeV One track (or daughter of recognized kink) must analytically extrapolate to cluster: d 50 MeV Associated cluster used to set event t 0 s (K L tag): 366 nb, using L datarec 436 nb, using s f = 3.1 m b, e KLtag (MC) = 60.7%

7. Event classification algorithm Unique vertex at origin, zero net charge: r xy < 5 cm, - 20 cm < z < 20 cm Two prompt neutral clusters: D (t - R/c) < min(5 s, 2ns) For each pair of clusters ( p 0 candidate): Close kinematics using vertex, m KS, m p0, and cluster directions Set t 0 using clusters Search for K L crash in 20  cone If no K L crash, search for K L vertex in 20  cone Veto vertices using tracks in K S vertex tree in post-reconstruction analysis If more than one p 0 candidate, correct candidate identified on basis of best alignment of K L direction and tagging momentum

8. Reconstruction of p + p - vertex e = 36.3% Track momenta are low and anticorrelated Vertex reconstruction efficiency dominated by acceptance

9. Reconstruction of p 0 clusters E > 25 MeV e = 73.3% r > 60 cm e = 96.6% E 1 + E 2 >100 MeV <250 MeV e = 99.98% cos( q 12 ) > 75  e = 98.6 % Distributions are for clusters corresponding to MC truth, as reconstructed Cut efficiencies shown evaluated in cascade Expect overall p 0 efficiency e  70% Find e = 59.9% Bug in tag! Cut on D t instead of D (t - R/c)

10. Simulation of K L crash: b * K S  p + p -, MCK S  p + p -, Data b*b* b*b* b * spectra for MC and data completely different: Evaluate K L crash efficiency from K S  p + p - events in data Stop decays?

11. Simulation of K L crash: b * Relative efficiency: Lower cut on b * Upper cut on b * Simulation of K L crash same for both K S decays t 0 correct in each case Overall efficiency: 0.2275 0.2

12. Simulation of K L crash: q LS Overall efficiency: cos -1 0.99 8.1° q LS Relative efficiency: Significant influence from reconstruction of K S vertex Relative efficiency: Extent/position of K L crash in MC not as bad as timing

13. Preselection efficiency: K L crash Efficiency No cuts on b *, q LS Default cuts on b *, q LS presentw/ bug fixed p + p - vertex, MC 36.3 p 0 reconstruction, MC 59.1 69.6 Crash and K S  p + p - p 0, MC 2.61.11.3 Crash given K S  p + p -, MC 15.17.2 Crash given K S  p + p -, data 31.725.6 Overall 5.53.94.7

14. FV for K L vertex analysis Fiducial volume for K L vertex: 23.2% selects region in which reconstruction efficiency high and constant plays important role in eliminating backgrounds (mainly K + K - ) 30 cm < r xy < 150 cm - 100 cm < z < 100 cm e MC (K L vertex | K S  p + p - p 0 )

15. Preselection efficiency: K L vertex Efficiency No cuts on FV, q LS Default cuts on FV, q LS presentw/ bug fixed p + p - vertex, MC 36.3 p 0 reconstruction, MC 59.1 69.6 Vertex given K S  p + p -, MC 22.313.7 Vertex given K S  p + p -, data 21.813.3 Overall 3.51.92.2 Vertex efficiencies include acceptance and BR for K L decays with vertices

16. Principal backgrounds Emphasis on K L crash sample for background elimination studies Cuts applied to K L vertex sample (almost) as an afterthought MC backgroundCrashVertex No cuts70439 b * /FV and q LS cuts 354 Composition of MC background in K L crash events: 26 K + K - events Both K +, K - both reconstructed and make vertex One K or its daughter makes an unassociated crash cluster Other K decays to pp 0, 2 g ’s fake p 0 at origin (no prompt g ’s in event) One K reconstructed, other decays to pp 0 before DC 44 K S  p 0 p 0 events Conversions on DC wall: vertex forms “fish” and tracks cross at origin Dalitz decays: p 0  e + e - g Crash background studied by using vertex sample and/or relaxing b *, q LS cuts

17. Background elimination Angle between p + and p - : cos q +- Angle between gg in p 0 rest frame: cos y Signal K S  p 0 p 0 K + K - Cuts made: |cos q +- | < 0.85 cos y < - 0.85 Signal 2646  2252Crash 3545  2922Vertex Background 70  11Crash 439  69Vertex

18. Background elimination D E 1 = (E 1 – E 1 close )/ s (E 1 ) D E 2 = (E 2 – E 2 close )/ s (E 2 ) Signal (crash & vertex) Background to vertex Background to crash Cuts made: D E 1 2 + D E 2 2 < (2.5) 2 Signal 2252  2103Crash 2922  2731Vertex Background 11  3Crash 69  28Vertex q +- and y cuts applied

19. Status of analysis K L crash Efficiency: 3.2% Events expected: 1.4 Events found: 11 Events in MC bkg:0 Efficiency: 1.5% Events expected: 0.6 Events found: 114 Events in MC bkg:6 K L vertex M miss

20. Summary and outlook Bug in EVCL tag a disappointment, but: K L crash sample included in ksl stream by K L crash tag K L vertex sample in 2001 data useable for study, at least Only ~10% loss in efficiency Presumably amenable to simulation Fixed version of tag ready for DBV-14 2002 data taken so far may be reprocessed at some point anyway

21. Summary and outlook Many additional handles on background: K S  p 0 p 0 Prompt cluster multiplicity Eliminate p + p - candidates that cross on DC wall K + K - More work on analytical expansion of p + p - vertex tree Use ADC information Much additional work on physics backgrounds to do Existing MC samples of K + K - Dedicated MC generation of K S  p 0 p 0 with p 0  e + e - g and/or conversions Work on noise and machine background not yet started Prospects seem good for eliminating background entirely