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

Notes on the decay K S  p + p - p 0 Branching ratio not well measured at present: CPLEAR ’ × E621 ’  1.1 × PDG Avg × Phenomenology & c PT2.4  0.7× 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 ] ~ Unlikely to be observed at KLOE

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

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

Data and MC samples Data:All 2002 dk0 DST’s as of 5 Jun 2002  L dt, VLAB: pb M total K L tags Useful control sample (downscaled 50×) MC kspppmp0, dedicated production Signal100K events MCall_phid, 10 M events BackgroundRuns (2.4 M events, DBV-8) Runs (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

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%

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

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

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)

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?

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:

Simulation of K L crash: q LS Overall efficiency: cos ° 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

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 Crash and K S  p + p - p 0, MC Crash given K S  p + p -, MC Crash given K S  p + p -, data Overall

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 cm < z < 100 cm e MC (K L vertex | K S  p + p - p 0 )

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 Vertex given K S  p + p -, MC Vertex given K S  p + p -, data Overall Vertex efficiencies include acceptance and BR for K L decays with vertices

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

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 < Signal 2646  2252Crash 3545  2922Vertex Background 70  11Crash 439  69Vertex

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 D E 2 2 < (2.5) 2 Signal 2252  2103Crash 2922  2731Vertex Background 11  3Crash 69  28Vertex q +- and y cuts applied

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

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 data taken so far may be reprocessed at some point anyway

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