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Rare Kaon Decay Physics

Rare Kaon Decay Physics. Lepton Photon Symposium Augusto Ceccucci*/CERN Fermilab, August 11, 2003 *Member of the NA48 Collaboration. Why study Rare Kaon Decays. Search for explicit violation of Standard Model Lepton Flavour Violation Probe the flavour sector of the Standard Model FCNC

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Rare Kaon Decay Physics

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  1. Rare Kaon Decay Physics Lepton Photon Symposium Augusto Ceccucci*/CERN Fermilab, August 11, 2003 *Member of the NA48 Collaboration LP2003, Augusto Ceccucci

  2. Why study Rare Kaon Decays • Search for explicit violation of Standard Model • Lepton Flavour Violation • Probe the flavour sector of the Standard Model • FCNC • Test fundamental symmetries • CP,CPT • Study the strong interactions at low energy • Chiral Perturbation Theory, Form Factors • I will give a review of recent experimental results • In addition to KL and K+, alsoKS rare decays (BR≤10-8) start to be studied • I will also briefly review the new initiatives that should lead to significant advance in the field by the end of this decade LP2003, Augusto Ceccucci

  3. Outline • Tests of the Standard Model • KL→p0 ee KTeV-E799 II (1999 data) • KS→p0 ee NA48/1 CERN (2002 data) • K+→p+nnBNL-E787 (1997 data, region II) • Other Tests of CP and CPT symmetry • KL→ppeeKTeV-E799 II (1999 data) • KS→3p0 NA48/1 (2000 data) • KS→p e nKLOE Frascati (2001) • Chiral Perturbation Theory • Dalitz decays: • KL→eeg, KL→eeee,KL→mmeeKTeV-E799 II • Non-Leptonic decays • KL→gg KLOE (2001+2002 data) • KS→gg NA48/1 (2000 data) • KS→p0gg NA48/1 (2000 data) LP2003, Augusto Ceccucci

  4. Kaon Rare Decays and the SM JCP=2(Triangle Area) is the unique measure of CP-Violation in SM JCP = Im(Vud*VusVts*Vtd) ~ cosqc sinqcIm lt In the Wolfenstein parameterisation (l, A, h, r): Im lt = A2l5h, Re lt = A2l5r (holy grail) CP-Violation LP2003, Augusto Ceccucci

  5. Theory of KL→p0ee (mm) • Complete re-analysis of the decay: (Buchalla, D’Ambrosio, Isidori, hep-ph/0308008) BDI • Short Distance (Direct CP-Violation) • From Standard Model fit: Im lt = (1.36 ± 0.12) 10-4 (CKM) • B(KL→p0ee)CPV-dir=(2.4 ± 0.2) ×10-12 × (Im lt /10-4)2 = (3.2 ± 0.4) × 10-12 • Indirect CP-Violation • BR(KL→p0 ee) CPV-ind ~1/330 BR(KS → p0 ee) • Direct and Indirect CP-Violating components interfere • CP-Conserving contribution • Need model ind. 3 par. fit (Gabbiani, Valencia, PRD 64 2001) • BRCPC < 3 ×10-12 (conservative, BDI) • They fix the 3 counterterms from KL→p0gg and KS→gg LP2003, Augusto Ceccucci

  6. KTeV-E799-II (FNAL) Pure CsI mgg~1 MeV TRD KL flux ~ 7 × 1011 LP2003, Augusto Ceccucci

  7. Experiment: KL→p0ee (mm) Published data: E799-II (KTeV) 1997 KL→p0ee KTeV 1997 data: 2 events consistent with the expected background of 1.06 ± 0.41 events • Irreducible background: KL→ ee(mm)gg (Greenlee, 1990) • Same final state as the signal, only gg mass resolution and kinematics are available to suppress these backgrounds • To keep it to the ~1 event level the acceptance is quite reduced • Possible future searches will be background dominated LP2003, Augusto Ceccucci

  8. KTeV: KL→p0ee KL→p0p0p0, pegn+gacc e+gX e-X gX KL→p0p0p0D, pen+p0acc KL→eegg crossing the signal box (BR~6 10-7 !!) DATA 1999 preliminary M(eegg) computed using the neutral vertex, assuming m(gg)=m(p0) M(gg) computed from charged vertex LP2003, Augusto Ceccucci

  9. KTeV: p0ee vs eegg kinematics KL→eegg “radiative” distribution Minimum angle between any e and g p0→gg decay asymmetry p0→gg “isotropic” distribution Expected background: 0.99 ± 0.33 events cosqp0 LP2003, Augusto Ceccucci

  10. One candidate in the signal box Combining 1997 and 1999: KTeV: KL→p0ee 1999 data, preliminary BR(KL→ p0 ee ) < 3.5 × 10-10 @90%CL BR(KL→ p0 ee ) < 2.8 × 10-10 @90%CL LP2003, Augusto Ceccucci

  11. NA48/1 (CERN) • NA48: e’/e, KL rare decays • NA48/1: KS rare decays • Upgraded read out • High intensity short neutral • beam from the CERN-SPS • Run in 2000 (only gs) and 2002 Liquid krypton calorimeter • NA48 ( e’/e ): • 1997-1999 • (2000) • 2001 Run 2002 LP2003, Augusto Ceccucci

  12. NA48/1: KS→p0 ee e+-e-+ (Odd Sign) DATA e+-e-+ DATA vs. MC Blind Control & Signal regions meegg (GeV/c2) mee (GeV/c2) mee > 0.165 GeV/c2 cut applied to reject KS→ p0p0Dwith one missingg LP2003, Augusto Ceccucci

  13. NA48/1: KS→p0 ee e+-e+- (Same Sign) DATA e+-e+- DATA vs. MC Search region meegg (GeV/c2) mee (GeV/c2) LP2003, Augusto Ceccucci

  14. NA48/1: KS→p0 ee Background from KL,S→eegg : measured using NA48 KL data from 2001 N(KL→eegg, 2001)  10 × N(KL,S→eegg, 2002) meegg(GeV/c2) mgg(GeV/c2) LP2003, Augusto Ceccucci

  15. NA48/1: KS→p0 ee Accidental backgrounds • DC proton beam • Read out window: ~ 200ns • Use time side band to measure background from time-overlapping fragments from differ decays • Major component: • epn+ p0p0(p0) • Confirmed relaxing E/P cuts meegg (GeV/c2) mgg (GeV/c2) LP2003, Augusto Ceccucci

  16. NA48/1: KS→p0 ee SUMMARY OF BACKGROUNDS: • Many other sources investigated and found to be negligible (e,g neutral cascade decays) • Blind analysis: Control and signal region remained masked until the study of the background was finished LP2003, Augusto Ceccucci

  17. NA48/1: KS→p0 ee • 7 candidates in the • signal region • 0 in control region • Background 0.15 • The probability that all 7 • events are background • is ~10-10 meegg (GeV/c2) mgg (GeV/c2) First observation of KS→p0 ee LP2003, Augusto Ceccucci

  18. The 7 KS→p0ee candidates Meegg (GeV/c2) t/tS Mgg (GeV/c2) Mee (GeV/c2) LP2003, Augusto Ceccucci

  19. NA48/1: KS→p0 ee BR(KS→p0ee, mee>165 MeV/c2) = (3.0+1.5-1.2(stat)± 0.2(syst))×10-9 • Assuming vector interaction and unity form factor: • In remarkable agreement with L. Sehgal prediction: ~5.5 ×10-9 NP B19 (1970) • In the notation of D’Ambrosio et al. JHEP 08 (1998 004): • BR(KS→p0ee) ~ 5 |as|2 |as|=1.08+0.26-0.21 BR(KS→p0ee) = (5.8 +2.8-2.3(stat) ± 0.3(syst) ± 0.8(theor))×10-9 Preliminary LP2003, Augusto Ceccucci

  20. Sensitivity to Im lt -as IF the interference is constructive some sensitivity to Im lt is retained LP2003, Augusto Ceccucci

  21. KL→p0ee(mm) Perspectives Expect KTeV to update KL→p0mm (1999 data) NA48/1 analysis of KS→p0mmis in progress • Detector s(gg)×2 • Very ambitious, KTeV already state of the art • KS-KL time dependent interference ×2 • Position experiment between 9 and 16 KS lifetimes (hep-ph/0107046) • KS-KL time independent interference ×3 • Assume constructive interference (theoretically preferred) • Data Taking ×5 • Run in “factory mode”. After all E799-II run only for a few months to collect ~7 × 1011 KL decays • Beam intensity ×4 • Need ~1012 protons/sec, slowly extracted, high energy, DC • Tot ~ ×240 →sens~ ×15 • close the gap between current upper limit and SM • Where? When? *Admittedly aggressive Road Map* LP2003, Augusto Ceccucci

  22. K+→p+nn (reminder) • The hadronic matrix element can be extracted from • the well measuredK+→p0 e n • No long distance contributions QCD NLO Buchalla, Buras 1999 As an example, within the SM, using ACP(J/KS) and ek as input: BR(K+→ pnn) = 7.1 ± 1.0 × 10-10 (Kettell, Nguyen, Landsberg, hep-ph/0212321) LP2003, Augusto Ceccucci

  23. K+→p+nn Region I 211 < P < 229 MeV/c Region II 150 < P < 195 MeV/c p+ in the K+ CM LP2003, Augusto Ceccucci

  24. AGS-E787 K+→p+nn Region I • Stopped kaons (~6 ×1012) • Analysis of Region I: • 2 events • background: 0.15 ± 0.05 Data 1995-1998 Pub.1997-2002 PRL 88 2002 BR(K+→ p+ nn , Region I) = 1.57+1.75-0.83 × 10-10 0.29 < | lt |/10-3 < 1.2 68% CL LP2003, Augusto Ceccucci

  25. 1997 (preliminary) No new events Background 0.5 ± 0.2 1996 One event found Background 0.7 ± 0.2 E787- K+→p+nnRegion II PLB 537 2002 1996 data 1997 data NEW RESULT! BR(K+→ p+ nn , Region II ) < 22 × 10-10 @90%CL LP2003, Augusto Ceccucci

  26. Successor of E787 Many improvements Better photon vetoes Run 12 weeks in 2002: Expect Region I result soon Expect much better sensitivity than E787 in Region II Expect from data 2002 an overall sensitivity comparable to E787 Approved for 60 weeks When will the next run take place? K+→p+nnE949 LP2003, Augusto Ceccucci

  27. Current Status G. Isidori STILL A LARGE WINDOW OF OPPORTUNITY EXISTS LP2003, Augusto Ceccucci

  28. CPV asymmetry from the interference of IB and DE diagrams in K→ p+p-g* BR~3 ×10-7 CPV asymmetry and form factors from full statistics (5056 events) AL= (13.3 ± 1.4 ± 1.0)% (Theory: ~14%, Sehgal et al.) Form Factors (preliminary): a1/a2 = -0.75 ± 0.03 ± 0.02 gM1 = 1.10 ± 0.10 ± 0.06 KTeV: KL→ ppee (1997+1999, preliminary): KTeV KL sinfcos f NA48 KS LP2003, Augusto Ceccucci

  29. NA48/1: KS → 3p0 CP-Violating In SMh000~e • Near Beam • NA48/1 (2000) ~6.5 106 3p0 • Far Beam: • NA48 2000 > 107KL→3p0 • To normalise the acceptance • Analysis in bins of energy D(E) is the K0 K0dilution (from NA31) LP2003, Augusto Ceccucci

  30. NA48/1: KS→ 3p0 CPT TEST: KL ~ (e+dCPT)K1 + K2 KS ~ K1 + (e-dCPT)K2 From the 2 parameter fit, using BS unitarity relation: Im dCPT = (-1.2 ± 3.0) × 10-5 Assuming CPT conservation in decay: M(K0) –M(K0) = (- 1.7 ± 4.2) × 10-19 GeV/c2 Im h000 From one parameter fit: BR(KS→3p0) < 3.0 × 10-7 90%CL BRSM ~ 3 × 10-9 Re h000 LP2003, Augusto Ceccucci

  31. KLOE (LNF) 2002 2001 Integrated luminosity (pb-1) 2000 Days of running • DAFNE f Factory: • e+e- → f → KSKL (K+K-) Tagged KS and KL LP2003, Augusto Ceccucci

  32. KLOE: KS→pen KLOE Preliminary (2001 data): BR(p-e+n) = (3.44 ± 0.09stat± 0.06syst) × 10-4 BR(p+e-n) = (3.31 ± 0.08stat± 0.05syst) × 10-4 BR(p e n) = (6.76 ± 0.12stat± 0.10syst) × 10-4 LP2003, Augusto Ceccucci

  33. KLOE: KS→ pen Semileptonic asymmetries (preliminary) CPT test First ever measurement: A(KS) = (1.9±1.7±0.6) ×10-2 c.f. KLw.a. A(KL) = (3.322 ± 0.055) ×10-3 DS=DQ test Re (x+) = (2.2 ± 5.3 ± 3.5) ×10-3 c.f. CPLEAR Re (x+) = (-1.8 ± 4.1 ± 4.5) ×10-3 PLB 535 (2002) LP2003, Augusto Ceccucci

  34. Kaon Dalitz decays: Motivation • Allow to study the K-g*g(*) form factors • These form factors are related to the dispersive amplitude of KL→ mm which is not under good control • Short distance contributions to KL→ mmare sensitive to Re lt TWO MODELS: • BMS (Bergström, Massó, Singer, 1983) • Pseudoscalar/vector contributions: aK* • DIP (D’Ambrosio, Isidori, Portoles, 1997) LP2003, Augusto Ceccucci

  35. KTeV: KL→ eeg Employ TRD to reduce background Ke3 eeg Kp3 • In the 1997 data, KTeV has identified 93,383 KL→eegover a background of less than 0.1% • To determine the acceptance it is very Important to understand the tracking for close pairs • Uncertainty dominated by the error on the normalisation mode: KL→p0p0Dp0D with p0D→eeg BR(KL→eeg)×106 = 10.19 ± 0.04(stat) ± 0.07(syst) ± 0.29(norm) Preliminary LP2003, Augusto Ceccucci

  36. KTeV: KL→ eeg aK*=0.0 aK*=0.20 aK*=-0.36 aK*=-0.16 Measured to ~7% Precision! aK*= -0.186 ± 0.011 ± 0.009 LP2003, Augusto Ceccucci

  37. KTeV: KL→ ee ee 1997+1999 Data (preliminary) • Signal ~1100 events • Background: 5 events (mainly due to KL→eeg + conv) • Normalisation: KL→ p0p0Dp0D BR(KL→ ee ee) = (4.16 ± 0.13 ± 0.13 ± 0.17) ×10-8 a K* = -0.03 ± 0.13 ± 0.04 Theory: ~3.5 10-8 LP2003, Augusto Ceccucci

  38. KTeV: KL→ mm ee DATA 1997+1999 PRL 90 (2003) • Signal: 132 events • Background ~0.8 event • (KL → m+m- g ) • BR(KL → m+m- e+e-)=(2.69 ± 0.24 ± 0.12)×10-9 LFV • BR(KL → m-+m -+e+-e+-) < 4.12 × 10-11 90%CL LP2003, Augusto Ceccucci

  39. KTeV KL→ eemm Combining KL→ mmg, KL→ 4e, and KL→mmee, KTeV measures: a(DIP) = -1.53 ± 0.10 • aK*(mmee)= -0.19 ± 0.11 LP2003, Augusto Ceccucci

  40. K-g(*)g* Form Factor aK* ~2.6 s LP2003, Augusto Ceccucci

  41. KLOE: KL→ gg • Data 2001-2002 • 362 pb-1, 109f • KL tagged by KS→p+p- • 1.6 ×108KL • KL→ 3p0suppressed requiring 2 body kinematics • 27375 KL→ gg • PL B556 2003 (KL   ) / (KL  )= (2.79 ± 0.02stat ± 0.02syst)  10-3 In good agreement with the NA48 result (PL B551 2003): (KL   ) / (KL  )= (2.81 ± 0.01stat ± 0.02syst)  10-3 LP2003, Augusto Ceccucci

  42. NA48/1: KSγg BR ( KSγγ ) = (2.78 ± 0.06stat ± 0.03syst ± 0.02ext )×10-6 PLB 551 (2003) LP2003, Augusto Ceccucci

  43. KSγγ measurements O(p4) 2.78 ± 0.07 The NA48/1 result has an accuracy better than 3% It differs by30% from O(p4) prediction of CHPT Used to fix one O(p6) counterterm: 8mK2/Fp2 a1 = 1 ± 0.3 BDI (hep-ph/0308008) PL B551 2003 NA48/1 LP2003, Augusto Ceccucci

  44. NA48/1: KS PRELIMINARY: first observation Zq=q2/MK2 BR(KS γγ, zq0.2 ) = (4.9 ± 1.6stat ± 0.8syst )×10-8 CHPT predicts (Ecker, Pich and PLB 189 1987): BR(KS ) zq > 0.2 =3.8  10 –8 LP2003, Augusto Ceccucci

  45. NA48/2 and OKA: K+/K- • Search for direct CP violation • in Dalitz plot slope asymmetry • in K±   decay • Ke4 decays • Rare K± decays *NA48/2 is taking data* NA48/2 Very Preliminary K± → p± ee Simultaneous K+ and K- beams Similar sensitivities expected from OKA @Protvino (2004?) LP2003, Augusto Ceccucci

  46. CKM@FNAL-MI (2009?) • Proposal to measure ~100 K+→ p+n n in flight • Make redundant measurements: spectrometer and RICH • Built full size prototype of SCRF for 22GeV/c separated beam • Measured inefficiency of photon vetoes @1GeV to be 5×10-6 • ×6 better than needed • Demonstrated operation in vacuum of straw tubes • Awaiting approval ratification by P5 LP2003, Augusto Ceccucci

  47. E391a@PS-KEK • First dedicated experiment to search for KL→p0 nn • SES~ 3 10-10 • Based on pencil kaon beam and photon vetoes • Scheduled for ~100 days KEK PS beam in 2004 • This is a Stage I project for further study at J-PARC LP2003, Augusto Ceccucci

  48. KOPIO@BNL (2009?) • Aim to collect 60 KL→p0 nn events with S/B~2 (Im ltto 15%) • Measure as much as possible • Energy, Position and Angle for each photon • Work in the Kaon Center of Mass • Micro-bunched AGS beam • Use TOF to measure KL momentum • Start construction in 2005? LP2003, Augusto Ceccucci

  49. Conclusions • The field of kaon rare decays is quite active • New experimental initiatives are planned • Significant tests of the SM are to be expected • by the end of the decade High Energy Frontier Rare Processes LP2003, Augusto Ceccucci

  50. Spare Material LP2003, Augusto Ceccucci

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