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Rare Kaon Decays Experiments

Rare Kaon Decays Experiments. Augusto Ceccucci/CERN LNF Spring School, May 17-18, 2004. 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

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Rare Kaon Decays Experiments

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  1. Rare Kaon Decays Experiments Augusto Ceccucci/CERN LNF Spring School, May 17-18, 2004 Augusto Ceccucci/CERN

  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, kaon structure • 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 Augusto Ceccucci/CERN

  3. Outline • Search for Lepton Flavour Violation • BNL E871, E865 • Standard Model and CP-Violation • K0L→p0 ee, K0L→p0mmKTeV-E799 II • K0S→p0 ee, K0S→p0 mmNA48/1 CERN • K0L→p0nnKTeV • K+→p+nnBNL-E787 / E949 • Other tests of CP Violation • Chiral Perturbation Theory, Kaon structure • K+→p+ ee, K+→p+mm • KS,L→gg NA48/1, KLOE • KS,L→p0gg NA48, NA48/1 • Kaon Dalitz Decays KTeV • Proposed/Future Experiments: • BNL/J-PARC/FNAL/CERN Lecture I Lecture II Augusto Ceccucci/CERN

  4. Kaon Mesons Main Decay Modes Augusto Ceccucci/CERN

  5. Bag of tricks for the Rare Kaon Decay Practitioner • Identify an intense source of kaons • Proton Accelerators • e+e- storage ring (phi factory) • Prepare homogeneous kaons beams • “Separated” beams (when possible) • Well collimated beams (Constraint on transverse momentum) • Ideal “beam”:  → K0S K0L • Construct a fast, large acceptance detector • Design a very selective and efficient “trigger” • Rejection factors of 100-1000 are not unusual • Find an appropriate normalisation channel • With topology as similar as possible to the signal one • Protect Nature from human bias • “Blind” Analysis • Be paranoid about backgrounds • Consider all possible sources • Measure from data as much as you can “inverting” cuts Augusto Ceccucci/CERN

  6. Proton Accelerators * Foreseen **used the 800 GeV TeVatron beam e+e- Storage rings ( factories) DANE (KLOE), VEPP II (CMD2, SND) ** Planned Kaon experiment  2003 Augusto Ceccucci/CERN

  7. SEPARATED K+ BEAMS RF2 RF1 DUMP DUMP L Require DFpp = 360o • For same DF, keep L/p2 constant, i.e. L ~ p2, but decays ~ p • If phase difference DFpp = 360o, then DFpK = 93o , DFpe = 8o • Loose this phase advance if p different from nominal momentum • The frequency f is limited by technology and by coherence lengthto about 6 GHz. Electrostatic separators: D = (m12-m22)cEL/2p3 (Viable only up to a few GeV) Radio-Frequency separators: DF = 2p (L f / c) (b1-1 – b2-1) with b1-1 – b2-1 = (m12-m22)/2p2 Augusto Ceccucci/CERN

  8. A momentum change of 14% changes the pp phase difference by 90 degrees Can only tolerate a Dp/p of 1% DFpK p/po DFpp 14% Augusto Ceccucci/CERN

  9. Master Formula Augusto Ceccucci/CERN

  10. Forbidden DecaysLepton Flavour Violation Augusto Ceccucci/CERN

  11. Lepton Flavor Violation* • Puzzling replication of generations…. • Foreseen in many extensions of SM: • Generation-Changing gauge interactions • Left-Right symmetry • Technicolor • Compositeness • Super-symmetry * Neutrino oscillations not discussed Augusto Ceccucci/CERN

  12. Processes mediated by Generation-Changing Bosons Cahn, Harari (1980) m-e conversion x m→ e g x x x K+→p+m+e- |Dg|=1 |D g| = 0 |D g| = 1 x x m→ eee KL→me Augusto Ceccucci/CERN

  13. AGS-871: K0L→me Searched for K0L→me(Lepton Flavour Violation) Measured very precisely K0L→m+m- Observed the rarest (hadronic) particle decay: BR(K0L→ e+ e-)= 9 +6 -4 10-12 • Hottest neutral kaon beam • 20 KW (~1.5 1013 /3.2 sec, 24 GeV protons) • 2 108K0L per AGS spill • 15 MHz Kaon decays • Beam stopper after the first two tracking stations • n/K ratio ~ 8 • Benchmark for high intensity detector • Straw chamber tracker • Rate up to 750 KHz/wire (K. Lang et al. NIMA522 2004) • Double Magnetic Spectrometer (PT kicks: 418 and 216 MeV/c) • Provides redundant momentum measurements • Allows one to trigger on “parallel” tracks from kaon two body decays • Muon Range Stack: • 26 V + 26 H hodoscopes (prop. tubes) located between steel, Al, and marble absorbers (5% increments of muon range) Augusto Ceccucci/CERN

  14. AGS-871: K0L→me PmeTmax= 238 MeV/c Steel, Marble, Al absorbers 5% m range increments Redundant electron identification Augusto Ceccucci/CERN

  15. AGS-E871: K0L→me • Background from semi-leptonic decays: K0L→ p e • with p→ mn decay in flight: Mmax(me)=489.3MeV • Excellent mass resolution (~ 1 MeV) Required • Scattered on vacuum window and first • tracking station: • Irreducible background @10-13 Augusto Ceccucci/CERN

  16. AGS-E871: K0L→me Excluded Region Search Region BR(K0L→me) < 4.7  10-12 90% CL Augusto Ceccucci/CERN

  17. AGS – E865: K+→p+m+e- Searched for Lepton Flavour Violation Measured K+→p+e+e- and K+→p+m+m- Measured K+→p+p-e+n(Ke4) • 6 GeV/c un-separated positive beam • 1013 p/ cycle on 10 cm long Cu target • Double magnetic spectrometer • S(P) = 0.003 P2 GeV/c • Redundant e PID: 2 Cherenkov + Shashlyk-like calorimeter • Backgrounds from: • K+→p+ p0→p+e- e+ g (p0 Dalitz decay) • K+→p+p+p- (t decays) • Accidentals (time-wise overlap of different kaon decays) Augusto Ceccucci/CERN

  18. AGS – E865 • 108 K+ /pulse • 109 p+/p /pulse Augusto Ceccucci/CERN

  19. AGS – E865: K+→p+m+e- Likelihood incorporating information from: • Vertex and track quality • Reconstructed beam parameters • PID and timing • Three-track invariant mass • K+→p+p+p- 10% prob. of finding smaller Likelihood Augusto Ceccucci/CERN

  20. AGS – E865: K+→p+m+e- Data MC Monte Carlo B(K+→p+m+e-) < 2.8 10-11 90% CL Augusto Ceccucci/CERN

  21. Lower limits on “horizontal” bosons (gX/gW)~1 >150 TeV/c2 >60 TeV/c2 >37 TeV/c2 • Further progress on LFV expected in the muon sector: • m→eg PSI • m- N →e- N MECO@AGS, J-PARC? Augusto Ceccucci/CERN

  22. Charged LFV limits versus time 1 10-2 - N  e-N +  e+ +  e+ e+ e- W. Molzon 10-4 10-6 10-8 10-10 E871 10-12 K0 +e-K+ + +e- 10-14 SINDRUM2 10-16 MECO Goal  1940 1950 1960 1970 1980 1990 2000 2010 Augusto Ceccucci/CERN

  23. Rare K decays and Standard Model Augusto Ceccucci/CERN

  24. CP-Violation in SM A phase in the quark-quark current leads to CP-Violation (Kobayashi, Maskawa, 1973) Ng=2 Nphase=0  No CP-Violation Ng=3 Nphase=1  CP-Violation Possible 6 unitarity relations (triangles in the complex plane) lt = V*tsVtd Im lt 0 CP-Violation Paradigm shift: After the demonstration of the existence of direct CP-Violation, e’/e 0, (NA48, KTeV) and of CP-Violation in B mixing (BaBar, Belle) one is searching for inconsistency in the CKM model Augusto Ceccucci/CERN

  25. 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 CP-Conservation Kaons provide quantitative tests of SM independent from B mesons Augusto Ceccucci/CERN

  26. K0L→m+m-Motivation Short distance contributions to KL→mm sensitive to Re lt Buchalla & Buras 1994 Long distance contributions: • Absorptive part (Im Agg) is dominant (2 real photons) • Dispersive part(Re Agg) depends on the • K-g*g(*) form factors that can be studied with • the Dalitz decays: • Is much less under control • Can interfere with the SD piece Augusto Ceccucci/CERN

  27. AGS-E871 K0L→m+m- ~6200 events Limits on r limited by the error on Agg and g*g* form factors Augusto Ceccucci/CERN

  28. Progress onK0L→p0ee and K0L→p0mm Augusto Ceccucci/CERN

  29. Study of direct CP-violation Direct CPV is expected to be sizeable in KL→ p0l+l- But Indirect CPV and CPC Contributions have to be addressed K0L→p0ee (mm): Motivation Direct CPV Indirect CPV CPC 0++, 2++ Augusto Ceccucci/CERN

  30. K0L,S→p0ee (mm): Experimental Consideration • The recent progress on K0L,S→p0ee (mm) has been possible thanks to a new round of experiments (FNAL-KTeV and CERN-NA48) approved to measure Direct CP-Violation in two pion decays of the neutral kaons (Re e’/e) • To measure Re e’/e , these experiments were equipped with state-of-the-art electro-magnetic calorimeters to reconstruct the 2p0 decays. These calorimeters are essential for the study of rare kaon decays with photons in the final state. • Irreducible background: K0L→ eegg (Greenlee, 1990) - TheK0L→ p0 ee mode is background limited • 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 Augusto Ceccucci/CERN

  31. KTeV-E799-II (FNAL) Pure CsI mgg~1 MeV TRD KL flux ~ 7 × 1011 Augusto Ceccucci/CERN

  32. FNAL-KTeV Augusto Ceccucci/CERN

  33. Fermilab - KTeV Augusto Ceccucci/CERN

  34. NA48 Detector & Data Taking NA48: ’/ 1997 ’/ 1998 ’/ 1999 no spectrometer 2000 KL NA48/1 KS ’/lower inst. intensity 2001 2002 NA48/1: KS 2003 NA48/2: K Total: 5.3M KL00 1996 Magnetic spectrometer Liquid krypton EM calorimeter NA48/2: K 2004 Augusto Ceccucci/CERN

  35. Liquid Krypton Calorimeter 9 m3 of Lkr (13212 cells) 1.25 m deph (27 X0) s(E)/E = 3.2%/E  9 % /E  0.42% s(mgg)~1 MeV/c2 ;s(t) ~ 300 ps Augusto Ceccucci/CERN

  36. Re e’/e measurements versus time Augusto Ceccucci/CERN

  37. Re(’/) Results 2=6.2/3 Final result (1997-2001) Half statistics (1997) Direct CP violation proved at >7 level…after 36 years! Augusto Ceccucci/CERN

  38. NA48: Re e’/e=14.7 ± 2.2 10-4 Top 10 articles from Physics Letters B: • 1. The hierarchy problem and new dimensions at a millimeter http://dx.doi.org/10.1016/S0370-2693(98)00466-3 Physics Letters B, Volume 429, Issues 3-4 , 18 June 1998, Pages 263-272 Nima Arkani-Hamed, Savas Dimopoulos and Gia Dvali • 2. A precision measurement of direct CP violation in the decay of neutral kaons into twopions http://dx.doi.org/10.1016/S0370-2693(02)02476-0Physics Letters B, Volume 544, Issues 1-2 , 19 September 2002, Pages 97-112 J. R. Batley et al. (NA48 Collaboration) • 3. Has the GZK suppression been discovered? http://dx.doi.org/10.1016/S0370-2693(03)00105-9 Physics Letters B, Volume 556, Issues 1-2 , 13 March 2003, Pages 1-6, John N. Bahcall and Eli Waxman • 4. Testable scenario for relativity with minimum length http://dx.doi.org/10.1016/S0370-2693(01)00506-8 Physics Letters B, Volume 510, Issues 1-4 , 21 June 2001, Pages 255-263 Giovanni Amelino-Camelia • 5. Role of effective interaction in nuclear disintegration processes http://dx.doi.org/10.1016/S0370-2693(03)00801-3 Physics Letters B, Volume 566, Issues 1-2 , 24 July 2003, Pages 90-97 D. N. Basu • 6. Determination of solar neutrino oscillation parameters using 1496 days of Super-Kamiokande-I data http://dx.doi.org/10.1016/S0370-2693(02)02090-7 Physics Letters B, Volume 539, Issues 3-4 , 18 July 2002, Pages 179-187 S. Fukuda et al. • …. Augusto Ceccucci/CERN

  39. KTeV: K0L→p0ee WC CsI Charged Vertex e g d12 g D e Neutral Vertex D ~ 1/m(p0) sqrt(Eg1Eg2) d12 Augusto Ceccucci/CERN

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

  41. 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 Augusto Ceccucci/CERN

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

  43. KTeV: K0L mmgg BR(KL m+m-gg,Mgg>1MeV/c2) = BR(KL m+m-gg, Eg*>10MeV) = 4 events seen First observation [PRD 62, 112001 (2000)] Augusto Ceccucci/CERN

  44. KTeV: K0L p0mm  BR(KL p0mm)  3.8 x 10-10 (90% C.L.) [PRL 86, 5425 (2001)] 2 events in signal region Data Background MC Augusto Ceccucci/CERN

  45. Interpretation of KL→p0ee(mm) p0 KL KS e e • Before interpreting the results one has to address the • CP-Conserving amplitude (see later) • CP-Violating from K0-K0bar mixing • This was exactly the goal of NA48/1 at CERN • The results will be described in some detail Augusto Ceccucci/CERN

  46. First Observation ofK0s→p0ee and K0s→p0mm Augusto Ceccucci/CERN

  47. MDX100 magnet MTNV magnet Artist’s view of the Target station (Vertical section) KS KL 400 GeV protons W insert Be target Pt Converter Horizontal (KL) beam axis Bronze plug 1:1 0.6 m 10mm MTNV magnet 0.5 m MDX100 magnet 1:25 6.23 m CERN-NA48/1: High Intensity K0S Converges to KLaxis at -0.6 mrad Augusto Ceccucci/CERN

  48. NA48/1: K0S→p0 ee Example of calculation of charged vertex for K0S→ p0 p0D • The charged vertex is used to compute M(eegg) • The neutral vertex is computed imposing the Kaon mass Augusto Ceccucci/CERN

  49. NA48/1: KS→ p0 ee KS→ p0p0D→ggee(g) KS→p0 ee MC MC • To reject the KS→ p0p0Ddecays that may mimic KS→p0 ee if a g is lost, a cut mee>0.165GeV/c2 is applied Augusto Ceccucci/CERN

  50. 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) Augusto Ceccucci/CERN

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