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New Results on Rare Kaon Decays in NA48

New Results on Rare Kaon Decays in NA48. Kirsten Holtz Universität Mainz on behalf of the NA48 Collaboration (Cagliari,Cambridge, CERN, Dubna, Edinburgh, Ferrara,Firenze, Mainz, Orsay, Perugia, Pisa, Saclay, Siegen, Torino, Vienna, Warsaw). Overview.

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New Results on Rare Kaon Decays in NA48

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  1. New Results on Rare Kaon Decays in NA48 Kirsten Holtz Universität Mainz on behalf of the NA48 Collaboration (Cagliari,Cambridge, CERN, Dubna, Edinburgh, Ferrara,Firenze, Mainz, Orsay, Perugia, Pisa, Saclay, Siegen, Torino, Vienna, Warsaw)

  2. Overview New Results on rare KS and KL decays: • KSgg • KSp0 e+e- • KS,L p+p- e+e- • KL 3p0 Dalitz plot slope K. Holtz • NA48 Collaboration

  3. The NA48 Kaon Beams 1997-1999: 3.21010 KLdecays/year; 6.5107 KS decays/year 1999: 2 days HIKs run: 2.3108 KS decays; no KL beam K. Holtz • NA48 Collaboration

  4. The NA48 Detector Magnetic Spectrometer: Liquid Krypton Calorimeter: K. Holtz • NA48 Collaboration

  5. Ksgg • KS,L  ggare sensitive to higher order loop effects of Chiral Perturbation Theory, no short distance contributions unambiguous prediction of branching ratio • Br (KL gg) already measured precisely • Theoretical prediction (by cPT): Br (KS gg) = (2.3 ± 0.2)×10-6 • NA31 measurement (1995): Br (KS gg) = (2.4 ± 0.9)×10-6 K. Holtz • NA48 Collaboration

  6. KS gg Event Selection • Two clusters in LKR calorimeter required • Kaon energy between 60 GeV and 170 GeV • LKR center-of-gravity < 7 cm • no hadronic energy, no DCH hits, no AKS/AKL hits • decay region: -2 < zvertex< 5 m KS p0 p0 with two missing g’s shifts vertex down-stream by > 7m 500 400 ggfrom 300 2p0 200 gg signal h  g g 100 from AKS 0 -1500 -1000 -500 0 500 1000 1500 Zvertex [cm] K. Holtz • NA48 Collaboration

  7. KS gg Result • 450 K ggcandidates in signal region after all cuts • background subtraction: • 11 ± 8 L np0 (center-of-gravity side-band subtraction) • 2 ± 2 KS  p0p0 • maximum likelihood fit tosignal region + subtracting KL  ggcontribution: 149 ± 21 KS gg • Normalization:7.5 106 KS  p0p0 Data 500 Fitted KSgg KL gg 400 ggbackground from 2p0 (MC) 300 200 ggsignal 100 0 -400 -200 0 200 400 600 800 1000 1200 Zvertex [cm] Br (KS gg) = (2.6  0.4stat  0.2syst ) 10-6 K. Holtz • NA48 Collaboration

  8. KSp0 e+e- • KL p0 e+e- : CP violating and CP conserving contributions • KSp0 e+e- directly connected to the amplitude of the indirect CP violations in KL p0 e+e- • Theoretical expectation: Br (KSp0 e+e-) = 5.2 × 10-9as ~ O(1) aS: strength of the indirect CP violating component in KL p0 e+e- important for future measurements of KL p0 e+e- • NA31 measurement (1993): Br (KS  p0 e+e-) < 1.1 × 10-6 (90% CL) K. Holtz • NA48 Collaboration

  9. KSp0 e+e- Event Selection • two oppositely charged tracks • four clusters in LKR calorimeter: two of them associated with tracks E/p > 0.9 • center-of-gravity of the clusters in LKR < 10 cm • |mgg - mp0| < 2.5 MeV/c2(2.5 s) • |mgge+e- - mK0| < 2.5 MeV/c2(3 s) • no hadronic energy, no AKS hits background rejection: • KSp0D p0D (with p0D e+e-g):|meg - mp0| > 30MeV/c2(for all eg combinations) • KSp0p0D (with p0D e+e-g ): me+e- > 165 MeV/c2(to take into account resolution effects and multiple scattering) KS p0 e+e- MC Meg[GeV/c2] forbidden region Meg[GeV/c2] KS p0Dp0D MC Meg[GeV/c2] forbidden region Meg[GeV/c2] K. Holtz • NA48 Collaboration

  10. KSp0 e+e- Result • 9 candidates remain after all cuts but me+e- • all candidates are compatible with Ks p0 p0D background expectation of  12 events no signal event found • Normalization:  8  104Ks p0 p0D (integrated flux of 3  108 Ks ) • indirect CP violating amplitude of KL p0 e+e- 7 Entries Data 6 Cut Ks p0p0D MC 5 4 Br (KS p0 e+e- ) < 1.4 10-7 at 90% CL 3 2 1 0 0 0.025 0.05 0.075 0.1 0.125 0.15 0.175 0.2 mee[GeV/c2] Br (KL p0 e+e- )indirect CPV < 4.1  10-10 K. Holtz • NA48 Collaboration

  11. p+ p+ p+ e+ KL KS g* g* KL KL e+ p- g* e- e- e+ p- p- e- KS,L p+p- e+e- • Main contributions to KLp+p- e+e- process: • Interference of CP-even (IB) and CP-odd (M1) amplitudes causes large asymmetry in distribution of angle  between p+p- and e+e- planes • Ks p+p- e+e-: no significant asymmetry expected Direct Emission (E1,M1) Inner Bremsstrahlung (IB) K Charge Radius K. Holtz • NA48 Collaboration

  12. KS p+p- e+e- Event Selection • two positive and two negative tracks • electron (E/p > 0.85) and pion (E/p < 0.85) identification • Ks identified by using the tagging detector • center-of-gravity of the clusters in LKR < 8 cm • no AKS hits, no hit in MUV detector • 477.7 MeV/c2 < mppee < 512.7 MeV/c2 background rejection: • KS p+p-with in time gconversion:490.7 < mpp < 504.7 MeV • KSp+ p-p0D (p0D  e+e-g) with missing g: p2 < 0.02 GeV2/c2 • 0 p0D (p0D  e+e-g) : |mpp - mL| > 4 MeV/c2 pp K. Holtz • NA48 Collaboration

  13. MC Ksp+p- e+e- MC Ksp+p- p0D Data KSp+p- e+e- Result • 1998 data: 56 KS p+p- e+e- eventsfirst observation! • Combined 1998+1999 (incl. Ks high intensity run 99) Br (KS p+p-e+e- ) = (4.50.7stat 0.4syst) 10-5 Br (KSp+p-e+e- ) = (4.3  0.2stat 0.3syst) 10-5 PRELIMINARY RESULTS Br (KL p+p-e+e-) IB = (1.3  0.1) 10-7 No asymmetry is observed: Asppee= (-0.2  3.4stat  1.4syst) % K. Holtz • NA48 Collaboration

  14. KL p+p-e+e- 1/G dG/df Data MC f=cos()sin() KL p+p- e+e- Result • 1998 and 1999 data • similar cuts applied like in KS p+p- e+e- • additionally: 482.7 MeV/c2 < mppee < 507.7 MeV/c2 • and: p2 < 510-4 GeV2/c2 ALppee= (13.9  2.7stat  2.0syst) % PRELIMINARY RESULTS As measured by KTeV (Phys. Rev. Lett. 84(2000) 408) Br (KL p+p-e+e-) = (3.1  0.1stat  0.2syst) 10-7 K. Holtz • NA48 Collaboration

  15. KL  3p0 Dalitz Plot Slope • K  3p Dalitz plot distributions: |M(u,v)|2 1 + gu + hv + ju2 + kv2 +… • KL  3p0: simplification to |M(R2,)|2 1 + h  R2 with R2 = (u2+v2/3) and  = arctan(u/ v) only quadratic slope h left! • Combining slope h with slope parameters in K± decaysallows to probe the validity of the DI = 1/2 rule K. Holtz • NA48 Collaboration

  16. KL  3p0 Dalitz Plot Slope theoretical predictions unclear: • J. Kambor et al. (PRL 68,1818 (1992)) h = (-12 ± 4)  10-3 • G. D’Ambrosio et al. (Phys. Rev. D50, 5767 (1994)) h  +1.4  10-3 • L. Maiani, N. Paver (2. DAFNE Phys. Handbook (1995)) h = (-1.2 ± 3.6)  10-3 only one previous measurement: • E731, 1992: h = (-3.3 ± 1.1stat ± 0.7syst)  10-3based on 5  106 KL  3p0decays K. Holtz • NA48 Collaboration

  17. Normalized Events R2 Data / normalized MC KL  3p0 Dalitz Plot Slope • six clusters in LKR calorimeter • center-of-gravity of clusters in LKR < 10 cm very clean events, no background left • ~ 14.5  106 3p0 events11.8  106 MC events fit of slope h: • divide data by normalized MC (h=0) and fit slope in region 0 < R2 < 1.9(to avoid resolution effects at the edge) Data Monte Carlo Fit region PRELIMINARY RESULT h = (-6.1  0.9stat  0.5syst)  10-3 R2 K. Holtz • NA48 Collaboration

  18. Summary KS gg:Br (KSgg) =(2.6  0.4stat  0.2syst ) 10-6 (published in Phys. Lett. B493 (2000) 29-35) KS p0 e+e-:Br (KS p0 e+e-) < 1.4  10-7 at 90% CL (final result to be published soon) KS p+p- e+e-: Br (KS p+p-e+e- ) = (4.5  0.7stat 0.4syst)10-5 based on 1998 data (published in Phys. Lett.496 (2000) 137-144) Br (KSp+p-e+e- ) = (4.3  0.2stat 0.3syst)10-5 preliminary result Asppee= (-0.2  3.4stat  1.4syst) % preliminary result based on combined 1998 and 1999 data KL p+p- e+e-:ALppee= (13.9  2.7stat  2.0syst ) % preliminary result Br (KLp+p-e+e- ) =( 3.1  0.1stat  0.2syst ) 10-7 preliminary result based on combined 1998 and 1999 data KL 3p0 Dalitz plot slope: h = (-6.1  0.9stat  0.5syst)  10-3 preliminary result K. Holtz • NA48 Collaboration

  19. Outlook 2000: No drift chambers  running for neutral decays only • Ks  gg : ~ 30  1999 data • Ks  3p0 : expect statistical error on 000of ± 0.02 • KL  3p0 Dalitz plot slope: more statistics, less systematics 2001: new drift chambers  NA48 finishes Re(e’/e) measurement • hoping for 50% - 100% more data for rare KL decays 2002: full year of high intensity Ks and hyperon data taking • ~ 50  the statistic of 1999 data • observation of Br (Ks  p0e+e-) • neutral hyperon decays: expecting ~ 30000 0 beta decays 2003/2004: K±program • measurement of CP violation in K± p±p±p • form factor measurement ofK±  p±p e±n K. Holtz • NA48 Collaboration

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