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Recent results of the NA48/2 experiment

Recent results of the NA48/2 experiment. Mauro Raggi LNF On behalf of the NA48/2 Collaboration PHI PSI 08 International Workshop on e + e - collisions Laboratori Nazionali di Frascati, Italy 7-10 April 2008. Outline. NA48 history and detector NA48/2 recent results in charged Kaon decays

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Recent results of the NA48/2 experiment

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  1. Recent results of the NA48/2 experiment Mauro Raggi LNF On behalf of the NA48/2 CollaborationPHIPSI 08International Workshop on e+e- collisions Laboratori Nazionali di Frascati, Italy7-10 April 2008

  2. Outline • NA48 history and detector • NA48/2 recent results in charged Kaon decays • BR and FF in K±→p±e+e- (New preliminary) • BR and kinematics in K±→p±gg (New preliminary) • Measurement of K±→p±e+e-g (New Final) • Lepton universality in RK=Ke2/Km2 • NA62 prospects for RK PHI PSI 08, LNF 7-10 April 2008

  3. NA62 2007 Ke2/K2 run 10 years of History • NA48(1997-2001):Direct CP-Violation in neutral K • Re(ε’/ε) = (14.7 ±2.2)·10-4 NA48/1(2002):Rare KS decays and hyperons NA48/2(2003-2004):Direct CP-Violation in charged K • Ag(K±→π±π+π-) = (-1.5±2.2)·10-4 • Ag(K±→π±π0π0) = (1.8 ± 1.8)·10-4 NA62(2007-?): • RK(Ke2/Ke2) PHI PSI 08, LNF 7-10 April 2008

  4. PK = 60±3 GeV/c Width ~ 5 mm K+/K-~ 1 mm 54 60 66 Simultaneous K±Beam ~71011 p/spill 400 GeV/c Simultaneous K+ and K- beams: Flux ratio:K+/K– ~ 1.8 largecharge symmetrizationof experimental conditions PHI PSI 08, LNF 7-10 April 2008

  5. LKr EM calorimeter Spectrometer - 4 Drift Chambers- Magnet Trigger Hodoscope NA48 detector layout PHI PSI 08, LNF 7-10 April 2008

  6. K±→l+l– Theoretical framework K  *  l+l–:suppressed FCNC process Usefull test for cPT dee/dz ~ P(z)·|W(z)|2 z=(Mee/MK)2, P(z) is a phase space factor Form-factor models: (2) D’Ambrosio et al. JHEP 8 (1998) 4, (3) Dubnickova et al. hep-ph/0611175 (1) polynomial: W(z) = GFMK2∙f0∙(1+z) (2) ChPT O(p6): W(z) = GFMK2∙(a++b+z) + W(z) (3)Dubna ChPT: W(z) = W(Ma, Mρ, z) (f0,) or (a+,b+) or (Ma,Mρ) determine a model-dependent BR PHI PSI 08, LNF 7-10 April 2008

  7. Measurement technique and goals • The BR is measured normalizing to K0D • To reject K0D background a Kinematic cut has been applied: Mee>140 MeV • This cut suppress the low Mee region (z<0.08), most interesting for model dependent BR determination • NA48/2 analysis goals • Model-independent BR(z>0.08) in visible kinematic range • Model’s parameters and BRs in full kinematic range PHI PSI 08, LNF 7-10 April 2008

  8. NA48/2 K±→p±e+e- data sample Kaon decay flux (2003+2004):K=1.701011 FlaviaNet ‘08BR(K2) used K±→p±e+e- K±→p±p0D 7146 events (Mee>140 MeV)Background = 0.6% (K0DK0De + particle misID) 12.23 mln events Background = 0.15% (K0D) PHI PSI 08, LNF 7-10 April 2008

  9. Raw fit results (preliminary) polynomial: W(z) = GFMK2∙f0∙(1+z) ChPT O(p6): W(z) = GFMK2∙(a++b+z) + W(z) Dubna ChPT:W(z) = W(Ma, Mρ, z) (1) (2) Analysis cut:z>0.08, or Mee>140MeV/c2 (3) Available data set unable to distinguish among models Model-Independent BRMI(z>0.08) can be computed by integrating dG/dz PHI PSI 08, LNF 7-10 April 2008

  10. Preliminary BR results (1) (2) (3) Including uncertainty due to the model dependence, (full z range) BR=(3.080.04stat0.04syst0.08ext 0.07model)10–7=(3.080.12)10–7 CPV parameter (first measurement! correlated K+/K– uncertainties excluded): (K±ee) = (BR+–BR–) / (BR++BR–) = (–2.1±1.5stat±0.3syst)% PHI PSI 08, LNF 7-10 April 2008

  11. BR(10-7) NA48/2 NA48/2 New “naïve” WA ‘08 ‘92 ‘75 ‘99 ‘08 ‘99 ‘00 ‘92 VMD models [PRD60 (1999) 053007] Results comparison PHI PSI 08, LNF 7-10 April 2008

  12. Relevant only @ low mgg K±→p±gg physics O(p4) in cPT:B=D=0;Aloop diagrams contribution, C WZW anomaly (10%) O(p6) in cPT: unitarity corrections can increase the BR by 30-40 %[G. D’Ambrosio and J. Portoles, Nucl.,Phys. B386 (1996), 403] PHI PSI 08, LNF 7-10 April 2008

  13. BR dependence on ĉ Both the BR and the mgg spectrum shape depend on ĉ: The spectrum dependence will be used to extract the ĉ value PHI PSI 08, LNF 7-10 April 2008

  14. K±→p±gg data sample Previous measurement by E787:BR=(1.10.32)·10–6 ĉ=1.8±0.6Based on 31 events 5 BG events 1164 candidates3.3% BG 1164 events in 40% of the full data ~40 times larger wrt to world sample BG mainly from ppg(IB) good agreement with MC O(p6), ĉ=2measurement of ĉ is ongoing Preliminary BR result: MC O(p6), ĉ=2 BR(O(p6),ĉ=2)=(1.070.04sta0.08sys)·10–6 PHI PSI 08, LNF 7-10 April 2008

  15. First observation of K±→p±e+e−g Never observed before Like in gg ĉ determines BR and meeg shape Theoretical expectation (Gabbiani 99):BR(K±→p±e+e−g)=(0.9-1.6)·10-8 Normalization channel: K±→ p±p0DKaon decay flux: K=1.48·1011 (’03-’04) • Event sample: • 120 candidates events with • 6.1% Background Model-independent BR(Mgee>260MeV/c2): BR(±e+e−g)=(1.19±0.12stat±0.04sys)·10−8 Using Gabbiani ChPT O(p4) model: ĉ=0.90±0.45 [final result published, PLB659 (2008) 493] PHI PSI 08, LNF 7-10 April 2008

  16. 404 events 534 events 112 events Ke2/Km2 measurement physics Test of lepton universality V-A couplings Within SM Theoretical prediction for RK=RK(0)(1+dRK)=(2.477±0.001)·10-5 PDG average: RK=(2.45±0.11)·10-5 Experimental error (4.5%) 100 times bigger wrt theoretical [V. Cirigliano and I Rosell, Phys.Rev.Lett.99:231801,2007] PHI PSI 08, LNF 7-10 April 2008

  17. SUSY LFV mechanism Ke2/Km2 SM SUSY If tanb=40 and MH+=500 GeV with |DR31|2= 5·10-4 The effect can be as high as 2% and therefore measurablePR D74 (2006) 011701 (A. Masiero, P. Paradisi, R. Petronzio) PHI PSI 08, LNF 7-10 April 2008

  18. Present status of NA48/2 Ke2/Km2 2003 data taking:- 1 month of data taking with downscaled trigger - trigger efficiency 2004 data taking:- 56 hours of dedicated run with minimum bias trigger - K2 background subtraction in Ke2 sample 2 new preliminary result by Na48/2:NA48/2 (‘03 data 4670 ev): RK=(2.416±0.043sta±0.024sys)·10−5 NA48/2 (‘04 data 3407 ev): RK=(2.455±0.045sta±0.041sys)·10−5 PHI PSI 08, LNF 7-10 April 2008

  19. NA62 2007 data taking Ke2/Km2 • Dedicated2007 data taking: • 4 months of data taking (excluding detectors prototype tests)- More than ~1105 Ke2 events collected- Aims to a precision better than 0.5 % on RK • Reduction of systematics • New beam and spectrometer configuration: • Kaon momentum: (60±3) GeV/c→(75.0 ± 2.5) GeV/c • PT kick from spectrometer magnet: 120 MeV/c→263 MeV/c • → improved missing mass resolution • → improved Ke2 / K2 kinematic separation • Direct measurement of K2 background and electron mis-identification probability • Minimum bias 1 track trigger (as for 2004 run) PHI PSI 08, LNF 7-10 April 2008

  20. Summary • Preliminary BRs in K→pee • BR=(3.080.12)10–7 (including model dependence errors) • BRmi(z>0.08)=(2.26±0.08)·10-7 • Preliminary BR of K→pgg • BR(O(p6),ĉ=2)=(1.070.04sta0.08sys)·10–6 • Final BR and FF of K→peeg • BR(±e+e−g)=(1.19±0.12sta±0.04sys)·10−8 • ĉ=(0.90±0.45) • Preliminary results and prospect in Ke2/Km2 • 2003 preliminary: RK=(2.416±0.043sta±0.024sys)·10−5 • 2004 preliminary: RK=(2.455±0.045sta±0.041sys)·10−5 • More than 110K Ke2 events collected in 2007 dRK/RK~0.5% PHI PSI 08, LNF 7-10 April 2008

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