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 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 Mauro Raggi PHI PSI 08, LNF 7-10 April 2008

10 years of History NA48(1997-2001): Direct CP-Violation in neutral K 2007 Ke2/K2 run NA62 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) Mauro Raggi PHI PSI 08, LNF 7-10 April 2008

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

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

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 Mauro Raggi PHI PSI 08, LNF 7-10 April 2008

Measurement technique and goals Previous Measurements Sample BR Bloch et al., PL 56 (1975) B201 41 (K+) (2.700.50)·10-7 Alliegro et al., PRL 68 (1992) 278 500 (K+) (2.750.26)·10-7 Appel et al. [E865], PRL 83 (1999) 4482 10,300 (K+) (2.940.15 )·10-7 NA48/2 analysis goals Model-independent BR(z>0.08) in visible kinematic range Model’s parameters and BRs in full kinematic range 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 Mauro Raggi PHI PSI 08, LNF 7-10 April 2008

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

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)  = 2.420.15 f0 = 0.5290.012 ρ(, f0) = –0.963 a+ = –0.5760.012 b+ = –0.8300.053 ρ(a+, b+) = –0.913 Ma = (0.9510.028) GeV Mρ = (0.7050.010) GeV ρ(Ma, Mρ) = 0.998 (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 Mauro Raggi PHI PSI 08, LNF 7-10 April 2008

Preliminary BR results BRMI= 2.26  0.03stat 0.03syst 0.06ext = (2.26 0.08) 10-7 z>0.08  = 2.35 0.15stat 0.09syst 0.18 f0 = 0.532 0.012stat 0.008syst 0.007ext 0.016 BR1= 3.02 0.04stat 0.04syst 0.08ext (3.02 0.10) 10-7 a+ = –0.579 b+ = –0.798 0.053stat 0.037syst 0.017ext 0.067 BR2= 3.11 (3.11 Ma = 0.965 0.028stat 0.018syst 0.002ext 0.033 [GeV/c] Mρ = 0.711 0.010stat 0.007syst 0.013 [GeV/c] BR3= 3.15 (3.15 (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)% Mauro Raggi PHI PSI 08, LNF 7-10 April 2008

Results comparison  Measurement BR(10-7) BR(10-7) Bloch et al., New “naïve” WA NA48/2 ‘75 ‘92 ‘99 ‘08 BR(10-7) NA48/2 VMD models [PRD60 (1999) 053007] ‘92 ‘99 ‘00 ‘08  Measurement BR(10-7) Bloch et al., 2.700.50 Alliegro et al. 2.750.26 Appel et al. 2.940.15 NA48/2 prel. (08) 3.080.12 Measurement Process d value Alliegro et al K++e+e– 1.310.48 Appel et al.[E865] 2.140.20 Ma et al.[E865] K+++– 2.45+1.30–0.95 NA48/2 prel. (08) Ke+e– 2.350.18 Mauro Raggi PHI PSI 08, LNF 7-10 April 2008

K±→p±gg physics Relevant only @ low mgg O(p4) in cPT: B=D=0; A loop 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] Mauro Raggi PHI PSI 08, LNF 7-10 April 2008

The spectrum dependence will be used to extract the ĉ value 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 Mauro Raggi PHI PSI 08, LNF 7-10 April 2008

Preliminary BR result: K±→p±gg data sample Previous measurement by E787: BR=(1.10.32)·10–6 ĉ=1.8±0.6 Based on 31 events 5 BG events 1164 candidates 3.3% 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=2 measurement 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 Mauro Raggi PHI PSI 08, LNF 7-10 April 2008

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±p0D Kaon 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] Mauro Raggi PHI PSI 08, LNF 7-10 April 2008

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 112 events 534 events 404 events [V. Cirigliano and I Rosell, Phys.Rev.Lett.99:231801,2007] Mauro Raggi PHI PSI 08, LNF 7-10 April 2008

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

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 Mauro Raggi PHI PSI 08, LNF 7-10 April 2008

NA62 2007 data taking Ke2/Km2 Dedicated 2007 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) Mauro Raggi PHI PSI 08, LNF 7-10 April 2008

Summary Preliminary BRs in K→pee Preliminary BR of K→pgg 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% Mauro Raggi PHI PSI 08, LNF 7-10 April 2008