4 July 2006Alan Norton, QCD Montpellier1 Search for direct CP Violation in charged K decays QCD Montpellier, July 2006 Alan Norton, CERN On behalf of the NA48/2 collaboration Cambridge, CERN, Chicago, Dubna, Edinburgh, Ferrara, Firenze, Mainz, Northwestern, Perugia, Pisa, Saclay, Siegen, Torino, Vienna

4 July 2006Alan Norton, QCD Montpellier2 Direct CP Violation in K  

4 July 2006Alan Norton, QCD Montpellier3 Direct CP Violation in K  

4 July 2006Alan Norton, QCD Montpellier4 NA48/2 beams setup 1cm cm m He tank + spectrometer Front-end achromat Momentum selection Quadrupole quadruplet Focusing  sweeping Second achromat Cleaning Beam spectrometer (resolution 0.7%) ~7  ppp, 400 GeV K+K+ KK Beams coincide within ~1mm all along 114m decay volume focusing beams BM z magnet vacuum tank not to scale K+K+ KK beam pipe Simultaneous K + and K  beams: large charge symmetrization of experimental conditions Be target 2-3M K/spill (  /K~10),  decay products stay in pipe. Flux ratio: K + /K –  1.8 P K spectra, 60  3 GeV/c

4 July 2006Alan Norton, QCD Montpellier5 2003: ~ 50 days 2004: ~ 60 days Total statistics in 2 years: K      +   : ~3·10 9 K    0  0   : ~1·10 8 >200 TB of data recorded NA48/2 recorded data samples

4 July 2006Alan Norton, QCD Montpellier6 K   K mass reconstruction  +  0  0 invariant mass, GeV/c 2 Resolution: 0.9 MeV/c 2 M K PDG ± 6 MeV cut 30.3M K +    contribution 16.9M K - K + : 2.00x10 9 events   M =1.7 MeV/c 2  K  : 1.11x10 9 events K+++K+++ K-+-K-+- K0+00K0+00

4 July 2006Alan Norton, QCD Montpellier7 Direct CP Violation in K   decays Kinematics: s i = (P K  P  i ) 2, i=1,2,3 (3=odd  ); s 0 = (s 1 +s 2 +s 3 )/3; u = (s 3 -s 0 )/m  2 ; v = (s 2 -s 1 )/m  2. BR(K ±  ±  +   )=5.57%; BR(K ±  ±  0  0 )=1.73%. “Charged” mode g =  ± |h|, |k| ~ Direct CP-violating quantity: the slope asymmetry A g = (g +  g  )/(g + +g  )  0 Matrix element: |M(u,v)| 2 ~ 1 + gu + hu 2 + kv 2

4 July 2006Alan Norton, QCD Montpellier8 K   decays: extraction of A g g=0.638c0.020 BUT there are experimental asymmetries which do not cancel in the simple ratio g(  ±  +   ) = ± g(  ±  0  0) = ± 0.004

4 July 2006Alan Norton, QCD Montpellier9 K   decays: acceptance cancellations N(A+B+K+) N(A+B-K-) R US (u)= N(A+B-K+) N(A+B+K-) R UJ (u)= N(A-B+K+) N(A-B-K-) R DS (u)= N(A-B-K+) N(A-B+K-) R DJ (u)= Z X Jura Salève B+ B–B– Achromat Polarity: A+: K+ Up A-: K+ Down Four ratios cancel left-right detector asymmetries

4 July 2006Alan Norton, QCD Montpellier10 K   decays: acceptance cancellations R = R US ×R UJ ×R DS ×R DJ f 4 (u)=n∙(1+  g  u) 4 Δg = 2g  A g ≈ −0.43  A g Normalization Slope difference Use a quadruple ratio to cancel also global time instabilities and beam-line biases

4 July 2006Alan Norton, QCD Montpellier11 K   decay asymmetry results A g 0 = (1.8 ± 2.2 stat. ± 1.0 stat.(trig.) ± 0.8 syst. ± 0.2 ext. ) x = (1.8 ± 2.6)x10 -4 A g 0 = (1.8 ± 2.2 stat. ± 1.0 stat.(trig.) ± 0.8 syst. ± 0.2 ext. ) x = (1.8 ± 2.6)x10 -4 A g = (  1.3 ± 1.5 stat ± 0.9 trig ± 1.4 syst ) x = (  1.3 ± 2.3)  A g = (  1.3 ± 1.5 stat ± 0.9 trig ± 1.4 syst ) x = (  1.3 ± 2.3)  Charged ( ): Neutral (2003):  Statistical errors dominate in both cases  Charged and Neutral results are consistent ( despite different systematics )  About 10 x better than previous measurements  Compatible with SM predictions

4 July 2006Alan Norton, QCD Montpellier12 K   charged asymmetry Ford et al. (1970) HyperCP (2000) preliminary 2003 final 2003 preliminary NA48/2 (results superseding each other) A g  10 4

4 July 2006Alan Norton, QCD Montpellier13 K   neutral asymmetry NA48/2:2003 final result TNF TNF(2004) Smith et al. Smith et al. (1975) A g x 10 -4